Alternator or switch?

[Toddavid]

2014 Chaparral with 380-C-D V8.

2 batteries, less than 2 years old.

Last season, I noticed my voltage would sometimes ride in the high 12v range. Never had a dead battery, always cranked strong.

I know the alternator from this era is supposed to be a “smart“ one, where charging output is regulated to what the battery array needs, not just fixed output like older design, so I assumed my batteries just were nice and strong.

Yesterday on my ride back to the marina, charging voltage was hanging out at 12.5v for quite a while. That was a red flag. Every once in a while it would pop up to 13.3v for a few seconds and then drop down to 12.5v again.

Once back at the marina, I decided to turn the cut-off switch to the other battery and restart the engine to watch voltage. 13.5v, holding steady. Hmm. Turn off engine, switch back to the other battery, restart engine, now 13.5v and holding steady, unlike before.

So is this an alternator or a switch issue? Switch is only a couple years old, alternator is original. 490hrs.

Thanks.

 

[airshot]

Using a digital voltmeter, what us your battery voltage after resting for a couple hours ?? Can't test if recently charged. You might need to get a load test on your batteries, usually free at most auto parts stores. Unfortunately I have saw some new batteries go bad quickly...

 

[Scott Danforth]

a 12 volt battery is dead at 12 volts, fully charged at 12.7. alternators charge between 13.4 and 14 volts. I think your $1 air core dash gauge is off.

 

[Toddavid]

Using a digital voltmeter, what us your battery voltage after resting for a couple hours ?? Can't test if recently charged. You might need to get a load test on your batteries, usually free at most auto parts stores. Unfortunately I have saw some new batteries go bad quickly...

I have a load tester, and both batteries test fine.

 

[Toddavid]

a 12 volt battery is dead at 12 volts, fully charged at 12.7. alternators charge between 13.4 and 14 volts. I think your $1 air core dash gauge is off.

I am reading this voltage via a scan tool and also via the on board digital display (they correlate).

 

[dubs283]

There's nothing "smart" about newer engine alternators. They work the same as older style regulator controlled alternators. The only caveat is a lot of manufacturers are installing on/off/emergency start only battery switches with an acr used to control/isolate house battery charging but that system has nothing to do with the alternator itself

The alternator's regulator has a sense circuit that compares battery voltage (static) to charge voltage and compensates (regulates) the output back to the battery. Most alternators are regulated to 14.5-14.8 max so anything higher than that with known good batteries is bad. Decent output for a sound battery/charging system is +/- 13.5 volts continuous at 1000 engine rpm and above. Below 1000 rpm one may see less than 13.5 but should but should be above static battery voltage

Seems like you've troubleshot thoroughly and the conclusion is faulty wiring/connections or a failing regulator.

 

[Toddavid]

There's nothing "smart" about newer engine alternators. They work the same as older style regulator controlled alternators. The only caveat is a lot of manufacturers are installing on/off/emergency start only battery switches with an acr used to control/isolate house battery charging but that system has nothing to do with the alternator itself

The alternator's regulator has a sense circuit that compares battery voltage (static) to charge voltage and compensates (regulates) the output back to the battery. Most alternators are regulated to 14.5-14.8 max so anything higher than that with known good batteries is bad. Decent output for a sound battery/charging system is +/- 13.5 volts continuous at 1000 engine rpm and above. Below 1000 rpm one may see less than 13.5 but should but should be above static battery voltage

Seems like you've troubleshot thoroughly and the conclusion is faulty wiring/connections or a failing regulator.

Ok, thanks for this explanation.

It’s behaving as if it has a faulty exciter circuit, which on an “old school” alternator would be via the alternator dash light.

How is the exciter circuitry handled on newer alternators?

 

[Scott Danforth]

How is the exciter circuitry handled on newer alternators?

By a 12 volt reference signal from the key switch to the excite terminal. In a car, this is controlled by the BCM

Dash light is the terminal next to the excite terminal

 

[bruceb58]

You need to measure the voltage AT the battery to verify what you are seeing elsewhere.

 

[Fun Times]

2014 Chaparral with 380-C-D V8.
Switch is only a couple years old, alternator is original. 490hrs.

Why was the battery switch changed from I'll assume new?
Seems time to pull the switch and inspect all sides of the switch, cable connections, wire crimps, wiggle and measure voltage all the while inspecting.
Yours wouldn't be the first switch to go bad internally or externally.

 

[tpenfield]

When the condition exists, Check the voltage at the battery, and if you can, the voltage across the switch.

The switch contact may have become slightly corroded and operating the switch 'cleaned' the contacts. See if the condition re-occurs and then check the voltages.

 

[dingbat]

Sounds weird, but take a look at the starter circuit

Had the exact same thing happening in my truck last year. Really weird things happening from a voltage perspective. Charge, low charge, no charge. Start, no start.

It wasn’t until I learned the ECM stores a charge profile for that particular battery that things started to make sense. Reset the ECM per factory instructions. Returned the full voltage charge but it cycled high/low rather quickly, pointing to a battery problem or a fairly large parasitic load. Hum…..

Battery was 4 yro so changed it to be safe. Same thing…crawled under truck and found a good bit of corrosion in the starter. New starter and things went back to normal.

 

[Toddavid]

Why was the battery switch changed from I'll assume new?
Seems time to pull the switch and inspect all sides of the switch, cable connections, wire crimps, wiggle and measure voltage all the while inspecting.
Yours wouldn't be the first switch to go bad internally or externally.

Typical failure. Went to turn it one day, and it broke apart in my hand. I even carry a spare with me now.

 

[Toddavid]

Sounds weird, but take a look at the starter circuit

Had the exact same thing happening in my truck last year. Really weird things happening from a voltage perspective. Charge, low charge, no charge. Start, no start.

It wasn’t until I learned the ECM stores a charge profile for that particular battery that things started to make sense. Reset the ECM per factory instructions. Returned the full voltage charge but it cycled high/low rather quickly, pointing to a battery problem or a fairly large parasitic load. Hum…..

Battery was 4 yro so changed it to be safe. Same thing…crawled under truck and found a good bit of corrosion in the starter. New starter and things went back to normal.

Considering how buried the starter is in my engine bay, that might be a challenge. Time to break out the endoscope…

 

[Toddavid]

When the condition exists, Check the voltage at the battery, and if you can, the voltage across the switch.

The switch contact may have become slightly corroded and operating the switch 'cleaned' the contacts. See if the condition re-occurs and then check the voltages.

Yeah, the correlation with the switch turn was interesting. But it never cut power all the way when voltage was dropping, so it was more of not understanding how the exciter circuitry worked on a more modern boat. Does the 12v reference signal to the alternator run through the switch? I’m thinking it doesn’t?

 

[Toddavid]

So it seems that it was neither.
After having the problem resurface next time out, I decided to start taking things apart and ohming things out.
Everything was tight and conductive until I got to the auxiliary ground strap on the alternator body. It was just barely loose.
I cleaned it and tightened it, restarted engine, and charging voltage jumped back up to 13.8v.
Three times out since then and all has been well.