It could be that it has huge, very fast spikes on the output of the alternator. They wouldn’t do immediate damage but could do a job on the battery and possibly other electrical components over time. You wouldn’t be able to see those with a multimeter.
Unless you’re getting a LOT of AC, I don’t think this will hurt a battery. Other systems, yes, but the battery won’t care. It’s not like it’s stuffed full of sensitive electronics. I would be interested to see what the battery voltage and charge state is after a few months with the new replacement. Maybe it’d be worth measuring the temperature of the battery after driving too. I’d suspect that the battery is being over or undercharged, or cooked to death.
@Jesmed: I fail to see how that device can “protect the engine computer and 12V accessories from surges” It looks like a cheap voltmeter with a few LEDs thrown in to indicate if your voltages are way off, though it might be useful to monitor your charging voltage while driving if the vehicle doesn’t have a voltmeter on the dash.
It al depends on how high or low those spikes go, if they are there. They can exceed a battery voltage by several multiples And totally hose up how that battery is being charged. They can ring, try to drive negative for a brief period, etc. While that may be in the order of microseconds, it could take its toll over time
Who really knows what’s going on without looking at it. I wonder whether the op has had the problem properly diagnosed by now.
@oblivion, I agree that “protection” claim is dubious. But the thing is useful as a basic voltmeter that will tell you whether or not the alternator is putting out sufficient voltage.
“But assuming your car’s electronics aren’t showing any ill effects (which may be related to ripple), how can a 0.2v or a 0.3v ripple cause a battery to not charge properly - especially if the DC charging voltage is in the proper range?”
It won’t prohibit charging. What is does do is cause some premature degradation- on the order of a few percent at the lower end.
Without spending a lot of time typing, once the battery is at float charge level, those excursions are like shallow discharge cycles happening constantly. This causes internal heating and sulfation.
There’s likely to be a boatload of information out there for UPS applications but the principals also apply to lead acid service batteries in automotive applications.
The ripple will also have a deterimental effect on any electrolytic filter caps in the electronics for the same reason.
AC ripple is deadly to cars electronics or any electronics for that matter. Solid state electronics work on 5vdc levels and switching levels is how they are triggered. AC over .05vac will play havoc on a processor and its output to the system control chips.