Ammeter At 15 a

T

tmurph

Junior Member
All of a sudden, my 1930 , 6v with alternator, is reading 15 amps, drops when I turn on lights.
Thoughts?
Thanks
 
Measure the voltage at the battery or at the terminal on the starter switch. It should be about 7 volts when the battery is fully charged. After you start the car the alternator will put out more current to re charge the battery. Measuring the voltage will tell you you if this is the case. If the battery is bad it may never get fully charged so the alternator will put out lots of current to try and charge it. Check the level of the electrolyte. There could also be loose or corroded connections on the battery terminals or the ground strap or anywhere in the electrical system. In that case the alternator will sense a lower voltage and compensate by increased current.
 
I had a similar situation when I first got my A. It would start and run good. But the alternator charged at 15-20 amps continuously. It turned out the battery had very low specific gravity (probably sulfated from not being used). No matter how hard the alternator tried, it could not charge the dying battery. A new battery was installed and the problem was resolved.

Check your battery with a hydrometer, available at any FLAPS.
 
The battery should pass a load test but the problem is that few folks have a 6-volt load tester. a test can be done two ways without a load tester. One way is to turn on the headlamps and have someone crank the starter while watching the lights. It's normal for the lights to dim but if they go completely out then that's showing battery weakness. Another way is to crank the starter with the ignition off and see how well the battery will handle that load. If it craps out quick then the battery is bad.

A lead acid battery and this includes AGM types, is around 2.12 volts per cell. A fully charged 6-volt battery will read between 6.3 to 6.4 volts. It will quickly drop off after setting for a while but should remain at least around 6.1 to 6.2-volts.

One of the problems with the alternator 6-volt conversions is that they put out a higher than normal voltage. Instead of 7.0 to 7.2-volts they can put out as much as 7.8-volts. It's just the way they make the regulators for the conversions. As far as amperage output, the alternator will show a charge for a while after starting then taper off to maybe a needles width above the center after it's charged. If you turn all the lights on then it will show an average output that will swing the needle further but it doesn't always show the exact amperage of the current draw from the load being applied. A lot of this is due to the higher voltage output. The higher voltage is a little bit hard on the battery and tends to evaporate electrolyte faster than normal. A person can correct for this by running the lights ON all the time.

If a person seldom uses headlamps then the old 3-brush generator is hard to beat for keeping the battery just right. Setting the 3rd brush for high output all the time would also require running the headlamps all the time so it's not a perfect set up. It's too bad that the voltage regulators for the 3-brush aren't currently available. That is a good set up but it requires maintaining the battery and all electrical connections in tip top shape.

Any high ammeter draw can also be indicative of a loose connection or a bad wire or ground somewhere. Bad connections make resistance and resistance draws current.
 
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Excellent write up rotorwrench!

I have reverted from alternator back to a stock generator and original Ford script cutout. I have also installed LED tail lights and the new focused beam LED headlamps. With my 3rd brush set to the lowest output setting, with the lights OFF, I get 4-5 amps positive on the ammeter. With the lights ON, I still get a slight positive charge - maybe 1 amp. For me, this is the ideal combination - much brighter lights at the rear for safety and excellent headlights, while the generator is at its lowest setting and never needing to adjust the 3rd brush. Its a happy combination :-)
 
What is the voltage of the battery when the engine is running at a fast idle? Also measure the voltage at the generator terminal under the same condition.
 
Sooo, here’s a head scratcher, I went for a ride, the fan belt delaminated, I put on a new belt, ammeter is back where it should be. Thoughts?
 
I agree with NDNCHF. I too have converted all my lights to LED including the headlights and turn signals . I have a solid-state voltage regulator that looks like the original cut out controlling the output of the 6volt generator. The new focused LED headlights do not dim at idle and draw very little current. The highest wattage consuming device is the starter motor. I have installed an electronic ignition module which greatly improves engine starting and minimizes starter motor power consumption.
 
T Murph, Did you ever measure the voltage when the engine was running? A volt meter is a much better measure of the health of the charging system and battery. You can add a volt meter and keep the ammeter. Your 6 volt system should measure 7 to 7.1 volts after about 5 minutes of driving and the ammeter should read 5 amps or less. With an alternator the ammeter will read zero when the battery is charged.
 
I love my Tom Wesenberg Electronic Voltage regulator, original 6V POS ground running a Model A Autolite long generator. Diode cutout , EVR modified slightly as per Tom's instructions for running one of these. 1930 Roadster. I ran an original Model A cutout that in fact he rebuilt for me for quite some time before the diode one. Using it on another Model A.

I show about 2 amps charge driving around, when you flip the lights 'on' the ammeter needle dips for just a second to about -2 or -3 on the ammeter and then comes right back to 2 amps charge and stays there at idle or full throttle makes no difference.

My batteries now last for years. They love this setup.

Sure miss Tom:(
 
Tom's electronic regulator is a marvel of modern technology. It is too bad we lost Tom and his amazing skills. On the positive side, the use of LED tail lights and the latest generation of LED headlight bulbs largely mitigates the need for a regulator. A stock 6v + ground generator with the 3rd brush on its lowest setting still provides a slight positive charge on the ammeter with the lights on. There is no need to ever adjust the 3rd brush. LED bulbs are yet another marvel of modern technology.
 
Thank you all for your input. I changed out the alternator for the generator, still 14 - 15 amps, however when I put headlights on it drops to negative 15, with alt. It dropped to 3ish. Thoughts?
 
Sounds like the contacts on the ammeter or something related are loose/dirty. Put a VOLTMETER on the battery when car is running at fast idle. What is the voltage? Sounds like you need to go through all the wiring connections. Clean and tighten.
 
tmurph said:
Thank you all for your input. I changed out the alternator for the generator, still 14 - 15 amps, however when I put headlights on it drops to negative 15, with alt. It dropped to 3ish. Thoughts?
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The generator needs the third brush adjusted for different loads. Higher output for lights, lower when they're off. Alternator adjusts output automatically, and ammeter shouldn't change after starting discharge has been restored. Your alternator may need a new regulator. Check battery voltage with the alternator running. Should run about 7.5 volts.
 
I would pull back the instrument panel and check things in there. The modern ammeter replacements leave a lot to be desired. The originals are better and more sensitive. I would find a way to independently test the ammeter to see if it functions normally. A person can do this with a battery charger and a battery. Amp meters are wired in series between load and battery. Positive charge will show above zero amp readings. Any load on the battery will show below zero readings.

Installing a generator will generally require adjustment of the 3rd brush. The current should be set around 4 to 5 amps with the lights off and engine running.

With a good amp meter a person should see predicatable changes in amp readings when operating the car and making different selections of the headlight switch as well as operation of the brake light switch. The amp meter should also give predictable negative indications while the engine is shut down. If a Model A has the service bulletin update for coil connections then the amp meter will fluctuate from zero to some point above zero while cranking the engine with ignition on. This shows the amperage draw of the coil as the points open and close. Press the brake pedal with engine off and a person should see how much current the brake lights draw. Headlights are a big current draw and should show that draw with the lights on. It should be around 12-amps more or less depending on headlamp selection.

If a person is not seeing predictable amp meter readings then I'd find an amp meter that does. It takes a good amp meter to properly adjust the 3rd brush. Since the battery is what regulates the system voltage then it goes without saying that the battery and all battery connections to the car have to be in good working order. A bad battery or poor connections can give excessive amp meter readings and can damage the generator.

Alternator conversions have their own internal voltage and amperage control module. With a regulated alternator, the amp meter readings will be very limited except when the alternator is off line. The alternator control automatically adjusts for load or current draw changes while on line. Due to this, the amp meter generally doesn't show much charge after the battery is fully recharged from depletion created by cranking the starter. If it shows a high current output then it indicates a problem. The problem could be battery related or wiring related but it could also be alternator related. It's supposed to regulate itself but they don't always work like they should.
 
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