Hi Earl,
Most older DC blower motors were built with series connected armature &
field windings. They will rotate in the same direction regardless of
which way the power is connected. These motors "can" be reversed by
INTERNALLY reversing the connections of the field or of the armature but
not both.
Some newer motors have permanent magnets in place of the field windings.
This type of motor will run backward if the supply connections are
reversed.
If a full wave bridge rectifier were connected between the supply
connections & the permanent magnet motor, the supply polarity could be
connected to the motor either way & it would still run in the same
direction - As Jim H. says.
To my knowledge, all Healey blower motors were of the first type. Not to
say that the "reversing motor" in question has not been changed to a
permanent magnet type somewhere along the way. Either that or your
theory about blockage may be correct.
Certainly an interesting thread.
Dave Russell
Earl Kagna wrote:
> Gentlemen:
>
> Stranger and stranger!
> Conclusions? All I know is that any Healey that I've done a polarity
> conversion on has had the heater air delivery system continue to work as
> before without interchanging the blower motor leads, notwithstanding the
> fact that the systems were pretty anemic right out of the factory. I wasn't
> aware of any polarity sensing electronics built into the blower motors
> themselves, but it must be there (thanks Jim). I know for sure that there
> are no diodes etc. in my tri-carb's original wiring (we won't talk about the
> Pertronix ignition here, right!). I'm also pretty sure that the blower
> motor spec did not change throught the 6 cyl. production, but I could be
> wrong.
>
> I strongly suspect that the original poster (sorry, I've forgotten who) that
> had the air reversal problem has an almost total air blockage somewhere
> beyond the blower motor.
>
> I'd like to say that I've learned something from this thread, but if I have,
> I'm not yet sure what it is - other than my Healeys don't have a problem in
> that area. I would welcome more comment from any lister with more knowledge
> of these things than I, who can explain these results. I can't account for
> David J's results in similarly bench testing an old blower unit this
> morning.
>
> Let the flames continue!
>
> Earl Kagna
> Victoria, B.C.
> BT7 tri-carb
> BJ8
>
> Subject: heater fan sucks
>
>
>
>>I have converted at least a half dozen Healeys to NEG
>>ground, including my present two, without interchanging
>>the blower motor wires - they've all continued to move
>>air in the right direction.
>
>
> I don't doubt that for a moment . . . but the reason is not the permanent
> magnet motors. Diodes in the wiring (or integral to the motor) will maintain
> the polarity seen by the motor regardless of the polarity of the wiring, so
> the motor will always spin in the same direction.
>
> Jim Hill
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