AGM Battery Failure - Two Sets in Two Years

[rslifkin]

Originally Posted by Bycrick

Rslifkin — I agree: they’re hardly a panacea. They need some intelligent external control, not beyond that the voltage someplace is more than something. I like your idea of interlocking them to the engine, but I’d have the alternators (and all the other charge sources, connected to the house bank and only use the ACRs to charge the starter bank. Different horses for different courses.

Feeding to house first, then ACR to start is a fine way to do it, but I did it the other way for 2 reasons. It was less wiring to change on my setup, and being a powerboat, I consider starting power safety critical. Plus, my engines use power to run, so if the ACRs weren't closed yet and alternators went to house, I'd be drawing down the start batteries. I'd rather make sure the start batteries are always topped off while running.

[Bycrick]

"For every complex problem, there’s always a solution that’s simple, easy and wrong." There’s no right answer to this issue, only compromises. I don’t have a power boat, so I have different issues. When I got my current boat, I had to reponer. I wanted to change the OEM alternator for a high-output alternator. Yanmar David that doing that would void the warranty on the new engine. Hence I have two alternators and separate systems. That saved me from all the decisions of what other paths I might take. But it had nothing to do with what was right, or best. ACRs aren’t the spawn of the devil. They have their uses. But they have their dangers and complexities that a lot of people don’t ever understand. "It was installed at the factory so it must be right." "It’s all automatic, so it must be working." I’ve been doing this for ten years so it must work." Right. Sort of like the kids who arrived in Panama with a seized up engine. No oil in the pan. "I put oil in in San Francisco before I left six months agot.i only had to check my car once a year."

[Stu Jackson]

Originally Posted by Bycrick

Since Maine Sail is here, I’d like to ask a question. Up thread there were comments about and ACR/VSR won’t cause "over charging" of a starter battery when connected to a bigger house bank. "Each battery in parallel will take what it needs." But I remember reading one his posts a long time ago that pointed out that when a battery is REALLY fully charged, it may only be drawing milliamps of current, but all of that would be going into outgassing or heat. Leave it like like for a long time and the smaller battery will lose electrolyte. What have I missed?

The answer is in the link I provided that you are referring to.


Perhaps read it again, it's all about the voltage.


Unless your charger, alternator or solar/wind system is pumping out an incorrect voltage for you bank you will not over charge using an ACR.

[Bycrick]

Stu — The link doesn’t work for me, but I did go to MS web site where I got sidetracked as usual. I did read the one on "Making Sense of ACRs." A lot of interesting stuff that I’d never read because I don’t have an ACR.

I agree completely that the question is "all about voltage." Part of the discussion problem is "What is the definition of overcharging?" Assume that all my charging sources put out the correct absorbtion voltage. I have a 500Ah house bank and a 100Ah starter battery. As MS points out, the starter battery is very unlikely to be at less than 90% Starting doesn’t take a lot of energy. On the other hand, the house bank is quite likely to be at 70-75%. As MS points out, the house bank voltage will quickly rise to above 13.x volts and the ACR will close. So, both batteries are in constant-current charging until the voltage rises the absorbtion voltage set-point. This CV stage is held (hopefully) until the tail current drops.

During the CV phase, the current through each of the parallel batteries is determined by its acceptance rate. So far, everything is fine. But at some point, the starter battery a decreasing share of the total. After all, it’s a smaller battery and barely discharged. But the house bank, being bigger, will require a much longer absorb time. So, you’ll leave the poor starter battery at absorbtion voltage for longer than it needs to be. During that excess time, it will be converting a greater percentage of what little energy there is into outgassing and heat, because it can’t charge any more. So, over time, a flooded battery will lose water. A VRLA at very low charge rates might be fine if it recombines the gasses fast enough.

So, I’m defining "overcharging" as excessive time at the right charging voltage, rather than "too high" a charge voltage.

Please try and send the link again. And thanks.

[Stu Jackson]

Originally Posted by Bycrick

Stu — The link doesn’t work for me, but I did go to MS web site where I got sidetracked as usual. I did read the one on "Making Sense of ACRs." A lot of interesting stuff that I’d never read because I don’t have an ACR. >>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>


Please try and send the link again. And thanks.

Here's the text of the link:


In another forum (C36IA) we were discussing using combiners or ACRs. Maine Sail, quite properly, corrected my incorrect assumptions.

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Quote:
Originally Posted by stu jackson c34 View Post
Sam, glad you survived. Instead of the ACR you might be better off with an echo charger. The toggle is on the ground line from my combiner to avoid overcharging the reserve bank when motoring for long periods. With the echo charger limiting the charge amperage to the reserve bank to 15A, you won't need one.


Stu,

I am shocked to hear you of all people spout this misinformation about an ACR. This is a misunderstanding and common myth that folks who know little about how electrical systems work, or how batteries charge, feel about how an ACR works. What you stated above, about over charging a start battery, is not possible with an ACR. The only way for this to be possible if you are also over charging the house bank. You can not over charge the start bank with an ACR, or by combining them with the BOTH feature.

Here's an excellent example of why that myth is just that, a myth.

The old start battery on our boat was charged for 2800 engine hours, with a DUMB REGULATED alternator and 5 solid years of solar during a 5 year world cruise. Our friends Norm and Judy did this once in a lifetime cruise on our boat boat before we bought her.. The batteries were purchased at the beginning of the cruise were combined during charging with a Yandina combiner.

When we bought the boat the batteries had been used for five straight years 24/7 with over 98% of the time spent on the hook cruising. That is a LOT more abuse than most boaters do in a lifetime. for the average boater that is 28 years of engine use!!!!! Over charge? The battery banks still worked when we purchased the boat at year six. I retired the house bank but the start battery was still actually fairly healthy so I gave it to my brother for his Mako. It started his boat into the batteries 8th season before finally getting weak enough to be of concern.

That battery was combined every day for five straight years via either solar or the dumb regulated alternator.

The bottom line is that current simply flows where it is needed, batteries will take what they need when batteries are combined, and the voltage becomes equal among the new combined bank. Unless your charger, alternator or solar/wind system is pumping out an incorrect voltage for you bank you will not over charge using an ACR.

A few weeks ago I had a customer over to my shop and was talking to him about an ACR. He regurgitated the same myth you just did. I had two batteries on my bench for equalization and they were both at varying states of charge but both above 80% SOC.

I connected them in parallel and then turned on the charger. I then put my clamp meter on each battery and each battery was taking a different level of current. One battery was near full and was taking just 2 - 2.2A the other battery was taking about 11 - 11.3A. The"combined" bank, both batteries, were at 14.4V but each battery was taking only what it needed. He immediately understood, by seeing it, that the batteries take what they need and only what they need in current.

I see and measure this stuff on a daily basis.. Had a house bank a month ago of Odyssey AGM's taking 120A of charge current from the alt. That bank was combined with a much smaller Odyssey starting battery. It was taking about 1.4A of charge current... All batteries in parallel and the house bank getting 120A and the start getting 1.4A. You don' need an Echo to limit the current the batteries do that on their own..

That said I do have a switch in the neg leg of my ACR. I use it to turn off the ACR so I am not burning amps in "combined" mode when charging off solar and so all the current can flow to my house bank without any "phantom loads".

I will be installing a Sterling ProLatch R soon, which is an ACR with near zero draw when combined, and a very, very low standby current. Once I get to that I won't need the switch in the neg leg...
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-Maine Sail


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I wrote back:

I am chastened.

Interestingly enough, that's the way I use our system. Combiner off when not on the boat using solar to the house bank instead of plugged in to shorepower, combiner on when charging with shorepower (like at marinas for weekends) or the engine.

[Bycrick]

Stu — Got the article. Thanks. See PM.

[Stu Jackson]

Originally Posted by Bycrick

Stu — Got the article. Thanks. See PM.

I got a nice pm and replied. My reply was written before some of the newer posts on this thread. We seem to agree it's a management issue. Here's what we shared by pm:


Originally Posted by Bycrick
Thanks for the text. Maybe I’m just dense, but if one accepts the argument that "as long as the voltage is correct one can’t 'overcharge' a battery" then I should be able to leave a battery on the charger at its absorbtion voltage essentially forever with no ill effects. If that were true, there’d be no need for a float stage. With batteries constantly being used, I don’t think the excessive time on absorb is going to ruin them instantly. But I would think that a something like a DC-DC charger that shut-off when the tail current dropped to a set point would be a better solution.

My problem isn’t just with ACRs. I’ve got a guy in the anchorage with a Duocharge who left it on his windlass battery for months. Voltages were absolutely correct. It was dry and burned. The smell is what finally alerted him to something being wrong. Yeh, it was his fault for never going to the forward cabin and being too lazy to turn off the plainly labeled switch. The same problem exists with windlass batteries that are rarely used. I started thinking about it in the thread where the guy wanted a battery to run his SSB radio.

So what I’m looking for is a DC-DC charger or even an ACR that actually shuts off when the target battery is charged. Completely. Not a trickle or as much as the battery will accept.

Hi,

The concept of that link was at the beginning, where the original answer I gave on the C36 forum was what Maine Sail said where I was wrong. That was: concern for overcharging a start bank with an ACR.
This, then, assumes that one is either running an alternator or a shorepower charger. In the first case, there is a limit to how long this would happen on a sailboat. When I sailed my boat from San Francisco to BC in 2016, we sometimes had 10-13 hours a day under power. But it eventually was turned off. And then I plugged into shorepower when we docked for the night!
So I used the switch I installed on my ACR to turn it off! Also included in that link/text.
The answer to your question, and your friend’s problem, is a management issue.
Without a shunt and management software that doesn’t exist (unless on some brand new charger that measures trailing amps at absorption voltages – I don’t know of one), your last paragraph makes sense, but doesn’t exist without a shunt, and without hands-on management of the system, and a knowledgeable skipper.


Does that help?

I agree that leaving any battery on charge, regardless of voltage assuming it's above the 12.7V or .8V of full, is crazy. So why would one do that?


I don't leave my charger on once my bank is full. Even during winter, when I run a heater, I don't keep the charger on.


Management 101.



Stu

[sailjumanji]

I am sensing serious thread drift here. That said, the BEP VSR is only triggered by cut in voltage of 13.2, and cut out at 12.8 volts. There is a wire on the back that a switch can be added that when turned off, will prevent it from cutting in. I was about to wire the switch in, and Seawind says they are going to reconfigure and probably remove the VSR. With a 130 AH AGM start battery, and house bank of two 225 AH AGM, there really never is an equal voltage until absolutely full. And until I recently installed a separate shunt on the start battery side, we never really knew what that battery was doing, current wise. I have some misgivings about removing the VSR from the system because it worked well on my last boat for 16 years. But there is also a series of on/off and a parallel switch, and if either battery became depleted and needed a jump, that could be used to bail out.

As for leaving charger on, mine has been on the last two days. Since the batteries filled up yesterday afternoon, it has been on float. Refrig is running at around 10 amps, but battery current and they are both at around 0 amps. So it is working the way it is supposed to.

[rslifkin]

As a note, those BEP VSRs are the same ones I'm using. That enable/disable is what I used to make them ignition interlocked.

[Bycrick]

Yes, I’m afraid I let/helped the thread drift. I apologize. If I’d known what was going to happen, I’d have started another thread. Sorry.

[sailjumanji]

Originally Posted by Bycrick

Yes, I’m afraid I let/helped the thread drift. I apologize. If I’d known what was going to happen, I’d have started another thread. Sorry.

No problem. Just trying to get it a bit redirected. I learned something. But OTOH, I think we've probably run to the end of constructive and informative comments on my issue anyway. I appreciate everyone's responses. It was good to hear others experience and opinions, much more expansive than my own. Thanks to all that posted.

[sailinglegend]

Originally Posted by Bycrick

My position is that when one parallels different sized batteries, the smaller battery will end up being fully charged first. At that point, while it won’t accept much current,... whatever current it accepts will either "boil" the water out or be lost as heat. ... I’m also willing to be convinced that my thesis is incorrect.

It's the voltage that does the damage not the current. A battery starts to gas when the voltage is above about 14.4v - or absorption voltage. Gasing helps to stir up the electrolyte and the charger will only hold the battery at this voltage for a few hours and then drop to float - so no more gasing.

House banks should be charged first which means any VSR will not close until the house bank has got up to the closing voltage. This will slowly climb to 14.4v and yes the starter battery will be charged first but the house bank will not stay at 14.4v for ever.

MaineSail's article is now 8 years old so go with his website not Stu's link - sorry Stu!

[Jammer]

Originally Posted by Stu Jackson

I agree that leaving any battery on charge, regardless of voltage assuming it's above the 12.7V or .8V of full, is crazy. So why would one do that?

It isn't crazy and it is in fact very common in telecommunications and other standby applications. Exactly where they voltage sits varies depending on the circumstances. Usually around 12.8 (per six cells in the string; telecom voltages are usually 24 or 48 volt) depending on temperature though with some newer banks a lower voltage is used.



Batteries exhibit self-discharge. The extent of this varies depending on battery age, type, and plate metallurgy. For example FLAs with higher amounts of antimony in the plates (to improve cycle life and durability) will have higher self discharge while AGMs will have lower self-discharge. Self-discharge increases with age even for AGMs.


The constant charge voltage overcomes the self discharge.

[rslifkin]

Leaving a battery on a charger 24/7 isn't crazy. If the charge voltage is a properly selected, appropriate for the battery float voltage, it should be possible to leave the batteries on the charger for years without them being overcharged.

[Jammer]

Originally Posted by sailinglegend

It's the voltage that does the damage not the current.

Battery wear and damage is a function of many things, temperature, current, state of charge, voltage, time.


With AGMs the problem of greatest concern posed by overcharging is loss of electrolyte, since lost electrolyte cannot be replaced. AGM cells are equipped with catalytic recombiners that convert hydrogen and oxygen gas back to water. These catalytic devices only work up to a limited rate and if it is exceed the batteries will vent and electrolyte will be permanently lost. The gassing rate they can accept is best understood as being proportional to the charge current as the voltage at which the maximum point will be reached can be affected by temperature and the age of the battery.


Even with an ACR this point shouldn't be reached on a high-quality AGM.


Subjecting the start battery to extra "absorption" cycles that it does not need is probably best understood as contributing to the exhaustion of its cycle life. Since most people replace the start battery at the same time as the house bank, this doesn't matter much.