Oct 13, 2013

How To: Setting Up the HP DPS-1200FB Power Supply


Alright, guys! I’ve gotten TONS of requests for a tech tip that describes how to deal with the mini-marvel that is the Hewlett Packard DPS-1200FB power supply, so here we go. For those of you who are curious about the specs, check this out: 1.5″ x 7.75″ x 3 1/2″ and weighing in at around two pounds each with a capability to supply 900W (75A at 12V). Now THAT’S crazy!

Before we get started, please read the disclaimer below.

DISCLAIMER: This is a description of a method that I have personally determined to be adequate for amateur modification of this particular server power supply and this supply ONLY. This is, in no way, meant to represent the best, safest, or even correct way to do things. Remember that we’re dealing with electricity here, which means you’re taking your life into your own hands. The responsibility is YOURS and no one else’s. Please proceed at your own risk and DO NOT attempt anything described herein without ensuring that you have taken all the necessary precautions to safeguard yourself and others from injury.

Ok, now that we’ve got that out of the way…

There are two parts to this tip. First, we’ve got to figure out how to get the damned power supply to even turn on and provide an output, right? This one is pretty simple… Familiarize yourself with your DPS-1200FB supply output board before you do anything. As you look at the printed circuit board at the back end of the supply, you should notice a few key features:

From left to right:

1. Six thin terminals labeled 33 through 38. The labels are actually only on 33 and 37, but you can fill in the blanks.

2. Two wide terminals labeled 51 and 64…these are your return (-) and +12V (+) output terminals, respectively.

Without connecting the correct thin terminals with the proper resistor, the supply will never provide output power (indicated by the green LED by the fan turning on). The reason for this is that when these supplies are plugged into a large server farm, these circuit boards connect into a set of matching terminals that allow the supply to operate correctly. Since we don’t have that, we’ve got to fool it into thinking the “safety” is off…

So, what you’re going to do is solder a resistor of 330-1000 Ohms between terminals 33 and 36 as seen in the photo below:


These resistors can be bought from Radio Shack for about $1 each and have leads that are easy to form to the dimensions of the supply terminals. The one shown in the photo is a 1W, 1000-Ohm metal film resistor.

To solder it correctly, tin the solder terminals first and then, holding the body of the resistor carefully with a pair of pliers, solder each leg down making sure that they are hardened before moving to the next one. Make sure that the leads do not come in contact with the case of the power supply or any other terminals or else your supply will not work correctly. Also, make sure that as you solder stuff on to your terminals, you don’t get any excess solder in the gap between adjacent terminals or you’ll short stuff out. I like to use a hobby knife to clean the areas in between the pads after I’m done soldering and I’d suggest that you get in the same habit so that you don’t run into any issues later on down the road.

Before moving on, plug the supply into a wall socket and check first that the green LED comes on and then second, that you are measuring approximately 12V between the two wide terminals on the output circuit board using a digital multimeter. Depending on how your supply was used prior to you acquiring it, you may see a voltage between 11.7V and 12.7V. Don’t worry, I’ll show you how to adjust this later…

Ok, at this point, we’re almost ready to use our supply. Now all you have to do is decide what type of output terminals you’d like to use. I recommend either bullets soldered directly onto the two board terminal pads or female banana plugs. The banana plugs are generally more convenient, but you need to be careful to choose a set that can handle the kind of current that you’re going to be pushing. Let’s do the math really quick… 900W at 12V is an output current of 75A. Most banana plug systems can’t handle that, so please think this through.

If you do decide to go with a connector type of questionable capacity, then please make sure that you do a test charge first while monitoring the temperature of the output connectors with an IR temperature gun or something similar.

So, next up on the list of things to do is to figure out how to connect two of these in series so that we can get 24V on the output instead of just 12V. In order to do this, one of the two supplies need to be “floated” so that it’s output side is not grounded through the case. There are two methods for doing this:

1. Cut the input side 120VAC ground connection to the case or remove the grounding prong on the power cable. This maintains a connection between the chassis or case of the supply and the output, but will require the floating supply to be insulated externally so that it doesn’t short out to the other supply while operating. This is a pain and it’s not safe…

2. Maintain the input ground point and float the output board so that the case is still grounded and everything is safe!

You can probably guess that we’re going to do #2. I do NOT recommend doing #1, but there are a lot of people who do things that way, so please make sure you know what you’re doing and understand the implications of your actions before you go messing around with the input side grounding scheme.

So, on to #2…

1. First, make sure the supply is unplugged and powered down and then remove the top metal case from the supply you’d like to float.

2. Pull the rubber insulation cover from the top of the supply and set it off to the side. We’ll need this later, so do not damage it.

3. Carefully remove the fan housing and AC plug input socket. Make sure that you also pull the green LED out of its housing or you won’t be able to take the circuit card assembly (CCA) out of the case.

4. Unscrew the three Phillips head screws that hold the CCA to the bottom metal case and put them off to the side. At this point, you should be able to gently remove the entire CCA from the bottom half of the case and be left with the metal bottom and the black rubbery insulation cover.



5. Now, you’re going to need three nylon screws and nuts that will take the place of the three steel screws you just removed. This is how you’re going to float the board from case ground. I found a few really nice nylon screw/nut pairs at Home Depot and the work great, but you can use anything you’d like as long as it’s an insulating material like nylon.

6. Get out your drill and a drill bit of appropriate size to match the plastic fasteners that you’re using and VERY CAREFULLY drill out the three holes on the CCA so that they new hardware will fit. Do the same on the bottom of the case, but drill it from the outside so that the metal bosses pop out completely.


7. Now, make sure you can fit the plastic fasteners in and then replace the black rubber insulator cover and re-install the CCA, fan housing, and AC input socket. Make sure that the fasteners are secure and tight enough so that they will not come undone under normal handling and traveling conditions.



8. Before we go any further, reinstall the top case making sure that the black insulator goes back in place where it was originally. Once we’ve got the supply rebuilt, we need to ensure that our floating scheme worked. Using a digital multimeter in resistance measurement mode, check the resistance between the two output terminal pads an the metal outer case. You should read a very large number of “off-scale” if you did things correctly. This means that your output is no longer connected to the grounded case.

9. Next, power up the supply and verify using your digital multimeter that you’re getting approximately 12V across the output terminals. Congrats! You’ve successfully floated your power supply.

10. Now, to connect the floating supply in series with another supply, connect the positive terminal on the grounded 12V supply to the negative terminal on the floating 12V supply. Check again with your digital multimeter that you’re getting around 24V between the negative terminal on the grounded supply and the positive terminal on the floating supply before you plug your charger in.



If you’ve gotten this far, then you should be ready to rock! Again, please make sure that you do a test charge where you closely monitor the progress of your new system. Take temperature measurements of the output terminals, wires, and cases to make sure that nothing is amiss. Once you’re confident that everything is running smoothly, you should be ready to blast those big packs with 1800W of 24V power!

So, last but not least, you probably want to know how to adjust the output voltage on these things, huh? Easy. Power down your supply and remove the top case. Then pull the insulator off to the side again and look at the circuit board on the right side of the assembly when you’re looking at the supply from the output end. If you look close, you’ll see three small circular metal devices in a row with a flat edge on one side of each circle. These are trimming potentiometers and are used to tune various features of the circuit. The one you want is the third one (all the way to the right).

This is a one-turn, continuous pot where the flat represents the “dial” indicator. So, with the flat starting at around 4:30 on the clock, you get 11.7V and one full rotation later it’s at 12.7V…a little bit further and you’re back at 11.7V again. Get it? To turn this pot, very carefully use a pair of needle nose pliers and MAKE SURE THE SUPPLY IS UNPLUGGED! Check your output voltage with your digital multimeter each time you change the pot until you get what you’re looking for. Remember, if you have two supplies in series, you’ll have to do this twice. Since these supplies are effectively voltage sources, they stack well in series without voltage matching, so you don’t necessarily have to get their output voltages to match perfectly.


Once you’ve got everything set and working, make sure to close up the supplies and mark them so that you know which is the grounded and which is the floating. They’ll be safe to touch with your unprotected hands as well as together and you’ll still have the AC ground on the input sides. So, that’s about it! As always, if you’ve got any questions, you know where to reach me… Be safe and good luck!

– Justin


  1. Thanks for doing this Nick. Glad you choose the safer route for grounding. Also, to avoid the buck/boost transitions common with 6s packs, I would set each supply no higher than 12v.

    1. The fan speed is automatically adjusted based on the load and even when it’s on full-blast, it’s actually pretty quiet. I haven’t had time to figure out how to manually adjust it yet, but I’m messing around with it… 😉

  2. Great tip…and love listening to your show all the way over here in sunny Ireland 🙁

    Could you show a close up pic of how you connected the binding posts to the power supply board…looks like you just soldered them straight to the surface of the board?


  3. Great article! Very timely as well since my PSs are on the way 🙂

    Since we’re soldering anyway how about adding a Zener diode on the DC – to ground for a little added safety? Would you do an addendum on that?


      1. Hi . Quick question on the zener diode . which direction is it installed going from dc negative to the case ? Does the anode or cathode get connected to the dc negative .

  4. Thanks Justin, this is great. I have to give this a try. Got two 1200FBs for $30. Soldered on the resistor and got 12v on both. Now time to hunt for the nylon bolts. Mine also has a ground wire from the AC plug to the case. Should I remove that too?

    1. As Alex already said, please keep the AC ground plug attached to the case. Since you’re isolating the DC output via the nylon hardware, you don’t need to remove the AC ground…that way everything is still safe. 😉

  5. Great Tech Tip!
    One Question – I am looking for the binding posts like you used and the largest I can seam to find is a 30amp rating ?
    The spec’s on power supply are 12V at 75 amps.
    Was going to run a pair of the power supplies in series for 24v to power my two PL8’s (they suck some serious input amps to get to their 40 amp output for 6S charging – not that hard to do with 3 pairs of 5000mah batts. on thier parallel board)
    Am I going to have a melt down?

    I was thinking about using soldering bullet connectors to the power supplies and then using EC-5 plugs for the rest of the connections.

    What do you think ??

    1. Binding posts rarely go over 40A from what I’ve seen. You can use bullets directly soldered onto the backplane (ie-EC5’s, 8mm bullets, etc…). I wouldn’t plan on anything more than probably 60A for each connection set just to make sure it doesn’t melt the solder. But even at 40A with a PL-8 I’ve had EC-5’s melt the solder. I’ve had really good luck soldering 10ga wire to route the power away from the supplies and it seems to keep the heat in check pretty well (although you want to keep your wires as short as absolutely possible).

  6. Thanks for the great article. Our local Radio Shack did not have the right resistor (when do they ever?)so I had to order some – 500! I’d be happy to sell the extras to folks for basically postage cost- say 3 (in case of mistakes) for $1.50 shipped in an envelope. Let me know.

    1. Wow! 500?! That’s a ton of resistors, dude…that’s a very nice offer too for anyone who’s in your same situation. I was lucky and could get some at my local, but not everyone has that option. Thanks! – Justin

      1. email me at “[email protected]” and I’ll send you some for free.

  7. Thanks for the great write up Justin. I was looking for a reason to tinker and not to just buy the Meanwell and this little PSU was it! Even though it cost me about $100 to get them from the USA (mostly shipping) still cheaper than most other comparable options! I have them all wired up and working just fine, so now for the hard bit – making it all look pretty in a case 😉

  8. Can anyone tell me which is the load share pin? I’d like to connect two of these in PARALLEL, not series. I have not been able to find a full pinout diagram for the DPS-1200FB.

  9. Sorry for my ignorance and maybe I’m missing the obvious (wouldn’t be the first time :)) but if the units are still grounded by the AC failsafe what the reason behind needing to keep up with which is the float and which is the ground unit?

    1. On some supplies, the ungrounded DC side will output a small amount of RF noise. This will be eliminated if the DC ground is grounded to the case. Its also eliminated in the ungrounded supply when the DC- is connected to the grounded supplies’ DC+ In this configuration, the supply which provides the 24V DC- will need to be grounded to address the possible RF noise issues.

      1. I use three in series for my dual PL8 and I have a fourth one on the shelf as a spare. To keep them all the same, I floated all four and drilled a hole through each of the negative PCB connectors for a #6 screw. Then I just lug a jumper from the AC power ground to whichever PS is first in the series.
        I also drilled #10 holes through each PCB tab (both DC+ and DC-) and use #10 silicone wire jumpers, lugged at both ends, for my series and DC+/DC- connections. The advantage is a solid connection with no solder to melt. And by bolting through the PCB I’m using the foil on both sides of the PCB to conduct current.

        1. Wow, glad that worked. The thing that concerns me about drilling through the PC Board is that these boards tend to have circuit layers on the internal layers. Drilling through the board can short the power to the internal layers, say if they had to run a signal trace through this area internal. The other issue that can arise is moisture ingress into the fiberglass layers once they are cut through with a drill bit. This can cause the PC board to delaminate as things heat up. This can lead to circuit failure over time. Since your post is a bit older, would not mind a follow up on how it is holding up. Thanks Justin for your original post.

  10. Justin, Thanks for the great write up. I am running 2 of them in series outputting 24 volts. I have a Hyperion EOS 720i Super Duo and a Turnigy Mega 400 Watt X2 in my case. I am impressed. They are the best supplies I have used. The case is a perfect match match for my 2000 watt generator.

  11. In process of completing my build, thanks Justin!
    – Is it possible to add a voltage potentiometer to be able to use both power supplies in series but dial the V back from 24v if needed! (using only one set of banana posts)

    1. I would really like to know the answer to this as well. In fact, I have already attempted to research how to achieve this as an add-on rather than attempting to modify the internals of the power supplies themselves (not fully being known by myself). My best attempts have come up with a simple PWM controlled with a potentiometer which is connected to the +/- 24v legs. The downside to this is that unless I drop significant dollars I’m limiting the amps. For example using a unit like this is rated at 30a continuous http://www.ebay.com/itm/10-50V-40A-DC-Motor-Speed-Control-PWM-HHO-RC-Controller-12V-24V-48V-2000W-MAX-/261354955983?pt=LH_DefaultDomain_0&hash=item3cd9f824cf
      I’m not that electronic savy, so I’m hoping someone with more know how will respond with a cost effective method even if it requires some soldering of components from radioshack/whereever…

    2. Boehmr, great question…I’m not aware of an easy way to do this and honestly, it’s probably easier to just set up two power feeds: one off of the grounded 12V supply for your low voltage stuff and then the 24V that runs from the return of your grounded supply and the positive terminal of you floating supply.

      If someone has done this before, I’d love to see it! I think it would be a cool little electronics project.

    3. You can run the supplies at different voltages without any kind of issue. Actually, it’s darn-near impossible to keep them outputting exactly the same unless you have them in parallel and the voltage comparing circuitry is wired up (aka-how they work in a hot-swap situation). These supplies only allow a little bit of voltage swing up or down, so I’m not sure what you’re trying to accomplish. I think the potentiometer drops it to something like 11.7V and as high as 13.6V before looping back around. You can use a fixed resistor by hacking the potentiometer, but that can get you into OVC protection if you go too high on the voltage. I’m not sure what the voltage floor would be, but I’d wager it wouldn’t be much less than 11.0V, if it even goes that low unfortunately.

  12. Justin,
    Just completed build. Everything wired up, and when I go to multimeter in series I only get about 16-17V..not 24V. Each separately was measuring at 12V. Why would this be happening?

    1. I’ve seen this happen before. Unfortunately, the supplies didn’t last much longer after that time in my case. I would check your meter first (new battery or test on a known circuit). Meters are pretty finicky with cheaper models unless you calibrate them. Try seperating the two and see if they are putting out the full voltage. If they are, but not when joined, it could be your ground is messed up somehow.

  13. Hey I’m hoping you can help, my ground supply turns on great, my float supply clicks when I plug it in once and that’s it, no green light and no fan. I tried two different resistors and redid it several times to verify the solder isn’t touching anything else? Any ideas? I really don’t want to buy another and start again

    1. Michael, good call on checking on the resistors! That’s a possibility, but if you’ve already eliminated that one, then get out your multimeter and make sure that you’ve actually got isolation between the case and the output side of the floating supply before you connect it to the grounded supply. If you’ve got a short between the the positive terminal and ground through the case, then it will trip the safety feature on the supply and shut down the output.

      Also, I know you said you checked for solder, but it doesn’t take much to bridge the gaps on those small solder pad terminals, so go over the board with a hobby knife and scrape in between terminals to make sure you’re really clean.

      1. Also, make sure you’re on the right pins. I had to goof around with mine to figure them out since there wasn’t a handy guide like this when I started modding them. Sometimes you REALLY think you’ve got it wired up right and there’s some kind of minutiae detail that you might’ve overlooked. Especially if you’ve never tried this stuff before or it’s outside your comfort/skill level (trust me, I was nervous as a worm in a hen-house the first time I tried modding a supply!). These puppies are really easy to get going and if they’re not, at least they don’t cost a lot to replace from e-bay or wherever else you can find them.

  14. Hello Justin.
    I got two dsp1200 and made one floating to use in series. They are working fine, except the fans runs full at startup protocol, but after it during the use , fans almost no run and ps case get very hot. Is that normal?


    1. What size resistor did you use? Do you have the voltage as close together as possible?
      The cases to get pretty warm even at idle, but the fans should speed up as more load is placed on them. They usually take about 28A or so to even come off idle to begin with. Are you able to run them by themselves individually to see if that makes a difference?

  15. Is it possible to just use one of these power supplies? I have a DC charger that has a maximum amp draw of 57 amp at 12v so there really is no need to run two of these. Plus if I’m only charging 3s packs at this point. Anyway, I don’t see anyone talking about how to modify one of these power supplies to be safely used.


    1. Yes, you can use just one. The best part is you don’t have to do any internal modifications either. Just solder on the resistor to the back pins and add bullets or wiring as needed for DC and you’re set! The only time you have to modify them is if you want to run higher voltage (24V, 36V, 48V, etc…) and you only have to do it on the successive supplies because they will be grounded through the first supply to Earth Ground.

  16. @turbomatt It is not required to use 2 PSU’s but when using a 24 volt capable charger you make life for the charger a lot easier when using it it with 2 psu’s in series. That is when you expect to get close to the limit of 1 psu. If not just use it with 1.

    @justin: I successfully used 330 ohm 1/4w resistors to fire up the PSU’s. I actually used rubber grommets(that fit m3 bolts) to isolate/float the print board. Works like a charm.
    Voltage adjusted to 12.93 Yeah baby so much nicer than my DPS600 setup 🙂 🙂 Again thanks for your efforts and for inspiring me 🙂

  17. I’m not sure if it’s been covered, but I noticed you removed all four mounting screws on the float supply. This is essentially the same thing as cutting the Earth ground pin off the power cord because you are separating both the AC and DC sides from the E-G which is what you advise against in your description (not accusing, just pointing it out). I see this in a lot of P/S conversions and it’s a mistake that probably shouldn’t be repeated.

    With this supply, you only have to float or modify the two screws towards the rear backplane which is the DC portion of the PCB. If you float the front two screws, you have no continuity to the case which is essentially your last line to E-G if something happens to the circuit.

    You can test this with your DVM on the diode setting (or resistance if you prefer, but I like to hear it beep and infinite ohms could mean anything). Take out the two screws from the backplane, but don’t lift the PCB up. You should get continuity to the E-G. Lift the board and it will show that it’s dosconnected.

    1. Hey Skunk,

      Thanks for all the great comments and help with some of the others’ questions. Regarding the floating configuration, the AC is still grounded through the earth ground wire that connects the case directly to the AC socket on the input side of the supply.

      I ohm’d everything out to determine my plan of action and I’m pretty sure that I concluded that I needed to float all three of the metal fastener connections to the case.

      Maybe you’re thinking of a different supply? This one only have three case connection points…one up front and two at the back. Plus, the AC ground strap which should cover us from a safety standpoint with the others removed.

      I definitely want to make sure we’ve got the correct answer to this one for anyone who wants to follow along with the build steps because safety is the #1 priority. Thanks!

      1. Justin, you are correct on the three points, but you still only have to separate the back two to get the DC side floated. Removing the front screw from the PCB is one less path for the safety net aspect, so to me “best practice” is to leave it in place even if the strap is there as well. Since this only has to be done on successive supplies in series, it could save a few pennies on screws and time drilling out the other point(s). Not that it takes long to mod them in either scenario, but I apply to the KISS rule whenever possible. Especially with electronics. 🙂

        1. Skunkworx, you’re absolutely correct! I went back and checked one of my supplies and the front-most chassis connection is an earth ground path parallel to the green earth ground wire that runs from the AC input socket. So, you don’t need to isolate there, but eliminating it doesn’t eliminate the ground path, it just reduces redundancy from single-fault to zero-fault redundant… 😉 Thanks again!

      2. Justin, what is your method now on grounding on isolating the front circuit board mounting screw… Or not isolating . I have isolated mine and was thinking about changing it back to being grounded based on this thread.

    1. Yep, technically the floating supply chassis still has a ground path to the AC ground strap on the base supply even if you’ve taken all of its own internal safeties out, but I don’t recommend relying on this to mitigate the risk to people or hardware. I am ok with only running the earth ground on the floating supply via the AC input and not having the 3rd fastener up front connected, but taking them both out of the loop would be unwise.

  18. ? Iv been running one of these as a 12v supply with a 1k resistor to switch it on, the psu was working great then the next time I came to use it, it wouldn’t switch on. But the fan was running any ideas people.

    1. Check that you don’t have any solder or other conductive material connecting any of the adjacent solder pads near the resistor. Are the resistor leads touching the chassis? Unfortunately, I have heard from a few people who have had these supplies just die randomly… 🙁

  19. 1st off thank you for this info. Helped me allot. I do have an issue. I wired two of these Hp ‘s in series and floated the DC ground. Turned on and everything worked fine. I plugging in my new hi amp icharger and played with it. Got 24.5 volts output. Well I acvidently turned off a light switch operated plug which turned off the floated PS. Five min later I notice that the PS was only supplying 12 volt to the icharger. I imedeatly turned back on the top power supply. Well the led turns on for a sec and then turns back off. I de-soldered the series connection and the one PS is cont. To turn on quickly and then back off. No output. Do I need to buy a new 2nd power supply? Again both worked perfectly before each putting out 12v and 24v in series.

    1. Similar issue here. Mine was a power blip at my house. charger actually remained powered somehow. maybe backfeeding from the batteries while i was charging i dont know. But now only one of my PSU works. odd. Happens ai guess.

  20. Just as an update, I serched around for a while to figure out how to hook these puppies up to 220V and it looks like the cable is called an “L6-30P to C13 power cord”. This uses the same connector that you plug your stove or laudry drier machine into for 220 at your house (sometimes they have them near water heaters in the garage as well). These are also the same connectors on the face of many larger generators that provide 220 in addtion to a few 120V outlets.

    You can get the cables on Amazon or wherever else they sell them, but they’re pretty pricey ($25-$45ea. depending on length and shipping costs). You could make your own cables of course, and that way you could add in a splitter for two C13’s if you had stand-alone units. Not that you would really need to use 220V, but they would run a bit cooler that way and you could use a much thinner extension cord compared to 120V. You could also splice in a regular NEMA 5-15 tip instead of a C13 onto it to use with a regular extension cord for extended distances and then use another splitter at the end to go to the supplies. I don’t like that many different connectors so I would plan on making dedicated sets, but again it’s a good way to get just a bit more out of these amazing supplies if you could really use it. I have two PL-8’s, so you know I’ll be maxing them out for sure!

  21. Is the “DP-580 G5” the same unit? I have seen a couple of different versions with the same specs on the data sticker. I found 2 of these for $30 ea. Does that sound right?

    1. Cory, I’m not personally familiar with the DP-580, so I can’t say whether it has the same internal configuration as the 1200 and if it can be modified in the same way. Sorry, man. 🙁

  22. So, I’ve built two sets of these HP supplies so far, and both have just “failed” on me. I know they were set up correctly, as they both worked great for a little while, then one set failed completely charging at 30A and one set ended up outputting only 11.8V while charging receiver packs. I’m not sure if they don’t like being run in series or if they just aren’t robust enough for the way we treat them. I think I’m done with the experiment for now. I enjoyed doing it and learned a bunch, but now I gotta go buy a more expensive solution. Yuck. 😉

  23. squid628, keep in mind you’re buying a used power supply. Unless you know where it was being used, under what conditions, and for how long, you’re taking a certain amount of risk. I would suggest that you may just need a better provider rather than throwing in the towel on the whole idea. I know that JC (who sells them modded on here in the forums) has had to change his source at least once.

    1. I have over 50 cycles each on the sets he made for me charging consistently at 37A and they often get left running for hours or even overnight without a load because they’re so quiet – I just forget they’re on!

  24. can some one point me in the right direction to solder in some resistors in place of the potentiometers to get 13V what resistor value thanks in advance

  25. Okay, picked up a lot of 4. So I have 3 spares after using my one good one from the last set. Adjusted voltages and have them at 25.7V unloaded and 25.4V loaded. Running on a Ryobi 2200 inverter generator from Home Depot. Charged 6s 30A on each output of my 307 Duo at the same time. Looks fine so far. Let’s see how it goes this time! 🙂

  26. Justin,
    April 3, 2014 at 9:29 pm
    I’ve performed the mod as described, the DC output tests islolated from the AC ground. When two are hooked in series, when the cases are separated I get 24.6V, but when I allow the cases to touch the the output voltage a lot greater than 24.2 combined, say 100V. I’ve opened the cases back to verify that everything is tight, What did I do wrong? Have you seen anything like this?

  27. Thank you for such a clear explanation. Other have talked about using this PSU, but your instructions are by far the best.

    In the other replies there has been some mention of connecting these in parallel for more amps. Connecting desktop PSUs in parallel doesn’t work well, but you suggested these might work since they were designed for that originally. I’ve got 4 of these PSUs really cheap that I’m planning to use for a custom computer build rather than than as a battery charger. I’m needing about 300 amps at 12 volts, so I’d like to connect 4 of these in parallel.

    Is the voltage comparing circuitry you mentioned above a feature built into the PSUs or a feature of the servers that normally use these? If it’s a feature of the PSU, any suggestion of where to get more info on the wiring required?


    1. Greg, the circuitry is built into the supply, so there is a pin combination that would enable parallel operation and current sharing, but I don’t personally know what it is. I would suggest searching the internet for the pinout diagram for the DPS-1200. I’m sure there are others out there that have figured this out… Thank you for the kind words, by the way! 😉

    1. It is not unsafe to touch if you perform the floating procedure that I describe above, Vend3tta. You just don’t want to cut the ground pin or strap on the input side of the supply to float it or else the case is hot.

  28. I’m looking for the nylon connector bolts to isolate the ground. Does anyone have the part number for them from home depot the one here doesn’t carry them and can’t find them anywhere.

    1. you can get the screws and bolts at Ace Hardware. They are in the bins and called nylon binding posts. i bought some today and the screws and post come together. they are >60 cents each. and the thread is 10-24.

    2. The ProBoat PRB4218 Nylon Screw w/Nut:IM26 is a perfect replacement for the metal screw.

      I put a nylon washer underneath the board and replaced the metal screw with the nylon one, for each of the two DC-side metal screws.

      There’s no need to drill out the old nuts, or to remove the circuit board at all.

      Total Cost for two: $5.60.

  29. How warm should one of these supplies get (case for example) with ambient temp at 85, at idle and at 3 amps output? My buddy connected one up for me and it seems to get warm, not sure what is normal. Mine got pretty warm, you could hold it, but it was hot.

  30. Hey Justin. I use to be in the power supply business, but recently due to a huge promotion at work I am going to get out. For one, I no longer need the extra cash, and for two I no longer have the extra time to make them. Anyway, I have 200 of these in inventory that I had plans to build but now I just need to sell them. I am going to put them on eBay, can I link to your site here on my eBay add?

  31. Justin, I tried to link this video to a person looking for help over on HeliFreak. I was greater by a warning message that was inserted in my post in the spot where I had the link to RCHN. What did you guys do or say to get Mr. James undies in such a bunch that he would take the time and effort to keep a link to your site from happening? I just could not believe he would stoop to such a level. ROG

    1. One of mine did today. I was running two for 24 volts. Had a power flicker in my house and lost a PSU. Icharger 308duo rebooted running on only 12 volts.


  32. So I am in Australia and running these bad boys at 240v. So that’s 2400 Watts at 75/80 amps. Now Can I….. Hook theses up in Series (i used plastic washers and plastic bolts to take the DC ground off so I didn’t need to drill the case) to get 24 volts, and still use one power supply hooked up to my fans ans LED lights which run at 12V???? I will be using the grounded PSU to supply the 12 volts. Is this doable or will it harm the power supply?

  33. Just want to follow up that the Tech Tip write up is excellent, but as a n00b, it was unclear as to what and how the bullets are to be soldered directly onto the power supply. I rubbed a couple of brain cells together, and I figure what you have pictured are dual binding posts, to use with a banana plug. Maybe you’re using spade terminals like these
    ….and those spade terminals are soldered onto the output terminals (labeled 51 and 64) of the power supply. I hope I’m on the right track….

  34. Great TUT Justin,i am just waiting on mine to arrive 2 days (i hope) i am planing to use just a single PSU to run my Turnigy Mega 400w X2 charging 1 @ 4s 10000mah 10c lipo on each side at around 7-8 amps,i am glad that you wrote how to turn the output voltage up a little, i would like to get close to 13v if possible, i would like to eventually build this all into a nice casing with green led moved to front and maybe a volt/amp display, could you tell me how i would connect a display like this, i read somewhere that i would need to use a shunt ?? any info: on this would be appreciated.

  35. I can put a run of 18v @ 20V with 100 amperes.I was thinking to parallel the first 5 volts (if any) with one of 13v to get 18 v.me let me know if it works or a better way.

    Thanks in advance

  36. Can anyone explain this…
    PS 1 mod complete with floating.
    I have 2 multimeters – A is a Sears pocket auto range LCD Digital Multimeter and B is a Cen-Tech simular or the same as shown in the write up.
    PS 2 reads an output voltage with meter A of 12.25v and with meter B reads 12.4v.
    On the PS that has the float – Meter A is 12.23v and meter B is 10.8v. Simularly when the jumper is added meter A reads 24.49v and meter B reads 23.8v.
    If I check batteries both meters read similar voltages. Only when checking the floated PS does the one meter read 1.4v lower.
    Any thoughts or wxplaination is appreciated.

  37. Tried grounding the front Circuit board screw and isolating the back two… And measureD 12 volts between the negative DC output terminal to the case, and same on the positive terminal to case.( case was of course ground to the AC ground through the small link. Weird.. The voltage between both output terminal was 12.4 volts. I removed or isolated the front single screw and then the voltage was nil between the output terminals.

    Help on this please… What to do.

  38. I am running two of these for my 308 duo. Had a power outage in my house while charging and only 1 of my PSU’s is working now. Any idea’s what went wrong? The guy I purchased from is happy to repair it for me. But i’d still like to know what maybe happened. Thanks guys.

  39. Justin, it would be nice to edit the instructions to include exactly what nylon screws you used. That was the most time consuming part of my build.
    Thanks for the instructions on this. I now have 2 sets ready to go.

  40. Can someone please help me I would like to use the Lite ON Dell PS-2112 with iChanger but I dont know which pins to jump.. can someone please help me out..

  41. Floated one of my supplies this afternoon but it no longer has any voltage on the terminals. The fan is running and the LED is lit. It worked before the float process but not after. I removed and replaced the resistor but same result. I only floated the two screws by the output terminals. I left the single screw by the AC jack stock.
    Any ideas??


  42. Hello,
    I performed the modifications as describded, floating the second power supply.
    Initially, I just isolated the 2 output conections, leaving the input one connected to chassis since it appeared there is infinite impedance between this one and the 2 others.
    As a result, output voltage on the floated PS alone isn’t stable at all, and voltage control isn’t able to produce more than 11,2V on output. Pulling 5 amps, Voltage decrease to 10V, jumps to 12V when load is disconnected, … back to 11,2.
    While (re)connecting ground output to chassis, suddenly 12,7V stable (voltage control pot. was at maximum).
    Went then to isolating the third connection to chassis to be 100% in line with description, nothing changes (ie random voltage at the output).
    Same behavior when pluged without the earth connection.

    My guess : for output stability, a connection between input ground and output ground is necessary -at least on my sample-, and originally done trought the chassis.
    I propose to reconnect it by a wire, keeping the whole insulated from the chassis. It will for sure work.
    Any idea about a potential safety issue or other mess when 2 PS connected serial?
    Thanks for your support,

    PS: french guy, please forrgive if any approximate wording

  43. Good evening friend I would like to help me with a problem that I have’m trying to light a fountain and already check the connection to the diode but not throwing the 12V outputs that could be what happens with that

  44. Hello,
    I am French and I don’t know everythings on your site.
    I have problem because with ground connection
    The ground is burning,
    Why it is necessary to cut the ground.
    Why Schould I make isolation ?
    I crash 2 HP 1200 FB for this reason ?
    I miss understand
    Help me

  45. Hello one and all. Been reading these pages with great interest. Thanks to them I now have my new 24V HP DPS-1200FB power supply ready to hook up to a new iCharger 4010Duo once it and most of the parts for the 10S6P e-bike battery pack I’m building arrives in the mail. Not having nylon screws easily available, and not wanting to experiment with the lot that comes from China, I found an alternative that does not involve using hot-glue which some people have used and which I resist fearing that the glue will melt when things start to get warm. I instead used an item very familiar to lovers of BBQ everywhere – the lowly bamboo skewer, which if small enough will fit the metal screw inserts perfectly and accept threads with remarkable strength. A bag of 100 costs a few dollars and will contain at least several skewers of the correct diameter. Too fat and the skewer will twist apart, too small and the threads won’t grip, but a fat skewer chucked in a drill and pressed against some sandpaper will get you one the correct size in no time. Just twist the things into one of the threaded inserts until it comes out with clean threads about half an inch long. Cut them with a Dremel cutoff wheel about 1 inch long (including tip, which you’ll cut off later) then carefully cut a slot 3/32 inch deep (use your calibrated eyeballs) into the cut end to fit a small slotted screwdriver. Next, drill a close fitting hole into a small piece of fiberglass perfboard or similar material to serve as a screw head. CA glue this flush onto the slotted end of the skewer-screw being careful to dig out the glue from the slot with another skewer. Trim the head with a Dremel sanding drum, and the tip with a cutoff wheel, and you’ll have a remarkably strong screw that’s resistant to high temps more so than hot-glue and probably nylon as well. One other thing you should do is to countersink very slightly with a 1/4 inch drill bit (or countersink bit if you have one) the bottom of the two circuit board screw holes to keep the metal inserts from contacting the ground plane around the holes. Pictures available once I figure out how to upload them.

  46. Hello all! Ive had an issue with floating the power supply. The first one I drilled through and killed the PS. I bought a new one and instead I 3D printed some standoffs that were glued to the bottom of the case where the metal threads used to be.

    Now after putting the case back together, my voltage between the + and – terminals fluctuates between 10.5v and 13.8v. When doing a continuity test, Ill get varying readings between 1v to 3v.

    All three standoffs were removed and replaced, but I have no idea whats causing this to still be slightly grounded? Any help would be appreciated!

  47. Does anybody know if anything has to be done to hook two of these up to double amperage for powering 12 mobile applications or just positive to positive and negative to negative? Thanks for any help

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