Amp Meter discharge, but no charge.

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Model T Ford Forum: Forum 2016: Amp Meter discharge, but no charge.
Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Batta - Dayton, Ohio on Saturday, December 03, 2016 - 05:24 pm:

I am having an issue that I have not been able to track down a solution yet. Let me start with it did work at one time and showed a positive charge while driving.

Below are the facts of what I have done or checked thus far:

1. Good 6 V Battery
2. Braided negative battery cable to frame.
3. Heavy battery cable from battery to starter switch.
4. Replaced the amp meter with a new one. (Same result)
5. Voltage Regulator is in place
6. Replaced Generator with rebuilt one. (Same result)
7. Adjusted the 3rd brush with no change at Amp meter.
8. All wiring is new as of 3 year ago.

With car off or running, when I turn on headlights, the amp meter does show a discharge. No matter what I have done thus far, I am not able to get a + charge displayed on amp meter.

I am open to suggestions and guidance.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Peter Claverie, Memphis TN on Saturday, December 03, 2016 - 06:09 pm:

An educated guess --- I believe this shows the voltage regulator is working correctly. You did say "voltage regulator," not "cutout."

With the engine not running, the ammeter should show zero. If you turn on the lights, it should go fairly far to negative. Just how far depends on the bulbs you are using and the range of the meter.

With the lights off, if you start the engine the meter should show a plus amount for a little while, then settle down so close to zero that you probably can't see the difference. This means the generator has replaced the juice needed to spin the starter, and the battery is full again.

If you turn on the lights with the engine running, the meter might jump a little toward negative, then return to zero as the voltage regulator returns the generator to the proper output to offset the draw of the lights. But this might happen so fast you don't see it.

If the engine is running on "batt" the slight draw will be similarly offset by the regulator, although most of us pretty quickly switch to the "mag" in which case there is no involvement of the coils with the battery circuit.

If it works as I have described, everything is working as it should.

By the way, some folks like to adjust things (third brush) so that the generator is always charging the battery a little bit. If things are right, this is not necessary - although not a problem (unless you get it too high, in which case you can "cook" a battery).

Hope this helps!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Peter Claverie, Memphis TN on Saturday, December 03, 2016 - 06:14 pm:

I just re-read your post. If you are unable to get the ammeter up to zero with the engine running well above idle and the lights on, the generator isn't putting out enough amperage. This will call for either or both of:

"Flash" the generator to polarize it.

Adjust the third brush.

Instructions are available elsewhere on the Forum. Just be careful, if you "flash" the generator, to have the voltage regulator well out of the circuit, lest you blow its innards.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tony Bowker, Ramona, CA on Saturday, December 03, 2016 - 11:02 pm:

I suspect you are not telling everything that we need for a diagnosis. Do you have a cut-out or a voltage regulator.
The former will charge at a constant rate.
The later will change the charge rate depending on the state of the battery.
Do NOT FLASH your system if you have a voltage regulator, i think it can cause damage.
Let us know what is sitting on top of the generator......


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Barker - Dayton, OH on Saturday, December 03, 2016 - 11:22 pm:

Tony - Scott has a FP voltage regulator.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Batta - Dayton, Ohio on Sunday, December 04, 2016 - 01:16 am:

It is a FP Voltage Regulator.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stephen, South Texas on Sunday, December 04, 2016 - 08:08 am:

1. Use a volt meter and check the voltage across the battery terminal posts.
2. Measure the voltage from ground to the VR terminal.
3. Start the car and place on fast idle.
4. Measure the voltage from ground to the VR terminal.
5. Measure the voltage from ground to the generator post.

Take those measurements and report back.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Sunday, December 04, 2016 - 08:28 am:

Since it has been determined that you have a FP voltage regulator then let me suggest that you check out your Generator/VR system this way:

1) Turn off all lights and leave them off for the time being.

2) Use an analog meter (not digital type) and connect it to measure the voltage from the output screw terminal of the VR (+) connection to the mounting screw of the VR (-) ground connection. With engine not running you should measure the battery terminal voltage which would be about 6.3V if the battery is fully charged but has not been on any charging source for at least 24 hours.

3) Start the engine and as you advance the throttle speed you should see the output of the VR go from 6.3V to 7V but then go no higher than that regardless of further increase in RPM. The VR output voltage will stop at 7V. As you reduce the RPM the voltage will remain at 7V until you get to the lower RPM range when it will drop back toward the battery voltage again.

4) Do not attempt to make any measurement of the generator post during this test since the signal there is meaningless to your test. You can be mislead by any reading you get there because you need a different type of measurement device to measure that and everything you need to know takes place at the VR output screw connection.

I would be happy to help you further OFFLINE and you can PM me. Too many different ideas get involved when you use a committee to debug electrical issues and sometimes more problems are inserted than are solved. Experiments can just increase the repair bill if not done carefully.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Sunday, December 04, 2016 - 08:29 am:

Should have read first. Stephen has the same idea in mind.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stephen, South Texas on Sunday, December 04, 2016 - 09:00 am:

No problem John. I defer to your expertise in this matter.

Ken


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Sunday, December 04, 2016 - 09:14 am:

The fastest and best test is just to watch the voltage at the VR output with an analog meter. That will confirm that the generator/VR are both OK or if something is wrong with that combo. Nothing meaningful can be measured at the generator post until you first determine if the whole thing is working right.


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