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High current LiFePO4 cells for Bowthruster

You are only going to be using the bow thruster for close quarter maneuverability. I don't believe that's the time to have a BMS trip out your battery.
Exactly!

I know what you all are saying, I will continue connecting the thruster directly though. And then the two winches connected through BMS and charging / balancing through BMS.

As said before - the thruster is only used in very short bursts when I arrive at a harbour single handed.
 
Exactly!

I know what you all are saying, I will continue connecting the thruster directly though. And then the two winches connected through BMS and charging / balancing through BMS.

As said before - the thruster is only used in very short bursts when I arrive at a harbour single handed.
you will be fine, just monitor total voltage and if possible each cell via bms.
bypassing BMA for thruster is a very good idea.
One small rash on the skin will cost $$$$, you can buy many 280ah EVE lifepo4 cells with that, ask how I know.

One thing you will be surprised by is the low sag when let the thrusters loose and how much more responsive the motor is with Li battery.

If you have space for flooded cells now, you can more than quadruple the capacity with Li cells.

My small dinghy has a well for 2x31d house batts, I could probably 3x280ah batts of 12v each, I am opting for 2x280 batts of 12v each.

I am going from 200 Ah @12v [100ah usable] to 560 ah @12v [400ah usable] plus it will weight 1/3rd ...
 
Exactly!

I know what you all are saying, I will continue connecting the thruster directly though. And then the two winches connected through BMS and charging / balancing through BMS.

As said before - the thruster is only used in very short bursts when I arrive at a harbour single handed.
With a distributed battery setup you need to think carefully about what happens when the bow BMS cuts out. If the the winches & windlass are still connected (but now to the main battery), then you must insure that the long run of wire from the main compartment is sufficient to handle the Entire load. Given the boat was designed with distributed batteries I would suspect that the long run is much smaller AWG than the direct connection to the local battery. If you can arrange for the BMS to disconnect the loads, not just the battery then you would be OK. Be careful. You really don't want extremely overheated wire in some invisible spot.
 
With a distributed battery setup you need to think carefully about what happens when the bow BMS cuts out. If the the winches & windlass are still connected (but now to the main battery), then you must insure that the long run of wire from the main compartment is sufficient to handle the Entire load. Given the boat was designed with distributed batteries I would suspect that the long run is much smaller AWG than the direct connection to the local battery. If you can arrange for the BMS to disconnect the loads, not just the battery then you would be OK. Be careful. You really don't want extremely overheated wire in some invisible spot.
It is also possible that there are fuses / breakers in all the right spots, all properly sized to protect the wire size associated with them. Then you will just have some “pops” under the transferred high load. Exciting, but hopefully safe. But... I would make double sure.
 
Yeah I think you all are right and he will be fine with whatever he decides. I think that most sailboats don't even have a bow thruster. My boat doesn't have one but I doubt that it was even an option in 1958. Hey, we're not attempting to land SN-9 here. Right?
 
Yeah I think you all are right and he will be fine with whatever he decides. I think that most sailboats don't even have a bow thruster. My boat doesn't have one but I doubt that it was even an option in 1958. Hey, we're not attempting to land SN-9 here. Right?
unless you are sailing a laser/butterfly alone, you will probably have 2 on a snipe or more on a larger boat.
with twin screws coming in and controlling the bow is an art.
With my single screw, prayer is key for me ;-)
 
unless you are sailing a laser/butterfly alone, you will probably have 2 on a snipe or more on a larger boat.
with twin screws coming in and controlling the bow is an art.

I don't want another hole in my boat. But twin screws sounds good to me. My plan is to bolt two of these onto my transom:
http://www.caroute-outdoor.com/inde... - Brushless Electric Boat Motor For DIY.html
Brushless Electric Boat Motor For DIY

These would be my auxilaries, the prime mover still being my glorious old Yanmar. But if these really can handle the 2.7kw advertised input power then, combined, that adds up to 7.2 horsepower, roughly equivalent to the existing inboard. I am going dual to get the power I want, but this also introduces the intriguing possibility of differential power for maneuverability. I only say possibility because the transom is not all that wide. But nice if it works.

Returning to topic, these are high power thrusters by today's standards but the current is only 35 amps each because of running at 48 volts. To my mind, 48 volts is a necessity for marine propulsion, anything less amounts to cruel and unusual punishment of the electrical harness.
 
You may be better off going with 1 or 2 sealed or AGM batteries for your bow thruster the same as you would do for your high amp engine starter since you will only be using the bow thruster periodically & in short bursts. From what I have heard your bow thruster batteries should be mounted in the bow to keep the power cables short. Then smaller wires to the battery charger. I suppose that you would use some type of left/off/right contactor in the power cables?
I am done with batteries with Lead in them :D I currently have a 50Kg 230AH Exide that is going to be replaced by a LFP solution.
 
I am done with batteries with Lead in them.
There's that, thanks for the reminder. I always recycle mine but a quick google shows that's far from perfect:
https://e360.yale.edu/features/getting-the-lead-out-why-battery-recycling-is-a-global-health-hazard

...but until subzero LFP performance improves, having the batteries shut down in the dead of winter means my anchor light goes out, my bilge pump stops working, I can't start the engine, probably other issues. So a pure LFP design is (ahem) a non-starter for me.

A heater doesn't solve this - my boat lies at anchor, off grid without shore power. With lead-acid, solar panels keep her happily alive all winter, so I'm just going to keep doing that for the time being. At least I might cut the 12v bank down from two to one when the LFP bank goes in.
 
There's that, thanks for the reminder. I always recycle mine but a quick google shows that's far from perfect:
https://e360.yale.edu/features/getting-the-lead-out-why-battery-recycling-is-a-global-health-hazard

...but until subzero LFP performance improves, having the batteries shut down in the dead of winter means my anchor light goes out, my bilge pump stops working, I can't start the engine, probably other issues. So a pure LFP design is (ahem) a non-starter for me.

A heater doesn't solve this - my boat lies at anchor, off grid without shore power. With lead-acid, solar panels keep her happily alive all winter, so I'm just going to keep doing that for the time being. At least I might cut the 12v bank down from two to one when the LFP bank goes in.
You can still discharge LFPs below 0 degrees C. But charging requires heating them up before you start charging. No big problem just turn on the diesel heater for a while :)
 
You can still discharge LFPs below 0 degrees C. But charging requires heating them up before you start charging. No big problem just turn on the diesel heater for a while :)
Nice try, but I'm not on the boat much in the winter. I also don't want to create artificial deadlines to go out there just to tend to the batteries. After all, that's why I installed the solar panels.

Not sure whether you were joking, but a fossil fuel cabin heater would be a horribly inefficient way to warm the batteries, as little heat will make it into the engine compartment. Sailboats are usually poorly or totally uninsulated, so the vast majority of that fossil fuel energy will go into heating the great outdoors. I think I mentioned earlier, I plan to use the 12 volt lead acid bank to thaw out the LFP cells as necessary.
 
the current is only 35 amps each because of running at 48 volts
Whoops, sorry, too late to edit. It is actually 56 amps, still perfectly fine. #6AWG or #4, depending on battery distance. At 12v that balloons to 224 amps and #1AWG at minimum, starting to get seriously awkward and expensive. Then the fuses and switches...
 
I am actually getting more and more confident that my setup for the bow thruster is going to work.

I will connect the batteries without BMS but be using an active balancer circuit that I just ordered:


BTW I just learnt that LiFePO4 cells are quite tolerant to overcharging - and can actually handle voltages up to 4.2V without damage.

See this document:


This makes me even more confident - I will of course keep an eye often on the cells and see how they behave and balance and so forth :)
 
I am actually getting more and more confident that my setup for the bow thruster is going to work.

I will connect the batteries without BMS but be using an active balancer circuit that I just ordered:


BTW I just learnt that LiFePO4 cells are quite tolerant to overcharging - and can actually handle voltages up to 4.2V without damage.

See this document:


This makes me even more confident - I will of course keep an eye often on the cells and see how they behave and balance and so forth :)

I have done 3 full charge and discharge of my EVE 280ah cells WITHOUT a bms, I watched how the voltage of cells went up and then down.

As long as I keep it over 11.8 v under load, all my cells stay with 1/100 volts,

The key is as Will put is to TOP BALANCE the cells to start with and then watch your Amp Hours [thanks Snoobler],

Last tight I tried out Overkill Solar's BMS (which is a JBD I am told] to discharge and then to watch the voltages as I discharged circumventing it.

I am also going to use the cells to power my little boat, knowing my SOC is key, have a bidirectional AH meter is my pick. I can't find a waterproof one :-(
 
I strongly suggest installing a standard BMS, either relay or FET type. You can use FET BMS to drive a relay output for higher loads.

Its okay to have the thrusters feed bypass the BMS cut-out. However you must ensure there are zero parasitic loads on that feed. This means LEDs, digital monitoring circuits, etc.

The reason for this, is that if the charging fails (fuse, equipment failure etc), the cells could be pulled down to zero over weeks/months, and destroy them. The bms can disconnect the other smaller loads, but anything that bypasses it must be free of standby consumption.

An active balancer is not a replacement for a cell level disconnect. Since the thrusters are manually controlled, you will notice if the pack is getting low due to their performance. On the charging side you will have no notice if a cell goes high. Without a BMS to disconnect the charging you can cook a cell. Not a pleasant thing to do in a closed space.

As a note if this was my vessel, I would probably route the thruster relay power through a FET BMS, and then install a bypass switch on the console for emergencies.
 
TKB4 - There are 2 types/styles of BMS's - One type that has the negative wire go through it (Daly, Overkill, etc.) These BMS's have discharge limits. The second style uses a contractor to shut-off the power. Batrium, Rec-BMS, and Orion Jr. These tend to be more expensive - then you have to get all the stuff around them - Contractors, etc.
You can also make a small BMS run a Contractor - then all your high powered stuff goes through the contractor.
The contractor I will be using is Tyco EV200AAANA - Gigavac also make some.

Mine will be a house battery on a Diesel MotorHome - I wanted to keep the Boost ability. It sounds like you are going to use the battery as a starting battery.
Here are the challenges that I know about:
1. Alternator voltage - you will need to regulate the alternator so the voltage works with lithium - the default is constant 14.2-ish volts - this will overcharge the battery and have the bms shutdown the battery - which leads to point
2. if the alternator is charging and the bms cuts off - you can get an alternator spike and possible blow the alternator diodes.
3. Cold - alternator will start charging when the engine starts - you could be charging a too cold battery (i know you probably live in an area where that's not a problem - lucky you).

Looking at the market I found a Balmer regulator that can charge lithium batteries, a Sterling alternator protect - that will save the alternator if the battery drops out unexpected. and I figure designing a case with some heaters could overcome the cold - if one was willing to turn on the heaters - then wait to until the battery was warmer to start the vehicle.

What other challenges do you see in using a lithium as a starting battery?
From balmar:

If the 614s were manufactured after July of 2017 they have a Lithium profile pre-loaded. If they are older than that you can manually load in the profile. With regards to the BMS, if it has a Charge Controller Relay, you would route the Brown Ignition wire through that relay. This way before the BMS disconnects the battery from the alternator , the 614 is shut down and the alternator is also. If it doesn't have a Charge Controller Relay you should get an Open Circuit Protection Device from ECPC or Sterling. This will protect the alternator if the battery is disconnected.
 
Hi, My friend work at Sleipner and was testing the thrusters with lithium batteries her the other day. he burned three thrusters that day. :)
Sleipner thrusters are made for use at a 10.5V and when he feeded the thrusters with almost 13V they fried.
So you should be careful to use those kind of applications with lithium batteries without consulting the producer of the thruster first. Be at least shure to hold an eye on the temperature internally of the thruster, so your boat will not catch fire.
 
Always watch your voltages and max current rating of thrusters, blaming a battery for owners oversight not fair on the battery. :p

I am looking to add another thruster in my boat, either mounted on the outboard or transom for some shallow beach, panfish boating.
 
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