How do I determine if I have an alternator or a generator?

Per Engstad · Nov 13, 2018

We probably (I know, I have to check the serial number, but the tractor is two hours drive away) have a TEA-20 that was restored about 18 years ago. It is in fairly good condition, with the exception that it will not start when it is warm. After having maintained the carburettor and changed the start switch, I suspect an electrical problem. What puzzles me is that every drawing I have seen, and all the forums, tell that it should be a positive ground system. Our tractor is not. The negative terminal of the battery is connected to ground at the back side of the steering weel. Also the negative output from the coil is connected to the distributor. Otherwise the wires are connected the usual way.

Before I change it to a positive ground 12 volt system, I believe I need to be sure if I have an generator/alternator. But how do I tell if it is a generator or an alternator? It has two wires and was manufactured by Lucas.

Final question: What is the purpose of this device?

Any help is very much appreciated!

miner09 · Nov 13, 2018

You have a generator.

centash · Nov 13, 2018

While I am not too familiar with Lucas systems, any alternator I have seen is
shorter and has a larger diameter than that one shown. It looks like every other
generator I've seen as well. But, Lucas may have made something a bit different.
The other item looks like a flasher unit, maybe for flashing warning lights. Where
does the wiring lead to?
Ben

Bob · Nov 13, 2018

It's apparently been working as a (-) system, the coil is connected as it would be for a (-) ground system, I'd leave it as it is, less chance of making a battery charging or boosting error in this day and age when (-) ground is the norm.

WHATEVER is causing the hard starting when warm won't be cured by the polarity swap, either.

The little gadget in the last two photos is a turn signal flasher.

Does the tractor have turn signals, or at least a flashing warning light?

Per Engstad · Nov 13, 2018

(reply to post at 20:41:41 11/13/18)

Thanks a lot for the advice! I will leave it as a negative ground system and keep searching for electrical faults.

The tractor does have a turn signal, so it makes sense that it is a turn signal flasher.

Again, thanks a lot!

rvirgil_KS · Nov 13, 2018

"What puzzles me is that every drawing I have seen, and all the forums, tell that it should be a positive ground system. Our tractor is not."

Actually the original manuals and diagrams are not saying "it should be positive ground", they are saying "it was originally positive ground". You have a generator and the tractor should work equally well on either polarity if the system is properly configured and generator is properly polarized. If you change to an alternator it must be negative ground unless specially modified.

Negative ground is not the cause of your starting problem. Next time it won't start when warm, pull wire out of center of distributor, put it next to the engine and crank the engine with switch on. If you do not get a strong spark find out why

How do I determine if I have an alternator or a generator?

Per Engstad

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miner09

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centash

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Bob

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Per Engstad

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rvirgil_KS

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