POWER SUPPLY LOAD 15 VDC MAX


On several occasions I have wished that I had a way of loading a power supply.  I purchased a 50 amp rack mount power supply off of ebay that didn't work.  After sending my money back the seller told me to keep the power supply rather than paying for the return shipping.  Since the supply was now free, I decided to see if I could repair it.  I wanted to be able to test the power supply if I was able to repair it, so I started looking for some parts to build a load that I could use to test the power supply with.  In order to get the parts cheaply, they mostly had to come from China and took a long time to get all the parts together, but I finally fixed the power supply and completed the load.  Below is a few pictures of the process.

Parts for load.
Assembly of some parts for project (others were still on order)  A complete parts list at       bottom of page.















































Schematic Drawing of Project




























Resistors installed on heat sinks and wired to be installed in project box.







































All parts installed and ready to be tested.








































Power Supply Loading Astron RS-35M to 25 Amps.  Each switch provides around 7 amps of load depending on voltage value at load terminals.





































SUMMARY OF PROJECT

It took a while to get all the parts because I wanted to spend as little as possible on this project, so most were ordered on Ebay and came from China.  I would recommend if you build this project that you wait and get all the parts before you start to assemble it.  Since I already had the two 50 mm fans, I used them.  They do ok, but the load when all resistors are in has to dissipate as much as 800 watts.  That's a pretty good foot warmer, so things warm up quickly. I have decided to add another fan and will install it when I get it.

Below is the final list of parts.
PartOrdered FromCost
1 - 255mm X 74mm x 158mm Project Box  Ebay  $25.99
10 - Blue LED 12V DC 20A Toggle Sw  Ebay$6.99   (8 used)
10 - 2 ohm 100 watt wirewound resistor Ebay $11.90 (8 used)
50 - #6-32 Button head socket cap screwsEbay$6.94   (16 used)
1 - Ammeter 0-75 amp with shunt   Ebay$9.68
2 - Aluminum Heat Sink 100mmX100mmEbay$14.18
2 - 50mmX50mm cooling fan Had These Already$8.00   (just ordered another for $4.00 from Ebay)
2 - 50mmX50mm finger guard Ebay$1.86
2 - 1/4"-20 x 1-1/4"  Silicon Bronze BoltsBolt Depot$1.76
8 - 1/4" Silicon Bronze Washers (0.267 x 0.687 x .040)Albany County Fasteners$2.80
6 - 1/4"-20 Silicon Bronze NutsAlbany County Fasteners$2.16
4 - 1/4" Fiber Washers  Bolt Depot$0.64
Misc. Parts$2.10  (I love how "miscellaneous" always makes the total come out even)
 Total Cost  $95.00


Suggestions:
I used #10 AWG from the load side of the shunt resistor to the #14 AWG solid bus on the switches.  Solder the #10 to the #14 in the middle of the switch bus so the bus does not have to carry all the current, but half to each bank of four switches.  On the negative side of the resistors, I split the resistors into two banks of four and ran a #14 AWG solid wire between them.  I then soldered a separate #12 AWG to the middle of each bank and connected them to the negative input bolt.  For the negative connections on the switches, I used #14AWG solid for the negative bus at the switches and #20 AWG from one of the negative buses on the resisters.  For the switches to the resistors, I used #18 AWG from each switch to each resistor.

If you need more load than what this load will deliver, you either can buy a larger project box, more resistors, heat sinks, switches, and a ammeter to size or build another one like this and put them in parallel.  If you build one in a larger project box, you will need to either parallel the feed wires to the switches or use larger wire.