Charging problem

[dasein668]

Ok, so I've been noticing a persistant under-charging issue with my set-up this season. It seemed to work fine last year, so I know the basic system design isn't causing the problem, but rather I suspect some sort of alternator issue.

I've got a standard-issue Yanmar 55 amp (I think!) alternator, internally regulated.

Yesterday I got to the boat and found that the house bank voltage was 12.01 volts, starting battery only slightly higher.

I fired up the engine and found that with the alternator running, the voltage across house battery one was only 13.7 volts rather than the expected 14.2 or so volts. This, even when I spun the engine up to 2400 rpm. Voltage at the second house battery was 13.4. I tested postive side and ground-side voltage drop between the batteries and alternator, and found the ground-side differential to be .09 volts. The postive-side showed .05 volt drop for battery one, and .3 volts for battery two (account, I suppose, for the difference in battery voltage shown during charging!)

I ran the engine for about an hour. After shutting down and letting the batteries rest for 30 minutes, I showed an at-rest no-load voltage of 12.35, which still seems pretty low.

I'm most concerned about the charging voltage, which seems too low, right? Should I suspect a bad alternator? Bad regulator (which amounts to pretty much the same thing, with an internal regulator, right?)? Or something else?

[Figment]

Thinking of the stupid stuff first....
Might you have a drain somewhere?

I gather that you don't usually arrive at the boat to find the batteries at 12.01v, but rather closer to 12.5 or so, right? what's drawing juice while you're away? Might something also be drawing while you're charging?

(this from the guy who checked on the boat tuesday to find the battery stone-dead because he'd left the ignition circuit on when he left the boat sunday)

Nope. Nothing more productive to offer. sorry!

[westsail42]

How old are the batteries? Is there a chance there is sulfation? Have they been equalized periodically?

I just recently had a similar issue with my house bank. After running the engine, they would not seem to "top up". This last trip we had a long day of motoring, so I ran three successive equalization cycles (the boat has a Balmar alternator and Max Charge regulator). At 14.9, 15.1 and 15.2 volts for about 90 minutes. We had not equalized the batteries for some time. This seemed to help quite a bit.

Your standard Yanmar alternator is pretty much an automotive alternator (we have one too, the Balmar replaced it). With a constant "fixed" voltage probably around 14.7, 14.8 volts. If your battery voltage is low enough, it will "bring down" the voltage that is measured across the terminals when the engine is running. This would account for the 13.7 volts.

I would guess your alternator and regulator are fine. It is probably a Hitachi, which are pretty robust alternators.

Do you have an AC battery charger installed? Does it have an equalization feature? If so try running that a few times to get rid of any sulfation (at least reduce it). Keep an eye on electrolyte levels between equalizations and top up if needed.

These are flooded cells I assume.

One more thing. What does the hydrometer say about the charge of the batteries? If it is "green", properly charged, and you ware only getting 12.01 volts at rest, then your batteries might be toast. Been there too.

$.02

[dasein668]

Ok, good info, thanks.

Figment, I don't suspect anything of drawing down the charge?I haven't changed anything over last season's set-up, and I didn't have this problem, though I will give it a solid look-see tomorrow. I think, more likely, I just haven't put much juice back into the batteries. I haven't motored much this season. Still, I don't usually have an issue even if I go for a month or more without running the engine. Hmm.

westsail42: I confess that I've never run an equalization on the batteries. I don't have an AC charger on board, and my charger at home is not equipped for an equalization cycle. And with the internally regulated single-stage alternator, obviously... I do keep the electolytes topped up, however I haven't tested with a hydrometer in two seasons. It broke in a box over winter and I haven't, cough cough, replaced it yet.

The house bank (2 x 100AH Trojan deep-cycle lead-acids) is now coming up on 5 years old. The starting battery (automotive Group 57, 520 CCA lead-acid) is now on it's third season.

Your standard Yanmar alternator is pretty much an automotive alternator (we have one too, the Balmar replaced it). With a constant "fixed" voltage probably around 14.7, 14.8 volts. If your battery voltage is low enough, it will "bring down" the voltage that is measured across the terminals when the engine is running. This would account for the 13.7 volts.

Well that's interesting about the voltage. Puts my mind at rest a bit.

I suppose I might have overreacted to the low batteries. Maybe I ought to give it a little bit more engine time and see how it goes. Failing that, I guess I'll haul the things off the boat and try to equalize 'em before the cruise.

[dkall]

Five years is getting up there for them there batteries. Picked up from the Rolls people that when your charging them don't fill the water up only a hair above the plates, charging add the water back. Not good to fill it up higer and have it boil off.

Now I have AGM's and don't need to worry about water. Hope I'm happier.

[westsail42]

Not sure if this is your situation, but suffice it to say that keeping them on a "trickle charge", especially over the winter, will not preserve the batteries. They will eventually go bad prematurely. They should be "discharged" (not completely) and/or equalized periodically (ideally once a month).

I have had numerous motorcycle bateries on "trickle charge" over the winter (s), voltages measuring perfect, only to find "click"... it wont turn over.

Boats are no different...

Flooded cells of course ;-)