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BMS design for boats

Goboatingnow

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Hope this block diagram is visible note it’s not electrically perfect

This bms is based on a battery by battery basis in this case each battery is 4 series cells resulting in a nominal 12v 100Ah battery

The bms has a high side mosfet disconnect and uses an ATTINY connected to a dedicated analog front end. ( there are several haven’t finalised one yet. ) these chips handle the large common mode voltage of the series series

Some things are omitted. The current is sensed using the Vds drop across the mosfets ( bidirectional mosfet switch. ) however I could equally use a simply sense shunt as some front ends have a shunt reading ability.

The mosfets are high side so the system ground remains intact so comms can continue even post mosfet disconnect

A haltek switched capacitor active balancer is present running under the ATTINY control. This prevents balancing until the upper knee voltage is approaching.

Each cell has voltage sensing to 1mV accuracy and temperature measurement per cell.

A wired OR fault and alarm lines run between each BMS per battery. Alarm is a pre warning of impending disconnect and fault Indicates disconnect.

As can be seen each battery unit is connected to a ESP32-C3 ( RISC V) based communications monitoring unit. This communicate to the bms modules via LIN bus which is a simple serial system. The esp polls each bms and equally monitors the fault and Alarm lines.

The comms module has CAN WIFI and Bluetooth supporting potential connections to Victron VE.CAN or Bluetooth setup apps. It’s intended that charge and load commands would be issued over CAN. But equally dedicated IO lines could be provided if needs be to allow selective load disconnect strategies or charge start stop.

I’m working on this project post Christmas as I’m currently designing a new alternator controller
 

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I’m keen to see this one in action. Also interested in your alternator controller.

I would have liked to design and manufacture my own BMS. Couldn’t justify the extra cost.
 
Why not actively balance throughout the discharge cycle?
In theory active balancers can but they transfer SOC based on cell terminal voltage. Firstly under discharge this is notoriously inaccurate and secondly with the flat VI curve , you can end up unbalancing cells rather then balancing them

You could rebalance based on cell SOC , I am computing cell SOC anyway but I’m not planning a specific cell to cell transfer balancer

The only practical point to balance is as you approach the upper “ knee”
Where the VI curve is more defined and cell voltage is more indicative of SOC.
 
I’m keen to see this one in action. Also interested in your alternator controller.

I would have liked to design and manufacture my own BMS. Couldn’t justify the extra cost.
The bms parts count not including enclosure is $40 for 4 batteries. I have SMD solder reflow ability so can solder my own ics. I tend to use 1206 SMD parts which are easy to have solder

The only tricky part is the TI battery management chip I’m going to now use , it’s a TSSOP so 0.5mm pin spacing

The alternator controller is based on the ST L9918 alternator controller , paired to a micro with CAN bus, but now I’m thinking of pairing it to a ESP-C3 which could offer CAN Wifi and BLUETOOTH
 
I should say my boat orientated networking concepts have evolved. I’m now have a nmea2000 gateway to wifi ( YDWG-2) and a wifi gateway to 4GLTE ( RUT955)

Hence before I was using LIN and CAN on boat projects ( I have a Lin Based panel display system as well as LIn “smart shunts”)

But now I’m think wifi is the way to go Pulling wires on a boat gets old fast .

So I’m now doing a esp-c3 smart shunt aimed at wifi , this will allow me to easily “instrument “ major power sources and consumers without pulling extra wires.

Hence my current projects in design are now being refocused away from CAN and towards boat wifi

This means everything can be monitored and controlled over 4G too
 
I’ve not completed my chip review and settled on a single chip atmega406 BMS chip.
 
Thought you'd be interested in this link, even though it parallels LFP with FLA, due to the modular aspect.
 
Thought you'd be interested in this link, even though it parallels LFP with FLA, due to the modular aspect.
Once the ISO spec is incorporated into the RCD next year you’ll never see that type of product on a boat
 
Have you checked out the TAO BMS ? It is designed with marine application in mind. Not sure how well it integrates parallel packs, but might be worth checking out for comparison.
 
I like the TAO BMS design, it is called a "Complete Energy Management System" and it could be used the the Small Boat BMS/LFP with Backup, quite easily. You would not need the CerboGX or Color50 as it has excellent instrumentation. See Phillipe's Post #2 response to my questions and following responses.

I was checking the prices for his complete TAO BMS $492 plus the BMS Moniter $295 and For the full 12v BMS Kit $795 (which support up to 6 relays and a shunt),

while the 12v REC active BMS is about $456 with harness and shunt and no monitor, plus the CerboGX $300 and Touch50 $230 is totals $986.

You could use the REC Lcd Touchscreen for $208 instead of CerboGX and Touch50 to reduce cost to $686, but you would then not have control of the chargers. So I think TAO BMS might prove to be slightly less expensive, which will still control the chargers, but will not allow using the considerable potential communication advantages of the CerboGX system.
 
The Tao will integrate with the Cerbo anyway like the Rec

The other option is Victron Venus OS ABYC or node red /signal K. This is incredibly powerful and free but a reasonably learning curve.
 
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