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post #1 of (permalink) Old 09-06-2005, 09:48 AM Thread Starter
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-OT- Generator/starter - Regulator Setup

Yep, a real live Generator/Starter with two relay(?) regulator.

My garden tractor wasn't charging it's battery I was fiddling with the relays(?) in the regulator but eventually found the problem was a circuit breaker that wouldn't allow the voltage to the battery. (??) THe generator would put out 15 volts but there was only 12.3 volts at the battery.

Well I jumpered the circuit breaker and now it charges at 15 amps but only up to 13.2 volts. It started around 12.6 volts when I first got the connections fixed. After running if for several hours it eventually dropped to only 5 amp charge but still only 13.3 volts.

I realize (I think) that one relay(?) is to control the amount of current and one to control the voltage.

But how do you set them up? I quess I could take them back to the shop and have it setup again but is there some way to do the setup myself? What voltage should it run at? Same as for any electrical system in a car?

Takes me back to my NSU TTS days. [img]/ubbthreads/images/graemlins/smile.gif[/img]
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post #2 of (permalink) Old 09-06-2005, 11:21 AM
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Re: -OT- Generator/starter - Regulator Setup

Usually there are three relays associated with a DC generator - A voltage limiter, a current limiter, and third to disconnect the battery from the generator when the generator output stops.

Without the latter there will be a dead short backwards through the armature to ground that will toast the battery pretty quickly.

The voltage regulator will have pretty fine windings between the output and ground.

The current regulator will have heavy windings in series from the output to the battery.

I can't recall how the cutout relay is wired. If you have only two relays there might be a big diode in the circuit.

Both the current and voltage regulators switch the current to the windings. They are normally closed relays. I think they draw power from the generator output, before the cutout relay. The current passes through one set of points to the second set of points and then to the generator windings. As the spring tension is increased, the points stay closed with higher voltage or current. There are usually screws attached to the springs to adjust the value.

If you get the voltage regulator set too high it will overcharge the battery. Get the current regulator set too high and it will roast the generator. Look for a rating plaque somewhere on the generator.

If the generator is also the starter, the starter solenoid will have to supply current to the windings. That will probably come from an extra terminal on the solenoid.

It must be 40 years since I looked at a generator circuit, and I've never seen a starter/generator circuit. I hope this helps.


A lead-acid batttery is a lead acid battery. Charging voltage is the same - about 14.5 volts. You can only adjust it when the current relay is not cycling, and the battery is near fully charged.

Current depends on the generator size and design. You need an ammeter to set it, and will need an electrical load in excess of the set value. Several headlamps in parallel will probably be enough. The voltage relay must not be cycling when you set the current limit.

In normal operation, either the current or voltage regulator will usually be cycling except at low engine speed.
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post #3 of (permalink) Old 09-06-2005, 02:13 PM
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Re: -OT- Generator/starter - Regulator Setup

It must be an old IH Cub with a starter-generator? Positive or negative ground?
If is we are talking about stuff most of these guys never knew existed...

I still use generators in my alternative energy experiments, and I used to do a LOT of old farm equipment when I had the Engine Electrics business.

If so, one winding is a high voltage cutout, the other winding is a low voltage cut in.

You found the problem, the circuit breaker...
13.5 volts is enough to charge the battery, and you say there is enough amperage to do the job...
I guess my question is, why are you wanting to mess with it?
Do you know how expensive those generators are if you smoke this one?
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post #4 of (permalink) Old 09-06-2005, 03:41 PM
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Re: -OT- Generator/starter - Regulator Setup

one winding is a high voltage cutout, the other winding is a low voltage cut in.

[/ QUOTE ]

The low voltage cut-in is what connects the generator to the battery once it starts producing?

How do they get by without a current regulator? Limited engine speed range?
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post #5 of (permalink) Old 09-06-2005, 05:15 PM
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Re: -OT- Generator/starter - Regulator Setup

Voltage regulators used on alternator type charging systems evolved from the generator days.

The Generator produces DC or Direct Current, and since the rectifier required to make the DC needed for the vehicular system (charging battery, mostly) was a complicated thing prior to the days of solid-state electronics, generators were a given in the electrical systems of all vehicles until that time. The Selenium Rectifier, and later, it's more efficient cousin, the Silicon Diode, changed all that, and so we universally have Alternators on vehicles today.
Alternators require less maintenance, less moving parts, less hand fitting and are substantially cheaper to produce and operate.

Regulators on generators usually used three separate coils,
1. One for voltage regulation,
2. One for current regulation,
3. One as a cutout to disconnect the generator from the battery when the engine was not running.
(The exception to this basic rule (guideline really...) is for the Starter/Generator)

When generators were replaced by alternators the voltage regulators became more simplified and only required a coil to control the field circuit.

Voltage regulators control the field circuit by rapidly switching on & off.
When more output is needed from the alternator, the field circuit is turned on longer and when less output is needed, the circuit is off longer.

The mechanical type of regulator was known as a "B" circuit in which the field circuit was controlled by the amount of current sent to the alternator brush terminal.

The electronic type of voltage regulators are an "A" circuit type. In this type of circuit, full battery voltage is sent to one field terminal on the alternator from the ignition switch.
The second field terminal of the alternator goes to the voltage regulator which now controls the circuit by switching the ground on and off.

The "Cut-Out"
When a generator armature is producing a higher voltage than the battery, current will flow to the battery.
But when the opposite is true, the current will flow in the other direction, causing the generator to "Motor."
---In fact this is one way to test a generator - apply battery (-) to the field and armature terminals, and (+) to the case, and it should spin, hence the term 'Motor'.
This means of course, that when the motor isn't running, the generator armature must be disconnected from the system.
The old mechanical regulators were in fact two devices in one - the field voltage regulator, and the cut-out.

Since an alternator system is protected from this reverse flow by the very nature of the rectifier (passes current in only one direction), an alternator Voltage Regulator would not in itself be enough; if the enterprising tuner were to find that an alternator-style Voltage Regulator worked with the generator, he would also have to provide against this reverse flow possibility.
No problem, solid-state electronics to the rescue once again!
All would be taken care of by the incorporation of a 15 or 20A diode in the charging circuit to prevent this reverse flow.
See your friendly local electronics supply store for such a diode.

In the case of the Starter/Generator, the key switch is the 'Cut Out'.

Testing the ability of the generator to produce current is fairly simple - connect a load of some kind, such as a headlight sealed beam, get the thing spinning somehow - holding the drive gear against a drill press belt, or buffing wheel, or even starting the vehicle with it in place will do this just fine -, and applying some voltage to the field windings to get it started generating will do the trick.

If the system is still in one piece, to check the system, all one need do is measure the system voltage at the battery.
It should increase from around 12V to 13.8 (or so) when the motor is started.
For a quick check, starting the motor and momentarily disconnecting the battery will serve to check generator output.
If the unit has coil ignition, and it keeps running, then the charging system is obviously working.
With magneto ignition, turning on the lights will give you a check.
If the indication is that there's no output, first check the regulator by looking for field voltage between the generator's "F" terminal and ground (it's a negative voltage on (+) ground systems, remember.)
If no field voltage is present, proceed as described below.
If one is, you have trouble. Read on, as we discuss testing the generator out of the bike or car.

A generator which has been used recently will begin to produce current on its own, with no field voltage applied.
This is because of a phenomenon called residual magnetism - some magnetism remains in the soft iron field core between uses, and this will "kick off" a rising spiral if the field is simply connected to the armature output for testing.
But if the generator hasn't been in service for some time, this "jumping" of the A and F terminals won't be enough to tell you if you have a generator.
You'll have to connect some battery power to the field while testing for armature output.

So here are the test connections:
First, connect the load ( a headlight high beam is fine.
One side to the case of the generator, the other to the generator's "A" terminal.

Now for the field winding.
Connect the case of the generator to the battery (+) terminal.
You want control of the output, so you will only momentarily connect the "F" terminal to the battery (-) terminal to provide field voltage when you have the generator spinning.
Get it spinning and do this, and your headlight should light up.
Remember that supplying a full 12V to the field will result in full field voltage, which will easily blow the headlight, so a momentary connection is all that will be required - or you could have connected two headlights in series - they will handle 24V this way, which the generator probably won't put out, even with full field voltage.

If the generator checks out, congratulations!
Now all you need is a Voltage Regulator - actually, a Field Voltage Regulator.
Most of these will be, of course, mechanical - no solid-state electronics.
Solid state electronics are available, but from specialty suppliers, and at premium costs!

Fortunately, since they all work on the same principle - that of varying the field voltage to correspond with sensed output voltage (itself varying with load and rpm,) many different brands of voltage regulator can be used.

In The Day, American Delco voltage regulators were the cat's ass!
Lucas regulators, being expensive and delicate, were often substituted for Delco in Canada, and older English car and bike collectors still lust after them...
I used some from mid-'50's & very early 60's Chevrolets with good results. Again, you should find an OLD automotive electrics shop to source a suitable one of these.
Avoid Ford parts - many models of Ford, at least here in North America - grounded the field terminal to increase output instead of applying voltage. Different setup and hard on equipment.
If you can't find an automotive shop that knows anything about generators, try a shop that specializes in old farm equipment.

Once you've got a suitable regulator, and you're generator's working, all you have to do is make the connections. D on the Dynamo to A on the regulator, F to F, and BAT to battery hot terminal, through the ammeter if you have one.

Of course, maybe your load won't light. If not, check your connections, ensure that the headlight isn't burnt out (use the battery to test them both) and if all these check out, then your generator's in trouble. It will in all likelihood be an open field, since there's only one field circuit, but the armature circuits are multiple, each being connected to an opposite pair of commutator bars - spinning in a magnetic field, each good pair should produce some output, and the likelihood of them all being shot (open) is low.

If you're getting no output, the first thing to do is to check the field continuity - although if the field is shorted, it will of course show conductivity. You might try taking the generator apart, and applying voltage to the field windings, to see if they become a magnet - do they draw power (look for a spark when disconnecting) - will they attract steel objects to their poles when energized.
If not, it's safe to assume it's time to go looking for another winding or set of windings.

You might try another field, ie case, if you're fortunate enough to have a collection of parts. If not, look for a good and old automotive electric shop, and have them test the generator. Anyone with green hair, hat worn sideways or backwards, or piercings in his face should be regarded with suspicion, since it's been quite a while since the days of generators.
The two individual field windings are replaceable, if you can find some OEM parts somewhere, and if not, should be rewindable.

If the fields check out, then the problem would appear to be something to do with the armature.
Are the brushes properly connected, and of sufficient length to contact the commutator properly?
Are the commutator bars insulated from one another, or is there a buildup of carbon between them (you can clean the spaces with a blade or saw of the proper width.)
Finally, a silver-hair & knowledgeable repair shop man may still have a "Growler" - a device which is used to check armatures of motors and generators.
Large (industral size) starter rebuilders may still have a Growler.
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post #6 of (permalink) Old 09-06-2005, 05:18 PM Thread Starter
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Re: -OT- Generator/starter - Regulator Setup

I have an old IH Cub also but this problem is in a MTD 990. Just your typical 1 cylinder B&S

It's negative ground.

I just wanted to be sure That there isn't going to be a problem with the lower voltage.

And thanks for the complete testing senario. I got several others I'm going to check. Fortunatly there is a reliable rebuilders near were I work. They want both the generator and the regulator together when they rebuild it. You can't buy these anymore and had this one rebuilt about 8 years ago. I notice the case getting quite hot lately and may need to take it in again after the season is over.

I notice when I recharge the battery with the jeep the generator/starter spins right over and has no problem starting the tractor. When it's been charging on it's own it has a problem turning the engine over. That's why I wondered if it could be something with the voltage. I just replaced all the heavy wires going to the battery But it's s hidden I have pull the tractor apart to get to the starter solenoid to give a good inspection.
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