ATX Power for experiments

[BoyntonStu]

Perhaps this photo will help.

It can deliver regulated 14.75 V at almost 30 A.

It is a very good automobile alternator simulator.

It can also be used a a battery charger.

Note the homemade #10 wire shunt.

The multimeters were $2.99 at HF.

They will be direct wired to the last 2 ATX's for 10 V as a substitute for their 9V batteries.

The project cost me less than $20.

BoyntonStu

[Q-Hack!]

Gotta hand it to you... you are a master at thrift recycling.

[coffeeachiever]

Gotta hand it to you... you are a master at thrift recycling.

Agreed. Nice job Stu. Especially since so many of us are on such a tight budget.

[BoyntonStu]

Perhaps this photo will help.

It can deliver regulated 14.75 V at almost 30 A.

It is a very good automobile alternator simulator.

It can also be used a a battery charger.

Note the homemade #10 wire shunt.

The multimeters were $2.99 at HF.

They will be direct wired to the last 2 ATX's for 10 V as a substitute for their 9V batteries.

The project cost me less than $20.

BoyntonStu

I took the 10 V from ground to the output of the first ATX.

The 3 ATX supplies are insulated from each other.

When I powered the meters up they worked fine BEFORE plugging in their test leads.

They read 000

When I inserted the ground test leads, the meters read - (Negative).


Something is going on between the battery connection, the internal meter wiring, and the ATX supplies.


Is there a solution? Diode isolation perhaps?

I can use a separate 9 V power adapter but that would not be as efficient.

Confused!

BoyntonStu

[Q-Hack!]

ATX power supplies don't have a 10v lead. However, there is a +5 and a -5 lead. You are probably going to need to use one of the +12v lead to power your meters. Its the yellow wire.

http://wiki.xtronics.com/index.php/ATX_Pinout

Edit: When you connected the ground lead of the meter to the ground potential of the power supply it dumps your -5 to ground. This gives you a +5 volts to run the meter.

[Q-Hack!]

Those DMM's should run ok at +12v. But if you want to be safe, pick up a NTE1957. Its a 9v voltage regulator.

http://www.nteinc.com/specs/1900to1999/pdf/nte1957.pdf

[Q-Hack!]

Another option...

Get one of these: http://www.radioshack.com/product/index.jsp?productId=2062599

Wire it such:


Red wire..........ATX(+5)-----Vin(7805)Vout-------(+10V) to meter power
white wire........ATX(-5)----------|

Black wire ATX (Grnd)-----------------------------(GRND) to meter power


By wiring the -5v to the ground pin on the 7805, you effectively isolate it from being grounded by the DMMs common lead.

[BoyntonStu]

I am using only the +5 V each from THREE ATX supplies in series.

This generates 15 V @ 25 Amps.

I connect between ground and up two ATX's for the 10 Volts.

It should be a perfect +10 VDC source.

That is what is so confusing.

I hope that this clears it up for you.

BoyntonStu

[Q-Hack!]

Ah, I understand now... that does make it perplexing.

[Q-Hack!]

Just to make sure I understand correctly...


(+)ATX3(-)---(+)ATX2(-)---(+)ATX1(-)
.|............|............|......|
+15v.........+10v.........+5v.....Grnd

Assuming you used pins 4 (red) and 5 (blk), I don't know your setup. Should work unless you are also trying to do the same with another voltage at the same time. I know that most ATX power supplies use a common ground for all DC voltages.

Which brings up another question... How are you turning on each of the ATX power supplies? Grounding pin 14 is the preferred method. Since you raised the voltage potential of the ground in each ATX, you would be applying +5V to pin 14 on ATX2 and +10V to pin 14 on ATX3. You will need to make sure that you use the ground potential of ATX1 for each.

[BoyntonStu]

Just to make sure I understand correctly...


(+)ATX3(-)---(+)ATX2(-)---(+)ATX1(-)
.|............|............|......|
+15v.........+10v.........+5v.....Grnd

Assuming you used pins 4 (red) and 5 (blk), I don't know your setup. Should work unless you are also trying to do the same with another voltage at the same time. I know that most ATX power supplies use a common ground for all DC voltages.

Which brings up another question... How are you turning on each of the ATX power supplies? Grounding pin 14 is the preferred method. Since you raised the voltage potential of the ground in each ATX, you would be applying +5V to pin 14 on ATX2 and +10V to pin 14 on ATX3. You will need to make sure that you use the ground potential of ATX1 for each.

We may be getting somewhere.

Each ATX has the green wire connected to the black ground inside the box.

he remaining black wires go the the red of the next box.

The mount is plywood and there is a piece of plywood between each ATX.

Here's another clue.

If I use a 9V battery the meter reads right.

If I use a AC/DC 9 V plug the meter is not correct.

I believe that the AC supply is having its effect.

I am using only 2 wired for the AC.

I don't know whether the ATX cases are at ground potential.

I was careful with the polarities while soldering the 2 wire connections.

The output is certainly ~ 15 VDC.

The 10 Volt point measures 10 Volts.

Still confused.


BoyntonStu

[BoyntonStu]

All was needed was a 500 ohm resistor across the 12 V Adapter.

Any stray transients are grounded.

Next, I will try the 10 V tap.

FWIW

BoyntonStu

[Q-Hack!]

All was needed was a 500 ohm resistor across the 12 V Adapter.

Any stray transients are grounded.

Next, I will try the 10 V tap.

FWIW

BoyntonStu

Impedance matching?