hobby variable dc power supply Power Supplies - External/Internal (Off-Board) - 1075 New Products. 3 ohm). The LM317 has a low current rating that limits its use. This benchtop power supply solves that problem, This product fits the bill allowing for a nice little benchtop module which sits on your desk and is a single stop solution for all power supply needs for all your projects. It provides all controls and short circuit protection with acceptable regulation and a ripple free supply and yet uses very few components. Fig. It has very good regulation and ripple and can be adjusted to between 20 and 30V output while delivering up to 60 Amps. The large brick size AC to DC power supply is rated at 19. 001A), Data Hold - 110V/115CM Alligator Leads MDC01 988 $69 97 ($245. KORAD KA3005P - Programmable Precision Variable Adjustable 30V, 5A DC Linear Power Supply Digital Regulated Lab Grade It has an easy to read 4 digit LED is used to display the voltage and current values and 4 programmable storage setting. Reliable Electric DC-2 Variable Speed Motor Controller. Excellent Product. TI suggests that for either sensored or sensorless operation, the chip should be teamed with a microcontroller such as the popular MSP430. Each of the schematic is very simple to construct and will function without problems if you respect the maximum power supply ratings. Absolutely not. Adjustable DC power supply: A very nice adjustable power supply unit may be built using just a couple of transistors and a few other passive components. Is anyone familiar with this control? It is 20 yrs old and obsolete, and uses a custom Crydom CY4913 control scr/relay. Hobby & Models. Sales, Supplies, and Service. I haven't tried to use this for electroplating yet but I may bring it to the shop the next time our zinc rectifier goes down. Think of an industry-standard variable power supply but with more powerful features. The PSE series power supplies are rugged AC-DC power supplies (switch mode) encapsulated in an ultra-compact, low profile housing. -February, 2002 12v to 19v Laptop Power Supply (Concept) - Concept Only. The Universal Power Supply output voltage can be set to anywhere in the range 1. Most powder coating gets done at around 45 – 50 Kv setting but even down at 10Kv works not too bad. The easier it is to set up a power supply, the more productive you will be. 3V, and 1. This is an excellent hobby unit as and this unit is also used as the driver for our HV250 high-voltage DC power supply which produces 25,000 DC Variable open Variac Transformer TDGC2-2D with 20 Amp Max Output and LCD Digital Display. KORAD KA3005D - Precision Variable Adjustable 30V, 5A DC Linear Power Supply Digital Regulated Lab Grade This is packed with features and at a cost that can't be beat!! It has an easy to read 4 digit LED is used to display the voltage and current values and 4 programmable storage setting. 5v to 24v. But if you make a power This style power supply is also available in a version for 12 volts. MASTECH HY3002-2 VARIABLE DC POWER SUPPLY DUAL output lab grade variable DC power supply is excellent for lab use with the two variable 0-30 volt 0-2 amp outputs. For smaller voltages, we normally use batteries as a reliable source. pdf), Text File (. Transformer, bridge rectifier, some massive elctrolytic caps and a few regulators (7805, 7905, can’t recall what the variable voltage ones were) all in Driven by the free WaveForms software (Mac, Linux, and Windows compatible) software, Analog Discovery 2 can be configured to work as any one of several traditional test and measurement instruments including an Oscilloscope, Waveform Generator, Power Supply, Voltmeter, Data Logger, Logic Analyzer, Pattern Generator, Static I/O, Spectrum Analyzer If the CNC shield outputs PWM but just can't handle the current requirement for the spindle, all you really need is a circuit consisting of a small resistor taking the PWM signal to the gate of a MOSFET which controls the motor . Easy to use, well built and the fan keeps things cool & quiet. In its "intended" use, the controller runs from two lithium-ion batteries with a total voltage of around 7. This power supply replaces the PS2012 to meet new efficiency requirements for DC power supplies. The DP800 Series is a family of linear power supplies systems with 3 outputs and up to 195 Watts in total. The automotive DC motor is small, yet powerful for completing hundreds of different kinds of electrical experiments and projects. Rating-Input: 12V-28V DC updated to 12V-24V Output: 3V/5V/6V/9V/10V/12V DC 2. Product Title AC DC Power Supply Adapter AC 100-240 Volts 50/60Hz Average rating: 5 out of 5 stars, based on 1 reviews 1 ratings. Shop online and save! See full list on brighthubengineering. The power supply that comes with these sets is usually a very small wall pack plug-in that cannot be easily expanded. DC Power Supply Variable, Adjustable Switching Regulated Power Supply 30V 5A with 4 Digits Display, Course and Fine Adjustments (00. 5in long X 5in wide X 2. It will keep a stable voltage when it has any load. I want to say While there are more efficient ways to do this, this will allow the tutorial to work with as many DC motors as possible. 15. Traxxas EZ-Peak Live 4S "Completer Pack" Multi-Chemistry Battery Charger w/Two Power Cell 4S Batteries (6700mAh) Available in Stores 8 Reviews Average Rating:5 The LM338 Power Supply input voltage is rectified with Graetz (B1 bridge diode) and filtered through capacitors C1 4700uf and C3 100nf. 20” x 5. Your train moves at a speed deter-mined by the track voltage. There are plenty of DC controllers available on eBay. 0 amps) Turn off the power supply Open the test leads (remove the short) Connect the load and turn on the power supply 6. 1/2-2HP. 5V to 30V by selecting two resistances. The motor +ve goes to the power supply +ve, and the MOSFET sits between motor -ve and power -ve. They could be configured with Anderson type quick connects and changed out quite quickly and easily. 2A, 80W max output. INTRODUCTION: It is a simple variable dc power supply which gives 5 to 12 dc volts as an output. 25 amps max. Product Description. so you wouldn’t be caught dead dropping money on some fancy power supply for this new hobby. The 300W version gives 2X44V DC. At a time when quality continues to be compromised in favor of overseas cost savings, Bridgewerks stands firm in its commitment to offer the best power supplies available anywhere, guaranteeing our customers unquestionable quality and lifelong An essential part of an AC-DC power supply circuit is the filter, used to separate the residual AC (called the “ripple” voltage) from the DC voltage prior to output. Variable 3 - 24 Volt / 3 Amp Power Supply This regulated power supply can be adjusted from 3 to 25 volts and is current limited to 2 amps as shown, but may be increased to 3 amps or more by selecting a smaller current sense resistor (0. Power your devices with accuracy and the confidence that only comes with a professional lab power supply. Today the variable voltage controlling the high power stage (ampligier) suppling the field windings for a PMDC motor is digital logic level ( ie 3-5 volt logic circuit/computer), usually using PWM ( ie pulse width modulation where the duty cycle is the percentage/fraction of the bus/supply voltage applied to the coil -- basically a switch DC power supply). Power supply outputs a maximum current of 125mA@12V and 200mA@10V or less. 400 mA Variable DC Power Supply(115 VAC) 1 Power Cord Description: This is q Hoefer Scientific PS500X 500V. Regulated Power Supply, Variable. cheap when compared to The category of DC power supplies discussed in this section changes AC line voltage into DC voltages. If you have a spare laptop power adapter can help as an input power source. 5-30V 1A$22. The 20 amp PS2012E regulated power supply can be used to operate up to 4 five amp boosters. 50W OCL main amplifier using LF351 with PCB This 50W OCL main amplifier circuit has high quality and economical,it is designed simple, easily created, electronics rookie. Washdown DC motors can handle wet and high humidity environments. This vendor also sells a 15 volt, 4 amp unit for about $20. I did a search on “(variable, controller, controler) motor” and bid on this one. This power supply has a reliable circuit design with momentarily short circuit protection. The motor power supply should be compatible with the DC motor. The circuit diagram of the power supply is shown in Fig. 3V for the microcontroller and then 12V for steppers and 22V for the amplifier, Its not fun having a separate power supply for each project. Our current products that offer dimming controls like this are the Magnitude Dimmable Power Supplies. Check the specs to be sure they’re compatible with your motor. , TDK-Lambda & more. A low ripple regulated DC power supply designed based on transistors is shown here. 5 to 9. The Voltage Potentiometer control is below the On-Off Power Switch. 3 ~ 3. Machined metal front bezel with illuminated power switch. Power Supply. This simple unit provides a dual-rail variable output ranging from ±2. Also has a High-Low frequency range switch. This circuit may allows you to use up to more than 5A,… Build an Adjustable 2-30 volt power supply with the LM317. Then connect a fully charged battery/ variable power supply to test points TP observing polarity. This Variac transformer compares favorably with the Variac 3PN1010B model for 25% the price, and with a high efficiency output and no waveform distortion, this Variac autotransformer can be used for a wide array of professional and DIY applications. 2V to 30V. 75in tall. eBay: $50. Power Supplies and Wall Adapters available at Jameco Electronics. Add to Cart This # ToolkitRC # P200 tiny # 200W 30V 10A variable DC power supply is fantastic. If the temperature is less than 25°C, then the DC fan will remain off and details will be displayed on the LCD. The control system can control and monitor the power supply output voltage and current from virtually anywhere there is an Ethernet connection. 90-180V 10A. It has only 3 connections (input, output and ground) and it provides a fixed output. 5A and 12V/1A Outputs is ideal for a wide range of applications including bench testing, field service, hobby, and telecommunication equipment. 3A DC to DC Hobbylinc carries 89 model trains power supply / transformers at discounts up to 35%. 5 amps but it only has a 1 amp current meter and best of all the voltage is variable from 1. 95 $ 12. CAT. It is used as an interface between utility and most of the power electronic equipment’s. I'm currently working on a product which uses a size 2430 "hobby" brushless motor and 25A electronic speed controller (ESC). A good power supply is essential to electronic projects. com What you will get: 1 Hoefer Scientific PS500X 500V. We also stock powerboards, lab power supplies and Powershield uninterruptible power supplies (UPS). 950 meters with two digits Slip it in pants' pocket for walking and jogging; One-IC two-tones Siren Double tone Police sound Single tone old ambulance sound; Personal Alarm Small, portable, anti-bag-snatching unit Also suitable for doors and windows control; Variable DC Power Supply Voltage Hobby Circuit designed by Dave Johnson P. The holy grail but also the most expensive option is to use a lab style bench variable power supply to power the circuit. There are many sizes, power types, and power adjustment options in available in power supplies. SMPS designs designed as IR2153 amplifier power source based on IR2153 Integration. E. This is a 3A adjustable regulators using IC-LM350 that looks like LM317 Variable DC Power Supply, but high current higher 3A, adjust voltage 1. View. Make sure you are getting the right type of power supply for your layout. NO:MP3314. ATX Power supplies have standard sizes and connectors for use with ATX motherboards. Both S-350-12 and S-400-12 power supply dimensions are 8 1/2in long X 4 5/8in wide X 2in tall. The beauty is the DC power is very strong and super constant at any rpm, but the biggest thing is you only need 1/2 the hp rating in a DC motor as you would for A/C. Each output channel has replaceable 5A fuse and corresponding ground connection with binding post. Brand New. Forget the batteries! This safe and reliable power supply is a convenient source of low voltage DC power. MG has a variable power supply (MGPS10AD) 0-20 VDC but it's output is only 10 amps, is that sufficient for your higher voltage cars? Another thought, why not two different power supplies, one set for 12 VDC and another set for the higher voltage. Select precise voltage level and current limits to prevent overheating, burnout, and over-current. Variable DC Power Supply - Free download as PDF File (. The chip can supply up to 3. Model #DC-92U. The project has been designed using LM2576ADJ, LM317-ADJ Regulator My bench power supply is based on a LM317 variable voltage regulator, will supply current up to 1. [Tron] didn Typically, dc power supplies provide a well-regulated current or voltage level that is preset and then the supply turned on and off as needed. The variable power supply they plug into, though: that’s another story. 37, buy best xys3580 dc dc buck boost converter cc cv 0. It uses two 7805 regulators; input up 35 volts AC or DC from a transformer or other power source. Circuits have Short circuit protection. Hobbyking - the world's No1 Online Hobby Store. This circuit is not an absolute novelty, but it is simple, reliable, "rugged" and short-proof, featuring variable voltage up to 24V and variable There are many sizes, power types, and power adjustment options in available in power supplies. And I have visited many many more layouts from G to Z and I just don't get why folks think that DCC is a worse power supply then DC. Provides quick access to the typical voltages needed including 3. 7 - 24V Current limiting range: 50mA - 2A A Variable DC Power Supply is one of the most useful tools on the electronics hobbyist's workbench. wrote: "I designed a variable voltage DC linear power supply for powering ham radio equipment that may fit the bill for up to about 35 amps in the way that I built mine but with the linear regulators I used it is scalable by using more or less regulators with a maximum of up to 9 amps per regulator chip. This waveform then adjusts output voltage according to the preferred designated value. You can use it to power your battery charger or as a variable bench power supply. DC Power Supply Variable 30V 10A, KAIWEETS 4-Digits Display(00. 2 V to 10V adjustable from 15V to 30V 3A DC input. eBay: $50. 00 : Motor Speed Control Unless you want your trains to run at full speed all of the time some sort of variable power motor controller needs to go between the fixed voltage power supply and the track. The one shown here is the Siglent SPD3303X which is one we use and can recommend. This article explains a variety of low cost ways to obtain and control your plating power requirements. Digital Step-Km Counter Max. These WILL NOT work for HO slot car tracks. The main power connector supplies power to the motherboard of the computer. Hobby Zone carries a wide selection of the best radio control brands and hobby products - including airplanes, cars and trucks, quadcopters, and boats. 2-30V/1. All RC Battery Chargers. The DP800 Series Power Supplies combine the ability to source, analyze, and coordinate over time in a powerful new package. I know the motor is good; but can't get the 90vdc out of the power supply/control board. Simply power it by only a few volts and a very low current to get it working. 5 out of 5 stars432. Get the Charger you need to charge Lithium Polymer, Ion, Iron Phosphate, LiPo, LiIon, LiFe, Nickel Metal Hydride and NiMH Batteries. 5 A over an output-voltage range of 1. The most common and versatile regulated DC power supply is the constant current (CC) or constant voltage (CV) type which as the name implies can provide either a constant current or constant voltage within a certain range, see image below. Bridgewerks designs, develops and manufactures the finest model train power supplies in the world. 00 CyberPower Universal 3-12V 600mA AC-to-DC Power Adapter with Replaceable Tips $21. Hobby Tools & Supplies Menu; Hobby Tools & Supplies. Watch. com DC Variable Power Supply – With one of the best hobbyist benchtop power supply, you can get the ideal voltage supply you need for your project. Benchtop Power Supplies are in stock with same-day shipping at Mouser Electronics from industry leading manufacturers. The circuit described here is of an economical smooth variable power supply which offers 0V to 24V. First, AC power is converted to DC power, followed by the switching on and off of the power transistors, causing a voltage waveform at the desired frequency. It has only 3 connections (input, output and ground) and it provides a fixed output. Whether you need one of these handy tools in the classroom, in your job, or as a tool in a particular hobby, you will be able to easily find an affordable used adjustable power supply for sale on eBay that will suit your needs. Use the Current and Voltage Adjustment knobs for setting variable Current and Voltage output signals respectively. I have been in this hobby about 35 years now (man I sound old) and I have personably worked on/owned layouts from Lionel to HO DC, To HO Command Control (pre DCC) to Modern DCC powered HO. Input to connector CON1 can be AC or DC. This will allow you to set the voltage to a specific value depending on what you need for your project. PS2012E 20 Amp Power Supply 13. Its design is stylish and innovative, improving your automotive prowess for the long run. A typical commercial powder coating gun has a variable power from zero to 100Kv. They provide stable output power, built-in voltage and current measurement, and output voltage and current from 6 V to 600 V and 1. Here are 4 simple 12V power supply circuits with output voltages around 12V. With 60a and 1200 watts total output, the Titan can supply the most power-hungry dc chargers with plenty of current to easily keep those big packs charging at 2c ratings. I did a search on “(variable, controller, controler) motor” and bid on this one. It also buys you some protection as you can set a maximum current allowed. http://www. More buying choices$80. Turn the switch S1 to the off position and switch on the power. 99. 3-22V Regulated Power Supply 5V Regulated Power Supply 1. Power Supplies/DC Power Supplies Template; Outputs: Single: Voltage Output 1: Variable: Max Voltage Output 1: 30 V: Min Voltage Output 1: 0 V: Current Output 1: Variable: Meter Type: Digital: Switching: Yes: Linear/Switching: Linear: Max Display Resolution Current: 1 mA: Max Display Resolution Voltage: 10 mV: Constant current/voltage: Yes: Remote Sensing: Yes: Test Equipment General Attributes The tranformer's job is to take the 120V AC voltage from the mains line and step it down to 24 volts. DC/AC Invertors Switching Power Supplies Variable AC/DC Power Supply AC/DC Adaptors Universal AC/DC Laptop Adaptor/Charger DC/DC Converter DC 24V to 12V: Soldering Equipment Antex Horn Speakers Waterproof Speakers Switches - Toggle/ Push Button / Rocker / Micro / Electrical Digital Multimeter Analogue Multimeter Oscilloscope Crimping Tools Turn on the power supply Turn the current knob to the desired current value (0. Controlling a single power supply will require a 100K ohm potentiometer for 100% intensity (100K ohm) to approximately 10% intensity (10K ohm) based on where the wiper is positioned. If you're in the business of building projects and testing circuits regularly, acquiring a variable DC bench power supply is highly recommended. The PSE series DC power supplies feature a universal input from 85-264 VAC with single or dual outputs from 15 Watts up to 60 Watts (above 30 Watt, single output only). 3A - steady 1. There are actually a few different ATX power supplies, all of them are designed to provide 3. The LM317 is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1. Paired with the Turnigy Reaktor Quad Core 300W X 20A it charges Four 5000mAh 6S packs at 2C, and balanced complete in 25mins. Model #DC-92U. A Variable Frequency Drive converts power through three different stages. The Powerwerx dual metered digital power supply model SPS-30DM is designed to supply 25 Amps continuous and 28 Amps surge. 5A Switching Power Supply Rating Required Select Rating 1 star (worst) 2 stars 3 stars (average) 4 stars 5 stars (best) Name Feb 3, 2021 - DIY Analog Variable Bench Power Supply W/ Precision Current Limiter: In this project I will show you how to use famous LM317T with a Current Booster power transistor, and how to use Linear Technology LT6106 current sense amplifier for precision current limiter . This is a basic universal variable Power Supply voltage regulator circuit using an LM317, 3-terminal regulator in a TO-220package. Bench Variable Power Supply. 3V, 5V, 12V and -12V. 1 - 17 VDC - continuously variable Current Output: max. This is an 80W 3-in-1 (3 output ranges) Switching DC Power Supply. Description. You previously purchased this product. UNIROI 30V/10A DC Power Supply Variable is small-sized and lightweight, features high accuracy, reliability. DC Power Supply Variable, Adjustable Switching Regulated Power Supply 30V 5A with 4 Digits Display, Course and Fine Adjustments(00. NO: MP3316 These switchmode plugpack adaptors are slim in size, lightweight, and feature manually selectable variable voltage outputs. Our products cover speed range from low speed gear motors to high rpm variable speed motors. GPIB interface is available as an option Starting from If the board is used only as variable power supply, input voltage 4 to 6 volts can be given to the input points or Mobile charger to Micro USB socket. 90. eFuel 60A 1200W 15-24V Variable DC Allied offers AC and DC power supplies of all kinds including, DIN rail mounted industrial power supplies, sealed LED drivers, desktop and wall plug adapters. The higher the voltage the stronger the ionization and better the powder transfer. 3-12V DC 27W Power Supply 7DC Plugs and USB Outlet CAT. A DC power source is required to operate any plating or anodizing operation. You can use it to power your battery charger or as a variable bench power supply. In our tutorial we are going to use our DC Hobby Motor which works with 4. com 0 – 40 V, 0 – 4 Amp Continuously Variable Power Supply Circuit This unique work bench circuit utilizes only a few inexpensive transistors and yet delivers some truly useful features. Variable DC Power Supply October 12, 2010 A Variable DC Power Supply is one of the most useful tools on the electronics hobbyist's workbench. 2V up to about +/-25V, will current limit at around 800mA Variable load tests voltage sources : 07/19/2001 EDN - Design Ideas / The circuit in Figure 1 serves as a variable, current-sink load for testing voltage sources. This controller converts commands received from an R/C radio, wireless modem, joystick, or computer into high current 12 to 40 Volt output for driving one or two DC motors. By using a potentiometer, R2, as one of the resistors you can dial up the output voltage wanted. variable dc power supply Universal Selectable-Voltage AC-to-DC Adapter: 13. There are easier ways to get a simple power supply like this one (re-using a wall-wart, for instance). DC output voltage 14. You will eventually get some optional gadgets that need that desk space. then click the following link, to be taken to the MPJA website. 99$126. The S-700-12 is 9. 1 VDC output. The change in power that the dimmer creates on the AC input side will vary the voltage on the DC output and control the brightness of the LEDs. 2 Amps - x 10 Supplies 0-260V AC Variable Autotransformer Variac - 500VA. Generally, to convert line frequency ac to dc, a line frequency diode bridge rectifier is used. While there are many existing designs for adjustable power supplies, this one makes improvements that make it more useful for hobby designs MIC2941 regulator has guaranteed 1. It is built around bridge rectifier (BR1), adjustable voltage regulator LM350 (IC1), transistors BC327(T1) and BC337(T2), and a few other components. World's Largest Supplier of Amateur Radio, Ham Radio, and Communication Equipment. General purpose DC motors generate a constant torque throughout their speed range where a wide operating speed range with constant torque is required. com 12V DC 1. It features user variable output (5~16 VDC) by adjusting the front mounted knob, or fixed 14. 3V Power Supply; Variable Power supply by David Celestin ; Fast Electronic Fuse by Miroslav Adzic ; Adjustable Power Supply with Charger by Milardo de Guzman; Multiple Output DC 48V Phantom (Microphone) Power Supply 12V Regulated Inverter Supply 9 Volt 2 Ampere DC Power Supply 3-30V 3A Adjustable Regulated DC Power Supply Adjustable 1. Mouser is an authorized distributor for many bench top power supply manufacturers including B&K Precision, TDK-Lambda, Keysight, Keithly Instruments, Inc. 5 out of 5 stars. This family of affordable 750 W and 1500 W single-output programmable DC power supplies consists of 24 models for simple DC power applications. We are using L293D motor driver IC for controlling DC fan/motor with Arduino. 4,867 Switchmode Power Supply - 3 to 12V DC with USB Outlet 27 Watt Output - 2. 99 RCA 2. range: 9. Under 1A. . Power up your foam cutting tools with our wide variety of power supplies. It is the same as the Hoefer PS500XT except that the Hoefer PS500X does not have a timer function. , TDK-Lambda & more. Our team's dedication to AC/DC power supplies is certain to help you find a reliable power supply quickly from TRC. If battery is also provided, it can be a Portable power supply. Current Price $12. here we use a simple full wave rectifier along with a voltage regulator which give a constant output and its output can be increased by using a pair of voltage divider resistor in which one resistance is variable to get variable output. This Miniature DC Motor is ideal for all your hobby needs. Bench power supplies basically function like any other AC-DC converters, only at a higher level. The most popular model trains power supply / transformers brands include Woodland Scenics, MRC, Bachmann, NCE Corporation, and Digitrax. We always used to make our own in the 80s. 5A Universal AC-to-DC Power Adapter $34. Reliable Electric DC-2 Variable Speed Motor Controller. Such transistor voltage regulators are suitable for application… Everyone needs a variable power supply for bench testing of your motors right? Well, a lot of the motors out there seem to run on 12 & 24V, which is no problem, but what about the ones that take 90V? Must you make/buy a separate power supply for each one? My goal right now is to run some 24V brushed DC motors (Yaskawa Minertia R-series servo The DP800 Series Power Supplies combine the ability to source, analyze, and coordinate over time on a powerful platform. For the two variable outputs the voltage is variable from 0 to 30 volts and the Variable Regulated Power Supply Description: the project aims to construct an adjustable regulated power supply that can provide DC voltage ranging from 1. A typical hobby servo An ordinary DC motor has two hookup wires and simply turns continuously when power is applied. Excellent Power Supply. Power Supplies Since an AC power supply used for a radio needs no adjustments or meters to read, (a useless option in most cases) I think under the desk is a better place for a power supply. 2% + 1 mA; Load Regulation: CV <= 0. $126. Thus, if you need a 5 VDC, 100 ma. Jan 7, 2021 #1 There are two main designs for variable regulated DC power supplies: Linear DC Power Supply and Switching DC Power Supply. Electronics is my hobby, and as a hobbyist I need custom made power supplies more often than others. 5 VDC power. Free shipping. and d. Mouser is an authorized distributor for many bench top power supply manufacturers including B&K Precision, TDK-Lambda, Keysight, Keithly Instruments, Inc. The circuit is based around the 7805 voltage regulator. Whether you need one of these handy tools in the classroom, in your job, or as a tool in a particular hobby, you will be able to easily find an affordable used adjustable power supply for sale on eBay that will suit your needs. This type HTC Instruments SMPS 3005 DC 5A SMPS Power Supply - HTC Brand: SMPS-3005 DC 5A SMPS Power Supply - Model: HTC-U2 - Warranty: 6 Months Rs. Add to cart. • Up to 77% high efficiency • 100MR at 500VDC Isolation resistance • ±1% Output voltage accuracy • 300µs Transient recovery time • Short-circuit protection • Internal input filter • What you need is either a control unit incorporating a transformer (and rectifier, unless your mains supply is Direct Current) and a control knob with which you can regulate the voltage (to control the speed of the locomotive), or you should have a separate transformer (+rectifier) supplying approx. HeNe Laser tube power supply x-ray tubes plasma tubes negative ion generators, etc. Power Supplies / Rectifiers. The feature includes continuously variable voltage from zero to the maximum transformer voltage and current variable from zero to the maximum applied input level. Gives a regulated 0-36VDC @ 2. 5V to ±15Vdc with precise tracking of the positive and negative output voltages, still retaining the current limiting and short-proof capabilities of the "master" circuit. It delivers more power with less heat for more efficient operation. This is the typical function of a power supply in an electronic device such as a computer or battery charger. Allied also has and assortment of uninterruptable power supplies (UPS) to power you equipment in the event of blackouts as well as power inverters that supply AC power from a battery. This is power supply circuit which have 2 output that are static output and adjustabled output. 25A output Low dropout, only 40mV - 400mV compared to 1. Hobby power supply available at Jameco Electronics. txt) or read online for free. Measure the input voltage to pin 3 of IC2. Model #: B07JCYQ644-AE; Item #: 9SIASSADJV3284; Return Policy: View Return Policy $ Digital Power Supply 30V 5A 110V Precision Variable DC Digital Adjustable Lab. This is a practical hobby power supply kit for all your projects. 00. $69. Handy conversion kit plugs into your ATX power supply to create a benchtop power supply with enough juice to run most of your electronics projects. New, unused, with manual. 8 VDC. Using a variable/programmable power supply allows digital or analog control of the power supply output by a control system for maximum versatility. 99. 25 V to 32 V. Like command control, these trains still require a constant voltage to the rails. There are many sizes, power types, and power adjustment options in available in power supplies. We offer high quality products with unrivalled support from our local engineering support, in-house design facilities and manufacturing locations around the world. 6a They are widely used as LED Driver Power Supplies, Servo Control Power Supplies for CNC and Robotics or just prototyping and projects requiring 9. These are handy protections to have in the prototyping environment where the unexpected happens! DIY Variable Power Supply With Adjustable Voltage and Current: Hey Guyz, This time I'm making a variable bench power supply. 12V dc power supply schematics Steve G. 01V, 00. 5 - 35 Volt DC Regulated Power Supply Ampere or Current Booster Discrete Virtual Ground Stabilized Regulated Power Suppl Our selection of switching DC power supplies is one of the largest stocked offering in the USA. Get same day shipping, find new products every month, and feel confident with our low Price guarantee. IR2153 SMPS 300W Version: In general, IR2153 Supply voltage is taken over 220v filter capacitor, that is, over + 310V resistor or mosfet regulator. c. US! MP3020D LED Variable Adjustable Lab DC Bench Power Supply 0-30V 0-20A. LM317 Variable Voltage Regulator; LM317 Regulator With Pass Transistor; Variable 3 - 24 Volt / 3 Amp Power Supply; Variable Voltage and Current Power Supply; Lithium Ion Battery Charger using a 555 Timer, LM339 and TL431; Lithium Ion Battery Charger Using a TL431 And Single Transistor; 2 watt switching power supply; Low Power DC to DC Converter DC Power Supply Variable (0-30V, 0-10A) KAIWEETS® Lab Power Supply, 4-Digital LED Display Adjustable Regulated Bench Power Supply for Lab Teaching, Electronic Repair, DIY, with 5V/2A USB Port. 01A) Adjustable Switching Regulated Power Supply with 115CM Alligator Leads, USB Interface, US Power Cord. Linear Regulated Dual Polarity Power Supply "There are two versions of the power supply which are fundamentally very similar. Transistor Variable power supply 1A, 0-30V; 0-20V,1A DC adjustable Regulator using transistor A variable DC power supply is an integral part of any power supply unit used in the all-electronic equipment’s. 51/100 cm) DC Power Supply Variable, Adjustable Switching Regulated Power Supply 30V 5A with 4 Digits Display, Course and Fine Adjustments(00. If you want it to spin in the opposite direction, you'll need to reverse the power. Other uses include science projects or any other use where stable voltage up to 30 volts is required. Makermotor provides variable speed gear motors and single speed motors for applications such as bbq rotissier motor, experimental motor for lab, conveyor motor system, and welding turn table. High Power Density 15KW in 3U Programmable DC Power Supply. mpja. Most of the DC power supplies currently being manufactured provide only 12 to 13. Variac Transformer TDGC2-2D is an affordable, versatile way to control AC voltage output. These power supplies work by varying the power on the AC side of the circuit via a TRIAC dimmer. First power supply circuit is built with BD139, one zener diode and a few passive components. The circuit provides good load regulation, its maximum current being not more than 500mA, sufficient for most applications. This is because our DC power supply will supply variable DC voltage of 1-20V. Regulated DC Power Supply using transistors. It is most likely a Linear design without Switching at high frequencies. 2 –30 V. 01V, 0. There are two outputs; one regulated at 5 VDC, and the other one is variable. You can convert anything by just making adapters for the motors , the 56C face mounts are nice, but there are plenty with plate mount also. Which type of power supply you use in your electronics project comes down to the unique requirements of your design. By using two power packs, you can use toggle switches to alternate which power pack is Suppliers of Precise Variable Cv Cc Power Supplies, Precise Variable Power Supply, Thane, India (022) 2173 62 42 / 2173 62 43 / 324 30 817 response@sairushpowersupply. " DC Power Supply Variable (0-30V, 0-10A) KAIWEETS® Lab Power Supply, 4-Digital LED Display Adjustable Regulated Bench Power Supply for Lab Teaching, Electronic Repair, DIY, with 5V/2A USB Port 4. Check the specs to be sure they’re compatible with your motor. Visit Us Today. Call our Customer Service at 818-675-9000 if you find a lower price on any of our items we'll match it. Takes a 100-240VAC, 50/60Hz input. Quantity. Small 6x5x2. Our power supply range includes an extensive selection of batteries, consumer plugpacks, laptop power supplies and accessories. 4. We help you save time, resources and money. Arduino cannot supply variable DC output! Arduino lacks a true analog output! Use Pulse-width modulation (PWM) to simulate a variable DC supply voltage! PWM is a common technique for supplying variable power levels to “slow” electrical devices such as resistive loads, LEDs, and DC motors! 5V 2. So I Buying Advice - Which Hobby Type Variable DC Power Supply and AC Power Supply To Buy? Thread starter ZeusMC; Start date Jan 7, 2021; ZeusMC Member. This simple MOSFET controlled transformerless power supply circuit can be used for delivering a continuously variable 0 to 300V DC output and a current control from 100 mA to 1 Amp. Typical AC-DC power supplies will employ either some or all of the above components in its circuitry as either an Unregulated or Regulated Power Supply. But it still has the same characteristics as a fixed regulated power supply. 001A), Data Hold - 110V/115CM Alligator Leads MDC01 4. by Lewis Loflin. 30v 0. regulated supply, you might select a used "9 VDC" wall wart rated at 100 or 150 ma. the electric circuit consists of an AC Transformer followed by a rectifier bridge then smoothing capacitor and an adjustable voltage regulator integrated circuit. The static output is stabled and regulated output. Small Variable Power Supply by Miroslav Adzic ; Soft Start power Supply by Miroslav Adzic ; Universal PSU By Volker Jeschkeit; Add-On Current Limiter by Ron J ; 1. Hobby power supply for electronic hobbysts. There are plenty of DC controllers available on eBay. 95. 8-23VDC. Dial easily turns to select the desired voltage and it plugs into a standard electrical outlet. You must look to make sure a power supply qualifies for alternating current (TRIAC) dimming by checking the specs. You pick the 5A at 5VDC unit at 3-7/8" x 4" x 1-3/8" or the 8A at 5VDC at 5" x 3-7/8" x 1-1/2". Size of board: 3-1/2" x 2". Separate controls for voltage and current is a must on a lab DC power supply, and the voltage control should either be a multi-turn control or there should be a separate fine tune control. 1. The 2N3055 and 2N3053 transistors should be Available from RC Accessory, the Titan is a monster of a power supply with dual outputs and adjustable voltage from 12v up to 24v. 3 ohm). 3, 5 and 12 volt outputs. $36. 400 mA Variable DC Power Supply. The LM317 is an inexpensive solution to simple variable power supplies. Especially with these 100-120VAC input regulated switching power supplies with trim pots to adjust the output 0. 5A Short circuit protection Lead: 6ft long, 18AWG Select the appropriate Adaptaplug suitable Turnigy 1200W Power Supply (US) May 19, 2019. 001A), Data Hold - 110V/115CM Alligator Leads MDC01 Uniroi Dc Power Supply Variable 0-30V 0-10A Dc Bench Power Supply With 3-DIGIT LED Display Alligator Clip Leads Input Power Cord. 371. Description: Every hobbyist runs into the problems when you need 3. Hobbylinc carries 89 model trains power supply / transformers at discounts up to 35%. Hobby guns may have fixed voltages or a high and low setting. Only US$24. This circuit is not an absolute novelty, but it's simple, reliable, "rugged" and short-proof, featuring variable voltage up There are many sizes, power types, and power adjustment options in available in power supplies. In addition this circuit to be either be battery powered 9-25 VDC (maximum 25V @ 300 mA), or powered from a wall transformer also 9-25 V (maximum 25V @ 300 mA) with either an AC or DC output. Shop with ease and confidence at the USA's largest 100% power supply focused distributor. With these costing you only $25 and having short circuit protection, thermal protection, Overload protection and varied output voltages of 3v, 5v and 12v but we will me modifying it to give out 1. What is a variable power supply? Simply said it is a power supply that can adjust the output voltage or current. or Best Offer. c. You can read about all kinds of things people do to power their hot wire foam cutter including things like running 110V through a light bulb in series with the foam cutter, battery chargers, dimmer switches, Variacs, "wall warts", batteries, and so on. Parts List. Features: are a locomotive, a power pack capable of producing variable voltages, and two wires. Main Power Connector. 01% + 1 mV, CC <= 0. There are many sizes, power types, and power adjustment options in available in power supplies. 1-10V Dimming: 1-10V dimming can be used to control dimmable power supplies such as 12V Mean Well HLG-40~240 Series or 24V Mean Well HLG-40~240 Series. Before connecting the battery, set the input voltage to IC2 using a fully charged battery or variable power supply. The capacitance C3 bypassing the ADJUST pin to ground will improve the ripple rejection capability while the diodes are used to protect the regulator from excess flowing through it if a battery or any other voltage source is connected across the output terminals of the regulator. 5V either way, vented housings, 5-pole terminal blocks for AC in, chassis ground and DC out. The Keysight E36313A is a programmable 160 watt-triple output DC power supply with USB and LAN interface. Power supplies and DC power - Deliver the power that your model railroad needs with our range of power supplies, including wiring components and standard DC power packs. 01V, 0. DC DC booster section has a tiny preset. I have a big screen HP laptop computer. 8A. 25V - 2. This is the simple solution. They’re more intuitive and offer a lot more options for environment control and simulation. Voltmeter and Ammeter. Usually, theseunits use vacuum tubes in the output stage, and consequently, requirea very high voltage power supply : often in the 4000 to 10000 volt DC range. It can drive 2 DC motors and we can also control the speed by providing PWM signals. 20” x 2. 5 A from an 8 to 60 V supply. DC power supplies normally have two specifications, the output voltage and the output current. 5 mV RMS, CC <= 3 mA RMS; LCD reading accuracy: +/-1% for voltage and +/-2% for current This small regulated switching power supply features 2 Powerpole outputs in front and 1/4" binding posts in rear. I have several surplus laptop power supplies often rated at 19V at several amps. 01% + 3mV, CC <= 0. Power Supplies: Low Volt DC High Amp HEALTH, HEALING, WELL-BEING Body Energy Charging Machines Lakhovsky Multiwave Healing Machines Negative Ion Well Being Machines Ozone Purifiers and Sanitizers Pulsed Magnetic Healing Machines Books and CDs NEON & PLASMA DISPLAYS Neon Xfmrs: Conventional (UL2161 & non-UL) The best guide you’ll ever find for a DIY power supply is one of [Dave Jones]’ earlier video series going over the construction of an adjustable power supply based on an LT3080. . Whether you need one of these handy tools in the classroom, in your job, or as a tool in a particular hobby, you will be able to easily find an affordable used adjustable power supply for sale on eBay that will suit your needs. 1. 60V 5A DC Bench Power Supply Variable Precision Adjustable Regulated Power Supply 4-Digital LED Display-with Alligator Leads and US Power Cord for Lab Equipment DIY Tool Repair Electronic Research. Our Crafters and Multi-Heat Pro Power Stations can be used Worldwide! To see the tools in action, check out our Video Turorial page . With one channel isolated users can reconfigure instruments into any number of systems or applications. Variable Dual Lab Power Supply: can supply from +/-1. View in Order History. The static output is stabled and regulated output. 5 amps, which is about 180 watts. In the program we have set four different conditions to run the DC fan. Tools; Paint & Brushes; eFuel 60A 1200W 15-24V Variable DC Power Supply. New, unused, with manual. For a shunt wound DC motor rpm is nearly linear with voltage, and even more linear with PMDC. . To protect against my high voltage research projects from going up in smoke permanently, I developed an easy circuit which is able to render a variable voltage The multi-output power supply is a very useful project for hobbyist, the small module provides 12V, 5V, 3. And if you want to know how far it has turned, you'll need to devise a way to measure that. 26” (mm: 183 x 132 x 57. 3-12V DC 27W Power Supply 7DC Plugs and USB Outlet High performance motor controllers for DC motors. 0V DC and a battery case that holds 4 x AAA batteries (approximately 6VDC). AC AC Wall Adapters (309 items) AC DC Configurable Power Supplies (Factory Assembled) (9191 items) AC DC Configurable Power Supply Chassis (215 items) Variable 3 - 24 Volt / 3 Amp Power Supply. , you might select a small "12 VDC" wall wart rated at 100 ma. Unregulated Power Supplies I have tried twice to get help utilizing a Trotter 525 treadmill motor. Jul 26, 2020 - Explore Ramonitogamboa212's board "12v variable power supply" on Pinterest. Prices Today for a lab power supply well exceed $180. BR1 = Bridge Rectifier, 100V - 3A C1 = 2200 µF, 63VIC1 = LM317, adjustable regulator C2 = 0. Bench Power Supply, DC, Programmable, 3 Output, 0 V, 6 V, 0 A, 5 A. 3 A to 180 A. 6-36v 5a power module adjustable regulated laboratory power supply variable sale online store at wholesale price. This circuit is not an absolute novelty, but it is simple, reliable, "rugged" and short-proof, featuring variable voltage up to 24V and variable current limiting up to 2A. Switching, Table-top, Medical, LED, DIN Rail and more! Electronics Component distributor offers same day shipping, adds new products every month and has a low price guarantee. Red Panda - Benchtop Dual Regulated Variable power supply Cheetah - 150 watt Amplifier using 2SC5200 / 2N3055 / 2N3773 NPN Transistors Gir Lion - 600 watt Mosfet Amplifier using IRFP240 9240 Hot Wire Foam Cutter Power Supply Design. A Variable DC Power Supply is very important for electronics projects, prototyping and hobbyists. Features variable frequency using a potentiometer. 5A 18W DIN Rail Power Supply. Also, with these devices, you can get the freedom to regulate the control and voltage supply using simple dials, which adds extreme benefit to these power supply devices. These best lab power supplies are from famous brands, very affordable for any budget, and have one year warranties. * Variable Laboratory DC Power Supply Voltage range: 0. 4. 12V DC to your separate 12V DC controller that has a voltage regulator knob but does not incorporate its own transformer. XP Power is a leading global supplier of power supplies with the widest product range in the industry. However, in the electroplating industry, plating engineers refer to power supplies as rectifiers. Can power many Arduino projects. 5A variable regulated power supply. Power Supplies New Zealand - Powerbox, have a complete range of power supplies - AC/DC Power Supplies, DC/DC Converters, AC/DC Power Modules, DIN Rail Power Supplies, Single and Multi Rail Enclosed, LED, and Open Frame power supplies, Security power supplies, UPS and Battery Chargers plus Desktop & Wall Mount Power Adapters, AC Transformers, AC-DC Invertors, Euro Cassettes, Laboratory power 3-12V DC 18W Power Supply 7DC Plugs and USB Outlet. Therefore, we lower the very high voltage that we get from the mains outlet from the wall into a smaller voltage. See more ideas about circuit diagram, power, electronics circuit. 3) Aluminum, perforated cover fully encloses the supply (UL “finger safe”) 53 joules of capacitive energy storage for lossless storage of regenerated energy and reduced output ripple. The Extech 382213 30V/3A Digital Triple Output DC Power Supply with Fixed 5V/. We stock a huge selection of RC products from Planes right through to Drones and all accessories. These often have more than one output voltage that can be adjusted over a range of voltages such as 0-32V. This is the most useful equipment for a hobbyist and DIY maker cause while making or testing circuits, it needs different values of voltage and current. The selection becomes a bit more complex, if you desire a 12 volt regulated supply. See full list on powerelectronics. 00. Hobby power supply for electronic hobbysts. As your needs grow, you can employ a larger transformer of fixed voltage. " from Wayback Machine. If you need a 9 volt regulated supply at 70 ma. 6 out of 5 stars 969 The KORAD KD3005D is variable from 0 to 30V DC, and can support up to 5 amp loads! This unit has built in overload protection for current, short circuit, and even temperature. Benchtop Power Supplies are in stock with same-day shipping at Mouser Electronics from industry leading manufacturers. 90-180V 10A. Slim profile - why take up a huge footprint out of your small work space? It has 50% more power than the typical 1200Watt hobby bench power supply if you don’t want to be bothered with converted computer server supplies. A variable dc power supply is one of the most useful tools on the electronics hobbyist's workbench. Check Store. Each $80 Mastech HY1803D variable dc power supply. 5 to 15. This is power supply circuit which have 2 output that are static output and adjustabled output. In this blog we will make a High Current power supply with LM317 Voltage Regulator and a couple of Power Transistors I am an IT guy, as you know. I found a used industrial model on E-bay several years ago, 0-60 vdc, 0-6 amps, cost a couple of thousand new, but I think I paid like $25 + shipping for it, about the size of a large shoe box. The LM338 has a protective structure in its structure that prevents overheating and damages the output transistor caused by a short circuit. The versatile Car DC power supply will power just about any DC powered item in vehicle. The DRV8313 does not include sensor inputs. With one channel isolated users can reconfigure instruments into any number of systems or applications. Types of Power Supplies. Some of our customers manage to plate using a 6 or 12 volt battery, or charger, and bulbs as a current control. 1/2-2HP. Variable Power Supply using LM317. This is the cream of the crop when it comes to power supplies. It is a Smoothly Variable Regulated DC Power Supply. 4V, but I want to run it from a mains-derived power supply instead. Of course the output is short-circuit protected too. . 0V for LM317. KEYSIGHT TECHNOLOGIES. Instead of using batteries, which have a limited lifetime, a variable DC power supply can be used which is implemented in this project. The 62000H Series DC Power Supplies offer a high power density envelop of 15KW in a 3U enclosure, deliver low output noise and ripple, have excellent line and load regulation, and have fast transient response. 2 volts to 13 volts which is pretty much all you need for doing hobby electronics. Hobby Power Supply Kit - CK0400, Soldering required. There is no question that a programmable DC bench power supply can be a very useful thing to have around. 05(2 used & new offers) Bestsellerin Lab Power Supplies. There are more efficient and complex power supplies in the world. Galley; Majestic Transformer Co design and manufacture high quality bespoke and custom built electrical transformers Variable DC Power Supply from are manufacturing premises in Poole, Dorset, England. 1 µF V = Meter, 30V, Ri = 85 ohm C3 = 1µF, 40VTR1 = Transformer, 25V, 2A Plug = 3-wire plug & cord R1 = 18K, 5% S1 = On-Off toggle switch R2 = 220 ohm, 5% D1 = 1N4001 R3 = 27K, 5% Fuse = Because so many electronic devices need DC to function properly, a versatile power supply is the perfect addition to a hobbyist's collection of test equipment. 5 out of 5 stars 440 Power Supplies and DC-DC Buck Converters for Electronic Hobbyists. 1V at 25A continuous, 30A surge. 99 Variable AC Power Supply: Rino odorico: Everything Else: 12: 14th March 2013 04:56 AM: Charging batteries with a variable power supply: jacquesl: Power Supplies: 4: 13th March 2013 07:52 PM: Bipolar Variable Power supply for protoboard: jman 31: Power Supplies: 10: 24th March 2009 02:39 PM: Variable Pc Power Supply-2 (part1) 1. AC-DC Power Supplies from XP Power . This design was conceived as an add-on for the Variable DC Power Supply, a very successful circuit posted to this website. power supply for circuit breaker testing; Continuously variable 24-250 V AC or DC output; Separate outputs for close coil, trip coil and spring charging motor voltage; Direct triggering for minimum trip voltage testing; A variable DC voltage is needed to test a circuit breaker. But it turns out a obsolete computer power supply is perfect for the job instead. 5" footprint. 2% + 3 mA; Ripple noise: CV <= 0. Adjustable outputs: 0-18V and 0-3A; Line regulation: CV <= 0. As your layout grows you’ll want to create electrical “blocks” of DC power. This is an excellent introduction to power supplies - DIY Kit 4. You can adapt it to your own requirements as explained in the notes below. Currently we only make linear DC power supplies with output below 20A. MULTICOMP. Reliable and stable a. Complete with all parts, PC board and instructions. Whether you need one of these handy tools in the classroom, in your job, or as a tool in a particular hobby, you will be able to easily find an affordable used adjustable power supply for sale on eBay that will suit your needs. 2v and 9. Modern HO slot car motors require at least 18 VDC, and 1 ampere or more of current for proper operation. 3V-12V DC, 1. For an electronics professional, hobbyist, or a beginner, the best lab power supply that I and field professionals recommend is either the Tekpower TP3005T, or Siglent Technologies SPD3303X-E, or the Rigol (DP823). 1: Circuit diagram of the simple power supply with adjustable voltage and current with LM350. The circuit is based around the 7805 voltage regulator. Brand New. Schematic drawings and parts lists can be found in amateur radio publications, or you can get assistance in your quest by any well informed ham operator. VARIABLE REGULATED POWER SUPPLY - Hobby Engineering The power supply secondary circuits are isolated from the 120V primary circuit via the power trans- The Model XP-650 and XP-750 are solid-state DC power supplies, continuously variable from 0 to 40 volts. 01V, 0. Linear DC power supplies have exceptionally low ripple but tend to be heavy and less efficient, while switching DC power supplies have very high power efficency, and good noise and ripple performance for most of applications. 5A Nickel-plated metal For powering electronic devices up to 2. DC motors produce a high starting torque and power to drive equipment such as conveyor belts, elevators, cranes, and hoists. Here are two simple AC-DC power supply circuits, one without a filter and one with: 75 VDC output; 350 Watts continuous power (500 Watts with fan cooling) Compact size: 7. The DRA18-12 is an AC-to-DC DIN-rail mount Power Supply with fixed output. It’s because, I can’t afford a lab bench power supply worth several hundred dollars. This regulated power supply can be adjusted from 3 to 25 volts and is current limited to 2 amps as shown, but may be increased to 3 amps or more by selecting a smaller current sense resistor (0. The most popular model trains power supply / transformers brands include Woodland Scenics, MRC, Bachmann, NCE Corporation, and Digitrax. Always delivers the power I need. Skill Level 2. Whether you need one of these handy tools in the classroom, in your job, or as a tool in a particular hobby, you will be able to easily find an affordable used adjustable power supply for sale on eBay that will suit your needs. Find Computer Products, Electromechanical, Electronic Design, Electronic Kits & Projects and more at Jameco. The DP800 Series is a family of linear power supplies systems with 1, 2, or 3 outputs and 140 to 200 Watts in total. In these circuits, 18k 2w resistor is connected FOR HOBBY USERS DM-330MVT DM-330MVE The Next Generation of Communications-Grade Switching Power Supply ¡30A regulated class highly reliable power supplies ¡Noise-Offset circuit to eliminate possible pulse-noises of the switching circuit ¡Short circuit protection, current-limiting systems and extreme-temperature protection ¡Preset voltage feature YouTube video Current Boost LM317 Adj. hobby variable dc power supply