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Date: Sat, 06 Mar 2010 06:05:20 -0500
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Subject: Re: [LML] Solid State Contactors -- SuperSwitch?
From: bob mackey <n103md@yahoo.com>
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Most solid state relays will fail on over-current by overheating and
diffusing the junctions.
When that happens, the device becomes conductive and stays that way
until the wires burn off,
or the power is removed. So your concern about being unable to shut it
off is real. However,
mechanical relays also fail with contacts welded shut. I don't know
which is more reliable
in your application.

The SuperSwitch is probably an off-the-shelf solid state relay,
relabeled by Lamar.
The first SSR with 100A rating on Digikey sells for $126.50, so
wholesale price is half that or less.
On resistance is 5 mOhm. At 100A starting current, the voltage drop
would be 0.5V and power
dissipated would be 50W. For continuous high-current use, it will
require a heat sink.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CC1685-ND

-bob

Colyn asks:
> I looked at this seriously but at the time there was very limited information available on the web site for evaluating the failure mode.
> My biggest concern about a starter contactor is that there is the potential for a dead short in the starter and I want to know I can get the thing
> turned off.