Parallel Overkill BMS Success

[Toastie]

Since I've been searching this group for awhile about this topic and not finding any others trying this, I had to do it...
Thanks @Will Prowse for sharing that video of the dual Daly 60 amp bms modules in parallel!

Dual Overkill 120 amp BMS running in parallel WORKS GREAT- though per Steve at Overkill, it is not recommended.
I have new 4s 280 amp hour cells, grade A...Top Balanced in bulk with AGM battery charger, then topped off with a Hobby LiFe charger. My plan is to get 4 more cells, but I wanted to plan for that time about 2 months from now for shipping. I also have a 2000 watt inverter I wanted to run, which should draw about 180 amps under my planned, short duration, max load.
Wiring the BMS modules using a Victron BMV-712 and a hobby load tester, I was able to see the 60 and then 135 amp draw split between the two modules. It is not a perfect 50/50 split, but really close... The BMV was showing the load split and the BMS reflected this as well! Both BMS modules show the same cell voltage. Charging using a AGM charger at about 20 amps is working fine too.
Does it work? YES! There seems to be zero issue in doing this too while bench testing.
My WHY is explained above... The how is here too. I am actually using TWO AGM battery chargers as well. I DID want the reliability, local prep with wires, etc of Overkill. Also the Stateside shipping speed.
While I didn't read about it on the internet, I did watch Will's video using two 60 amp Daly BMS in parallel...
I thought this through and checked everything step by step very cautiously...
NOT doing it on the cheap either... the two Overkill BMS were about $250 with lugs crimped, etc. While I DO feel comfortable using this setup longer term, I will be getting four more cells and splitting up the BMS. Once again, in emailing Steve at Overkill, he did say he recommends against this usage, but if it works...it works, right? I WILL be monitoring cell voltage from the app and multimeter more cautiously as this is in use.

For the next few camping trips, I will be good to go until the next four cells roll in...
Pretty stoked!

Initially, I did encounter an issue with one BMS. But it's unrelated to using in parallel. I swapped the temp probe and the issue stayed with the board... so? The BMS works fine until it hits high voltage/low voltage/overcurrent shutdown. Then it gets locked out of self-reset with discharge turned off. Working it out with Overkill, but probably a faulty module... The other one works perfectly.

In response to a couple questions I had...
Cell voltage on both BMS matches and pack voltage matches too. When testing with two different multimeters on cell terminals, individual voltage is off by about .10 volt. BMS measures higher... Multimeter pack voltage is also off from BMS, but matches the BMV-712 exactly. This variance is noticed with either bms from multimeter and whether they are in parallel or singularly wired.

Hope this helps for anyone wondering the same as I did... Please ignore the wire mess too. I'll have it all cleaned up and dialed in as I get the cells in a box! I think I may also make a stud for the main positive and Neg. Putting two lugs on there and balance leads seems too little thread engagement ...

Thanks for the info I may do this myself, still no problems?

 

[SoundinSpirit]

Thanks for the info I may do this myself, still no problems?

Correct! Using it camping right now. The largest draw I've had is about 150 amps for a short term. Most is slow 15-20 all night. Charging I've gone up to 130 amps for a short bit. Too high, but I wanted to try it out. That was with the solar charge controller and the 80 amp inverter/charger.

 

[Toastie]

Correct! Using it camping right now. The largest draw I've had is about 150 amps for a short term. Most is slow 15-20 all night. Charging I've gone up to 130 amps for a short bit. Too high, but I wanted to try it out. That was with the solar charge controller and the 80 amp inverter/charger.

Great.. enjoy your camping, so do you have two Bluetooth dongles attached to the bms’s ?.. I love this bms and the app.

 

[SoundinSpirit]

Yes,

Great.. enjoy your camping, so do you have two Bluetooth dongles attached to the bms’s ?.. I love this bms and the app.

Correct! Each module has its own Bluetooth. Only needed to keep tabs. And, it's only $8.
Sorry for the delay, I didn't get a notification! Lol...
I really taxed it yesterday, testing and playing.
I don't have an edited video, but raw one... Ran the single battery and dual BMS up to 1.9kw!
Remember, double the numbers in this picture for the parallel output. They split everything equally.
I had the electric hot water heater turned on and the AC fan only on high speed. Battery and bms’s did great!

 

[TimR]

Hello everyone
I'm working on my 280ah 12v build. I'm early in the process gathering all the components. My plan is to build one pack for this summer as I'm also installing a Victron 12/2000/80, Renogy 40 amp mppt charger, and Renogy battery monitor. I will be making changes to the location of the existing power centre in my 2010 Sabre TT, requiring opening and extending a cabinet wall to place the battery packs closest to the solar charge, inverter/charger, trailer power centre.
I'm currently waiting for some cable and the 280ah cells (mid-late April).
In the winter, I will order another set of cells and build a second pack, and move one BMS over to the other pack. It will then provide 560ah with the same 240 amp capacity. More than enough for our use.
Here is a few pictures of my progress with a mockup mdf block for the cell size.
I plan to run the cable through the case and terminate with an Anderson Plugs, as I will remove the packs during the winters up here in Canada.

 

[time2roll]

Yes,

Correct! Each module has its own Bluetooth. Only needed to keep tabs. And, it's only $8.
Sorry for the delay, I didn't get a notification! Lol...
I really taxed it yesterday, testing and playing.
I don't have an edited video, but raw one... Ran the single battery and dual BMS up to 1.9kw!
Remember, double the numbers in this picture for the parallel output. They split everything equally.
I had the electric hot water heater turned on and the AC fan only on high speed. Battery and bms’s did great!

Does the BMS keep track of the battery level of charge correctly when using the two in parallel?

 

[williamsk913]

Hello everyone
I'm working on my 280ah 12v build. I'm early in the process gathering all the components. My plan is to build one pack for this summer as I'm also installing a Victron 12/2000/80, Renogy 40 amp mppt charger, and Renogy battery monitor. I will be making changes to the location of the existing power centre in my 2010 Sabre TT, requiring opening and extending a cabinet wall to place the battery packs closest to the solar charge, inverter/charger, trailer power centre.
I'm currently waiting for some cable and the 280ah cells (mid-late April).
In the winter, I will order another set of cells and build a second pack, and move one BMS over to the other pack. It will then provide 560ah with the same 240 amp capacity. More than enough for our use.
Here is a few pictures of my progress with a mockup mdf block for the cell size.
I plan to run the cable through the case and terminate with an Anderson Plugs, as I will remove the packs during the winters up here in Canada.

Hi, how are you setting the total battery amps for each bms? Total battery pack or 140a (assuming equal split)? How much off are the draws between each BMS? Doing something similar, about 4 amps difference between each BMS at heavy loads, but not sure how to set battery amps and battery cycle ahs. But it works and they measure the voltage as being the same.

 

[TimR]

Still waiting for the cells to arrive. I will have a max system draw estimate of 200 amps, but most times should be in a comfortable low amps of maybe 50 amps. I would only draw higher when boon docking and needing the 2000 watt inverter (about 160 amp) at load, occasionally.

For the BMS, setting battery to 280 amp would be correct for single BMS, I think I should setting to 140 on each BMS, as the draw would be split, I'm only looking to pull 100 amps through each BMS to keep them happy, which would remain the same when I build the second pack. I can increase the BMS setting when second pack is built, and at no time will I need to run the cells at 1C (280 amp). Charging I will also keep it conservative at first, inverter/charger I will set to 60 amp, the solar is not an issue currently as I only have 185 watts of panels, so If I get 17 amps from solar, I would be surprised.
Also, using the two BMS, the cells have double the balancing, and individual cell voltage monitoring. Should one BMS go down, I can operate off a single BMS, but not use the inverter.
For monitoring, I have the Renogy battery monitor and 500amp shunt, so regardless of what the BMS readout of capacity use, I would refer to the Renogy monitor.

Sound and Spirit has made a good YouTube video at FamilyDIY of his setup.

I really like Will Prowse's video testing two BMS, and he has also a great video on the OverKill BMS testing.

I would love to see Will do the same parallel OverKill 12v 4s 120a test on 280ah pack.
I really like using a supplier based in North America for the BMS, I appreciate them shipping with the test sheet, and Steve stands behind the product.

I hope this helps, but I'm new at this and learning as I go, I will post more info as I build, for now the wait for the cells is killing me!
My plan is to have it all complete for our May long weekend camp trip. Yes I'm in Canada, and we have a snow alert for tonight.
Trailer is still in hibernation, so I'm not even working on the interior cabinet work. There always next month. ;-)

Regards Tim

 

[Terrapin]

This is great news! I did look under Will's videos but the only weak spot in his channel is the titles of his videos are not named to be search keyword friendly. ...I have been planning on this set up to have microwave capabilities in the trailer. TY for bringing up as a solution. It keeps me from asking about it. My second battery will be a much smaller 70ah one to go along with the main 280ah 4S. I am even going to try to same a hundered or more by using a Daly 100A "not-smart". I will just watch very carfully and hope they play firendly on the bench till I am 100% confident as you did except with a hall effect off the bank, the Overkill on the large and a Aili shunt on tiny. From what I've been seeing the batteries self level to a degree. If they do get antsy with eachother I'd probably just get another Daly instead of the Overkill. I am not real impressed with with the droid experience on it. But it's only been 3 days Imay catch on eventually.

If anyone can link me to that video It would be appreciated...

 

[HRTKD]

I don't endorse running two BMS on the same battery. But if I had to do it, I would have balancing turned OFF on one of the BMS. Having balancing turned on for both could lead to some confusion on the part of the BMS. That's my theory.

 

[SoundinSpirit]

Hello everyone
I'm working on my 280ah 12v build. I'm early in the process gathering all the components. My plan is to build one pack for this summer as I'm also installing a Victron 12/2000/80, Renogy 40 amp mppt charger, and Renogy battery monitor. I will be making changes to the location of the existing power centre in my 2010 Sabre TT, requiring opening and extending a cabinet wall to place the battery packs closest to the solar charge, inverter/charger, trailer power centre.
I'm currently waiting for some cable and the 280ah cells (mid-late April).
In the winter, I will order another set of cells and build a second pack, and move one BMS over to the other pack. It will then provide 560ah with the same 240 amp capacity. More than enough for our use.
Here is a few pictures of my progress with a mockup mdf block for the cell size.
I plan to run the cable through the case and terminate with an Anderson Plugs, as I will remove the packs during the winters up here in Canada.

Hey Tim, Are you going to leave the MDF there for the cells to be compressed inside the Plano case? If so, I don't think they'll fit. I used the same Plano pack for my builds and thee is JUST enough room for the cells and BMS. I didn't internally fuse the cells, but I do like your idea!

 

[SoundinSpirit]

Still waiting for the cells to arrive. I will have a max system draw estimate of 200 amps, but most times should be in a comfortable low amps of maybe 50 amps. I would only draw higher when boon docking and needing the 2000 watt inverter (about 160 amp) at load, occasionally.

For the BMS, setting battery to 280 amp would be correct for single BMS, I think I should setting to 140 on each BMS, as the draw would be split, I'm only looking to pull 100 amps through each BMS to keep them happy, which would remain the same when I build the second pack. I can increase the BMS setting when second pack is built, and at no time will I need to run the cells at 1C (280 amp). Charging I will also keep it conservative at first, inverter/charger I will set to 60 amp, the solar is not an issue currently as I only have 185 watts of panels, so If I get 17 amps from solar, I would be surprised.
Also, using the two BMS, the cells have double the balancing, and individual cell voltage monitoring. Should one BMS go down, I can operate off a single BMS, but not use the inverter.
For monitoring, I have the Renogy battery monitor and 500amp shunt, so regardless of what the BMS readout of capacity use, I would refer to the Renogy monitor.

Sound and Spirit has made a good YouTube video at FamilyDIY of his setup.

I really like Will Prowse's video testing two BMS, and he has also a great video on the OverKill BMS testing.

I would love to see Will do the same parallel OverKill 12v 4s 120a test on 280ah pack.
I really like using a supplier based in North America for the BMS, I appreciate them shipping with the test sheet, and Steve stands behind the product.

I hope this helps, but I'm new at this and learning as I go, I will post more info as I build, for now the wait for the cells is killing me!
My plan is to have it all complete for our May long weekend camp trip. Yes I'm in Canada, and we have a snow alert for tonight.
Trailer is still in hibernation, so I'm not even working on the interior cabinet work. There always next month. ;-)

Regards Tim

Thanks for calling out my video! Much appreciated.... just don't get sea sick watching it! Lol.... I have more cells coming in any day, so I plan a redo of this setup with single and parallel BMS again aaannd using a gimbal this time!
Will was my inspiration for using dual BMS as he did it previously with 60 amp Daly BMS. I don't plan to keep using Dual either, but I like the redundancy of it for RV use with only one battery. I'll be increasing our rig to two or three 280 amp hour 12 volt batteries. They will all be single BMS.

 

[SoundinSpirit]

I don't endorse running two BMS on the same battery. But if I had to do it, I would have balancing turned OFF on one of the BMS. Having balancing turned on for both could lead to some confusion on the part of the BMS. That's my theory.

I thought about doing that too @HRTKD, but in reality, they are both trying to achieve the same balance goal and they only balance at the top of charging voltage, from my understanding. I'd like to test it more, but honestly, I can't think of a way to manage a test like that.... lol! I have a stack of BMS and about 40 cells coming in soon, so if you can think of a way of testing cell balancing turned on vs. off in parallel application, I would be happy to test it out.

 

[TimR]

Hey Tim, Are you going to leave the MDF there for the cells to be compressed inside the Plano case? If so, I don't think they'll fit. I used the same Plano pack for my builds and thee is JUST enough room for the cells and BMS. I didn't internally fuse the cells, but I do like your idea!

The big mdf block I built to the size of the pack of 280ah cells and will be removed, as it was just for mock-up till the cells arrive.
The BMS are held on a 1/4” piece of Baltic Burch plywood with tapered Burch ends.
There is some room for foam packing all around the cells.
I will decide later when cell are install if I can manage the wires and keep the internal fuse.
I selected the negative line as with two BMS, I have two ring terminals to connect to my line to the external Anderson plug that I will mount on the lid. The positive line can go direct from the battery to the Anderson plug.
Similar to how BigBattery.com fuses theirs.
I like your through case terminals, I will use heavy grommets with the lines through the lid.

 

[TimR]

This is great news! I did look under Will's videos but the only weak spot in his channel is the titles of his videos are not named to be search keyword friendly. ...I have been planning on this set up to have microwave capabilities in the trailer. TY for bringing up as a solution. It keeps me from asking about it. My second battery will be a much smaller 70ah one to go along with the main 280ah 4S. I am even going to try to same a hundered or more by using a Daly 100A "not-smart". I will just watch very carfully and hope they play firendly on the bench till I am 100% confident as you did except with a hall effect off the bank, the Overkill on the large and a Aili shunt on tiny. From what I've been seeing the batteries self level to a degree. If they do get antsy with eachother I'd probably just get another Daly instead of the Overkill. I am not real impressed with with the droid experience on it. But it's only been 3 days Imay catch on eventually.

If anyone can link me to that video It would be appreciated...

I was just thinking
I have always heard to always match the cells, so I think the same would be for the amp hour capacity
If you ran them in the same system, the smallest would empty first and BMS shutdown, then you would have increase load to other pack.
when charging smallest would fill faster and BMS shutdown its charging. Charge would then all go to larger cell. The smallest cell BMS would engage when cell volts are in tolerance to accept charge, then kick out again.
That is assuming the charger doesn’t stop due to sensing the voltage of the smaller cell.
If there is a large voltage difference when you connect in parallel, I would think there could be a rush of current as they try to balance. If the larger allows 120amp discharge through the BMS, and the smaller only allows 50amp, the smaller BMS would shut down due to high current.
I could be totally out to lunch!
Maybe others know correctly what would happen.

 

[Terrapin]

I was just thinking
I have always heard to always match the cells, so I think the same would be for the amp hour capacity
If you ran them in the same system, the smallest would empty first and BMS shutdown, then you would have increase load to other pack.
when charging smallest would fill faster and BMS shutdown its charging. Charge would then all go to larger cell. The smallest cell BMS would engage when cell volts are in trance to accept charge then kick out.
That is assuming the charger doesn’t stop due to sensing the voltage of the smaller cell.
I could be totally out to lunch!
Maybe other know correctly what would happen.

IDK... it's a total crap shoot experiment. 99% of the time I will be drawing at absolute most 40watts from the battery. Then very rarely mabey three times a week I would be running the microwave during inclement weather for pretty shrot times of prob 7-10 min tops. It's rated at max draw of draw of 1300A AC through the inverter. Maybe a switching system to only connect the small battery as needed ... but voltage differences scare my of that. We'll see. I really don't know the interplay. My dream secenario is that the big one would simply balance with the small during times of little or no use. I honestly have no clue how they will interact...

 

[TimR]

I have received my first 4 cells from Exploric, I must say I was a little disappointed as they are a bit puffy. I have reach out to Gina over the past month and still waiting or a reply to my questions. Cells are not same as pictured in their ad, Listed a new CALB, but no QR codes, no labels on the cells, not data sheet. I suspect looking over the Exploric site, these are 310ah cells, as the have the treaded posts, and rated lower to 280ah as they are used or grade B, just not sure without open communication, it seems Gina is boasting my requests for information.

Anyway, I built the battery pack, tested running a dust collector load about 500 watts over 7 hours, and surprising I stopped when I reached 12v and 280 ah. I currently have the two 120a Overkill BMS in a Plant box, until I build my other pack. The BMS's worked perfectly pulling equal watts through each bms.
I tested this past weekend in my RV. Sorry, lots of pictures, (each worth a thousand words)

 

[TimR]

More pics - sorry they are out of order.
Test started late in the evening, so I ran the load stopped, let the cell rest, then finished the test the next morning. You can see times on phone screen shots. I used Anderson connectors, so I can remove the battery packs when I stop the trailer for the winter here in Alberta.

 

[SoundinSpirit]

More pics

I have received my first 4 cells from Exploric, I must say I was a little disappointed as they are a bit puffy. I have reach out to Gina over the past month and still waiting or a reply to my questions. Anyway, I built the battery pack, tested running a dust collector load about 500 watts over 7 hours, and surprising I stopped when I reached 12v and 280 ah. I currently have the two 120a Overkill BMS in a Plant box, until I build my other pack. The BMS's worked perfectly and I tested this past weekend in my RV. Sorry, lots of pictures, (each worth a thousand words)

Nice! I've had parallel BMS running for months now in my first build and have done it a couple times more since then, WITHOUT issue. Running only one pack, it's a nice backup safety.
A couple folks think I'm nuts, evidently, but to be honest... Whatev! Guess I'm just not "clinically diagnosed", lol... Glad it's working for you!

On the swelling, did they arrive bloated? Or happen during charging? All mine from Shenzen Basen arrived concave slightly. 24 cells in total...

For sure, keep an eye on them, I would be concerned for sure from what I've read.
I've not compressed any of my cells beyond ample kapton tape. I've charged up to 130 amps and discharged up to 220. But only for short durations. Mostly it's about 80 amps max regularly.

 

[TimR]

They arrived with that puffy in the middle. I have compressed them with strong zip ties and plywood end boards to contain, maybe allow some breathing, I also have dense foam stuffed in the Plano box, I should receive my second set of cells in the next couple of weeks, thanks when I will pull this pack out and move a BMS to the new pack. As for backup, I think with having twin packs, should one BMS go down, I can run on only one. I hardly run my A/C and only when connected to shore power. (it does start on my current pack even without Soft Start)