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Old 06-23-2017, 07:08 AM   #1
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State of Charge

We have a Magnum Energy MS 2812 inverter/charger, battery monitoring kit (shunt) and advanced remote control charging and monitoring our ~1,250 AH AGM housebank. Initially, this kept the bank at a 100% state of charge, according to the monitor. Over the past 3-4 weeks the SOC has been dropping and the charger has been going into it's "maintain" mode--basically a standby status as if the bank were at a 100% SOC.

Periodically, the charger enters the float stage for a few hours and then reverts to maintain/standby. While all this is happening, another meter on the remote monitor says the bank is consistently fully charged at 12.8 volts. We are using very little DC power; the boat is hooked to shore power and the bank's SOC -- as indicated by the remote monitor -- has been declining slowly but steadily--from 97% three weeks ago to 88% now. But still at 12.8 volts.

My question: why is the same monitor indicating a fully charged bank (at 12.8 volts) while telling me the SOC is 88% (and dropping)?

Magnum's techs think the absorb setting needs to be lengthened--or maybe the heat is suppressing the voltage the bank is able to absorb--but otherwise don't have a lot of insights into what's going on.

Has anyone with one of these units experienced this? Is SOC something I need to worry about if the bank's voltage is topped off?
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Old 06-23-2017, 08:01 AM   #2
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Does that SOC monitor have a manual reset? Some require a periodic zeroing when the bank is full. Check what the manual on the SOC meter says.

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Old 06-23-2017, 10:11 AM   #3
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I'm not familiar with the Magnum SOC meter, but I have the same MS 2812.

I would first just double check to see if you have your Magnum setup correctly for your bank.

Setup 03: Set the AmpHr capacity of the bank to your 1250 Ah. That should give you an absorb charging time of about 3.5 hours. I believe later revisions of the remote may have this accessed via the meter button on the remote and then selecting BM Setup -> BM Amp Hours. If your battery bank size isn't correct, the SOC will be off.

Setup 04: Set the battery type to "Custom". You then set the absorption voltage, float voltage and equalization voltage. US Battery recommends for their AGM batteries that you have, an absorb voltage of 14.7v, float voltage of 13.4, and equalization voltage of 14.7v

Setup 05: Set Max Charge rate to 100%. This will allow you to use all 125amps of the MS2812 charge capacity. US Batteries tech support recommended that you charge up to 25% of the C20 value. For your bank, that would be over 300amps. So you want to use all 125amps the MS will produce.

There is also a menu selection in the BM Setup menus (hit the Meter button on the remote and turn the knob to get to BM Select) where you can set the Charge efficiency for your batteries. The SOC monitor has an "Auto" selection which will likely work the best as it should eventually figure out your banks charge efficiency (basically how many amps of charge current do you have to put into the batteries vs the number of amps that you draw out. If a bank was 100% efficient it would be 1 to 1)

I believe that the MS SOC meter will figure out your charge efficiency over a time after a few cycles.

It takes time to get a large bank like yours fully charged. If you have the size of the bank, and the charge voltages set correctly, your bank should be fully charged after being in float for a number of hours. So if your SOC meter keeps dropping % after the batteries should be fully charged, I would suspect either the charge efficiency is not set to "Auto" or your bank size isn't set correctly.
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Old 06-23-2017, 11:42 AM   #4
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How does the reduced capacity of aging batteries affect those readings on that type of instrumentation?
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Old 06-23-2017, 11:25 PM   #5
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How does the reduced capacity of aging batteries affect those readings on that type of instrumentation?


That is a big downside. They do a good job of counting amps, but the amount of amps decreases as the batteries age. I am not smart enough or patient enough to do a proper load test.

I seem to recall that CMS wrote that he might discount the Ah of a new bank by maybe 5% and then decrease it by 3%/year after that.
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Old 06-24-2017, 06:36 AM   #6
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Perhaps it is just time for an equalizing charge?
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Old 06-24-2017, 08:00 AM   #7
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Thanks for all the ideas.

I've gone over the manual (my head hurts) and have a few things to check out when I'm back at the boat this morning. I upped the absorb time from 3.0 to 3.5 hours yesterday; this is actually higher than US Battery recommends, so I'll likely return it today. I also moved the absorb/float charging voltages to the higher range of what US Battery recommends for these AGMs; we'll see if that made a difference. (I did an equalization charge about a month ago, but maybe it's time for another. Also, I do not find a reset SOC function.)

Another thing I noticed was the SOC is set at 50%. If I read the manual correctly, you can either bring the bank to full charge using time or SOC parameters. Not sure how or why it's set so low, but it sure sounds suspicious. I'll move it to 100% today and see if that helps.

(The manual is well-written and comprehensive, but it would help to have a EE degree to get through it.)
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Old 06-24-2017, 08:50 AM   #8
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Angus

Two things. First, your very nicely done battery bank re do may have a wiring setup that is confusing to the shunt. Try moving the shunt to the other end of the bank.

Second, take a picture of your setup, and with a wiring diagram forward to Magnum. If they have no on spot recommendations they should pony up and consider a charger issue at play. I have two Magnum BMKs and two chargers. Never a lick of trouble in their 5 years of continual duty.
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Old 06-24-2017, 09:16 AM   #9
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I have a Victron battery monitor, BMV-700. Prior models required a manual reset periodically as it measures watts in and out. Mine has an automatic reset. When the charging rate drops below a certain level, for a certain period of time, at or above a certain voltage, it resets to 100%. The reason I mention this is that the battery charger should determine the batteries full based on the values you program in. The battery monitor should read 100% when the charger says the batteries are full. It seems to me that the monitor needs to reset manually or automatically to match the charger saying the batteries are full.

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Old 06-24-2017, 09:56 AM   #10
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Absorb Charge Done

The Magnum Battery Remote Control provides three options for determining when the absorb charge stage is finished. The one you select controls absorb stage termination:
Absorb Time Done - this is a hard preset length of time for absorb mode
Absorb Done - Amps - this monitors amps going into the battery and when the rate falls to a certain level - the manual says C/20 - the absorb mode ends.
Absorb Done SOC - Magnum says SOC is the best way to determine when the batteries are fully charged and the absorb mode ends and float mode begins. SOC is most accurate as the DC loads ( or other charge sources )connected to the battery do not affect the SOC reading.

It sounds like you are using Absorb Time Done to terminate the absorb charge mode. I do not think 21/2 hours is nearly enough time to give you a full charge.

If you want to use SOC go to the Setup button and go to 03E. Select Absorb done SOC - 100%.

Can you clarify what you mean by " SOC set at 50%" . Where is that setup located in the menu.

Finally, the location of the shunt is critical. Needs to be absolutely the first stop after the batteries.

Yes, the manual will cause a headache. But once you get it, all the answers are there.
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Old 06-24-2017, 10:00 AM   #11
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If you want to reset your Magnum BMK unplug it for 30 seconds or so and then reconnect. The display will read Thinkin'. It will stay in the thinkin' mode for quite a while (8-12 hours or more) sorting out and calibrating to your batteries.
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Old 06-24-2017, 10:16 AM   #12
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Probably more than folks want to know about wet cell batteries:
http://www.trojanbattery.com/tech-support/faq/

and even more here;

http://batteryuniversity.com/
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Old 06-24-2017, 11:17 AM   #13
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I just unplugged and replugged the BMK, but the readings remained the same. So I shut down all AC and re-energized; that restarted the bulk/absorb process; it's now in absorb charging at 14.5 volts and the amps are slowly declining. I also set "absorb done" to 100% SOC (up from 50%), so we'll see if all this helps. It still shows SOC of 84% but that may change now that I'm pegging a full charge on SOC vs time.

All, thanks again for the ideas--I really appreciate it. Just to answer a few points. I'm certainly no electrical expert, but the system was designed and final-inspected by a guy who has sold and installed hundreds of these units, so I feel pretty good about the configuration. (Unfortunately, he's out of pocket.) I may have messed up some of his settings while I was noodling with this.

MR, my manual says the shunt must be the LAST thing all D.C. loads pass through on their way back to the housebank. So it's located inches away from the negative terminal/lead on the bank. (Positive lead is at the opposite end of the bank.). Also, the "SOC set at 50%" was my imprecise way of referring to the "Absorb Done SOC" setting (which was at 50%; now at 100%). Sorry for the confusion.

Hopeful news: the charger has been in absorb for over 20 minutes and SOC has risen one percent.

Edit: "Charge efficiency" was set at 50%. I reset to auto, which the manual recommends.
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Old 06-24-2017, 11:22 AM   #14
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Quote:
Originally Posted by angus99 View Post
Thanks for all the ideas.



I've gone over the manual (my head hurts) and have a few things to check out when I'm back at the boat this morning. I upped the absorb time from 3.0 to 3.5 hours yesterday; this is actually higher than US Battery recommends, so I'll likely return it today. I also moved the absorb/float charging voltages to the higher range of what US Battery recommends for these AGMs; we'll see if that made a difference. (I did an equalization charge about a month ago, but maybe it's time for another. Also, I do not find a reset SOC function.)



Another thing I noticed was the SOC is set at 50%. If I read the manual correctly, you can either bring the bank to full charge using time or SOC parameters. Not sure how or why it's set so low, but it sure sounds suspicious. I'll move it to 100% today and see if that helps.



(The manual is well-written and comprehensive, but it would help to have a EE degree to get through it.)


US batteries recommends that in absorb charge you hold the voltage at 14.7 until the acceptance current is down to under 3% of the C20 Ah capacity and hold that for 2-3 hours. For your bank, that would be about 3.5 amps?

Your MS 2812 is likely newer than mine but I don't believe I can set that parameter? On the MS2812 I believe you set the Ah of the battery bank and that determines the length of time for the absorb phase. The larger the bank, the longer the absorption time. You also set the hold voltage for the absorption phase at 14.7 v for the US AGMs. I could be wrong.

From the information that I can see on the Magnum SOC meter, it doesn't have a reset feature like my Xantrex Linklite. The MS automatically adjusts itself (nice feature). It will only read 100% SOC however after these three conditions have been met.
1. Stable charge voltage over a period of time (not sure how long but I'm sure this condition is being met)
2. Charge current is down to a low % of total bank Ah capacity, normally less than 2%. ( am not sure how or where this is specified)
3. Ah removed from the batteries are within 1% of the Ahs that have been returned. (This likely relates to the charge efficiency discussed in the BMK manual)

So if your SOC meter isn't returning to 100, one of those three conditions haven't been met. My guess it is 2 or 3. You have a very large battery bank and the MS 2812 can only charge so fast. You might want to see what current is being put into the bank hear the end of the absorb phase and then what current is being sent during the float. If that current never gets low enough, the SOC meter won't ever figure you are at 100%.

I think that the most likely cause may be #3. If the charge efficiency that the BMK is using isn't accurate, then it won't have the Amp Hours in vs out figured accurately. There is a section in the manual that describes how to check this.

I think the suggestion to call Magnum may be the best bet at this point.
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Old 06-24-2017, 11:38 AM   #15
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Originally Posted by Miss Rachel View Post
The Magnum Battery Remote Control provides three options for determining when the absorb charge stage is finished. The one you select controls absorb stage termination:
Absorb Time Done - this is a hard preset length of time for absorb mode
Absorb Done - Amps - this monitors amps going into the battery and when the rate falls to a certain level - the manual says C/20 - the absorb mode ends.
Absorb Done SOC - Magnum says SOC is the best way to determine when the batteries are fully charged and the absorb mode ends and float mode begins. SOC is most accurate as the DC loads ( or other charge sources )connected to the battery do not affect the SOC reading.

.

Do you know if this varies by model and version? The version that I have only shows time, based on amp hours. Mine is original to my boat which is a 2010. Absorb Done - Amps would be a better way to do it if that can be set.
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Old 06-24-2017, 12:04 PM   #16
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angus 99. I think you are on the right track. You should see amps going in declining (Meter button - 04D). Take what is going in and divide it by AH In/Out(Meter button -04E). That should give you a very ballpark idea of how long absorb mode will be active. Let us know what has happened after a few hours.

dhays - My boat was commissioned in 2013, so I think that is the vintage of my ME-ARC. On page 2 of the manual it says it is for "ME ARC with revision 2.1 or higher". Press the TECH button, go to 02 and it will tell you what revisions you have.
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Old 06-24-2017, 01:35 PM   #17
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Update: SOC is 90%; still absorbing at 14.7V and 58 amps.

Staying aboard tonight, so will be able to monitor it consistently.
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Old 06-24-2017, 05:07 PM   #18
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WooHoo!!!

Thanks again, folks.

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