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Discussion Starter #1
I just got done converting my '68 142 from a generator to alternator using Ron's bracket/kit. The car starts up and is charging fine although it seems a bit high to me, anywhere from ~14.8 - 15.3 from idle to revving. Is that still an acceptable range or do I have an issue? The alternator has an internal voltage regulator.

Thanks
 

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c;

Over 15V is on the high side and getting onto overcharging of the Battery range...I suggest you check the chassis connections of the Alternator (it gets its chassis connections through the paint-free areas on the bracket, connected to paintfree areas on engine, and also the engine to chassis strap, and finally the chassis to Battery Strap), any poor chassis connection in-line with the internal VReg can result in a voltage drop (which gets added to its internal reference), resulting in a higher ref V than it should be, with your symptoms. Also have the state of Battery checked...an open (or high resistance cell) might allow buss V to soar also... If your Battery checks OK and you assure all low-side connections (external to Alt) are shiny, clean and tight, and you still see these voltages, I would have the Alt itself (did you get one of the recommended Delco rebuilt quality units, or a $40 Pep Pills Boys special?), checked by a qualified automotive electrical shop.

Please let us know what you find, so that any newly learned items can be fed back into the documentation.

Cheers
 

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Discussion Starter #3
Ok will take a look, thanks! The alternator was rebuilt and around $75 so hopefully its decent.

Wish I had tested the voltage before frying the generator, that would help narrow things down. Only had this car a few weeks though and didn't think to do it.
 

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Is it a single wire alternator, alternator with an integrated voltage regulator or ancient external regulator alternator?

If it is a single wire alternator or internal regulator alternator, the voltage regulator normally takes its voltage reference between the alternator frame and effectively the B+ terminal. Measure the voltage between the B+ terminal and the alternator case to determine true alternator output voltage. On this type of alternator a bad connection between the alternator frame and the engine block would typically drop the voltage as measured at the battery because the resistance is outside of the regulator measuring circuit. However, alternators with internal regulators typically have the regulator / brush assembly screwed into the back of the alternator and the ground reference for the regulator is typically through those screw connections. A bad electrical grounding connection between the regulator body and the frame of the alternator will, as Ron correctly points out, give you high output voltage.

If you have an alternator with an external regulator, bad electrical connections can cause voltage control problems of both kinds.

Depending on your alternator style, definitely check the grounding of the alternator and the regulator. If your alternator is hitting 15.3 volts, depending on the alternator model that might be approaching the full field saturation voltage of the alternator. That would be a sign of an internal short in the alternator or the voltage regulator (or really bad grounding for the regulator).

Are you using a multimeter to measure the voltage? Does it read accurately? A simple test would be to measure the car battery voltage with the engine switched off. If it is around 12.2 volts then the meter is probably accurate enough for these measurements.

15.3 volts will shorten the life of your battery. Don't be driving the car around with this problem.
 

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Discussion Starter #5
I checked the grounds from the battery and reinstalled the alternator but still get 15.3 charging and low 13s at the battery when the car is off.

It’s an alternator with an internal regulator and ill check the voltage output at the alternator. I’ve been sorting out the suspension so haven’t been driving.
 

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If all external connections have been checked and high output voltage remains, it's time to suspect the Alt and its VReg.

Good Hunting!
 

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I checked the grounds from the battery and reinstalled the alternator but still get 15.3 charging and low 13s at the battery when the car is off.

It’s an alternator with an internal regulator and ill check the voltage output at the alternator. I’ve been sorting out the suspension so haven’t been driving.
With the engine turned off, if you are measuring voltages in the 'low 13s' at the battery terminals your voltmeter may be out to lunch. The nominal cell voltage on a lead-acid cell is around 2.2 volts / cell so for a 6 cell battery about 12.6 - 12.7 volts after the battery has been sitting for a number of hours without the engine running would be indicative of full charge. If 'low 13s' is significantly above 13.0 volts then you voltmeter might be in error giving you high readings. An older fully charged battery that has been sitting for a number of hours probably should read closer to 12.6 volts.

If the voltmeter is accurate and you are measuring 15.3 volts between the alternator B+ terminal and the voltage regulator mounting screws on the frame of the alternator. If that voltage is 15.3 volts, then the voltage regulator is likely out of spec.

Edit - corrected cell voltage reference
 

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142g has a point which i didn't mention...right after turning motor (and Chg Sys) off, Batt will read high (see "surface charge" at link, but this is unlikely if voltage readings are accurate and Batt has been being overcharged) but if after settling down for 24hrs, it still reads that, I would agree with him that accuracy of your meter is suspect. I'd double-check it against another meter...

See also: https://batteryuniversity.com/learn/article/water_loss_acid_stratification_and_surface_charge

Cheers
 

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Discussion Starter #9
Are you using a multimeter to measure the voltage? Does it read accurately? A simple test would be to measure the car battery voltage with the engine switched off. If it is around 12.2 volts then the meter is probably accurate enough for these measurements.
Good call, I've just been using this cheap Harbor Freight multimeter I keep with my tools, dug out my Klein Multimeter and its almost 1v lower. Never had something like this happen, in my experience multimeters either work fine or don't work at all.

So looks like Im all good, thanks for all the replies though, glad it was just something dumb like this

 
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