12 volt 20A battery charger using computer PSU

[Bud Weather]

I agree with the theory, and I'd give it a try...
but my gut sensation is that they'll go up in smoke.

My 2 cents,

Bud Weather
http://www.thesolarshop.net/

 

[Norman Webb]

I am trying to recall my electronics 101 education.

Can I series the 5V supply of three computers power supplies to give a 15V
20A fast charger?
Old AT psu's are a dime a dozen and much cheaper than a 20A 12 volt
charger.
This would be powered by one of those el cheapo 500W generators to top up my
225Ah batteries of my solar setup.

 

[Vaughn]

I am trying to recall my electronics 101 education.

Can I series the 5V supply of three computers power supplies to give a 15V
20A fast charger?

The answer may not be as simple as you first think. Remember that these
power supplies are switchers and are not necessarily transformer isolated. For
starters, do a simple test to find out if the power supplies are referenced to
AC ground. If so, it won't work. That done, you are still not home free but at
least you have a good start.

Also, I remember that you have to do something to make them start. I seem
to recall that they need +5 on a certain lead.

If you could lay your hands on a surplus 24 Volt transformer and a Variac,
you would just need to add a heavy diode bridge and an ammeter and stick it all
in a case to build yourself a dumb fast-charger that would probably last you for
the rest of your life. You might even be able to substitute a lamp dimmer or
fan control for the Variac.

Vaughn

 

[William P. N. Smith]

Can I series the 5V supply of three computers power supplies to give a 15V
20A fast charger?

If you can limit the current it might work, but the supplies will do
foldback (shutdown on overcurrent) instead of a hard current limit at
(say) 20A. Look for a surplus 15V power supply with adjustable
current limit or a real battery charger...

 

[Norman Webb]

Vaughn wrote in message ...

Also, I remember that you have to do something to make them start. I seem
to recall that they need +5 on a certain lead.

The old AT type just needed a load to start.

The "new" (last ten years??) ATX supplies have some type of signal between
the psu and motherboard

 

[rebel]

I am trying to recall my electronics 101 education.

Can I series the 5V supply of three computers power supplies to give a 15V
20A fast charger?
Old AT psu's are a dime a dozen and much cheaper than a 20A 12 volt
charger.
This would be powered by one of those el cheapo 500W generators to top up
my
225Ah batteries of my solar setup.
/////////////////////////// Why don't you try this one.--
http://theepicenter.com/tow02077.html

 

[Ptaylor]

I am trying to recall my electronics 101 education.

Can I series the 5V supply of three computers power supplies to give a 15V
20A fast charger?
Old AT psu's are a dime a dozen and much cheaper than a 20A 12 volt
charger.
This would be powered by one of those el cheapo 500W generators to top up my
225Ah batteries of my solar setup.

In short,No.

Why?
Because the secondary side ground(5/12V neg wires) is connected to earth
ground.(non-isolated)If you connect another supply to it in series (+ to
-) you've just shorted the second supply to ground,through the first
supply's ground connection-The magic smoke comes out.(possibly from both
supplies!)

It may work if you left the earth grounds disconnected (and don't let
the cases touch eachother/anything -they're internally grounded
also.)..but this may also pose a shock hazard,if something were to go
wrong and pose a short to the case.

 

[Norman Webb]

Ptaylor wrote in message ...

In short,No.

Why?
Because the secondary side ground(5/12V neg wires) is connected to earth
ground.(non-isolated)If you connect another supply to it in series (+ to
-) you've just shorted the second supply to ground,through the first
supply's ground connection-The magic smoke comes out.(possibly from both
supplies!)

It may work if you left the earth grounds disconnected (and don't let
the cases touch eachother/anything -they're internally grounded
also.)..but this may also pose a shock hazard,if something were to go
wrong and pose a short to the case.

I haven't got the multimeter out yet because I haven't picked up the psus
but that makes sense.

Another option might be to change the 12V regulator to one with a higher
voltage.

The only reason I am playing is I have time to spare but not a lot of money.

 

[Martin Riddle]

In short,No.

Why?
Because the secondary side ground(5/12V neg wires) is connected to earth
ground.(non-isolated)If you connect another supply to it in series (+ to
-) you've just shorted the second supply to ground,through the first
supply's ground connection-The magic smoke comes out.(possibly from both
supplies!)

It may work if you left the earth grounds disconnected (and don't let
the cases touch eachother/anything -they're internally grounded
also.)..but this may also pose a shock hazard,if something were to go
wrong and pose a short to the case.

That maybe true, but maybe not depending on the manufacturer. A UL approved supply's does not have current carrying ground. Grounds
are for safety. It might be that the secondary (-) is isolated from ground. Or can be easily isolated. Allowing the stacking of
supplies.

Cheers

 

[Ptaylor]

That maybe true, but maybe not depending on the manufacturer. A UL approved supply's does not have current carrying ground. Grounds
are for safety. It might be that the secondary (-) is isolated from ground. Or can be easily isolated. Allowing the stacking of
supplies.

Cheers

In almost every PC supply I've come across,the AC earth ground and the
secondary side ground (DC negative) are connected together through a
thick trace on the circuit board,and it's metal case.If you know where
to cut the copper traces with an X-acto knife,you *can* isolate them,but
this probably a bit tricky for most,unless you have a bit of electronics
know-how.

One thing you might be able to do,is to parallel the 12V outputs of
multiple supplies,but I hold no responsibility if it goes up in smoke.

 

[Norman Webb]

Ptaylor wrote in message ...

In almost every PC supply I've come across,the AC earth ground and the
secondary side ground (DC negative) are connected together through a
thick trace on the circuit board,and it's metal case.If you know where
to cut the copper traces with an X-acto knife,you *can* isolate them,but
this probably a bit tricky for most,unless you have a bit of electronics
know-how.

One thing you might be able to do,is to parallel the 12V outputs of
multiple supplies,but I hold no responsibility if it goes up in smoke.

You would need blocking diodes from each supply I think and there goes
another 0.4v-0.7v drop. :-(

 

[als]

I am trying to recall my electronics 101 education.

Can I series the 5V supply of three computers power supplies to give a 15V
20A fast charger?
Old AT psu's are a dime a dozen and much cheaper than a 20A 12 volt
charger.
This would be powered by one of those el cheapo 500W generators to top up my
225Ah batteries of my solar setup.

Possible? Yes.
Practical? Maybe.

First item: isolate the cases. Connect each through 1 or 2 uf cap to earth
ground. An old oil (motor run) cap will work fine. Wouldn't hurt to tie
one case-to-case, also.
Second: add a small load (enough to get regulation) to the +5v outputs of
each supply. Usually, 20 ohms or so, but some may need 10 or less.
Third: add some sort of current limiter to the output. A couple of auto
headlamps would work.
Be aware that most PeeCee supplies will not be able to supply a continuous
20A load indefinitely. But should be able to charge at least a single
225AH if it is not drained too badly.

There are available, on the web, plans for the conversion of such supplies
to a 13.8v output, but from the question you are asking, you probably do not
want to tackle that type of project.

<als>

 

[William P. N. Smith]

There are available, on the web, plans for the conversion of such supplies
to a 13.8v output

Cool, do you have any references? I've found one that involves
rewinding the transformer, but that seems a bit much, and one at
www.siliconchip.com.au that's not available online...