Starter Motor

[Peted7202]

Is a starter motor positive or negative earth? Mines a Lucas25147D and was on postive earth but want to convert to negative.

[geoberni]

Neither,.......and both.
They are series parallel wound so not polarity sensitive.

I suggest you look up how to change from pos to neg earth and you'll find the full list of what to do.

[philthehill]

All the 'A' Series starters I have fitted work in either positive or negative earth mode so you should be able to use the starter as already fitted.

[svenedin]

Just to say that you may or may not find your heater blower is less effective after changing polarity. If it doesn't work so well, just change the wires around (what was earth becomes live and vs versa). The rest is covered many times. The reason is some heater motors have permanent magnets and run backwards with reverse polarity and some use field coils and are unaffected by polarity change. Be aware that if you have any LED bulbs, these are polarity sensitive and also any electronic versions of fuel pumps and ignition.

Stephen

[Peted7202]

Can I bench test the starter with a multimeter?

[geoberni]

Can I bench test the starter with a multimeter?

You can always test electrical items for something with a multi-meter, but test for what exactly?

You've been told it doesn't make any difference, so what are you thinking you might test it for?

Can we assume it's not on the car at the moment and has been off for some time?

The simplest thing to do is stick a car battery across it and see how well it runs.
Using suitable size cables such as jump leads.
Making sure the motor is restrained as if left laying loose it will try to twist from the torque .

It might be worth looking at the brushes to see how worn they are if it's off the car, but the Lucas 25147D is a 35J, so that means you need to know what you're doing as it involve removing the end plate and the brushes are the triangular ones that bear on the disc shape commutator.

[Peted7202]

Thanks. Yes it's been off the car for 2 years. The testing is just for knowlege e.g. what should resistance be?

[oliver90owner]

Can I bench test the starter with a multimeter?

Personally, I would not bother. If it runs, it ain't broke so no need to fix it.

The starter motor draws a (relatively) huge current to spin the engine. At the initial start the resistance will likely be lower than a cheap multimeter might indicate a higher reading than the true value if you are a beginner.

Ohm’s Law is “Volts = current in Amps x Resistance”. The motor draws well in excess of 100A at initial energisation (zero rpm). It will draw less once up to speed (because it is then an inductive load rather than a resistive one. Re-arrange the equation to find the resistance (R).

I believe the starter is 0.8kW, so will draw over 70A when running at full speed.

[myoldjalopy]

"Personally, I would not bother. If it runs, it ain't broke so no need to fix it." Words to live by......

[geoberni]

Sorry for the delay in posting this.
Yesterday I changed over from Talktalk to a new Full Fibre service with BeFibre and the Message Board didn't like it.....

IP Blocked.JPG (69.79 KiB) Viewed 8903 times

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All resolved now apparently....

Thanks. Yes it's been off the car for 2 years. The testing is just for knowlege e.g. what should resistance be?

I've absolutely no idea. I don't think it's even mentioned in the Lucas Workshop Manuals for Starter Motors....
2 years, a mere blink of an eye ...
Some new motors would sit on a warehouse shelf longer than that.
Just test it with a battery and if it doesn't work, then worry about it.

[Peted7202]

I have a M35J 25206H starter motor can this be used in place of a M35G 25079J?