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Old Oct 12, 2012, 04:07 PM
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Build Log
Converting Dell 7000814 Server Power Supplies

This build thread is about converting a Dell 7000814 power supply for Dell 2850 Power Edge servers into a battery charger (actually a general purpose) supply. Itís aimed at the person who hasnít done this before and might be a bit nervous about taking something this on, but I also hope itís useful to anyone who is a bit more experienced and wants a guide to doing a quick conversion. Iím doing this for a few reasons:

1. These power supplies are cheap and there are lots of them around. I got mine in a lot of 2 for $19.99 including shipping on eBay, which was a very good deal. As I write this, thereís a lot of 2 available with free shipping for $26. If you donít see a good deal, wait a few days. Something will turn up. There is another power supply for the Dell 2850, the model NPS-700AB. It has exactly the same form factor and its conversion should be pretty similar. It is different internally, though, and itís circuit boards include an output voltage adjust pot that allows more output voltage control than Iíve so far figured out for the 7000814. Iíll explain more about that when I get to the relevant part of the build thread, but converting the NPS-700AB should be pretty similar.
2. This is a fairly easy conversion. Thereís a lot of info on this in other threads that describe everything Iíve done, but its scattered around and it took me a bit of searching to find all the info I needed to do what I did. My thanks to all who posted their pieces of information. I would not have tried this without their contributions.
3. Alone, these power supplies deliver a well regulated 11.9 volts at up to 57 amps. A simple addition that up to 12.5 volts. Two supplies can be hooked up in series after this conversion to deliver 25 volts at the same current.

First, the disclaimer: This build thread involves going into the power supply. You do this at your own risk. While thereís nothing particularly dangerous or difficult in any of this, I take no responsibility for your final result. Read the whole thread before proceeding to see if you want to take this on. Iíll point out the pitfalls including one I stepped into during the thread.

Having said that, thereís not much to it. If you have the right tools, most of which are pretty common, you shouldnít have much trouble. Tools needed are screw drivers, small and large needle nose pliers, wire cutters, tweezers, a soldering ironÖ the usual stuff on a hobby work bench. It would be nice to be able to drill a half inch hole fairly accurately, but Iíll describe a way around that. Once you have all the parts, the whole project will take a few hours.

Letís get started.
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Old Oct 12, 2012, 04:11 PM
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Below are pics of a vanilla Dell 7000814 power supply. You can read the specs right on the label. Weíll be using the 12v output and pretty much ignoring the 3v output.

First you need to open the box. Remove 6 small countersunk screws that hold the two halves of the case together. You might as well also remove the hot-swap handle used to get this thing into and out of its slot in a server rack; you wonít need it any more.

When you open the case, youíll notice that the stuff in the two halves is connected by two sets of wires at different ends of the case. At the end that had the handle on it, there is a plug that connects the input power to the power supply electronics. I used a large needle nose pliers to squeeze the little nylon handles on each end of the plug to release the plug. At the other end of the case, the fan end, are 3 wires on a connector that power the fan. Unplug the fan wires from the circuit board and the case halves will separate nicely.
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Old Oct 12, 2012, 04:16 PM
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Pictured below are the two halves of the power supply. To make it possible to use two power supplies in series to deliver about 24 volts, we need to isolate the power outputs from the case ground. The case will still be grounded through the 3-pronged power plug, but the 12 volt outputs will float, which just means that neither side of the 12 volt output is connected to the case.

To isolate the power supply from ground you need to change out the 5 metal screws that hold the two circuit boards in place with nylon machine screws and nylon washers. Youíll need 5 each 4-40 ľ inch machine screws and 5 each #4 nylon washers. I got mine at a local Ace Hardware but if you canít find nylon hardware close by, you can find it on line.

Iíve indicated on the pictures the screws you need to change out. Donít forget the washers. They go between the circuit boards and the case mounting ears and theyíre important. One of the pictures below shows the smaller circuit board already mounted. The nylon washers for the larger circuit board are already on the case mounting ears.

Note the large rectangular pads on the smaller circuit board which connect the two boards using larger screws. These pads are the plus and minus 12 volt output rails. Donít screw the larger board to these rails on the smaller board yet.
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Old Oct 13, 2012, 07:36 PM
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The next step is to mount the banana connector into which youíll plug your charger leads. For this I bought several banana connectors off eBay for pretty cheap, but the downside is that the really inexpensive ones come from Hong Kong in about 2 weeks. You can also get them from Radio Shack as ďChassis-Mount Dual Female Binding PostĒ, no. 274-718 for $5.29 each. Any kind of connector will do as long as it can be mounted to the supply chassis and can handle the current.

I mounted my binding posts in the chassis. This is, I believe the safest and most useful way to go, but you can also connect directly to the 12 volt output terminals on the fan end of the power supply, and Iíll describe that later in the thread.

Hereís where you want to be able to drill a couple of accurate holes about Ĺ inch in diameter at the locations shown in the pics below. I chose this location because the space under the holes is open so the part of the binding posts that protrudes into the chassis and the leads that will connect to them have some room. With holes drilled, mount the binding posts.

Make short pig tails by putting crimp terminals on the ends of two 5Ĺ inch pieces of #10 wire. You might get away with #12, but for the higher currents this supply can handle, #10 is probably safer. I suggest using silicon insulated wire as itís very flexible and will stand up to any heat in the power supply. One good source of this wire is www.epbuddy.com.

Connect one end of each of your pig tails to the bottom of the binding posts and the other to the 12 volt output rails using the bigger screws from the disassembly. Observe polarity or strange things will happen. This happened to me, Iím sorry to say. The positive 12 volt rail is the one on the same side of the small circuit board as the fan connector.

Now you can button the chassis up using the 6 small screws that youíve hopefully not lost since you took the supply apart.
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Old Oct 14, 2012, 08:01 PM
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Now we have to deal with connections on the back panel that will allow the power supply to work when not plugged into the hot swap socket in a server rack. This involves connecting pins on the header at the fan end to trick the supply into thinking itís in a server rack. This will accomplish three things:

1. Cause the supply to deliver power to the 12 volt outputs which weíve redirected to the banana binding posts on the top of the chassis
2. Raise the output voltage from 11.9 volts to 12.5 volts
3. Lower the fan speed so the thing doesnít sound like a jet engine.

The first picture below shows a pin-out diagram of the supply.

1. To make the supply work delivering 11.9 volts, its default voltage, connect pins A1, B1 (Ground) and B6
2. To raise the output voltage from 11.9v to 12.5 v, connect A2 to a 12v output through a 470 ohm resistor
3. To lower the fan speed, connect C2 to D3 (Ground). I did this through a switch that can break the C2-D3 connection so I could have full fan speed if I ever need it.

You can solder these connections, but the space is tight. Instead, I bought some female pin sockets similar to the kind in a servo connector at a local surplus junk store (www.surplusgizmos.com) (25 for 50Ę), crimped them on some thin wire, put heat shrink around the sockets and pressed them onto the pins. The jumper for the first connection described above is shown in a picture.

For the voltage-raising connection, I crimped a socket onto the lead from a 470 ohm resistor and soldered one end to one of the 12 volt outputs next to the pin section.

I epoxied a switch for the fan speed control to the top of the pin header and connected the leads from the switch as indicated above. All this is shown step-by-step in the pictures. Lastly, and not shown, I placed a strip of electrical tape across the pin header and the external outputs to keep them from accidentally touching things they shouldnít touch.

Depending on where you get the extra parts, you can have a converted power supply for less than $5 more than you pay for the raw supply. And if you convert two supplies, you can connect them in series for about 24 volts or there about. Not bad.

Thatís it as far as this conversion goes. If I ever find out how to do finer voltage control than what Iíve done here, Iíll post to this thread. Some folks have also done fan speed control by wiring in an LM34 temperature sensor so that the fan speed is controlled by the temperature of the supplyís internals. This is a nice touch, but I didnít have any LM34s and no local source, so the switch is good enough for me. If youíre interested, do a search in this forum for LM34 and youíll find all you need.

Again, thanks to all who contributed what I needed to know to do this conversion. Itís all here and done by folks who know more about this than I do. I just pulled it all into one place.
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Old Oct 20, 2012, 12:28 PM
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This is a great thread with all the info to work with this power supply, thanks for the info... Do you know any other power supply like this or with more power that work in 120v AC?
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Old Oct 23, 2012, 01:53 PM
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Thank you Much for the informational thread.
I had success with all of it except slowing the fans. Both power supplies are working great at 12.5v but still loud. The C2 Tach_1 connection doesn't do anything to the fan speed when grounded.
Could someone provide a suggestion for slowing the fans?

Thanks,
John
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Old Oct 25, 2012, 12:50 PM
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Found another instruction that said pin B2 will allow fan control. Pin B2 worked on my 70000814 fan.
Thanks to KRCM where the file if from.
http://krcm.mywebnow.org/index.php?topic=330.0
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Old Oct 25, 2012, 01:00 PM
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Anybody had some info about a power supply that can work in 110v AC? Looking something like 2000watts or more...

Thanks in advantage...
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Old Oct 25, 2012, 01:30 PM
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Many listed in main power supply conversion thread.
http://www.rcgroups.com/forums/showthread.php?t=1292514
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Old Oct 25, 2012, 11:45 PM
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Skydivejohn,

The trouble you're seeing with the fan speed control is because some pin-out diagrams list the rows, A, B, C, D, from the top, and some from the bottom. So try grounding either B2 or C2, depending on which pin-out diagram you're looking at. The good thing is that you can't do any harm if you get it wrong the first time as the other pin, C2 or D2, is a spare and is not connected to anything. This is just lucky, but, hey, I'll take my luck where I can get it. :-)

wevets
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Old Feb 07, 2013, 07:09 PM
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FYI:

I just did this on the 7000814 and 1 thing did not work as expected:

The fan speed adjust using C2 to D3 did nothing for me switched or jumped. B2 also did nothing. At one point as I was trying jumpers the fan all but stopped and then very slowly started coming back to full RPM.

I did get an increase in voltage jumping A2 to 12V so I eliminated the resistor. When jumped, fan speed increased slightly.

Thanks!

***EDIT***

I must have had a bad connection to B2 as when I removed the switch wiring and then re-soldered to the pins the fan now slows to a very quiet speed with the switch closed!!!

Now to do PSU #2. BTW, I got both on ebay for $14.25 shipped! They appear to be unused as there is no dust anywhere inside or on the fan blades.
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Old Feb 07, 2013, 09:31 PM
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Here's my handi-work. I soldered everything. With a tapered, thin tip it was pretty easy to do.


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Old Feb 07, 2013, 10:18 PM
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I love the connectors in the top. Thats what I was planning on doing as well but had some reservations since I hadn't seen it done before.

Did you connect to the output screws on the board inside the supply?
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Old Feb 08, 2013, 06:29 AM
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Quote:
Originally Posted by PlaneCraz3d View Post
I love the connectors in the top. Thats what I was planning on doing as well but had some reservations since I hadn't seen it done before.

Did you connect to the output screws on the board inside the supply?
Yes, I used Wevets photos to guide me. The binding posts gave me some concern as the conductors are fully exposed going through the case. I'd recommend that anyone using them either insulate the area exposed to the case with tape or shrink wrap or be very careful when positioning them and then test for continuity with the case prior to powering the supply up. My first one was no issue...the second one both pins were grounded to the case requiring me to re-position the binding posts slightly. I also drilled the holes much larger than required in anticipation that I'd either insulate or have to move them a bit.

I'm very pleased with the way these turned out. My iCharger 3010B should arrive tomorrow along with 20 or so LiPo batts so I'll be able to try everything out.
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