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Old 1st August 2008, 08:22 PM   #1
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Default +- 30V from two dual +-15 supplies?

Greetings,

I have two surplus DC regulated power supplies; each of them has dual outputs of +-15V. I need one +-30V supply. I'm thinking about the following. In each PS tie the 0s of each output, this should give two supplies: +30 and -30, depending on what will be further referenced as 0. Then tie the 0s of these supplies to obtain +-30V PS.

Are there any caveats in this arrangement?

Thanks!
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Old 1st August 2008, 09:17 PM   #2
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Slightly confused by your words, but basically you need to connect the supplies in series with each other - negative of the 'upper' one to positive of the 'lower' one then this junction becomes your 0V poiint. But be sure to see first if any of the outputs is connected to earth. If it is then you can't do this as you will end up shorting one of the sides.
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Old 1st August 2008, 09:59 PM   #3
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OK, thanks!
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Old 4th August 2008, 07:09 PM   #4
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Hi richie00boy,

I managed to find the schematics of the outputs. It shows that the +/-15 are connected sharing a common return, so I can obtain 30V straight from +out and -out. So can I connect two such supplies in series for +/-30V?

Thanks!
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Old 4th August 2008, 08:15 PM   #5
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Need to the the whole schematic! My concern is that COM terminal, it seems to be possibly connected to your +15 0 -15V midpoint. If this is then earthed through the case there may be problems connecting two supplies in series.
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Old 4th August 2008, 08:31 PM   #6
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Hi richie00boy,

This is the full schematics, it doesn't look like the COM is earthed.

Thanks!
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Old 4th August 2008, 08:43 PM   #7
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As Richie pointed out it depends on if the common 0 terminal
is floating or connected to earth. When you first hook these
supplies in seriese you might make this connection through
a 1/2w 10ohm resistor or a 1/2A fuse just to be safe.
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