Engine batterie dying too quickly

[stormalong]

I suggest that you re-think your whole DC electrical system for how you use the boat.

First things first. Your alternator sounds like standard automotive. It does little or nothing to put power back into your batteries. An alternator that puts out a lot of power at low rpm is needed. An automotive alternator or the stock alternator that comes with your engine is pretty useless. Calling it a 60 amp alternator is more marketing than reality. You need a hot rated, high output alternator that works at low RPM. An external regulator to get decent output from it is also needed. And the pulleys that drive it must be able to transfer the needed horsepower to the alternator.

If you are in a marina with power a good battery charger will solve your short term problem while you design your ultimate DC system. Charging two battery banks can be done in a couple of ways. If you are on a mooring the solution is different. A lot of solar and a battery combiner or ACR is a good way to be sure that both banks get charged. A combiner/ACR also works with a single output battery charger so it is a solution for both methods of charging.

Next: get rid of the off-1-both-2 battery switch. It is an old concept that does not work well. All loads, including the windlass should be on the house bank. The engine start battery is there only to start the engine and run the engine instruments when the engine is running and NOTHING ELSE. Each battery should have it's own on-off switch, a switch to join the two banks for when the start battery is dead is OK. If you do the electrical correctly you will never need that joiner switch.

Boat electrical systems are not easy. Some thought on how you use your boat and where your power comes from are essential before changing your system.

[GILow]

Originally Posted by stormalong

I suggest that you re-think your whole DC electrical system for how you use the boat.

First things first. Your alternator sounds like standard automotive. It does little or nothing to put power back into your batteries. An alternator that puts out a lot of power at low rpm is needed. An automotive alternator or the stock alternator that comes with your engine is pretty useless. Calling it a 60 amp alternator is more marketing than reality. You need a hot rated, high output alternator that works at low RPM. An external regulator to get decent output from it is also needed. And the pulleys that drive it must be able to transfer the needed horsepower to the alternator.

If you are in a marina with power a good battery charger will solve your short term problem while you design your ultimate DC system. Charging two battery banks can be done in a couple of ways. If you are on a mooring the solution is different. A lot of solar and a battery combiner or ACR is a good way to be sure that both banks get charged. A combiner/ACR also works with a single output battery charger so it is a solution for both methods of charging.

Next: get rid of the off-1-both-2 battery switch. It is an old concept that does not work well. All loads, including the windlass should be on the house bank. The engine start battery is there only to start the engine and run the engine instruments when the engine is running and NOTHING ELSE. Each battery should have it's own on-off switch, a switch to join the two banks for when the start battery is dead is OK. If you do the electrical correctly you will never need that joiner switch.

Boat electrical systems are not easy. Some thought on how you use your boat and where your power comes from are essential before changing your system.

There are some good ideas here, but I think they are a distraction from what is going on now.

The OP has an electrical leak (plus maybe a faulty alternator) to fix, THEN, sure, they can revisit their system. But what they describe as their setup now is not all that bad and can work well. It should not be seen as the cause of this problem.

[stormalong]

Originally Posted by GILow

There are some good ideas here, but I think they are a distraction from what is going on now.

The OP has an electrical leak (plus maybe a faulty alternator) to fix, THEN, sure, they can revisit their system. But what they describe as their setup now is not all that bad and can work well. It should not be seen as the cause of this problem.

.07 parasitic draw is only 12 amp hours per week. If the OP had a decent charging system - alternator, shore power or solar, and a battery combiner that would be insignificant. The OP's batteries die over a period of months, not days or weeks.

I stand by my post.

[Wotname]

@kriskro.

Please don't get distracted into redesigning your present setup - it will work just fine and serve you well once you get the existing fault(s) rectified. Yes, there are better arrangements but that doesn't mean your existing setup is in anyway contributing to the premature failing of your start battery. Thousands of boats for many decades have similar arrangements as your boat and they work OK. Maybe you will wish to improve it in the future but IMO, now is not the time!

Track down the mystery current first!
Tell us what the engine (or alternator) model is. The alternator may need fixing but we don't have enough evidence yet to be sure.

Fitting a more fancy charging system now is simply papering over the cracks.

[GILow]

Originally Posted by stormalong

.07 parasitic draw is only 12 amp hours per week. If the OP had a decent charging system - alternator, shore power or solar, and a battery combiner that would be insignificant. The OP's batteries die over a period of months, not days or weeks.

I stand by my post.

“Only 12 AH”? The average starter battery has about 80 AH capacity. 12 AH loss per week would take it below 80% in a week and below the critical 50% in a bit over three weeks.

Putting some kind of charging system in place to plug the gap without finding the cause is a high risk strategy because as soon as that charging system fails (and it will) you toast the battery. Or the leak gets worse and exceeds the stop-gap measure’s capacity to replace the lost power.

And the OP DOES have a solar charging system already and it appears to be managing the house bank without problems. At least, the OP has not stated there is a problem.

I’m not saying your ideas are wrong, some of them have merit. (Though I, personally, keep my house and engine batteries totally separate and simply carry a decent set of jumper leads for emergencies.). I am simply saying there is an underlying problem that needs to be identified and fixed FIRST.

Any other approach risks masking a significant problem that WILL, eventually, resurface.

[Compass790]

I'm with the 2 Aussies in posts #'s 32 34 & 35,
Fix the problem first

It's a worry that after 30mins running & 3 hrs sailing his start battery cannot start the motor.
So possible faults are, assuming he switched to house batteries when he started sailing:

Battery has internal short so self discharges rapidly or has so little real capacity left from being chronically undercharged that it stuffed again.

Alternator not charging sufficiently.

From experience a half hours run is plenty to get a start from a 780 cca start battery even when battery was down to 11.8 v before the engine was started. This was from a 55 amp alternator that actually only puts out 35 amps as measured by clampmeter.

If he didnt switch to house batteries it's possible ( I think) that the parasitic drain is much larger when battery switch is on start battery position.

I know Wotname knows infinitely more about electrical stuff than me so anything wrong in this post will be corrected so I don't mind posting with little theoretical knowledge.

My guess is that it's likely to have an alternator problem going thru a battery a year if he uses monthly but accept the need for more evidence.

I hate parasitic drains but if I couldnt find it I'd definitely hook up the solar to the start battery as well.

[stormalong]

Originally Posted by Wotname

@kriskro.

Please don't get distracted into redesigning your present setup - it will work just fine and serve you well once you get the existing fault(s) rectified. Yes, there are better arrangements but that doesn't mean your existing setup is in anyway contributing to the premature failing of your start battery. Thousands of boats for many decades have similar arrangements as your boat and they work OK. Maybe you will wish to improve it in the future but IMO, now is not the time!

Track down the mystery current first!
Tell us what the engine (or alternator) model is. The alternator may need fixing but we don't have enough evidence yet to be sure.

Fitting a more fancy charging system now is simply papering over the cracks.

Originally Posted by GILow

“Only 12 AH”? The average starter battery has about 80 AH capacity. 12 AH loss per week would take it below 80% in a week and below the critical 50% in a bit over three weeks.

Putting some kind of charging system in place to plug the gap without finding the cause is a high risk strategy because as soon as that charging system fails (and it will) you toast the battery. Or the leak gets worse and exceeds the stop-gap measure’s capacity to replace the lost power.

And the OP DOES have a solar charging system already and it appears to be managing the house bank without problems. At least, the OP has not stated there is a problem.

I’m not saying your ideas are wrong, some of them have merit. (Though I, personally, keep my house and engine batteries totally separate and simply carry a decent set of jumper leads for emergencies.). I am simply saying there is an underlying problem that needs to be identified and fixed FIRST.

Any other approach risks masking a significant problem that WILL, eventually, resurface.

Drawing down the engine start battery with a windlass and not putting the power back in due to a low output alternator is a bigger deal than a 12 AH per week battery drain unless the owner does not use the boat very often.

A battery combiner would immediately solve the slow power drain issue. Should the 70 ma drain be hunted down and fixed? Sure but that won't cure the problem. Getting the windlass draw off the engine start battery is more important. Getting the alternator to put more power into the battery is more important.

The OP does not say how often he uses the boat. He is putting the boat away with a partially discharged battery and letting it sit for whatever period of time that is. That is the big issue here. With a battery combiner the OP will have some trickle charge on the start battery.

[Compass790]

The OP does not say how often he uses the boat. He is putting the boat away with a partially discharged battery and letting it sit for whatever period of time that is. That is the big issue here. With a battery combiner the OP will have some trickle charge on the start battery.[/QUOTE]

See post #9
With his usage profile it made me suspect alt.
But yes he should have his solar going to start battery as well regardless as he has the setup for it.
Don't understand why you would leave the start battery out of the solar setup when you can have both.

[stormalong]

Originally Posted by Compass790

The OP does not say how often he uses the boat. He is putting the boat away with a partially discharged battery and letting it sit for whatever period of time that is. That is the big issue here. With a battery combiner the OP will have some trickle charge on the start battery.

See post #9
With his usage profile it made me suspect alt.
But yes he should have his solar going to start battery as well regardless as he has the setup for it.
Don't understand why you would leave the start battery out of the solar setup when you can have both.

OK, I missed that bit of info since it was not in the first post which I have re-read several times.

The point is that he is undercharging the engine start battery and leaving it that way. And he has a parasitic drain. He has to get power back into that battery more frequently which is the point of my post that has drawn so much criticism.

Fixing the parasitic drain by itself will not solve his problem.

[GILow]

Originally Posted by stormalong

Drawing down the engine start battery with a windlass and not putting the power back in due to a low output alternator is a bigger deal than a 12 AH per week battery drain unless the owner does not use the boat very often.
...

I really don't think we are all disagreeing here, it's just about priorities. I feel it is best to deal with the underlying issues FIRST, then consider the final configuration options. There are some excellent discussions on the topic of engine and house battery systems all through CF. (Personally, I like the simplicity of the OP's system, though mine is simpler still.)

But, I do disagree with the windlass inclusion. As I posted earlier, the power draw of the windlass is, for practical purposes, academic. Do the numbers, I was so surprised I did them again. The actual amp hours used by a windlass are astoundingly low.

Max 150 amp draw (maybe more for the OP, but it will be in the ballpark for their boat size), for 30 seconds, call it a minute for lots of chain.

That's 150 amps x 1/60 hours, which is 2.5 amp hours.

The measured parasitic draw will use more in couple of days.

[GILow]

Originally Posted by stormalong

.. He is putting the boat away with a partially discharged battery and letting it sit for whatever period of time that is. That is the big issue here.

Respectfully, no, we don't KNOW that. The OP could be putting the battery away with a full charge. The alternator may be fine and the measured voltages given may simply be an indication of the terrible state of the current battery.

But the OP HAS discovered a significant parasitic power loss and it alone can easily account for the problems the OP is having.

Everyone's mileage will vary, but as noted earlier, I got ten years of service out of batteries that were ONLY charged by the engine, on a boat that was lucky to get run every two weeks and more likely to get run once a month at best. I would not recommend this setup to anyone, but it is a useful reference. Incidentally, those batteries were from Century Marine, the same as the OP is using.

[Wotname]

@kriskro, be cautious about leaving your start battery connected continuously to another charging source (e.g. solar). Your start battery is a maintenance free lead acid battery (i.e. not AGM etc) and as such, the battery should not be left on a float voltage for long periods (i.e. weeks) due to risk of drying out of the electrolyte.

[GILow]

Originally Posted by Wotname

@kriskro, be cautious about leaving your start battery connected continuously to another charging source (e.g. solar). Your start battery is a maintenance free lead acid battery (i.e. not AGM etc) and as such, the battery should not be left on a float voltage for long periods (i.e. weeks) due to risk of drying out of the electrolyte.

Crikey mate, I hadn't considered that! My old Votronic regulators had a separate charge circuit for the engine battery. That circuit was capped at one amp though. I wonder if that's a safe current or would it have ruined the engine battery?

(I never got to use it anyway, because my engine bank was 24 volts while the house bank was 12 volts.)

[mitiempo]

Originally Posted by GILow

Crikey mate, I hadn't considered that! My old Votronic regulators had a separate charge circuit for the engine battery. That circuit was capped at one amp though. I wonder if that's a safe current or would it have ruined the engine battery?

Safe at a float voltage of 13.5, but not if near 14 volts or higher.

Batteries do not gas at 13.5 volts.

My preference with chargers that have the option is 2 stage charging if the boat is not used regularly though. This is a full charge and the charger then goes into a sleep mode until the voltage drops a bit. If the boat is a liveaboard with draws on an ongoing basis then 3 stage charging with float works.

I agree the op should find the parasitic power loss before anything else is done.

After that is done I agree with stormalong's post totally.

[Wotname]

Originally Posted by GILow

Crikey mate, I hadn't considered that! My old Votronic regulators had a separate charge circuit for the engine battery. That circuit was capped at one amp though. I wonder if that's a safe current or would it have ruined the engine battery?

(I never got to use it anyway, because my engine bank was 24 volts while the house bank was 12 volts.)

You get a lot of internet chatter about all things "battery" but there is much difference between say one battery and another even of the same generic type. Take AGM, some tolerate float voltages, some don't, some tolerate storing fully charged for 2 years, others don't.

At the end day, I take my advice first from the manufacturer and then from a specialist battery store owner who has much experience with any particular battery.

In the OP's case, the manufacturer (Century) advises against floating that particular style of battery. The logic is sound and I don't argue with them - unless I know better