RE: solid state relays

[rcohen@ameritech.net]

All this talk of avoiding relays, and using transistors or 'solid-state
relays'seems,to me, to be rather misguided. Properly spec'd and applied,
electro-mechanical relays should outlast just about any other part of your
car.

A common mistake in selecting relays is the fallacy of 'if I need a 1 amp
relay, a 10 amp should be adequate.' The contacts in the 10 amp relay will
fail early in this application, as there is insufficient current to 'clean'
the contacts. A 10 amp relay is made to switch 10 amp loads, not 1 amp
loads.

The paragraph aboveis a paraphrase from Sylvania, a manufacturer of relays.


-----Original Message-----
From: owner-quattro@audifans.com [mailto:owner-quattro@audifans.com]On
Behalf Of Cordeiro, Alan
Sent: Friday, May 07, 1999 1:07 PM
To: 'quattro@audifans.com'
Subject: solid state relays


Dave,

There are many different types of solid state relays, the main
similarity is that they all have no moving parts.

A.C. solid state relays are usually Triacs with a control voltage,
D.C. solid state relays tend to be plain transistors intrernally, and
will have the standard "VCe Sat" voltage drop. Many times they
come with built in opto-transistor based isolators.

One way to reduce the drop is to use Germanium transistors, but
the last of those animals I used were the good old OC71s from Mullard.
A good germanium power transistor will keep the drop in the 0.15 to
0.2 volt range, if you can find one......

Alan

>Date: Fri, 7 May 1999 08:53:50 -0500
>From: "Browning David (TVCS)" <BrowningD@tce.com>
>Subject: RE: transistors instead of relays

>What about solid state relays?  Anybody an expert on those?

>dB
>'86 4000 H1/H4's w/ relays.