Battery SOC question

[Dranoel]

I have the BMK as well. You should consider what has been discussed here when you set your LowBatteryCutOff. Your temporary draw may pull you below that number and shut you down sooner than you intended, as I've experienced :-)

[757driver]

Unless you are running a large DC load such as a coffee pot or microwave on the inverter then 12.2 v and 93% SOC does not corolate. Give the BMK a few charge and discharge cycles and see if readings get more accurate.

By the way do you have your BMK set to Auto or a manual input for 100 % SOC?

[C.Martin]

Good points..

SOC, when left in Auto...will continue to refine itself. Of course it needs to know the proper storage capacity of the bank.

Battery voltage as a SOC measure as stated...only somewhat accurate, and only when the batteries have been sitting idle for some period of time. Usually, not the case while we are looking...

A couple of gotchas to look out for...

Proper installation of the shunt. The Magnum ME-BMK Manual diagrams the shunt connection. Batteries on one side...Inverter in the other. This is a bit oversimplified. They forget to make sure ALL the NEGATIVE leads (except the tiny power leads to the BMK module) have to be removed from the battery bank and relocated to the load side of the shunt. The only NEG cable going to the battery bank (again except for the BMK module) is from the battery side of the shunt. If you, like many people have, take the installation instructions too literally, you’ll have moved the Inverter ground cable and have unknowingly left the chassis ground, House ground, solar ground...etc...still attached to the battery. The shunt can only calculate the SOC if ALL current going in or out passes thru the shunt.

The other thing which is easy to do is program the wrong aH. Easy to assume that eight 200aH batteries equals 1600aH. But if they are 6v batteries...then it takes two of them to make 12v... So, as far as the Magnum is concerned...it’s really four 200aH batteries...so, 800aH is what you would have to input when programming the system.

Either of these common mistakes can make the SOC reading become terribly flawed.

I did the same test that you’re doing when designing my solar system. Unplugged the coach...and came back every so often to write down how many aH I had used. I let it go for 30 Hours or so...and came up with what Inbelieve to be a fairly accurate average aH per hour usage. This is so helpful when trying to design a solar system to meet your expectations.

[Presidio]

Guys,

The BMK is set to auto. The connection between battery, shunt and inverter/bmk is done 100% right. I had a qualified engineer going over it.

Batteries are set correctly. 4 Trojan 305Ah 6V for a total of 610Ah.

[SCVJeff]

Almost everyone responding here is correct. The BMK looks at everything to calculate a proper SOC; voltega, current drawn and averaged, battery temp (sometimes a big deal) etc, and that's factored against the AH capacity you tell it is in the battery stack. Unless you're an anal battery engineer that wishes to do continual load testing and continually adjust the BMK battery capacity manually, just leave it in Auto. The more you cycle it, the more accurate it will get as it figures out what's really behind the curtains. I'm an engineer and have several ways to look at the battery condition (just to see if they all agree), and I r a r e l y look at anything but SOC anymore. I also have the AGS programmed to respond only to SOC

[hclarkx]

Originally Posted by SCVJeff

Almost everyone responding here is correct. The BMK looks at everything to calculate a proper SOC; voltega, current drawn and averaged, battery temp (sometimes a big deal) etc, and that's factored against the AH capacity you tell it is in the battery stack. Unless you're an anal battery engineer that wishes to do continual load testing and continually adjust the BMK battery capacity manually, just leave it in Auto. The more you cycle it, the more accurate it will get as it figures out what's really behind the curtains. I'm an engineer and have several ways to look at the battery condition (just to see if they all agree), and I r a r e l y look at anything but SOC anymore. I also have the AGS programmed to respond only to SOC

It sounds like the Auto setting is a lot smarter than one might glean from the manual. Wild guess is that if it "learns" and takes into account varying load/charge impact on "charge efficiency" on a real-time basis, it probably will also recognize the drop in battery capacity as the battery ages. That would be very useful. It might not read-out the ever declining AH capacity to 50% but when the SOC starts dropping more quickly that will become obvious.

I went LFP a while back. All of these difficulties in tracking SOC go away with LFP. With charge efficiency above 99%, SOC is always very accurate. And solar power goes 44% further in terms of delivered AH (assuming lead acid turn-around efficiency is about 70%).

[Smitty77]

I will share that sometimes SOC does not give an accurate indication of battery level.

Before I do so, I'll confirm we have a MS2812, BMK, AGS, SBC, Temp Sensor, etc. - and we've lived off of BMK Meter SOC for the last 4 1/2 years. Also concur the more cycles, the better refinement via Auto. Do take a good look at your ending AH's in after say 10 cycles, confirm it's Positive. (On average, our 800AH bank, would in with about a +20AH's Total In. So look at a percentage wise close number of AH's in for your 610AH bank.)

OK, why do I say that 'sometimes' SOC level does not give an accurate accountability of the battery bank level?

Well, I'm going thru that now myself! Our X's 4 L16's Lifelines are 5 years old, and lived their life on the top 25% of SOC usage. (To be clear, going into the evening at 100% SOC, we'd be usually at the ~75% SOC level in the AM, after electric coffee brew. And we do have a Samsun RF18. And we do not conserve too much energy. I went with 800AH of battery bank, because our energy audit showed we should be living on the top 25% of battery capacity SOC if we went with 800AH's. And I did this to hopefully get another year or two out of these expensive batteries. As mentioned in this thread, it 'should' be all about Life Cycle usage. With the less SOC Out/In equating to extension of the number of Life Cycles. (DOD 1000 for Lifeline at 50% SOC.) And note, that for the last two or so years, we boon dock way less then 15% of the time. And have used the Magnum Lifeline AGM1 Charge setting for the bulk of these years. (Just changed to Custom, from the Feb, 2017 slight increase of Float level from Lifeline.).

Over the last two weeks of this trip, we've been boon docking a few nights, and woke the first night to Magnum Fault red line flashing. Error History recorded Inverter/8.5V 44A/and the temps. This was just about 5:30AM, so it almost made it thru the night. Again, started at 100% SOC. When I got up and saw the red light Fault indicated on the ARC50 remote. I was surprised to see SOC was still above 75% SOC. So the 8.5V history fault recording was puzzling.

Full charged again that night, and I did find our Ice Off had inadvertently been turned to Ice On for the Samsung. So I changed that back to where it belonged. (We use Ice Trays, I removed the Ice Maker to have more freezer space.)

I'm at an age, where I'm up 3-4 times per night! So, I checked SOC, Voltage (Under load voltage.)/ Current AH's usage - at each of those times. 4:15AM, and still showed 90% SOC (A little higher then normal, probably due to the Ice Maker off again.). at 5:45AM I got up for the day, and SOC showed 85% SOC. But under load Voltage showed 11.7V, and as I watched it for the next 4-5 minutes, it drifted down by .1 to .2V's at a time. When it got to around the 10.4V range, I turned the Inverter Off, to keep from going into Fault mode again. During this 4--5 mins of observation, I checked the Current AH draw multiple times, and it stayed steady between 15-18A draw. (Idle plus Samsung plus a misc parasitic draws.).

I left the inverter off, and the charger off until about noon. Did not 'disconnect' the house battery bank - but very little draw as the House was being supported via Shore Power. (I had turned Shore Power off the night before, and turned it back on after I turned off the Inverter.).

OK so semi rested batteries for about 6 hours. Full bank read 11.8V, so approximately Depth of Discharge a little less then 75% SOC (Lifeline Info). Another hour went by, before I decided I should go read the individual 4 L16's. They were 4.14 / 4.5 / 5.89 /6.15V.

So here is my conclusion about sometimes SOC does not tell you the full status of your batteries capacity/health. I still reflect 85% SOC, due to the AH's Out. But, the true condition of this bank of batteries at that time, were really at about 25% SOC. I conclude that my 5 year old Easy Living Lifeline's - were on their way South. With two of the bank, attempting to make up for the two weaker brothers.

By the way, I did have a Load Test of House and Chassis in Sept/Oct 2017, they all passed. (House bank Load Test was for the bank, not individual batteries. So perhaps the weaker batteries were again being propped up.).

In the last two weeks, I've been getting some help on RV.Net Tech section forum, and have been Equalizing/Conditioning the Battery bank. Have done two 8 hour cycles of Conditioning, with about a 5% draw down and Full Recharge between the cycles. Not much difference so far.

I was also challenged that possibly the 800AH bank was never fully being charged by a single MS2812 with a max 125AH capable charge. C/20 is 160AH's, and 125AH's is below that. When I had the MS2812 installed, I called Lifeline Tech Support to ask them about using the Magnum AGM1 setting. They reviewed the numbers with me, and said that was a fine charger for maintaining my bank of batteries. So, off into the sunset we went...

I'll stop here. But enjoying the expensive lesson on learning that Battery Management and Care is a sport that requires experience. I've certainly expensively 'Burned as I learned!' on this one. (5 years, vs the 7-8 years I had anticipated getting form the light easy life and low DOD Life Cycle usage - is why I call it expensive...). This trip is over early April. We'll turn the inverter off and on a few times during the evening when we boon dock a bit more over this trip. To keep the draw down overnight easier, while still keeping the fridge off/on a few hours during the night.

When back to home, I'll probably do the Lifeline Recovery Process. I've sent Lifeline an email reviewing what's going on, to ask for guidance on what it was that went wrong with the way I managed/cared for the batteries. And I've also asked them for places the recommend in my area to try and Recover these X's 4 L16's. I'd like to limp along for at least another year if possible. But if I were a betting man, I would not wager that these batteries will been my coach for very much longer. Sad, but probably reality!

OP. My main reason for sharing this, is two fold:
1) Be sure you've programmed your Charger for your specific battery type. If AGM, and not Lifeline, then probably AGM2 profile. But validate that with your battery manufactures tech support.
2) I do recommend the advice I received on a PM via RV.Net. To at least yearly, charge your batteries up full. Do a full disconnect of all draws and charging, and then do individual battery voltage readings. And map this on a spread sheet. This should provide a trend of battery capacity as they age.

And to be clear. I'm not knocking Lifeline, Magnum (Or MidNite, as I have 1200W of solar feeding thru their Classic 150 Controller. I do remain puzzled, and still trying to understand, how this bank of I felt well cared for and pampered batteries seem to be shot, or fading quickly, at age 5 years.

Best to you, and all,
Smitty

[757driver]

Smitty,

It would appear that the Auto Charge Effeciency setting (if that is what you are using) does not work that well after a few years. Also with the battery bank size do you still have it set to 800 AH capacity or have you decreased this value over the years. After 4.5 years you would probably be lucky to have a total capacity remaining of 600 AH.

[Smitty77]

Thanks Don!

And yes to Auto. Also had it the bulk of these ~4 1/2 years set to the Magnum AGM1 Lifeline setting. Changed mid May/June 2017, when I heard about the Lifeline Tech Manual's 02, 2017 change to bump Float up a bit. It took about 10 cycles before I was showing ~ +20AH' Total In, when reaching 100% SOC.

I called and talked with a Lifeline Tech when putting in the MS2812, explained my battery bank and asked if he supported the Magnum AGM1 or should I do Custom settings. He and another Tech talked some, and the answer was to run with the AGM1 setting.

As I've been researching, I've had two questions pinged my way that has me wondering!

First - One gent said he was not sure the Magnum's 125A was going to be enough to reach the Lifeline recommended AH's for 800AH (160A). He said on his boat, he'd set his battery bank up so he could isolate 400AH's per side, and then would A/B charge these two banks with his MS2812. (I'm going to ask Magnum their opinion on if the MS2812 is undersized to charge a 800AH bank. As many of us seem to have that size and larger banks.)

Second - Is your asking if I'd adjusted the MS2812 downward to reflect aging batteries. (And no, I did not set the AH's down from 800. Probably naive on my part, but I thought that the MS2812 AGM1 setting would automatically account for this. And probably wishful hearing on my part, because the Lifeline Tech's conclusion when I talked with him - was that the MS2812 was sophisticated enough to 'program and forget', as far as caring for the batteries.

Last Wed I sent Lifeline a summary of how I've cared for this bank, asking them if they felt I'd done something wrong. I specifically pointed out that IMO, they'd had an easy life, and living on the top 25% discharge of the bank should have consumed very little of their total 400,000 (50% SOC of 800 AH's = 400. X's 1000 Life Cycles DoD = 400K AH's (Unless I have that messed up!) I realize this potential AH's as far as Life Cycle usage - lots of variables. But thought it was reasonable due to low Life Cycle consumption to have seen 6-8 years out of this bank. (Or heck, I would have bought a 600AH bank instead, which my energy audit showed should have supported our needs quite well. Added and paid for 200AH's extra to have some more contingency, as well as I hoped a few more years of usage out of this bank.

After a test last night turning off the Inverter for 2-3 hours at a time, to try and make it thru the night with the bank - it's not looking to encouraging. Have performed two Condition cycles of 8 hours, and Amps never tapered down below 15A. Probably a bad cell, or just dried up the juice! Going to do as close to get to full charge again today (On Shore Power for one night.), then turn off the inverter and solar controller, and let the batteries rest as long as I can before we have to move on Sunday. Take multi meter readings of each battery, to see what I get. Might get lucky and two of them are the bad brothers, bringing down the other two. If so, I'll disconnect those two - and then get along for the rest of this trip on 400AH's. (Yep, will set the AH down on the MS2812 too. Will try 300AH's. (Though I don't recall ever reading about adjusting AH bank size down due to aging batteries. Thanks for that tip!).

I'm also kicking around picking up one of the $20 off Good Sam's Duracell Grp 31 AGM's, and just jumper cabling them to the house bank (4 or 2 batteries, depending what the multi meter readings show tomorrow.). See if that can help 'augment' the bank to get thru the night. We're only out on this short trip until the first week of April, and I don't plan to replace the L16's until I get home. Not sure what with.... We'll see. But also suspect the Grp 31 would just be drawn down too, as I've always read that the weakest battery seems to win in a bank! But, might get us thru the night.

Thanks again, and best,
Smitty

[757driver]

Originally Posted by Smitty77

Thanks Don!

And yes to Auto. Also had it the bulk of these ~4 1/2 years set to the Magnum AGM1 Lifeline setting. Changed mid May/June 2017, when I heard about the Lifeline Tech Manual's 02, 2017 change to bump Float up a bit. It took about 10 cycles before I was showing ~ +20AH' Total In, when reaching 100% SOC.

I called and talked with a Lifeline Tech when putting in the MS2812, explained my battery bank and asked if he supported the Magnum AGM1 or should I do Custom settings. He and another Tech talked some, and the answer was to run with the AGM1 setting.

As I've been researching, I've had two questions pinged my way that has me wondering!

First - One gent said he was not sure the Magnum's 125A was going to be enough to reach the Lifeline recommended AH's for 800AH (160A). He said on his boat, he'd set his battery bank up so he could isolate 400AH's per side, and then would A/B charge these two banks with his MS2812. (I'm going to ask Magnum their opinion on if the MS2812 is undersized to charge a 800AH bank. As many of us seem to have that size and larger banks.)

Second - Is your asking if I'd adjusted the MS2812 downward to reflect aging batteries. (And no, I did not set the AH's down from 800. Probably naive on my part, but I thought that the MS2812 AGM1 setting would automatically account for this. And probably wishful hearing on my part, because the Lifeline Tech's conclusion when I talked with him - was that the MS2812 was sophisticated enough to 'program and forget', as far as caring for the batteries.

Last Wed I sent Lifeline a summary of how I've cared for this bank, asking them if they felt I'd done something wrong. I specifically pointed out that IMO, they'd had an easy life, and living on the top 25% discharge of the bank should have consumed very little of their total 400,000 (50% SOC of 800 AH's = 400. X's 1000 Life Cycles DoD = 400K AH's (Unless I have that messed up!) I realize this potential AH's as far as Life Cycle usage - lots of variables. But thought it was reasonable due to low Life Cycle consumption to have seen 6-8 years out of this bank. (Or heck, I would have bought a 600AH bank instead, which my energy audit showed should have supported our needs quite well. Added and paid for 200AH's extra to have some more contingency, as well as I hoped a few more years of usage out of this bank.

After a test last night turning off the Inverter for 2-3 hours at a time, to try and make it thru the night with the bank - it's not looking to encouraging. Have performed two Condition cycles of 8 hours, and Amps never tapered down below 15A. Probably a bad cell, or just dried up the juice! Going to do as close to get to full charge again today (On Shore Power for one night.), then turn off the inverter and solar controller, and let the batteries rest as long as I can before we have to move on Sunday. Take multi meter readings of each battery, to see what I get. Might get lucky and two of them are the bad brothers, bringing down the other two. If so, I'll disconnect those two - and then get along for the rest of this trip on 400AH's. (Yep, will set the AH down on the MS2812 too. Will try 300AH's. (Though I don't recall ever reading about adjusting AH bank size down due to aging batteries. Thanks for that tip!).

I'm also kicking around picking up one of the $20 off Good Sam's Duracell Grp 31 AGM's, and just jumper cabling them to the house bank (4 or 2 batteries, depending what the multi meter readings show tomorrow.). See if that can help 'augment' the bank to get thru the night. We're only out on this short trip until the first week of April, and I don't plan to replace the L16's until I get home. Not sure what with.... We'll see. But also suspect the Grp 31 would just be drawn down too, as I've always read that the weakest battery seems to win in a bank! But, might get us thru the night.

Thanks again, and best,
Smitty

Smitty,

I feel your pain. From what you describe you have indeed gently used those batteries. I too would have expected more from Lifelines.

With regards to the rate of charge yes Lifeline AGM’s can take a high rate of charge (1C+) but your MS2812’ s 125 amp charger is still putting 15.6% of C into the batteries which will take longer but I don’t think it is hurting your batteries nor preventing them from getting a full charge. If you want to ask someone about it I would talk to Lifeline not Magnum. Most AGM batteries have a recommended max. charge rate of 15-20% of C so you are right in the ballpark. Lifelines may be a little different but for the most part a slightly lower rate of charge and thus less heating of the batteries is beneficial for longevity.

Under the Settings menu on the MS2812 the AGM1 setting is only one part of the entire setup equation. Other key settings are rate of charge, battery bank AH, or Absorb Time (depending on the vintage and revision of your remote panel).

One important point to clarify here. On the version of the Magnum remote that I have (yours may be slightly different) is the Absorb Time (or Amp Hour) setting in the setup menu is used for determining the Absorb Time after the Bulk phase is complete. A setting of 800 AH will give approximately a 2.5 hour Absorb time. When you add in a BMK kit to the Magnum remote the Amp Hour setting under the Meter button is a different AH setting and is used in conjunction with the charge efficiency setting to properly determine SOC. It is the AH setting under the meter menu that should be slowly decreased as the batteries age to get a more accurate SOC readout. If a 4.5 year old 800 AH battery bank is not scaled back as the batteries age it will over estimate the SOC. If the actual remaining capacity is 600 AH (instead of the original 800AH) using 300 AH from the battery bank will show 62.5%SOC instead of what it actually is 50% SOC if the AH setting is not dialed back.

What I have found is the faster the battery bank gets through the Bulk phase when charging the quicker it will drop in overall voltage when discharging. A sign of a battery bank (or 1 or 2 batteries) that is on the way south. I would talk to Lifeline more and see if there would be any benefit to running more conditioning charge cycles to try and revive the bank and perhaps get another year or so.

If you do find 1 or 2 bad batteries separating them out of the mix may be an overall improvement to your situation even though the total capacity is reduced. Experimentation may be the only way to tell for sure.

Best of luck.

[Smitty77]

Thanks again Don. As you can imagine, I've been rechecking settings quite a bit the last week!

The scaling back of Band SOC size for age, is the one I've never accounted for... And I admit, I'm wondering if the change I made about 2 1/2 years ago on the MidNite Classic 150 to use Ending Amps to stop Absorb was a good move or not. That was the last time I talked with Lifeline Tech Support on the phone, having them reviewed my Ending Amps work up.

We were able to get a site with power for one night. So I did a partial test recommended on the RV.Net Tech from a few Guru's of electricity!

-We were at full indicated charge via the Magnum and MidNite Classic 150
-Tured off the inverter and charger of the Magnum as well as the Classic 150 controller solar feed was turned off too. 1:00PM yesterday.
-Did not disconnect the batteries, as LP Detector, Fantastic Fan Rain Sensor's, etc. were still being fed some power from the bank
-Camp host came by and said we could move to the next non powered site in about an hour, as the occupants told them they were leaving early
-So took 8:00AM so approximately 17 hours or so of almost resting for the bank of L16's
-I will note that BMK Meter showed the Shunt Valve saw 53AH's pulled out in this time period, representing the parasitic draws

Multi Meter Readings:

Bank = 12.61V
Bat 1 = 6.31 Bat 2 = 6.29 Connected = 12.6V
Bat 3 = 6.31 Bat 4 = 6.29 Connected = 12.6V

Lifeline Depth of Discharge chart I have shows:

0% 6.4V or more 12.8V or more
25% 6.25V 12.5V
50% 6.10V 12.2V
Etc.

Using 800AH, 53AH's is ~ 6-7%
Using 600AH, 53AH's is ~ 8-9%

====

Not sure how to interpret this info. Not fully resting. But still not as far as a drop as I'd had expected if the L16's are going out as fast as I think they are...

I did not bring my Kill-A-Watt with me. But think I'm going to visit Home Depot or Lowes and pick up another one to keep in the coach. I've had two or three PM's from people that had their Samsung still keep the food cold, and the ice hard, but whose Defrost mode never shut off. Control Board needed to be replaced.

So a test of 24 hours or so will be good to compare with my 7 days amortized test of Samsung consumption when we put it in about 4 years ago. Sure would not hurt to validate it's not just banging away AH's while boon docking over night!

===

One step at a time!
Smitty

[Smitty77]

As FYI for anyone reading this in the future. I did check my BMK-Meter Absorb setting. I had it set to complete at 100% SOC. Have changed it back to 2 1/2 hours.

So if my reported SOC was not actually as high as it should have been, I sure could have been 'walking this battery down' by shorter then ideal Absorb cycles... (When on shore power, which has been the bulk of the time the last few years. Maybe max 15% Boon Docking with Solar doing the charging the last year or so.

Best to all,
Smitty

[hclarkx]

Smitty,

Just some thoughts for now or down the road.* As batteries get older and drift apart, two series 6V batteries that measure different 50% or similar discharge voltages really need to be conditioned / equalized individually.* You really want them to have equal voltage when you get them up to 14.4 V.* The weaker one might need extra equalization to bring it back.* This requires a 6V charging system so may not be practical.

Also, my experience with solar has shown me that SOC tracking is anything but a science.* My battery is an LFP with less energy going into heating when charging and discharging but still, the problems are similar.* Higher loads or charging rates mean higher losses/heating in the battery.* The SOC monitor is supposed to take that into account but since the losses vary with SOC and battery temperature and charge level and load level, this is very tricky business.* And, when using solar it's even trickier since 100% charges may be fleeting.* In my case over a recent three week period my solar only ever got my LFP up to about 90% and several times I was down in the 30's (this is permissible with lithium batteries).* Then one day I got down to 26% (lots of rain) and the voltage drop under load suggested much lower SOC than that.* From LFP charge curves I determined that I was actually below 5%, not at 26%.* Clearly my SOC was losing its grip on the actual charge through all of these partial charges and discharges.* Later I figured out that when it said 90% it was actually 70% or less.*

In your case this would all be above about 75% but if the solar rarely got the batteries to a true 100% (14.4 V) then the SOC tracking could easily drift off.* I understand that SOC monitors depend on occasionally seeing a full charge to get a fresh calibration on the true 100%.*

If your SOC is telling you 100% before the charge voltage gets up to 14.4 (or 14.6 or whatever is the case for your batteries), then it has drifted off.

My understanding is that the SOC monitors need to see fairly frequent 100% charge levels to reset their 100% point.* In my case it took a lot more charge going into the battery with the 100% SOC reading not changing.* When I started discharging from that new much higher state of charge the SOC started moving down right away.

If your solar is doing much of your charging, then you could be accumulating error in the SOC reading and running the batteries at alower SOC than is indicated.* With the high and difficult to track losses in an LA battery this could happen much more easily than in my LFP case.*

The next time you top off the batteries, watch the SOC ... if it stops at 100% before you get the batteries to a true 100%, then it was reading low.*

Harrison

[BigBillSD]

Wow. Voltage reading to determine battery state of charge is a fools errand in our coaches. We are always either charging or discharging the batteries. So the voltage is always incorrect. I tried using that info for a year, pretty much a joke on me.
Bought a Trimetric https://amzn.to/2G7cyQ1 for my coach that give me real information about how many amps I used and how many I have put back in, but your BMK that uses a shunt should be just as good!

Bottom Line, believe your BMK no matter what. Call Magnum if you need help with it. Their tech support is grade A. -Bill