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Q & A

Strange Battery Behavior

I have recently been having a few issues with the domestic batteries. The set up is 5 110amp Hr batteries, charged via altenator and Victron inverter cahrger. last saturday, the lights went out. Checking the voltage it looked OK (12.45V) but all the circuits were dead.
strangely though, we have 1 circute, which does not go through the main domestic isolator switch (for monitoring when we are off the boat, and this was still powered up OK
I switched the inverter off and after a few seconds the lights came back on.
The system has been in place for a number of years with no recent changes. Until recently, all has worked fine.
Can anyone suggest what might be going on.

Asked by: duncan  | 4.18pm, Tuesday 25 April

WW says:

How old are the batteries?
Was the boat connected to shore power?
Was the inverter supplying mains power?
Does the inverter go through the isolator switch or is it seperately fused?

Rupert Smedley  | 6.36PM, Tuesday 25 April

After some thought as it is an intriguing problem, I think it might be a combination of two faults. Your batteries are probably coming to the end of their useful life; this is characterised as increasing impedance and decreasing capacity. Assuming that you have the conventional battery isolators with the removable red plastic key; these are not good switches and can introduce unwanted resistance, with corrosion even stopping the current flow when in the ON position. If the isolator switch has not been operated for a while, I think that the switch went "Open Circuit" and when you switched the inverter off, the reduction in current draw from old batteries caused a voltage spike which restored the switch contact, and the lights came back on.
The solution is to replace the isolator switches with better ones and probably consider a new set of batteries.

Rupert Smedley  | 2.15PM, Friday 28 April

Readers say:

Batteries are about 4 years old
Not connected to shore power
Inverter supplying 240v mains power.
Inverter goes through a seperate breaker

duncan  | 9.15PM, Tuesday 25 April

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