Charging System Fluctuates

[Fred Mc]

Last fall, after the voltage regulator failed I got a replacement circuit board from Luke for my GM PD4106(12v)

Now, the alternator appears to be charging intermittently(like it switches  every second or two) So it goes from battery voltage of 13.5 to 15v or so.If you turn on the headlights you can see the lights alternately go bright then dimmer every second or so.

Any suggestions on what to look for.

Thx
Fred

[chessie4905]

Is this at idle or at speed? With an electrical load? Still does it with blowers on? Are batteries fully charged? Make sure connections at batterys are clean and tight. Same at Alternator.

[buswarrior]

Yup, x2, confirm the batteries are sound.

Cheap load tester is a busnut's good friend, multimeter is not the tool for deciding if batteries are sound.

Happy coaching!
Buswarrior

[PNWorBUST72]

Whats a decent load tester on a budget?

[bobofthenorth]

+1 on checking the connections, particularly anything you touched while changing the regulator.  And don't neglect the grounds - in fact my money would be on a bad ground.

[TomC]

My alternator does that too-even with new digital regulator, new batteries, etc.

[chessie4905]

A decent load tester on a budget is the underfloor blower motors. Those suckers can load the system quite well.

[buswarrior]

Old school automotive tester.

Amazon for example:  $32 https://www.amazon.com/dp/B015EEWURW?ref_=Oct_CARAsinC_15707371_3

Never guess whether a battery is good or not again.

Not suitable for Nasa grade OCD, but good enough for a "normal" busnut?

Happy coaching!
Buswarrior

[eagle19952]

Old school automotive tester.

Amazon for example:  $32 https://www.amazon.com/dp/B015EEWURW?ref_=Oct_CARAsinC_15707371_3

Never guess whether a battery is good or not again.

Not suitable for Nasa grade OCD, but good enough for a "normal" busnut?

Happy coaching!
Buswarrior

[chessie4905]

That works good for car batteries, but you need more of a load than that can produce. Here is some info on other items that will work you may already have.

https://www.homepower.com/articles/solar-electricity/equipment-products/load-testing-batteries-without-load-tester

[eagle19952]

it isn't the load, it's the duration of the load that matters.

you can hold the load longer than the suggested.
and get an answer that will tell the tale.
i seriously doubt that the blower motors draw 100 amps running.

[HB of CJ]

Low possibility, but might it be a continuously tripping and immediately resetting automatic resetting circuit breaker?  Headlights or tail lights comes to mind.   You may or may not hear it during driving depending where it physically is.

[chessie4905]

Blower motors, defroster motors and headlights all on will get the job done, while you check the voltage at batteries. Done with automobiles for years. Now they use electronic testers to check condition of batteries.

[Fred Mc]

"Low possibility, but might it be a continuously tripping and immediately resetting automatic resetting circuit breaker?  Headlights or tail lights comes to mind.   You may or may not hear it during driving depending where it physically is."
It may well have always been like that and I never noticed it before. I think Tom C mentioned that his bus does the same thing. I recently added a voltmeter to my dash and that is where I first noticed the fluctuation. And because the bus is undercover I could see the effect on the headlights. I almost NEVER drive at night so wouldn't have noticed that.

[chessie4905]

A constantly resetting circuit breaker can be detected with an ir gun, another reason to have one of these babies. Btw, on sale at HF now, $17.99.