V6 - 3 speed Radiator Fan Query.
 

I've recently fitted a full set of new brushes to an early 3-speed radiator fan motor. Initially, everything worked fine (it would cut in around 100'C and cool the engine to maybe 95'C), but after testing when it has cut in maybe 8-10 times, it started to run very slowly as if being blown by the wind, then eventually stopped completely.

Stripped the front end off the car again, removed the fan and connected 12V directly to the wiring from the control box. Both higher speeds worked perfectly, but slow speed was again very slow, and often the motor will only turn on this setting if you spin it by hand first.

Opened up the motor again and all looks good, new brushes still intact and moving on their springs, all soldered connections intact and full continuity through the purple low speed wiring.

Then yesterday whilst scratching my head and playing with the other speeds, I noticed that when the 12V is applied to the purple wire, the motor is actually now trying to turn in reverse....???:shrug:

Could anyone throw any light on this please - as mentioned, it worked perfectly to start with a few days ago, but there seems to have been a gradual deterioration during use, the only thing I can think of is as the new brushes have worn to the shape of the commutator, could the fresh dust be causing some kind of shorting issue within the armature ?

Thanks in advance :}

The purple wire doesn't carry 12 v Paul. It's an earth for the fast speed.

Regarding the poor slow speed performance, did you buy the brushes from Engineering Carbon Products Ltd? Their brushes come pre-shaped to the commutator.

Simon

Absolutely correct on the purple wire, despite what the wiring diagram says ;)
We discovered this the hard way some time ago.;)

Ahhhhh.......thank you very much chaps ! Unfortunately I don't have a wiring diagram so had applied simple logic (obviously incorrectly...:duh:) that I have four wires going into a three speed motor - one is black so that'll be the earth whilst the colours will supply the various feeds.

Don't suppose anyone could point me in the direction of the aforesaid wiring diagram please ?

Yes Simon, brushes came from Engineering Carbon Products. My commutators are both (I have the original plus a spare, which I'd made one good motor from) are both worn, but I'm guessing most early 3-speed units will be by now, as they approach 20 years old.

Having said all this, it still doesn't explain why it worked initially but has then come to a gradual halt ? Could it be that the commutator is too worn ? What should I be looking for - it appears to be a solid lump copper with small square sections machined into the outer edge where the brushes touch. Is this correct ?

Thanks again in advance:}

That sounds about right. Here's more info on the commutator: https://the75andztclub.co.uk/forum/s...d.php?t=192954


TC

Actually I don't think it is correct as rather than a solid lump of chopper, what you see are individual segments built on a base of bakelite. I've been told to score each segment after filing with a kraft knife, removing any conductive material that could cause electricity to flow from one segment to the next. Don't know if this is your problem but that's the way I've been told to do it by ASEA motor builders.

Regards

Red = slow speed supply
Slate = medium speed supply (together with red)
Black = slow and medium speed earth (not relay controlled)
Purple = fast speed earth (together with red, slate and black)

I hope that makes sense!

You said that the medium and fast speed work but the slow speed is, errr, too slow. That points to a problem with the brush fed by the red wire. Have you done a resistance check from the relay to the brush braid?

Simon

I've only checked purple continuity at present, but will test the others tomorrow.

How does the highest speed occur Simon, as you don't mention a feed for this, just an additional earth (the purple) ?

I had guessed the three wires supplied different voltages to obtain the different speeds - is this correct ? Or is it that the various wires all supply 12V but to more windings on the armature to give more speed ?

Thanks again...

Correct! Fast speed is achieved by adding an extra earth (the purple wire) to the medium speed.
No. Red and slate supply 12 v, black and purple are earths.
Red (+12v) and black (earth) gives slow speed.
The above plus slate (+12v) gives medium speed; that's two supplies and one earth.
The above plus purple (earth) gives fast speed; that's two supplies and two earths.

Clever eh?

Simon

Firstly, I'll start by thanking all those that have given info and tried to help out with this thread :bowdown::bowdown:

To update, today I tested the continuity of all the wires going to the motor, from relay box to tip of each brush, and all appeared to be ok. So next, I carefully cleaned up the commutator with fine wet & dry, then dug out & cleaned up all the gaps between the radial contacts.

Upon putting it all back together, the motor would spin up but occasionally after allowing it to stop, it then wouldn't restart spinning, as if there was a 'dead spot' on the armature ? So took it apart again and checked the continuity of the windings, but could find no fault ??

Upon retesting, the same problem reoccurred....so I decided to swap the electrical board over to a spare armature & casing (albeit from a diesel) and hey presto, problem seemed to have disappeared :}:}

So ultimately I'm not entirely sure where the original fault lays, but I'd say there was an intermittent fault in the old V6 armature, but this time I'll refit the unit to the radiator in the car without the bumper, etc. and leave it running for an hour or two whilst keeping an eye that the fan cuts in regularly and doesn't have any reoccurrence of the problem.

Looking forward to a positive result...:duh: