72 volt LiFePo4 battery bank suggestions

[Floodhound]

Greetings,

I'm new here so forgive me if this is covered already.

I am building a battery bank for an electric drive sailboat 30kw max PMAC motor and bought 24 LiFePo4 CALB 100ah batteries. I can't find much information about using a BMS or making the battery bank. If you have a link could you please provide it for me.
Otherwise I plan to balance the cells then clamp them together in a 24s configuration. One of my concerns is load testing, not too many people make 72volt systems that I am aware of. Would you load test them or simply go for it? Also finding a affordable BMS seems impossible presently, any help would be appreciative. Thank you.

 

[snoobler]

Calb 100Ah datasheet

100Ah cells are typically limited to 200A discharge, though they can go higher for brief periods. 200Ah * 24 * 3.2 = 15.4kW, so your selected battery can only supply 50% of the max power of which the motor is capable, and it will only run the motor at that power level for maybe 30 minutes.

Current is current, so it doesn't matter if it's 12, 24 or 72V. Load testing is presumed to be good.

Here's an up to 24S Ant BMS:

18.8US $ |Smart 8s- 24s 300a 200a 100a Lithium Battery Protection Board Bms Lipo Liion Lifepo4 Lto 13s 14s 16s 20s Bluetooth App Control - Battery Pack - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

 

[Ampster]

Orion, Emus and Thunderstruck make BMSs for larger strings. They are considerably more expensive than the one posted above but have features designed for a propulsion system. I have been in a situation trying to sail off a lee shore and that made me respect whatever auxiliary propulsion I had available. A BMS to manage a battery system for that purpose is not where I would cut corners. It all depends on where you are standing.
Thunderstruck Motors actually does a fair amount of propulsion systems for boats in the Bay area of Northern California. I have been doing business with them for eight years. They are very helpful.

 

[Floodhound]

I mention 30kwatt max meaning I can run the motor for about 1 minute at that wattage. My motor efficiency increases with volts. So at 72 volts it is 72% efficent where at 48 volts its rated at 48% efficient. I plan to run the system max power 10kwatt as thunderstruck motor advertises.

Im really looking for advice on an affordable BMS. Thanks for the links. I also need to know If load testing the bank is necessary and a safe way to secure that many cells. Thank you.

 

[luckybeanz]

Hi Floodhound, how did your conversion go? I have started a thread about sailboat conversions here https://diysolarforum.com/threads/e...-steps-forward-1-step-back.14251/#post-163949 as I couldn't find any specific thread on the topic.

I am also looking at BMS options so would be interested to hear what you went with and how the thunderstruck kit has worked for you. I was actually looking at the same kit, but instead chose a direct drive kit with an induction motor, hoping the install will be as simple as the thunderstuck kit...

 

[Ampster]

I am also looking at BMS options

Thunderstruck makes a BMS that handles 24 cells. There my be others ones that are competively priced around $500. The cost of components that can handle more than 60 volts is apparently why there are fewer low cost BMSs for more than 16 cells.

 

[newbostonconst]

Ebay has a 24s active balancer. You can also cascade multiple 12s balancers.

Good luck.

 

[Ampster]

You can also cascade multiple 12s balancers.

Good thought. Not perfect, but a cost effective workaround. What implications does that have on current measurements? I presume one would have to use external contactor(s) triggerred by cell overvoltage or one of the sub packs going over limit.

 

[luckybeanz]

Thunderstruck makes a BMS that handles 24 cells. There my be others ones that are competively priced around $500. The cost of components that can handle more than 60 volts is apparently why there are fewer low cost BMSs for more than 16 cells.

Thanks guys. I think I've settled on either the EMUS mini or the REC -- since I am in europe what I save on shipping and VAT pretty mush covers getting anything from the US. Benefit of the REC is that it talks to victron devices, I'm still waiting to hear back from EMUS if it supports victron, I have read in the victron forums that it does but it has not been validated.

What I am left debating is the 48v bank can either be 2P16S, which will only need 1 BMS, but requires me to double up on bus bars as the ones that come with the cells only support 400A. That should be fine as my nominal load would only be around 250, but there is a possibility of peak loads in rare instances of close 460A. Though my question on this is do I need to double up on all or only the series connections? Or 16S2P which then requires 2 BMS but allows for more redundancy and each pack only needs to support half the peak. The cells arre 272AH Lishen with a 2C for 60sec peak rating.

Here is my battery design:

 

[Ampster]

I used an EMUS on a VW conversion with 36 cells eight years ago and it worked great. I have not used the mini but it should work fine for 16 cells. Did I miss the design change from a 24 cell (72 volt) design?