27 replies to this topic

[MRA]

It's a DC motor so of course it will turn the other way......

however, having never had the pleasure of stripping a Mini heater.... I can't speak with a great deal of authority on this specific subject, but I have worked on other fans in the past and they all had some form of direction in built by design of the blades on the fan......

The really early fans, had a little propeller blade, much like the cooling fan on the engine and definately needs to have the correct rotation to blow air in to the cabin

[Shifty]

Interesting!!

My Elfs heater is utter crap and I have changed it to neg earth. I'll have to try swapping the motor polarity and see if it improves at all.

[dklawson]

It's a DC motor so of course it will turn the other way......

Which begs the question... Why is it that when you change the car's polarity you don't have to do anything to change the starter motor? It's a DC motor also. So why does it work? An inertia starter turning backwards wouldn't ever engage the ring gear. Inquiring minds want to know.

[bmcecosse]

Only motors with permanent magnet field will run op direction on a polarity change - ie model trains, that sort of thing! MOST DC motors (wipers/starters/washer pump) etc run SAME direction with polarity change - because they have FIELD windings that also change polarity with the rotor. You weren't paying attention in Physics MRA!!
The question here is - does the heater motor have magnets for the field ? Seems unlikely - but another forum has several folks who claim the heater motor runs different direction - and that's the only explanation!

[miniman_7]

My understanding is that the only things that need to have their wires reversed are the coil and ammeter (if you have one). Everything else should be ok. Only exception would be a positive earth radio, which I guess, if isolated from the car body could be wired in to satisfy its needs

[midridge2]

some of the old radios have a switch for converting the polarity, i have on my motorola.

[dklawson]

Radios, tachometers, electric fuel pumps... there are some things that must change or they will fail.

Only motors with permanent magnet field will run op direction on a polarity change - ie model trains, that sort of thing!

I'd never even thought about the wiper motor but it has permanent magnets so it must be running "backwards" after a polarity swap. If it is running backwards, this clearly doesn't seem to affect anything adversely.

[Shifty]

Tell you what, next weekend I'll swap the polarity of my Elfs heater motor and report back if it makes a difference.

[Pigeonto]

Wow does this mean that you have one of the few efficient Mini heaters then
[/quote]
I have noticed several comments on how bad heaters are -especially at demisting. I unfortunately have just had to fit a new matrix.Took out complete assembly with main aim to address the prob. This may only apply to my type which is a 92. The flap which diverts the air upwards for demisting missed the plate it is supposed to seal against by 1/4 inch so the air took easiest route:-down.When fitting new matrix I put much better sealing strips around it to make air pass through not beside it. Then I fitted sealing strip on the plate so flap seals against it in demist position so no air comes to car,it all goes up.Heater is very good AND demist works well now.Pain in neck but well worth it

[MRA]

Radios, tachometers, electric fuel pumps... there are some things that must change or they will fail.

Only motors with permanent magnet field will run op direction on a polarity change - ie model trains, that sort of thing!

I'd never even thought about the wiper motor but it has permanent magnets so it must be running "backwards" after a polarity swap. If it is running backwards, this clearly doesn't seem to affect anything adversely.

Fair point about the other motors......

I was thinking it doesn't matter if the wipers go either direction really as it is a mechanism.... mush like a crank, conrod and piston assembly..... the piston willl go up and down irrespective of the direction of the crankshaft

[dklawson]

I'm currently tinkering with some AC motors for the house (air conditioner pooped out). I may pull some of my spare Mini electric motors down and experiment with them when I get the house behind me.

I'd never really thought about the motors on a car when you swap polarity. I've just followed the published instructions and accepted things. I guess it's time to do some research.

[MRA]

The last one I did must of been over 20 years ago..... and I didn't change any motors just the Alternator and I did away with the regulator completely just compared the original wires to the later alternator models in the good old haynes manual

[MRA]

Only motors with permanent magnet field will run op direction on a polarity change - ie model trains, that sort of thing! MOST DC motors (wipers/starters/washer pump) etc run SAME direction with polarity change - because they have FIELD windings that also change polarity with the rotor. You weren't paying attention in Physics MRA!!
The question here is - does the heater motor have magnets for the field ? Seems unlikely - but another forum has several folks who claim the heater motor runs different direction - and that's the only explanation!

I was sick that day