ANT BMS. Final answer? Yes, final answer.

[Deleted member 9967]

If you know what you're doing and know what loads are on your system and have intricate knowledge of the entire system, you can do that and not run a BMS. This is especially the case if you have very low C rates and know that you won't run into conditions that a BMS is designed to handle such as temperature issues, over/under voltages, etc. Personally, I always use a BMS - not worth the risk not to. If something goes wrong, I want a last line of defense.

Understood. I am getting a BMS if only to monitor things and try to figure things out.
Just was asking for people opinions on this after 5 pages of BMS etc discussion.

 

[Gazoo]

I read the entire thread and have an observation.

I know of someone that has some batteries in their house in a back room where extremes in temperature are not an issue.
What they did was charge all of the Lifepo batteries up to about 3.65 each.
Then they let them sit in parallel mode for three days.
After this they set them up in series mode and used them daily. No bms, no protections, nothing.

Just used them at night. Charged them in the day.
When the charged sensed they were full, it turned off.
He "resets" the batteries every six months by fully charging them and then letting them sit in parallel again for three days.

He has done this for at least five years now and has had no problems.
Is he lucky?
Or is this viable for most of us?

Thanks guys.
Oh and to refer to an earlier debate here. I choose redheads because I am one LOLOL ?

It's very possible the batteries were capacity matched to begin with. The ones we are getting are not. Do you know the brand of the cells?

 

[Deleted member 9967]

It's very possible the batteries were capacity matched to begin with. The ones we are getting are not. Do you know the brand of the cells?

Sorry, I only know that they are lifepo and they came from China. Just like the ones I am getting.
Which they showed me were all 3.32 volts and 280 Ah. So I am guessing that mine are what you said "capacity matched"?

 

[Gazoo]

No the cells we are getting are not capacity matched. They will be close in capacity and are close enough to serve our purposes. If we were to order directly from EVE we would be paying up to 3 times the cost of the cells we bought and honestly I don't know if they are matched or a request needs to be made. I have the same cells coming as you do...8 of them. I don't like cross posting, but Steve wrote an excellent post of what it means to have matched cells:

EVE-280 cells should these be clamped tight or spaced for expansion?

To properly Match & Batch cells (of any kind): Simple breakdown each cell must be mounted into a testing machine, each cell has to be fully charged to 100% and IR tested. Each cell is discharged at Varying Rates and at specified setpoints, IR evaluated & recorded @ that Volt Setpoint. Each...

diysolarforum.com

As far as the other person you know, maybe they are staying within the knees of the cells SOC. Even with perfectly matched cells I would still use a BMS.

 

[Dzl]

I know of someone that has some batteries in their house in a back room where extremes in temperature are not an issue.
What they did was charge all of the Lifepo batteries up to about 3.65 each.
Then they let them sit in parallel mode for three days.
After this they set them up in series mode and used them daily. No bms, no protections, nothing.

Just used them at night. Charged them in the day.
When the charged sensed they were full, it turned off.
He "resets" the batteries every six months by fully charging them and then letting them sit in parallel again for three days.

He has done this for at least five years now and has had no problems.
Is he lucky?
Or is this viable for most of us?

Thanks guys.
Oh and to refer to an earlier debate here. I choose redheads because I am one LOLOL ?

My 2 cents,

Going without a BMS is nothing new, and if done correctly, you won't have a problem.. until you have a problem.. A BMS is primarily a safety device. Like many safety devices, you don't need it unless and until you do. Like not wearing a seat belt or not having a smoke alarm no harm will immediately come from it, but the risk and consequences of a failure or error are greater.

The primary utility and purpose of a BMS in my eyes is automated cell level protection. It protects (to some extent) against human error, misconfiguration, or equipment failure elsewhere in your system. Balancing is nice, but not its primary purpose.

Setting automated control, safety aside and layered protection aside, your friends pack may actually be better off than most of us, because he is essentially top balancing and resetting his pack once every 180 days, something that most of us will do only once. If his cells are fairly well matched, and/or if he stays out of the knees, he will probably be fine until something goes wrong. However, as has been noted by many here, the 280Ah cells (probably virtually all grey market cells-- but its more pronounced with larger capacities), are not tightly matched, which increases the need for maintenance balancing, as well as the probablility of needing the protection a BMS provides.

One other note, from a practical standpoint (again ignoring all safety and protection considerations), I would not trade the cost savings of foregoing a BMS for the added hassle and inconvenience of a 4 day (as your friend does) or even a 1 day balancing process every 6 months. Even though I think that this may be a good practice with or without a BMS, its a lot of work, and also presents new opportunities for user error.

So no, I dont think he 'lucky' he is just taking on more risk and responsibility and workload, and foregoing automated protections of a BMS for a much more hands on approach. Its a viable approach for someone that is experienced, attentive, and risk tolerant, but my opinion is its definitely not reccomended for beginners or the absentminded, and its not really worth it for most of us regardless of our level of expertise.

 

[Deleted member 9967]

No the cells we are getting are not capacity matched. They will be close in capacity and are close enough to serve our purposes. If we were to order directly from EVE we would be paying up to 3 times the cost of the cells we bought and honestly I don't know if they are matched or a request needs to be made. I have the same cells coming as you do...8 of them. I don't like cross posting, but Steve wrote an excellent post of what it means to have matched cells:

EVE-280 cells should these be clamped tight or spaced for expansion?

To properly Match & Batch cells (of any kind): Simple breakdown each cell must be mounted into a testing machine, each cell has to be fully charged to 100% and IR tested. Each cell is discharged at Varying Rates and at specified setpoints, IR evaluated & recorded @ that Volt Setpoint. Each...

diysolarforum.com

As far as the other person you know, maybe they are staying within the knees of the cells SOC. Even with perfectly matched cells I would still use a BMS.

Thank you for the link.

 

[Deleted member 9967]

My 2 cents,

Going without a BMS is nothing new, and if done correctly, you won't have a problem.. until you have a problem.. A BMS is primarily a safety device. Like many safety devices, you don't need it unless and until you do. Like not wearing a seat belt or not having a smoke alarm no harm will immediately come from it, but the risk and consequences of a failure or error are greater.

The primary utility and purpose of a BMS in my eyes is automated cell level protection. It protects (to some extent) against human error, misconfiguration, or equipment failure elsewhere in your system. Balancing is nice, but not its primary purpose.

Setting automated control, safety aside and layered protection aside, your friends pack may actually be better off than most of us, because he is essentially top balancing and resetting his pack once every 180 days, something that most of us will do only once. If his cells are fairly well matched, and/or if he stays out of the knees, he will probably be fine until something goes wrong. However, as has been noted by many here, the 280Ah cells (probably virtually all grey market cells-- but its more pronounced with larger capacities), are not tightly matched, which increases the need for maintenance balancing, as well as the probablility of needing the protection a BMS provides.

One other note, from a practical standpoint (again ignoring all safety and protection considerations), I would not trade the cost savings of foregoing a BMS for the added hassle and inconvenience of a 4 day (as your friend does) or even a 1 day balancing process every 6 months. Even though I think that this may be a good practice with or without a BMS, its a lot of work, and also presents new opportunities for user error.

So no, I dont think he 'lucky' he is just taking on more risk and responsibility and workload, and foregoing automated protections of a BMS for a much more hands on approach. Its a viable approach for someone that is experienced, attentive, and risk tolerant, but my opinion is its definitely not reccomended for beginners or the absentminded, and its not really worth it for most of us regardless of our level of expertise.

I understand "safety devices" as I worked security for 5 years about 40 years ago. I also did some security work on computers about 15 or so years ago. So I am very cognizant of safety devices. ?

Not sure what the "knees" are though.

Yes he balances them twice a year or has done so.
I think he did it that way because the BMS at the time were not great or simply too expensive.

I tried to get the Chargey BMS but the bank I sent the money to screwed things up and the deal can't go through. So kind pissed at that but that is for another topic.

Thanks for your input.

 

[Sojourner1]

Not sure what the "knees" are though.

The knees are the points during charging or discharging that the voltage can rise or fall rather fast and possibly kill the cells.

 

[Dzl]

I understand "safety devices" as I worked security for 5 years about 40 years ago. I also did some security work on computers about 15 or so years ago. So I am very cognizant of safety devices. ?

Not sure what the "knees" are though.

Yes he balances them twice a year or has done so.
I think he did it that way because the BMS at the time were not great or simply too expensive.

I tried to get the Chargey BMS but the bank I sent the money to screwed things up and the deal can't go through. So kind pissed at that but that is for another topic.

Thanks for your input.

Sorry, 'the knee' is slang for the points in the voltage curve where voltage starts to rise or fall rapidly and the curve gets 'steeper', which is also where you will see imbalances become more pronounced.

edit: switched out the image

 

[Sojourner1]

Is that an old lfp gragh or you just grabbed a chart from a different lithium chemistry? You might confuse new folks.

 

[Dzl]

Is that an old lfp gragh or you just grabbed a chart from a different lithium chemistry? You might confuse new folks.

Not positive, one or the other, just the first image i found on an image search for 'lifepo4 voltage curve' that illustrated the knee

I will add disclaimer about voltage so the new folk dont get the wrong impressions re: voltage. (changed to a different image)

 

[Deleted member 9967]

Sorry, 'the knee' is slang for the points in the voltage curve where voltage starts to rise or fall rapidly and the curve gets 'steeper', which is also where you will see imbalances become more pronounced.

The knees refer to the steep part

I thought it might be. And the upper area is the elbow?
Anyhow, got it now and thanks

 

[Deleted member 9967]

The knees are the points during charging or discharging that the voltage can rise or fall rather fast and possibly kill the cells.

View attachment 24643View attachment 24644

Thank you for this.

 

[Kmartin]

Ok so i just got my 16 280ah cells. Ill be doing two 8s2p banks for 24v 560ah. I dont think 100 amp bms for each pack is big enough. Next step up is 300amp. Is that ok?

 

[MisterSandals]

I dont think 100 amp bms for each pack is big enough. Next step up is 300amp. Is that ok?

You size the BMS for the current running thru it. More than likely your load will be your largest current (like with a big inverter).
I cannot tell if you are (incorrectly) estimating BMS amps based on your battery amp hours (capacity).

 

[Kmartin]

I've got a Schneider sw4024 4000 watt. 7000 surge for 5 sec which is max i should size bms for i assume. Will i ever use that much power? Maybe but very rarely.

 

[MikeBou]

I'm looking for some clarity on the "Coulomb counting" the Ant BMS advertises. Does it accurately measure state of charge? how?

I'm familiar with shunt based and hall sensor based monitoring but this doesn't appear to (to my untrained eye) use either method. Are there other accurate methods (the ad states ~5% accuracy).

ANT bms uses Hall effect sensor. There’s a Hall speed setting for it in the App

 

[heirloom hamlet]

Ok so i just got my 16 280ah cells. Ill be doing two 8s2p banks for 24v 560ah. I dont think 100 amp bms for each pack is big enough. Next step up is 300amp. Is that ok?

Did you ever put this system together?
I've been running a LV2424 to the very same 280aH pack, and the same BMS. However I now want to connect a second pack like you describe here, but I am not certain how the BMS connections will change from the diagram. Do you have any insight on that?

 

[Ojeysky]

Did you ever put this system together?
I've been running a LV2424 to the very same 280aH pack, and the same BMS. However I now want to connect a second pack like you describe here, but I am not certain how the BMS connections will change from the diagram. Do you have any insight on that?

You just need to get same BMS for the new pack and put the 2 battery packs in parallel. If you want to use existing BMS then you need to put each of the new cells in parallel with each of the old cells

 

[heirloom hamlet]

You just need to get same BMS for the new pack and put the 2 battery packs in parallel. If you want to use existing BMS then you need to put each of the new cells in parallel with each of the old cells

Well, I have a second BMS too. I think you are saying do a 2p8s arrangement...will the BMS work the same?
Do you know if there is a way to do a 8s2p arrangement and connect a separate BMS to each battery pack?