Date:         Sun, 11 Apr 2010 15:29:19 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: SPDT or DPDT switch?
Comments: To: colorworks@GCI.NET
In-Reply-To:  <A22E65000C31414DBDA9E5F95A6A8357@troyb5bff49d63>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 01:26 PM 4/11/2010, Troy wrote:
>Just a quick question about switches: I need a switch that when
>toggled in one position will operates one appliance, and when
>toggled in the other position will operates a second, different
>appliance. Do I need a single pole double throw switch, or a double
>pole, double throw switch? I'm guessing the latter, but wanted to
>doublecheck. The SPDT

If you're operating both appliances from the same circuit then an
SPDT will do nicely; connect the supply to the center terminal.

If you're operating from different circuits or voltages then you need
a DPDT; connect each supply to one of the two center terminals.

Note that most switches don't have DC ratings unless they're intended
specifically for automotive use.  A decent rule of thumb is that the
switch should handle about the same number of amps at 12 v DC as it's
rated for at 110 v AC.

If you don't want to run heavy wiring to the switch, use a small SPST
switch to activate an SPDT (or DPDT) relay which will do the power
switching for you.  If you need a "both off" position it gets a bit
more complicated as the relay will have the NC contacts closed when
it's not activated.

Yours,
David