The post describes a simple but extremely versatile 100 amp, variable voltage power supply circuit using just a few BJTs in parallel and in a common collector mode. The idea was requested by Mr. Andre.
Technical Specifications
Hello Swagatam, I was wondering if you could possibly assist me. on the blogs I have seen some diagrams for simple variable power supplies.
Firstly I know very little about electronics, but with a shopping list and a diagram I am sure I would be okay.
I would like to build a simple variable power supply with an input of 220/240 volt ac and an output variable voltage of approx. 1.5V to approx. 15V and a variable output current of up to approx. 100A.
I have started zinc electroplating as a hobby (have sweaty hands and want to protect all my tools) the chemical company gave me these as a more or less dependant on my zinc plating bath size.
At the moment the little 6V 8A Ryobi battery charger works for a few minutes, overheats and cuts out till it cools down again. I would really appreciate any assistance you could give me on this.
Many thanks
Andre
The Design
A very straightforward circuit design for the proposed 100 amp variable voltage power supply can be witnessed in the following diagram.
The design basically utilizes a common collector or an emitter follower topology for implementing the operations, by incorporating just a few Darlington power transistors, some resistors and a pot for varying the output voltage.
As can be seen in the diagram, the collectors and the emitters are all joined in common across each other while the bases are made into a common line via individual limiting resistors.
The free ends of these resistors are joined together with a pot across the negative line of the circuit, which determines the voltage regulation at the output of the circuit.
For acquiring more current, more number of transistors may be added in the design, and for reducing the output amps, these may be simply deducted from the configuration.
For inputs above 50V the pot must be upgraded to a high wattage type to sustain the high voltage across its terminals.
All the power devices must be mounted over a common aluminum heatsink without any mica isolation, so that the dissipation is shared uniformly across all the devices and a thermal runaway situation is prevented.
The circuit is simple and effective
I have a problem with short circuit protection at 50V output.
It does not respond fast enough even if I limit the current at 2.5A
Even a relay current cut off circuit is to slow
The TIP142 blows instantly
Any recommendations?
Regards
Naude
You can add a current control feature to the above design as shown below. The current control transistor can be a 2N2222. Make sure to add a series 2.2K resistor with the potentiometer. The current limiting resistor RX can be calculated by solving the formula, RX = 0.7 / Max current.
https://www.homemade-circuits.com/wp-content/uploads/2023/07/100-amp-current-controlled-variable-power-supply.jpg
Thank you. Will try
I looks as if with the 2k2 there my output will only be 46V if my input is 56V and I need at least 50V max
OK, in that case put the 2.2k resistor in series with the wiper arm of the pot, just after the arrow head. This is actually to safeguard the 2N2222 current limiting transistor. However I think 2N2222 is rated at a maximum of 40 V, in that case you can use some other NPN transistor which can handle upto 100V.
Of coarse! I see. Thank you
I will report back
Hi
I had time to test the current limiting today
Like all the other methods it does limit current what it was designed for but on 50V with a dead short on the output it is just not fast enough and blows the darlington collector emmitor
Hi, maybe the current limiting resistor value was not appropriate, you can try increasing the value of the resistor, that might solve the issue. If not then it is unfortunate.
I am sorry to say that this is not a good circuit and its construction should not be recommended. Unbalance of collector current of transistors followed by thermal runaway is unavoidable
Emitter resistors are provided to avoid thermal runaway. The circuit may not be efficient but very easy to build and implement.
I am trying the 100amp power supply and it would not work , is they any one who got it to work
What kind of problem are you facing? Try with 10 amp first and check the response.
I am getting the same input voltage at the output and not adjusting, what I did to get it to work I place the input voltage on the base, and the base resistors on the collector and got a good variable voltage on the emitter but it cannot handle a load, it falls off from 13.8v to about 5v.
If the voltage is not adjusting then something might be be wrong with your transistor or the connections. Try with a small load at the output and check whether it is adjusting or not.
Hi Swagatam,
Good day to you. I am Manjunath. I have read your articles and the answers are good. I have a question that is how to convert DC 5Volts 3 Amp from the Battery pack of DC 12Volts 90Amp? Please give me your ideas for me.
2nd question is how to make a charger (Input AC ~220 Volts) for a Battery pack of DC 12Volts 90Amp.
Thank you Manjunath, for liking my articles.
You can probably try customizing the following circuit for boosting 5 V to 12V
https://www.homemade-circuits.com/wp-content/uploads/2021/05/boost-charger-compressed.jpg
You can adjust the number of turns of the coil to test the output response.
For the charger you can simply refer to the following article:
12V Battery Charger Circuits [using LM317, LM338, L200, Transistors]
Hi Swagatam,
I am asking about the buck converter from 12volts 100 Ah battery to 5v 3A., not for the boost converter. If you have any ideas on it please share them. You are only the person who can help me…Please help me on this.
Hi Manjunath,
OK for a buck converter circuit you can customize the following circuit according to your own needs:
PWM Solar Battery Charger Circuit
If you have any further queries, please let me know.
Hi Swagatam,
I am always inspired from your post as they’re always helpful and great.
This circuit is interesting i want to test it as i have a SMPS 12v and 100amps. But one thing is confusing. In the given above circuit you used 11 transistor as each can bear 10A so overall 110A safe range for 100A.
If i connect my SMPS with it and for example voltage is decreased using the pot (given in your design) wouldn’t be the current at the output become high enough to blow transistors immediately.
I see that the circuit doesn’t have protection against overload and short circuit at the output. Please guide me if anything i can add or modify for it. Many thanks & Hats off always
Hi karan,
The number of transistors are actually not accurate, for 100 amp current there must be at least 20 nos of TIP142. More the numbers cooler will be the transistors.
The current through the transistors will depend on the load, not on the voltage adjustments. But yes wider input/output differential will cause the transistors to heat up a lot, that’s the drawback of all linear power supplies. To correct this, the input voltage range from the SMPS must be reduced appropriately.
Protection has not been provided, you can add a current limiting by adding a common 2N2222 limiting circuit network, as explained in the following concept.
2 Best Current Limiter Circuits Explained
Hi
I want to DIY Electroplating IGBT controlled full DC Rectifier 0-30 Volt DC and 500 Amp. Please help me out I saw some readymade circuit on Aliexpress but without full diagram
Hi, sorry, presently I do not have the requested circuit with me…
Hi Swagatam. I am searching a circuit which I can use as battery charger and as welding machine. I mean, by the primary of the transformer regulate the current and voltage. Where I can set up voltage for battery charger and charging current. I I need a welding machine use it with this application. Max voltage 40 or 48 and current from 30 to 1000.
Is it posible to design?
Hi Rafael, 30 to 1000 amp looks too high, and will require special mosfets to control the current….the transformer primary cannot be used for regulating the current.
If possible I will try to find a suitable circuit for you soon…
hello sir,
I need 5 volt dc and 100 amps power supply circuit diagram so please send me as soon as possible and send me your phone phone number for further conversation.
thanks
Hello Mohd, sorry I do not have a 5V 100 amp smps circuit with me at this moment…
how is this circuit going to give 100 amps, when you have 11 resistors in parallel of 3 w each, 10 amps makes more sense, but how is it going to pass 9 amps through a 3ohm resistor and dissipate 3 watts ???????
It is just an idea, you can customize it by reducing the resistor value, or add more number of transistors stage in parallel.
Looking for advice regarding a magnetiser I want to build for magnetising tachometer magnets. I would like to utilise the core of a welding transformer to wind a U shape electromagnet of 1500 turns which will carry 8 amps of current at 120V DC. The current will be switched on only for a few seconds at time to produce the magnetising field. I need a circuit for producing the 120V DC from a 240 V 50hz transformer. In that circuit I would like to use an SCR to turn on the current flow and have means of turning it off, either mechanically or electronically. Please advise if this is of interest to you,
You can try implementing the following design
I like to know more about this news letter
I assembled the circuit but the pot is extremely sensitive to any movement. When I connect a 12v motor and I set it to 12VDC output, the voltage drops to just over a volt using 22vdc battery as the supply voltage. Did I assemble incorrectly? I checked all the voltages across the TIP142’s, and all the voltages are almost the same in reference to ground. By the way, the motor works fine just using the battery. I need to make this circuit work so that I can connect multiple devices to a battery set and make sure all the current is drawn through the BMS. Thank you
What is the current of the motor? And how many TIP142 have you used?
Hello again Swagatam,
I’m building a power supply that will be 60v @ 20a. The transformer that I’m using after rectified and a smoothing cap is at 90v. It’s over a 1000va transformer. I want to get it regulated down to 60v. Would this circuit work with just a few TIP142s. I also have some 10k precision pots that are rated for higher voltage, but would probably end up using fixed value resistors. Or would you have a better solution.
Thanks, Ken
Hello Ken, yes, the above circuit can be used for the mentioned purpose….. for more info regarding the same and all the calculations you can refer to the following post:
How to Design a Stabilized Bench Power Supply Circuit
I would like to build a simple variable power supply with an input of 110 volt ac and an output variable voltage of approx. 1.5V to approx. 15V and a variable output current of up to approx. 100A
You will need an SMPS design for this, however I do not have this circuit with me at this moment
Hey there,
I am looking for a 8.1 100A buck converter. The power source is an Hp server power supply as seen here (https://www.ebay.co.uk/itm/HP-Proliant-1000W-Pwr-Supply-DL380-G5-DL385-G5-379124-001-HSTNS-PR01-403781-001/143648658961?hash=item2172209611:g:sw4AAOSwYxBemwUa)
Would this be possible. This will be used to charge a 3s2p supercapacitor. if possible Constant current and voltage.
Hey, can you provide the input voltage source specifications for the buck converter?
It’s 12v max 82A
You can try applying the following concept, but the transistors and the inductor will need to be heavily upgraded to handle 100 amps
PWM Solar Battery Charger Circuit
hello, i would like to ask if i can use this circuit to regulate the output of a 12v SLA battery to 100amp only? or less lets say 80amp. thanks.
Hi, no, the above circuit will regulate only voltage, not current.
do you have any circuit that can regulate sla battery current? thanks
You can use the following concept:
https://www.homemade-circuits.com/regulated-car-battery-charger-circuit-for-garage-mechanics/
You can replace the transformer with your battery, the output will produce a voltage and current regulated supply
Dear sir,
The request is , Quote “I would like to build a simple variable power supply with an input of 220/240 volt ac and an output variable voltage of approx. 1.5V to approx. 15V and a variable output current of up to approx. 100A.” Unquote.
If you clarify on following points i will be happy. The quote mentioned variable output current of upto 100A .Is the current variable in your circuit or it is fixed 100 A.
Where the input is to be connected, i think a separate 230 V Ac to 12 V Dc has to be wired separately?
In the above mentioned circuit, one is 150 A and other 100 A, what is 150A and 100 A. Why both outputs are given
Dear K premila,
The current is not variable, it will almost equal to the input current supply.
the circuit is designed to work with a 100/150 amp transformer.
The output is shown as 100amp to indicate that a minimum 100 amp can be achieved without fail with an input of 150 amp.
If you want to avoid the transformer, it may be possible by replacing all the BJTs with MJ10023 and by feeding a rectified/filtered 310V at the input side, this design being not isolated from mains this configuration can be dangerous to touch, so proceed with caution
Thanks for your clarification
Regards
Premila
you are welcome!
Ola Swagatam,
como faço para te enviar um arquivo para analise?
Olá Swagatam,
como posso enviar um projeto para analise?