ECN Forum Forums Technical Discussion Electrical Theory and Applications DC voltage dip during outage

Cool link JF. This is actually a diesel boat. SSN's only have one battery, 126 cells. Ours was located under the torpedo room (how smart is that?), which is not in the front of the boat.

These things are incredible. Very heavy, yet have now been crash tested by driving into the side of an underwater mountain at 40mph and surviving.

Radar

Just a update regarding this problem.
The battery bank in question was "load tested" and passed. It more then met the requirements of the station.

We are now in the process of installing some temp relays at different locations along the internal dc bus/wiring at the station, to try and locate the problem, utilizing there event functions and some installed parameters.
If there really was one.

HP

Highplotter, sorry to join the discussion so late, but thought I would add my 2-cents worth. I design battery plants for telephone offices and have some thoughts.

I assume your 130-volt dc batteries consist of of 60 cells, correct?

With the rectifiers on, the batteries should float at 135 VDC (2.25 volts per cell). Once the rectifiers turn off, for what ever reason, the batteries would supply power. Intially when the rectifiers turn or trip off-line the voltage will drop from 135 to about 125-to-130 VDC, then slowly discharge to a final discharge voltage of 105 VDC before exhausted.

A dip of 50 volts as soon as the rectifiers trip off-line indicates a serious problem. It could be a lot of things like:

Shorted cells
Open cells.
Bad batteries in the string
Poor terminal connections.

If I were you, I would get my hands on a DLRO ASAP and test all the intercell connections, battery terminal connection, and battery conductance.

Derec,

Thanks for your response. I related in my other posts that all battery tests came back within norms. If I could figure out how to, I would post the latest test sheet. Ive tried several times and the columns do not stay centered.

We think now that the protective relays are picking up the dip "downstream"...and we are in the process of trying to hunt down problem. Whats funny is, I have talked to a few battery experts since this occured, and non even knew HOW to monitor the batteries output over such a small period of time. A 10 cycle dip is small, and not picked up a Fluke.

HP

HP

HP, that is the thing. The batteries should not drop at all, which leads me to believe inter-cell or battery terminal connectors are bad. Only a DRLO will find that problem.