Alternator Voltage

[Gary F.]

Replaced my battery yesterday and had the alternator tested. The tech. said the volatage was low, it was putting out 13.4 volts at idle. He said it should be putting out 13.8 volts. I turned on the headlights on high beam and turned the ac on high. The voltage dropped to 13.25. Is the within normal range? The mb is 85 300D






Whom the gods will destroy, they first make proud.

[lrg]

It sounds like it's within acceptable limits to me. I'm not surprised that the voltage dropped a bit under heavy load at (I assume) idle. What happens when you rev it a bit with all the power stuff on? If the volts go back up I'd not worry about it. Also, be aware that these most frequently fail because of worn out brushes and the brushes themselves can be changed (a little tricky) or you can replace the whole voltage regulator/brush assembly (easy but costs more). My guess is that you don't need to run out and buy a new alt. just yet.

A few years ago I took an old Dodge into one of the small starter/alternator shops to have them run a 'free' check on the electrical system.
The fine young fellow there showed me how the alternator needed a replacement because the voltage under a load showed only 13.4 volts. So I asked him just how many cars do you test and find have 13.8 volts. He thought about it and said. Maybe one of two a week.
I decided it didn't need an alternator yet. I later cleaned the connections on the rear of the alternator and the voltage with the same test came up to about 13.6 v.
Now you don't suppose this was...? No, I didn't either.

I think Old Deis hit this one right on the nose. There is nothing to worry about when an alternator is making 13.4. It's when it shows no voltage increase when the engine is started that you should worry.

I expect this guy was trying to sell you an alternator. When it stops charging the battery, it will be time to worry about it, and even then, most likely replacing the $14 voltage regulator/brush unit will fix it.

Good luck,

[PaulH]

Gary, why not buy the Voltage Reg./Brush set now and keep it in your trunk and you'll have it when you need it at a cheap price. $14 is cheap insurance.