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micky micky is offline
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Default Why is there a thermistor in the power door lock circuit.

On Wed, 21 Sep 2011 20:17:01 -0400, Jamie
t wrote:

micky wrote:
On Tue, 20 Sep 2011 20:52:53 -0400, micky
wrote:


What would the role of a thermistor be in the power door lock circuit
of a car? It's in series with the door lock "motor", which might be
a solenoid or maybe a rotating motor.

Is it possible that it is meant to lower or turn off power to the
mechanism if the circuit is left closed for some reason and the
solenoid would otherwise overheat?

The symbol it uses for a thermistor is a resistor symbol in an
elongated circle, like a high school running track around the football
field. Is that the usual symbol for a thermistor.



Well this says the symbol is retcangle with the stick figure of a
hockey stick across it.
http://www.best-microcontroller-proj...c-symbols.html
What's with Toyota anyhow? Are they wrong about the symbol, or maybe
they're wrong when they call it a thermistor!

Are you sure it isn't a circuit breaker?


Well, at the beginning of the the Toyota Electrical manaul, are two
pages with 36 electrical symbols and what they mean, and for this
circuit, the diagram uses a symbol which it says at the start of the
manual represents a thermistor, but it's not the symbol everyone else
uses.

Plus they use the same symbol** for the intake air temp sensor, the
engine coolant sensor, the Air Conditioning room temp sensor, and the
AC ambient temp sensor. . Might those really be thermistors too?

**a zigzag resistor symbol inside a circle that has been elongated in
one direction, like a model train track cricle with extra straight
track in opposite sides. .

I haven't taken apart the door yet, so I don't know what is actually
there.

My plan was to add to the passenger door-unlock output of the
door/burglar alarm Eloectronic Control Unit a wire to a relay, which
relay would unlock the trunk. What's connected to that output now is
the door lock/unlock motor (solenoid?) and this "thermistor", in
series, according to the diagram, and I wanted to understand what is
there now and what it does, before I start fiddling with the circuit.
The other end of the door lock circuit goes to ground and so will the
other end of my relay circuit.

I'm reticent because with the previous car and the previous alarm,
that I installed from scratch, everything was fine, except to open
the trunk, I had to hold down the third button for several seconds.
Because my turnk lid didn't move when unlatched, I thought it would
work better for me if I connected the trunk relay to the both-door
unlock output of the alarm I installed, in parallel with the
door-unlock relay. . However that appeared to screw everything up,
so that many of the alarm functions no longer worked. I must have put
too much drain on that output, even though I just doubled the drain
(two standard automotive relays instead of one) I shoulld I guess
have put the second relay in series with the first one, so that when
it powered the door-unlocks, it also powered the trunk relay.

I'm trying not to make the same sort of mistake here.

Thanks.

Those are BI-metal
and will open if they get too hot. They are also used in a
time applications in cars.



Jamie