Upgrade LiFePO4 BMS to "Manageable"

[Just John]

Do you think I'd have a problem fitting my own BMS in there? It's a JBD, but i'm not sure if the dimensions are the same. Close for sure.

I'm not sure which BMS you have, but I'd contact them and ask. I also have a 4s 120 amp JBD, and although the length is shorter, the width is the same and it should work just fine. You might have to tape it to the printed plate, I can't say for sure. The plate is a VERY good/tight fit for the 150 amp BMS, press to fit type of thing, and I've already had it in and out once. It's such a good fit, I'm not taking it out again, but the width is identical, so the 120 should work very well.

 

[BobCollins]

The Bluetooth option won't be affected by the plastic (ABS) casing.

Good Luck, Have Fun.
Steve_S

You might not know that the SOK's standard batteries use a metal case. It would make an imperfect Faraday shield for a Bluetooth radio.

 

[corn18]

If anyone finds this thread in a search, I added a cell monitor to my 2x12V SOK 206Ah batteries. Fairly easy to do. Just drill a hole and run the balance lines from a hobby Li voltage monitor to the cells. Works a treat.

I bought this:

https://www.amazon.com/ISDT-Battery...424670&sprefix=8s+voltage+mon,aps,126&sr=8-21

 

[Koert]

Yesterday, our four SOK 206Ah batteries were delivered and I'm very disappointed to find that they won't work for us.

It was my mistake. I thought the 50 amp charging limit (only 25% capacity) was a recommendation, not a trigger that would shut down the battery. My next mistake was assuming that I would be able to reset that parameter in the BMS, but that's not possible.

We want 800Ah of batteries so that we can go for several days when solar charging isn't available, or so we can run the air conditioner on hot nights, and then quickly recharge the batteries in the shortest time possible. With a 50A limit, no matter how much charging is available, these will take four hours to charge.

(Why is that important? For example, last night we started charging one battery with the charger set at 60A (which seemed to be working but this morning charging had been completely disconnected and the battery was in a protected state. It wouldn't have been a problem if the battery had woken up on its own, but it didn't. Imagine camping and having the generator running all day, only to find the batteries weren't charging because the current was momentarily too high. That could ruin a trip, along with a freezer full of food.)

So, I'm left with two options. Either return the brand new batteries for a refund or replace the BMS's with ones that allow a higher charge rate in emergencies. Looking at SOK's refund policy, it looks like it will cost at least $900 to return the four batteries! Maybe changing out the BMS's is actually the less expensive way to go.

This is going to be a lot of work (and about $5,600) to end up with what I could have originally put together for about $3,000.

The SOK batteries were shipped from only an hour south of here. Maybe they'll do me a favor and let me drop the batteries off for a full refund.

 

[RVLiFe]

Yesterday, our four SOK 206Ah batteries were delivered and I'm very disappointed to find that they won't work for us.

It was my mistake. I thought the 50 amp charging limit (only 25% capacity) was a recommendation, not a trigger that would shut down the battery. My next mistake was assuming that I would be able to reset that parameter in the BMS, but that's not possible.

We want 800Ah of batteries so that we can go for several days when solar charging isn't available, or so we can run the air conditioner on hot nights, and then quickly recharge the batteries in the shortest time possible. With a 50A limit, no matter how much charging is available, these will take four hours to charge.

(Why is that important? For example, last night we started charging one battery with the charger set at 60A (which seemed to be working but this morning charging had been completely disconnected and the battery was in a protected state. It wouldn't have been a problem if the battery had woken up on its own, but it didn't. Imagine camping and having the generator running all day, only to find the batteries weren't charging because the current was momentarily too high. That could ruin a trip, along with a freezer full of food.)

So, I'm left with two options. Either return the brand new batteries for a refund or replace the BMS's with ones that allow a higher charge rate in emergencies. Looking at SOK's refund policy, it looks like it will cost at least $900 to return the four batteries! Maybe changing out the BMS's is actually the less expensive way to go.

This is going to be a lot of work (and about $5,600) to end up with what I could have originally put together for about $3,000.

The SOK batteries were shipped from only an hour south of here. Maybe they'll do me a favor and let me drop the batteries off for a full refund.

Are you planning on always charging one battery at a time? What is your maximum charge rate that you plan on charging? Do you not want to connect them in series or parallel? You do realize that is 50A each battery correct? You're leaving out a few pieces of information I think. I have no issues charging two batteries in parallel near 90A. You could theoretically charge all four batteries at the same time near 200A without issue. That should be more than adequate for most people I would think. I find that 4 hours to charge a battery is just fine since I get around 6 hours of good sunlight where I am. Even with a generator I don't find it an issue.

 

[Koert]

Are you planning on always charging one battery at a time? What is your maximum charge rate that you plan on charging? Do you not want to connect them in series or parallel? You do realize that is 50A each battery correct? You're leaving out a few pieces of information I think. I have no issues charging two batteries in parallel near 90A. You could theoretically charge all four batteries at the same time near 200A without issue. That should be more than adequate for most people I would think. I find that 4 hours to charge a battery is just fine since I get around 6 hours of good sunlight where I am. Even with a generator I don't find it an issue.

We typically consume about 150Ah per day and can recharge about 300Ah on a sunny day. I bought four 206Ah SOK's so that we'd be able to last through longer stretches of dark skies and so we can use the air conditioner if necessary. For both of these instances, the ability to quickly recharge is important.

At maximum current, these batteries take four hours minimum to fully charge. Other batteries can be charged in as little as one hour and even SOK's smaller battery, which is at the slow end of the range, takes two hours.

Clearly, I don't have enough solar to completely recharge all 824 amp-hours in one day. On a typical day, I get about 300 amp-hours so we count on being able to recharge that additional 500 amp-hours of battery capacity as quickly as possible, using generator and alternator charging. With slower charging the extra capacity isn't nearly as useful.

With faster charging batteries, we could top them off in about 5 hours. With the SOK's we'd have to run the generator for 10 hours. That's a big difference!

But the other problem is that these batteries actually turn off if that 50A per battery limit is exceeded. When we use all three sources, we have potential combined charging of about 225 amps. (Before discovering the 50A limitation I was planning on increasing our charging ability by another 150 amps.) That means we have to continually manage the current going to the batteries so that we don't find ourselves in a position where we think we're charging and we aren't.

I realize that we could get by with these batteries, but if they can't be quickly charged we may as well just stick with the 300Ah LifeBlue battery that they are replacing. The extra 500Ah isn't going to be of very much benefit to us.

And, to be clear, it's my fault. I would have appreciated if some of the reviewers had emphasized this point and the ramifications, but I believed what was convenient and thought that the 50 amp limit was just a recommendation, not an on/off trigger.

 

[RVLiFe]

We typically consume about 150Ah per day and can recharge about 300Ah on a sunny day. I bought four 206Ah SOK's so that we'd be able to last through longer stretches of dark skies and so we can use the air conditioner if necessary. For both of these instances, the ability to quickly recharge is important.

At maximum current, these batteries take four hours minimum to fully charge. Other batteries can be charged in as little as one hour and even SOK's smaller battery, which is at the slow end of the range, takes two hours.

Clearly, I don't have enough solar to completely recharge all 824 amp-hours in one day. On a typical day, I get about 300 amp-hours so we count on being able to recharge that additional 500 amp-hours of battery capacity as quickly as possible, using generator and alternator charging. With slower charging the extra capacity isn't nearly as useful.

With faster charging batteries, we could top them off in about 5 hours. With the SOK's we'd have to run the generator for 10 hours. That's a big difference!

But the other problem is that these batteries actually turn off if that 50A per battery limit is exceeded. When we use all three sources, we have potential combined charging of about 225 amps. (Before discovering the 50A limitation I was planning on increasing our charging ability by another 150 amps.) That means we have to continually manage the current going to the batteries so that we don't find ourselves in a position where we think we're charging and we aren't.

I realize that we could get by with these batteries, but if they can't be quickly charged we may as well just stick with the 300Ah LifeBlue battery that they are replacing. The extra 500Ah isn't going to be of very much benefit to us.

And, to be clear, it's my fault. I would have appreciated if some of the reviewers had emphasized this point and the ramifications, but I believed what was convenient and thought that the 50 amp limit was just a recommendation, not an on/off trigger.

I can see where you have limitations with this battery. To be clear, I have found many references to the 50A limit several times on this forum and I was always convinced that the lower charge rate was actually just a way of ensuring a greater battery life and higher number of charge cycles. For your application, with a smaller solar array, with your need for fast charging, I can see your concern. I full time RV and boondock for 6 months without any power other than 600 Watts of solar and 2 of your same SOK's. Charging has never been an issue and as far as the AC goes, That is when I use the generator. Occasionally, I may need to charge using the generator on those cloudy days but usually only enough to get me thru the night. The solar tops everything off by the next day anyway. My suggestion would just be to buy some more solar panels since they are the cheapest part of your system anyway. Not really sure why you feel you need to charge everything up in one day if your only using 150A in a day. You really only need to put in what you take out and it sounds like you are capable of putting in 300A in a day anyway. Who cares if it takes 2 days to charge what you took out in 5 or 6 days. One extra solar panel would probably do the trick. I may have more of a simplistic view of things but I always feel that as long as you have more money coming in then going out you should be OK. Same with your Ah of your batteries. I'm sorry but I just can't understand the need to charge so fast and what benefit you are gaining unless you live in an area that doesn't get many sunny days. Even then I would just consider getting some additional ground deployed panels to help out.

 

[Koert]

I can see where you have limitations with this battery. To be clear, I have found many references to the 50A limit several times on this forum and I was always convinced that the lower charge rate was actually just a way of ensuring a greater battery life and higher number of charge cycles.

The bigger problem is that when the charge limit is exceeded (which is easy to do when combining the alternator, generator, and solar) the batteries actually turn off until they are reset. And if one battery turns off, the charging limit is further reduced, guaranteeing that the others will turn off.

The reasons not to worry about fast charging are also reasons not to worry about having a larger battery bank. If I didn't want to be able to use the air conditioner on consecutive nights, recharging during the day, I would have just saved the $4,800.

Again, it's my fault for not doing due diligence. I saw the references to the 50 amp charging limit and just thought that there's no way the 206Ah battery would have the same charging limit as their 100Ah battery. And, since the 50 amp charging limit is low for a 100Ah battery, I made the bad assumption that it was just a recommendation and not a trigger point that shuts everything off.

 

[Just John]

It was my mistake. I thought the 50 amp charging limit (only 25% capacity) was a recommendation, not a trigger that would shut down the battery. My next mistake was assuming that I would be able to reset that parameter in the BMS, but that's not possible.

I'm puzzled why you would think that. When an electrical appliance says it works on 120v only, do you think that is a suggestion only? Would you then plug it into 220v and complain it's expensive to return, and blew a fuse?

 

[Just John]

The bigger problem is that when the charge limit is exceeded (which is easy to do when combining the alternator, generator, and solar) the batteries actually turn off until they are reset. And if one battery turns off, the charging limit is further reduced, guaranteeing that the others will turn off.

The reasons not to worry about fast charging are also reasons not to worry about having a larger battery bank. If I didn't want to be able to use the air conditioner on consecutive nights, recharging during the day, I would have just saved the $4,800.

Again, it's my fault for not doing due diligence. I saw the references to the 50 amp charging limit and just thought that there's no way the 206Ah battery would have the same charging limit as their 100Ah battery. And, since the 50 amp charging limit is low for a 100Ah battery, I made the bad assumption that it was just a recommendation and not a trigger point that shuts everything off.

The charging limit is a BMS limit, very unlikely to be a cell limit. The charge rate is indeed ideal to lengthen cell life, .2C or .25C is great for that, and makes it pretty easy to get them recharged with a full day of sun.

To be honest, the BMS having half the charge rate as discharge rate is pretty common with cheap BMS, it means the have half the FETs on the charge side than they do on the discharge side. You could of course rip them open and replace the BMS.

Even though the cells are likely rated for 1C, even if you replaced the BMS, I wouldn't recommend charging (or discharging) them above .5C.

 

[RVLiFe]

The bigger problem is that when the charge limit is exceeded (which is easy to do when combining the alternator, generator, and solar) the batteries actually turn off until they are reset. And if one battery turns off, the charging limit is further reduced, guaranteeing that the others will turn off.

The reasons not to worry about fast charging are also reasons not to worry about having a larger battery bank. If I didn't want to be able to use the air conditioner on consecutive nights, recharging during the day, I would have just saved the $4,800.

Again, it's my fault for not doing due diligence. I saw the references to the 50 amp charging limit and just thought that there's no way the 206Ah battery would have the same charging limit as their 100Ah battery. And, since the 50 amp charging limit is low for a 100Ah battery, I made the bad assumption that it was just a recommendation and not a trigger point that shuts everything off.

Yup, sounds like you already have it figured out what you would like to be able to do. No sense in being unhappy with them. Send them back and get what you really think you need. Too much money spent on them if they aren’t going to perform the way you want them to. Wish I needed more but I can already go 6 days on the two I have and charge them in one day of even nominal sun. Wish you well!

 

[Koert]

The charging limit is a BMS limit, very unlikely to be a cell limit. The charge rate is indeed ideal to lengthen cell life, .2C or .25C is great for that, and makes it pretty easy to get them recharged with a full day of sun.

To be honest, the BMS having half the charge rate as discharge rate is pretty common with cheap BMS, it means the have half the FETs on the charge side than they do on the discharge side.

Haha, not just that, but they also saved money by using the 100Ah battery's BMS on the 206Ah battery!

A previous thread had a spec sheet for the cells. It listed the standard charge current as 1/2C which would be 100 amps for the 206Ah battery, not 50 amps.

In normal day-to-day use, the charge limit shouldn't be a problem. But in unusual conditions, which is why I wanted a larger battery bank, these would take four times as long to recharge as most of the competitors.

You could of course rip them open and replace the BMS.

It looks like their refund terms will cost me close to $1,000 to return the batteries, so I'm definitely going to explore other alternatives for a BMS.