What Ken said.
Positive is always positive.
Neg is always neg.
48 volts is 48 volts.
If someone wants to say a load or source is -48 or +48 it just means the
opposite polarity is tied to earth or chassis ground.
If they say a load needs -48, it could mean that the load has the positive
power wire also connected to the case.
If a source says it is a -48 source, it could mean that the source has the
positive lead connected to ground.
You can always test a source. Ground to the wire. If you measure 48 volts
between ground and one of the power wires, then it is referenced to ground.
If you are on the positive wire to ground and you see 48 volts, then it is a
neg ground system. If you are on the neg wire to ground and you see 48
volts then you are on a positive ground system.
Positive Ground System == -48 or whatever volt system
Neg Ground System == +48 or whatever
BUT many sources and loads are floating where neither power lead is
connected to chassis/earth/ground
Sometimes they will call those 48 VDC system. But sometimes they will call
them a +48 VDC system when really it is simply a 48 VDC system.
Anytime -48 is printed on something, time to take it seriously. They
probably mean it.
-----Original Message-----
From: Christopher Tyler
Sent: Monday, April 8, 2019 9:54 AM
To: AnimalFarm Microwave Users Group
Subject: [AFMUG] DC/DC converter question
I have a Meanwell SD-350C-24 DC/DC converter for +48v in to +24v out. I just
learned that our DC plant at this site is -48vdc.
I'm assuming that I can't just plug it in backwards. But we've never had to
deal with -48vdc before, am I wrong in this assumption?
--
Christopher Tyler
MTCRE/MTCNA/MTCTCE/MTCWE
Total Highspeed Internet Services
417.851.1107 ext 9002
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