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6v generator to 12v generator

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JohnG(TX)

01-23-2003 12:15:48




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I have read somewhere that you can modify a 6v regulator to be a 12v regulator by bending something or modifying a spring. Does anybody know anything about this? I have read that the generator will do 12v, but not put out the current. It should have the same power output since P = I * V, if you double the voltage, the current will drop in half. Any ideas on this, or am I all full of beans?




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Bob M

01-23-2003 19:10:31




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 Re: 6v generator to 12v generator in reply to JohnG(TX), 01-23-2003 12:15:48  
Hey John - As others have noted you can indeed mess with the regulator and generator and make the system generate 12 volts. However there are a couple additional things you should be aware of:

1 - A 6 volt generator will run hotter when operated on 12 volts. This is because running on 12 volts doubles the current thru the generator field coils. And since heating of the coils varies as the SQUARE of the current (P = I^2 * R for you engineers...), doubling the current causes 4 times as much heat to be developed in the fields. Probably OK if the tractor is used only itnermittantly in cool weather. But if it's run hard in 100 deg ambients, you will increase the risk of frying the generator.

2 - You can tweak the regulator to make 12 volts by increasing the spring tension on the regulator relay. This is the relay whose contacts are help CLOSED by spring tension. (The other relay is the cutout - it's contacts are help OPEN by a spring). It's kinda fussy to set just right, but it can be done. However on a 2-element regulator like the Farmalls use, the voltage regulator relay serves also as a current regulator. So when you mess with the voltage setting you increase the current limit. If your battery shorts a cell or a fault develops in the wiring, the regulator won't limit current to a safe value for the generator, and poof!.....your generator is again fried.

Bottom line is you can make your 6 volt generator give 12 volts - just be aware of the risks!

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Dave

01-24-2003 07:38:27




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 Re: Re: 6v generator to 12v generator in reply to Bob M, 01-23-2003 19:10:31  
Bob: Good point on doubling the field current, but I have a couple engineer-to-engineer questions.

First, what is the 'weak link' in the generator? I know (now) that my 6-volt gen is running double current in the field windings, but I am also running only half current in my armature (this was the reason I considered it safe and went ahead and did it). Shouldn't this help me out? I guess it would be best to run both sets of winding below their design amperage, but I was wondering how sensitive the field actually is to over-current, especially when my armature is only making one-quarter the heat than it would if run at 6 volts. Also, the exterior field windings seem more likely to shed the extra heat. I agree this is not optimal but was also wondering how different the 12-volt field windings are from the 6-volt (wire guage, number of turns, etc).

Also, do you know what the typical rated field current is for these type generators? I guess I could go out and measure the ohms of the field and divide it into 6 (or 12), but that would not tell me what my field is rated to take. I guess I should be somewhat cautious since I think my generator is oiginal and the insulation isn't the greatest. But I was just wondering how cautious I should be. For the wndings, I would take it that the field would be the 'safer' of the two to run over-current (no brushes, etc.) I was just curious if you knew how much.

Thanks for your insightful, technical remarks. I learned something!

Dave

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Bob M

01-24-2003 11:40:11




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 Re: Re: Re: 6v generator to 12v generator in reply to Dave, 01-24-2003 07:38:27  
Interesting question John! There's not really a definitive answer to what is a generator's 'weak link' after being setup to provide 12 volts. But here's my thoughts:

For the field winding, running over the design current causes higher temperatures in the winding as previously discussed. High temperatures - especially deep in the windings - result in rapid deterioration of the insulation. When the insulation deteriorates enough that a short develops between windings or to a pole shoe, you've got failure. Also higher temperature may cause the solder in soldered connections to slowly creep - especially with the vibration experienced by a generator humg on the side of an engine. When enough solder creeps out or weakens in a connection, the winding goes open and again you've got failure.

The armature on the other hand usually fails when a solder joint at the commutator lets go. These joints are under considerable mechanical stress due to centrifugal force when in operation. So vibration and metal fatigue also may play a role. However armature winding insulation failure can also occur, same as in the field windings.

Field resistance is determined by the wire gage and by the length of wire comprising the winding. Typical rated field current for a 6 volt generator? Depends on the factors above, also on the coil temperature (higher temperature -> increased resistance -> reduced current). However 2-4 amps is what I've typically observed on a 6 volt system.

Regarding relative heating between the field and armature after switching to 12 volts, analysis is a bit more complex for the armature. Granted, the reduced armature current results in reduced heating (P=I^2*R). However armature current is not cut in exactly in half like you'd expect on 12 volts. This due to the increased field magnetic strength caused by the increased field current draw. End result is heating is somewhat reduced, but NOT by a factor of 50%. Further, because the current in each winding reverses polarity with each 1/2 revolution, there's hysteresis and eddy current heating going in the iron parts of the armature. How this affects the total heating in the armature is beyond my analytic capability however (I'm an ME by training, not an EE!)

Bottom line is I guess I'll agree with you: You are probably less likely to experience problems running over current through the field vs the armature. But that's just my guess....

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Heath

01-23-2003 18:21:31




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 Re: 6v generator to 12v generator in reply to JohnG(TX), 01-23-2003 12:15:48  
I don't know the details but you are correct. You can bend an arm in the requlator and your 6v generator will produce 12v and work. I can find out more if you want but it won't be until monday at the earliest. Let me know if you want me to find out.



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JohnG(TX)

01-23-2003 18:36:08




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 Re: Re: 6v generator to 12v generator in reply to Heath, 01-23-2003 18:21:31  
I am very interested in exactly what needs to be done. I don't need much charging capacity since I have no lights and will be installing a magneto shortly. I only need to charge for starting. The tractor (1942 M) starts extremely easily in all weather, not that it 'NORMALLY' does not get very cold in Texas. I have a new 6v regulator and need to know exactly what needs to be modified. My email is:

jhgold@stic.net

Thanks for the help.

JG

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Heath

01-24-2003 10:27:38




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 Re: Re: Re: 6v generator to 12v generator in reply to JohnG(TX), 01-23-2003 18:36:08  
The coil spring needs to be shortened on the coil which is connected to the F (field) terminal. It has lighter windings than the cutout coil which disconnects the battery when you shut the tractor off. If you have a 3 brush generator I am not positive it will work but I can check Monday if you want. This advice comes from Ed Dombrock, former IH service manager from the St. Paul, MN branch and he currently is instructor at WITC New Richmond. He has done this many times and it works well. Let me know if you need me to ask for more advice.

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steve

01-23-2003 16:17:48




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 Re: 6v generator to 12v generator in reply to JohnG(TX), 01-23-2003 12:15:48  
a good 6 volt generator will put out about 15 volts when run wide open. you can ground the "F" terminal and start tractor, then measure the voltage across the "A" and "F" terminals. If it is above 12, you can then install a 12 volt regulator to "regulate" the voltage. You are right about the current draw. THe two main porblems you will run into are that 6 volt generators only put out about 8 amps (most of them) so you can use it to trickel charge a battery, but dont run a bunch of lights. second problem is you r 6 volt system is positive ground and when you boost the generator to 12 volt it will still be positive ground. Most new systems are negative ground. Only way to get around that is it install a different generator, or get it rewound. Best bet is to get a regulator at Auto Zone for a generic unit, like 1960 chevy pickup, should cost about $25. make sure it can be polarized positive or negative. then you are all set. leave the system positive ground.

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Dave

01-23-2003 14:31:19




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 Re: 6v generator to 12v generator in reply to JohnG(TX), 01-23-2003 12:15:48  
You can get a 12-volt cutout, or remove the relay from a 6 volt regulator and replace it with diodes. I now run my 41 A this way with a 12 volt battery and bulbs but the same 6-volt gen. It does charge at a slower rate, and won't begin charging until I am at about half throttle (below that it turns too low and won't make enough voltage to charge a 12-volt battery). I have heard of some people using a smaller generator pulley to make it spin faster to overcome this problem.

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Norm in Alabama

01-23-2003 13:23:36




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 Re: 6v generator to 12v generator in reply to JohnG(TX), 01-23-2003 12:15:48  
John, any of your local auto electric shops should be able to help you with that problem. They could supply you with a 12v regulator and even rewind your 6v generator to 12v output. They do that here so I presume your local shops can too. I hope this helps you some.



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