On 27 Jan 2007 03:55:29 -0800, "CS" wrote:

I want to fit a small fan to vent my battery box when the battery is
charging. I only want the fan to run during charging, so was thinking
of a relay that would only close when the voltage is above 28v or so.
Any ideas???
Colin,
A Voltage Controlled Relay will do what you want. Kits are available
for 12v which could possibly be modified for 24v. Alternatively knock
one up with a bit of Vero board and an op-amp or comparitor.

I cannot remember what you are doing about Battery Condition
monitoring? Should you make a wise choice and fit a "Smartgauge", the
fan control becomes easy. Take a look at
http://www.smartgauge.co.uk/venting2.html and other pages. I am only
suggesting this as a spin off of using a Smartgauge for monitoring.
Its an unneccessary and expensive option for just fan control.

Any system hat you use should obviously work whether charging from a
mains source or from the alternator. If you consider a "Smartgauge"
then give me a call (my number in the "Where to buy" section.
(Richard)
Richard

Nb "Pound Eater" Parkend G+S