question

@ExpressLife, I think the giveaway clue here is that your "total charge cycles" is also at "0", probably because you have 200Ah of capacity and your deepest discharge yet has been -14Ah. The BMV will sync after a charge cycle, but you're not discharging enough for it to even register a charge cycle.

You could do one of two things (though I kind of suggest you do both): 1. Fully charge your bank (independently verify that it's fully charged, don't go off the BMV alone) and then perform a manual sync, and/or 2. Put a load on the bank and run it down a bit. -14Ah is only ~7% discharged... you should try to take the bank down by at least 40% (60% SOC, or roughly 80Ah usage) and then charge them back up to give the BMV an opportunity to even register a charge cycle... right now all it's seeing is a little top-off from time to time, which doesn't give it a chance to learn the bank's behavior.

If at all possible, I'd cycle them like that a few times (5-6 times, if possible) to give it a solid bit of data for its algorithms to work from.

Bottom line, you have enough capacity that you probably don't have to worry about it... you could leave it the way it is and you'll eventually discharge it enough that it will register a charge cycle and it'll go through its learning process, but if you want that process already in place before you go off boondocking, running the bank down and back up 5-6 times is the best way to do it.

On a side but more critical note, I see that you have it set for 12v nominal battery voltage, yet it's showing max battery voltage of 20.44v, and your start battery at 21v?? This is not okay...

First, since you're using the temp sensor rather than the start battery voltage lead, you need to go into the BMV aux input settings and select your temperature sensor rather than the start voltage. Settings>Misc>Aux Input>Temperature. Then back out and go to Settings>Display and uncheck "Starter voltage display"; that way it's not trying to display your starter voltage when the aux input is hooked up to a temperature sensor instead (I'm assuming that you correctly have only the temperature sensor leads connected to the shunt PCB terminals).

Secondarily, however, you quickly need to establish when and why the BMV ever saw 20.44v at your battery bank, because that's definitely super duper not okay.

@Justin Cook, thank you for your detailed response. I've taken your advice on discharging the batteries for a few days and will report back. I've left my settings alone for now. To address the other half of your response, thank you for noticing that 20.44 volts. Its absolutely impossible for the BMV to have ever seen that voltage, the very first time I plugged it into my system that's what it reported, but at that time I had 13.3v on the batteries. As you can tell, I've been very conservative with my system so far because I'm still in the process of building the rig and have not yet taken it on the road. I assure you at no time did I ever charge the batteries that high, and its very annoying to me to see that 20.44v every time I look at the BMV history. Furthermore, I have never hooked it up to the starter battery (my AUX input is set to temp) and of course my starter battery isn't 21v either. Could this be a faulty unit and explain my issues with sync as well? Note that the BMV will not register a sync when I do it manually either.

I hope this thread can help others understand the quirks of a lithium system too, and have a couple more thoughts.

Battery Capacity

As for putting 180 amp hours instead of 200. I was merely trying to report the 'usable capacity' of the batteries. For example if I had 200ah of lead acid which only has 50% usable capacity, shouldnt I put 100ah in the BMV? Please correct me if I'm wrong, I want to understand this as much as possible.

Absorption time

Renogy's internal battery monitor will only balance the cells when the battery voltage exceeds 14.4 volts according to their documentation. This is different from Battleborns from what I understand. This isn't that big of a deal for me I just plan to change the charge profile in the MPPT once a month or so to balance the cells. However, I've read that a long absorption time can result in overcharging lithium batteries. Is this true? I agree with @klim8skeptic about increasing the time slightly with my current settings (perhaps to give the BMV a little more time to register a sync) but it will not balance my cells if I'm only charging the 13.9v because of Renogy's internal monitor as far as I'm aware. Question: will changing the charge profile on the MPPT affect the BMV?

DC/DC charging

To make things more complicated, I also have a DC/DC charger in the rig which isn't as configurable as the MPPT. It has dip switches to choose preset charging profiles. Same question as above, will charging with the DC/DC (which has different settings then the MPPT) affect the BMV's readout?

Thanks everyone! I really appreciate the help and hope this thread helps others.

Just to add.... I too have 20v registered as my max voltage. Unsure as of why...

@ExpressLife, @Ken Bryant, it sounds like you may have a defective unit... most likely the PCB on the shunt, not the entire unit, though sometimes a bad data cable can cause this as well. One thing to check is to open up the fuseholder on the red wire from the temp sensor (or the fuseholder on the single power supply lead if you're not using the temp sensor) and make sure that it's a 1A fuse instead of the old 100mA fuses... the 100mA fuses are (now) known to cause voltage drop that can result in weird readings at the display head.

Recommend that you contact the distributor from whom you purchased the BMV and they should (depends on the level of service offered by the distributor) walk you through some troubleshooting steps on the BMV and -if everything else checks out five-by- they will likely ask you to return the PCB off the shunt, the display head, and likely the data cable where possible. They'll test each component separately and send you a replacement component for whichever is found to be defective. At least, that's what we do at my distributorship... I suppose the process may be entirely different at different dealers.

Re battery capacity no, put in your actual Ah capacity. The BMV (a properly-functioning one) will learn where your discharge threshold is; you can also set a low SOC alarm at whatever point you desire (say, 30% or so for LFP) just to alert you in case you're ever getting close. In the case of a 200Ah FLA battery bank, you would still enter 200Ah as the capacity, but charge efficiency should then be set around 95% and the Peukert exponent would be set at 1.25%; the monitor then uses these values and its own proprietary algorithm to establish the actual SOC and time remaining in the bank based on that data, and the data it collects regarding how the bank is acting over time.

Re absorption time: it's not that a longer absorption period will result in overcharging an LFP system, particularly since you have full control -through the MPPT and, hopefully, your DC-DC charger- of your absorption voltage, it's just unnecessary for them to have a long absorption time because there aren't any lead plates absorbing charge. Still recommend that you increase the time to half hour or so. Not sure about the Renogy issue... we don't carry anything Renogy because we don't trust the brand, given that it's a re-branding company rather than a design/production company. Most LFP systems I've seen, however, are just fine charging at 14.4, why not dial up your Bulk charge voltage so your cells get balanced regularly? I mean, they shouldn't need it... if they're paralleled properly they should pretty much charge/discharge in a fairly balanced way and not need the balancing very often... just thinking you may as well take advantage of that Renogy feature since you have it.

DC to DC Charging does not adversely affect the BMV. So long as your shunt is connected properly, that is with the only thing being connected directly to your battery NEGs being the "battery" side of the shunt and all other system NEGs being connected to the "load/chargers" side of the shunt, including obviously the negative cable from your DC-DC, then the BMV will register the charge coming in off your DC-DC. All good.

Changing your MPPT settings will not change the BMV display either, other than (as above, assuming the MPPT is connected correctly with its battery NEG output connected to the "loads/chargers" side of the shunt) the BMV registering the charge coming in from it. In both cases, changing your charge profile will not directly affect the BMV but it does obviously affect your charge rates/voltages/etc, which the BMV will notice, and display appropriately.

I was noticing this aswell when i first installed my BMV712, but i was only doing small discharges ie 10-15ah

I then took my system out camping and started doing 40-60ah discharges and bam, first day after a night of camping it did a sync, and every day since then,

Im guessing top of charges do not trigger a sync

..just to chime in and say my BMV 712 has wonky, or at least completely random, Maximum Battery Voltage value of 20.41V, in the history screen. So far i see no information in the manual as to what the MBV is relative to, or how it can be programed. I'll just ignore this value.

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