expresslife avatar image
expresslife asked

BMV-712 not synchronizing with solar lithium setup

Hope this community can help. My BMV 712 detects a full charge but does not sync. I have 200ah of Renogy lithium batteries charging with a MPPT 100/20 on 300 watts of solar. The BMV-712 smart with temp sensor is connected to the MPPT with a VE network. I've configured my settings based on the recommendations from Victron for lithium and the SOC will jump to 100% but it does not register a sync. Its been a week with these settings, full charge every day but no sync, worried that its not a true SOC measurement. MPPT and BMV settings are listed below and in screenshots attached.


absorption - 13.9

float - 13.5

absorption time - 2min (fixed)

tail current - 3 amp


charged voltage - 13.6 (.3 under the absorption as recommended)

tail current - 4%

charged detection time - 3m

Peukert exponent - 1.05

efficiency factor - 99%

Thanks all!

MPPT ControllersBMV Battery MonitorLithium BatterySOC
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Sten avatar image Sten commented ·

your MPPT absorbtion time is to short. it's 2 min. and the BMV require at least 3 min. to recognise the syncronization. you could also lower the charged detection time.

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7 Answers
Justin Cook avatar image
Justin Cook answered ·

@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.

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klim8skeptic avatar image klim8skeptic ♦ commented ·

@Expresslife Some extra comments, Set the battery capacity in the bmv to 200a (your battery size?)

Also some absorption time is useful to balance the cells, maybe bump the "fixed absroption" time up to 30 mins.

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Justin Cook avatar image Justin Cook ♦♦ klim8skeptic ♦ commented ·

Good call on the absorption time, Klim, I missed that. The 190Ah as opposed to actual 200Ah is, I suspect, an example of the "tell your monitor that you have less capacity than you actually have so you have a secret reserve" practice that's running somewhat rampant out on the various solar forums, particularly among the off-brand DIY users, since many of their monitors are straight from Guangzhou and, frankly, I wouldn't trust them either if I had one.

Since I haven't been able to tell that it does any specific harm (besides just being annoyingly unnecessary when using quality components), I stopped trying to convince people to stop doing it.

All that being said: @ExpressLife, for what it's worth I second both of @klim8skeptics comments. You don't need to trick your BMV into keeping a secret reserve by telling it your capacity is less than it is, go ahead and program that bad boy up... and like Klim says, a little absorption time on an LFP bank is not a bad thing.

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expresslife avatar image
expresslife answered ·

@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.

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sailor-jerry avatar image sailor-jerry commented ·

I just replaced my old 600 series with a new 712 and also had the crazy high voltage in history. I believe this is just a weird reading when you insert the fuse the first time. Like you it bothered me seeing it in history so I cleared the history in setting number 63 and it's been reading accurate eversense. Note, this will show a 100% soc immediately after the history clear but should sync after running out some ahs. As for battery capacity I set mine at 85% of listed capacity simply because my BMS stops charge at 95% and stops discharge at 10% thus 85% of capacity

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Ken Bryant avatar image
Ken Bryant answered ·

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

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Justin Cook avatar image
Justin Cook answered ·

@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.

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expresslife avatar image expresslife commented ·

I spoke with a rep from Victron, and he has informed me that the unit will not sync until your capacity has dropped below 90%. This is in section 4.3 in the manual found here

So that explains my sync issue hopefully. Sorry for not realizing that sooner.

As for the history data, @Ken Bryant, he suggested we reset the history using setting 63 from the head unit and see if we experience any more spikes like 20v.

Thanks to all that have helped.

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pstover avatar image pstover expresslife commented ·

Caution regarding the "unit will not sync until your capacity has dropped below 90%" statement that can be found in the manual (link provided above). Indeed that is what is stated in Version 13, April 24th 2020 of the Manual currently available online via the link.

However, I recently purchased a BMV-712 Smart from Amazon and the printed manual was Version 8, November 8th, 2018. It does NOT include the explanation of when automatic sync occurs in section 4.3. I just spent an hour trying to figure out why auto sync wasn't happening when I brought the SoC up from 93% to 100%. Then I did a search and found this very helpful answer!

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Ken Bryant avatar image Ken Bryant commented ·

@Justin Cook.. you suspect we both have a defective unit ?

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Justin Cook avatar image Justin Cook ♦♦ Ken Bryant commented ·

@Ken Bryant Well, try the reset on the head unit first as @ExpressLife just mentioned, but if that doesn't work, then yes, in a manner of speaking, I suspect -in particular- the shunt PCB or the data (UTP) cable. "Defective" is perhaps a strong word to use; most defects that I've seen in cables and in PCBs are actually damage caused during either shipping or installation... I suppose "malfunctioning" would be more appropriate.

In either case, try the reset and if you're still showing impossible voltages on your display, contact your distributor and they should be able to walk you through a troubleshooting process and start an RMA if it's found that one of the components is genuinely malfunctioning.

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expresslife avatar image expresslife Justin Cook ♦♦ commented ·

@Justin Cook, @Ken Bryant. Just an update for you guys. I checked last night and did indeed have a 100mA fuse. I ordered a 1amp fuse and will check back in when it arrives. Also I was confident I would see a sync yesterday since I drained the battery bank below 90% but did not. I will reset my history when the new fuse arrives.

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Gregory Cavanagh avatar image
Gregory Cavanagh answered ·

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

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rodney-abbott-buchanan avatar image
rodney-abbott-buchanan answered ·

..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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sailor-jerry avatar image
sailor-jerry answered ·

Clear your history

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