200A BMS with low-temp cut-off?

[Horsefly]

Greetings folks! This is my first post, so go easy on me.

I've been reading as much as I can here (what a great resource!), and learning lots.

I've got a 24V off grid cabin system, with a 4000W inverter, 1700W of panels, and a 60A MPPT charge controller (the electronics are all Schneider). I designed and installed the system in the spring / summer of 2017. We used AGM lead-acid batteries, as that seemed like the best choice at the time. At the time I was very interested in LiFePO4 for the future. I've got two hurdles to get over before I can go with LiFePO4: Max current draw, and temperature.

My nominal load on my inverter is pretty low, but I do have two bigger loads: An 800W microwave (draws about 45A from my ~25VDC battery) and a 0.5hp well pump (draws about 55A from the battery). Neither of these is used more than about 10 minutes per day, and the chances of both being on at the same time is almost zero. The bigger issue is that the well pump is an old induction motor, and it pulls close to 34A@115VAC for a fraction of a second when it starts. That translates to something like 160A@25VDC pulled from the battery.

The cabin is at about 9000 ft elevation, so yeah it gets cold. I've got a temperature logger up there through this winter, but it will be May before we can get up there and see how cold it gets in the basement of the cabin. Until then I've been thinking through strategies for my future LiFePO4 battery. Although I'm experimenting with some ways to heat them in an insulated box (and would love to hear from anyone here with some experience in that), my main thing is preventing my charge controller from killing the cells by charging when the temp is below 32°F.

So I think I need a BMS that can handle 200A, and I need it to have a low-temp cut-off so that I don't kill the cells. I've read that the low-temp cutoff doesn't work as advertised for lots of of the available BMS's. I've read great things here about the Overkill BMS, but the 24V version only goes to 100A. Does anyone have some experience with another BMS that FOR SURE has a working low-temp cutoff?

Thanks in advance for your thoughts!

Steve

P.S. I've got an email off to Overkill to see if a 200A 24V version is in their future, which would solve my problem!

 

[snoobler]

Welcome to the forum.

In addition to the BMS, some solar charge controllers have low temp cut-off as well.

I don't have a 200A BMS option for you.

You might find this concept interesting:

Simple, Indipendent Battery Box Heater

To get the document, click on the orange button at the top of the page. This is a simple 20W battery Box heater that operates independently of the rest of your system. I use this for storing unused cells in a very cold climate, but it can be...

diysolarforum.com

 

[BarkingSpider]

Use a chargery BMS and a their external DCC contacter/relay. Great products.
Alternatively, since the pump only runs for a few seconds, that could bypass the BMS as its unlikely to cause a problem.
Surge amps from big motors is a tough problem to solve for a typical BMS.

 

[Horsefly]

Welcome to the forum.

In addition to the BMS, some solar charge controllers have low temp cut-off as well.

I don't have a 200A BMS option for you.

You might find this concept interesting:

Simple, Indipendent Battery Box Heater

To get the document, click on the orange button at the top of the page. This is a simple 20W battery Box heater that operates independently of the rest of your system. I use this for storing unused cells in a very cold climate, but it can be...

diysolarforum.com

My charge controller is a Schneider MPPT60-150. It's a rock-solid box as all the Schneider boxes are, but these guys were not forward thinking enough to have a low-temp cut-off, unfortunately.

Thanks for the pointer to the heater box. I was considering something similar, but I was going to put one or two of my existing 12V AGM batteries and a PWM charge controller, so that it could heat the battery box even in the absence of sun.

 

[Horsefly]

Use a chargery BMS and a their external DCC contacter/relay. Great products.
Alternatively, since the pump only runs for a few seconds, that could bypass the BMS as its unlikely to cause a problem.
Surge amps from big motors is a tough problem to solve for a typical BMS.

@BarkingSpider - Great handle you have there. ?

Hmmm... I guess I hadn't thought of bypassing the BMS, although that would introduce some other problems. I have a big E-Panel where everything is wired, there is only one pair of 0/4AWG cables going down to the batteries. Also, the inverter is also a source of charging (via a generator we have connected to the inverter), so I would need to cut it off as well, which would cut off power to the pump. Still, I'll have to think about it a bit more.

I should clarify that the pump actually runs for 2.0-2.5 minutes each cycle, which I would guess is not "just a few seconds". It runs to fill up a pressure tank, and doesn't run again until we've used up what is in the tank. On a normal day it probably runs 4 times in a 24 hour period, but if there are more than a couple of people, the showers and toilet flushes could easily take that to 8-10 times.

 

[Steve_S]

@BarkingSpider - Great handle you have there. ?

Hmmm... I guess I hadn't thought of bypassing the BMS, although that would introduce some other problems. I have a big E-Panel where everything is wired, there is only one pair of 0/4AWG cables going down to the batteries. Also, the inverter is also a source of charging (via a generator we have connected to the inverter), so I would need to cut it off as well, which would cut off power to the pump. Still, I'll have to think about it a bit more.

I should clarify that the pump actually runs for 2.0-2.5 minutes each cycle, which I would guess is not "just a few seconds". It runs to fill up a pressure tank, and doesn't run again until we've used up what is in the tank. On a normal day it probably runs 4 times in a 24 hour period, but if there are more than a couple of people, the showers and toilet flushes could easily take that to 8-10 times.

I suggest you have a peek at My DIY off-grid Cabin setup in Ontario Canada (24vdc-120vac) | DIY Solar Power Forum (diysolarforum.com)
The similarities might help provide some ideas.

 

[AussieSim]

This is the 200A BMS that I am using in 24V and 48V packs.

It comes with Bluetooth and 3 temperature monitors (although the internal 2 read a higher temp than the external lead probe) and I haven't personally tried the low temp disconnect trigger.

It is made by JBD

200A Smart BMS from LLT Power

Hi! Anyone used this BMS from LLT Power: https://www.lithiumbatterypcb.com/product/7s-to-20s-200a-smart-bluetooth-bms/ Model No: JBD-AP20S002 Looks like a good bargain, what your views?

diysolarforum.com

 

[Horsefly]

I suggest you have a peek at My DIY off-grid Cabin setup in Ontario Canada (24vdc-120vac) | DIY Solar Power Forum (diysolarforum.com)
The similarities might help provide some ideas.

Hey @Steve_S - Sounds like we have quite a bit in common (besides both being named Steve!). I used a Midnite Solar E-Panel as well, but the one that was designed to attach to the side of the Schneider CSW4024 Inverter/Charger. Really a solid product. I also used Canadian Solar panels, but I used 6 of the 280W panels, in a 3S2P config, connected with the Midnite MNPV3 combiner box. Couple of pics of system below.

If you are in Ontario, didn't you need to do something to avoid low temps on the LFP cells? Maybe I didn't look close enough, but I didn't notice anything.

 

[Horsefly]

Also @Steve_S - I may not understand the concept of your battery set up.

1. You have both FLA and LFP? I see you can switch between the two, but don't you have to change the charge profile each time you switch? Is the FLA now just a failsafe in case the LFPs fail?
2. I also see that you have 2 174AH packs and 2 280AH packs, wired in parallel. Since they are wired together, they obviously have their voltages going up and down together. That would imply that as the 174AH packs start to run out of juice, they are effectively charged by the 280AH packs, right? I need to think about that to get my head wrapped around the idea.

I'm an Electrical Engineer (actually, a retired manager who graduated long ago with an MSEE), so some of this comes pretty easy to me. Some of it, not so much....

 

[Horsefly]

Well I got an email back from Steve @ Overkill. I guess we're all named Steve! He answered my email in about an hour, which seems to verify the good comments people here have made about Overkill.

Anyway, he says the 100A 24V version of the Overkill BMS can handle 280A for up to 10 seconds, and that it is tunable in the configuration. That probably solves my problem there.

 

[Steve_S]

My Powerhouse is heated with a recovered RV Furnace (LPG and uses only 12V), so it has it's own battery & solar too.
Yes, I run the FLA as secondary power now. I have 8 days worth of power reserve if I have to squeeze it. It is manually switched and I have "Confiiguration Profiles" that I can send to the Midnite Classic and for the Samlex Inverter, I swap the SDCard.

The LFP stay pretty even across the board during load / charge and I do not see the 174's taking charge from the 280's when this hit low SOC. Now I don't think it would be the same if I had say 100AH & 280AH. It would certainly be more even at the Hi & Lo ends if the packs were all 280AH.

I ended up with 175's because of the ShunBin disaster. Long story short, a prebuilt 2V/400AH battery assembly, that ended up being Used 174AH cells in parallel in a nice lovely stainless box. A disaster assemblage, which I disassembled and converted to two 8S packs each with BMS & Active Balancer.

 

[Horsefly]

Thanks @Steve_S

Our cabin is not accessible for about 5 months of the year, so leaving LPG heat going is a non-starter, even if just due to the risk. I think I will end up shuttling the battery box out when we close up the cabin, and shuttling it back when we open in the spring. Any solution I can come up with to keep them warm over the winter is just enough of a MacGyver that I'd likely find dead cells in the spring.

I went to the other thread and read about the ShunBin fiasco. Geesh. Things do seem to have improved, but the Alibaba / AliExpress market still seems a little like the wild west.

By the way, the active balancer you are using (QNBBM-8S) is the one I am leaning toward. I've become convinced that using an active balancer can help smooth out the inconsistencies and get more Ah out of the inevitable lower-grade, mismatched cells I will probably get.

 

[Steve_S]

The QNBBM's work but DELIGREEN SUX and they bought out QNBBM.
I cannot and WILL NOT recommend anything from Deligreen ever.
Consider the Heltec Active Balancers, they were my other choice but got refocussed on QNBBM... should have gone with #1 instinct call.

The SHUNBIN KRAP was bought via Amazon.CA - They are still flogging krap on Amazon.* and people are still getting scammed, writing it up and still more get scammed.

I am hoping the new Chargery BMS With Active Balancing comes out soon, if I am going to replace one set of BMS & Balancer because of one fookered QNBBM then I'll replace the fleet with one type and then I'm done... I've had enough furtling about.

One QNBBM Failed and fried one cell in an 8S Pack, a non-replaceable one at that... So that is an 8S pack will have to get disassembled and changed into a 4S leaving me with 3 oddball cells. This is a subject I am Very Angy About... feckin deligreen and their BS.

Amy Wan at Luyuan is very good, I have been dealing with her quite some time and am now even helping her revamp the sales since she took over the company. Lots of people here buy from her and no one has had issues, some orders in excess of 200 cells at a time. She is now sourcing cells direct from Manufacturers (Eve, Lishen, CATL) and NOT from brokers and as such has an edge over others. Little more costly than some of the cheaper dealers but there are no B Class cells... Grade-A or Bulk Commodity and she will be offering Matched & Binnes Sets of 4,8 or 16. (properly done not just voltage matched).

Site will be changing shortly...
Shenzhen Luyuan Technology Co., Ltd. - Lifepo4 battery, LTO battery (alibaba.com)

Luyuan Tech Basic Lifepo4 Guide | DIY Solar Power Forum (diysolarforum.com)

 

[Horsefly]

That guide definitely has your fingerprints all over it. Well done - It is awesome!

I'll rethink the QNBBM balancers. Sounds like it may not be the way I should go. I'll look for the Heltec.

I've got some time for this project. The lead-acid batteries are still fine, and I'm guessing they will continue through this year. So this may be a 2022 project for me. At the rate things are changing, the choices may be completely different in a few months.