Battery killed by Rad fan turning on by itself

[Tatsfield]

If the speed controllers were inadequately designed, Volvo would for ever be replacing them at their own expense, so I suppose the design is adequate for the purpose of the component. I had a Peugeot where the ventilator fan speed controller was very finned and lived in the cold air intake ducting where it was cooled to the maximum and it still blew the power transistor after 10 years. This type of circuit gets very hot.

[Freewheel]

Left the car overnight and no strange current draws on the new battery. I did see the fan do it's little twitches and movements right after I shut everything off, so I was a bit worried that it was up to it's tricks again.

To test battery voltage without lighting the car up, I ran a couple leads up the windshield from the battery so I could put a meter on them without getting into the car and popping the hood.

Checked every hour for a couple hours before bed and then in the morning. No apparent drawdown other than the battery itself starting at an energized state of 12.99 volts and coming to rest at 12.8.
(during the period that I was having problems, it would draw down about .1 to .2 volts an hour)

Fingers crossed that the issue has sorted itself out with just the price of a new battery, and not the additional cost of a fan control module...

Thanks everyone for your responses!

[dieselderv]

Yep my fan does this too and it killed my previously dying battery doesn't twitch though just comes on after a long run ,when locked up

[oragex]

Originally Posted by Freewheel

I started testing for parasitic power draws and got a draw of 3 amps with the vehicle off. Then a door was opened and the car came to life and blew up my 10 amp multimeter - that ended that diagnostic process ...

I guess it blew because the radiator fan was spinning? That thing will definitely draw more than 10amps and toast a 10amp multimeter indeed...

[Freewheel]

Yes, I think it was the fan spinning that blew the meter- though there's there's a lot of electrical activity that seems to happen when doors open on this car- I always hear a solenoid in the engine compartment for example...

Anyway, the car has been working fine with its new battery, and I think we may be able to to put all the strange fan behaviour and overnight parasitic draws, down to low battery weirdness, and then not letting the system reset itself when I changed the battery.

My daily driver is a 32 year old diesel Landcruiser, so I'm not used to having to treat cars the same as a finicky laptop computer where the most important repair tool is the simple reboot.