Series PS putting out different voltages

[Herky]

I have two Dell power supplies that I want to put in series...one puts out 11.5v, and the other puts out 12.0v! they are identical, off Ebay.

Model 7001072-Y000. They are slightly different than the model 700 shown on Tjinguytech's webpage in that I cant find any voltage adjustment pots inside.

any thoughts?

Also, any problem running them in series anyway?

thanks

[Fauropitotto]

From what I can tell, they all have pots on them buried somewhere.

My power supplies were off by 0.2V, and I was able to easily adjust. However, not while it was running for some reason.

You will load one more than the other if you don't balance them properly. Someone more educated than I could probably speak on the safety or longevity in ignoring the voltage balance issue.

[Herky]

thanks-I guess I could dig around in there some more...

[DrSteve]

If you are running them in series why does it matter if the voltage of one is slightly different to the other? They will both supply the same current.

If they were in parallel, that would be a different matter.

[Herky]

Why would it be a different matter for parallel?

[Gregor99]

Originally Posted by DrSteve

If you are running them in series why does it matter if the voltage of one is slightly different to the other?

It doesn't. But if one wanted to be technical, there would be slight imbalance in wattage output between the two supplies. Using 45 amps, the wattage would be:

11.5v 517w
12.0v 540w

Again, not really an issue unless you were close to the maximum wattage. I'd be more concerned about the supply that arrived at 11.5v. There may be wiring issue, or mod to turn it one might have an issue. I'd keep an eye that one as you ramp up the power. Its resting voltage is fairly low. Add good load and it trigger the under voltage protection on the supply and may go into standby.

Regardless, I like to have my supplies at roughly 11.9v each to keep the charger out of the buck/boost transition range when charging 6s packs.

[DrSteve]

Originally Posted by Herky

Why would it be a different matter for parallel?

If they were in parallel, the voltage difference would mean that your would have a current flowing from one power supply to the other - not sure how much current, but it's not what you want to happen.

Ideally when in parallel the power supplies should be identical, I believe some have a special pin that should be tied together on the two supplies to make sure they both output exactly the same voltage.

[Herky]

Thanks for the input guys. I've been running it with no issues (other than the screaming fans!).

I tried to jumper C2-D3 but it didn't slow them down. May just disconnect them...i'm not planning on pulling more than about 500 watts out of it...bet it never gets warm (at leas inside the house).