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Farmall & IHC Tractors Discussion Forum
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oops put power to field of gen

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happy

09-26-2003 18:50:56




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Oops my friend was talking to some and got some bad info. he was told to put the bat connection to the field post on his generator. what i dont know is did he damage the generator??? and can it be fixed (this was on a H altough it shouldnt matter)
thanks




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gene b

09-27-2003 02:30:07




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 Re: oops put power to field of gen in reply to happy, 09-26-2003 18:50:56  
Try it and see if it will charge should polarize the gen. Too bad as there is another post telling you bad info. If they dont know the correct procedure they should not post. I changed a B for a guy who had it wrong but he had the field going to the ARM and lucky didnt hook up the BATT.



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Gary_N_WV

09-27-2003 05:29:41




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 Re: Re: oops put power to field of gen in reply to gene b, 09-27-2003 02:30:07  
Happy,
Please disregard my earlier posting.
I was not saying that you "should" hook the Field" terminal to the regulator "batt" terminal.
What I was saying is that the field in the generator has voltage supplied (through the regulator)to it in order to produce the electrical field that is required to make the generator charge.
Since this "field" coil normally has voltage supplied to it, then perhaps by hooking it up wrong, it wasn't damaged.
Normally these old generators are designed to withstand a little over voltage etc.....if the field coils were in good shape and you didn't smell buring wires or see smoke, then you might have lucked out.
Please note that I'm not saying that .....hooking the batt. to the field is correct..... or that by doing that in error, that you didn't ruin something.....I'm just saying that the chances are good that you didn't ruin the generator.


Gary

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Doug in OR

09-27-2003 08:45:08




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 Re: Re: Re: oops put power to field of gen in reply to Gary_N_WV, 09-27-2003 05:29:41  
The regulator does not provide a "voltage" to the field terminal. It provides a current path for the field windings. You can take the field terminal and short it to ground and it will do no damage. In fact, this would drive the generator to full output. Voltage and current are two different things. I really don't see how putting the battery voltage on the field would hurt anything - unless the generator was not turning. This might cause a high current in the field windings - causing them to burn out.

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Gary_N_WV

09-27-2003 10:57:04




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 Re: Re: Re: Re: oops put power to field of gen in reply to Doug in OR, 09-27-2003 08:45:08  
A field coil has "resistance"..... any time you pass current thru a resistance, there is a difference of potential across it, sometimes refered to as an "IR drop".
And yes....if you ground the field terminal, the generator will charge.....but were is the other end of the wire that a field coil is made up of?....It is connected to the Battery (in one fashion or another).
Usually, when the relay that controls the field current is open , there is a small resistance added in series with the circuit. If you look on the bottom of a voltage regulator you will see a wirewound resistor which is wound around a piece of ceramic.....this is the resistance.
When 2 resistances are put in the field circuit (the little wirewound one and the "field coil" itself, the battery voltage is devided between them,....lets assume for clarity that both the wire wound and the field coil is of equal resistance...when both are in the circuit, there would be 1/2 the battery voltage across each one....so, your field coil would have 1/2 the voltage across it ...but, when your relay grounds the field, which shorts across the resistor mounted on the voltage regulator, then you have the full battery voltage across the field windings.

Anyway, ....this is all "moot"..... .We have gotten off the track of what "happy" seemed to be concerned about, and that was ...if the generator was ruined by applying battery voltage across the field winding....and I doubt it !

Gary

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rustyfarmall

09-27-2003 05:50:06




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 Re: Re: Re: oops put power to field of gen in reply to Gary_N_WV, 09-27-2003 05:29:41  
An alternator needs voltage supplied to it in order to excite the fields, so it will charge.
A generator, on the other hand, will create electricity without being wired to anything, all you need is something to turn it.



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Gary_N_WV

09-27-2003 08:08:18




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 Re: Re: Re: Re: oops put power to field of gen in reply to rustyfarmall, 09-27-2003 05:50:06  
Rustyfarmall,
I totally agree that a gen. will charge....if...your pole shoes actually still contain magnetism.
Let me ask a couple of questions here..

Why do you polarize a regulator ?

When you polarize a regulator…..are you actually polarizing the regulator or the generator fields?

What exactly does a field coil do, if a generator will charge without it being excited?


Here is the way I understand it…
When you are told to polarize the regulator, you are actually polarizing the generator fields.

Supposedly, the pole shoes stay magnetized, but along with varying the magnetic field, the field coils also keep a magnetism in the pole shoes.

The magnetic field is varied by voltage being applied to the fields by the regulator.

The more voltage applied to the fields…the more the generator will charge.

A regulator does basically 3 things……….it applies voltage to the field coil to increase the output of the generator when needed…..or takes it away when you don’t need it.
It contains a cutout relay to connect the generator output to the battery when it is charging, so it will charge the battery…..disconnects it when the output from the generator decreases to a point that it would discharge the battery.
The regulator also contains relays to limit the upper and lower voltages that is being sent to the battery, and it also limits the amount of current to prevent burning up your generator.

Please note…that this is just a basic explanation……….

By the way…..I love this forum …there is much knowledge to be gained here……..


Gary

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Gary_N_WV

09-26-2003 19:58:16




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 Re: oops put power to field of gen in reply to happy, 09-26-2003 18:50:56  
I may not totally understand what you are saying here, but.....normally battery voltage is usually applied to the field post of a generator to make the generator charge.....but....it is usually not full battery voltage..... ..... .
I wouldn't think it should hurt the generator.



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Nebraska Cowman

09-26-2003 18:58:47




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 Re: oops put power to field of gen in reply to happy, 09-26-2003 18:50:56  
I guess you won't know till you try it but those generators are pretty forgiving. I had a tractor regulater stick once and the generator got hotter than 7734. I rapped it sharply to unstick the points and ran it for several years without a problem.



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