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Old 04-11-2024, 11:23 AM   #1
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Battery Monitor Accuracy

I am curious to know how others have found the accuracy of the Victron Battery Monitor (BMV-712) that Escape installs. Last year was our first season of camping with our new Escape 21C, and for the most part we were very impressed with the performance of the two solar panels and two lithium batteries that our trailer came equipped with. However, on two occasions we woke up in the morning without any power. In both cases we went to bed with the State of Charge (SOC) reading about 60 – 65 % and the voltage reading about 13 volts. The only draw overnight was the propane detector and the fridge running on propane. A combined draw of about 11 watts. The Discharge Floor on the Battery monitor setup is set to 30%. Over approximately the 8 hours while we slept the SOC dropped from about 64% to 56% at which point we lost all power. During the same 8 hour period the voltage dropped from about 12.9 to 12 volts. This happened in the fall when we were getting very little solar gain, but even without much solar gain I was expecting the 65% SOC would last us a couple of more days.

My questions are:
Why did we lose power when the SOC was still reading 56% and the battery discharge floor was set at 30%? Is this the degree of accuracy we should expect from the battery monitor?
What voltage should I consider to be 100% charged and what voltage should I expect to see when I reach a 30% SOC?
Is it normal for the SOC and Voltage to drop much more rapidly when they reach about 13 volts?
Like the SeeLevel gauges, does the battery monitor accuracy improve the more you use it? If so, is all this learning lost if the batteries are disconnected?

With the loss of power, we were no longer able to use the battery monitor app to see what was going on, so I plugged the trailer into the truck and let it run for 10 – 15 minutes. As soon as I plugged into our truck, we regained power and I was able to check the battery monitor again. The SOC was now reading 100% and the voltage was back up to 13.2 volts. I wasn’t surprised that the SOC read 100% when the trailer was receiving power from the truck, but I was surprised that it continued to read 100% once it had been disconnected from the truck. The SOC charge continued to read 100% until the batteries were connected to shore power and fully charged and then it went back to giving readings that were more accurate (more closely matched the battery voltage). Is this normal operation for the SOC of charge to jump to 100% as soon as it is connected to a power source and then stay at 100% even when the trailer is disconnected from a power source?

Attached are two screen shots of the battery monitor app before we lost power and after I plugged into the truck.

I would love to hear other people’s experiences to know if this sounds like normal operation or if you think we have an issue.
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Old 04-11-2024, 01:25 PM   #2
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I have always had problems with the Victron Battery Monitor. I likely am doing something wrong but for the life of me I can't figure out what. I have spoken to Victron to make sure my settings are accurate. I re-sync after I fully charge the batteries, but when I am boondocking I seldom get a reading below 98%, even though the voltage is dropping to 13 volts etc. For me I have given up using the SOC as a guide and simply go with the voltage. This is unfortunate as the voltage is not always accurate. Reads higher when a charge is going in and likewise reads lower when a discharge is happening (we have the compressor fridge so when it kicks in the voltage drops, but once it is finished the voltage goes back up) I think this is pretty normal for the voltage to swing a bit up and down depending on what is happening. A proper SOC reading would be great, but I just can't seem to get there
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Old 04-11-2024, 01:37 PM   #3
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Two thoughts occur to me, in the first image your voltage is below 13.1. I'm attaching a battery chart of lithium batteries and at 13.1 it says that your battery is at 40% so the SOC % isn't matching the voltage. Next when you hooked up you vehicle it jumped to 100% at 13.2. When I received my trailer last year ETI had the set up the Victron app incorrect in a couple of places. One of which was that the SOC was to read 100% when it got to 13.2 volts rather than 14.2. (some folks will state it should be set higher than 14.2 but I've checked with manufacturer of the OEM lithium batteries) I'd start checking there. It's under the battery section of your app. Mine was returning to 100% as soon as it reached 13.2 like yours. If it is set to 14.2 and is returning the SOC to 100% before reaching 14.2 I am going to have to defer to others much more knowledgeable than me which doesn't take much. I've also learned over time to pay attention to not just the SOC % but the actual voltage as well and referring to the chart attached.
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Old 04-11-2024, 01:46 PM   #4
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This is the same chart I use. So with the voltage reading and the chart I have a pretty good idea of where my SOC is, but it takes a while to get used to it. Becuase the voltage can drop quickly when there is a draw on the battery it can be a bit spooky. One minute you are looking at 13.2V, then the fridge kicks in and the voltage drops to 13 or some other lower voltage than one would expect. Fridge no longer is drawing and voltage goes back to 13.2. Likewise when there is a charge coming in from solar or others the voltage gets to 13.2 or 13.4 etc and you think you are good to go. Then the charging stops and it drops down to 13.1. I find when there is little going on the voltage is very steady. Our voltage could be at 13V when we go to bed and when we wake up it is still at 13V. Just during the day it can move around a bit depending on whether there is a draw or input. After keeping an eye on it over the last year or so I am pretty comfortable at estimating the SOC. Just would be nice to have the monitor give me an accurate number
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Old 04-11-2024, 01:51 PM   #5
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Jeremy, Do you remember what settings were set wrong by ETI and what you changed them to?
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Old 04-11-2024, 04:48 PM   #6
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I realize that you probably don't have a Battleborn battery, but for FYI, the Victron parameters for their LiFePO4 batteries are in the link:

https://battlebornbatteries.com/faq-all-about-bmvs/

I would hope/expect the battery marketer that ETI uses would have similar information.
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Old 04-11-2024, 04:55 PM   #7
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Yegegg, some settings were fine, others were as if it was set up for lead acid. The converter was set to LA, the charged voltage was set to 13.2, tail current was off and so was the charge efficiency factor I believe. I tried to find the email I sent to ETI about in trying to help them improve their set up process in the production line and it turns out it was sent with their feedback form so I don't have a record of what I sent them. Here is what I current have my settings set to.
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Old 04-11-2024, 06:25 PM   #8
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Thanks MVA and Jeremy. These are helpful.
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Old 04-11-2024, 07:16 PM   #9
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Does not sound normal. I would check all of your Victron BMV settings, charge the battery to 100% and then manually synchronize (sets SOC at 100%). It’s very possible your SOC is way off. Voltage is not a good indicator for lithium batteries. That’s the whole reason behind a shunt based battery monitor that measures current in and out of the battery. Unfortunately I would not trust that Escape set it up properly at the factory.
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Old 04-11-2024, 07:30 PM   #10
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You stated you have lithium batteries, probably LiFePO4 batteries.

I think your "discharge floor" is set too high. I was advised for our LiFePO4 batteries to use 10%.

Our BMV-712 is always within 5% of the claimed SOK of our batteries, usually 1-3%. It took awhile for me to get the batteries set. Even though I have supposedly have 211 ah's of batteries (one is 106 the other is 105), with the 10% floor I input 185 ah's for "Battery capacity".

It took a while to finally get our BMS to be correct.

I would change your "Discharge floor" to 10%, more inline with LiFePO4 batteries.

If you want to continue to use 30% for the discharge floor and have 200 ah batteries, I would use 140 ah's for my "Battery capacity" (200 X (100%-30%) or 200 X 70%) to start.

Finally when I set my "Battery capacity" to 185 ah's it show a reasonably accurate SOC. In theory it should have been 190, but over time found 185 to be more accurate. If you're looking for 100% accuracy, good luck. I'm happy with >95% accuracy.

Food for thought,

Perry
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Old 04-12-2024, 11:00 AM   #11
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I will try that. I have 4x100A Battle Born Batteries. The settings were done by myself and I used the information that Battle Born gave me. I did set the battery capacity at 400A, but will try setting at 360 and see what happens. I do re-sync to 100% after I know the batteries are fully charged. I would be very happy with a 95% accuracy
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Old 04-13-2024, 12:14 AM   #12
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Thank you all for the excellent feedback. I truly appreciate you taking the time to respond to my questions.

Jeremy, thank you for the chart showing the voltage and corresponding capacity. This will give me a much better idea of the accuracy of the battery monitor. Thank you also for the screen shot of the battery settings. I'm very anxious to compare it to the way mine is set up. I had a similar experience with the set up being incorrect when we picked up the trailer. Escape later send me an email with the updated settings (see attached) but it didn't have any where near the detail that your screen shot does. I find it interesting when I look at the voltage/capacity chart and see that 30% capacity should correspond to about 13.0 volts. When I look back at the graph from my battery monitor the batteries did not cut out until they reached about 12volts. If the discharge floor was set to 30%, shouldn't they have cut out sooner?

Perry, thanks for the suggestion on adjusting the discharge floor and battery capacity. I understand that fully discharging lithium batteries does not damage them, but does it ultimately shorten their life span (number of cycles) if you do? I have attached a graph from the spec sheet of the Hublion batteries that Escape installs. https://hubpower.ca/wp-content/uploa...100-LFP-24.pdf
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Old 04-13-2024, 08:46 AM   #13
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Quote:
Originally Posted by Live In The Moment View Post
Perry, thanks for the suggestion on adjusting the discharge floor and battery capacity. I understand that fully discharging lithium batteries does not damage them, but does it ultimately shorten their life span (number of cycles) if you do?
I bought 200 ah's of LiFePO4's to use, and don't worry if they go 9 or 12 years. We've never owned a trailer longer than six years. Besides, battery technology will have improved so much in the next decade I'll be getting rid of these fussy, lithium based batteries for sodium or silicon batteries sooner than 10 years.

In the 15 months we've had our LiFePO4 batteries we've killed them twice with our furnace use when the temps get below 24 F and we were camped in heavy shade with only our 100 watt portable panel for charging.

14.2v seems awfully low for LiFePO4 batteries. We charge at 14.6. Others use 14.4, but this is the first I've heard of 14.2 for LiFePO4's.

We camp 150-170 nights a year and our camper sits at a seasonal campsite the rest of the time where we go to have a fire, cook, drink beer/wine to discuss our future. Our batteries show less than 50 cycles, so in theory our batteries should last 15-25 years. Yeah, right!

EDIT: I see in one spot they claim they are Lithium Ion batteries yet lower down I see LFP, so are they really Lithium Ion (I wouldn't own one) or Lithium Iron Phosphate (99% of today's lithium for RV's are LiFePO4)? A nominal voltage of 12.8v tells me they are not LiFePO4. Lithium Ion are much more prone to fires.

Enjoy,

Perry
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Old 04-13-2024, 10:35 AM   #14
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Perry, here is a snip from the OEM battery data sheet. Also when my OEM converter charges the batteries I've never seen it go much past 14.2. Maybe to 14.24. To my knowledge I can't change what the converter charges to. I agree their choice of words to describe the battery chemistry is not consistent but it's LiFePO4.
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Old 04-13-2024, 10:41 AM   #15
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Originally Posted by Live In The Moment View Post
If the discharge floor was set to 30%, shouldn't they have cut out sooner?

I'm assuming no it would not cut out as it was reading the SOC. The SOC %, assuming it was incorrect and not the voltage, never got to 30% so it didn't cut out.
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Old 04-13-2024, 06:18 PM   #16
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Originally Posted by Perry Butler View Post
I bought 200 ah's of LiFePO4's to use, and don't worry if they go 9 or 12 years. We've never owned a trailer longer than six years. Besides, battery technology will have improved so much in the next decade I'll be getting rid of these fussy, lithium based batteries for sodium or silicon batteries sooner than 10 years.
Thanks Perry. This definitely helps to put things into perspective. Unfortunately, our trailer is in storage so I can't go check myself, but is there a place in the battery monitor app that shows the number of cycles? What constitutes one cycle? If your SOC drops from 100% to 95% and then your solar tops it back up to 100%, is that considered one cycle? I'm surprise that your batteries only show 50 cycles if you have camped 150-170 nights.
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Old 04-13-2024, 06:38 PM   #17
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Originally Posted by Jeremy Kessenich View Post
I'm assuming no it would not cut out as it was reading the SOC. The SOC %, assuming it was incorrect and not the voltage, never got to 30% so it didn't cut out.
What do you think caused the eventual cut out of the power? It looks like the batteries were at about 12.0 volts and a 56% SOC when the power cut out. From the battery spec sheet it looks like the BMS Low Voltage Cut Off is 9.6 volts, so I don't think it was the batteries own BMS. Sorry if the answers to these questions seem obvious but trying to understand the electrical/solar system has been a steep learning curve for me. I truly appreciate your patient responses.
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