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From: email@example.com (Bob Wilson)
Subject: Re: Help with relays please.
Date: Fri, 27 Sep 2002 03:07:43 -0000
Organization: Your Organization
X-Newsreader: WinVN 0.99.9 (Released Version) (x86 32bit)
In article <firstname.lastname@example.org>,
>I have a truck winch that is controlled by a number of relays. The
>relays fail after a short period of time. There is nothing wrong with
>the winch motor. The 12 volt relays switch 12 volts at a peak current
>of about 400 amps. Would it be possible to replace each relay with a
>triac and a simple circuit? Any help would be appreciated.
>Thanks, Martin Perry
Triacs are useless to control DC. They are intended to control AC. SCRs
*could* be used, but once you turn an SCR "on" it will remain on until the
current through it stops (by an external means). Thus, once you turn on the
winch, it will never turn off until your battery is dead.
A Triac is simply (in essence) a pair of SCRs connected in anti-parallel and
controls current in BOTH directions (something that is irrelivant for a DC
The very BEST thing to control high current low voltage DC is ....a relay.
Nothing is more reliable in real-world applications. A relay generates no
heat, whereas any semiconductor switch with 400A going through it will
generate a HUGE amount of heat and will require heat sinking. Further,
unlike a semiconductor switch, relays can stand huge amounts of overcurrent.
You either have an underrated relay, or some other problem. Cure the
disease, not the symptom!
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