# want to rewire power supply

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Anonymous
a b B Homebuilt system
a b ) Power supply
July 26, 2005 4:27:17 PM

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

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Anonymous
a b B Homebuilt system
a b ) Power supply
July 26, 2005 4:27:18 PM

"Mike Hollywood" wrote:
> 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
Anonymous
a b B Homebuilt system
a b ) Power supply
July 26, 2005 5:42:23 PM

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
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Anonymous
a b B Homebuilt system
a b ) Power supply
July 26, 2005 5:42:24 PM

"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
> 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

..
Anonymous
a b B Homebuilt system
a b ) Power supply
July 27, 2005 1:48:17 PM

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

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

mike

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

From: "Jon Danniken" <jonREMOVETHISdanniken@yahoo.com>

Newsgroups: alt.comp.hardware.pc-homebuilt

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

Subject: Re: want to rewire power supply

> "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

>> 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

>

> .

>
Anonymous
a b B Homebuilt system
a b ) Power supply
July 27, 2005 8:19:52 PM

In article <wNidnWBhT4r6-XvfRVn-iA@comcast.com>, Mike Hollywood says...
> 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.

--
Conor

-You wanted an argument? Oh I'm sorry, but this is abuse. You want room
K5, just along the corridor. Stupid git. (Monty Python)
Anonymous
a b B Homebuilt system
a b ) Power supply
July 27, 2005 8:19:53 PM

Conor wrote:

> In article <wNidnWBhT4r6-XvfRVn-iA@comcast.com>, Mike Hollywood says...
>
>>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.
>

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.
!