gas engine electrical questions

I have a Wisconsin THD 18hp gas engine. It has serial number 2942748. In the manual it says, "Beginning with engine serial number 3988441, the standard wiring circuits of all 12 volt electrical equipment for Models TH, THD is negative ground polarity instead of the previously furnished positive ground."

My engine is equipped with a generator (not alternator). It starts right up and runs reasonably well (I'm about to do a tuneup) but the ammeter shows no charging going on, and in fact I have to charge the 12V battery to run the thing. The original mechanical voltage regulator has been replaced by a solid-state kit which can be wired for 6V or 12V, negative or positive ground. It is currently wired up for negative ground, and the negative battery cable indeed goes to ground.

I am wondering a couple of things. First, according to the manual, my engine should have a positive ground, not a negative ground. If a positive-ground engine were connected as a negative ground, would the starter motor turn it over backwards? If the field magnet were an electromagnet then it seems possible that the polarity on the starter motor is irrelevant. I'm working on the assumption that someone replaced the battery cables and rewired the thing for negative ground by mistake, and that might be what's wrong with my charging system.

Also, assuming the manual is wrong about the ground polarity, is it possible to bypass the (2 terminal) voltage regulator by simply jumping its terminals, to see if the generator puts out current? If I'm thinking it through correctly, this should apply full battery power to the generator's field windings, so it should put out max power. I have learned the hard way to not just jump in blindly and start shorting things, though - sometimes that leads to the magic smoke escaping, and it's sooo hard to put back in. :-)

Thanks, Grant

Reply to
Grant Erwin
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Sounds like you might need to flash the field coils . Great thing about generators , they don't care about polarity - as long as the field windings have the correct magnetic polarity to match the reg and battery hookup .

Reply to
Snag

Followup: I got the numbers off the Autolite generator (GAS 4305) and this corresponds to a six volt positive ground generator. So the answer to why the charging system isn't charging is simple: someone swapped the system over to negative ground, put in a 12V battery, but left the generator alone. It stands to reason that a 6V generator doesn't have much of a chance charging a

12V battery.

More worrisome, the manual says:

"The wiring diagram, Fig. 18, illustrates a negative ground circuit. If polarity of generator is for a positive ground circuit, terminal connections at ammeter, ignition coil, and battery are reversed from those shown. DO NOT use positive ground generator and regulator in a negative ground circuit, or vice versa. Polarity does not affect starting motor, coil, and distributor."

So now the question shifts to: since my engine has been wired up backwards for at least a decade, is there any hope of making the generator generate again, assuming I rewired the system and battery to 6V positive ground again?

Grant

Grant Erw> I have a Wisconsin THD 18hp gas engine. It has serial number 2942748. In > the

Reply to
Grant Erwin

The simple solution when dealing with old charging stuff like this is to just stick a more modern car alternator with integral regulator (often a "one wire" type) on in place of the old stuff and be done with it. $40 at a salvage yard and an hour of work retrofitting is usually all it takes.

Reply to
Pete C.

Can't do it this time, Pete. The distributor mounts on the generator ..

The wiring diagram for my engine is:

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GWE

Reply to
Grant Erwin

A series wound starter motor will turn the right way regardless which way it is wired. There are two types of generators - internally grounded and externally grounded Internally grounded generators require an alternator that feeds the feild. Externally grounded generators require a regulator that grounds the feild. The right regulator is required - wrong one will NOT work. Then the generator needs to be "flashed" to magnetise the feild poles the right way so the residual magnetism will "kick-start" the generator. On an internally grounded unit you disconnect the reg from the feild terminal and momentarily short the feild terminal to the battery positive.

Reply to
clare

On positive ground the coil SHOULD be reversed. Reverse coil polarity CAN cause hard starting

Reply to
clare

You may not be able to remove the old generator in this case, but you can most likely bypass it and hang a new alternator elsewhere. Once for a small car will be pretty compact.

Reply to
Pete C.

True. I could make a bracket which put the alternator's pulley inline with one of the 3 belts which go between the gas engine's drive sheave and the air pump's driven sheave. That's not a bad idea. I suppose something like an alternator from a '78 Chevy truck would work, eh?

Grant

Reply to
Grant Erwin

On my '70s Deere 500C backhoe which originally had a 55A Motorola alternator with external regulator, I just replaced it with a $25 salvage '90s Delco CSxxx alternator. In my case it fit the mounting bracket directly and all I had to do was take the serpentine belt pulley off the Delco alternator and bore and fit the double V belt pulley on in it's place.

Reply to
Pete C.

Yup. Mine isn't set up for a belt-driven unit - the generator it's fitted with is gear-driven. So anything I retrofit has to include a way to drive it, ergo stealing some drive off the main belts.

Grant

Reply to
Grant Erwin

nce charging a

t. If polarity

If it helps space wise, I grabbed a alternator from a Suzuki Samuri, it's about the size of an orange, but puts out 45 amps as I recall, and uses an internal regulator. I use it on my 67 E type race car to save weight and keep the distributor-less ignition and electric fan happy. Beats having to charge the battery between races....

Reply to
oldjag

Was it complicated to wire up? I was thinking of one of those GM one-wire alternators, purely for simplicity of wiring .. this machine doesn't have an idiot light, but it does have an ammeter.

here's the circuit:

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Grant

Reply to
Grant Erwin

Nonsense - the simple solution is to repolarize the generator and move on with life - I switched my morgan from pos to neg ground by just swapping the battery around and repolarizing and all is well - of course the ammeter read backwards but that isn't a problem - you can't do this with an alternator, but it works fine with an old style generator

Reply to
Bill Noble

I know I shouldn't admit this here on this ng, but I have taken such problems to a place in mpls mn called Schelin Electric. They always have the solution.

Pete Stanaitis

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Grant Erw> I have a Wisconsin THD 18hp gas engine. It has serial number 2942748. In > the

Reply to
spaco

In my case since I was replacing an alternator, all the connections were already there. The big B+ charge terminal to the battery, ignition switched batter connection for the field terminal and the connection for the indicator light. The one wire types make it that much simpler, connect it to the battery and you're done.

One thing to be careful of would be your ammeter since a more modern alternator should have a much greater amp capacity than the old generator.

Reply to
Pete C.

His regulator is not an original mechanical type, so it will not just swap around. The regulator is probably also undocumented and unsupported.

Reply to
Pete C.

Hmmm. Have to remember that one for my Honda Odyssey FL350 - I have the stock lighting coil loaded to the max with two driving lights (Unity hose lights) and a set of Fiamm electrtic horns. (Wired through an alternating flasher for Hi-Lo.) Now to find a place to hang it and put on a crank pulley...

All the charge light circuit requires is a panel lamp holder with the right size bulb, one side goes to ignition and the other to the alternator sense lead to tell the field to turn on. Or you could use a red clearance/marker light, as long as it's isolated ground.

Worked the same as older Generator cars with a sense lead to the regulator. Came on just fine on the early Corvair with the late model alternator conversion - I have a Sonalert in parallel with the lamp for "The Fan Belt Just Broke/Jumped, Dummy!" duty.

You might need to add a diode in series if the pilot lamp supplies reverse power to the coil - if you turn off the ignition and it keeps running till you pull the Charge lamp, that's why.

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Reply to
Bruce L. Bergman

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