Hi Greg,

On 26-Mar-04, Greg Mayman wrote to George White:

 GW>> That would be better as a technical explanation. In fact older
 GW>> vehicle flasher units were capacitor/relay oscilators. Time has
 GW>> dimmed the

 GM> We never had any like that here, on either locally made or
 GM> imported US/British/Euro/Japanese cars.

Probably not, the stuff I worked on was for commercial vehicles and
had to last _much_ longer than the stuff on cars. Typically a
truck/bus would be expected to do in a year the total lifetime mileage
of a car (ie about 100,000 miles). Time off road for a small component
to be fixed costs lots of real money, so they'll pay more up front -
it matters to the operators.

 GM> The only ones I saw before the electronic flashers were ALL
 GM> thermal types using a wire that expanded in length slightly when
 GM> heated, coupled with a magnetic circuit to give it some
 GM> hysteresis.

I only ever saw thermal ones in cars too...

 GM> I have seen homemade ones using capacitors and relays, even made
 GM> some myself, but they needed either two relays or a microswitch on
 GM> the relay rather than a conventional contact.

 GM> But for a 12 volt relay the capacitors were in the thousands of
 GM> microfarads, and in the "old days" would have been far too bulky
 GM> and expensive for auto use.

In the "old days" we used them... The capacitor was, if memory serves,
a 500 micro farad unit. But remember too that we were working on 24v
systems and were able to specify the relay totally (we made them!).

George

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