First LiFePO4 build, need advice on BMS

[Master Tinkerer]

First of all, big shout out to Solar supply house, I ordered the 302Ah CATL Cells Friday night 9 PM, received them today, Tuesday 1 PM. Can’t beat that! (I’m in Los Angeles)

I am using these to replace two 100 amp hour AGMs in an existing system I’ve built. I have a 3000 W inverter running some big loads that are meant to run one at a time, like a 2kw induction cooktop, 2.7kw on-demand water faucet, 700 W microwave, etc. It must be taken into consideration multiple loads will, for sure, be turned on at once creating a peak load over 3kw for a bit until the inverter shuts down.

My understanding is, and please correct me if I’m wrong, you can set a 250 amp BMS to shut down at a preset amperage let’s say 240 A, which will be an extra layer of protection for the inverter.

Question 2
3 kw at 12 V is 250 amps, is this the size BMS I should get?

Question 3
Brand Recommendations?

This is a fairly expensive build, failure/fire is not a good option. Also, this is an Overland/off-road vehicle which does hundreds of miles every year on washboard roads, it is amazing the vibration does not break more stuff then it does, but it does break stuff.

 

[Rocketman]

Did you get 4cells or 8 (or more)

For your BMS - there are two ways of the bms switching power - using an external contactor -which is done by higher end bms’s (Batrium, Orion, Rec), or using Mosfets - Overkill, Daly, etc.

My RV needs dictated a very large amps - so I went with Batrium bms. I also made a smaller battery and used overkill bms on it.

One of the issues can be pushing the mosfet with too much power - many people will derate those bms’s by half.

 

[Master Tinkerer]

4 cells, don't think the system will ever see 300A.

 

[Master Tinkerer]

the inverter should kick off at 250A

 

[Steve_S]

We always suggest "derating" a BMS so as to not push them to the performance limits.
LFP can discharge up to 1C (302A) and take 0.5C Charge (151A) and can handle a 2C Burst for 10 seconds.
If you use up to 250A, then you would be looking for a 300A BMS (especially if FET based) but even those with Relays/Contactors it's best to go one step up.

Smart BMS can be programmed in various ways, all depending on make model & type. Most can limit the amount of charge they will accept and limit discharge as well. Do remember that the Inverter can handle surges High Frequency will do 2X surge while Low Frequency can do 3x.
Most popular BMS' at present being used "by the masses of DIY" are Jk/Heltec, JBD and QUCC.

My own production packs use Chargery BMS with Solid State Contactors, with a QNBBM Active Balancer on each pack and my utility packs use JBD Smart BMS with Capacitve Active Balancers. I also use Matched & Batched A+ Cells, Bulk Grade and used EV Grade LFP, so a broad mix.

Overkill Solar, Current Connected are US Vendors carrying the above components

Battery Management Systems Archives ~ Current Connected

Filter by Category REC 16S Q-BMS (9) REC 4S A-BMS (6)

www.currentconnected.com

Shop – Overkill Solar

This is where you can browse products in this store.

overkillsolar.com

12v bms, 12v bms direct from Dongguan Jiabaida Electronic Technology Co., Ltd. in CN

12v bms from Dongguan Jiabaida Electronic Technology Co., Ltd.. Search High Quality 12v bms Manufacturing and Exporting supplier on Alibaba.com.

dgjbd.en.alibaba.com

Alibaba Manufacturer Directory - Suppliers, Manufacturers, Exporters & Importers

Alibaba Manufacturer Directory - Suppliers, Manufacturers, Exporters & Importers

cncdheltec.en.alibaba.com

Alibaba Manufacturer Directory - Suppliers, Manufacturers, Exporters & Importers

Alibaba Manufacturer Directory - Suppliers, Manufacturers, Exporters & Importers

cncdheltec.en.alibaba.com

Battery Blancers/Equalizers - Changsha Deligreen Power Co., Ltd. - page 1.

* Many are available via Amazon/Ebay etc BUT, if you buy from China and airfreight a BMS (small. light and not that $$) it can be in your hands pretty quick.

You may also want to download this resource I wrote up, it will help you commission your packs.
Luyuan Tech Basic Lifepo4 Assembly Guide

Hope it helps, Good Luck.

 

[HRTKD]

To get a high amp draw, I put in two 4s LiFePO4 batteries. Each battery has its own 120 amp BMS from Overkill Solar. Combined, that's about 240 amps. For my RV trailer, that's plenty but I don't have the induction cooktop and water heater that you do.

 

[kshopper2084]

Not to "steal" the thread, but I have a similar situation, adapting my old diesel pusher motorcoach (1997 Monaco Dynasty 36') to use a 280Ah 12v LiFePO4 House battery, and a wet acid Chassis/engine battery.

Now I'm trying to figure out what size BMS I should get for my 280Ah battery.

Battery Cells

• 1C charge/drain: 280A
• Up to 2C drain bursts: 560A

Coach Inverter Output

• 2000VA @ 84% efficiency: 193A
• 4500VA (15 sec peak) @ 84% efficiency: 435A

Do I need to size the BMS to handle the short 435A burst capability of the inverter? Or can I go with say a 200A BMS and expect that it too can handle a higher burst of short duration?

Another factor is that I'd like to retain the ability of my coach to temporarily bridge the House (LiFePO4) battery to the Chassis battery (wet acid) during engine starting. There is a button on the dash to do this, useful if your chassis battery runs low to get the coach started. I assume that depending on the charge state of the Chassis battery this could result in a full 2C drain from the House battery for a few seconds? How do I account for that in my BMS spec? Keeping in mind I'm trying to keep costs low.

 

[Rocketman]

Kshopper2084 - here is my write up- to see what I did - only difference is my rig is a 2000 Monaco Dynasty. If you want to discuss some things - (battery heat, size, etc) let’s take the discussion over to my thread.

Batrium Watchmon Install

Hello everyone, I have a 2000 Monaco MotorHome, I will be installing eight 272ah Lishen LiFePo4 cells making a 2p4s 12v 500Ah (useable) battery. My two largest loads are a Victron MultiPlus 12/3000 inverter/charger and the engine "Boost" if my chassis battery gets low. For the BMS I chose a...

diysolarforum.com