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oceanfrank avatar image
oceanfrank asked

BMV 712 works on battery only, but not on shore power

I have a BMV-712 connected to two 100amp batteries that are in connected in parallel, giving me 200 amps. Works perfectly when I am battery only. I can watch the amps go up 0.1 Amp for each LED light I turn on in the popup camper. I connected a portable fridge, and it goes up 5Amps as expected. Connected another one and it goes up another 5Amps. However, when I connect short power, I cannot detect anything. The amps reading started out close to 15amp and then just continuously dropped 0.1 amps every sec or two until it got to roughly 11.4amps. Then if I turn on one portable fridge, the amp reading would decrease 0.4 amps, turn on the second one, and the amp reading would again decrease another 0.4 or bring it to 10.6. I would have thought the amp reading would have gone up by 10-11amps. So is it measuring how much it is charging the battery? Very confused. Does the BMV-712 only measure battery use and cannot tell you how many Amps are used when connected to shore power?

Frank

BMV Battery Monitor
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3 Answers
kevgermany avatar image
kevgermany answered ·

Bottom line is that the 712 only measures current through the battery. Assuming you're wired up correctly, the loads like fridges, lights will be taken off shore power before the battery gets any charge. All you'll see in the 712 is the balance of power either charging the battery or if shore power is inadequate, you'll see the amount the battery has to supplement shore power by to make up the shortfall.

You don't say what else is in the system, but to measure shore power and/or non battery loads off shore power you need to add more measuring devices.

I've found that using a single 712 in my camper is more than enough. It's really there to tell you what's happening to the battery and what's in it. I use a CCGX for everything else, this pulls in the figures from solar, shore power etc. What it misses is the charge from the engine alternator, fed Orion, but that's covered indirectly by the 712.

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mvas avatar image
mvas answered ·

Can you share a schematic diagram of the battery bank, BMV 712, charger and loads? When connected to shore power, is the 15 amps CHARGING the battery bank? Then when adding loads, the charging amps decreases?

If the BMV 712 is the only thing connected to the negative terminal of the battery then it measures amps IN or OUT of the battery.

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oceanfrank avatar image
oceanfrank answered ·

Thank you MVAS and Kevgermany. Your explanation Kevgermany makes sense and explains why another person installed the CCGX (at least partially) in a similar popup camper similar to mine (to which I was trying to mimic). They demoed the readings for me, which sold me on the 712. However, for some reason, I expected the 712 to measure everything regardless of the power source. I did not comprehend at the time it was only measuring the battery because he was not utilizing shore power. He too also had a CCGX, but again I did not realize this was used to measure the shore power side. This is the part I did not catch at the time, as we did not discuss this. But, thank you for the explanation. But as I digested what you said, it all makes sense now... Basically, what I am seeing is the excess electricity charging the battery for now. Once the energy requirements exceed shore power, I will see battery use, not charging, read outs. Thank you for taking the time to explain.

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kevgermany avatar image kevgermany ♦♦ commented ·
There's often more to these things than you realise. Glad to help.
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