Proper Charging Voltage

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Mar 19, 2010 | 04:04 PM

jfoltz

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Proper Charging Voltage

All,

I recently replaced the alternator and voltage regulator in my '86 F-150 with the 300. The battery wasn't charging and finally let me sit until someone could jump me. Now, 2 months later, it's acting the same. Last Tuesday, it wouldn't start after a 20 or so mile trip. I had it jumped and it made the trip back home without any problems. Today, several days later, I went to start it and it wouldn't start. Both times it wouldn't restart, the battery voltage was reading about 11.56 or so.

So my question is this: what should my meter be reading when the truck is running? I think currently (after the alternator/regulator swap) it reads about 12.5 or 12.7 Volts. Do you think that the battery is bad after too many jumps or do you think my charging system is not doing it's job?

Thanks!

Mar 19, 2010 | 04:27 PM

rustybaker

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Shoud be reading at least 14.2.. Alternator isn't charging right.

Mar 19, 2010 | 04:57 PM

jfoltz

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ok, thanks. I'm going to replace the belt since I don't know how old it is and i know it's been squealing. Is it safe to assume that if the belt is slipping and causing the alternator pulley to turn slower than normal that the alternator wouldn't be putting out the proper voltage?

Mar 19, 2010 | 05:49 PM

Shark Racer

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Where are you taking the reading at? Positive post of alt to ground or across the battery terminals?

You should get readings at both places. If it's the same at both, the alternator is bad.

I don't think it's the belt in this case, but it'd be wise to replace it anyhow.

Mar 19, 2010 | 07:41 PM

TheKirbyMan

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From: Mexia, TX

FWIW, with my truck running, I get a higher reading through an ignition-hot circuit I have my Autometer voltmeter on (a bit over 14) than I get when I check the voltage at the battery posts (13.7). Everything works fine and the battery is charged.

Mar 19, 2010 | 11:37 PM

jfoltz

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I was getting the reading from the positive and negative terminals on the battery. I didn't think to try positive to a ground.

Mar 20, 2010 | 12:05 PM

86bigred

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From: patricia ab canada

if you get different readings between the ault and batt,i would clean up ALL connections.positive and negative,you should have close to the same voltages from the batt and the output at the ault.dirty connections create resistance and heat and can cause havoc on electrical systems.most problems are due to dirty or bad grounds.imo