Starter terminals and resistance

[Bensdexta]

On the original starter, is the upper terminal in the pic below (ie the top one when mounted on the tractor) the live feed from the solonoid?


Is the lower terminal an earth? If so, is it ever used?

What should the resistance be between the live terminal and earth?

TIA

[russelm]

The upper terminal (with the brass nuts) is the live feed.

Generaly the chassis connection is via the casing (there is no such thing as an earth on a vehicle ...unless you connect it to a bloody great big spike which has been driven into the ground.....or in our case, if your ploughing maybe!)

[Bensdexta]

The upper terminal (with the brass nuts) is the live feed.

Generaly the chassis connection is via the casing (there is no such thing as an earth on a vehicle ...unless you connect it to a bloody great big spike which has been driven into the ground.....or in our case, if your ploughing maybe!)

So the lower terminal is not essential, as we rely upon the casing of the starter to provide the return to the chassis?

What should the resistance of the starter be, or can I just assume a starting current of 450A and use Ohms law to give 12/450 = 27mOhms (ie not much!)

TIA

[dexta roadless]

that right. you can't measure this with a normal ohm meter

[russelm]

Starter motor resistance will be very low and the order of mohm's....which you wont be able to measure with any accuracy without specialist equipment.

Starting current is mega high for a stalled motor but, as the motor starts to turn the back EMF produced reduces the current significantly.

[Bensdexta]

OK thanks,

And that second terminal is superfluous if the starter case is properly 'earthed' to the chassis via the bolts and mounting flange?

[dexta roadless]

I use this terminal just as an extra safety I have a 16mm2 cable from this to the alternator ground and a 25 mm2 from this to the battery earth connection

[Bensdexta]

I use this terminal just as an extra safety I have a 16mm2 cable from this to the alternator ground and a 25 mm2 from this to the battery earth connection

OK, thanks

[russelm]

If all joints are clean then the resistance from the casing via the block to a good short battery neg connection from the battery to the bellhousing bolt will be less then that of a direct connection.