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MG TD TF 1500 - TD Wiper Fuse

I posted this question on the current thread about wiper wire, but my timing was poor (kind of the story of my life) and it got lost in the discussion of series/parallel wires, so I'm starting a new thread.

One post on the other thread says “At stall the TD wiper motor only draws about 2 amps”. When I rewired my car I used Evan Ford’s article as a guide to add fuses. The 4-amp fuse he recommends for the wiper motor blows after about half a cycle of the wipers. I haven’t gotten around to trouble-shooting it yet because I never plan to drive in the rain and it may never rain again in Southern California anyway, but it would still be nice to have a working system. Any suggestions about where I should start trouble-shooting?

Incidentally, I didn’t like the Moss wire either, so I reused the original wire which was still in serviceable condition.

Joe
Joe Olson

I would be very interested in the outcome of your investigation Joe as I'm intending to fit an in line fuse behind the dash. If the motor operates but blows a 4 amp fuse & the result that others suggest is the draw is in the order of 2+ amps, I'll hold off on the fuse until this one is resolved. Good luck! Cheers
Peter TD 5801
P Hehir

When the wiper motor draws 2 amps on average, which sounds reasonable, it will still have peaks at disruptive points where the mechanical load gets higher. This can be the turning point at half cycle or some sticky area on the windscreen or a short blockage of the wipers. The fuse needs to be big enough to cater for these or it blows all the time.
In addition, inline glass fuses come in different speeds, a fast one blows at a very small (time wise) peak while a slow one will need an extended peak load to blow. For a motor, you definitely want the latter. You might want to measure the current with an ammeter to see the fluctuations and watch what happens when you slow down the wiper a bit with your hands.

Main purpose of the fuse is to safeguard against a short. I would use not less than a 10 amps fuse for that.

Rgds Mike
Mike Fritsch

Joe, you have an electrical problem in your wiper motor. Remeasured this morning and again saw that the wiper motor current draw is about 1.8 to 1.9 amps with the blades on dry glass. There is an a/c component of about .090 amps (90mA) in that. A 4 amp fuse should sit there dumb and happy forever. Bud
Bud Krueger

I opened up the motor today to look for the problem. It spins freely by hand, but when I apply power to it, it shorts out and blows the fuse after less than one rotation, with a spark that appears to come from the area of the brushes. It looks to me like the blobs of solder (see the picture) where the tiny wires of the armature windings are attached to the commutator are contacting the brush housings. Could this be the cause of my problem? If so, what are some possible solutions? Before replacing it on the car months ago, it ran ok using a battery charger, so I don’t know what’s changed since then. I’m running out of 4 and 5 amp fuses and am not sure just what to do now. I’m hesitant to try higher capacity fuses if it should draw only 2 amps or so. Thanks for any suggestions.
Joe



Joe Olson

Joe, how are you with using an ohmmeter? With power disconnected - You should be able to put an ohmmeter across the power terminals and watch the meter while you rotate the armature. You should see an abrupt change when the problem comes up. The motor is electrically isolated from ground. At least it should be. Happy hunting. Bud
Bud Krueger

Thanks Bud. Assuming I'm using and reading my multimeter correctly, the resistance varies from about 3.5 ohms to 6 ohms as I rotate the armature, but I can't detect an abrupt change. When I apply power to the motor it rotates slightly, sparks with a "pop" and blows the fuse but I haven't been able to figure out exactly what's shorting, so the hunt goes on. I haven't found anything in the archives which usually answers my questions.
Joe
Joe Olson

Joe, I seem to recall that the armature tends to move somewhat in a radial direction as it begins to rotate. You might have to try the 'tune for maximum smoke' test. Any chance that your wiper motor is sitting on a work bench with a power supply handy? Can you apply power to it through an ammeter? It would be good to know if it's trying to draw a much larger current than the 4 amps. Would the motor run if you had a 6 amp fuse in the line? If you can get it to run you should be able to see some sparking, or other indication of a the problem are, such as a bit of smoke. What sort of resistance readings to you get between each of the power input terminals and the case? Good luck. Bud
Bud Krueger

If it comes down to it, you can rewind the armature by hand. I did this a couple of years ago. Regards, tom
tm peterson

Joe, I had a similar problem with a generator on one of my old farm tractors. It's 6 volt, but that shouldn't matter. It would short out causing sparks to come out around the brushes. I found out that it had developed a lateral movement toward the rear, moving the armature closer to the brass brush holders. Solution was to put a round shim in the rear bushing and hold the armature shaft further forward and the problem went away. I have no idea how your wiper motor is designed, but it looks from your photo that might be the problem. PJ
Paul S Jennings

Joe, try contacting Lew Palmer; he rebuilds these professionally and would have some useful advice, no doubt. lpalmer at roundaboutmanor dot com
Geoffrey M Baker

6 Ohms makes a little over 2 amps, 3.5 ohms gives you nearly 4 amps. That could blow a fuse that is close to that rating.
However, if there is a temporary short from a casing or the blobs, you should be able to see it on the meter.

Best would be indeed to run it from a power supply with an ammeter in between that reads up to 10amps and a 10 amp fuse.

Best Regards
Mike
Mike Fritsch

Hi Tom. I tried to have an armature rewound here in Sydney about 18 months ago. I contacted 22 auto electricians & 16 said no over the phone. Six said they could, then said "no way", "you gotter be joking mate" & offered other words of encouragement when they saw just how fine the wiring was. I couldn't find anybody here who either had the skill or the inclination to rewind one. I still have the armature & am prepared to give it a go. Are you able to suggest where I can source the wire from, how much I will need & can you identify the gauge for me? THIA. (Apologies for the slight side track here Joe) Cheers
Peter TD 5801
P Hehir

It is true that I used to rewind these, but no longer can. The shunt winding wire is no longer available and the armature insulators take me so long to cut it is no longer viable. I do, however, have a source for new armatures, should anyone need their wiper (CW1, CWX, etc) rebuilt. Other rebuilds not needing an armature rewould also possible. Typically around $100 USD plus parts to rebuild. Contact me at lew (at) roundaboutmanor (dot) com (not the address given above).
Lew Palmer

Thanks guys for all your comments and suggestions. I'm thinking now that maybe I should have called this thread "Much Ado About Nothing". I overcame my reluctance to try a larger fuse today and discovered the motor runs very happily on a 7.5 amp fuse with no undue sparking or other signs that it's going to self-destruct or start a fire. The only ammeter I have is the one in the car, so I plan to put the wipers back on the car and see if I can read the current draw with any accuracy. Does anyone see any problem with this approach?
Joe
Joe Olson

Joe, that's a lot of current draw for one of those motors. If it's drawing 5 amps that's about 2.5 times what is expected. Maybe you have a motor that's been rewound with larger gauge wire and few turns. That's a lot of power (12v*5A=60 Watts) rather than the normal 24Watts. It'll probably get hot. On top of that it could be a problem on a 'dark and rainy night'. If it were mine I'd contact Lawrie Rhodes and have it redone. He has an ad in TSO: info@british-car-part-restoration.com (508) 359-2077 Bud
Bud Krueger

The only problem I can see is the accuracy of the ammeter in the car - you can probably identify if it draws less than 10 amps but most likely not if it´s 2 or 4.
What you could do, though, is take light bulbs of various wattage (back light or side light is 5, indicator is 20, headlight is 40-60 depending on the type) and connect them in parallel with the wiper and see if where the meter approx. doubles. Or connect only a bulb, watch the meter reading and "calibrate" it that way.
If Bud is right, you should get a roughly similar reading to an idicator bulb with 21 Watts. If it´s drawing increased current, you would be closer to the reading of a headlight bulb.

Make sure you have at least a 10 amps fuse in when you do that, though, otherwise it might deplete your inventory too much.

Rgds, Mike
Mike Fritsch

Well, my problem has disappeared, but I’m not sure exactly why. Maybe there was some conductive crud or corrosion in the motor causing enough of a short to trip a 5 amp fuse, but it’s running just fine now. I had a Homer Simpson D’oh! moment today when I remembered that the battery charger that I have been using to test the motor has, of course, an ammeter built right into it. It’s been right there in front of me for two or three days now and I hadn’t given it a glance. I connected the motor to the charger with a 7.5 amp fuse (it’s only a 6 amp charger) and ran the bare motor for a few minutes. The ammeter read between 1 and 2 amps, just like Bud said it should, so I put a 4 amp fuse in the circuit and it continued to run without a problem. What did I say about much ado about nothing? I’m sure there’s a lesson here... now if I could only figure out what it is. Thanks for your encouragement - it was a big help.
Joe
Joe Olson

Sonuvagun! Only thing I can guess is that there was some high spot that has been taken down and is no longer being a problem. If it's running reliably with the 4 amp fuse you're in fine shape. Hooray for self-healing TDs. Bud
Bud Krueger

I would still advise for a stronger fuse, or any slight blockage (e.g. blade stuck after longer non-use) might blow it. At least make sure you have a spare in case it rains when you are on the road.
Rgds, Mike
Mike Fritsch

I have a good supply of spare fuses of all amperages in the glove compartment and the fuse block is easy to access, but I don't think it really matters much when it comes to the wipers, as I really don't think I'll ever use them. I've had the car for a long time and I have been trying to remember when I last drove in the rain. I think it was way back in 1961 when the car was my daily driver! Since then it's only been a fair weather friend. I'd have to install a new top, too, as it's been on the car since I bought it and is not very weather tight anymore. I haven't used it in years either. So why fix the wipers? Just so I can say they work.
Joe
Joe Olson

Peter,

If you are still needing a wiper armature then you might consider looking at this one on eBay. It's located in New Zealand I think.

Item number 181632694640.

Just paste the number into the eBay search.
Kirk Trigg

Kirk, chased up the armature with a copy & paste on 181632694640 but got "no result". I'll go searching anyway. Thanks for the lead. Cheers
Peter TD 5801
P Hehir

Peter,

It comes right up for me using that item number. Maybe try logging in to ebay US or something first ?

Kirk


Kirk Trigg

This thread was discussed between 07/01/2015 and 12/01/2015

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