Not Charging - what's up?

Walt Ebie

Walt Ebie

Senior Member
Have had my '30 coupe since last August so I'm still a relative 'newbie' in many areas, but I'm learning - with some help. Here's the deal: driving along and notice the ammeter is not charging. It has been until now. So break out the Les Andrews books and dig in. So with my voltmeter here's what I know: battery is good - 6.5V. Have 6V at both wingnuts on the terminal box. Resistance across the cutout terminals looks like an open circuit. Generator output at a fast idle shows about 18V - too high, I know, so I'll move the 3rd brush down some. Also put a jumper across the cutout terminals and still no charge on the ammeter. The ammeter stays about centered while engine is running and turning on the lights will show a discharge. I'm using a solid state cutout so there should not be a 'sticking' problem with that. The ammeter on the car was wired backward when I got it and I changed that so I'm pretty sure it's wired right. So what do you think? Where do I go next?
 
i think your right on track.. lower the output as you mentioned and at idle it will read around 0 and discharge with the lights
the back of the les andrews red book is a voltage vs amps conversion chart
 
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The third brush controls the amperage output not the voltage,
the voltage is controlled by the battery unless you have a voltage
regulator.

Bob
 
You have an open charging circuit and an unregulated generator, that's why you have such high voltage at fast idle. Can you lower the fast idle down so you have about 8 or 9 volts showing at the generator terminal? Then using your voltmeter start at the generator and work towards the battery checking the voltage at each connection. When the voltage drops from 9 volts to the 6.3 volts of the battery, that is the bad spot. Do you have a blown fuse or poor fuse connection, if you use a fuse?

If the battery cranks the engine like it should, I'll assume you have good connections at the battery posts and ground strap.
 
Still trying to solve my charge problem: I have slowed down the idle and that didn't make any difference. Also found that the 3rd brush was all the way up and even when I moved it about half way down (which should increase the output) the VM still showed about 17-19V on the output side (side toward the fan). Also noticed that although I have started and stopped the car numerous times during this work, the battery stays at a full 6.6V and starts the car very easily. So maybe it is being charged and the ammeter is the culprit?
 
It still sounds like you have an open somewhere, so, do as Tom suggests. If the ammeter normally reads zero and then a discharge when a load is added [ any lights] then I doubt the meter is bad. An easy way to check is to jump the ammeter terminals and see what happens.
 
What is the voltage on the other side of the cutout? The generator is not seeing a load so thats why the voltage is high on it. Follow Tom's instructions to the letter and you'll find your problem.
 
Most likely you only have 4 places to check to find your problem. Since the engine starts and runs fine, you can forget the battery and cables, as well as the ground. And I mean the battery ground. Be sure the generator has a good ground (the mounting bolt), as I've seen rust at the mount and that caused the generator to cook itself.

So with the engine at fast idle check both sides of the cutout for voltage, then check both terminal box wing nuts for voltage. If you have a fuse, then check both sides of the fuse. Actually since the coil is working the fuse must be good if you have a fuse. And depending on where the coil power is taken, the ammeter may have to be good to feed the coil. That pretty much leaves the cutout of the wire leading to the terminal box.
 
There's another way to check this out, with the engine off. Just turn the lights on and make sure both headlamps and taillight are on, then start at the starter switch and check the voltage at the end of the battery cable, both terminal box wing nuts, and the cutout output terminal. All should read the same, or within a couple tenths of a volt. So far I'm thinking the cutout is bad, but you said you jumped across the terminals and the ammeter still doesn't show a charge. Be sure you have a good clip lead. I had one once where the wire broke inside the rubber boot for the clip, and it made me wonder for a bit why things weren't adding up.

Something just isn't adding up here. Where do you live?
 
Try cleaning the area of the frame where your battery ground cable is attached. It may be you are losing the ground on the battery. Clean the battery terminals also.

Tom Endy
 
Okay, I checked the voltage at the battery cable/starter = @6.3v; both terminal wing nuts, @6.3v; and the cutout output = @6.3v. When I put on the jumper (across the cutout) engine would run very rough - hardly run at all. Remove the jumper, runs okay. But in the process I found this - maybe part of the problem. Cowl lights run okay, switch to the left; but turning on the headlights (which were running okay a week ago) now blows the fuse. Also, the previous owner was running 30 amp fuses. Does that sound like the right size? But, other things aside, I guess I need to find the problem with the headlights - sounds like a short somewhere.
 
A dead short there is bad. It would burn any size fuse. 30 amp is not to heavy. I use a 30A breaker. I like Toms idea of checking your ground to frame. Disconnect the lights via no fuse. What happens now to the charging ? Sounds like an internal wiring or ground problem. I bought an A Model that some mechanic wired and quite honestly I just got a new wiring harness and started over. 70 year old insulation generaly has broken down for the most part. Perhaps after you check the ground. Disconnect the auxiliary wire at the starter and the generator wire on the feed side of the cutout (your still using the diode cutout) Run a wire directly to the battery - terminal and jump the ignition side of the coil from the battery- terminal. I am assuming you have a positive ground? Then test, I have not worked much on A's of late however if my memory serves me correct they were stock with a positive ground, lets check that fact out. My present car has a 12V alternator with a negative ground, halogen lights work very nice to drive at night and very bright tail lights. If you not interested in showing in my view that's the way to go. I did the same on my T Model and never looked back one wire alternator.
 

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I'm not as sharp as you folks, so I keep two or three extra parts ( starters, generators, cutouts......) as they are a quick change and this helps me not find out how dumb I am. Also I have a need to drive my A every day and don't want to be without these items. Sorry I have no diagnostic advise.
 
I would leave the headlamps/horn wire OFF the cutout, so you take them out of the mess, then just work on fixing the charging system first. Once you have the charging system fixed, then check out the lights circuit.

Remove the lights/horn wire, then with the engine at fast idle jump the cutout terminals and read the voltage at the cutout.
 
In order to troubleshoot this, you need to measure across the cutout. Put one lead of the meter on one side, the other lead on the other side of the cutout. If its a diode cutout it should be .7 V or less. A standard cutout near 0V. A voltage regulator cutout, connect an ammeter inline to check the current flow.
 
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