First of all... the disclaimer:
I am posting about what I did to build my own supply... your results may vary. Traxxas nor myself is responsible for your actions... if you get some crazy idea; take ownership of it!
Second of all; please read this entire thread before asking questions.
The answer you seek may have already been covered.
I chose a server power supply due to a couple of facts...
1) They do not dip down in voltage when pulling high amperage out of them
2) They are cheaper than most (if not all) ATX power supplies that will not voltage dip
3) They are more robust than ATX supplies
4) They have some very key safety features build in
eBay has LOTS of server power supplies available... they do not need to be new. Just because the server they were powering is out of date does not mean the power supply is out of date.
Unfortunately, most sellers will not respond to requests for pictures of the "business" end of the supply. So there is a bit of a gamble if the supply is even able to be converted unless the pictures of the business end is already there or you have read of someone converting a similar supply.
I was able to find both of mine for $15 shipped. That is about the cheapest I have ever read a pair of supplies going for... shipped at least. These buggers are not light, so shipping is going to be a killer if it is not included in the price. I would say an average price for a pair is between $20-30 shipped. Beware of the super cheap ones... they may be cheap for a reason; just be sure to do your homework before you purchase.
Be sure to add a few bucks in your budget for the proper wire, connections, ect. I have a total of $30 into my supply.
What to look for:
Pins and tabs. Some have circuit boards that stick out that slid into the server case. These are usable... but you must be comfortable soldering onto a circuit board and the solder joint must be good enough to carry the full load of the supply. The supplies with pins and tabs are a little easier to work with. Some have special sockets that may be impossible to use... depending on if the socket is removable/solderable.
Voltage and wattage. Obviously you are going to want one that is capable of supplying what you need. But, if you come across one that is a little on the weak side for the right price, these can be hooked up in parallel and series to fit what you need.
If you think you only need one, get two. If you ever need to hook two of these bad boys together, whether it be parallel or series, it is better for them to be identical. The easiest (and cheapest) way to get two identical power supplies is to get them at the same time from the same vendor. Worst case scenario... you have a backup.
Google the part number of the one you want... there just might be someone else that has bought it to convert it. This would be the absolute best case scenario as all the pinout work might be posted about it!! This search might also turn up some information on if it cannot be converted or if it is a "junk" supply.
There also might be a good shot of the business end... gotta love Google!
Server power supplies are designed to only be operational when they are installed into a server station. However, there is a way to trick the supply into thinking it has been installed through its' pins. You can see these pins in the pictures below.
Connecting 3-4 of these pins directly to one another will allow the supply to turn on. As far as I know, no two different power supplies have the same pinout. Some supplies have a pin that is a little bit shorter than the others... this is a good indicator that this is one of the pins that is required to be connected as it is the last one to slide into the station. Some supplies do not have this convenient feature and you will need to use a lot of trial and error to get your supply running. I was fortunate enough to get one of these supplies... it took me 45 minutes to get mine running... lol. To find my pinout I used a section of very fine gauge wire and start connecting them with the unit plugged in until it turned on.
There are two stages of activity for most power supplies... soft on; where the fans run at half speed but no power is produced... and full on; where fans run at full speed and full power is available. I found soft on before I found full on.
The fine gauge wire is used so that if a pair of pins that should not be connected get connected the wire will burn out before the supply is damaged. But, to be honest, the supply should shut itself down before any damage occurs; one of the many great safety features of a server power supply.
Once you get it powered up there are a few different ways to hook up...
1) Solder heavy gauge wire to mounted copper piping to use clamps that came with your charger
2) Solder heavy gauge wire to a row (or single) of 4mm jacks (pictured below)
3) I have seen where some have simply clamped onto the tabs
You can hook two (or three) of these up in series.
This will increase voltage while available amperage remains the same.
The benefit of this is feeding your charger high voltage means it has to to less work to feed your packs high amperage. (great for parallel charging)
To do this will require you to defeat the ground on one of the supplies. I chose to do this to the supply that feeds the negative side of my charger. If you do not defeat the ground, the supplies will not operate. I was able to defeat my ground by simply not hooking it up to the incoming AC. Some supplies have grounds elsewhere that must be defeated for this to work.
This, however, does not totally defeat the "direct short" safety feature. If you happen to touch or short out my two supplies together, they stop producing electricity, the fans slow to half speed, and the LED's will flash.
BUT, your results may vary... it is better to test before this feature is needed and take precautionary measures like cover the supplies (yet provide ventilation)
If the supplies you purchased are not up to the task of supplying your high amperage charger, connecting these in parallel will keep the voltage the same, but double the available amperage.
So you went really cheap on your supplies and you need to hook up two sets of two in series and then hook those two sets in parallel for one mega supply to power your needs.
If you have to ask how to do this... don't!!
I have seen a few hooked together where they have two plugs.
I chose to use just one plug and hooked the AC side in parallel.
AC power comes in from the IEC connection and feeds the positive supply power, neutral, and ground while there is a set of jumper wires that feed the negative supply only power and neutral.