Dear folks

I have a blower motor venting 3 battery compartments on a 24V system.
The motor is said to draw 2.5A. I want this to run whenever the
batteries are charging, they may be charged from engine, genny or
shorepower. It seems to me that the simplest solution would be a voltage
sensitive switch to activate the motor whenever the system voltage rises
above a threshold of around 27V.

I can't seem to find a suitable switch. A battery combining relay could
be used I am sure, but I can't find a small one for 24V systems and it
seems crazy to waste money and space on a massively over-rated combiner.

Such systems must exist, eg to prevent fridges killing batteries but I
can't seem to find a supplier.

Does anyone have any suggestions ?

Thanks

Steve