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Rotation of heater motor

Posted: Wed Feb 12, 2020 1:50 am
by winabbey
A member of the Ausmini forum is asking about the rotation of the motor in the Smiths metal cased heater. Regardless of which way he connects the two wires, negative and positive, the motor spins the same way.

I checked the Smiths plastic cased heater in my 1970 Cooper S and find the rotation reverses when I swap positive and negative leads.

Are there any electric motor specialists on here that can comment? Was a different type of motor used in the Smiths heater during its life?

Re: Rotation of heater motor

Posted: Wed Feb 12, 2020 7:26 am
by winabbey
I see the person with the query has posted here so feel free to ignore my post - viewtopic.php?f=3&t=27731

Re: Rotation of heater motor

Posted: Wed Feb 12, 2020 11:23 am
by Tds76
Thanks for putting this out there. We must have been posting at the same time.

In terms of resolving my issue - the picture Bill added on the Aus forum showed the same direction as my heater motor turns so it has become somewhat of a moot point. Having said that, I’m still interested in the answer as to why the motor only turns one way.


Cheers, Paul.

Re: Rotation of heater motor

Posted: Wed Feb 12, 2020 1:06 pm
by woodypup59
If the motor had permanent magnet stator, it will be reversible by swapping power connectiions.

More powerful motors have an electromagnetic stator (like a starter motor) so always turn the same way, no matter the polarity.

I assume your heater is the latter.

If your motor and fan was fitted in the other end of the heater box it would go the right way wouldn't it ?

Re: Rotation of heater motor

Posted: Fri Feb 14, 2020 7:49 pm
by camshaft2
I think these motors are series wound motors so the field and armature windings are in series. Changing the polarity of the dc power source has no effect, much the same as your starter motor if you change from positive to negative earth which doesn’t spin the other way. I think you have to swap either the field or armature polarity but not both in order to change direction.

Re: Rotation of heater motor

Posted: Sat Feb 15, 2020 11:20 am
by winabbey
Which Smiths heaters in their range had what type motor? Is it a metal heater versus plastic heater thing, or a date change?