Noob Question re BMS

Get all your technical information about electric bikes here.
User avatar
bobbill   100 W

100 W
Posts: 226
Joined: Apr 09 2018 10:15am
Location: SE MN Winona

Re: Noob Question re BMS

Post by bobbill » Jul 24 2021 5:37am

HK, Merci. I might be okay, after grief.

What I did, briefly, ignorant dude I am, is mess with product that failed, with one set. O had to redo non-weld packs and got another set of cells, the 30Qa.

Made another pack and it ran for a a very short bit and quit, (BMS) shut it, after this bunch screwed me and had a small fire with first batch...no parts. So, had the Panesonics and cobbled another pack, which is the one that failed on the road. Both sets of cells, 30
Qs and Pani PFs all match etc (out in garage til later).

I was so pissed at Av and spent so much time and money, I bought ready-made from Amazon...runs fine, so far.

I plan to take two pack out each ride...one to play; one to get up hill. Taking the ready-made for hill climb home.

At this point at noon will recheck voltage on cells and if all are 6-7.1 will assemble in NESE modules, connect the BMS and ride.

Sound like a plan?

I should note, was advised to set 6.5v as magical ideal for storage, then charge in close-sets...so BMS, finds easier balance of each group (is a 10S 4P pack) Was also told that tenths of volt differences are neglisable i.e. 6.9 or 7.1 in pack as BMS will balance...

I know this is basic stuff, but picky....have done 4 gas rigs and all 4 as group were easier than this one venture...FWIW, but figure to win at any rate...I tend to do decent work but am scared of these cells, after one fire and so on.

Here is pic of first 4cycle rig...

And pic of current Swift Zootr, before geared hub/controller added. Pack hangs from bars in small bag...spare in back; so you have idea...!

Next rig on a Rans Dynamik...if I can get it together...
Attachments
CNC1A1Big.jpg
CNC1A1Big.jpg (174.87 KiB) Viewed 143 times
3058.jpg
3058.jpg (48.73 KiB) Viewed 143 times

HK12K   100 kW

100 kW
Posts: 1145
Joined: Jul 24 2019 12:49pm

Re: Noob Question re BMS

Post by HK12K » Jul 24 2021 7:00am

Where are you getting this idea that the cells should be at 6.0-7.1 volts? :shock:

The cells should be at 4.2 volts absolute maximum. (4.1 volts will provide better cycle life however, meaning more recharges before pack replacement is necessary)

The best voltage for long term storage would be around 3.8 volts.

The absolute minimum will depend on the specific cells and their respective chemistry. Generally if they go below 3.0v they risk permanent damage.

If you charge these batteries to anything over 4.20 volts you risk experiencing another fire.

If you have already charged these batteries to over 4.2 volts, discharge them and discard them immediately. They will be unsafe to use in any way.

Discharge them outdoors by submerging them in a bucket of saltwater, away from people or property.

User avatar
bobbill   100 W

100 W
Posts: 226
Joined: Apr 09 2018 10:15am
Location: SE MN Winona

Re: Noob Question re BMS

Post by bobbill » Jul 24 2021 9:08am

HK, a number of sources say not to do max V and store or override charger limits....isn't a 36 v pack, at 44 or over a little hard on cells?

Good example of why I ask seemingly dim ?s. Various advisors....

Frankly, the rchargeeady made pack charges and that is it...it stored all winter with single

Now, I find my Sperry thingy has different reading than the cell charger.

Must be standards...FWIW

HK12K   100 kW

100 kW
Posts: 1145
Joined: Jul 24 2019 12:49pm

Re: Noob Question re BMS

Post by HK12K » Jul 24 2021 9:51am

A cell implies the individual batteries inside of the pack, not an assembly of multiple batteries. So to be clear, and decimal points count, have you been charging those individual 18650 cells to 6.00-7.00 volts each?

If so they're ruined and cannot be used again. Ever. At all.

If any one of those individual batteries was charged to more than 4.20 volts, they're damaged internally and are now a safety hazard under any circumstance.

If however you forgot to add a digit or decimal and we're talking about an assembled 10S pack, then the total fully charged voltage should never exceed 42.00 volts. (I would consider 41.00 volts fully charged for day to day use)

I found your other thread from June. I wish Spinningmagnets had replied to you further there as it sounds like the Chinese gal may have given you some terribly bad advice if she suggested you charge each cell so high. We could have saved you a lot of headache and expense.

If you don't have one already you need to get a multimeter stat. They're cheap and easily available.

john61ct   100 GW

100 GW
Posts: 7734
Joined: Dec 18 2018 2:06pm

Re: Noob Question re BMS

Post by john61ct » Jul 24 2021 10:15am

BMSs do not balance all the time, nor should they.

No matter what device is doing the balancing or if done manually by you, it is an occasional maintenance procedure that is performed at a single spot in the voltage / SoC% curve.

At all other points in the curve, the cells will be "out of balance", varying voltages, and that is how it should be.

And again, only 1S voltages count, your talking about 6.6 - 7.1V is a mistake showing ignorance of how batteries work.

john61ct   100 GW

100 GW
Posts: 7734
Joined: Dec 18 2018 2:06pm

Re: Noob Question re BMS

Post by john61ct » Jul 24 2021 10:17am

I assume these are LFP being measured in 2S units?

I doubt li-ion 1S could even reach 7V without exploding

User avatar
E-HP   100 MW

100 MW
Posts: 2726
Joined: Nov 01 2018 9:20pm

Re: Noob Question re BMS

Post by E-HP » Jul 24 2021 10:21am

bobbill wrote:
Jul 24 2021 5:37am
At this point at noon will recheck voltage on cells and if all are 6-7.1 will assemble in NESE modules, connect the BMS and ride.
Please provide a picture of these cells and how you are measuring them at 6.-7.1 with your meter, so people don't waste their time guessing what you are talking about. None of it make sense, but a picture is worth a thousand (confusing) words, as the saying goes.

HK12K   100 kW

100 kW
Posts: 1145
Joined: Jul 24 2019 12:49pm

Re: Noob Question re BMS

Post by HK12K » Jul 24 2021 10:36am

He said earlier they were 30q's and Panasonics. Which Panasonics is anyone's guess, but everyone here should know what a 30q is. Assuming he was accurate, of course.

Pics would definitely clarify things though.

User avatar
Chalo   100 GW

100 GW
Posts: 9107
Joined: Apr 29 2009 11:29pm
Location: Austin, Texas

Re: Noob Question re BMS

Post by Chalo » Jul 24 2021 10:47am

My best guess is that the OP is measuring voltages on only one side of the pack, so getting increments of 2S. I hope that's the case, anyway.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

User avatar
E-HP   100 MW

100 MW
Posts: 2726
Joined: Nov 01 2018 9:20pm

Re: Noob Question re BMS

Post by E-HP » Jul 24 2021 11:12am

HK12K wrote:
Jul 24 2021 10:36am
Assuming he was accurate, of course.

Pics would definitely clarify things though.
I would say most people know what a 30Q or 18650 battery looks like, but I'm not getting the impression that is true in this case, so seeing is believing, since the words are obviously creating confusion.

john61ct   100 GW

100 GW
Posts: 7734
Joined: Dec 18 2018 2:06pm

Re: Noob Question re BMS

Post by john61ct » Jul 24 2021 11:24am

Chalo wrote:My best guess is that the OP is measuring voltages on only one side of the pack, so getting increments of 2S. I hope that's the case, anyway.
Yes that is most likely the explanation, putting the DMM on every other series join.

But then they are only measuring at below 50% SoC.

john61ct   100 GW

100 GW
Posts: 7734
Joined: Dec 18 2018 2:06pm

Re: Noob Question re BMS

Post by john61ct » Jul 24 2021 11:31am


bobbill wrote:isn't a 36 v pack, at 44 or over a little hard on cells?
The canonical way to reference pack voltage is to state the chemistry and the series count.

The batteries you state are 3.6 - 3.7V nominal

So presumably "36V" pack means 10S

if so then multiply the below numbers by 10.

Absolute lowest end of the range you should see / allow in normal cycling is 3.0V

for longevity 3.2-3.7V at rest, say an hour after a discharge cycle

higher end of that range is better, can mean triple the lifespan.

At the high end, charging to 4.05 - 4.15V lower the better, 4.2V absolute top, stressful and shortening lifespan.

44V is WAY too high, dangerous.

And you are telling us 6 - 7V ??

That really needs to get cleared up, top priority




User avatar
E-HP   100 MW

100 MW
Posts: 2726
Joined: Nov 01 2018 9:20pm

Re: Noob Question re BMS

Post by E-HP » Jul 24 2021 11:44am

john61ct wrote:
Jul 24 2021 11:31am
44V is WAY too high, dangerous.

And you are telling us 6 - 7V ??

That really needs to get cleared up, top priority
I think the fires :flame: are a good indicator that there's at least a few bad assumptions being made. :shock:

HK12K   100 kW

100 kW
Posts: 1145
Joined: Jul 24 2019 12:49pm

Re: Noob Question re BMS

Post by HK12K » Jul 24 2021 12:09pm

E-HP wrote:
Jul 24 2021 11:12am
HK12K wrote:
Jul 24 2021 10:36am
Assuming he was accurate, of course.

Pics would definitely clarify things though.
I would say most people know what a 30Q or 18650 battery looks like, but I'm not getting the impression that is true in this case, so seeing is believing, since the words are obviously creating confusion.
I should have quoted properly, but my reply was more in relation to jon and his lfp assumption. In this case however a pic is worth a thousand words, without question. Maybe a video even.

john61ct   100 GW

100 GW
Posts: 7734
Joined: Dec 18 2018 2:06pm

Re: Noob Question re BMS

Post by john61ct » Jul 24 2021 12:09pm

I'm sorry, did I miss the OP reporting actual fires?

john61ct   100 GW

100 GW
Posts: 7734
Joined: Dec 18 2018 2:06pm

Re: Noob Question re BMS

Post by john61ct » Jul 24 2021 12:11pm


bobbill wrote: Cells vary in voltage from 6.1v to 6.9v, in 5 groups
Since OP's packs are probably 10S, this reinforces the likelihood they are only measuring every other series join in the string


HK12K   100 kW

100 kW
Posts: 1145
Joined: Jul 24 2019 12:49pm

Re: Noob Question re BMS

Post by HK12K » Jul 24 2021 12:17pm

Chalo wrote:
Jul 24 2021 10:47am
My best guess is that the OP is measuring voltages on only one side of the pack, so getting increments of 2S. I hope that's the case, anyway.
One would hope I guess. Based on his previous thread a Chinese sales rep suggested the 6-7 volt range, so perhaps they knew something that we don't about how he is performing his measurements. Still though if they're claiming fully charged at 7.1 for 2S that's 3.55v per cell, which is pretty much dead. Less than a typical storage voltage even. 6 volts would of course be 3.0 volts per cell, so unless he misunderstood and that was supposed to be the lowest allowable...

Yeah, more questions than answers

HK12K   100 kW

100 kW
Posts: 1145
Joined: Jul 24 2019 12:49pm

Re: Noob Question re BMS

Post by HK12K » Jul 24 2021 12:18pm

john61ct wrote:
Jul 24 2021 12:09pm
I'm sorry, did I miss the OP reporting actual fires?
Yes, I believe so, though it may have been in one of his previous threads I was perusing earlier. Unless I misunderstood him.

john61ct   100 GW

100 GW
Posts: 7734
Joined: Dec 18 2018 2:06pm

Re: Noob Question re BMS

Post by john61ct » Jul 24 2021 12:28pm


HK12K wrote:a Chinese sales rep suggested the 6-7 volt range, so perhaps they knew something that we don't about
No, if that is the case the rep was also clueless

which of course is very common, if not the norm.

______

> 3.55v per cell

is close to correct for LFP, which might be what is actually inside the packs


HK12K   100 kW

100 kW
Posts: 1145
Joined: Jul 24 2019 12:49pm

Re: Noob Question re BMS

Post by HK12K » Jul 24 2021 12:30pm

john61ct wrote:
Jul 24 2021 12:28pm
HK12K wrote:a Chinese sales rep suggested the 6-7 volt range, so perhaps they knew something that we don't about
No, if that is the case the rep was also clueless

which of course is very common, if not the norm.

______

> 3.55v per cell

is close to correct for LFP, which might be what is actually inside the packs
You forgot to quote the part where I said "about how he is performing his measurements"

But agreed about the reps. Though his previous posts reference 30q and Panasonic PF's going back for a few years now, and he has assembled packs previously, so doubtful they're lfp.

Can't seem to find the burning reference at the moment, but he has 8 pages worth of post history. Some of which references typically expected cell voltages.

We'll need more input. Lol
Last edited by HK12K on Jul 24 2021 12:39pm, edited 2 times in total.

User avatar
E-HP   100 MW

100 MW
Posts: 2726
Joined: Nov 01 2018 9:20pm

Re: Noob Question re BMS

Post by E-HP » Jul 24 2021 12:38pm

john61ct wrote:
Jul 24 2021 12:09pm
I'm sorry, did I miss the OP reporting actual fires?
"Made another pack and it ran for a a very short bit and quit, (BMS) shut it, after this bunch screwed me and had a small fire with first batch."

"...I tend to do decent work but am scared of these cells, after one fire and so on."

HK12K   100 kW

100 kW
Posts: 1145
Joined: Jul 24 2019 12:49pm

Re: Noob Question re BMS

Post by HK12K » Jul 24 2021 12:40pm

E-HP wrote:
Jul 24 2021 12:38pm
john61ct wrote:
Jul 24 2021 12:09pm
I'm sorry, did I miss the OP reporting actual fires?
"Made another pack and it ran for a a very short bit and quit, (BMS) shut it, after this bunch screwed me and had a small fire with first batch."

"...I tend to do decent work but am scared of these cells, after one fire and so on."
Haha, thank you. I was off re-diggng through his old posts again. I really should get some sleep. :lol:

... From the same post:

"So, had the Panesonics and cobbled another pack, which is the one that failed on the road. Both sets of cells, 30
Qs and Pani PFs all match etc (out in garage til later)."

Edit:

Also from the same post:

"At this point at noon will recheck voltage on cells and if all are 6-7.1 will assemble in NESE modules, connect the BMS and ride."

I believe that this strongly implies he's dealing with individual cells. And possibly the fire department if it's after noon where he is.

john61ct   100 GW

100 GW
Posts: 7734
Joined: Dec 18 2018 2:06pm

Re: Noob Question re BMS

Post by john61ct » Jul 24 2021 3:42pm

Maybe scrap / crap counterfeit cells too.

How do they "match"?

HK12K   100 kW

100 kW
Posts: 1145
Joined: Jul 24 2019 12:49pm

Re: Noob Question re BMS

Post by HK12K » Jul 24 2021 8:28pm

If he bought them from China that is all but guaranteed.

I suspect he means they match in soc, but aside from that we shall have to wait for him to elaborate.

User avatar
bobbill   100 W

100 W
Posts: 226
Joined: Apr 09 2018 10:15am
Location: SE MN Winona

Re: Noob Question re BMS

Post by bobbill » Jul 25 2021 8:12am

Thanks for help boys and girls...looks like things are working...

Put cells (PFs) in modules, goes B first, all cells at 3.6 give or take .1v only puculiarity is with BMS balancee wires need to number and mark each module to hook up correctly...
Now to charge as pack...

I did good, thanks to all y'all's help...
Last edited by bobbill on Jul 26 2021 1:52pm, edited 2 times in total.

Post Reply