OT alternator

What should the minimum voltage of a 12V alternator read across the battery terminals?

If you're in the 13 - 14.5 volt range you're good.

I was told you need 13.8 to charge a battery, might depend on the battery. This would be at fast idle.

Engine not running you should get around 12.3 volts give or take a bit. Engine running you should read around 13-14 volts but if the battery is at full charge it can be less but should still be a tad bit higher then non running

Hello pat sublet,

A fully charged 12 volt battery should be 12.6 volts at 70 degrees F. Charging voltage should be 13,8 to 14.2 volts.

Guido

Battery charge is really a specific gravity of the fluid. Since an instrument is required to measure that and not readily available, much less getting one calibrated, and now with digital multimeters, we use the digital voltage.

Well, that's ok, it has worked just fine for me. I used to take a battery charger, hook it to a battery and look at the amperes to determine level of charge. DVM readings are a lot easier.

I use 12.75 year round at 800' altitude fully charged benchmark.....on a battery that has sit at least 24 hours since having any kind of charge apparatus applied....gotta let it stabilize to get a true reading. Works for me.

To replace the charge in a battery, all you have to do is to push current into it. The amount of current can vary from micro amperes to a 100 amps or so on commercial fast chargers....a no no.

To push current all you you have to do is to have a charging source voltage higher than the current battery voltage. No specific number. Higher the number, higher the charging amperes.

Gotta be careful on charging too fast as the battery will overheat and boil out the water part of the sulfuric acid/water solution. You can put your hand on the side of it and if it's hot it's charging too fast. Other indicator is bubbling. Slow bubbling is letting off hydrogen gas and normal. Fast bubbling is recharging at too high a rate and will boil out your electrolyte.

I like a 10 amp automatic charger. Schumacher makes a nice one that TSC sells. Has auto and manual functions.

On the equipment charging system, actual voltage measured with the engine running has to do with charge state of the battery, rpms of the engine, and charging mechanism type. Varies. If you get over about 14.5V suspect your regulator is malfunctioning.

HTH,
Mark