I get it now, the 48v never changes just the ground reference. I'm guessing the reason no one uses negative ground loads on a -48 system is the chassis ground being bonded to the inputs return.
Could I therically isolate my eltek -48 from any ground and operate it as a negative ground system? Or if the chassis isn't bonded to either can I just avoid grounding the supply? On Mon, Nov 26, 2018, 10:29 PM TJ Trout <t...@voltbb.com wrote: > Chuck, > > Are you sure the eltek's don't have the chassis ground bonded to the > positive output ? > > So I'm assuming the complication here is that if you reverse the wires, > when you try to power a +48v device, and it's negative input is bonded to > chassis ground and you have a ground path between the two (like a metal > rack) or possibly somehow through the AC ground/neutral you cause a direct > short circuit? > > I see mentions of DC-DC converters, but I don't see the point of using a > 300w RSD converter with a 2000W rectifier shelf? > > > > On Mon, Nov 26, 2018 at 2:57 PM <ch...@wbmfg.com> wrote: > >> It is 48. Period. You choose the reference if you want one. >> >> If you tie the + terminal to chassis ground then the – terminal is the >> hot –48 VDC terminal. >> >> If you tie the – terminal to chassis ground then the + terminal is the >> hot +48 VDC terminal. >> >> If you don’t tie either to chassis ground, then you will have to have a >> common return bar that is on the opposite rail from your fuses and circuit >> breakers. >> >> *From:* TJ Trout >> *Sent:* Monday, November 26, 2018 3:40 PM >> *To:* AnimalFarm Microwave Users Group >> *Subject:* [AFMUG] Eltek Valere J series -48 or +48 >> >> I'm looking at the Valere series and I can't seem determine if it's +48 >> or -48, seems like it's +48 but I thought all the telecom stuff was >> positive ground. >> >> How do you go about powering negative ground loads from a positive ground >> power source? >> >> I'm assuming you can leave out the neutral and isolate the chassis? >> >> >> >> ------------------------------ >> -- >> 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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