Hello!

I noticed power supplies are expensive for hobby purposes, though they may give a higher voltage than PC PSU:s. Computer PSU:s are cheaper and quite easy to mod. I've been modding my Seasonic Super Silencer 460W with only one 12V rail of 25A. I'm using it to supply power to my charger, which have to charge my 25.2V battery's with 5A. This will require about 125W + a couple of watts of power-loss. Now it seems my modded PSU can't handle the power-requirements, despite the claims of supporting 25A on the 12V rail, which is 300W, much more than actually needed. First it was ok charging with 4.5A, now I can only charge with 3.5A, preventing the charger to complain about undervoltage. I'm using a 1 ohm 25W power-resistor on the 5V rail, and 3 2.2ohm resistors on the purple cable (I got the power supply to work best that way). Anyway, now I'm planning to buy a Antec Earthwatts 500W, http://www.hardwaresecrets.com/article/526/1, which has two 12V rails with each 17A.

My questions are:

1* Can I combine these two rails so I can take 34A (408W) from the PSU?
2* Any recommends of more beneficial PSU:s for my purposes?
3* What's the reason my modded PSU:s performance gets worse?
4* A question to Hardware Secrets: What load did you put on the 5V rail when you tested the above linked Antec PSU? Recommended loads/shortcuts on other rails?

/Vantskruv

1* Can I combine these two rails so I can take 34A (408W) from the PSU?

Yes and no. The maximum current stated on the label for each rail is an individual maximum current and usually give us a hint on what level the over current protection (OCP) is configured (usually up to 2 A above what is written).

Together they usually have a diffent combined maximum current/wattage.

Please read this tutorial for a full explanation:
http://www.hardwaresecrets.com/article/181

2* Any recommends of more beneficial PSU:s for my purposes?

Usually you need to pick a power supply with double the power you are going to actually be pulling. On the above mentioned tutorial we explain why.

3* What's the reason my modded PSU:s performance gets worse?

We haven't reviewed this particular power supply you have so we can't give you our comments on that.

4* A question to Hardware Secrets: What load did you put on the 5V rail when you tested the above linked Antec PSU?

This information is published on the review.

Recommended loads/shortcuts on other rails?

The power supply label/manual usually states the minimum current you should pull from the other outputs (usually 1 A each except on -12 V and on +5VSB).

Cheers,
Gabriel.

Thanks for your fast reply Gabriel!

I've read through the tutorial and I got more insighted of how the PSU works. Though a question still remains, I don't know if you can answer it, or someone else, maybe there is a technical difference between every PSU model and is impossible to answer. But I've noticed that putting a load on the +5V rail will increase and make the +12V rail/rails more stable towards 12V. But it isn't specified the lowest load I should use for my model, for now it is 5A (1 ohm resistor). If I would put a 5 ohm power-resistor, I would get a 1A load. Would that increase the stable voltage of the +12V rail? Also I had to put a load on the +5VSB to get my 12V work, otherwise the +12V would jump up and down between 9 and 11 volt, if I remember it correctly. Maybe if you put a different load there would produce a positive result of the +12V rail, increase or decrease the load? I don't know if this a special behavior of the ATX v2 PSU:s, or it is modelspecific. Or maybe it's only me digging for something in a empty hole?

Regards

/Vantskruv