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From: Frank Pittelli <frank-at-rctankcombat.com>
Subject: Re: Prof. Sommer's Controller Review [TANKS]
Date: Sun, 03 Apr 2005 16:56:50 -0400
Reply-To: tanks-at-rctankcombat.com

Joe Sommer wrote:
>>  BTW, if I was going to use 24V could I make the tri-pact control the 
>> same as I would for 12V or would I need different components??? 
> The Tri-Pact controller can be built to use 24V, but I would
> substitute 24V relays.  24V relays have higher coil
> resistance (360 ohms) than 12V relays (90 ohms).
> http://relays.tycoelectronics.com/datasheets/VF4.pdf
> Activating 12V relays with 24V will fry the coils.

I think you guys may be speaking about different things.

Chris, when you say "use 24V" do you mean using 24V for the "motor 
voltage" or using 24V for the "control voltage" or both?

I think Joe assumed that you wanted to use 24V for the "control 
voltage", which would in fact require a 24V relay, because 24V will 
definitely burn out the 12v coil in a standard automotive relay.

However, if you were talking about 24V "motor voltage", then you can 
still use standard 12v automotive relays, provided that you still use a 
12v "control voltage".  As I understand it, the "load" capacity of a 
relay is more dependent on the amp draw then the voltage (within 
reason).  After all, it's just a couple pieces of metal being pulled 
together.  As long as the contacts are designed to handle the arcs 
generated by high loads, the actual voltage of that load doesn't really 
matter (within reason).  So a standard, heavy-duty automotive relay 
should be able to handle a 24V load without a problem as long as the 
power requirements are roughly the same (which is true in this case). 
Joe, do you agree with this?

        Frank P.