Alternator Problem

[frank55a]

I have a Nu-Rex 6 volt positive ground alternator that I purchased about 7 years ago. It has given me great service, however lately it seems to be acting up.Starting this year it has always been charging.About 6 weeks ago I went for a 65 mile drive and about the first 20 miles it was pegged high, then it slowly dropped off to about 15 amps and the rest of the drive the charging rate remained 12-15 amps.I have had it out several times since then and the charging rate remains about 12 amps.

A couple of notes: 1) I have not made any changes to the electrical system; 2) All connections seem tight; 3) Apparently there are no grounds as the battery seems fully charged, the starter seems to spin at normal speed and the A starts right off.

Anyone ever have a similar problem? If so, what was the fix? Are there any tests I can run on the alternator? Any suggestions?

[Tom Wesenberg]

How old is the battery, and have you checked it for condition?

I'd say you have a regulator problem because the ammeter should never have to go more than 10 or so, and within a few minutes (when the battery is fully charged) the ammeter should be just barely to the right of 0.
12 amps will cook your battery. I've seen more than a few one wire alternators fail and charge too high.

[tbirdtbird]

Ditto Tom's first sentence
I would be suspicious of a battery failing. It should be load tested

[frank55a]

The battery is about 3 years old. As I said the starter seems to spin normally, but the load test is a good idea and will have that done tomorrow.

[Tom Wesenberg]

I spent most of today working on a guy's Model A.
He said his battery was about 5 years old. Well, times flies........doesn't it?
The battery was 11 years old, and the new battery took care of the starting problem.

I also had to fix the headlight wiring. Had it been left original I could have fixed it in less than an hour, but he had some cobbled up mess inside the buckets, and it took much longer to fix, but at least he now has lights again.

[Mike V. Florida]

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Assuming the ammeter is good and goes back to zero when the car is off;

The ammeter shows what the system is using. You say "..the charging rate remained 12-15 amps". That tells us that the alternator is putting out something so the alternator is not dead. Have you checked the voltage out of the alternator with the engine running at a high idle? I think the max it should be is 7.7 volts. If you are getting more then that the problem is the internal regulator in the alt.

If the voltage reading is not over that, then something is drawing the current out of the alt. In most cases it is the battery when the current is in the 12 amp range as you state.

[frank55a]

Thanks for the ideas. Contacted Bob Gay from Nu-Rex he pointed me to 3 simple tests that are on their web site, all had the proper results. He also suggested to check the battery with a hydrometer (had a cheap one with the 4 balls), the 2 end cells were only charged to 75% while the center cell was 100%. Pulled the battery and had it load tested, was told it passed but was on the verge of failing so replaced it. Started the A with the new battery 1st time pegged then slowly dropped off to about 15 amps in about 15 minutes. Put it on a small charger for about 1 1/2 hours, started and pegged high then started dropping off within about a minute to 12 amps and after about 10 minutes was down to 8 amps. Put it back on the charger for about 2 1/2 hours started and pegged high then started dropping off within about a minute to 8 amps and after about 10 minutes was down to 4 amps.

According to the battery shop the battery had not failed yet but was on the verge and apparently would hold enough charge to appear good but not a full charge.

I am sure the battery was the problem.

[tbirdtbird]

exactly