alternator check

[randy41]

the idiot light stays on indicating that my battery is not charging. this is a ford 1710. well i don't really need the battery 'cept for starting and gauges. but its been like this for a few days now but the light doesn't get dimmer and i have no trouble starting so i suspect that the light is misinforming me. is there some easy way to see if the battery is really charging when the tractor is running?

 

[swampvol]

Check it with a multi meter.
I think you should get ~14-15 volts while idling.

 

[Patches]

Check your battery voltage with a multi-meter before you start the tractor; should be 12 volts or a little more, then check it again while the machine is running; should be around 14+/- volts. If your voltage is still in the 12 volt range your alternator is done, unless of course you have an external voltage regulator which could also cause the problem

 

[randy41]

yes there is an external voltage regulator. i have a repair manuel and it tells how to check it out but it requires the use of some kind of load device that i don't have. but i do have a multimeter. according to the book the alternator puts out 5 volts or so at low engine speed and 14(?) at high speed. just looking for an easy way to check it. I will try checking the voltage at the battery while the engine is running at higher rpm's.
i just thought that if i was heating the plugs and then starting and then running the tractor for 45 minutes to an hour that that light would start to get pretty dim (like my brain) after a while.
i think i would be happy if i could just get it cranking without the starter and then i wouldn't need any electricity on it at all.

 

[Treemonkey1000]

It's not an alternator if it is putting out 5 volts at low rpms. The nice thing about alternators is they put out around 14 volts at all speeds. Like the other guys said if you have a voltmeter (DC) then test the battery post with the tractor off and started. Or if you have a hygrometer and can get to the battery cells check them.

 

[RickB]

Using a hygrometer to test an alternator is like trying to use a tire gauge to check engine compression. Use the VOM at the battery with the engine off; then engine on. Doesn't get much easier than that.

 

[randy41]

thanks Rick and others. i will do that.

 

[RonMar]

Actually a hygrometer isn't a bad idea, to check the state of charge of each of the 6 cells in the battery. I have seen bad batteries mis-diagnosed as alternator problems. I have also seen bad batteries mis diagnosed as a battery that was not charged, when in fact it had a bad cell and would not take a charge.

As mentioned, you should have in the mid 12V range(12.8 is typical for a battery with a reasonable charge) on the battery setting there before startup. If it is below 12V then that may be an indication of a battery going bad(cells not charging), or one that is not being charged because of a bad alternator.

When running, and charging properly, the battery voltage should be at 14.5VDC +/- 0.5 VDC. If it is low, it could be one of 3 things.
1. The alternator is bad and cannot produce the rated output voltage.
2. The regulator is bad, and cannot tell the alternator to produce the rated voltage.
3. The battery is bad, such as with a shorted cell, and is absorbing more energy than the alternator can output.

It is a system, and these 3 parts interact with each other. One way to eliminate a battery issue is to charge the battery using an external plug-in charger, or swap it out with a known good battery from another vehicle.

If you have a known good charged battery in there, and you are not getting your 14.5V at higher RPM, then you have an alt or reg problem.

Your manual saying it only makes 5V at lower RPM, leads me to believe that you have a generator and not an alternator. Alternators usually are capable of making rated voltage, even at lower RPM, but they cannot put out as much current at lower RPM.

Good Luck

 

[RickB]

Actually a hygrometer isn't a bad idea, to check the state of charge of each of the 6 cells in the battery. I have seen bad batteries mis-diagnosed as alternator problems. I have also seen bad batteries mis diagnosed as a battery that was not charged, when in fact it had a bad cell and would not take a charge.

As mentioned, you should have in the mid 12V range(12.8 is typical for a battery with a reasonable charge) on the battery setting there before startup. If it is below 12V then that may be an indication of a battery going bad(cells not charging), or one that is not being charged because of a bad alternator.

When running, and charging properly, the battery voltage should be at 14.5VDC +/- 0.5 VDC. If it is low, it could be one of 3 things.
1. The alternator is bad and cannot produce the rated output voltage.
2. The regulator is bad, and cannot tell the alternator to produce the rated voltage.
3. The battery is bad, such as with a shorted cell, and is absorbing more energy than the alternator can output.

It is a system, and these 3 parts interact with each other. One way to eliminate a battery issue is to charge the battery using an external plug-in charger, or swap it out with a known good battery from another vehicle.

If you have a known good charged battery in there, and you are not getting your 14.5V at higher RPM, then you have an alt or reg problem.

Your manual saying it only makes 5V at lower RPM, leads me to believe that you have a generator and not an alternator. Alternators usually are capable of making rated voltage, even at lower RPM, but they cannot put out as much current at lower RPM.

Good Luck

As the tractor continues to start well, I suspect the battery is good. The issue is whether the alternator is functioning.

 

[BobRip]

If the battery starts the engine it is fine. Check the voltages like suggested above.