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Old 08-09-2019, 05:07 PM   #1
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Magnum Energy BMK SOC issue

I don’t seem to get consistent and expected readings with my Magnum Energy Battery Monitor system for the State of Charge (SOC). I use it to monitor by Sportsmobile AGM battery bank with my Sprinter second alternator. Has anyone else had similiar issues.

For example, I will be at 100% SOC at home after a full charge. I can then be out camping and run the batteries down to 70%. I then may drive for 8 hours expecting to be fully charged again but the reading may actually be down to 60%. I can then just wait for 6-8 hours and see a reading of 80% or often 99% by the next morning with absolutely no further driving or charging. The problem seems to a significant delay of many hours in correctly reading a higher reading after I charge with my alternator. I had assumed the SOC would be close to a real time reading. Thanks for any ideas.
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Old 08-10-2019, 07:08 AM   #2
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I would suspect a problem with the unit. There really should not be a delay. I have to battery monitors on board, one being the BMK. There usually are the same. I have seen both of them claim 100% charged to early when on solar and the sun slowly drops mimicking a charger completing. That is a rarity, but can happen.

I would check and see how much current you are reading when charging off of the alternator, amp hours and such and see if they correlate.

Also give Magmum a call.

And I think user Fitz just mentioned he had a bad BMK, might want to touch base with him.
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Old 08-10-2019, 08:38 AM   #3
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Correct, I just replaced the unit. Very similar symptoms, the one symptom that convinced me (and the helpful Magnum rep) that it was bad was the Amp reading. It was obviously wrong when in use and it was holding a constant 26 Amp reading with everything disconnected. I changed out the unit and all is now well. Suggest you perform the same test, disconnect all loads and see what the Amperage reading is.
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Old Yesterday, 08:05 PM   #4
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I figured out my problem with my battery monitor. Sportsmobile wired it wrong at the BMK shunt. Changing the cables at the shunt solved the problem. The Magnum tech suspected incorrect wiring and sure enough he was right. Thanks.
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Old Yesterday, 09:35 PM   #5
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Good to hear that you found it!
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