Update. Replacement BMS? What's next?

jesfl

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Joined
May 17, 2020
Messages
81
Good evening,

About a month ago, I posted: Why Has My 6-Month Old "Once Perfect" Solar system Failed? It became a long thread over several weeks. I learned a great deal and I will be forever grateful for everyone who helped this struggling beginner.

At that time, the consensus was that it was BMS failure in the cheap Chinese batteries I tried to get by with -- BTR Power 12V 150Ah sold for RVs. Ha! They worked perfectly and were fantastic for 4-5 months, and then something happened to cause the BMS failure. Maybe I did something wrong, but I have no idea what? And, I may never figure that out.

Since then, I bit the bullet and bought 200Ah of high-quality prismatic cells and a Daly Smart BMS because I had to have battery power. That's installed and my system is working well, albeit with only 200Ah of battery vs. my previous 450Ah.

Adhering to someone's previous comment of "what do you have to lose," I also finally got brave enough to start tearing apart one of the failed batteries. Three photos are attached of the first phase tear apart process.

Here's the kicker and big surprise for me. Tested with my multimeter, the battery read 13.45 volts ! ! ! Shocker, because it would not work at all connected through the BMS I bypassed the BMS when testing and used the positive connection and the solder point for the BMS (Pix) on the battery as the negative connection. So, it is well-charged, essentially. That, I assume, confirms the BMS failure.

Questions:

(1) Is there something I can try with the battery stripped apart at this stage to somehow shock the BMS back to working? I am not sure I will keep the existing BMS anyway, except temporarily. I am thinking I need a higher-quality BMS replacement.

(2) Theoretically, it seems to me I should be able to replace the BMS without tearing apart all of the cells? How do I determine what specs of a BMS to purchase, hopefully, to simply cut off the current BMS and solder on a replacement? Can it be that simple?

I now have Daly Smart BMS that is working well. Everyone recommends the Overkill BMS, which may be great, but last I looked it was out of stock and expensive. Is there any BMS anyone can recommend that is decent quality and cost effective? I am a retiree, and buying a new battery has really put me in a huge $$$ hole.

(3) The "BTR Power" people have been no help. I tried their "fully charge the battery and the BMS will reset" every way to Sunday. That did not work. I now have asked for the specs and number of cells in the BTR 12V 150Ah battery. That was sent 4 days ago, no response so far.

Obviously, I would like the simplest route, given my very limited knowledge.

Does anyone have suggestions about what I should do next to figure out the replacement BMS? Must I go the next step and unbolt all of the cells? What would I learn from that (as a total novice)?

I am certainly open to any suggestions and/or corrections in my thinking.

Again many thanks for the previous assistance. I am hopeful of figuring out a solution for the BMS replacement and resurrecting the battery.

Jim S.
jesfl
 

Attachments

  • BTR 12V 150Ah Battery Cells Busbars.jpg
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  • BTR 12V 150Ah Battery BMS.jpg
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Just John

Photon Sorcerer
Joined
Aug 15, 2020
Messages
2,434
As long as you can wait for shipping from China, the Overkill BMS is just a JBD BMS.
You of course get much better support from the USA, and a real warranty with the Overkill.


You want the "4S LFP 120A UART". This comes with a bluetooth dongle so you can use your phone and actually see what is going on.
Same BMS Overkill sells, Overkill just does testing and support better (and will make custom cables, I prefer the threaded connectors to cables soldered on).
 
Last edited:

Just John

Photon Sorcerer
Joined
Aug 15, 2020
Messages
2,434
Good evening,

About a month ago, I posted: Why Has My 6-Month Old "Once Perfect" Solar system Failed? It became a long thread over several weeks. I learned a great deal and I will be forever grateful for everyone who helped this struggling beginner.

At that time, the consensus was that it was BMS failure in the cheap Chinese batteries I tried to get by with -- BTR Power 12V 150Ah sold for RVs. Ha! They worked perfectly and were fantastic for 4-5 months, and then something happened to cause the BMS failure. Maybe I did something wrong, but I have no idea what? And, I may never figure that out.

Since then, I bit the bullet and bought 200Ah of high-quality prismatic cells and a Daly Smart BMS because I had to have battery power. That's installed and my system is working well, albeit with only 200Ah of battery vs. my previous 450Ah.

Adhering to someone's previous comment of "what do you have to lose," I also finally got brave enough to start tearing apart one of the failed batteries. Three photos are attached of the first phase tear apart process.

Here's the kicker and big surprise for me. Tested with my multimeter, the battery read 13.45 volts ! ! ! Shocker, because it would not work at all connected through the BMS I bypassed the BMS when testing and used the positive connection and the solder point for the BMS (Pix) on the battery as the negative connection. So, it is well-charged, essentially. That, I assume, confirms the BMS failure.

Questions:

(1) Is there something I can try with the battery stripped apart at this stage to somehow shock the BMS back to working? I am not sure I will keep the existing BMS anyway, except temporarily. I am thinking I need a higher-quality BMS replacement.

(2) Theoretically, it seems to me I should be able to replace the BMS without tearing apart all of the cells? How do I determine what specs of a BMS to purchase, hopefully, to simply cut off the current BMS and solder on a replacement? Can it be that simple?

I now have Daly Smart BMS that is working well. Everyone recommends the Overkill BMS, which may be great, but last I looked it was out of stock and expensive. Is there any BMS anyone can recommend that is decent quality and cost effective? I am a retiree, and buying a new battery has really put me in a huge $$$ hole.

(3) The "BTR Power" people have been no help. I tried their "fully charge the battery and the BMS will reset" every way to Sunday. That did not work. I now have asked for the specs and number of cells in the BTR 12V 150Ah battery. That was sent 4 days ago, no response so far.

Obviously, I would like the simplest route, given my very limited knowledge.

Does anyone have suggestions about what I should do next to figure out the replacement BMS? Must I go the next step and unbolt all of the cells? What would I learn from that (as a total novice)?

I am certainly open to any suggestions and/or corrections in my thinking.

Again many thanks for the previous assistance. I am hopeful of figuring out a solution for the BMS replacement and resurrecting the battery.

Jim S.
jesfl
I'll be honest with you, looking at the busbars in your photos, I have no clue how those are arranged.
I can't even figure out how many cells you have in there.
Maybe others can assist, if it were me I'd take off the busbars to figure it out, but maybe someone else can give us a clue without that.

Looking at it some more, I think those are pouch cells. Pouch cells just don't have a hard case around them, same chemistry and everything.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
9,109
I wouldn't take it apart.
Order of the busbars seems pretty obvious. but double-check with DMM.
Number and position of bolts seems a little odd, would expect middle busbars to have twice as many connections as ends, but I see 6 vs. 4. A couple cell tabs can be seen going to some bolts.

Setting max/min voltages in the new BMS will be key. Maybe you can tell from knowledge/specs of the battery. But I think all you really have to do is find the top/bottom knees and set charger/inverter limits a bit closer to the flat part of the curve and BMS a bit further up.

Testing voltage under light and heavy load will indicate internal resistance. That extra voltage droop needs to be tolerated without disconnecting while in flat part of the curve, but disconnect has to still be at a voltage which wouldn't be too high/low in the case of no current.

(Lightbulb goes off - try this at your own risk) What if you paralleled these cells with your DIY cells (after bring to similar voltage.) Then you'd have a 4SnP battery, managed by one BMS. Somebody who's actually built a lithium battery (I haven't) can comment on paralleling other brand cells (hopefully same chemistry.) My thinking is you can't count on them sharing current evenly, but when discharged/charged to the knee, it should pause to let others catch up.

But a complete separate BMS seems good for isolation and redundancy. Same as the BMS you're using now to make it easy on your head.
 

time2roll

Photon Sorcerer
Joined
Mar 20, 2021
Messages
2,418
Yes the 4 studs bonded at the ends do not seem balanced with 6 studs bonded in the middle. The groups in parallel do not seem equal.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
9,109
Could even be 4p4s, with two tabs on each middle bolt of the busbars with 6 bolts.
But it doesn't matter - you've got what you've got, just need something to monitor cell voltages and balance. A 4s BMS.
 

Just John

Photon Sorcerer
Joined
Aug 15, 2020
Messages
2,434
Good evening,

About a month ago, I posted: Why Has My 6-Month Old "Once Perfect" Solar system Failed? It became a long thread over several weeks. I learned a great deal and I will be forever grateful for everyone who helped this struggling beginner.

At that time, the consensus was that it was BMS failure in the cheap Chinese batteries I tried to get by with -- BTR Power 12V 150Ah sold for RVs. Ha! They worked perfectly and were fantastic for 4-5 months, and then something happened to cause the BMS failure. Maybe I did something wrong, but I have no idea what? And, I may never figure that out.

Since then, I bit the bullet and bought 200Ah of high-quality prismatic cells and a Daly Smart BMS because I had to have battery power. That's installed and my system is working well, albeit with only 200Ah of battery vs. my previous 450Ah.

Adhering to someone's previous comment of "what do you have to lose," I also finally got brave enough to start tearing apart one of the failed batteries. Three photos are attached of the first phase tear apart process.

Here's the kicker and big surprise for me. Tested with my multimeter, the battery read 13.45 volts ! ! ! Shocker, because it would not work at all connected through the BMS I bypassed the BMS when testing and used the positive connection and the solder point for the BMS (Pix) on the battery as the negative connection. So, it is well-charged, essentially. That, I assume, confirms the BMS failure.

Questions:

(1) Is there something I can try with the battery stripped apart at this stage to somehow shock the BMS back to working? I am not sure I will keep the existing BMS anyway, except temporarily. I am thinking I need a higher-quality BMS replacement.

(2) Theoretically, it seems to me I should be able to replace the BMS without tearing apart all of the cells? How do I determine what specs of a BMS to purchase, hopefully, to simply cut off the current BMS and solder on a replacement? Can it be that simple?

I now have Daly Smart BMS that is working well. Everyone recommends the Overkill BMS, which may be great, but last I looked it was out of stock and expensive. Is there any BMS anyone can recommend that is decent quality and cost effective? I am a retiree, and buying a new battery has really put me in a huge $$$ hole.

(3) The "BTR Power" people have been no help. I tried their "fully charge the battery and the BMS will reset" every way to Sunday. That did not work. I now have asked for the specs and number of cells in the BTR 12V 150Ah battery. That was sent 4 days ago, no response so far.

Obviously, I would like the simplest route, given my very limited knowledge.

Does anyone have suggestions about what I should do next to figure out the replacement BMS? Must I go the next step and unbolt all of the cells? What would I learn from that (as a total novice)?

I am certainly open to any suggestions and/or corrections in my thinking.

Again many thanks for the previous assistance. I am hopeful of figuring out a solution for the BMS replacement and resurrecting the battery.

Jim S.
jesfl
Reading the label on the BMS in the picture, it is pretty certain those are lithium iron phosphate cells (3.65 and 2.5 volts). If you like the Daly, just get two more and replace the existing BMS. The JBD (or Overkill) would also work as a drop in replacement.

No need to tear it apart, just connect in the correct spots.
 

jesfl

Solar Enthusiast
Joined
May 17, 2020
Messages
81
You want the "4S LFP 120A UART". This comes with a bluetooth dongle so you can use your phone and actually see what is going on.
Same BMS Overkill sells, Overkill just does testing and support better (and will make custom cables, I prefer the threaded connectors to cables soldered on).

Thank you. Is the above Overkill "4S LFP 120A UART" is a simple exchange with the existing/old/failed BMS for a 150Ah battery with no configuration required? I also see a "155A" version. Since I don't understand a 120A vs. a 155A unit, it confuses me. Custom cables and threaded connectors are way above my limited knowledge. I don't even know where to start in thinking through or knowing how to use those options?

Yes, I will order the Overkill BMS and wait a month for it, after my question is answered.

Meanwhile, I sure would like to know if the cells will work and will hold a charge in use? If they won't, then buying an overkill BMS is just another waste of $$$'s for me.

Therefore, I am wondering if I can buy a simple, cheap, fast delivery (amazon.com) BMS with no setup/configuration required to install on the battery cells temporarily? I then might: (a) begin further learning, and (b) use the battery and see if the cells are actually working correctly, charging/discharging? But, of course, I don't know if there is such a thing -- cheap, drop-in, no fancy Bluetooth or cold cut-off, etc. BMS? Do you have any suggestions? I see a lot of BMS units cheap on amazon.com as a possible short-term fix? I may be willing to waste $15-$20 for the learning and testing possibilities until an Overkill arrives.

Then there is this "BUT." If trying a cheap BMS causes any substantial risk of damaging the battery cells somehow, I'll cut off this line of thought.

As I understand it, the "4S" part of the descriptor means 4 Series which I assume means 4 cells in series? Do I understand correctly?

In the old battery from the BMS there are 3 white wire soldered connectors, one red wire soldered connection, and one black soldered wire connection. I assume this means whatever cells inside the casing are wired to be 4 battery units/groups in series? Is my understanding correct?

If yes, then I also assume that I do not need to know how many cells or what kind of cells are inside the casing? I just proceed as if there were 4 rectangular cells (prismatic, not the round type)? Correct?

As you see, my knowledge level is very low.

I will sincerely appreciate any further comments you have time to offer.

Thank you.
 

jesfl

Solar Enthusiast
Joined
May 17, 2020
Messages
81
I'll be honest with you, looking at the busbars in your photos, I have no clue how those are arranged.
I can't even figure out how many cells you have in there.
Maybe others can assist, if it were me I'd take off the busbars to figure it out, but maybe someone else can give us a clue without that.

Looking at it some more, I think those are pouch cells. Pouch cells just don't have a hard case around them, same chemistry and everything.

Obviously, I have no clue either about the cells inside the casing. I also am completely lost about "pouch cells" and how those might differ, or how they would affect a BMS choice?
 

Just John

Photon Sorcerer
Joined
Aug 15, 2020
Messages
2,434
Obviously, I have no clue either about the cells inside the casing. I also am completely lost about "pouch cells" and how those might differ, or how they would affect a BMS choice?
Here is an example of pouch cells.

Basically the same thing, just no hard case on the exterior.
 

jesfl

Solar Enthusiast
Joined
May 17, 2020
Messages
81
I wouldn't take it apart.
Order of the busbars seems pretty obvious. but double-check with DMM.
Number and position of bolts seems a little odd, would expect middle busbars to have twice as many connections as ends, but I see 6 vs. 4. A couple cell tabs can be seen going to some bolts.

Setting max/min voltages in the new BMS will be key. Maybe you can tell from knowledge/specs of the battery. But I think all you really have to do is find the top/bottom knees and set charger/inverter limits a bit closer to the flat part of the curve and BMS a bit further up.

Testing voltage under light and heavy load will indicate internal resistance. That extra voltage droop needs to be tolerated without disconnecting while in flat part of the curve, but disconnect has to still be at a voltage which wouldn't be too high/low in the case of no current.

(Lightbulb goes off - try this at your own risk) What if you paralleled these cells with your DIY cells (after bring to similar voltage.) Then you'd have a 4SnP battery, managed by one BMS. Somebody who's actually built a lithium battery (I haven't) can comment on paralleling other brand cells (hopefully same chemistry.) My thinking is you can't count on them sharing current evenly, but when discharged/charged to the knee, it should pause to let others catch up.

But a complete separate BMS seems good for isolation and redundancy. Same as the BMS you're using now to make it easy on your head.

Let me preface the following comments with . . . you have no idea what a knowledgeless beginner you are communicating with. That's my fault because I have ventured into a realm, Photon Sorcerer, well beyond anything else practical in my 70+ year lifetime. Therefore, I am having a very difficult time putting together the pieces from your comments because I have no base knowledge and some of your terminologies are completely new to me. I want to learn, but the comprehension is slow going for me. Now . . .

I absolutely do not want to take it apart further unless there is no other option.

Beyond that first sentence, you pretty much lost me because of my extremely limited knowledge. Since I do not understand your terminology -- my fault, not yours -- I can't put the pieces together of your line of thinking.

"Order of the busbars seems pretty obvious. but double-check with DMM." Sorry, but not at all obvious to me. DMM? Real beginner here.

"Setting max/min voltages in the new BMS will be key. Maybe you can tell from knowledge/specs of the battery." I'm lost here. Real beginner, please remember. Setting a BMS is probably beyond me without some very simple instructions. I have no useful knowledge about the battery and I have been completely unable to obtain any useful specs from the seller on eBay or from BTR Power from their website "support." BTR Power is useless in answering questions.

"Testing voltage under light and heavy load will indicate internal resistance." I have no idea where to start with this? Your comments following this sentence lose me completely. Sorry. Real beginner.

". . . at your own risk . . . paralleling cells . . . one BMS . . . " Not for me because inevitably I would make a mistake that will damage my one, new, working battery. Since I am boondocking in the west full time, I can't risk that because I must have a working battery. To you and others knowledgeable, something like this is undoubtedly very simple. Not to me. It is very frightening.

"But a complete separate BMS seems good for isolation and redundancy. Same as the BMS you're using now to make it easy on your head." YES, yes, yes. I need "easy on my (limited) head." I am trying to figure out what BMS will work so I don't waste more money, but please accept that I don't understand BMS labels or terminology. From previous comments, I am now directed to the Overkill 4S LFP 120A UART.

Thank you for all of your thoughts. As I learn, I pray someday I may understand all of what you wrote.

If you have a moment for follow-up comments, those also will be very much appreciated.
 

Just John

Photon Sorcerer
Joined
Aug 15, 2020
Messages
2,434
Thank you. Is the above Overkill "4S LFP 120A UART" is a simple exchange with the existing/old/failed BMS for a 150Ah battery with no configuration required? I also see a "155A" version. Since I don't understand a 120A vs. a 155A unit, it confuses me. Custom cables and threaded connectors are way above my limited knowledge. I don't even know where to start in thinking through or knowing how to use those options?

Yes, I will order the Overkill BMS and wait a month for it, after my question is answered.

Meanwhile, I sure would like to know if the cells will work and will hold a charge in use? If they won't, then buying an overkill BMS is just another waste of $$$'s for me.

Therefore, I am wondering if I can buy a simple, cheap, fast delivery (amazon.com) BMS with no setup/configuration required to install on the battery cells temporarily? I then might: (a) begin further learning, and (b) use the battery and see if the cells are actually working correctly, charging/discharging? But, of course, I don't know if there is such a thing -- cheap, drop-in, no fancy Bluetooth or cold cut-off, etc. BMS? Do you have any suggestions? I see a lot of BMS units cheap on amazon.com as a possible short-term fix? I may be willing to waste $15-$20 for the learning and testing possibilities until an Overkill arrives.

Then there is this "BUT." If trying a cheap BMS causes any substantial risk of damaging the battery cells somehow, I'll cut off this line of thought.

As I understand it, the "4S" part of the descriptor means 4 Series which I assume means 4 cells in series? Do I understand correctly?

In the old battery from the BMS there are 3 white wire soldered connectors, one red wire soldered connection, and one black soldered wire connection. I assume this means whatever cells inside the casing are wired to be 4 battery units/groups in series? Is my understanding correct?

If yes, then I also assume that I do not need to know how many cells or what kind of cells are inside the casing? I just proceed as if there were 4 rectangular cells (prismatic, not the round type)? Correct?

As you see, my knowledge level is very low.

I will sincerely appreciate any further comments you have time to offer.

Thank you.
I would go ahead and order the JBD BMS I linked for you. For under $60 each including slow shipping, you get a known good quantity. Basically you can just splice into the sense wires they used (and I noticed they are used battery packs, you can see where they cut and left the wires from the previous BMS). The JBD is about as cheap as you want to go, but if you find some cheaper with faster delivery you can always ask here before buying.

Yes, it certainly looks like a 4 sets of cells in series battery. You are correct, just pretend that it is 4 prismatic cells in series, that is what they did before you. The 120 means it can put out 120 amps continuous, I recommend it because everyone who has tried it confirms that it works as designed. Despite that being advertised as a 150 amp hour battery, it was obviously used before having a new BMS slapped on and being sold to you.
 
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jesfl

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Messages
81
Here is an example of pouch cells.

Basically the same thing, just no hard case on the exterior.

Thank you. Yes, that gives me a mental image of "pouch cells" and what might be behind the casing in my LiFePO4 battery. From the metal strips on the bottom of the "bundle" and the spacing of the bolts on top, it looks like the cells may be about 1-inch wide.
 

jesfl

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Joined
May 17, 2020
Messages
81
Reading the label on the BMS in the picture, it is pretty certain those are lithium iron phosphate cells (3.65 and 2.5 volts). If you like the Daly, just get two more and replace the existing BMS. The JBD (or Overkill) would also work as a drop in replacement.

No need to tear it apart, just connect in the correct spots.

Thank you. It is beginning to sort out a little for me. I just installed the Daly+new cells yesterday. It has Bluetooth, but I have not yet gotten the Bluetooth working. So, I have no idea whether I like it or not.

But why "2 more?" Are you thinking back to the many exchanges in my previous post after the BMS failure when I indicated I had 3 failed 150Ah batteries? I feel like I have to take this slowly, step by step, and deal with one of the failed BMS units and one of the remaining batteries at a time. Then, if I screw up, I only kill one battery?

"No need to tear it apart, just connect in the correct spots." Sounds simple, but to me, not exactly. So I just solder on the new BMS leads to the exact same spots as the old/existing ones? (I think it has been 50 years since I have done any soldering.) I also see where they seem to have soldered to small brass plates and then bolted those onto the copper busbars. I think I can handle that.

The connection from the BMS and the Pos (+) connection are soldered to nickel(?)-plated copper busbars. Could those be bolted on instead of soldered somehow? I'm feeling that might be safer for me.
 

jesfl

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Joined
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Messages
81
I would go ahead and order the JBD BMS I linked for you. For under $60 each including slow shipping, you get a known good quantity. Basically you can just splice into the sense wires they used (and I noticed they are used battery packs, you can see where they cut and left the wires from the previous BMS). The JBD is about as cheap as you want to go, but if you find some cheaper with faster delivery you can always ask here before buying.

Yes, it certainly looks like a 4 sets of cells in series battery. You are correct, just pretend that it is 4 prismatic cells in series, that is what they did before you. The 120 means it can put out 120 amps continuous, I recommend it because everyone who has tried it confirms that it works as designed. Despite that being advertised as a 150 amp hour battery, it was obviously used before having a new BMS slapped on and being sold to you.

OK, that explains the 120A part. I am placing the Overkill order. While I do not yet know how to use it, I do like the idea of monitoring via BMS.

So you are saying any 4S BMS with 120A (or temporarily 100A) output would work? So maybe I could buy a cheapie BMS, get some brass sheet, solder the leads, and work through that undoubtedly problematic for me process before I try it the first time on an Overkill BMS and damage it somehow? I am guessing it will be well past 1-month before the Overkill arrives. Further complicating the problem is that I am full-timing in my RV which means there is no easy ship-to address. So, I will have to ship it to my mail forwarding service for reshipment to me after it finally arrives. Slow, elongated process.

I believe you are correct about the "used" part. When I was tearing the first battery apart, I noticed a magic-marker notation of 140.4 with a following Chinese symbol. That caused me to question if that was the tested voltage. I now bet it was. BtrPower sells tons of e-bike batteries, apparently. Now I am guessing they appropriated some e-Bike cells and made the "150Ah" battery to sell into the RV market (per their eBay listing). When I get past this hump, I think I will contact eBay and see if I can get my money back from eBay because of that fraud. Worth a try!

Thank you, again.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
9,109
Let me preface the following comments with . . . you have no idea what a knowledgeless beginner you are communicating with. That's my fault because I have ventured into a realm, Photon Sorcerer, well beyond anything else practical in my 70+ year lifetime. Therefore, I am having a very difficult time putting together the pieces from your comments because I have no base knowledge and some of your terminologies are completely new to me. I want to learn, but the comprehension is slow going for me. Now . . .

I absolutely do not want to take it apart further unless there is no other option.

Beyond that first sentence, you pretty much lost me because of my extremely limited knowledge. Since I do not understand your terminology -- my fault, not yours -- I can't put the pieces together of your line of thinking.

"Order of the busbars seems pretty obvious. but double-check with DMM." Sorry, but not at all obvious to me. DMM? Real beginner here.

"Setting max/min voltages in the new BMS will be key. Maybe you can tell from knowledge/specs of the battery." I'm lost here. Real beginner, please remember. Setting a BMS is probably beyond me without some very simple instructions. I have no useful knowledge about the battery and I have been completely unable to obtain any useful specs from the seller on eBay or from BTR Power from their website "support." BTR Power is useless in answering questions.

"Testing voltage under light and heavy load will indicate internal resistance." I have no idea where to start with this? Your comments following this sentence lose me completely. Sorry. Real beginner.

". . . at your own risk . . . paralleling cells . . . one BMS . . . " Not for me because inevitably I would make a mistake that will damage my one, new, working battery. Since I am boondocking in the west full time, I can't risk that because I must have a working battery. To you and others knowledgeable, something like this is undoubtedly very simple. Not to me. It is very frightening.

"But a complete separate BMS seems good for isolation and redundancy. Same as the BMS you're using now to make it easy on your head." YES, yes, yes. I need "easy on my (limited) head." I am trying to figure out what BMS will work so I don't waste more money, but please accept that I don't understand BMS labels or terminology. From previous comments, I am now directed to the Overkill 4S LFP 120A UART.

Thank you for all of your thoughts. As I learn, I pray someday I may understand all of what you wrote.

If you have a moment for follow-up comments, those also will be very much appreciated.

Sorry, "internal resistance" and "knee" of the charge curve would be more difficult concepts.

Just John pointed out your old BMS says 3.65 and 2.5 volts (everything else is Chinese) so those are the max and min voltage settings you want your new BMS to have. Whether it comes pre-set or is programmable I don't know; someone who has used the recommended BMS can tell you.

"DMM" Digital Multi Meter is just a volt meter. You have four, approximately 3.35V cells wired in series. Checking voltage between terminals, with black DMM wired o negative terminal and the other terminals in order should measure 3.35V, 6.7V, 10.05V, 13.4V. I think the order starts at one ends of the battery and zig-zags back and forth to the other end, but voltages will tell.

If voltages are out of order then figure out what order the cells are in. If voltages are negative then either you started at the positive end or have meter wires backwards. You can label terminals with a felt pen. It will be important to connect BMS wires in the correct order; it would be damaged if wired incorrectly. I think the BMS has a connector for its balance leads, so unplug connector while soldering wires and double-check their order before plugging in connector.

Remove rings or other jewelry. Wrap electrical tape around any wrenches or screwdrivers so no piece of metal is long enough to connect between two terminals. Wear safety goggles. These batteries put out several times as much current as a car battery, melt things faster.

Since voltage looks good, I think the cells are fine. If battery worked correctly and had sufficient capacity right up until it suddenly stopped working, it still has capacity.
 

Just John

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I have to go work (I'm a software release manager). I am over 60 as well, so don't feel lonely in that respect, but since I haven't retired yet, can still spend money on toys.

I will write a much more detailed reply later when I have the time. Daly has some bad defaults for voltage settings (3.75 and 2.1) that you really should change before you use your new cells and BMS too much.

Daly also will default to turning off the bluetooth, here is an example of how to fix that.
Post in thread 'More DALY smart BMS issues' https://diysolarforum.com/threads/more-daly-smart-bms-issues.19751/post-243924

Short term, you just want to change the default protection values, but just don't overcharge or over discharge the battery until you do.
 

Just John

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I believe you are correct about the "used" part. When I was tearing the first battery apart, I noticed a magic-marker notation of 140.4 with a following Chinese symbol. That caused me to question if that was the tested voltage. I now bet it was. BtrPower sells tons of e-bike batteries, apparently. Now I am guessing they appropriated some e-Bike cells and made the "150Ah" battery to sell into the RV market (per their eBay listing). When I get past this hump, I think I will contact eBay and see if I can get my money back from eBay because of that fraud. Worth a

My guess would be they tested your "150 amp hour" battery and found it to be 140.4 amp hours. Outright fraud is common with cheap Chinese batteries. They probably listed it as new as well.
 

GXMnow

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Those are pretty standard voltages for LiFePO4 cells. The packaging is large pouch cells. The setup looks to be 4S of 3P sections. The stack has 24 plastic "plates". It looks like each cell is sandwiched between two of the plates. The cell tabs are bent over at 90 degrees and bolted to the buss bar plates on top. Two tabs fold towards each other and share the bolts. So each of the buss bars with 6 bolts have 6 tabs clamped to it. The 3P from the previous group to the 3P of the following group. The end bars just have 3 tabs, two sharing a pair of bolts, and the third with 2 bolts. The construction is actually pretty good. 50 amp hour pouch cells in a fairly robust package. Much nicer than a pile of spot welded 18650's. The cut off ring terminals are a bit interesting. It looks like the supplier you got it from already replaced the BMS and did a sloppy job of it.

I agree there is no reason at all to pull it apart any further. The buss bar setup looks solid and should handle the current without a problem. For a short term test, you can try pulling some power from the cells off the end 4 bolt buss bars for a few minutes and make sure the cells put out power before you spend much money on replacing the BMS etc. Just don't run the cells below 2.5 volts. I would actually stay above 2.8 volts. If the cells prove worthy, it should not be a big deal to wire on a BMS. You just have the negative side high current cable and the 5 voltage sensing/balance leads. Any 4S LFP BMS should work just fine. 100 amp units are getting cheap now. As long as your charger and load stay between 2.8 volts and 3.6 volts, you don't need a fancy BMS. It is just there to shut off if something goes wrong. If a single cell does go above 3.65 or below 2.5 it just turns off until you can correct the situation. Being able to set the parameters and remote monitor it are nice, but each feature you add will increase the price. Even a non adjustable that has wider shut off is fine as long as you don't run the full capacity. If you get all 3 back running, along with your new 200 amp hours, you will have 650 amp hours, so you should be good to go.

Do you know what your maximum current draw should be? And how many amp hours you will actually use each day?

You could wire all 3 of the failed batteries in parallel with a single BMS. Maybe use Will's trick of using a small cheap BMS to operate a relay to handle the load. Use heavy cable to parallel the main positive and negative buss bars and run through the contactor to the load. Use 3 more cables, of about #8 awg or so to jump together the matching 3 bolt buss bars to force the cells to stay in balance from pack to pack. Then just wire up one BMS to the 5 balance leads of the middle pack. Now you have a single 4S 450 amp hour battery.
 
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