Ammeter/generator question

[Mshaynes21]

Hello
Just bought a 1930 model A Roadster. Car starts and ammeter sets at zero. When lights are on it goes a little to the left When I accelerate the ammeter pegs to the right. I pulled the generator cover and it still goes to 20 even with center brush pushed up all the way. Is it possible that my ammeter is not reading correctly or does this indicate a generator issue. Any help is appreciated. I don’t want to burn something up within the first week. Thanks!

[rotorwrench]

It's going to take you a while to know how your charging system is equipped and how well connected it is. The 3rd brush or field control brush of the Autolite type generator can be set to increase current output by moving the brush down toward the power output brush and decrease by moving it up toward the ground brush. Your adjustment is consistent with decreasing the output. The powerhouse type generators are just the opposite in adjustment so be certain what you have there.

There are some cut outs that are actually a regulator (Fun Projects) but it's hard to tell by looking at it. Some cut outs are still the original electro-mechanical unit and some are just a one way diode inside the can. It's hard to tell what you have now days.

If the battery or generator have any electrical connection issues then the generator can go unregulated. This also includes the charging circuit that connects through the terminal box and ammeter. Loose connections can do some damage so insure all are clean and tight. A bad battery can wreck your generator too so make sure it's in good condition. Check all grounding from battery to frame/engine and generator to engine.

[Herb Concord Ca]

To check if the ammeter is wired correctly, with motor off, just turn on the headlights, the meter should show a discharge.

[Gary WA]

don't run at 20 long you will sling solder from generator!!! destroying it.

[rotorwrench]

If connections all check OK then it may have some excessive wear in the generator or a bad connection in there. These systems are very simple but time can take it's tole on things. Worn bushings can cause armature rub. The insulation in the field or armature windings may be breaking down. It's hard to say what it may be but something isn't right. A person has to go through a process of elimination checking the easiest things first.

[Model A Ron]

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On a driver Model A I would and do run an alternator. More dependable in my opinion.

[Mshaynes21]

Thanks for all the info! I will go thru and see if I can’t find a loose connection somewhere.

[ndnchf]

It will likely come down to a poor/corroded or a bad cell in the battery.

I'll add that there is nothing at all wrong with using properly rebuilt original 6v generator. Especially if used with LED head and tail light bulbs. The generator can be set to a very low output. It will likely outlast the owner.

[nkaminar]

Measure the battery voltage when charging and fully charged. Set the engine to a fast idle, 1,200 rpm or so, and measure the battery voltage. You can measure the voltage at the starter switch and ground so you don't have to take the floor board out. When the battery is fully charged, after 5 minutes of driving, the 6 volt battery will read about 7 volts and a 12 volt battery about 14.

When the battery is fully charged and the engine at a fast idle or above, the ammeter will read 0 if there is a voltage regulator or you are using an alternator. This is as it should be because the battery is fully charged and doesn't need more current. Installing a voltmeter on your car, in addition to the ammeter, is a better method to keep track of the condition of the battery and the charging system.

When just starting out after a start, the ammeter will read high as it is charging the battery. 20 amps is excessive for a generator but not for an alternator. At idle it will read discharge, the amount depending on what electrical loads are on and what condition the generator/alternator is at.

[Rob Doe]

This was a good thread for me. thx, all, for posting.


Just a further comment, the Les Andrews blue covered book "Diagnosis and Troubleshooting" has wiring connections and testing procedures in chapter II. His method is "voltage drop" testing, and the tests can be done easily with a $10 voltmeter.