Multiple PSUs in series

[Cra$h 0veride]

Hey everyone,

Is anyone here familiar with setting up multiple ATX PSUs in series or have a link to a page that explains how?

THX,

:toast:

[n00b 0f l337]

Yes I've done it. Hijon is still selling my best group for powering my old 437watt dominator pro. Basically you have two psu's.
They can never touch each other.
The ground of psu1 goes to your tec, and the +12v goes to the ground on the other. Then psu2's +12v goes to your TEC. I wrapped one of the psu's in electrical tape though it still doesnt do much for grounding wise. It works well.

[Cra$h 0veride]

On that same note,

1- If I were to put 2 PSUs in series, the first 12V@25A and the second 5V@35A will the result be 17V@25A ?

2- If I were to put 2 PSUs in series, the first 12V@25A and the second 5V@35A then put 1 more but in parallel to the first 2 this one being 5V@35A, what will the result be ?

{(12V@25A and 5V@35A in series)5V@35A in parallel} = ?

I'm even confusing myself...

Anyways, I would really appreciate the answer if anyone can understand what I wrote.

THX
:toast:


Cra$h

[blander]

On that same note,

1- If I were to put 2 PSUs in series, the first 12V@25A and the second 5V@35A will the result be 17V@25A ?

2- If I were to put 2 PSUs in series, the first 12V@25A and the second 5V@35A then put 1 more but in parallel to the first 2 this one being 5V@35A, what will the result be ?

{(12V@25A and 5V@35A in series)5V@35A in parallel} = ?

I'm even confusing myself...

Anyways, I would really appreciate the answer if anyone can understand what I wrote.

THX
:toast:


Cra$h

if you wish a power supply with 35A @17V
you ned:
{(12V@25A and 12V@25A in parallel)5V@35A in series}

[RussC]

You cant put PSU outputs in parallel without a load sharing resistors. Essentially you need put resistors in series with each output before they are tied together. It needs to be a small resistor that can handle the power output of the PSU. In the range of 1/10's of an ohm. This requiers you to do some math using ohms law and power equation. These resistors keep the PSU outputs supplying even current. If this is not done, one PSU can be un-balanced(by many means) and will rail to full output while the other has no output. This may cause it to fail or fold back the current.

This is not a simple setup for a noob, but is not rocket science either.

RussC

On that same note,

1- If I were to put 2 PSUs in series, the first 12V@25A and the second 5V@35A will the result be 17V@25A ?

2- If I were to put 2 PSUs in series, the first 12V@25A and the second 5V@35A then put 1 more but in parallel to the first 2 this one being 5V@35A, what will the result be ?

{(12V@25A and 5V@35A in series)5V@35A in parallel} = ?

I'm even confusing myself...

Anyways, I would really appreciate the answer if anyone can understand what I wrote.

THX
:toast:


Cra$h

[Cra$h 0veride]

You mean I need to put a resistor on the 12v rail of each PSU?
That doesnt make sense, a resistor there is the same thing as the resistance the peltier produces. Please clarrify your statement.

[RussC]

Right,
You have to understand whats driving the power outputs to have an understanding why this works. Anytime you put power supplys in parallel for added current capability, you need to do this to "balance" the supplys. Like I said, the resistor is small, in the 1/10ths of ohms range, and will only limit the supply by a very small percentage. But the gain from parallel supplies significantly outweighs the loss ie you loose a some 5 or so amps of output from a 70amp total, but you keep the PSUs from burning up when the outputs become un-balanced. The resistors will be power units capable of greater than 1w dissipation, dependeding actuall load current.

If your running the supplys right at the max rails, you've designed the system wrong anyway, and will have a melt down, supply foldback or fuse blowing issues.

I can run the math if you like on whats lost by adding the resistors, but only if you really want me too.

RussC

You mean I need to put a resistor on the 12v rail of each PSU?
That doesnt make sense, a resistor there is the same thing as the resistance the peltier produces. Please clarrify your statement.