VCCA Home Forums TECHNICAL - GENERAL Electrical - 6 volt Light switch - 36 Master charge rate

I just purchased a 1936 Master. When I picked it up and while driving home I noticed that the ammeter was charging full + reading (20amps?). The generator Field terminal had a wire running to ground. I cut the wire and now the ammeter shows little or no charge with the light switch in. The charge rate will go to +10(?)with the light switch pulled to first position.

I know that the previous owner must have grounded the generator field for some reason. Could it have been because a light switch resistor is bad? Correct me if I am wrong but it appears that the light switch has two resistors. One for regular charge and the other for high charge. Since it charges in the first position out (high charge) but not the in position (low charge), is there possibly a bad resistor in the switch?

I did not check with a separate ammeter so I do not know the actual charge rate. Am I reading the car ammeter correctly? The gauge has a center line at "0" and two marks on each side. There are the numbers -20 and +20 marked. With the generator field grounded the ammeter needle pointed all the way to the right near the +20 number (past the second mark). With the ground disconnected and the light switch in the first position the needle pointed to the second mark to the right of center.

With the light switch pushed in your generator should charge about 12 amps safely while driving. With the light switch pulled out to the headlight position that will full field the generator to its maximum output to compensate for the headlights being on. There is a special light switch used in some applications that has a position between "off" and "Park" that will also increase the generator to its maximum output with the lights off.

It is possible that your resistance unit on your light switch is bad so that could be why your field terminal was grounded to the generator case to increase the output to the maximum.

You need to go back and re-read the previous postings regarding your problem. As mentioned earlier you have a three brush generator and the third brush IS ADJUSTABLE for the generator output. With the lights off, adjust the third brush so that the ammeter shows about 10 or 12 amps while driving. Then turn on your headlights to see if the generator output increases and what the ammeter reading is. If the output is too high (above 15 amps) then you need to decrease the generator output some by adjusting the third brush. At idle the generator output usually reads just a few amps on the plus side with the lights off.

With the cover band off, the third brush is the brush on top of the generator. There is a round head slotted screw on the side of the generator end frame that holds the third brush in place. Loosen the screw a few turns so that you can adjust the third brush. Moving the third brush towards you increases the output. Moving the third brush away from you decreases the output. This is explained in your shop manual. If you don't have a shop manual you can order one from the Filling Station.

JD
Is the information you posted above for the 36 Master be the same adjustments for a 35 Std? Ours is over amping and I haven't gotten around to making the adjustment as of yet. Thanks.....Bill

My earlier comments about charging were so well received that I'm going to make some more. I expect most people from the earlier thread will come over here.

Sure, your battery will last a long time when overcharged, especially if you don't drive much!

Topping up the water every 1000 miles shows serious overcharging, which can warp plates and deposit crud. A properly operating system should go many thousands of miles before needing water. Modern batteries never need it, because the are not overcharged and they catch whatever evaporates and keep it. OH, you are refilling with distilled water aren't you?

I don't know if the charge readings discussed are the total gen output or the excess over the car's needs. A 12A overcharge, beyond the load currents, is a gross overcharge and will eat water like crazy!

To really set the day current, I recommend getting the battery to full charge and adjusting the brush to hold the voltage at about seven. You really can't tell much from the meter on the dash, because the current, above the loads needed, to hold the battery at full is a fraction of an amp. That's why the battery minder things work. They supply maybe a tenth of an amp max to overcome the battery's internal leakage. We call it a trickle charge.

If you want to really get into this topic, take a battery to your bench, get it to full charge and connect a lab type variable power supply on it. Connect an ammeter in series with one lead and a voltmeter across the battery. Adjust the supply voltage to about 7.2V and see where the current settles. On a good battery that is not contaminated, you won't see much. That's the current you should supply after starting the car and driving long enough to get the bat back up.

In the daytime, the ignition is the only essential load and it's probably something like 3A. You can measure it with a multimeter on the 10A scale. Just put the meter in series with the hot lead to the coil. This has to be an analog meter to get proper averaging of the pulsing load.

So there's the story. A true regulator does exactly what you would do if you were constantly tweaking a rheostat (variable resistor) in series with the field, or continually adjusting the third brush to maintain the recommended full charge voltage.

And for max bat life, you shouldn't "fast charge" at a current that takes the 6V bat above the normal end point voltage. Most bats recommend max charge of about a tenth of their rated capacity, like 10A for a 100Ah battery.

If anyone wants to discuss designing an electronic regulator, I'd be happy to do so.

Bagsinky: Yes, even though you have a different model generator the adjustments would be the same. Disregard the part about the light switch since you don't have a resistance unit on your light switch to increase the generator output when the lights are on.

He could easily put a toggle switch and resistor under the dash and out of sight.

I don't think Bagsinky's generator gives easy access to the field if it's the same as my 33. The only wire coming out of mine goes to the cutout.

Voltage regulators that look like cutouts are available for Model A's, but they are cylindrical rather than rectilinear.

Wouldn't I need access to the field if I were to build a solid state regulator that would replace the cutout?

The field terminal was mentioned in an earlier thread, probably for another car.

I'm honestly not sure about your gen. Obviously one can build a regulator, but at light load the voltage may rise high enough to cause excess power dissipation in the regulator element. Obviously one could bring out a field connection, or use another gen, depending upon judging or how you feel about originality.

Another way to deal with the problem would be to dump some power into a load resistor, to form what's called a "shunt" regulator, but this might be a little complicated.

What I'd try first is using a series regulator and setting the third brush so it would just keep up plus a little extra when all loads wwere on. That would minimize the tendency for the gen voltage to rise at low load.

I may have seen an ad for the Model A unit, since I used to have a '29 coupe. Maybe the easy first experiment is to use one of those??

The generator used on the 1935 standard is a Model 943-J. There is no provision for a field terminal on the generator case. On that model of generator the fields are directly grounded inside of the generator case.

Why not leave it like it is and adjust as the manual (and JYD) said?....they perform perfectly OK unless your adding some high amp draw accessories.