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BMS comparison

Another bms is Batrium. It is another relay based one like Rec-Bms. To me it is easy to understand and to change things. It is also CAN-bus. But it’s also expensive.

I think one of its biggest advantages is you can use the same bms for a 4s, 7s, 16s or several 16s batteries with each cell being monitored.

I am really happy with mine.
 
You need a second contactor for the charging circuit?
That’s the usual configuration. I’ve got what amounts to two in my system. One for the high side (inverter/charger, alternator, and solar) and the other for my DC house loads.

How big are your DC loads? Mine are less than 50A, so I’m using a Victron Smart BatteryProtect as the low side. The 65A victron is relatively cheap. The only downside of this is they are only intended to work in one direction.
 
my usual DC loads (fridge, freezer, water pumps, lights etc) will be under 50A. It’s the bow thruster and windlass that create an issue for me.

I’ve considered running those straight from the battery, but having trouble making the leap of partially removing the BMS protection.
 
Both the thruster and windlass are usually solenoid ( internal "contactor") controlled. The activation device is a low current 12v switch.
The power for that switch might well come from your house 12v panel ( or could be rearranged to do that ) and hence the switch controlling the high current devices could plausibly be under the "control" of the BMS.

But check the wiring diagram carefully, the return path might be thru the heavy duty ground wiring, and hence unless the BMS disconnects the + side it won't have any effect.
 
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my usual DC loads (fridge, freezer, water pumps, lights etc) will be under 50A. It’s the bow thruster and windlass that create an issue for me.

I’ve considered running those straight from the battery, but having trouble making the leap of partially removing the BMS protection.
You probably don't even need to go straight to the battery. A good friend has a cheap 100A Daly BMS and his windless is fine. Remember, the engine should be running when you are anchoring, so the LFP battery only provides the difference between what the load is and what the alternator puts out.

Also, the rating is for continuous current, the BMS will handle more than that for short times. So, if your surge current is still under the BMS rating, you should have plenty of room. I expect that a 200A FET based BMS would handle most windlasses and thrusters without any problems at all.

Put a meter on your windless and thrusters, and find out what they really draws under load.

Another possibility, you can have a relay who's coil is controlled by the BMS. You do not need a special relay output on the BMS to do this, any FET BMS will work. Just connect the coil to the BMS load connection, in series with a switch to serve as a Windless disconnect. Then the common contact of the relay can go directly to the battery. So, you still have BMS protection, but the high load of the windless doesn't go through the BMS.

As I mentioned before, I am a fan of FET BMS's. FETS are more reliable than relays. In fact, the friend mentioned above with the Daly BMS used to have a BMS that used relays , one of his relays failed closed, and his battery melted. I helped him rebuild it, and he is much happier with it. FWIW, we selected the Daly because it was available for 24 hour shipping and he was pressed for time. It isn't my first choice, but no complaints, he has been using it a long time now without any problems.
 
Both the thruster and windlass are usually solenoid ( internal "contactor") controlled. The activation device is a low current 12v switch.
The power for that switch might well come from your house 12v panel ( or could be rearranged to do that ) and hence the switch controlling the high current devices could plausibly be under the "control" of the BMS.

But check the wiring diagram carefully, the return path might be thru the heavy duty ground wiring, and hence unless the BMS disconnects the + side it won't have any effect.
Holy crap. You just opened up my BMS options tremendously. I already have a solenoid with a switch in the dash. I can rewire that to go through the BMS easy enough.
 
I use an Orion Jr2 BMS on my DIY pack. It talks canbus to my Victron gear (just had to crimp on a RJ45 to the harness) and I get full SoC info via my cerbo - meaning phone, tablet, internet and the display I added for it.
For a budget option, Jr Rev C supports enough canbus message to work as well.
 
Coming back to this, I‘m leaning towards building a L.A. / LFP hybrid system using the Cyrix combiner from Victron. I can use this in combination with a Victron VE.Bus BMS to disconnect the the LFP battery out of the existing system. Then I would just need a way to disconnect my 25A charger from the LFP battery. Can the Ve.bus BMS directly control a 50A contactor or relay? Do I need any other VE.bus components in order to use this BMS right now?
 
You also need a shunt, fuse and holder. And 2 contractors, not just one.

When I priced it all before deciding against it the price for a REC BMS and what's needed to go with it was about $1000.
Please. Checkout Tao Performance BMS. It is the only one designed specifically for marine applications and can do Victron Canbus communication and a host of other benefits. Some issues if considering cheap dropins or cheap BMS...If you have a high load need like bowthruster or inverter run watermaker, etc. They will not handle heavy load nor give any warning prior to disconnecting the battery because of load, charging, low voltage, high voltage.
Tao and Rec will if properly configured.
 
Please. Checkout Tao Performance BMS. It is the only one designed specifically for marine applications and can do Victron Canbus communication and a host of other benefits. Some issues if considering cheap dropins or cheap BMS...If you have a high load need like bowthruster or inverter run watermaker, etc. They will not handle heavy load nor give any warning prior to disconnecting the battery because of load, charging, low voltage, high voltage.
Tao and Rec will if properly configured.
For my part (~60kWh 48V battery) and after having studied the question a lot and despite the price which can seem important (but in the range of Rec or other European manufacturers) I chose TAO bms.
Price/quality ratio, the best on the market today (in my opinion).
Features far surpassing all its competitors and above all the designer personally answers all the questions that one may encounter.
Moreover, he sets up and tests in real situation the configurations of the BMS he sells!
The icing on the cake: "handmade" and he is a passionate person.

Translated with www.DeepL.com/Translator (free version)
 
Please. Checkout Tao Performance BMS. It is the only one designed specifically for marine applications and can do Victron Canbus communication and a host of other benefits. Some issues if considering cheap dropins or cheap BMS...If you have a high load need like bowthruster or inverter run watermaker, etc. They will not handle heavy load nor give any warning prior to disconnecting the battery because of load, charging, low voltage, high voltage.
Tao and Rec will if properly configured.
I have looked at it. It is still quite expensive. Myself and many others run "high loads" like an inverter with induction cooking, bowthrusters, and watermakers on Daly and Overkill solar BMSs without problems. I have 2 years of full time cruising and continues use with times of heavy use on my overkill. Not a single lick of trouble, not a single disconnect. In fact, I have never heard of one actually failing from such use. I believe the risk to be overstated. It's not often given in the ratings, but FET BMS's do have a surge capacity much higher than the continuous capacity.

I don't really have anything bad to say about the Tao or the REC BMS. But they are both expensive and high end, and I don't think many people really need it.
 
For my part (~60kWh 48V battery) and after having studied the question a lot and despite the price which can seem important (but in the range of Rec or other European manufacturers) I chose TAO bms.
Price/quality ratio, the best on the market today (in my opinion).
Features far surpassing all its competitors and above all the designer personally answers all the questions that one may encounter.
Moreover, he sets up and tests in real situation the configurations of the BMS he sells!
The icing on the cake: "handmade" and he is a passionate person.

Translated with www.DeepL.com/Translator (free version)

For $1,500 USD!? Not even Batrium is that expensive!
Not that it matters, as their website says they have no stock due to supply shortages.

For my part, I'm using DiYBMS - https://github.com/stuartpittaway/diyBMSv4 - which has so far cost me under $200 to cover three 48v batteries, and I have enough leftover parts to cover a fourth battery once I get it top balanced and installed. Wifi, web interface, sd card logging, individual cell balancing, individual cell temperature, indicators on each cell to show error conditions, 4 relay outputs. The newer controller has a touchscreen LCD, CAN, current monitoring, and RS-485.

But I'm a DIY cheapskate, and this system isn't plug and play, nor is the software fully fleshed out (CAN isn't active, and RS-485 is only coded to support their current monitor right now - you'd have to write code and figure out the API of any additional device(s) you want it to talk to). If you don't tinker with electronics or software, you should probably stick with off-the-shelf units.

-Adam
 
You probably don't even need to go straight to the battery. A good friend has a cheap 100A Daly BMS and his windless is fine. Remember, the engine should be running when you are anchoring, so the LFP battery only provides the difference between what the load is and what the alternator puts out.

Also, the rating is for continuous current, the BMS will handle more than that for short times. So, if your surge current is still under the BMS rating, you should have plenty of room. I expect that a 200A FET based BMS would handle most windlasses and thrusters without any problems at all.

Put a meter on your windless and thrusters, and find out what they really draws under load.

Another possibility, you can have a relay who's coil is controlled by the BMS. You do not need a special relay output on the BMS to do this, any FET BMS will work. Just connect the coil to the BMS load connection, in series with a switch to serve as a Windless disconnect. Then the common contact of the relay can go directly to the battery. So, you still have BMS protection, but the high load of the windless doesn't go through the BMS.

As I mentioned before, I am a fan of FET BMS's. FETS are more reliable than relays. In fact, the friend mentioned above with the Daly BMS used to have a BMS that used relays , one of his relays failed closed, and his battery melted. I helped him rebuild it, and he is much happier with it. FWIW, we selected the Daly because it was available for 24 hour shipping and he was pressed for time. It isn't my first choice, but no complaints, he has been using it a long time now without any problems.
 
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