What is the normal "behavior" for the ammeter 6volt pos ground

B

Big_Guys_baby

Senior Member
Hey Barners,

Last weekend was huge for getting my car on the road. ******* a lot of loose ends and got her out on the road putting on some miles! I realized that I am still concerned about the charging system and I also realized that I really had no clue whatsoever what the normal behavior for the ammeter is.

I have been worried about getting stuck, so I have been persistently checking the battery voltage at the ignition switch. It has been consistently between 6.2 and 6.4 (napa battery, close to 2 years old) As I was driving last night home from work in her, the ammeter showed discharge most of the time as I was driving with the lights on. Got home and checked voltage and she was as good as when I started, checked voltage again this morning and same.

The ammeter needle doesn't really swing over to charge ever. It shows slight discharge when I am running during the daytime, it shows a bit bigger discharge at night. However it seems like the generator is keeping up.

Any info would be appreciated!
 
Assuming you have a three brush dynamo the charge rate is adjustable. With everything off my Model B charges at 12 amps or thereabouts. With headlights on it shows a discharge of around 2 amps.

Is your ammeter reliable and have you checked it with another piece of equipment?
 
Not enough information. We need to know what year a vehicle. Early vehicles have a genuine ampere meter with two terminals on the back but the later cars have an induction type amp meter where the charge wire passes by the back of the unit but is not physically attached.

The two units give different indications so it's hard to relate you what you need to know.
 
1946 Business Coupe.It has been a while since I looked at back of ammeter butI believe it just passes by the back and doesn't physically attach.
 
The wire that connects to the starter selnoid then goes the electrial system. That wire should pass through the ampmeter, the direction of the wire passing through the ampmeter you would have to determine on pos or neg ground. Use trial and error to see which way the needle deflects. This will show you how many amps are going to or leaving the battery. Everything like the lights will come out before the ampmeter, unless the generator is not supply enough ampers to supply the system, then it will show a discharge. John
 
Here are the specs for the generator for you to check at various RPM's. Sounds like to me that generator isn't charging or isn't charging enough. If recently installed or hooked up after a long time (months or years) the generator may need polarized to get going.

Generatorspecscropped_zpsbf868d61.jpg


As you can see from the following specs, you should be getting close to 7.2 volts when the generator is charging at fast idle. Check that voltage with fast idle and see. If the voltage at the battery doesn't rise at all from engine off to fast idle your generator is not charging.

RegulatorSpecs_zpsd16198e5.jpg


And, here's a schematic of the whole charging system if that helps understand how it all works.

ChargingSchematics_zps11ccf0cb.jpg


Since that diagram didn't come with a legend for the numbers I'll give it my best shot:

1. Generator battery/armature terminal.
2. Regulator armature terminal
3. Regulator field terminal
4. Generator field terminal
5. Generator ground (no specific connection, just through mounting on engine)
6. Regulator battery terminal
7. Connection to the rest of the car's electrical system
8. Ammeter (Battery gauge)
12. Starter solenoid connection
13. Battery negative post
14. Battery positive post
15. Connection of battery ground strap to firewall
16. Regulator ground terminal
17. Generator ground terminal (grounding directly to regulator)
 
Last edited:
Induction meters only show the amount of current flow at any given time. It may show a charge for a bit imediately after you start the car but will go back to neutral after the battery is up to full charge state. It will show a discharge when the generator is inoperative or not keeping up with the current draw such as at night with lights on and brake lights on with heater fan and other electrical accesories also on.

If you have a volt/ohm meter, you can measure the voltage at the battery with the car running. The voltage regulator will boost the voltage above the 6-volt mark. It may not read exactly 7.2-volts but it should be above 6-volts in most cases.
 
But it does sound like it is not charging...
Quick and dirty verification of generator charging:
1. Slow idle, headlights on, rev up engine to a bit above idle. Headlights should brighten.
2. Pull out throttle knob slightly so engine is running at a pretty brisk idle, remove on battery cable. If engine stops, generator is not working.

There is an easy way to "full-field" the regulator briefly, making gen go to full output regardless of what the regulator is doing. This is a worthwhile check because reg failure is much more common than gen. I've posted that on the HAMB because I can never remember it,along with instructions for properly polarizing the Ford system, another quick checkup item.
 
I have a 6 volt positive ground alternator in my F-3. The ammeter in this truck is the stock induction type meter. The ammeter shows that the system is charging right after the engine is started then gradually tapers back to the "neutral" position.
 
...and that is the normal position for an ammeter on a car with the regulated type generator (2 brush Ford) as it will be regulated to the current actually being used.
 
You must log in or register to reply here.
Back
Top