990 Implematic pos or neg earth?

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duffman
Posts: 33
Joined: Sun Sep 19, 2010 12:31 pm
Location: Norfolk

990 Implematic pos or neg earth?

Post by duffman » Mon Aug 31, 2015 5:51 pm

Hi, I have a 1964 990 Implematic, the battery terminals are missing except a lug still attached to the air cleaner frame that someone has cut the cable off. Does anybody know if this model is pos or neg earth? all other wiring and electrical components have been removed although I do have them (bought the tractor already stripped down).

Many thanks

Guest

RE: 990 Implematic pos or neg earth?

Post by Guest » Mon Aug 31, 2015 6:16 pm

By what you say the wiring state is in no-one could definitely tell weather it is positive or negative earth. The tractor should be negative earth but to make sure, when you reinstate all the wiring and cables connect everything up except for the two dynamo connections, connect the battery and then the small spade terminal on the dynamo and then 'strike' the large terminal connection on the large dynamo spade, this will make it spark a bit, that will polarise the system to negative earth, you're basically changing the flow of the current through the dynamo. When you start the engine the charge light should go out, if it does you've done it successfully, if not you'll need to strike the terminal again until it does. There are two types of Implematic 990, the first having two 6V batteries, one each side of the seat, and the second having a single 12V battery up the front in front the radiator. Do you have a wiring diagram for the tractor?

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duffman
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Location: Norfolk

RE: 990 Implematic pos or neg earth?

Post by duffman » Mon Aug 31, 2015 6:20 pm

Thanks for the speedy reply, very helpful info. No I don't have a wiring diagram.

JamesF
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Location: South Yorkshire

RE: 990 Implematic pos or neg earth?

Post by JamesF » Mon Aug 31, 2015 6:40 pm

They started out with positive earth but it did change at some stage.

I have a very early 990 implematic which is positive earth

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db2d
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RE: 990 Implematic pos or neg earth?

Post by db2d » Mon Aug 31, 2015 7:41 pm

The Dynamo Polarising method described will not work.

To polarise for a negative earth system fit the dynamo onto the tractor without connecting any wires or the fan belt. Fit the battery and negative earth cable and then flash the field winding terminal ( The small one ) with a wire from the positive terminal on the battery.

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duffman
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Location: Norfolk

RE: 990 Implematic pos or neg earth?

Post by duffman » Mon Aug 31, 2015 7:51 pm

Thanks for the replies all very helpful. I think I will go for the negative earth route and try the methods with the dynamo.

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mistermcgregor
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RE: 990 Implematic pos or neg earth?

Post by mistermcgregor » Mon Aug 31, 2015 8:16 pm

The method described by db2d is the correct one for a negative earth system. It is the field that has to be energised and any other connections could damage the dynamo.

Guest

RE: 990 Implematic pos or neg earth?

Post by Guest » Mon Aug 31, 2015 9:38 pm

Dynamo

Look at the Generator. You should see a large brown wire and a smaller wire connecting to a terminal marked F (for Field). Pull off the wire to the Field terminal. Connect a short jumper wire to the large brown connection (make sure you have metal-to-metal contact). Touch the jumper “lightly / slightlyâ€￾ to the Field terminal on the generator. You should see sparks, touch again (more sparks), and again (again more sparks). Now disconnect the jumper wire from the large brown connection, and re-connect the Field terminal wire. Your generator is now polarized negative earth. This is the correct procedure.

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mistermcgregor
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RE: 990 Implematic pos or neg earth?

Post by mistermcgregor » Mon Aug 31, 2015 10:33 pm

Would you please explain the technical reasons how your two different posts can achieve a negative polarisation

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harvey
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RE: 990 Implematic pos or neg earth?

Post by harvey » Mon Aug 31, 2015 11:30 pm

hi I've just bought a 990 implematic it's a late 64 registered in early 65, this one is still positive earth.I think they changed the very latest implematic to negative earth just before they brought out the selectomatic.

JamesF
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Location: South Yorkshire

RE: 990 Implematic pos or neg earth?

Post by JamesF » Mon Aug 31, 2015 11:41 pm

I could be wrong here but I think it changed from positive to negative when the three cylinder 880 implematic came out.

John_Allen
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Location: Cumbria UK

RE: 990 Implematic pos or neg earth?

Post by John_Allen » Tue Sep 01, 2015 12:09 pm

I have been asked by someone who knows if I would explain the correct way to polarise a dynamo

The best procedure for polarising a dynamo is to connect a lead from the live battery terminal on the starter motor and "flash" the other end of the lead to the small (F) terminal on the dynamo. It is said that the colour of the spark will change when the polarity has changed, though I confess that I have never noticed that! Two "flashes" is usually enough. Reconnect the dynamo leads and check that it is charging properly as, occasionally, the dynamo will seem to be correctly polarised but it isn't!

There is the chance that the regulator contacts may be open when using the "jump from D" method and that you don't actually do anything when polarising. You should always polarise a new dynamo when fitting one - they used to be "set" to positive earth, but more recently, they seem to be set to negative (or not set at all).

As an aside, there are answers here that are in similar vein to why I haven't posted for some time and haven't bothered to renew my membership. I haven't been following the forum - I'm only replying as a favour to my friend.

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