positive to negative ground

Lost in Sweden · Post by **Lost in Sweden** » Wed Mar 10, 2010 8:25 am

I have read up on that and most posts say, in the case of the generator, you disconnect the leads D and F and flash the F for a second (or 10s) from the newly reversed battery (flash with +, negative now ground). But some threads talk about 'rewiring' and issues with the regulator. As far as I can see though, concensus is that you dont need to do anything else but reverse the battery and flash. Comments? I assume the fanbelt still goes in the same direction?

Also, why install a alternator? Is not the generator sufficient?

Post by **Brian** » Wed Mar 10, 2010 8:40 am

You are right, all you need to do is connect the "F" terminal to the output terminal of the battery, whether this is + or -, it does not matter.

The only thing to remember is that the leads from the dynamo must be disconnected and the "flash" needs to be around 10 secs to make sure. The dynamo must be bolted to the tractor.

Foxen · Post by **Foxen** » Wed Mar 10, 2010 11:02 am

People usually change to alternators because of either of the following(or all)

1. Their generator is no longer charging the battery(usually this is because of regulator failure)
2. They've added one million 100w working lights on the tractor and wonder why they just "glow" slightly
3. They have a wrecked car with a good alternator laying around and feel the urge to put it to use

4. Or it's just because they are like me, an alternator usually reaches higher charging voltage/amperage at a lower rpm than a generator which means it will charge your battery/batteries faster than a generator

Regardless, a generator is more efficient than an alternator, but this is also some kind of moot point since for example the standard E1A generator is spec'd to 11Amps and the heavy duty is 22A, most 75A alternators will probably supply around 35-40Amps during normal tractor use(the generators need higher rpms to reach their 11 and 22A currents)

If your generator works well and you are happy with it, do continue to use it

I know where instructions can be found on how you adjust the regulator if it is "mis-aligned"...

Lost in Sweden · Post by **Lost in Sweden** » Wed Mar 10, 2010 2:12 pm

thanks for the advice. One more point. What is the best test to do just afterwards? I have read about linking D and T on the generator to a lightbulb, but not sure how that actually works out. I have a multimeter, which can be put to work.

niallsdexta · Post by **niallsdexta** » Wed Mar 10, 2010 4:31 pm

Forgive the question, but how do I know which way my dexta is and which way is the better way??

Lost in Sweden · Post by **Lost in Sweden** » Wed Mar 10, 2010 4:54 pm

I can answer that. Look at your battery and see what pole, +or - is grounded to the frame. As far as what is better, if your a purest, keep it + ground for the dexta's sake. If you want to put in some new meters (water oil temp) or most other electrical equipment (new alternator), then negative ground is needed. We used my + ground dexta to jump our car, and fortunately we did not touch frames. Now I know that was dangerous, but I did not then, which could have caused a 'problem' , at least what I have read.

Jan 59 · Post by **Jan 59** » Wed Mar 10, 2010 5:01 pm

Anybody ever thought about the voltage setting of the original Lucas voltage regulator. It is set at about 16.5 Volts. My fathers Dexta always had a battery with a wet surface and needed frequent topping up with destillated water. . We had the same with our Nuffield and our Claeys combine harvester (Ford engine)
New batteries (maintenance free) cannot be topped up and are rated for a maximum load voltage of 14.4-14.8 volts .
These batteries run dry when loaded with higher voltages. Strange enough have never seen any information regarding max loading voltage on batteries .
Anybody experience with this?
The Dexta ended up with a hole in the front of the fuel tank caused by sulpheric acid from the battery surface
Alternators usually match with the newer battery requirements.

Post by **Brian** » Wed Mar 10, 2010 7:02 pm

I doubt if the regulator would cause battery problems, most alternators run at far higher than 14 volts.

We have checked M-F tractors at 22 V and JD give problems when you fit ancillary equipment because of varying voltages up in the 18 - 20 volt range.

In the last few weeks I have had to redesign a circuit to include an optocoupler because of JD tractors.

Lost in Sweden · Post by **Lost in Sweden** » Wed Mar 10, 2010 8:17 pm

Does the ignition system of a dexta have a 'coil'? If so, does that not need to be reversed, when converting from positive ground to negative?

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Foxen · Post by **Foxen** » Wed Mar 10, 2010 8:27 pm

Is yours a petrol dexta?

The "coil" on your ignition switch(I presume it's that you're worried about) simply means on a diesel tractor that all equipment that's only supposed to work with the ignition switch in "on" goes there...("coil" is easier to have written on the backside of the connector plate than "ignition on")

Lost in Sweden · Post by **Lost in Sweden** » Wed Mar 10, 2010 8:42 pm

Its a diesel. So I don't need to do anything to it when converting from positive ground to negative ground?

Foxen · Post by **Foxen** » Wed Mar 10, 2010 9:45 pm

Lost in Sweden wrote:Its a diesel. So I don't need to do anything to it when converting from positive ground to negative ground?

No

Lost in Sweden · Post by **Lost in Sweden** » Thu Mar 11, 2010 3:27 pm

Well I did it. Tractor is negative ground. Not much of a spark though. Tractor started fine. About +13 V between the battery terminals when running at 1000 rpm. A bit higher than when I tested it just before the changeover. Warning light turned off at 600 rpm, as usual.

So, just to be sure, what test can I do to make sure the generator is appropriate for negative ground. As I said, I have a multimeter. I placed the red probe on the D terminal when it was running and the black on the frame, and got about +24 v (always increasing). I assume that good.

Any suggestions for other tests?

Post by **Brian** » Thu Mar 11, 2010 5:42 pm

Any generator (dynamo) will run either + or - , its the nature of the beast. You don't have to check anything once you have "polarised" it by "flashing".

A.B.Ames · Post by **A.B.Ames** » Tue Oct 19, 2010 3:26 pm

Hi all,
Sorry to bring up an old post but i wanted to ask/confirm one thing before i do this (below). After flashing F terminal all the wires are put back in place the same as before correct?
Thx for any assistance,
A.B.Ames

Brian wrote:You are right, all you need to do is connect the "F" terminal to the output terminal of the battery, whether this is + or -, it does not matter.

The only thing to remember is that the leads from the dynamo must be disconnected and the "flash" needs to be around 10 secs to make sure. The dynamo must be bolted to the tractor.

Post by **Brian** » Tue Oct 19, 2010 4:28 pm

Yes as far as the dynamo is concerned but you will have to make sure you have changed the battery by putting the negative terminal to earth.

A.B.Ames · Post by **A.B.Ames** » Tue Oct 19, 2010 5:26 pm

Thx Brian,
Thats what I thought just wanted to be sure first (cause sometimes what I thought causes things to go boom..). BTW wouldn't I have to have the Negative terminal to earth anyway to flash it?

Thx again, help greatly appreciated,
A.B.Ames

Brian wrote:Yes as far as the dynamo is concerned but you will have to make sure you have changed the battery by putting the negative terminal to earth.