want to rewire power supply

[Mike Hollywood]

I want to make a 17 volt dc power supply.

If i take an old at power supply and splice the 5 volt rail and 12 volt rail
in series, as if they were two batteries, would I have a working regulated
17 VDC supply?

TIA

mike

 

[Jon Danniken]

I want to make a 17 volt dc power supply.

If i take an old at power supply and splice the 5 volt rail and 12 volt rail
in series, as if they were two batteries, would I have a working regulated
17 VDC supply?

No, because the ground (return) values are at the same potential.
Considering your battery analogy, this is the equivalent of connecting both
(-) terminals with the batteries in series, which will place a direct short
across one battery.

If you don't need much current, you should be able to use the potential
between the (-12V) and (+5V) to get 17VDC. You'll need to keep within the
ratings of your PSU, of course.

Jon

 

[Mike Hollywood]

Jon, thanks for the head's up.

What if I take the (-) from the 12V+ and use that for one side of the load,
then connect the (+) from it to the (-) of the 5 volt and use the (+) of the
5 volt for the other side of the load?
Mike

 

[Jon Danniken]

"Mike Hollywood"

Jon, thanks for the head's up.

What if I take the (-) from the 12V+ and use that for one side of the load,
then connect the (+) from it to the (-) of the 5 volt and use the (+) of the
5 volt for the other side of the load?

Mike, it is easier to follow the conversation if you quote the context you
are replying to, then provide your content below this.

That being said, no; as I stated before, the returns (grounds) for all
connections out of your PSU are at the same potential. What you are calling
the "(-) from the 12V+) is the same return as for the +5V. To provide 12V,
you use two leads, one at 0V (the return, or ground), and one at 12V;
likewise, to provide 5V, you use two leads; one at 0V and one at 5V; the
*difference* between the two connections is the Volts you obtain.

I would suggest you obtain a multimeter so you can measure the voltage
difference yourself (along with other generally useful things)

Jon

..

 

[Mike Hollywood]

ok on the quote of original, I thought it was "cleaner" to not repeat what
already was posted.

ok on the measurements. Will do and let you know how I make out.

mike

----- Original Message -----

From: "Jon Danniken" <[email protected]>

Newsgroups: alt.comp.hardware.pc-homebuilt

Sent: Tuesday, July 26, 2005 2:21 PM

Subject: Re: want to rewire power supply

"Mike Hollywood"



Mike, it is easier to follow the conversation if you quote the context you

are replying to, then provide your content below this.

That being said, no; as I stated before, the returns (grounds) for all

connections out of your PSU are at the same potential. What you are

the "(-) from the 12V+) is the same return as for the +5V. To provide

you use two leads, one at 0V (the return, or ground), and one at 12V;

likewise, to provide 5V, you use two leads; one at 0V and one at 5V; the

 

[Conor]

I want to make a 17 volt dc power supply.

If i take an old at power supply and splice the 5 volt rail and 12 volt rail
in series, as if they were two batteries, would I have a working regulated
17 VDC supply?

No. A better idea would be to take -5V and +12V. That'll give you a
potential difference of +17V which anything attached as follows would
see as a 17V PSU.

Connect the 0V rail of whatever you're wanting to power to the -5V and
the +ve rail of whatever you're wanting to power to the +12V.

 

[David Maynard]

No. A better idea would be to take -5V and +12V. That'll give you a
potential difference of +17V which anything attached as follows would
see as a 17V PSU.

Connect the 0V rail of whatever you're wanting to power to the -5V and
the +ve rail of whatever you're wanting to power to the +12V.

There's no way to 'splice' the 12 and 5 in series anyway as they have the
same ground.

-5 and 12 will work, assuming nothing is ground referenced, but the current
will be limited by the least of the two. In this case, the -5v.