Multiple grounds on DC floating battery
Multiple grounds on DC floating battery
(OP)
I currently have a 250VDC battery which has multiple full positive grounds on it. I have pulled all the dc fuses one at a time and the dc potential on the ground still remains. I have been notified that this ground has been present for some time now and in my opinion other grounds have also accumulated. I have been pondering an ac test method. Where I would inject low voltages or currents at a specific frequency (which frequency I am not sure of 25hz ? ) to the battery terminal and check for AC current presence in the individual control circuits while the control circuits are live. If anyone has had any luck with this or could point me in the right direction (voltage with resistor vs current/Frequency suggestions) it would be appreciated.
Thanks
Thanks






RE: Multiple grounds on DC floating battery
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If we learn from our mistakes I'm getting a great education!
RE: Multiple grounds on DC floating battery
RE: Multiple grounds on DC floating battery
Let us know how you get on with the receiver design.
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If we learn from our mistakes I'm getting a great education!
RE: Multiple grounds on DC floating battery
RE: Multiple grounds on DC floating battery
Output of the isolation transformer was connected to ground through a tapped current limiting resistor. The other end was connected to the battery bus lead that showed a ground. A variable voltage transformer fed the isolation unit. We adjusted the variac to get enough AC current to detect.
A timing relay shorted out a portion of the resistor to give a pulsing AC current, jumping from 0.2 A to 2.0 Amps about 1 Hz. The pulsing was easier to see on the ammeter than a straight current.
We clamped on various circuits and followed the wires to the faulted conductors, locating multiple faults in a couple of hours.
RE: Multiple grounds on DC floating battery
UPS engineer http://www.powerups.co.uk
RE: Multiple grounds on DC floating battery
If so then your ground fault is within the rectifier or battery. Are the batteries Ni-Cad or VRLA? Ni-Cads with metal cases have been known to track down to earth on the battery frame.
Is there DC capacitors within the rectifier? If so sometimes the cases of these can cause earth faults as the negative terminal of the capacitor is connected to the case. If the capacitor is stud mounted on an earthed frame then this can cause a hard earth fault.
Hope this helps!
UPS engineer http://www.powerups.co.uk
RE: Multiple grounds on DC floating battery
One further warning about the Grouser and similar instruments: don't use it on the pilot wires of a differential protection scheme when it is in service, otherwise the relays trip and take out a big chunk of the network. Thankfully it was not one of mine - and I'm not sure I'd admit it if it was - but anecdotal from a neighbouring site. Heh-heh.
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If we learn from our mistakes I'm getting a great education!
RE: Multiple grounds on DC floating battery
RE: Multiple grounds on DC floating battery
Good luck, sounds like you are being forced to do things the hard way. You could always trip a few critical loads doing it their way, then ask again for the correct tools for the job.
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If we learn from our mistakes I'm getting a great education!