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Old Jan 02, 2009, 08:32 PM
mrforsyth is online now
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So. Cal.
Joined Oct 2004
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Poor Man's High Current 24V Power Supply

Ok Charles. Here's the answer you were looking for...

Subsequent our discussion about IBM 235 serial operation earlier this week I hatched an idea and decided to perform some testing. I rummaged around in my parts bin and fished out a ground lift plug (photo below) in order to isolate the returns for the two power supplies. I then verified with my DMM that the grounds were indeed isolated. I subsequently connected the 12V rails of two supplies in series and got 24.5 volts (no surprise there).

I've since been running one of my iCharger 106B's for the last 3 days on one of the isolated 235's and have had no issues whatsoever pulling over 20 amps continuous so it seems to be very stable. Voltage under load is consistent with the same 235 without the isolation plug.

As I have no chargers or other devices that can make use of 24V I was not able to verify high current operation of two supplies in series. However, unless I'm missing something it should work just fine up to the limits of each respective power form. By my calculations, this'll give you 30 amps at 24V, 20 amps at ~15.3V, and 30 amps at ~17.0V. Other combinations include 10.0V, 8.3V, and 6.6V, although I don't know of what use these would be.

Obviously, precautions must be taken to ensure that the cases of the power supplies do not come in contact with one another before connecting in series.

As I'm not a DC power supply designer, if anybody has any input on potential pitfalls in my thinking, please chime in.

Mark
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