Thread: May have just saved a battery

Originally Posted by DiscoJeffster

I’ll only add that I’d have thought the circuit breaker would be relatively agnostic to the voltage difference (~14V to ~18V) and I don’t believe the increase in voltage will cause a current increase (normally the opposite) so for a current sensing device to trip for that I’d be keeping an open mind. As you say, maybe try the fuse and measure voltages etc.

Actually the 4v volt increase over normal voltage levels, would cause a massive current increased draw from the battery alone and most of the other device in the vehicle would also add to the current draw.

As DC voltages rise, DC currents draw rises with the increased voltage.

Originally Posted by drivesafe

Actually the 4v volt increase over normal voltage levels, would cause a massive current increased draw from the battery alone and most of the other device in the vehicle would also add to the current draw.

As DC voltages rise, DC currents draw rises with the increased voltage.

Very true - as the battery sees the potential difference and tries to charge itself to the new potential. That’s obvious now you spell it out

Hi Ean, while not so common these days, but runaway alternator voltages of around 18v is usually cause by either a failed reg, or a bad earth return.

Any chance there is a loose or disconnected earth cable between the block and chassis?

Well I am not 100% sure what's happened . Put the 100amp blade fuse in and al good for about 5 mins , so I guessed if was a failed C/ B . The voltage was still high at 16.8 volts especially considering the battery was charged over night. I walked around and next thing I see the batt light back on and see the blade fuse had blown.
i did move away from that set up because over time the fuses would blow , so I had a spare and put that in and been for a 30 min drive and charge voltage is back down to the low 13s which is normal so at the moment things are running normally.

i might check the earth as you suggest Tim . I am flying out of the country on Monday so worse case is I will inspect it further when I get back. I suspect my Alt is starting to fail but I have been wrong many many time in the past so see how things go.

thanks for the replies.

Cheers Ean

Maybe just change it anyway so you know it has another 140,000km before that will be an issue, even if not directly related to this issue. After all, it’s just getting dusty on a bench