[TR] TRs 2-speed wiper motor workings..

[carlsereda]

I sure am interested Ed, and really appreciate your explanation. Let me
rephrase what I think you mean, to see if I understand this correctly.

1) With the field winding circuit closed (100 loops of lacquered wire) you get
the full magnetic field strength which runs the wiper motor at full speed.

2) With the field winding AND the shunt wiring (the added 10 loops of fabric
covered wire around the 100 loops of lacquered wire) circuits both closed, in
parallel, the shunt (the shorter path that doesn't induce a good magnetic
field) carries some of the electricity, reducing the amount of electricity
passing through the field winding which reduces the magnetic field strength,
and reduces the motor's speed.

3) I think the first switch position would be to blast the electric motor with
full magnetic field strength to get the cold electric motor started spinning,
and to run it at full speed, and the second position inserts the shunt
circuit to slow motor speed.

Sound about right?

Carl
'63 TR4 since '74
-------------------------------

Anyone that's still interested,

Spent the evening trying to figure out how the 2 speed wiper worked. Finally 
figured out the that second "winding" isn't a field winding at all. It's 
just a resistance wire that, when it's in series with the field winding, 
limits the current through it, weakening the field and producing the high 
speed mode. This high speed mode is produced by grounding only the red/light 
green wire. When both the brown/light green and red/light green are 
connected to ground simultaneously, the resistance wire is shorted, the 
shunt field current is increased because it now has a full 12 volts across 
it, and the motor runs at slow speed. Another clue to the function of the 
resistance wire and proof that it is not a field winding is that it cannot 
in itself cause the motor to turn, even w/o a load. This condition is 
produced by connecting only the brown/light green wire to ground. When you 
do so, nothing happens. Well, it does hum, draws a few amps, but doesn't 
turn.

Took me a while, but age has something to do with not being able "think 
outside the box". I kept trying to make sense out of my observations based 
on the supposition the both windings were field windings. They're not.

I have tested 3 of these motors. All work in the same manner.

If you check out the dash switch on a TR4A or a TR250, I'll bet that the 
first position, the "slow" position, connects both the N/LG and R/LG wires 
to ground. The second position, "fast", only the R/LG to ground.

Ed