Advice requested: Protecting batteries from alternator overcharging

[leecea]

I recently became aware that batteries can be overcharged and damaged by the engine alternator output when motoring for extended periods.

I guess my first question is whether I need to worry about this.

We have a 2004 Yanmar 3GM30F with the original alternator. We may leave the dock with fully charged batteries and then motor for a few hours (commonly 4-5 hours but maybe up to 8-10 hours). I believe the alternator output only goes to the house bank which is 4 x FLA golf cart batteries totaling about 450 amp hours. The start battery is connected via a DC-DC charger.

Am I at risk of damaging my batteries?

If so, what do I do?

I don’t need/want a new alternator and I see lots of devices advertised that claim to manage the charging. Some seem specific to aftermarket alternators like Balmar, but I’m not sure. I also read a thread talking about this saying I’d need someone to bypass whatever electronics were in the original alternator, before installing a new regulator.

If this is an issue, what would be the simplest thing to do that would help protect the batteries?

Thanks,
Andy

[rslifkin]

What voltage are you seeing at the batteries when motoring after they're fully charged? That will be the biggest thing that determines if you're at risk of hurting the batteries or not.

[GordMay]

“Balmar Smart Ready® Retrofit for Yanmar Engines Equipped with Valeo Alternators”
➥ https://balmar.net/smart-ready-retrofit-for-yanmar/

“... A Simple Retrofit of the 120A/12V or 60A/24V Valeo Alternator Converts the Alternator to Accept Balmar’s Famous Multi-Stage External Regulation* ...”

* Balmar Regulators ➥ https://balmar.net/application/marin...ar-regulators/

[PippaB]

I think you are, in general, worrying about nothing. Most (all?) internally regulated stock alternators are designed to not overcharge, and to run for long periods maintaining the batteries in float. Since you don't have exotic batteries these should work. Even after long hours of motoring. Same as the same alternator in a car that runs for hours and hours.

As rslifkin asks, what is the voltage you are seeing after an hour or two of running? If is it is between 13.2 and 13.8 the alternator is managing float. It should go above that (a little) during bulk charge then drop back down.

The reason for all the fancy alternator controllers is usually the opposite of what you are describing - getting a big battery to full charge using an alternator regulator designed for continuous running float charges of small starter batteries, and particularly when trying to limit engine run time to the shortest possible period. If you deeply discharge your house bank a lot and run for short periods a more advanced regulator could help by charging more and faster than your stock. If you are motoring for hours, and the regulator is working (see voltage check above) then your batteries should be fine.

Put it another way, think about all the trucks, cars, heavy equipment, and even boats (some the power variety ) that run engines for hours or even days continuously with the same simple regulators. They work. They are just not usually the best way to cram energy back into a battery quickly and to manage batteries through a lot of deep discharge cycles. It sounds like you have dock charging available for that, so managing through a few cycles with the stock regulator while you are out and about shouldn't be an issue.

[leecea]

Thanks for the responses. I'll need to check the voltages when I am out next. It would be good to have one less thing to worry about

[rslifkin]

As another thought, being that your batteries are flooded, if you're holding them at too high a voltage during extended motoring you'll get an additional indicator in the form of the batteries consuming more water than normal.

[Fuss]

they are flooded meaning you add water occasionally?
how old are they?
mine lasted 16 years before I damaged them and replaced with lifepo4. (lifepo4 can definitely be damaged)

Ok, back to flooded…
my 2v fork truck cells (the only ones anyone should have on a boat in the past) were charged to 29.6 bubbling profusely.
equalised at 32v with master switch off.

get those horrible flooded acid batteries bubbling …
or, they will be gone in 8 years max.

[barnakiel]

It is only an issue if your alternator gets stuck in the high volts position.


A plain car grade regulator (found on many boats) will not. Just like a car battery does not get damaged while driving for hours.


I have such an alternator and we motored a couple of times for over 10 hours. There was no damage of any kind.


The newer better regulators back off as soon as critical Ampers are noted. Just like a 3/4 stage shore charger does. Again, no damage, as the regulator will reduce Voltage to say 13.8 or thereabouts.


The only case in my 25+ years of intensive sailing when I did cook up the batteries was when I used a plain PWM solar regulator on a very moderate battery bank. We sailed for weeks in the tropics and the regulator dried the batteries out. I think it was time driven then rather than Volt/Amp driven.


barnakiel

[smac999]

your stock alternator is doing the same thing as millions of cars driving around for hours at a time.

are their better ways, yes. is your hurting much? no

[Locquatious]

Our wet cell batteries would overheat after extended motoring. They were in the engine compartment and we were in the tropics. We had a standard alternator with a regulator that stopped charging when 14.4V was achieved. We switched out the regulator to a 13.6V one, closer to the battery recommended float voltage in the warm climate. That solved the overheat problem.

Wet cell batteries are fully charged at 12.8V. So long motoring and charging at 13.6V will fully charge and soak the batteries, but not evaporate the water as quickly. Long motoring and charging at higher voltages leads to boiling the batteries and loss of water more quickly.

The cars and trucks place their batteries where there is plenty of air cooling of the battery in the engine compartment, or outside the compartment. I suspect those who have had success with higher voltage regulators do not have their batteries in the boat engine compartment. And if the batteries are far enough away from the alternator, there would be a voltage drop from wire resistance, lowering the voltage that the batteries see.

Choose your main charging source (solar, generator, smart regulated alternator) as the main source for 3-stage charging and battery conditioning. All other sources should be regulated to battery float voltage for the climate.

[sailingharry]

FLA (flooded lead acid) golf cart batteries are, by far, the most abuse-tolerant batteries made. The can be deep discharged and sit idle, with little damage. They can tolerate PSoC (Partial State of Charge). They can be held over-voltage (and in fact, as Fuss mentioned, they LIKE to be over-charged, it's called "equalization" and the bubbling disturbs sulfating). Of course, abuse isn't GOOD for them (except equaliztion, which is recommended on a periodic basis), but FLA is highly tolerant. The downside is all that bubbing acid, which requires monitoring and refilling with distilled water, and can damage surrounding materials.


In your case, other than slow recharge rates as mentioned above, you are not doing anything bad at all. Keep on keeping on.




Oh, to solve much of that misting stuff, I bought replacement caps for my FLA Golf Cart batteries on my last boat. $4 each, or $50 for your batteries. Pretty much eliminated lost water, and no visible damage to surrounding surfaces. I'm a believer. I think the size differences are related to capacity/effectiveness -- in other words, larger is better (cost/space issues aside).
https://flowsystemsusa.com/

[Fuss]

yes SailingHarry… the watering system for fla batteries.
I loved it,..maintenance free, just fill the container mounted about a meter higher than the batteries, and let the cell valves to their magic, never put water in a cell again.
but don't say this too loud …the FLA brigade don’t know about this and we don’t want to give them any more ammunition in their endless fight against Lifepo4.
shush…. here comes one of them now….

[Mark Johnson]

Originally Posted by leecea

I recently became aware that batteries can be overcharged and damaged by the engine alternator output when motoring for extended periods.

I guess my first question is whether I need to worry about this.

We have a 2004 Yanmar 3GM30F with the original alternator. We may leave the dock with fully charged batteries and then motor for a few hours (commonly 4-5 hours but maybe up to 8-10 hours). I believe the alternator output only goes to the house bank which is 4 x FLA golf cart batteries totaling about 450 amp hours. The start battery is connected via a DC-DC charger.

Am I at risk of damaging my batteries?

If so, what do I do?

I don’t need/want a new alternator and I see lots of devices advertised that claim to manage the charging. Some seem specific to aftermarket alternators like Balmar, but I’m not sure. I also read a thread talking about this saying I’d need someone to bypass whatever electronics were in the original alternator, before installing a new regulator.

If this is an issue, what would be the simplest thing to do that would help protect the batteries?

Thanks,
Andy

Since you have an internally regulated alternator, with wet batteries...
The alternator may well keep putting out juice to full batteries, but it is likely only a high V, like lower 14s, at most. Once the batteries are totally full, the Alternator should have tapered off from putting out 30+ A, to partly depleted batteries, to just 1 or 2 A.
So... if the charge going in is just an A or two, at a V of 14 or so, you should be fine.

You must have a charge monitor! Mine is an old Link 10. These give you V, A in or out, Ah in or out, and TTG at a given level of drain.

You may want to monitor water consumption more often, when motoring for days. If you upgrade to Hydro Caps, the water consumption goes way down.

[Peeew]

When I changed to a big bank of fast charging batteries I was concerned about hurting the Valeo alternator. So I decided to install a Balmar external regulator. I actually did the install myself and it was not a difficult job. I can see the charge slowing down when the alternator gets hot so it seems to be working well.

[grantheadifen]

If you think of voltage like water pressure - if a tank of water was at 13.8 psi and you put a hose up to it pushing into the tank 13.8 psi then no water would go in.