Help me not kill another battery bank

[stormalong]

Originally Posted by crayiii

Each engine alternator goes through a Cristec battery isolator that charges the start batteries and the house bank. I didn't see a voltage drop. No other charge source goes through isolators.

OK, I see that these are MOSFET type isolators.

That does not answer the full question. Are the alternators externally regulated? Is the battery voltage sensed at the batteries? Using an isolator like that with a splitter and sensing the voltage on the start battery which never gets discharged will end charging early. An ACR, aka battery combiner with the alternator output going to the house bank would be a more viable system.

[Scubaseas]

Did you try disconnecting and testing each battery individually with a good quality load tester or capcitive tester? Or try running the bank with one battery at a time to rule out each battery as being the culprit? From the sounds of what you have it sounds like a bad cell on one of the batteries could be the issue. I would certainly look to test that hypothesis.

Capacitor discharge testers on AGMS really doesn't work well from my experience at least with the cheap testers. A good load tester is preferred if using cheap equipment on AGMs.

[guyrj33]

I like the earlier suggestion of disconnecting one battery at a time to measure the resting voltage and also gauge the performance of the other two batteries.

Alternatively you could try running on one battery at a time, I suspect that would highlight the weakest battery up pretty fast.

[garychurch]

I had a similar problem. Batteries lost voltage quickly after they were fully charge. Answer was they were worn out and well past their useful life. Sounds like the batteries you purchased in the Caribbean were well past their shelf life.

[Chotu]

Originally Posted by garychurch

I had a similar problem. Batteries lost voltage quickly after they were fully charge. Answer was they were worn out and well past their useful life. Sounds like the batteries you purchased in the Caribbean were well past their shelf life.

Definitely

[roland stockham]

OK so here is my take, may be wrong of course but I hope it gives food for though.
1 You have a 3 battery bank so must be 12 volt batteries. That just halved you bank life Changing to 2 or 4 6v batteries or even going down to 2 or 3v will massively extend life. Generally the bigger the individual cell the more robust and longer life they are.
2 All batteries loose water over time. How much depends on how they are used but when they say 'seal for life' they mean the lfe of the battery is dictated by its electrolyte life, once that is used up the cell is dead. There may be plenty of good plate material left but it can't work without electrolyte. Nothing wrong with sealed cells if you need, for example' a cell that won't spill but you pay for that is a shorter life.
3 All leads acid chemistry suffers from insulation if not fully recharged regularly. This state is not always easy to tell especially in a system with constant discharge. In use a fully charged battery will show above 12v (or 6v etc) until the discharge current gets to a high level (different construction changes what it will supply before voltage drops). When charging voltage rises as SOC increases usually until the charging system cuts off so at some point during each day you should see the system drop the voltage as it switches to float. The charging system is nw only trickle charging the batteries but is supplying all the consumers and the battery is not discharging. It should then stay at float until the charging system is no longer producing enough to cover consumption when it will go back into a discharge pattern. This means you should be seeing afternoon voltages of 13.8v most days. If you rarely see that your batteries died due to under charging which I suspect is the case.
4 A critical aspect of all lead acid batteries is the 'gassing voltage' which is about 14.2 14.4v. There are systems to recombine hydrogen back into water but these still require limits max charge rates. Regardless of how much charge the battery will except below this point the charge rate will be drastically reduce once you reach this point. Taking an example of a 100a/h cell it could have a charge acceptance rate of C5 so take 20a at any voltage below 14.4v when the battery is discharged so in 1.5hr it will go from 50% to 80% DoD. The voltage limit is then reached and the charge rate rapidly falls, likely down to around C20 so the cell is now only charging at 5a. But you still need to put around 20a/hrs back in so to get to full charge will take at least another 4hr. That means a total charge time of at least 5 1/2 hrs by which time the sun is dropping and solar output is down so the cell never reaches full charge.
If on the other hand you could raise the max charge voltage to 14.8 volts you would have a longer period of bulk charging at 20A so would probably reach around 85% DoD before hitting the voltage limiter therefore only needing a further 15a/h to full charge (this increases bulk charge time by about 15min). Plus raising the voltage 0.4v will probably double the charge acceptance rate past the voltage limiting set point so that 15a/hr may only take around 2hr to get in. So your total charge time is now around 3hr 45min, easily achievable with a solar system. Fitting bigger banks or increasing solar output does not help. A bigger bank will mean a higher bulk charge rate and lower cycle depth but the taper to full charge is still there. More solar capacity does not help because the problem is charge acceptance not charge supply.


So the solution for a bank in continuous use is to go for a system capable of accepting a higher max charge voltage which also requires being able to replace lost water and fitting the largest size individual batteries possible rather than multiple small 12v batteries. As you probably guessed I am recommending flooded lead acid which will also cost significantly less to replace and should give at least 10yr life but I wanted to explain why.

Alternatively you could go to lithium but if you understood enough to join those developing this tech I doubt you would be asking this question! Lithium is only really cost effective if you run very high power consumers like electric ranges and A/C where it does gain strong advantages but if you get it wrong it is going to cost $$$.

[Suliwar]

Recommend to measure the voltage DURING charging across the terminals of the charging-source AND directly across the battery-terminals of each battery. Repeat this double measurement for each charging source separately. If there's a difference of more than 0.3V between the charging source voltage and the battery voltage, then the origin of Your problem lies in-between, and You need to identify at which point exactly the difference occurs.

[sailjumanji]

Had the same issue with two SETS of Mastervolt 225 AGM's. New boat commissioned Feb 2019. First set crapped out cruising in the Bahamas with 800 watts solar, Mastervolt Solar Chargemaster 60 amp MPPT, after four months. Went to West Marine in Ft Lauderdale and picked out the two newest Mastervolt 225 AGMs on their storage rack. Installed them. Got the boat back to Texas, and because of family issues, sat at the dock on Mastervolt MassCombi three-stage charger for about a year. On float. Tried a weekend getaway and those batteries were trash. Did capacity test and found one had 20 Ah remaining, and the other 30 Ah remaining.

Mastervolt replaced under warranty (1 year old), and we upsized to two 270 Ah Mastervolt AGMs. (Our THIRD set of MV AGM's.) Put on MasterShunt and everything on a Masterbus system so we can data log. Took out the VSR and put in a MacPlus DC-to-DC charger so that house batteries never see motor alternators. All settings were confirmed previously to Mastervolt spec. No hidden loads were found that might explain discharge.

Have yet to find any smoking gun. Although the MasterShunt is much better at calculating SOC and Ah consumed than the BEP DCSM. (DCSM showing batteries full, when MasterShunt still shows shortfall.) The only charge parameter we changed was the solar controller absorption time, as it was timing out after 3 hrs previously, and now we have it set for 4 hours. We have an interface in the Masterbus system that lets us use a PC with MasterAdjust software to set all charge parameters for each piece of equipment. Also, the MasterShunt makes some of the voltage sense wires obselete as the solar controller can just tie into the Shunt battery voltage for temp and volt drop compensation. But again, aside from 0.08-0.10 voltage difference on chargers, we haven't found anything. I think MV AGM's are very tender batteries. I would have gone Battleborn lithium but MV replaced the AGMs' under warranty, plus I was afraid it might actually be a boat system problem and I didnt want to trash expensive lithium batteries finding out!

We are currently using the DataLogger function on the MasterAdjust software to log all of the data for the chargers and shunt, to try to identify issues. Its logging on 10 sec intervals, and generates a txt file that is easy to dump into Excel and quickly do plots. But again, no smoking gun yet.

If you want to review my original post on this subject, here it is:

https://www.cruisersforum.com/forums...rs-239438.html

[philcun50]

Originally Posted by crayiii

I've measure each battery at the terminal, I've also measured at charge sources and battery isolators. I've also checked all these with a clamp to see if anything weird was going on current wise. The meters are Fluke.

Resting voltage is difficult while at anchor since we're living on the boat.

I know it's really just a guess but yesterday I ran the generator until we were seeing 14.2V and 5 amps being accepted. Everything but one fridge and the anchor light was off. The bank was 11.2V within 7 hours of the sun going down.

How long did it take for charge current to drop to 5amps? I’m assuming these are lead acid batteries. Sounds like you haven’t been charging them enough.
At 12v lead acid are half charged. 3 x 225ah is a lot of battery to charge with 30amps. You just go down, next day down further and so on. No matter how fresh your batteries were when you got them, not getting good charge into them is a killer.
You could have one crook one bring the rest down, circulating currents. To check if you have a dud you have to disconnect them all and let them rest a little. Though if ones had the biscuit it will show lower than the rest very quickly.
If your going to replace them get LiFePO4 and external regulators for your alternators.
Is the cabling to each battery the same length and size?

[secessus]

Tried to send this in a PM, but not a trusted user:

====

There have been reports of the Vics acting squirrelly on Adaptive and PSoC'ing batteries:

https://community.victronenergy.com/...5-minutes.html

etc

If you are seeing trunctated Absorption that might be it. Folks are working around by using timed absorption or setting Vfloat == Vabs.

[seabreez]

Originally Posted by crayiii

11 months ago I had three Mastervolt 225ah AGMs installed in the Caribbean. They now drop to 11 volts overnight with very little power draw.
Were the batteries bad to begin with?
Did the first couple of months without solid charging (getting them to 100%) kill them?
Did shore power plus solar/wind overcharge them?
Are the wind turbines with their dumb dump regulators causing problems?
I'm really not wanting to repeat this again with the new Firefly Batteries but I'm just not sure where we went wrong and would welcome advice from those with a better understanding of this.

Check the date on the batteries to see how old they are...

[Tony Tommasello]

Are the batteries charging properly? I learned in a course that if the batteries are in a hot compartment (i.e. dark hull, hot on sunny day, little ventilation) they will not charge. The instructor had a trawler with a dark blue hull and determined the temperature in the battery compartment to be over 180 degrees F. His batteries would not accept a charge on hot sunny days until this situation was remedied.

[argonauta1]

Roland and others have it right: stay away from AGMs. They are way too susceptible to the vagaries of normal yacht operations and do not respond well to anything but an ideal charging cycle. I tried two in one of my battery banks and they lasted less than a year. The other bank had four 6V golf cart type wired in series/parallel to provide 440 AH storage and they lasted 4 plus years. The new owner now has both battery banks with flooded lead acid. Only way to go! Incidentally, I did have gels in one bank for a while which were fine but of course more expensive. Less than ideal as folks will know there is a maximum charging voltage for gels which is lower than for lead acid so a complicating factor in voltage regulator settings.

[crayiii]

All three Mastervolts failed. Firefly going in.

[Thx4allthefish]

Most AGMs will get damaged or shorten the life of the battery when discharged past 50%. Sounds like that's likely what happened. Though I think firefly is one of the ones that doesn't mind discharging past that.