Power One Hackers Blog

Welcome to the Power One Hackers blog, for Power Supplies and related projects:high power electronic load, USB controlled voltage / current source, etc.   Post your questions, comments, ideas, etc. I look forward to hearing from you.

Here is the page supported by this blog:  http://www.djerickson.com/p1hack/

Dave Erickson


  1. I’m working on an isolated SPI / DAQ device to control VIs and E-Loads and just about anything else.

    I’ll keep you posted here.


  2. Dave Erickson says:

    Message from Dave:
    This blog should be back in business. Please forgive me if you have tried posting here unsuccessfully before.


  3. Bruno Ruinho says:

    good day! I have a “power one” HD-24 would transform it into a variable power supply. is possible?

  4. The HD24 is a great candidate for this change at 24V and 4.8A. It’s easier if you have a real schematic, but the HC15 schematic on my site will get you close. When you remove the board you can reverse-engineer the circuit to pins 4, 5 and 6 and the + and – sense pins. That’s where the changes are.

    With minor changes you can get the output down to about 2-3V. Any lower output and you need to eliminate the LM723. Here are the minor changes:

    Get the +IN pin 4 down from +7V to +2V (the minimum supply output). To do this, add a resistor divider like 5K + 2K to reduce the 7 V to 2V. 5K between pin 6 and 5, 2K between 5 and -SENSE. This may require cutting the trace to, or lifting pin 5, +IN. If you are lucky there is already a resistor between 5 and 6, and you can just remove it and replace it with the 5K. For 5K, use either 5.1K or 4.99K.

    You should then measure +2V on pin 5. The output voltage will now be pretty low and the adjust range low also.

    Then to increase the output range, remove the adjust pot and the resistor in series with it, and the resistor from the – input (pin 4) to -SENSE. Replace the adjust pot and series resistor with a 10K panel mount pot, wired to the board. Use a 10 turn pot for finer adjustment. Clockwise is increasing resistance and increasing voltage.

    Replace the resistor from pin4 to -SENSE with a value =
    2V /((24V-2V)/10K) = 910 ohms.

    I have been wanting to try just this change on this supply. Let me know how it goes. Don’t forget that you can’t get the full 4.8A current all the way down to low voltages unless you use a big fan!


  5. foollikeafox says:

    Hi Dave,
    i have a power-one HE12, the output is 24V, and if we use load, the voltage will below 12V. how can i fix it? i don’t have the schematic.
    thank you.

    • Dave Erickson says:

      It’s not hard to troubleshoot even without a schematic. You can use the schematic on my web site as a general guide. They are all pretty close to that.
      Check that the unregulated supply is over 24V. If that is Ok, the problem is usually either the LM723, the output transistors, or the driver transistor.
      I have seen the sense resistors (between the output terminals and the sense terminals) blown. Check them with a multimeter and replace if higher resistance than their labeled values. Not all supplies have sense terminals though.
      To check the transistors, put the DMM on the diode range and measure the B-E and B-C and E-C pins. B-E should be 0.6-0.7 in one direction, and higher in the reverse direction. Same with B-C. The E-C should read high, not shorted.
      Use the LM723 data sheet to check it’s pin voltages. Look for 7.1V on the reference pin.
      Good luck!

  6. jason says:

    Hi Dave,

    I have a MAP80-4010 multi-output supply. The -12v isn’t working and I’m looking for a schematic. Would you happen to know where to track one down?



    • Dave Erickson says:

      That’s a switching supply. More complicated than the linears, and hard to get documentations. I suspect the -12V circuit has only diodes, caps, possibly an inductor. Use a continuity tester to learn which parts are hoked to the -12, then check these parts.

      It’s probably the diodes or the output caps.

      Good luck, Dave

  7. archy587 says:

    Hey Dave, Really enjoyed your linear power supply hack. Im not really an expert in electronics but I’m trying to pick it up. Im interested in building ardunio based 3d printers (Repraps) like the mendelmax or similar.

    I found you page when trying to figure out how to fix my power one switching power supply, thought maybe you could offer some advice.

    It’s a 24v 10A power supply with remote load sensing circuit. from what I understand now, if your load is far away from your PSU, you can connect leads from the sense terminals to the load, so that the feedback is used by your PSU to regulate the voltage at the load, compensating for any losses occurred over long wires from the PSU to the load.

    Anyway, I didn’t know about this when I went to apply voltage to a power resistor, which I wired only to the sense terminals, rather than to the actual power supply output terminals. This resulted in the immediate failure of 2 capacitors which I believe were the output filter capacitors.

    So, that was stupid, I swapped out the 2 blown caps, wired up the AC input again, with nothing attached to the output side this time, and one of the same caps blew out immediately after plugging in the PSU. I’m assuming I did some kind of damage to the sense circuit, but I’m not sure what. All the fuses I can check are still in tact.

    Do you think there’s any coming back from this? anything else I could try to swap out?…besides the same blown cap that is..

    sorry for the long post, just didn’t really know how to give a short sweet description.

    any advice you have would be great! thanks!

    • Dave Erickson says:

      That is a risk of remote sense terminals. If you accidentally connect a load to them, then what you saw can happen.
      I suspect that the resistors between the sense and output terminals, one each for + and -, are also fried. You should measure 10-100 ohms between each sense and output terminal. If they are higher than that, either replace them on the board, add external 10 ohm resistors, or add shorting wires. The resistors may be discolored.

      Good luck,

  8. archy587 says:

    Oh man you nailed it!

    I see two 2.9 ohm resistors between the terminals, one of which reads 2.8 Kohm, and resistance between out- and s- is also 2.8k.

    Hopefully I can swap that out and be up and running again! thanks so much!

  9. corey986 says:

    Dave your page has been very helpful. But I was hoping you could help me hack an hc5-6 5v supply to produce negative 9v. Using your instructions and schematics I was able to modify a 12v to -9 but it runs too hot at 2-3amps for my liking. I have a spare 5v supply and figure maybe it’s better to get the 9v out of it.

    I know I’ll have to remove or replace the zener diode in the ovp part of the circuit. But I can’t seem to find any schematics online for the 5v supply to figure out what needs to change for 9v. I could trace it out but figure you may already know where to look and what may need to be changed.


  10. Dave Erickson says:

    Neither is ideal. The 5V supply may produce 9V at low load, but probably not at full load. If it has a 100VAC power tap on the transformer, use that and apply 120V to get some more voltage. Watch that the transformer doesn’t get too hot. As you point out, you’ll need to disable the over-voltage protect.

    If you turn the 12V down to 9V, at 3A that’s (12V-9V) * 2A = 9W more dissipation. Use a small fan and you should be OK.

  11. borisklompus says:

    Hi Dave,

    Thanks for posting so much great information about these power supplies.

    I have a question that sort of has nothing to do with any of the hacks you’ve described. In a few of your photos I see that you’ve got screws going into the output terminals of the supplies. I have a few surplus HCC15-3s, and I’m not having great results soldering wires to the output terminals. Did you just tap the terminal pins to fit a screw? I haven’t been able to find a disconnect pin which will fit inside the terminal, but using a screw is a great idea. I’ve also been thinking about drilling the terminals out completely to solder directly to the PCB.

    Any insight into this is greatly appreciated!

    Thank you!

    • Dave Erickson says:

      Power One and other linear supplies’ output terminals take a bunch of heat to solder, so use a large tip and about 700F temperature. I generally heat up the terminal and then stuff a 22awg wire into the hole on top, adding a bit of solder. But these so-called “turret terminals” are designed to accept a wire or two wrapped around the terminal and then soldered.

      Hope this helps.
      Dave Erickson

  12. nlrobbins says:

    Dave! Great info here and I’ve enjoyed reading over your posts. I have an audio related questions.

    I have an old Trident Series 65 console with a less-than-ideal stock supply. Lots of folks recommend (and report success with) using two of the PowerOne F24-12-A supplies to replace the +-18v stock audio rails.

    The stock supply has several outputs: +-18v (audio rails), +5v for logic, +48v for phantom, and +8.5v for meter lamps.

    I can provide the schematic for the stock supply if necessary. My question is this: how would I use two of these to only replace the audio rail supplies and use the stock supply for everything else?

    The outputs of the stock supply list three separate “earths” or grounds: case earth, electronic earth, and lamp earth. I get continuity between all those, and the schematics show the grounds are common.

    I’d love to get my hands on the schematic for the F24-12-A. I’ve looked around the web with not much luck. I did email the company and am waiting to hear back.

    The F24-12-A has + and – sense terminals as well.

    Any ideas would help. I’m stuck…

  13. cloudhop says:


    I need to obtain -6 v for an old modular synth..I have a HCC 5 Power One…can it be modified to obtain -6v output ?
    It would be perfect if it could.


    • Dave Erickson says:

      Should work OK, particularly if your load current is 1/2 of the rated supply current or less. You may need to remove an overvoltage SCR or module if it is there. Then adjust the voltage to 6V and try it out. If it won’t go all the way, you may be able to change one of the resistors a bit to increase the output. Measure the output with a scope or AC and look for 120Hz ripple which should be just a few millivolts. Don’t forget to wire it up with the power supply + to the Synth GND since you want -6V.

      Good luck,

  14. cloudhop says:

    Thanks so much for your time and help Dave…I’ll certainly try this and hope I get the -6v ..by the way do you know where I could find the schematics to the HC 5 if I need to change any component ?

    Best regards


  15. roy says:

    Hello Sir,

    How do I safely wire a two (2)+- 15v. 3a. Power One and two (2)
    +- 15v. 3a. Lambda power supplies to obtain 30 volts 6 amps
    Power Supply. Do I need some discrete (diodes) to isolate each
    one of them. If so , how are they connected ?

    Best regards ,

  16. charlesh3 says:

    Dave: I have a 28V 2A Power One supply in an old piece of broadcast equipment. It smoked when powered up and the output is now 50V. There’s no supply voltage to the 723, and that’s because 2 components are totally blackened. Yhe 2 components are between the big filter cap and the TO220 and are below the 4 diodes.
    Question 1: as CR1 in the very upper left of seems to be the rectifier, what is CR9 which is one blackened component. Andwhat is the other blackened component to its left that has no silkscreen?
    Question 2: Are the blackened components the cause of the problem or the result of a down stream problem in the main equipment?


    • Dave Erickson says:

      Hi Chuck,
      I can’t speak to that specific supply, but the parts are pretty simple. If it says CR and looks like a larger diode, it’s probably a 3A 100V diode like 1N540x. If its small, a 1N400x. The raw supply is just the transformer, diodes and caps. Get that part working, then worry about the LM723 and output transistors. You can check the transistors in-circuit with a meter on the diode range. If they read bad, remove them and get the rest working first before putting in replacements.

      I see some HC28-2 supplies on Ebay for cheap. It may be worth it to buy another just to help troubleshoot yours. Or to have a working spare.

      Best of luck troubleshooting,

  17. charlesh3 says:

    I’d attach a pic for your benefit but it doesn’t seem possible. CR9 is not a 1n4xxx or 1n54xx family part – it seems smaller. CR1 (undamaged) is a 1n4xxx and appears to be the main rectifier for the 720 supply, leaving me to wonder what CR9′s job could be?

    Any idea as to whether the power supply is the cause of the problem or a result of a problem in the load?


  18. charlesh3 says:

    I traced out the HC-28-2-A and find that CR9 is connected between VO+ and V+. I assume this is a form of overvoltage protection with the anode connected to VO+ and the cathode to V+. If so, shouldn’t any diode be OK and I can gran a 1n4001 from my parts bin? This diode (CR9) does not appear in your schematic for the HC-15.


  19. msp says:

    Hi Dave – I have a HB15-1.5-A that I wanted to convert to 12 vdc from 15vdc. It looks like I simply need to change R3 and R4 – they are currently 4.7k and 47 ohms, respectively. So what should I change these to (hopefully only one of them) to change the output from 15v to 12v? Also, how do I know if the over-voltage crowbar protection is on my supply?

    Thanks for your help!

    • Dave Erickson says:

      Hi Mark,
      I don’t have the exact schematic since PowerOne and others don’t publish them. The adjustment doesn’t have enough range to get 15V? If not, then I think you can find the resistor that connects the + output to the trimpot. That one sets the output voltage range. Use a DMM in Ohms mode, look for 0 ohms. Increase that resistor’s value, I’m guessing to double it. The value isn’t critical because the adjustment should then get you to 15V.

      The overvoltage circuit has a T0-220 SCR, also connected to the + output. You can remove the device or just cut the pin connected to the output. But the supply is probably designed to go to 15V or a bit above.
      Good luck, Dave

  20. sim says:

    Hello Dave,
    A question on LM317: mis-wiring it with Adj=5V gives Out=4.1V and In=3.51V (pin In with 470 ohms to ground and pin Out with 1k to ground). It gives ~8mA to pin In under these conditions. These values are for OnSemi’s device; Fairchild and Motorola give somewhat different values (Out~=2.1V, In~=1.6V)
    However the spice models do not correctly give the observed behavior (any that I can find online as well as manually entering the OnSemi LM317 from the data sheet).
    Do you have any ideas on how to correctly model this or what part of the schematic is likely to give this result on mis-wiring?
    Thank you for your help.

  21. Tropicalspeed says:

    Re: A real lab supply design
    Hi Dave,
    I’m building a variable supply from scratch and I am following your design mentioned above. You explained that the voltage sense circuit consists of a simple voltage divider that scales the FS voltage to +5 volts, yet you have two voltage dividers in your schematic; one on the Power One supply and another in your circuit. Am I correct in assuming that I only need a single divider for the voltage sense circuit?

  22. Nemo1956 says:

    I have a power one HD24-4.8A.
    I would like to use it at 13.8 but I can’t turn the voltage down below 21 volts.
    What do i have to change to do this?


    • Dave Erickson says:

      Hey Nemo,
      There should be a resistor plus a variable resistor in series, between the + output terminal and the – input of the LM723 (pin 4), See the “simplified circuit” schematic on my web page. To reduce the output voltage, reduce the value of the fixed resistor (R3 on my schematic, yours may be different), maybe start with 1/2 of the current value.

      Remember that with lower voltage, the power dissipated in the supply will be higher, so watch the temperature of the supply.

      Good luck!

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