DIYbanter - View Single Post - 1988 Plymouth Voyager turn signals not flashing.

David Farber

wrote:
David Farber wrote:
A couple more questions, for this simple kind of bi-metallic flasher,
what design differences are there between a variable load flasher and
a fixed load flasher?

A fixed load flasher starts out closed (on), and the bimetal heats
itself up from the current drawn by the lamps. Once enough current
has been drawn for long enough, the bimetal snaps open (off), cools
down, snaps closed again (on), and so forth. It depends on the lamps
drawing enough current to heat the bimetal enough to start flashing.

A variable load flasher starts out open (off), and has a heating
element in parallel with the bimetal. Any path to ground will run the
heating element, and the bimetal will eventually snap closed (on).
This shorts out the heater, the bimetal cools down, snaps open (off),
and so forth.

What would be the advantages to using a fixed load flasher?

If one lamp fails with a fixed load flasher, the driver can tell that
there is a problem, because the remaining turn signal lamps will just
come on steady. Also, the lamps that do work will provide at least
some indication to other drivers.

The hazard (4-way) flasher is usually a variable load flasher, because
it should flash no matter what; if the car has just been in a wreck
and some of the turn signal lamps are smashed, it can still be useful
to flash the remaining turn signal lamps as a warning to other
drivers.

Am I correct in saying that the larger, higher current filaments are
assigned to the flashing circuit?

Yep. The "bright" filament is always on the turn (or stop) circuit,
and the "dim" filament is always on the parking/running light circuit.

Thanks for your reply.

You're welcome!

Matt Roberds

Hi Matt,

I visited the car this afternoon and measured the current difference between
turn signals on and off. It was less than 4 amps difference. I started
pulling the lamps and looked into the sockets. Both front left sockets were
covered in a green chalky substance. I guess that would explain the problem
there. On the right side, one of the two signal lights glowed brighter than
the other. Also, the bulb numbers were different. I should have checked that
first time around. The voltage at the dim bulb socket with no load was 1
volt less (11v vs. 12v) than the battery voltage. Another bad socket?
Checking the rear lights I noticed that the smaller filaments were glowing
when the turn signals were activated. I checked the socket and bulb and it
didn't seem possible that the bulb could have been inserted so that the
terminals were reversed. I had another appointment to go to so I couldn't do
anymore investigating but the first thing on the to do list will be to
replace the corroded sockets.

Thanks for your assistance.
--
David Farber
Los Osos, CA