Victron Battery monitor doesn't jive

steved28 · 01-09-2023, 04:45 PM

I have a Victron BMV-700 battery monitor and recently installed 4 LifePO4 100Ah batteries. I have been testing my battery heating pads (12V) usage against battery life. When the heating pads are not drawing current, there is about 1A (dc) of parasitic draw. When both pads are on, the draw is about 11A. They cycle and have been in use for a few days.
This is where I have my dilemma. I have 400Ah worth of storage, the BMV-700 knows this. I have used 269Ah of storage, yet my SOC (according to the monitor) is at 55%. The usage number also comes from the monitor. The sitting voltage right now is ~13V.
So how can I have used well over 50% of my Ah rating, and be at 55% SOC? What am I missing and what should I be using to determine my remaining usage on my batteries?

Thanks for your input.

Marine359 · 01-10-2023, 07:28 AM

I don’t have a Victron Bev 700, but I do have a Victron Smart Shunt. I think they operate pretty much the same. You can’t get accurate SOC, unless you put a full charge on the batteries, then go to the menu and “synchronize SOC”. It works pretty well after you do that.

bigb · 01-10-2023, 07:50 AM

Quote:

Originally Posted by steved28

I have a Victron BMV-700 battery monitor and recently installed 4 LifePO4 100Ah batteries. I have been testing my battery heating pads (12V) usage against battery life. When the heating pads are not drawing current, there is about 1A (dc) of parasitic draw. When both pads are on, the draw is about 11A. They cycle and have been in use for a few days.
This is where I have my dilemma. I have 400Ah worth of storage, the BMV-700 knows this. I have used 269Ah of storage, yet my SOC (according to the monitor) is at 55%. The usage number also comes from the monitor. The sitting voltage right now is ~13V.
So how can I have used well over 50% of my Ah rating, and be at 55% SOC? What am I missing and what should I be using to determine my remaining usage on my batteries?

Thanks for your input.

That's odd. If there was some charging happening it could replace some of what you took out but then the "269ah consumed" would be adjusted down as the % remaining goes up as the charge builds. If power is interrupted to the shunt (and your auto starts synchronization is set to on) then everything starts over as the system assumes a recharge, but this means the amount depleted also would reset to zero. This would mean the display would report more than you actually have but it would also report less ah consumed than actually consumed. Just for S&G was there any interruption of power to the shunt/monitor during your test period?
If there is any consumption or charging going on that bypasses the shunt it will get out of whack (mathematically) but since yours is reporting 269 used and 55% remaining it looks to be a math error in the system if you have indeed programmed in the 400ah. But I don't see how that's possible. Assuming you made absolutely sure the 400ah is programmed in correctly? That seems the only logical conclusion, that the 400 ah is not programmed in. The system only uses math to calculate remaining capacity.
Please call Victron Tech support, I have used them and they are very good. Let us know what it turns out to be.
If for any reason power was interrupted during your testing period I recommend that you fully recharge, sync and start over.

steved28 · 01-10-2023, 11:48 AM

Thanks Brian, it is perplexing. The Victron is certainly not performing simple math. It seems to be basing the SOC on voltage. I will check again, but I am fairly certain I am set for 400Ah. And I manually synced after the last full charge. I do not know what I have set for auto sync, but will be sure to shut that off. Everything pulled (or put into) the batteries goes through the shunt on the negative side. And it seems to keep track of Ah very well in both directions. I am performing another test right now, the Ah's were down to -310Ah and my SOC said 47% !!! If it fails again, will definitely call support.

steved28 · 01-10-2023, 11:49 AM

Thank you Jim. I did a sync after the last charge, but am performing another as we speak.

bigb · 01-10-2023, 02:05 PM

Quote:

Originally Posted by steved28

Thanks Brian, it is perplexing. The Victron is certainly not performing simple math. It seems to be basing the SOC on voltage. I will check again, but I am fairly certain I am set for 400Ah. And I manually synced after the last full charge. I do not know what I have set for auto sync, but will be sure to shut that off. Everything pulled (or put into) the batteries goes through the shunt on the negative side. And it seems to keep track of Ah very well in both directions. I am performing another test right now, the Ah's were down to -310Ah and my SOC said 47% !!! If it fails again, will definitely call support.

It does not use voltage for SOC calculation except to watch for the fully charged voltage that you set into the system when you set it up. When it sees the fully charged voltage for 3 minutes it will automatically sync to 100% charge, from then on it only uses math to keep track of ah out and ah in until the next time it sees the pre-set "fully charged voltage" when it will sync again. The reason for this is because even though it is counting ah in and ah out and when you charge it would still be close to 100% just from counting but over time it would gradually "drift" and eventually become inaccurate, so by automatically synching at each full recharge it keeps it's accuracy during the mathematical additions and subtractions. I wonder if when your heaters cycled off the first time the battery voltage recovered to a high enough value to make the device sync? But even if it did I would think that the ah consumed would zero at the same time. What do you have your "fully charged voltage" set at in the software? I found this regarding power interruptions:

steved28 · 01-10-2023, 02:11 PM

Quote:

Originally Posted by bigb

What do you have your "fully charged voltage" set at in the software? I found this regarding power interruptions:

This was an area I was uncertain. I had it at 13.2 initially. I wonder of I should set it higher? Of course if it does not calculate SOC via voltage (and I hope it would not with LifePO4) then it seems irrelevant.

bigb · 01-10-2023, 03:37 PM

Quote:

Originally Posted by steved28

This was an area I was uncertain. I had it at 13.2 initially. I wonder of I should set it higher? Of course if it does not calculate SOC via voltage (and I hope it would not with LifePO4) then it seems irrelevant.

It is not irrelevant because it uses voltage to determine when the battery has been fully recharged and 13.2 is the setting for lead acid, when the heat pads shut off on the first cycle or first several cycles the voltage could have recovered to 13.2 and reset the battery bank monitor to 100% even though it wasn't fully charged. See chart below, I think you should change your fully charged voltage to the float voltage for your battery type which is probably 13.8 but look in your battery documentation to be sure. As long as your fully charged voltage is set to 13.2 the device will keep resetting to 100% every time it sees 13.2v for at least 3 minutes. (note: you can go into history and see when the last recharge was, if it shows a recharge when you didn't have it on a charging source it had to have seen the charged voltage setpoint at some point, for 3 minutes)

bigb · 01-10-2023, 04:18 PM

Battle Born recommends 14.2 volts https://battlebornbatteries.com/conf...etooth-dongle/

powercat_ras · 01-10-2023, 06:48 PM

The Victron has a setting to match it to the shunt being used, it defaults to the setting to match the 500 amp shunt they supply. I have the BMV-702 and in its manual there is some information about calibrating the unit, you might look at that. If that setting is wrong it will miscalculate the current flow in/out and that would mess up the calculation of real time battery amp-hours stored.

I can't think of anything else that would cause your issue, but there are a few settings that they recommend be changed for LiFe04 battery type. In particular they recommend a different correction factor for high current loading (Puckert factor) for LiFe04. The BMV-702 manual has the recommended settings, if you can't see it in an older BMV-700 manual you might download the BMV-702 or BMV-712 manual to get them.

bigb · 01-11-2023, 06:39 AM

To add to what I mentioned earlier the battery voltage could have also dropped to 13.2 during use which would also trigger a reset back to 100% on the Victron. If you look at the SOC voltage for a LifeP04 13.2 is only 70% charged.

**creativepart** · 01-11-2023, 07:29 AM

I too have the Smart Shunt and there are a number of settings you need to manually configure to set the device up for accurate reporting. If you have 13.2v as the fully charged voltage then perhaps some other settings need adjusted as well???

Also, are you sure you have all loads on your RV going through the shunt? For instance, does your battery heater negative load go through the shunt? Does any solar panel negative from your solar controller go through the shunt?

Here are the settings I have for my BMK, I’m not saying they are the correct settings but they are what I’ve been told by others to use.

steved28 · 01-11-2023, 08:40 AM

Well, after performing a full scale charge cycle, then syncing the monitor to 100% AND shutting off the auto sync function, today it looks much better. Currently I have 34.1Ah's used and the monitor is displaying a 94% SOC. That is right on for a 400Ah bank. I can only assume that during the last cycle, the SOC was auto reset at some point. BTW, during the Magnum 2012 float period the battery seems to be wanting to float at 13.3V, this is using the Magnum MC-R50-L remote with the new Lithium profile included. But I set the full charge to 14.4 after reading your responses. Thank you all for the replies, it helped set me in the right direction.

bigb · 01-11-2023, 10:25 AM

Quote:

Originally Posted by steved28

I set the full charge to 14.4 after reading your responses.

I think that should do it, the trick is to set it at a voltage that the batteries will be at for at least 3 minutes while fully charged.
As far as the "auto starts synchronization" setting that one confuses people, it is mainly for boats where you remove the batteries and take them somewhere else to charge till your next outing, then upon hookup the Victron syncs to 100% because it assumes the re-connected batteries are now fully charged. If you keep the batteries installed and connected all of the time this setting should be disabled, the Victron will still automatically sync every time it sees your charged voltage for 3 minutes.

dsbike · 01-16-2023, 06:23 AM

You do not mention the brand of your batteries. I installed Lion Energy batteries & I had the same issues as you seem to be having. I contacted Lion Energy & they sent me the correct settings for the Victron 700. They were different than Victron suggests. I have'nt been out since resetting & Have everything off for winter storage, so I can not verify that this worked. However with the last post you made I see you are now getting better readings after you made some changes.