Help with BMS selection

[jamie jones]

i could really use some help with picking out a BMS for my first attempt at building a battery for my van.
i have ordered (4) 272Ah Lifepo4 cells to build a 12v battery from Dongguan Lightning New Energy Technology Co., Ltd.
After spending idk how many hours reading thru the forums, i'm still not sure what BMS would work best for me. i would just order the Overkill as that seems to be highly recommended–but my concern is that i was planning on a 2000w inverter/charger, and idk that the 120a rating of the Overkill would be enough? I doubt that i will ever need the full 2000w, but my wife does want to be able to use her instant pot... i would think that i'd want a ~200a BMS to be safe, but there doesn't seem to be any consistently reliable recommended ones on the forums that i can find. The supplier of the battery recommended theirs: link. Does anyone have any thoughts on that or any other recommendations?

 

[MisterSandals]

Sounds like you have a good understanding of things.
Your special case of using the instant pot does not NEED to be powered thru the BMS; it may be a case where you keep an eye on voltage and become a human BMS (i was the BMS for a year).
If you have all orher functions, primarily charging thru BMS that can all run unattended.

Systems are flexible, it just takes a little effort for some special functions.

 

[HRTKD]

My Wife has an Instant Pot. It's not the largest one, maybe the 6 quart (Lux 6) version. At 1,000 watts I couldn't run that on my system because I have only a 1,000 watt inverter. But the Lux 3 at 700 watts might be doable. But it depends on if the device surges beyond the 700 watt rating.

I have 4s2p using the Overkill Solar 120 amp BMS on each battery. 240 amps total capacity. The battery/BMS is not the choke point in my system.

1000 watts / 12v = 83 amps
Figure 10% inverter inefficiency 83 amp x 1.10 = 91 amps. Looks like that would work on single 120 amp BMS, as long as your inverter can handle it.

 

[jamie jones]

Sounds like you have a good understanding of things.
Your special case of using the instant pot does not NEED to be powered thru the BMS; it may be a case where you keep an eye on voltage and become a human BMS (i was the BMS for a year).
If you have all orher functions, primarily charging thru BMS that can all run unattended.

Systems are flexible, it just takes a little effort for some special functions.

Thanks for the vote of confidence – i feel like i'm in a bit over my head

 

[jamie jones]

My Wife has an Instant Pot. It's not the largest one, maybe the 6 quart (Lux 6) version. At 1,000 watts I couldn't run that on my system because I have only a 1,000 watt inverter. But the Lux 3 at 700 watts might be doable. But it depends on if the device surges beyond the 700 watt rating.

I have 4s2p using the Overkill Solar 120 amp BMS on each battery. 240 amps total capacity. The battery/BMS is not the choke point in my system.

1000 watts / 12v = 83 amps
Figure 10% inverter inefficiency 83 amp x 1.10 = 91 amps. Looks like that would work on single 120 amp BMS, as long as your inverter can handle it.

yeah i was using that instant pot as an example because i think that'll be the largest single load i'll have, and that will won't be used all that much really. I'm doing a pretty minimal build on the van and most things will be simple DC stuff like the Espar, Maxxair, Macbook & phone charging etc. i just want to have the headroom for the occasional instant pot or... whatever.

 

[DeeK]

Hey, did you come to any conclusions on BMS? I am in the same boat. Did you look into the Chargery and the Dalys as well?

 

[jamie jones]

Hey, did you come to any conclusions on BMS? I am in the same boat. Did you look into the Chargery and the Dalys as well?

i've looked at everything i think, including the Chargery and Dalys. At one point i thought i'd go with the Daly, but they seem to have such spotty reliability from what a lot of people on here say about them... i just want something reliable. Still haven't decided, but i'm leaning towards the Overkill–they seem to be bulletproof.

 

[Rocketman]

There are 2 types of inverters- Internal switching lie Daly and external switching. The external switching use a contractor or relay. The three brands I know of are Batrium, Rec- bms, and Orion jr.

The external switching bms’s seem to cost more, plus the cost of the contractor.
In my use case Class A MotorHome- 500ah 12v battery powering a 3000w inverter. I choose to go with a Batrium.
Just a few more to look ? into.

 

[DeeK]

there's also the chargery bms, which i have had mixed luck with.

 

[Bob B]

there's also the chargery bms, which i have had mixed luck with.

I am a lot happier with mine after the software updates they have done. If you are going to switch higher current, the Chargery DCC's seem to do that very pretty well..... at least based on the majority of the reviews I have seen.
I'm using the Chargery to remote control devices.

 

[DeeK]

i am considering trying a chargery again but just as a simple method to operate high and low cutoffs for an RV battery.
i liked its ability to control dc contactors but wasn't crazy about the individual cell voltages bouncing around all over the place on my home system (4P16S 800AH).
plus, the current was never even close to accurate on it. I calibrated several times and it would seem like it was working and then went off again. maybe i was doing something wrong.
as a simple way to trigger contactors it should be ok because even though individual cell V was not reliable with it, the overall pack voltage was accurate.
i found the balance capability of the chargery too weak to be effective but lots of the balancing problem stems from imbalance in my cells. i got a 10A active balancer which works much better and now that i am doing individual capacity tests and better matching the cells, the balancer is having an easier time making all the cells play nicely with each other. i am now able to push much higher absorb voltages and longer times than possible before. i finally feel like i'm getting pretty much all the usable capacity out of my cells - closer anyway.
looked at the overkill but wasn't sure how it could be used in a 4P4S arrangement using their 100Ah cells.

 

[the_colorist]

The best budget BMS we trust in the field for client installations right now is ZEVA. I've had extensive conversations with the designer/creator of the BMS and have confidence in it for a budget BMS. He ships extremely fast as well. The LCD is also very nice addition.

It has has separate dry contacts for HV and LV which is extremely helpful. HV for shedding panels or signaling a CC off during charging. LV for shedding the inverter while keeping the CC connected and powered. We shed at a high enough voltage per cell that should an inverter shed occur, it's unlikely that powering the CC till morning charging starts would cause any single cell to fail. And if the inverter sheds and doesn't reboot in the morning, we'll know about it soon enough to fix something. It's not a perfect system but works for low-income systems where there isn't enough budget for BMS fully-integrated systems (Victron, SMA, Studer, Deye, etc).

Outside of ZEVA, other BMS units we have considered or deployed include:

REC BMS
Orion Jr. (1 & 2)
Batrium
EMUS
Movicom
Autarctech

Some of those have already been mentioned and I have a couple more I'm still vetting and may mention later. Some of those I have not tested but have heard enough or had discussions with the company that gives me some confidence in them.

We also use external active balancing on some systems/banks. Some don't need it IMHO so far (Nissan) but others do (EVE). We have used the QNBBM and they are very nice but overpriced IMHO. There is a new company that I'll be testing on the coming months that makes a capacitor-based active balancer with comparable specs but a fraction of the price. There are others but only one so far that I would try outside of QNBBM. I'll try and post some links later.

I would recommend a contactor based BMS like the ones above rather than the FET based BMS units. Most of the FET based BMS units use 8AWG paralleled cables which is a NEC code violation and a possible safety hazard for high current systems. The FETs may last under load but my option is that there is a good reason we don't design or use them commercially. Even EVs still use standard contactors. And you can source ~400A continuous duty contactors with ~3000A surge capacity from China for decent prices. I'll try and post a link to it later as well.

 

[DeeK]

i am considering trying a chargery again but just as a simple method to operate high and low cutoffs for an RV battery.
i liked its ability to control dc contactors but wasn't crazy about the individual cell voltages bouncing around all over the place on my home system (4P16S 800AH).
plus, the current was never even close to accurate on it. I calibrated several times and it would seem like it was working and then went off again. maybe i was doing something wrong.
as a simple way to trigger contactors it should be ok because even though individual cell V was not reliable with it, the overall pack voltage was accurate.
i found the balance capability of the chargery too weak to be effective but lots of the balancing problem stems from imbalance in my cells. i got a 10A active balancer which works much better and now that i am doing individual capacity tests and better matching the cells, the balancer is having an easier time making all the cells play nicely with each other. i am now able to push much higher absorb voltages and longer times than possible before. i finally feel like i'm getting pretty much all the usable capacity out of my cells - closer anyway.
looked at the overkill but wasn't sure how it could be used in a 4P4S arrangement using their 100Ah cells.

nix this, i just remembered that the chargery would operate the contactors on individual cells going out of range so the voltage inaccuracy would make it unreliable.

 

[Bob B]

nix this, i just remembered that the chargery would operate the contactors on individual cells going out of range so the voltage inaccuracy would make it unreliable.

If you have a Chargery update it to version 4..04 of the BMS and 4.02 of the display. You will be surprised how much better it works and a lot less bouncing around of the readings .... The SOC tracking is also greatly improved.
I have a 2P4S pack operating with a BMS8T .... I also powered directly from the battery thru a diode as shown in the latest manual.
Powering the BMS thru the external power input takes that current off the balance leads. After doing this, my cell voltages are all tracking within 2 mv of the Chargery reading ... except cell 1 which has about 6 mv difference.
I have checked my DVM against a freshly calibrated voltage source and it is reading within .002 volts at 5.000 volts.

A lot of the posts about the Chargery are old news unless they are within the last month or so.

 

[Mex Rider]

i could really use some help with picking out a BMS for my first attempt at building a battery for my van.
i have ordered (4) 272Ah Lifepo4 cells to build a 12v battery from Dongguan Lightning New Energy Technology Co., Ltd.
After spending idk how many hours reading thru the forums, i'm still not sure what BMS would work best for me. i would just order the Overkill as that seems to be highly recommended–but my concern is that i was planning on a 2000w inverter/charger, and idk that the 120a rating of the Overkill would be enough? I doubt that i will ever need the full 2000w, but my wife does want to be able to use her instant pot... i would think that i'd want a ~200a BMS to be safe, but there doesn't seem to be any consistently reliable recommended ones on the forums that i can find. The supplier of the battery recommended theirs: link. Does anyone have any thoughts on that or any other recommendations?

I have a 3000 watt inverter and two 100 AH batteries, each with an Overkill BMS. I have run my 1500 watt space heater and mt 15 amp chop saw without a problem and think there is an insta pot in my future...not worried about the Overkill BMS

 

[jamie jones]

I really appreciate everyone taking time to respond and for all of your help! So, i finally decided to go with the overkill. Unfortunately, they're back-ordered, but my cells aren't here yet anyway...

 

[lance]

There are 2 types of inverters- Internal switching lie Daly and external switching. The external switching use a contractor or relay. The three brands I know of are Batrium, Rec- bms, and Orion jr.

The external switching bms’s seem to cost more, plus the cost of the contractor.
In my use case Class A MotorHome- 500ah 12v battery powering a 3000w inverter. I choose to go with a Batrium.
Just a few more to look ? into.

In very early stages of designing my electrical system for a Sprinter build. I encountered the Batrium name after watching Tom Morton's build using a Tesla module. ( my original goal until @snoobler pointed me towards the logic of these 280ah cells and building my own battery.) It seems to me the task of the BMS is so critical in terms of protecting the battery and increasing it's life that I'm, if it is possible, willing to go with the best. Would it be safe to say that the Batrium (WatchmonPLUS?) would be in the best you can get range? It is available now and selling for (a painful) $800ish

 

[Ampster]

Would it be safe to say that the Batrium (WatchmonPLUS?) would be in the best you can get range? It is available now and selling for (a painful) $800ish

I don't know much about the Batrium but it is in the range of $500 to $1000 BMSs. Also in that range are the Orion Jr BMS. the REC and the EMUS Mini.
The important decision criteria for me is the features and the ability to communicate with an Inverter/charger.
Most of those above use an external contactor and a separate current shunt or other current measurement device. The Chargery also uses separate current shunt and contactor or SSR.

 

[lance]

The important decision criteria for me is the features and the ability to communicate with an Inverter/charger.
Most of those above use an external contactor and a separate current shunt or other current measurement device. The Chargery also uses separate current shunt and contactor or SSR.

Thank you... in reading about the Batrium (it looks like it is the WM7 I would need for 24v system) the only place that "contactor" is mentioned is here:

• Configurable 2 inputs and 2 outputs (i.e. remote circuit breaker trip, contactor or fan)

Could elaborate or point to a source of info regarding this external contactor? I'm assuming it is a separate unit that needs to be configured into the system but, this is the first time I'm encountering it.

 

[Ampster]

Could elaborate or point to a source of info regarding this external contactor? I'm assuming it is a separate unit that needs to be configured into the system but, this is the first time I'm encountering it.

Contactors are just heavy duty relays that are designed to be on most of the time and can interrupt large DC loads. I have used Tyco Contactors because I am familiar with them from converting a VW to an EV. Solid State Relays can also be used. That is the only choice for me because my Inverter does not have an external switch. If your inverter has a switch then wiring one of those interfaces to turn of the inverter would be much simpler.
What I was also familiar with in the EV world was CANBUS communication between the BMS and the charger and motor controller. That kind of communication can be found between some BMSs and Inverters and one that I was hoping for in my installation. Orion has one with Schneider and Victron and REC may have one with another Inverter. I think Batrium may also. As I mentioned earlier that interface is how I would decide on a BMS and/or and Inverter/charger.
I would be happy to elaborate or answer any other questions.