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Voltage reading on battery

1

10fingers

Member
Im getting an erratic reading from my volt meter when hooked up to the battery. The needle swings rapidly from 4 to 7 volts at 1/2 throttle. New voltage regulator has been installed. Is the needle swing normal?
 
Sounds like you are looking at an AMMETER, rather than a VOLTMETER.

Some ammeters are "damped" btter than others, and don't wiggle as much. (Likely a good-working OLD "made-in USA unit" will be more stable than a new unit from "the land of almost right".)

Beyond that, poor brush contact, raised mica between the commutator bars, or a bad regulator can cause the ammeter needle to flop around.
 
Yes that swing can be normal. If you are using a generator to charge the battery your meter is also reading the AC voltage coming from the generator. The best way to read the battery is to use a battery tester that will also work as a load tester. Besides being able to test the battery load capacity, it will also check the charging system and the device will also be able to put a load on the charging system. The most reasonalby priced battery, charging system load tester I have found is at Harbor Freight. Their tester works great for both generators and alternators, 6,8 and 12 volt systems.
 
[i:5e4f9011ae]"Im getting an erratic reading from my volt meter when hooked up to the battery. The needle swings rapidly from 4 to 7 volts at 1/2 throttle."[/i:5e4f9011ae]

If you've hooked up a [u:5e4f9011ae]voltmeter[/u:5e4f9011ae] [u:5e4f9011ae]across[/u:5e4f9011ae] the 6 volt battery and get fluctuating 4 to 7 volts DC with engine running, you have a problem. If the generator is charging, you should get the battery nominal voltage, around 6.8 volts DC.

You sure the voltmeter is correct? Have you checked with a multimeter across the battery when the engine is stopped and when running?

Bob in Oz
 
Other than your gauge moving about how's the rest of the electrics?

Does it start and run well enough?

If it does then I'd ignore the needle movement on the gauge. :wink:
 
Electrical system is not charging as well as can be expected by looking at my volt meter. Battery was charged, engine off and load tester applied. Battery passes test. Ammeter not working picked one up today and will install. Problem is it"s for a 12V system. Think it will still work? Previous posts on charging systems have stated that cleaning the brushes etc in the generator have proven successful. I will try this approach and get back with results. Thanks
 
Thanks Bob, Yup I checked the voltage with engine off and get a reading of 6.5volts. With engine on the needle on my volt meter swings wildly back and forth. Am I correct in my understanding that you can only measure the generator at the battery and not via the F and A posts on the generator?
 
An amp meter is sensing current, not voltage. In principal it should not care what the voltage is.

Looking at the Ferguson TEA20 12 volt wiring diagram I'm not sure what you would be reading across the F and A terminals? It looks like the voltage between terminal A and earth will read battery voltage. You could try reading the voltage across the armature terminal (or D terminal at the regulator) and earth as it looks like that should read the generator output voltage? I'm not too flash on voltage regulators, although don't overlook the fact that even a new regulator could be faulty! :cry:

You should be getting a smoothed DC charging voltage at the battery with the engine running. If you're not it can only be a bad connection (which I doubt in your case due to the regular fluctuations), regulator or generator. If you have a new regulator I'd suggest you have the generator tested by an auto electrician. Provided the field coils are OK, generators are fairly cheap to overhaul, bushes, brushes and a commutator clean.

Sorry I can't give you better advice.

Bob in Oz
'53 TEA20
 
That can only come from a bad connection. Battery voltage can't change rapidly with a decent connection and battery. Battery voltage by nature changes slowly.

So start by cleaning the battery connections and then sharpen the volt meter prods so they can penetrate oxides and the voltage seen should stabilize.

It is possible for all the plates to break off inside a cell, then the battery won't deliver power or take a charge.

Gerald J.
 
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