Joining of the +12v rails on PSU

[devilchrist]

I have the OCZ powerstream 500W PSU that spec says got +12v 18A rails.

Can I join these in parallell to make a single +12v 36A rail?

you may have guessed that I'm not really using this to run a computer, but a battery charger.

I'd assume that PSU rail is rail 1 and accessories is rail 2

 

[Gillbot]

I've found that old AT power supplies are the best for charging batteries. I use one still in my garage as a jump box. I cut all the leads out of it, attached some larger 8ga wire to the main +12 internal point and a good ground to the chassis. It's "rated" at like 65a on the 12v rail and I grabbed it from ebay for like $5 shipped.

 

[PM650]

Originally posted by: Gillbot
I've found that old AT power supplies are the best for charging batteries. I use one still in my garage as a jump box. I cut all the leads out of it, attached some larger 8ga wire to the main +12 internal point and a good ground to the chassis. It's "rated" at like 65a on the 12v rail and I grabbed it from ebay for like $5 shipped.

Every AT power supply I've seen had a very low-power 12V rail. Afaik, AT computers drew most of the power from the 5V rail.

OP: Yes, you can connect the rails together externally. The only thing separating them is current sensing resistors inside the psu, both 12V rails originate from a single source.

 

[Gillbot]

I should have added, they were "server" PSU's so that may be the reason for the high 12v rails on them.

 

[yh125d]

Originally posted by: PM650

Originally posted by: Gillbot
I've found that old AT power supplies are the best for charging batteries. I use one still in my garage as a jump box. I cut all the leads out of it, attached some larger 8ga wire to the main +12 internal point and a good ground to the chassis. It's "rated" at like 65a on the 12v rail and I grabbed it from ebay for like $5 shipped.

both 12V rails originate from a single source.

Not always. Higher end PSU's can come as a true dual rail, totally separate


But that is the majority yes

 

[PM650]

Originally posted by: yh125d

Originally posted by: PM650

Originally posted by: Gillbot
I've found that old AT power supplies are the best for charging batteries. I use one still in my garage as a jump box. I cut all the leads out of it, attached some larger 8ga wire to the main +12 internal point and a good ground to the chassis. It's "rated" at like 65a on the 12v rail and I grabbed it from ebay for like $5 shipped.

both 12V rails originate from a single source.

Not always. Higher end PSU's can come as a true dual rail, totally separate


But that is the majority yes

True, I suppose I should've clarified that I was assuming this 500W unit is nothing exotic.

 

[jonnyGURU]

You're going to kill that PSU using as a battery charger.

With no load on the +3.3V and +5V and maxing out the +12V, I give it about 5 minutes.

 

[devilchrist]

been using it for about 2 months charging at 100W on one rail. no problems.

why would it matter I only use the 12V rail?

 

[Gillbot]

Originally posted by: jonnyGURU
You're going to kill that PSU using as a battery charger.

With no load on the +3.3V and +5V and maxing out the +12V, I give it about 5 minutes.

If you are talking to me, I've been using my AT unit as a power supply and battery charger for years now without issues. I use it to jump start my car all the time!

 

[jonnyGURU]

Originally posted by: devilchrist
been using it for about 2 months charging at 100W on one rail. no problems.

why would it matter I only use the 12V rail?

Unless the PSU has DC to DC for the non-primary rails or there's a dummy load on the rails (typical of older units) a SMPS requires a minimum load on the rails in order to run. A group regulated PSU will actually run, but the voltages will be way off if the load is "lop sided". The Powerstream may be group regulated IIRC, so I'd be curious as to what that +12V rail is actually putting out considering you only have a 12V load on it and it's as high 100W.

Originally posted by: Gillbot

Originally posted by: jonnyGURU
You're going to kill that PSU using as a battery charger.

With no load on the +3.3V and +5V and maxing out the +12V, I give it about 5 minutes.

If you are talking to me, I've been using my AT unit as a power supply and battery charger for years now without issues. I use it to jump start my car all the time!

No.. not you. Older PSU's, like AT units, almost always have dummy loads on the rails.

 

[Gillbot]

Originally posted by: jonnyGURU

Originally posted by: Gillbot

Originally posted by: jonnyGURU
You're going to kill that PSU using as a battery charger.

With no load on the +3.3V and +5V and maxing out the +12V, I give it about 5 minutes.

If you are talking to me, I've been using my AT unit as a power supply and battery charger for years now without issues. I use it to jump start my car all the time!

No.. not you. Older PSU's, like AT units, almost always have dummy loads on the rails.

:thumbsup: