Yandina Ltd. makes just such a device. They are available here in 12v
or 24v versions:
http://www.backwoodssolar.com/Catalo...htm#VENT%20FAN



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???