I reiterate this once or twice a year: There is no such thing as a –48 volt power supply. There are only 48 volt power supplies.
Some people and some manufacturers will connect one of the outputs to the chassis/ground. Same with loads, some people and some manufacturers will connect one of the outputs to the chassis/ground. If the chassis of the supply and load are racked up so they are in electrical communication with each other then you have a third path for the current. You might want to make sure that third path is not shorting out the power supply. If nothing is connected to the chassis/ground it is “floating”. If either the power supply or the load is floating, then you can connect any kind of 48 volt power supply and it will work. So you have four configurations: 1.. Floating power supply floating load. 2.. Floating power supply, grounded power lead load. 3.. Grounded power supply lead, floating load. 4.. Grounded power supply lead, load with a grounded power lead. #4 is the only one that can get you in trouble. Lets say this is a 71.5 volt battery in your Delorian. And someone connected the battery such that the positive terminal is also connected to the chassis car chassis. And your Mr Fusion unit such that the negative terminal is connected to the chassis. And you ran wires, positive and negative from Mr Fusion to the battery. Do you see the problem? That negative wire is also connected to the positive battery terminal through the chassis. So the wire melts due to the dead short. Should I draw a schematic? I think original VW bugs were 6 bolts with positive tied to chassis. But nobody called a –6 volt battery? But that is what people try to do in the telco world... From: Chuck McCown via AF Sent: Wednesday, February 8, 2023 8:58 AM To: AnimalFarm Microwave Users Group Cc: Chuck McCown Subject: Re: [AFMUG] Neg 48V Power Supply Maybe use the volt meter first to make sure there is no potential between either power output to ground. From: Forrest Christian (List Account) Sent: Tuesday, February 7, 2023 7:54 PM To: AnimalFarm Microwave Users Group Subject: Re: [AFMUG] Neg 48V Power Supply Any isolated 48V supply works, just use the + wire for your return and the - for your -48v. I'm fond of the meanwell hlg supplies. The only gotcha is that some supplies will tie the negative wire to the ground pin on the ac plug, forcing it to be a +48v supply. You can use an ohmmeter to verify that this connection doesn't exist. Measure from the ground pin to the - output without the supply powered on. Shouldn't show continunity. On Tue, Feb 7, 2023, 7:27 PM Sterling Jacobson <sterl...@avative.com> wrote: I've got a few projects where I just need a simple telco -48v power supply from AC plug. I've got a lot of the "normal" PS units lying around. But what does it take to power a -48v device? Is it something I can/should just rig from a standard AC to DC 48v PS? Or is there something out there I should purchase instead that is fairly cheap? I'm using ITC Rectifiers for my -48v plant in several areas, I just haven't built out the DC plant in all areas but have one or two units that need it already on site. -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com -------------------------------------------------------------------------------- -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com -------------------------------------------------------------------------------- -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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