Help me not kill another battery bank

[sailorboy1]

Not really “a thing” i feel except for a few small cases

[sailjumanji]

Originally Posted by Pelican_38

A question for the collective smart folks - is shallow discharge a possibility in killing this bank? You don't say what your amp hour usage is overnight, but you mention you recharge 100% during the day. Assuming solar stops charging at night and wind charges continuously, is it possible that you are only using a small percentage of the bank many nights and fully charging it back the next day leading to early failure based on shallow discharge cycle?

Is that a thing?

Don't think so. What I've been told by Mastervolt is multiple days to a week between full recharge is a problem for AGM longevity.

[donradcliffe]

It is not a thing. Many battery manufacturers will give you a curve of the number of cycles of battery life vs the state of discharge for each cycle. Every curve I have seen is non linear, meaning for example that a battery discharged to 10% will last 6 or cycles as long as a battery discharged to 50%. That is the reason the experts say to keep your house batteries as one bank that is discharged nitely instead of two banks that alternate nights.

Originally Posted by Pelican_38

A question for the collective smart folks - is shallow discharge a possibility in killing this bank? You don't say what your amp hour usage is overnight, but you mention you recharge 100% during the day. Assuming solar stops charging at night and wind charges continuously, is it possible that you are only using a small percentage of the bank many nights and fully charging it back the next day leading to early failure based on shallow discharge cycle?

Is that a thing?

[Icarus]

If you checked for voltage drain and there isn't more than 50mA that means your batteries won't hold the charge.
Looks like you will have to replace the bank.
Good luck

[crayiii]

Okay, it’s only a few days on anchor with the new batteries so far but I’ve noticed a massive increase in charge acceptance over any batteries I’ve had in the boat. We purposefully brought the batteries down overnight so we could see the charge rate from solar and wind. We saw 90 amps going in the next day. We hit tail amps at absorption voltage (ran the generator to make sure) early afternoon. I’ve never seen our AGMs (Lifeline or Mastervolt) accept that level from the solar/wind. To be fair, all of the wiring from charge sources have been upgraded.

I’m now focusing on the alternators. We have two 125a Valeo alternators that just seem to sit at 14.1 volts the entire time. They are not a main source of charging but when we have to, we motor for extended periods of time (>24 hours at times).

In the past, when motoring, I’ve noticed the house bank at about 13.8v for extended times. I really don’t want to kill this bank but don’t know if this is a large enough concern to warrant investing the significant costs into external regulation of two alternators.

Any thoughts on this?

[rslifkin]

If the house bank is out of the engine room and stays cool, then 13.8 volts for hours shouldn't hurt it. It's well below absorption voltage and only a little above float. It's not ideal for quick charging, but if you're not expecting fast charging or a complete top-off from the alternators alone, I'd call it good enough.

[ClarkW]

If my root cause of your problem is correct, your new batteries will solve your problem.

I believe the short life of your bank is caused by too high a float voltage. The Mastervolt AGM batteries have a float voltage of 13.8V stamped right on them and you mentioned this voltage in your posts. I believe this is too high a float voltage for these batteries and I have had conversations with Mastervolt about this. All lead acid flooded cell batteries will gas at this voltage. AGM batteries are especially sensitive to overcharging. I learned this from Lifeline and they said that they will not warranty their batteries if the float voltage has been set above 13.2 V. There is a valve that releases the gas buildup. Once the gases are release, they can never get back in to recombine and the battery drys out and looses capacity.

I have 3 Mastervolt batteries as a house bank, 2 more to start the 2 engines, 2 for the bow thruster and one for the genset. The prior owner had replaced all the batteries every two years and when I got the boat they all falled within 2 years. The AH capacity slowly shrank until the inverter would low voltage alarm over night when the refrigerator alarmed. I run 8 hours a day for months on end. The AH are all returned to the battery by noon. With internally regulated alternators on both engines, from noon until sunset when I stopped, the batteries continued to charge at over 14V.

I replaced the batteries and added 3 stage Balmar external regulators and set the float to 13.8V and I added solar and did the same. Within only a few months, all the batteries were again cooked. I talked with Mastervolt about this float setting and they agreed to help me lower the float voltage on their inverter charger. To their credit, they replaced all the batteries under warranty. I lowered the Victron solar charger float voltage to 13.2 V and adjusted the Balmar regulators to 13.2 V. I also adjusted the inverter charger to switch out of absorption faster and similarly for the Balmar and the Victron solar charger. This is because the solar charger will attempt to 3 stage charge the batteries every day. Same is true with the Balmars every time I restart the engines after a lock. Same with the inverter charger each time I go for a short run. For these short runs, I didn't want long absorption charging when the batteries were already at 100% SOC and the other chargers were in float mode.

My experience showed that this 13.2 voltage was a bit low as it took several days in float mode to get back to 100% SOC when recharging from a deep cycle. I increased float to about 13.3 or 13.4 and this gets the batteries to 90% or more during a run from a deep cycle. The solar finishes it off. This has worked well on my trawler for the way I use the boat. The batteries are coming up on 3 years old and are going strong with no alarms the next morning even when I run the microwave at 130 amps (DC) in the morning. I'm hoping for at least 5 years or more based on others experience. On a prior boat with flooded cells, I routinely got 8 years out of the flooded cell batteries and the house golf carts gave me 13 years.

Clark
Sunset Delight
KE 52

[stormalong]

Definitely get external regulation for your alternators. If the alternators you have can stand it convert them. Built in regulators are designed for cars where the battery is only used to start the engine, not to recharge batteries that have been discharged by loads while the engine is not running. Also, internal regulators are not configurable for battery type. That might be a cause of early death of your gel cells.

Whatever brand you choose your external regulator should have a temperature sensor attached to the alternator.

[sailorboy1]

Originally Posted by crayiii

Okay, it’s only a few days on anchor with the new batteries so far but I’ve noticed a massive increase in charge acceptance over any batteries I’ve had in the boat. We purposefully brought the batteries down overnight so we could see the charge rate from solar and wind. We saw 90 amps going in the next day. We hit tail amps at absorption voltage (ran the generator to make sure) early afternoon. I’ve never seen our AGMs (Lifeline or Mastervolt) accept that level from the solar/wind. To be fair, all of the wiring from charge sources have been upgraded.

I’m now focusing on the alternators. We have two 125a Valeo alternators that just seem to sit at 14.1 volts the entire time. They are not a main source of charging but when we have to, we motor for extended periods of time (>24 hours at times).

In the past, when motoring, I’ve noticed the house bank at about 13.8v for extended times. I really don’t want to kill this bank but don’t know if this is a large enough concern to warrant investing the significant costs into external regulation of two alternators.

Any thoughts on this?

Actually i was thinking of this yesterday because I feel my FF G31s go into charge acceptance reduction kind of early. So I checked with Ocean Planet who says they will normally only accept 15-20amp each at 85% SOC

Just as fyi

[rslifkin]

For what it's worth, the set of Mastervolts I killed lived their whole lives with the float voltage set to 13.5. The only time they saw higher for long periods is when under way (powerboat) for a while with the batteries already fully charged, where they'd be held around 13.9 - 14 volts. They didn't seem to suffer at all from doing this for several 10 - 12 hour days in a row on a trip in 2019. But a trip where they saw some PSOC abuse for a week in 2020 seemed to push them over the edge from fine to significant capacity loss pretty abruptly.