Odd Charging Conundrum

[kevman65]

Let me start by saying, got the big red A on the dash this morning. Scrolled to messages and saw "Service Auto Stop Start" I don't use it, turned off with Tazer.

But I remembered reading about aux battery being the cause of this so I scroll to "Battery Voltage" and watch the volts.

I know something is amiss as at full interstate speed it reads 12.8, now comes the odd part, while coasting or braking it goes to 13.5-14.0 and once back into throttle 12.8 again.

This afternoon coming home from work, big red A is gone, but the charging oddity continues. Under throttle 12.8 and coasting or braking 13.5-14.0. Also, when braking to a stop, it holds at the high number and once stopped it drops to 12.8 again.

WTF is going on? Bueller, Bueller

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[Darkamek]

If the batteries are fully charged the alternator doesn’t charge. But when you come to a stop or coast the alternator charges, which is completely normal. Both my Gladiators do this.

 

[kevman65]

If the batteries are fully charged the alternator doesn’t charge. But when you come to a stop or coast the alternator charges, which is completely normal. Both my Gladiators do this.

Thanks. I'm used to the old school volt meter that showed alternator output and couldn't get that out of my head. Kept thinking under throttle it should be higher and under braking or coasting it should go down.

 

[ShadowsPapa]

Mine doesn't depend on "coasting" - driving along I70 at 80 mph it was sitting at 12.7 then after slowing down the system voltage went up. I figured it was because the fans weren't needed at speed so it stopped charging, then when we slowed down or went into a town, the voltage went up.
Mine has always followed that pattern - I've seen voltages well over 14 while driving around our area then at high speeds, the voltage drops to 12.x.
Makes a lot of sense since it needs to keep the fans running to keep it cool - but on the highway fans have little or no effect.
Those who have converted older cars to electric fans have noted this as well - the force of air coming in at highway speeds outdoes what a fan could supply so the fans don't run.

These are more load-sensing or load dependent and not voltage regulated like the old days where you regulated the output to 13.8-14.2 regardless. If it's running, that's the regulated voltage (depending on car, battery type, etc.)

Here's my chart on AMC carts over the years. The higher voltages are because the isolation diode used dropped output voltage by about 1.0 volts. So any regulator with the R2 model designation would actually result in an output of 1 volt less than that shown.

R2AM1 - 15.2​	15.2​	​
R2AM2 - 14.8​	14.8​	​
R2AM4 - 14.8​	14.8​	1969-1970​
8RB2005 - 14.0​	14.0​	1971-1972​
8RH2003 - 14.2​	14.2​	1973​

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