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Author Topic: -48v power supply  (Read 6651 times)
AI4NS
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Posts: 321


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« on: December 30, 2010, 07:57:02 AM »

I have a couple of Cisco power supplies that are -48V at 40 amps. Is there any reasonable way to invert them to +48V for use in an amp?

Mike
AI4NS
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KA5N
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Posts: 4380




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« Reply #1 on: December 30, 2010, 08:35:51 AM »

A -48 volt supply means that the negative side is isolated and the + 48 volt side is tied to common
(or ground if you prefer).  It makes no difference whether the negative or the positive side of the power supply is regulated, or whether the positive or negative side is common.
In other words a -48 volt supply is the same as a + 48 volt supply.  It just depends on how you hook it up.  It might be as simple as swapping a couple of leads to get the negative grounded or you might have to insulate the chassis to prevent some sort of problem.  I can't say just what without seeing a schematic. 
If you don't know much about supplies, I would suggest having someone with more experience look at
the supply.  Also sometimes power supplies built for computer usage don't lend themselves to amateur usage very well.  Remember if you do something wrong you could ruin a lot of nice ham gear if you connect the power backwards.
Allen
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AA4HA
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« Reply #2 on: December 30, 2010, 08:45:53 AM »

I am familiar with those supplies. Just check to see if the DC outputs are isolated from line ground. At the worst (if the positive-most lead is bonded to ground) you will need to let the power supply float the ground and maybe use an AC isolation transformer.

Those are heavy duty, very robust power supplies. I used them on carrier-grade microwave equipment with 3-4 radios per supply.

Tisha Hayes
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
WB2WIK
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« Reply #3 on: December 30, 2010, 08:58:50 AM »

These Telco supplies are mostly "floating" and can be used as +48V.  It's easy to check.

I have some at the shop which are -48V at 100A; they're still not that big or heavy, since they switch at 500 kHz (MagneTek models).  Never used them around radio equipment, though...might make too much noise in the HF spectrum to be useful around sensitive receivers.

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