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MG TD TF 1500 - Wiper Motor Voltage Increase

Seeing how our TF wiper motors are something to be desired, I am looking at one of these to see how the motor would respond to 13, 14 or 15 volts input. What do ya think? PJ
Forgot to ad, it sets on a heat sink.



Paul Jennings

How much voltage do you think the motor would take without damage? PJ
Paul Jennings

I would be concerned as all of the insulation on the field and armature windings is really old and likely not the best. Make sure the cable/drive/gearbox mechanisms are cleaned and lubricated. A meltdown would be rather costly. Suggest Rain-X instead! George
George Butz

Ditto on what George said,,

Use Rain-X,

and drive a bit faster to make the water runoff!

Steve
SPW Wincze

Paul, I'll add another ditto - plus increase the size of the wiring in your wiper circuit. Bud
Bud Krueger

Bud, All the wiring is new, a Moss harness, but do you think I should go larger? Even though the original switch works well, I intend bypassing it and putting a new toggle switch in the system to eliminate any voltage drop there. PJ
Paul Jennings

PJ

Reducing voltage drop outside the wiper motor is certainly the secret on the TD, Do not know the wire gauge in the TF harness but larger wire will do no harm.

Jim Haskins 1953 TD
J M Haskins

Paul,
With all of the extra voltage increase that you might be playing with in this experiment, you might want to invest in a good halon fire extinguisher. They don't mess up the paint.

Steve
SPW Wincze

Paul, I usually get into trouble when I branch out into TF things. In a TD the wiper motor current return path is via as long a length of wire as is used to deliver power to the motor. Increasing the size of these wires (just going down 1 gauge, e.g., 18 to 16) makes a noticeable difference. Bud
Bud Krueger

In order to charge a battery the generator/alternator must put out More than the terminal voltage of the battery. (Around 12.3V).
14.5 Volts out of the generator/alternator is not uncommon at moderate RPM's. So the motor insulation should be aduquate for that voltage.
If the wipers run OK at moderate RPM's but are slow at idle then perhaps a REGULATED 14.5 Volt source could be beneficial.
However the voltage drop between the wiper motor and battery should be measured. If it's more than 0.5 Volts over the RPM range larger feed wires would help.

Jim B.
JA Benjamin

Thanks fellas, a lot of good feed back on this situation. First thing I'm going to do is measure the voltage drop, if any, to the wiper motor and go from there. I figure 13 to 14 volts shouldn't over tax the motor if I go with the step up unit, it is adjustable. I'd be leery about going higher. Thanks for all the input, much appreciated. PJ
Paul Jennings

Paul,

The TF wiper mechanism is very similar to the setup in my Y-type.

The performance was greatly improved by dismantling, cleaning and re-greasing all the parts. That means the wiperaxles, -gearboxes, -cable and motor mechanism. The motor itself was also taken apart, cleaned and oiled in the right places. The picture is of the cleaned switch.
As said the difference was amazing.

With the risk of sounding pedantic I'd say; first look for the cause before battling with the symptoms? Putting more voltage on is like fitting a larger fan to a car with a clogged radiator?

That said if you have a freshly lubricated mechanism, there's no harm in experimenting new ways but please go easy on the higher voltage.

Willem


Willem van der Veer

Willem, My wiper system has been totally taken apart, cleaned and lubricated. Before doing that it would hardly move at all. The motor and gear box was also cleaned along with new brushes installed. I'm going to check for a voltage drop and take things from there. PJ
Paul Jennings

I just checked the voltage across the board and starting with 13.7 volts at the fuse block and the end of the power wire at the motor was 12.5 volts with the wiper on. I'm going to replace the switch with a toggle switch and check it again, the switch I don't have, so I'll have to wait until Monday. If that still doesn't bring the voltage up it'll get rewired with 14 gage wire. PJ
Paul Jennings

Since its cold and there is snow out there (The plow guy just came, another $200 down the tube) I did some calculations.
According to the Lucas Manual, I have, the CR motor draws between 1.75 to 3 amps. Lets say 2.5 for yours

Resistance of copper AWG Drop/foot at 2.5 Amps

#18 --- 0.064 Ohm/foot........ 0.16 Volts/Ft

#16 --- 0.04 Ohm/foot........ 0.1 Volts/Ft

#14 --- 0.025 Ohms/foot....... 0.63 Volts/Ft

#12 --- 0.016 Ohms/foot....... 0.04 Volts/Ft.

So If you see 1 volt drop and you have #18 wire your distance from the fuse block to the wiper switch to the motor could be 6-1/4 foot. (No or negligible switch drop)

If so going to #14 wire will result in a drop of 0.4V.

Going to #12 will lower this to 0.25 Volts.

So says Mr. Ohm.

Jim B.
JA Benjamin

Thanks Jim, good information. PJ
Paul Jennings

Paul,

The way you write about your car, it's no surprise that the mechanism is clean and lubricated. Please keep us informed an=bout the results.

Willem
Willem van der Veer

Along with voltage drop there is also amperage drop, and as Jim B charted above, all this was quite well known to MG when the cars were built. MG knew how long and what gauge the wire to supply a certain voltage range to the wiper motor that also had a voltage range they knew. There are other things to consider when re-designing the wiper circuit, like what level of current (volts and amps) will burn up the motor immediately, and what amount will overheat the motor when it is turned on for a while, and what is just right for prolonged use.

As for how much it can take, the amount of amperage you supply will determine how much votage you can supply. You seem concerned about voltage drop, but voltage drop is part of the design by MG.

You say the unit was rebuilt. How did the wires inside appear when you worked on it?
S Cole

Speaker wire seems to have a thinner insulation than other types. I was able to get to 14 gauge with a dedicated ground wire.

Jim
J Barry

If the original wires inside looked good, and the insulation was in good shape and not cracking off when you gave it a flex, then you may be ok doing some testing with different current or supply wire. If cracked or the like and you had to wrap them to ensure the insulation stayed put, maybe not such a good idea.

Curuius what type of grease you used to repack?
S Cole

For what its worth, after I cleaned and lubricated my wiper motor I could run the motor on the bench with a household 9 volt battery that was handy. I would lean towards reducing the voltage drop and not increasing voltage. Tim
Tim Debes

Duplex door bell wire. Compact and same solid copper wire as the original/ 18 or 20 ga/
S Cole

I did not read all Paul's posts with enough scrutiny. I was thinking he had taken apart and worked on the motor but it looks like the motor was serviced by someone else. Paul, when you hire someone to restore your car for you, I would hope you would be on good speaking terms. Why not ask your restorer about it. Or are you not on speaking terms any more? That would explain it.
S Cole

This is my solution. TD wiring to wiper motor using a pair of wires one green one black as original with the gauge recommended by the local auto electrician. This is covered in a grey heat shrink. I think this not only looks original but beats the Moss speaker wire approach hands down. Should also apply to the TF.

Just had to comment on S Cole's post. Paul would have to have a conversation with himself as he IS the restorer. I've been following his posts for ages now & if ever there was a hands on restorer he would have to be it. Cheers
Peter TD 5801


P Hehir

None of this will make a big enough difference - the CRT motor in the TF is gutless and has inadequate power. Unlike the TD it has to drive the rack and wiper gearboxes as well. I have three of them and even the best can barely move both wipers at once, and yes I have done all I can to lighten the load for them. All has been adjusted and lubricated, the wiper springs have been eased, the rubber ferrules lubricated and the screen polished. Raising the voltage to say 15V may well work, but I have chosen to fit a 2 speed 14W motor instead. I would rather have proper working wipers than an original wiper motor that doesn't do the job adequately.
Dave H
Dave Hill

Yes, surely you just had to respond to my post to make it sound like I was saying something nasty, Peter. If Paul is hands on with his various restorers, pays his bills, and stays on good speaking terms with them, bravo... that is how it should be. I am surely not implying that paying to have work done is some base thing, like you would be pleasured to infer to everybody here. Thanks so much. Nothing wrong with it at all, especially if you know what you want done, and how to get it. I take it that you like vague posts with carefully prepared ambiguities, so you can go off on people who are clear and concise and simply try and get to the truth through all the land mines Peter and Paul have laid out. There are better things to occupy your time, but apparently you two are unawares. Cheers-
S Cole

Mr Cole. I just didn't understand your post.. And still don't. Nor do I understand the one that followed! Paul does most of the work himself, as do I. This is the point I was making. I also don't get the bit about 'land mines Peter & Paul have laid out'. Paul's thread asks a question that is well worth discussing. My apologies, as you've obviously taken offense at a bit of my Aussie humour. My posts have always been about sharing & seeking accurate information. Nothing vague about any of them. But as it seems you are a recent contributor to the BBS you couldn't possibly know that. My sole motivation is & always will be to assist others who are also restoring their cars, to weed out misinformation & to identify parts that are not fit for purpose. I do this gladly & as a result I have made a great many friends both here & overseas through this forum. Cheers
Peter TD 5801
P Hehir

Will be going to a MGA DR-1 wiper motor assembly. Thanks for all the input. Thanks Peter!
Paul Jennings

This thread was discussed between 16/12/2016 and 25/12/2016

MG TD TF 1500 index

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