Question about a charging system...

[waterinthefuel]

My old tractor is showing no voltage increase on the battery terminals when running, but a deflection on the amp meter of 1-3 amps positive depending on engine speed. Is it possible to charge the battery with no increase in voltage? It's a big car battery on a small tractor so I was thinking maybe the battery is pulling down the voltage and it's not enough of a charging system to keep up.

The amp meter is acting like it should, but with no corresponding increase in voltage at the battery. From what I understand, that's not possible, but it's happening.

Anyone with more knowledge about this than me can explain whats going on?

 

[jlinder]

Re: Question about a charging system...

If you are only putting 1-3 amps into a big battery, and the battery is pretty fully charged, I doubt you would be able to see an increase in voltage unless you have a good digital meter.

The increase in voltage comes because the battery has an internal resistance. The higher the resistance (think a smaller battery) the more voltage increase you will see.

Go back to the basic formula- E=IR or Voltage = Current x Resistance. If your battery is pretty big you have a low internal resistance. For example, if it can supply 200 amps and only drop 2 volts you have an internal resistance of .01 ohms. In this case a 2 amp charge would only give a .02 volt increase. That would be tough to see.

 

[j_martin]

Re: Question about a charging system...

Depends. What's the voltage?

 

[marlboro180]

Re: Question about a charging system...

Umm, what kind of tractor? Small is kinda relative.. Alternator, generator, what is it ???

 

[dolluper]

Re: Question about a charging system...

Did you say voltage regulator anywhere...humm ...battery only charges when it guesses too...I'm inpressed

 

[waterinthefuel]

Re: Question about a charging system...

I doubt it has a voltage regulator, it's a 1974 Speedex. If I rev the engine the voltage climbs maybe a little bit, but almost 0. The battery is a regular car battery, on a little garden tractor.