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Tractor regulator

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dmg

Tue Aug 03 2010, 04:15AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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Posts: 627

Hi everyone,

We have a tractor whos regulator crapped out, the regulator took the feed from the alternator (whos voltage varied 10-20V) and fed it onto this epoxied up board, which outputed a constant 12V at around 7A,

This output then charged the battery while the tractor was running.

problem bieng, we do not have any replacements, and im not too sure of how these kind of regulators work (its maybe transistor regulator?)
all linear regulators I know off (in TO-220) can only handle 1.5A at best, no where near the 7A I need, are there any devices that I am missing that can handle this current? or is it better off to build a new regulator circuit?

also, there are only 2 wires comming out of the device (the case which was removed was grounded) and there was no rectifier before this device, just the AC feed to it (so im guessing its halfwave inside and a regulator for its output

Any help is greatly appreciated,
thank you.

radiotech

Tue Aug 03 2010, 06:28AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

Does the alternator have a field connection? ie the wire that goes to the sliprings to power the rotating field?

What make of tractor is this? garden tractor? What you descibe sounds like a mortorcycle alternator regulator. or a permanent magnet alternator. A 2N3055, (a real one, not a plastic one) could do this in a simple regulator circuit. with a zener diode in the base.

If it is an old auto type alternator (no regulator inside) it will have a F or field terminal (small) and an output stud (large)

Voltage regulation of old alternators fed enough current to the field to keep the battery voltage about 13.6 volts no matter what the load was. Also they made sure the field was cut off when the ignition switch was off and the engine wasn't running.

Renesis

Tue Aug 03 2010, 03:05PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

Why not base your circuit on an op-amp, a zener diode voltage reference and a transistor?

Radiotech says the voltage should be 13,6V, but i've always used and been told to use 14,7V regulators. Maybe because we need a little extra umph to fire up our engines here in the cold north.

I had this image lying around, but i have no idea wether the regulator is of the same design. The rest of the alternator circuit is pretty standard and shouldn't differ much.

You dont happen to know what brand of alternator you have? If its a common brand like Bosch or Lucas, then it shouldn't be too difficult to find a replacement.

radiotech

Tue Aug 03 2010, 03:50PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Re: cold north. If the voltage at the battery ismuch above 13.6 with the engine running and loaded (headlights on) the battery is on its way out (Getting soft) When this happens in my truck, I pull the battery and shift it to my backup lighting house system, where it works well for another 5 or 6 years,

Many years ago, a friend broght his 1948 Dodge 8 Cyl car to the coast from the Praries and it had an 8 volt battery. He had the battery rebuilder (they did that then) make him a special 4 cell 8 volt battery. He then went around to every light circuit in the vehicle and wound resistors to drop them back to 6 volts. He said that at -40 F. that old car started well with 8 volts. We had a repair shop in Saskatoon in the 70's that I had to travel to , I still have the fur cap you needed.

Renesis

Tue Aug 03 2010, 08:43PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

radiotech wrote ...

Re: cold north. If the voltage at the battery ismuch above 13.6 with the engine running and loaded (headlights on) the battery is on its way out (Getting soft) When this happens in my truck, I pull the battery and shift it to my backup lighting house system, where it works well for another 5 or 6 years,

Your sertanty made me unsertain, so i checked it up. And indeed, the battery voltage can very well be as high as 14,7V with the engine running, but 14,0-14,4 is a more common charging voltage. I did a quick check on my Passat, and my voltage regulator is rated at 14V, just like the one below. With the engine idling and the system loaded i measured 13,9V on the battery. The wiring in my charging circuit is in a somewhat poor state and i expect there to be a noticeable voltage drop, so the alternator is probably charging somewhere around 14,2V.

But i still think 13,6V is too low.

Renesis

Tue Aug 03 2010, 08:46PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

Dang, forgot the picture.

dmg

Wed Aug 04 2010, 02:21AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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Posts: 627

Thanks for your help everyone, but I think I will just build this circuit:

offcourse, there will be a rectifier before this, but I think it should work.
what are your thoughts on this?

kell

Wed Aug 04 2010, 03:41AM

Registered Member #142 Joined: Sat Feb 11 2006, 01:19PM
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Posts: 102

How many electrical connections does the alternator have? Is this a farm tractor or a garden tractor? Are you sure it's not field-regulated?
If you know more than you're letting on, maybe that's the right kind of regulator. Just use really good heat-sinking for the transistor.
Anyway, set it up to deliver at least 14 volts. The way you have it drawn, you would only get 12 volts out of it and you will have a battery deader than that Pattinson fellow. Because of the base-emitter drop in your pass transistor, the diode string that goes from the base to ground needs about .7 volt more than the desired output voltage. You could add several diodes or use a 14 volt zener in series with a diode (as drawn).

dmg

Wed Aug 04 2010, 03:58AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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Its a garden tractor, make bieng case , model 446, made in 1978, as for the connections, only thing I know is that there were 2 wires comming out to the regulator (with inbuilt rectifier) unit, and the metal case itself is chasis grounded.

radiotech

Wed Aug 04 2010, 06:52AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

What will the alternator do if the battery has drained down to 5 or 6 volts with this circuit. I would be looking for a circuit to do :

- charge at 7 amps as long as the battery was below 14 volts.
- not get blown to bits or short if the battery was fumbled in backwards
- act like a constant 14 volt regulator if the battery was removed
or the terminals worked loose while the tractor was running (so lights and other stuff would run without getting overvolted.
- Work well even if **these ** parts were on the machine :

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