Alternater 17.5volts

Anonymous-0 · Feb 15, 2011

Hi guys,

I am having some problems with charging my 12 volt. I went to the Universal 643 and it was dead. I jumped it and it of course it ran and would restart. Then I put volt meter on and it read 17.5 volts after I ran it for an hour of snow plowing. That seems high but its not my expertise at all. Turned it off, it sat a week, and dead again. It was a good new large battery. Is 17.5 telling me something?

Anonymous-0 · Feb 15, 2011

Not knowing the make, model or year of what you are trying to diagnose, I would make the following diagnosis: either a bad battery, or a bad VR, and possibly a bad diode, or 2 in the Alternator, or some combination of the above.

Janicholson · Feb 15, 2011

14.5 to 14.8 volts is commonly accepted as reasonable to keep a 12v battery charged. Your new battery is being destroyed. Make sure it has full water in each cell.
If you have an alternator (I have no way of knowing0 take it to be tested. If it is an internal regulator it needs a new one. Delco 10SI alternators with a 3 wire install (see Bob M diagrams for details) is the best answer. Do not listen to people who promote one wire alternators. Some do work, many have battery drain, and they are not the way that alternator is designed to work. Jim

buickanddeere · Feb 15, 2011

Is the meter set to AC and you are reading noise and ripple on the DC ?

bruster · Feb 15, 2011

When you get past 16V, as a rule your battery might be the cause of your problem.
While working for Roadway Express, MANY times after starting the trucks (mainly in the winter, Air start) I would have to "excite" the alternator with a touch of the cables from my batteries. If the meter was showing over16V, sure as shooting, the battery was bad. But, since it took only 15 min to switch out the alt. Big R said to do the alt. and leave the battery for later! Any mechanic knows the Quickest way to kill an alternator, is to run it trying to charge a shorted battery!

RodinNS · Feb 15, 2011

14.2 is generally considered nominal charge voltage. Some Ford/motorcraft alt's used to charge over 15 at times.
Things to check are... the basic connections at the alt and regulator. Make sure the alternator is properly grounded. If it has an external regulator you need to check all of the connections between the alt and reg to make sure they're clean and tight. If it's got an internal reg you need to determine where it takes it's 'sense' voltage from for the regulator. Again... if it was sensing from a remote location closer to the battery and NOT getting a clean sense... ie low voltage... then the reg is telling the alt to keep pushing because the battery is low... so check connections. I think that's more likely than a bad regulator simply because most I've seen go bad had some pretty wild voltages; sometimes 25+ volts. This one is just on the line...

Rod

Alternater 17.5volts

Anonymous-0

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Anonymous-0

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Janicholson

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buickanddeere

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bruster

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RodinNS

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