I mixed + and - 48 in a off grid solar system. I had one battery bank with
the positive to the common point/ ground. The other battery bank was
negative to the common point. From one battery to the other it was 96 volts
when went to the load.
But I had two 48 volt solar systems and charge controllers and they charged
each half of the total battery independently. One of the charge controllers
had to be mounted on an insulating board because its chassis was hot.
The whole -48, +48 thing is all about what is connected to the ground,
common point, return etc. If you ground the negative side of a battery you
have a positive voltage hot wire system. If you ground the positive side of
a battery you have a negative voltage hot wire. The battery itself does not
care.
If you load does not have an electrical connection to a grounded chassis, it
will not car either.
However if you have a device that is designed to be powered from -48 and
internally its positive 48 connections are all bonded to its metallic
chassis, it really needs to be powered from a floating supply or a -48
supply.
There is no good reason to ground either side of a DC supply in a system
these days. Originally telcos went with positive grounding so that if you
had an insulation fault in an underground cable, the -48 volt ring side (hot
side) of the phone line would tend to attract metallic ions from the
surrounding soil. If it was reversed the wire would donate copper ions to
the soil and quickly plate itself away to nothingness.
-----Original Message-----
From: Mark - Myakka Technologies
Sent: Monday, January 8, 2024 9:25 AM
To: af@af.afmug.com
Subject: [AFMUG] -48V kicking the dead horse
I know we have been though this many times and I thought I understood it.
-48VDC is the Negative side being HOT, correct?
It is BAD to try to mix -48VDC and 48VDC
There is no such thing as a -48V battery. A battery is a battery, correct?
How about the ICT Platinum power supplies. They show as 48VDC, can they be
used on -48VDC equipment?
I remember Check saying something about a way to test to see if a piece of
equipment that is Neg 48VDC is truly grounded as Neg 48VDC.
--
Thanks,
Mark mailto:m...@mailmt.com
Myakka Communications
www.Myakka.com
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