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Alternator charging voltage?

SJ073

Well-Known Member
#1
My old 105 amp alternator wasn't cutting it in my race car and after about 200 miles with all lights and fans on, I could see battery voltage dropping down around 11.1 volts. It seems like once we hit 10.9 or 10.8 volts, the electrical system starts to 'self correct' and things start to shut off.

So.....I installed a 170 amp alternator and now voltage and charging is great. Maybe too good. At idle with everything on (LEDs, 5 fans, radio, GPS, engine, fuel pumps etc) we are putting out around 14.4-14.9 volts at idle. Am sure at higher RPMs it's even more.

Question is - how much is too much voltage before we start roasting batteries, components, etc?
 

az_amsoil

Well-Known Member
#2
Your voltage regulator should cutout at ~14.5V...if you do spike over that, there is an issue with the regulator,. The way it works is the regulator controls the current to the rotor of the alternator, if the battery is health (good charge or ~14.5V), then the regulator will stop applying voltage to the field and the alternator will stop charging...however, once the battery drops below ~13.5V, the regulator applies a current to the field and the alternator will start charging. Basically, if the battery is weak, then the electromagnetic force (voltage) from the battery cannot hold off the current from the alternator and it charges...As the battery reaches full charge, the electromagnetic force becomes strong enough to oppose the current flow from the alternator, the amperage output from the alternator will drop to close to 0, while the voltage will remain at 13.5V to 14.5V. As you turn on more accessories, the load increases on the battery, thus lowering the electromagnetic force and start the flow of current from the alternator to the battery.

If your regulator is working properly, even though at full load you don't see a voltage drop, as you rev the motor, the voltage should not go much above 14.5V for very long.
 

SJ073

Well-Known Member
#4
Thanks for the responses guys, I have checked when the engine was running for less than 5 minutes too so lack of heat may play a factor too.
 

Chris Tobin

Well-Known Member
#5
Thanks for the responses guys, I have checked when the engine was running for less than 5 minutes too so lack of heat may play a factor too.
Also directly after starting the alternator is recharging the battery from starting so it may charge a little hotter/harder... If voltage is much higher than 14.5 V it can cause issues with not only your batteries, but also your electronics like your GPS, radio and so on...

Typically a charging system should top out at 14.4 V.
 
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