PSU + big power resistors = Explosion?!

[Man]

So, I've a couple of old PSUs lying around and I want to stress test them to see if their voltages are within tolerance under low to moderate load. Mostly just for fun, although I might end up using them is some sort of project. 

 

In any case, I'm thinking about ordering a 100W 1.5Ω power resistor from Motherland China and connecting it with the 12V which will put a theoretical load of around ~96W @ 8A on a single Molex but I'm not sure if it's going to be safe. 

 

Another option is buy two resistors, each rated at 100W 2Ω and connect them with Molex connectors from different rails, which sounds a little better and safer to me (72W x 2 = 144W @ 12V).

 

The problem is that I haven't done anything like this before so need some expert advice. I'm by by no means an electronics engineer, not even close! Just some crazy hobbyist playing around with old PSUs! I know I shouldn't but can't help myself.

 

Thanks in advance. 

[Electronics Wizardy]

If you want to test a psu, buy/make a dummy load. There much better than a power reistor for this as they can be easily adjusted. There also fun to make, basically some old mosfetts and op amp.

 

8a is a bit much for molex, Ive done it, but it will get hot, Get a adapter from somethinglike the 8pin pcie.

 

 

[Man]

7 minutes ago, Electronics Wizardy said:

If you want to test a psu, buy/make a dummy load. There much better than a power reistor for this as they can be easily adjusted. There also fun to make, basically some old mosfetts and op amp.

 

8a is a bit much for molex, Ive done it, but it will get hot, Get a adapter from somethinglike the 8pin pcie.

 

 

Can you suggest a good, cost effective dummy load with a power draw of 200-ish watts @ 12V?

[Electronics Wizardy]

8 hours ago, Man said:

Can you suggest a good, cost effective dummy load with a power draw of 200-ish watts @ 12V?

Either build your own, or get some of thsee on ebay https://www.ebay.com/itm/150W-200V-20A-Constant-Current-Electronic-Load-Battery-Discharge-Capacity-Tester/153508103140?hash=item23bdcbc3e4:g:6e8AAOSwZwxc8Iz1

[Hackentosher]

@Electronics Wizardy is right. You really shouldn't try to pull 8a through a shitty molex connector. I would (and have) cut off all the connectors on an ATX supply and solder the wires into one, better, connector. This can get a little messy though, so it may just be best to crack open the supply, remove all the spaghetti wire, and solder some heavy wire to the rails you want. Then connect all that up to a DC constant current load. Those are always good to have around for testing supplies like this, or discharging batteries down from their less-than stable 100% charge status. If you plan on doing a lot of DC loading, it may be worth it to step up to a bench unit like this one that can dissipate more power https://www.aliexpress.com/item/4000204243191.html?spm=a2g0o.productlist.0.0.c4b966bfMslRpq&algo_pvid=e3dadeb9-4596-4140-bde0-ccc25a952abd&algo_expid=e3dadeb9-4596-4140-bde0-ccc25a952abd-30&btsid=74219f63-8bb4-40a2-9a5c-c9f6de93f82a&ws_ab_test=searchweb0_0,searchweb201602_4,searchweb201603_53

 

For connectors, I really like AMASS XT series connectors, specifically the XT-60U. Those little bastards can handle a lot more than their 60 amp rating, they're cheap as beans, and easy to work with.

[mariushm]

Go to a cars / motorbike store and buy some 12v incandescent / halogen light bulbs. They're cheap as they're mass produced and they're big wattage.

You can buy them in various wattages like 10-20w (for turn indicators for example), 60w, etc and they have convenient sockets easy to solder wires on (or already have wires) 

 

Molex is rated for 5A, sata is rated for around 4.5A max (but i wouldn't use it for more than ~3.5A) on each voltage

 

The connectors (pins in connectors) on modular power supplies are rated for around 9-10A of current, so for example if you have a chain of sata connector that goes into a header on the power supply with a single 12v+GND pair , the whole chain of connectors shouldn't be used for more than around 10A or 100-120 watts.

 

 

[Man]

On 1/20/2020 at 3:09 PM, mariushm said:

Go to a cars / motorbike store and buy some 12v incandescent / halogen light bulbs. They're cheap as they're mass produced and they're big wattage.

You can buy them in various wattages like 10-20w (for turn indicators for example), 60w, etc and they have convenient sockets easy to solder wires on (or already have wires) 

 

Molex is rated for 5A, sata is rated for around 4.5A max (but i wouldn't use it for more than ~3.5A) on each voltage

 

The connectors (pins in connectors) on modular power supplies are rated for around 9-10A of current, so for example if you have a chain of sata connector that goes into a header on the power supply with a single 12v+GND pair , the whole chain of connectors shouldn't be used for more than around 10A or 100-120 watts.

 

 

Halogen lights are a brilliant idea! EXTREMELY cheap and MUCH safer than resistors, which tend to go boom!

 

Found 2 x 100W 12v halogen bulbs going for $2 each. Even cheaper than resistors, and I won't have to build a heatsink for them either. 

 

Solved!