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Old 06-08-2020, 10:53   #1
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AGM Charging Questions

I'm really trying to wrap my mind around our energy system on our boat. We are full-time liveaboard cruisers.

We have three 225ah Mastervolt AGM batteries in parallel, 1000 watts of solar (150/70 and 100/50 Victron MPPT) and two 400 watt wind turbines. Our battery monitor is a Victron 712.

We use about 390ah in a 24-hour period and regularly see 20ah+ being drawn.

It doesn't seem like the battery bank (6-months old) is accepting the charge current that's available.

This morning for example. When I got up, we were drawing 20ah and the voltage was 12.3. A couple hours later and the panels were in full sun and the batteries were taking 25 amps. It seemed low to me so I started the 12v watermaker that takes 20 amps.

The current going into the batteries dipped for a moment then went right back to 25 amps as the solar panels increased their output. It sat like this for 3 hours. At times we were drawing 40 amps with our equipment but the solar made up for it and the batteries continued to accept 25 amps.

It's now down to a much lower acceptance rate.

Does this just mean that the battery bank isn't getting drawn down as much as I thought it was and this isn't accepting the available current?
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Old 06-08-2020, 10:58   #2
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Re: AGM Charging Questions

I'd expect to see more current into those batteries even if they're fairly close to full. It's quite possible that your cables from the controllers to the batteries are too small. If there's any significant voltage drop there (even 3% is too much) you'll see lower charging current, as the voltage at the batteries will be a good bit less than the output of the controller.
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Old 06-08-2020, 11:02   #3
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Re: AGM Charging Questions

Without knowing your SOC you can’t make any assumptions at all, for example my 660 AH Lifelines will only accept 3.3 amps if at 100% SOC, but if at 50% SOC, they will accept 185 amps.

However a voltage of 12.3 should put you at the most about 60% SOC, and you should have been able to draw more than 20 amps charge

What was the voltage before and after you started the watermaker? It wasn’t float voltage was it?

A lot of controllers will drop to float way before the bank is fully charged, leading many to conclude that they are fully charged by noon.
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Old 06-08-2020, 11:03   #4
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Re: AGM Charging Questions

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Originally Posted by rslifkin View Post
I'd expect to see more current into those batteries even if they're fairly close to full. It's quite possible that your cables from the controllers to the batteries are too small. If there's any significant voltage drop there (even 3% is too much) you'll see lower charging current, as the voltage at the batteries will be a good bit less than the output of the controller.
I thought that as well but the cables are very large and the solar charger has no problem sending much higher current out when other loads (watermaker) are turned on.
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Old 06-08-2020, 11:06   #5
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Re: AGM Charging Questions

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Without knowing your SOC you canít make any assumptions at all, for example my 660 AH Lifelines will only accept 3.3 amps if at 100% SOC, but if at 50% SOC, they will accept 185 amps.

However a voltage of 12.3 should put you at the most about 60% SOC, and you should have been able to draw more than 20 amps charge

Want was the voltage before and after you started the watermaker? It wasnít float voltage was it?
Does it matter that the 12.3v that I saw was at a time there was a 20amp load on the batteries? When the last (refrigeration) was shut off, the voltage jumped to 12.5.
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Old 06-08-2020, 12:25   #6
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Re: AGM Charging Questions

Assuming the solar is putting out in excess of what’s used, then the voltsge will be higher than the battery resting voltsge.
Again, assuming the Solar is making more than the batteries will accept, (you proved they were with the watermaker) you should be at absorption voltage, which for me is 14.3V.
If you were at float voltage, then that’s the problem, the lower voltage will cut way down the rate at which a battery will accept current. The purpose of the higher absorption votive is to “push” more current in, faster, but if left there indefinitely, it’s going to overcharge the battery, so we cut back to float voltage, which won’t overcharge, but it takes forever to charge at float voltage.

So, are you at absorption voltage when the acceptance is low? Is absorption voltage correct?
If the answer to both of those is yes, then I’m afraid your bank is heavily sulphated.
If the answer is no to the first one, then that means your controller is cutting the voltage back way too soon, and your never fully charging the bank, which will lead to sulphation.

Of course if programmed voltage is wrong, you need to correct it.
I think it’s very, very common for controllers right out of the box to drop to float voltage way too soon, you will need to modify the programming so that absorption voltage is held long enough so that the bank is fully charged before it drops to float. That is done by guessing really as it’s on a timer and any difference in solar output or SOC will require a different absorption time, so it’s a guess, and guess long, because an extra half hour or even hour at absorption voltage wont hurt anything, but continually dropping to float prematurely will.

On edit, we are similar in bank size and Solar and even usage, but I think I use less, but don’t have wind. I have 660AH, 1000W Solar, and in the Bahamas in Winter meaning from Nov to Jun. I set my controller to stay at absorption voltage, I did that by setting absorption and float to absorption voltage.
I wasn’t overcharging my bank either, but then I don’t have wind
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Old 06-08-2020, 19:52   #7
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Re: AGM Charging Questions

Next time make a chart. With a bunch of readings every so often.

Ie

Time. , Battery voltage. (712). , Battery Soc. (712). , Battery net current (712) , Total Solar current (add both solar coNtrollers) Total wind current. Battery voltage shown on solar controller. , Solar controller state. (Bulk / float).

If you now the dc load. But that can be calculated from net and charging.
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Old 07-08-2020, 05:56   #8
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Re: AGM Charging Questions

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Originally Posted by crayiii View Post

This morning for example. When I got up, we were drawing 20ah and the voltage was 12.3. A couple hours later and the panels were in full sun and the batteries were taking 25 amps. It seemed low to me so I started the 12v watermaker that takes 20 amps.

The current going into the batteries dipped for a moment then went right back to 25 amps as the solar panels increased their output. It sat like this for 3 hours. At times we were drawing 40 amps with our equipment but the solar made up for it and the batteries continued to accept 25 amps.

So that was 553W at say 10-11am out of a solar bank of 1000W. That seems about normal.

Then 812W later in the day with better sun. Than seems normal also

To me the real question would be 1- are my batteries getting fully charged, 2-what is the current real capacity of my batteries.

But really to me your post just means that your batteries accepted all the charge in the morning that solar could provide and that in the afternoon your batteries became current limited due to higher charge state.
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Old 07-08-2020, 08:50   #9
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Re: AGM Charging Questions

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So that was 553W at say 10-11am out of a solar bank of 1000W. That seems about normal.

Then 812W later in the day with better sun. Than seems normal also

To me the real question would be 1- are my batteries getting fully charged, 2-what is the current real capacity of my batteries.

But really to me your post just means that your batteries accepted all the charge in the morning that solar could provide and that in the afternoon your batteries became current limited due to higher charge state.
I'm at absorption voltage 14.25 today at 11:30. There is currently 36 amps being accepted by the batteries.
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Old 07-08-2020, 09:40   #10
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Re: AGM Charging Questions

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I'm at absorption voltage 14.25 today at 11:30. There is currently 36 amps being accepted by the batteries.
Pay attention to when it drops to float, it shouldnít drop to float until or unless less than 5 amps are being accepted at absorption voltage. My 660 AH Lifeline bank itís 3.3 amps
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Old 07-08-2020, 09:45   #11
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Re: AGM Charging Questions

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I'm at absorption voltage 14.25 today at 11:30. There is currently 36 amps being accepted by the batteries.
well from that point it will take least 4 hours to get to 100% and the battery will be charge current limited the whole way
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Old 07-08-2020, 16:48   #12
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Re: AGM Charging Questions

You've got an issue. We have a house bank of two Mastervolt 225 AGMs, and a 130 AGM start battery. We were doing a solar panel test - four 200 watt panels - into a 12.2 volt start battery. (50% discharged) The controller started on bulk charge with 42 amps into the battery for almost an hour, before dropping down to absorption.

That said, our boat was commissioned new in Feb 2019. In June 2019 we changed out the two Mastervolt 225 AGMs because capacity had fallen and they couldn't run 10 amp refrigeration and house load overnight. We are about to change them again as they can't even sustain a 6 amp load overnight. Mastervolt is doing via warranty, otherwise I'd be changing company. We are also upsizing to two 270 AGMs. Also all systems onboard are Mastervolt/BEP, and we are going thru all looking for issues. So far nothing. Mastervolt says temps in Texas are hard on batteries, and I did wrong by leaving on their MassCombi on float when boat not being used. BS, because on my previous cat my Deka AGMs lasted ten years!

We have enough solar though that I can leave the shore power charger off which will adhere to Mastervolt suggestion.

Yeah, and my boat is about 1.5 years old. Otoh, I fully understand my electrical system now, and Seawind has not been hesitant to send parts 3 day shipping from Vietnam to try to fix. West Marine sucked when I approached them with 14 month old battery receipt for Mastervolt replacement. Said send the batteries back to Mastervolt for testing. Regional Mastervolt USA rep read all of the data and committed to replacement three days later. I guess an advantage of all systems and electrical is Mastervolt.

Now just gotta get these two 140 lb behemoths off the boat, and redo the hold downs for two 160 lb replacements.
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Old 08-08-2020, 06:18   #13
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Re: AGM Charging Questions

Out of curiosity, are your Mastervolt AGMs 6 or 12 volt? My pair of 6v / 400ah L16s from them have been good so far (installed spring of 2018), no noticeable loss of performance yet. Not sure if I'd buy another set or something else for replacement, but at the time, these were what I could get locally.
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Old 08-08-2020, 06:23   #14
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Re: AGM Charging Questions

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I'm at absorption voltage 14.25 today at 11:30. There is currently 36 amps being accepted by the batteries.
So, did you ever get to float yesterday and what was the acceptance rate when you did?
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Old 08-08-2020, 07:10   #15
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Re: AGM Charging Questions

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Out of curiosity, are your Mastervolt AGMs 6 or 12 volt? My pair of 6v / 400ah L16s from them have been good so far (installed spring of 2018), no noticeable loss of performance yet. Not sure if I'd buy another set or something else for replacement, but at the time, these were what I could get locally.
They are 12v. I was in Martinique and that's all I could get.
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