question

Tim Rohrer avatar image
Tim Rohrer asked

Is my system defying the laws of physics? :-)

I have a BMV-702 installed in my truck camper with two lithium 100 Ah batteries. The primary bank monitor is connected to lithium house batteries. I went ahead (because I could) and connected the feed coming from the truck as the second bank for monitoring. The batteries in the truck are isolated from the house batteries using a Blue Sea Systems isolator.

What is weird is that I've seen the BMV percentage of charge *increase* over night while boon docking. Once again this morning (after an overcast day yesterday with rain), the BMV was showing a fully charged system even though I saw it down around 90% yesterday.

The video is representative of what I've experienced The monitor may indicate ~90% charge when I go to bed, but be back up at 100% in the morning.

What could be causing this?



BMV Battery Monitorbmv power consumption
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1 Answer
Alexandra avatar image
Alexandra answered ·

@Tim Rohrer

Can you post a picture of your setting

It seems to be syncing to 100% when it shouldn't.


I am assuming you have it installed physically the correct way around. Loads and chargers on one side the the battery on the side marked battery.

Does the percentage go down in normal use when there are no charge sources and a load attached?


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Tim Rohrer avatar image Tim Rohrer commented ·

I believe I have it all correct. This is my third battery upgrade project and my second install with solar. That doesn't mean I am incapable of a mistake though.

I assume you wanted pictures of my setup?

shunt-setup.pngbattery-bmv-connections.png

I just turned off the solar charging and the battery bank (by volt meter) was 13.47V while the monitor was reporting 13.41V. I'd call that reasonably close. Also with the solar off, I have a negative draw on the bank. It is currently (pun intended) still showing 100% charge, but I have seen it drop as low as 90%. We've got 200Ah of batteries and no inverter so most of our usage goes to fans, charging electronics, and lights. I wasn't surprised to see the charge drop only to 90%, but yesterday with the rain I was expecting to be lower this morning. Instead I was back to 100%.

In the few minutes that I had the solar off, the percentage on the BMV dropped to 99.7%

Oddly, if I press Setup on the BMV display, nothing seems to be happening.

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