On 7/29/07, Dennis Haynes <d23haynes57@hotmail.com> wrote:
>
> Also, you want a truly reliable relay. Most important that it
> disconects when expected. You want double break contacts like in those
> solenoid type cans.  Not a small lighting relay.
>
>
I can say from experience that a good solenoid type relay is a must, with
special emphasis on the word "good". My initial installation of a Trojan
24TMX battery under the rear seat was wired to the big battery lug on the
starter with 2ga wire through a big 200A capacity monster of a solenoid
relay. I had a smaller, regular 50A RV type solenoid relay that I was going
to use, but my brother offered me that monster for free. Unfortunately, it
was not of quality manufacture, having been aimed at the "boomin' stereo
dood" market. My first trip with it I noticed a problem with the rear
battery running down to under 12V after only a day, no matter what use it'd
had. Then, on the return trip, I went under the seat to get something after
driving for 3 hours, and found that the solenoid relay was HOT, as in burn
your hand hot, and my brand new Trojan battery was down to 10 volts. I
disconnected it and upon later investigation found that the armature inside
was shorting to ground when the relay closed due to poor design of the
interior insulation. The battery and the alternator were probably dumping
dozens of amps through that thing to heat it up like that. As a result, I
ended up having to get ANOTHER  $170 battery because the first one never
came back from being overdrained. My current setup is through a real 3 stage
charge controller, with a real RV relay as a crossowver for jump starting if
my front battery dies.  Definitely watch out if you're looking at buying a
"stereo dude" relay. Bad things can happen due to sloppy workmanship.

--
John Bange
'90 Vanagon - "Geldsauger"