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Smart BMS 12/200 with Balmar MC-612 cutting alternator input

Hello, firstly the setup.

Smart BMS 12/200

X3 Smart 200ah lithium

X2 100/30 smart mppt

X2 410 watt panels

X1 smart battery protect 100a for mppt charge

X1 smart battery protect 220a for load

Super AGM 110ah start battery

105 amp alternator

Balmar MC-612 regulator

(Balmar settings)

Bulk voltage 14.4

Bulk time .3 (factory)

Absorption voltage 14.4

Absorption time 2hrs

Float voltage 13.5

Float time .3 (factory)

Alt temp 108c

Positive voltage sense connected to starter battery. (Not lithium side)


Engine is running at 1200 RPM at the dock. I started charging via alt at 82% as seen in video the BMS % drops down as starter batt voltage reaches 13.92v. Slowly starts applying amperage until nearly 55amps (100amp fuse on alternator side of BMS) this only lasts until starter voltage climbs back up and repeat. The BMS doesn’t have charge settings so how do I get this issue solved

How do I stop this cut off?
The link for the video is below because the file format is not acceptable on this site for some reason. https://m.youtube.com/watch?v=Mu0TSW1yR4U

I have attached a pic of my wiring diagram and video of the problem.

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Lithium BatteryBMSalternator
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2 Answers
svgemini avatar image
svgemini answered ·

Update for those who are following. I figured out the problem. The batteries were balanced so that wasn’t the issue. The Balmar positive voltage sense absolutely matters where it’s is hooked up. Additionally it needs to read both battery banks. Connecting positive from start and positive after the battery protect the to positive sense pin now let’s the Balmar see a combined voltage and prevents the start battery from being overloaded and full field dumped after BMS cuts off lithium charge.

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Paul B avatar image
Paul B answered ·

first of all you need to check your batteries and make sure that the cells are balanced, if you have unbalanced cells then the bms maybe turning off due to one cell being high. please check this and advise

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All three batteries are balanced as stated on their respective Victron connect app.

please send a screen shot of the cell voltages for ALL the batteries when the BMS cuts off

Edited _ I am presuming that the batteries have been connected correctly to the BMS

Since I could not get the bms to charge consistently from the alternator I turned on shore power and brought the batteries through their absorption phase and into float. They have been balanced since the installs initial charge up two weeks ago.
Yes the batteries are connected correctly to the BMS. Daisy chained together then to the Smart BMS 12/200.
Did you see the video? Is it normal to have the start battery voltage raise while the lithiums are being loaded?
the system is newly installed amd this is the first time I’m running the engine to charge. This boat will be offshore for most of its life so I won’t be around shore power.
Also, am I correct by having the regulators “positive battery sense” connected to start battery positive? Would it matter if it were connected to Lithium positive?

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Yes I can see the screens but for the BMS to turn off - really a cell has to go high and you will only see this at 14 to 14.4 volts - also the alternator may supply huge amps depending on its size. so you need to check the batteries when the system is at 14 odd volts then each cell will be around 3.5 volts

were you put the reference voltage connection is upto you but it needs to be after the bms not on the batteries otherwise if you do get a disconnect then the voltages may go high.

So maybe its best to leave that on the engine battery - but the voltage on both should be the same (well close)


also check the BMS fuse sizes as well - I have not used that style of BMS myself as I personally like using the GigaVac heavy duty relays that are NOT current limited (well they are but 400amps), especially as the battery banks and alternators are getting very large now - I have seen a 900amp alternator at 24 or 48 volts) as the right size battery bank can take everything a alternator can throw at it. Like this boat has a 100 Kw battery bank 4 x 8Kw Quattros plus the large engine Alternator - this bank can absorb 4000 amps at 2C and 2000 amps at 1C but its near impossible to send that many amps to it .

anyway there are lots of diferant ways to do things and there is nothing wrong with the unit you are using as long as it suits your systems


NOTE that balancing only occurs at 3.5 volts or above (depending on the battery bms that is) so you need to hold that voltage until they are balanced then go to float. but if any cell goes over 3.65v then the bms turns charging off or turns the banks charging off