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Old Feb 21, 2009, 06:27 PM
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Melbourne, Australia
Joined Jul 2005
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A simple high quality 12Volt 100Amp Power Supply- Part1

With the growth in big LiPo packs and more capable chargers such as the Hyperion Duo2 and Hyperion EOS0720iNET there is a difficulty in finding a decent capacity bench power supply, particularly if you want to run two or more chargers at once. Power supplies for 12 or 13.8V up to 10Amps are reasonably cheap and available, up to 20-25 Amps are a bit harder to find and cost more, and over 25A are fairly rare.

There are plenty of articles on converting an ordinary PC power supply to a 12Volt high Amp supply and this has the advantage of low cost and many of us have done it. But there are a couple of disadvantages:

1) It involves opening a (potentially lethal) supply and modifying it, using external load resistors or changing the voltage sensing circuit, which is simple enough but outside many modeller's comfort zone.
2) The performance is generally woeful at high current because of poor regulation unless an expensive high-end supply is used thus defeating the low cost part. The most common way to do the conversion is to put a load resistor on the 5Volt output since these supplies are designed to maintain the voltage on the 3.3 and 5V lines which feed the motherboard. The bigger the load, the better the regulation but that also produces significant heat.
My typical converted cheap 550Watt PC supply drops to 10.5 Volts at 20 Amps. See picture PCsupply.pdf

An alternative that has been popular in the US is to use a second hand IBM Server Power supply which is of much higher quality, requires no internal modification and can deliver 12V at 30Amps. They are model IBM 235 Server Power Supply, part number 49P2020. Unfortunately they are becoming rare even in the US and I have never seen them available in this country. The trick is of course to get them to turn on at all since they are "hot-pluggable" and contain a lot of smarts to ensure they do not supply current until various logic is correct. Everydayflyer and teegreen have both promoted these on the forums and I understand from them that the solution originated 2 or 3 years ago, when the surplus electronic supply company called All Electronics was selling two of these power supplies in their server case for around $30 and someone included a sketch on their web page on how to do the connection. The thread is “What power supply should I get?” at http://www.rcgroups.com/forums/showt...=799781&page=7

I have just built the same thing using a currently obtainable HP server supply and figured out how to make it run. It delivers 12.77V under no load, and 12.27V at 118 Amps. That's a lot of power. This is a very high quality, compact, beautifully made power supply and dead easy to modify. It involved NO modifications to the supply at all apart from soldering on the output wires to the terminals at the back so it’s safe. I think I could have a finished working unit in 15 minutes now I know how, and the only parts needed (in addition to the connecting wires) is a servo lead and any small switch such as a Rx battery switch. The skill level needed is the same as that to solder a Deans Ultra or bullet connector to a battery lead. The cost will depend obviously on where you can get the power supply. It’s a HP PROLIANT DL580/ML570G3 RPS REDUNDANT POWER SUPPLY. P/N: 348114R-B21. These Proliant servers are very common and are designed to run continuously with high reliability. The power supplies are designed to run in pairs for redundancy and be hot pluggable (you can yank one of them out while the computer is running and the other one keeps on going).
I have seen the supplies advertised as a retail item from reputable suppliers on the Internet for about $100. (All prices are in US$ for comparison). In Australia, HP get rid of all of their excess stock, returns etc through a mainstream on-line auction house called GreysOnline. Almost every day there is a new listing of laptops, servers, printers and the like. Often there will be power supplies, sometimes as part of a bundle with other gear. They start the bid at $25 or less and depending who wants one at the time they can sell at that price to a single bidder. I paid $54 for mine but I saw someone get three of them and 10 CD drives for $12! You may find HP do something similar where you are. The cheapest comparable item I have seen available ready to go is a 43 Amp supply which sells for $100 and anything that offers 100A is much more expensive.
In the next post I’ll show how I did it with some pictures. You could run 4 chargers from one of these each drawing 25Amps, to simultaneously charge multiple packs and it wouldn't break a sweat!
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Last edited by jj604; Aug 06, 2010 at 05:14 PM.
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