Do some BMS's cut battery instantly when its voltage reaches max. discharge??

[mickyd]

Got a FREE Craigslist triangle battery, 13S8P (104 cell). The owner indicated it was getting a bit tired but still had life in it. Cells are Dynabat MX18650-26P, 3.6V, 2600 mAH, 9.36 Wh.
Cell spec sheet pdf file - https://drive.google.com/file/d/1Y744v5nayKX0M1GqN49DiZ70qXpBICfC/view?usp=sharing

Battery came with a 54.6V 3A cooling fan charger. Charged it until the green light came on at which point, the charger automatically shut off.

Don't have any BMS specifics since it has foam cushion glued over its label and can't remove it without boogering up the label.

Put the beast on my wife's Trike which has a generic Amazon 1000W front hub motor / independent controller. Took it for a slow paced flat test ride to see what it's range would be (which turned out to be about 10 miles). Plan was to drain it to the point of obvious reduced power. I started feeling a slight power reduction / fluctuating lag as with my other e-bikes, then the power cut off instantaneously.

So, my question is...what caused the power to cut off instantly?

NOTE: The voltage of the entire pack after 1 hour cool down was 47.35V with the following voltages from adjacent BMS plug wire connectors. The number in (-0.xx) is the difference from the HIGHEST series pack.

1- 3.66(-0.04) BLACK LEAD
2- 3.57 (-0.13)
3- 3.68 (-0.02)
4- 3.70 (0.00) HIGHEST PACK
5- 3.64 (-0.06)
6- 3.67 (-0.03)
7- 3.44 (-0.16) LOWEST PACK
8- 3.67 (-0.03)
9- 3.65 (-0.05)
10- 3.66 (-0.04)
11- 3.69 (-0.01)
12- 3.68 (-0.02)
13- 3.64 (-0.06) RED LEAD
Total voltage = 47.35V

 

[amberwolf]

I guess that's what I get for not testing it first. (I just copied and shortened the link from the original post it was from).

I did some poking around and it looks like that ASIN (Bs0838QQ5QN) doesn't exist on Amazon anymore. Best guess is either the page itself really is gone (that happens on Amazon for various reasons, including sellers being removed from Amazon for various reasons, so all their products go away too), or that the original link is not accurate / was copied or pasted with incorrect characters.

But the process itself, if starting from a *good link* that goes to a page that's really there, does work.


For instance, this link

https://www.amazon.com/iCreatin-Adaptor-Lithium-Battery-Automatically/dp/B07S21YNRG/ref=sr_1_1_sspa?crid=3KXXJQW0FC0SB&keywords=4.2+volt+charger&qid=1665679579&qu=eyJxc2MiOiIyLjUxIiwicXNhIjoiMi41NSIsInFzcCI6IjIuMzAifQ%3D%3D&sprefix=4.2+volt+charger%2Caps%2C148&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExVTJJWlVJWjdMQVZFJmVuY3J5cHRlZElkPUEwMjI4MTkyMzBVWlVESDgwNEs3MCZlbmNyeXB0ZWRBZElkPUEwODU0MjYzT05MVjRJS0lDWlNZJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

can be shortened all the way to
https://www.amazon.com/dp/B07S21YNRG
or only to
https://www.amazon.com/iCreatin-Adaptor-Lithium-Battery-Automatically/dp/B07S21YNRG
and both work fine. (yes, I actually tested them both ok this time, in both chrome and my ancient firefox :lol

 

[E-HP]

I guess that's what I get for not testing it first. (I just copied and shortened the link from the original post it was from).

I did some poking around and it looks like that ASIN (Bs0838QQ5QN) doesn't exist on Amazon anymore. Best guess is either the page itself really is gone (that happens on Amazon for various reasons, including sellers being removed from Amazon for various reasons, so all their products go away too), or that the original link is not accurate / was copied or pasted with incorrect characters.

But the process itself, if starting from a *good link* that goes to a page that's really there, does work.


For instance, this link

https://www.amazon.com/iCreatin-Adaptor-Lithium-Battery-Automatically/dp/B07S21YNRG/ref=sr_1_1_sspa?crid=3KXXJQW0FC0SB&keywords=4.2+volt+charger&qid=1665679579&qu=eyJxc2MiOiIyLjUxIiwicXNhIjoiMi41NSIsInFzcCI6IjIuMzAifQ%3D%3D&sprefix=4.2+volt+charger%2Caps%2C148&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExVTJJWlVJWjdMQVZFJmVuY3J5cHRlZElkPUEwMjI4MTkyMzBVWlVESDgwNEs3MCZlbmNyeXB0ZWRBZElkPUEwODU0MjYzT05MVjRJS0lDWlNZJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

can be shortened all the way to
https://www.amazon.com/dp/B07S21YNRG
or only to
https://www.amazon.com/iCreatin-Adaptor-Lithium-Battery-Automatically/dp/B07S21YNRG
and both work fine. (yes, I actually tested them both ok this time, in both chrome and my ancient firefox :lol

Both work. Seems like all you have to do is add the Amazon part number after the slash
https://www.amazon.com/dp/

 

[mickyd]

Mo bedda amberwolf and e-hp.

 

[mickyd]

AFTER FULL CHARGE
Full chg (Diff. from highest)
1- 4.04V (-0.11)
2- 4.10 (-0.05)
3- 4.13 (-0.02)
4- 4.10 (-0.05)
5- 3.98 (-0.17) Below 4.00
6- 4.11 (-0.04)
7- 3.80 (-0.35) Lowest
8- 4.06 (-0.09)
9- 4.15 (0.00) Highest
10- 4.09 (-0.06)
11- 4.09 (-0.06)
12- 4.07 (-0.08)
13- 4.05 (-0.10)
Fully charged 52.77V

This was a free 13S8P battery stated by previous owner as "tired". It DOES provide adequate range for its purpose of running errands.... about 8-10 flat miles. However, if there is anything that can be done to easily extend that, I'd do it.

You mention manually charging. Based on the after charge results with group voltages all over the place, is that still an option?

So I let this battery sit for for a couple weeks after the above charge and all groups maintained the charge. I located a Hitec X1 AC Plus 2-6S balance charger / discharger and am going to try to balance charge low groups 5 and 7 to the pack average.

Thinking of using the method indicated by john61ct doing one group at a time using the '+/-' charger output with header pin leads connected to the appropriate BMS connector slots OR, can I use the 'balance socket' output to do both at the same time?

No need to buy a 1S charger unless for convenience

https://www.rcgroups.com/forums/showthread.php?3713527-iCharger-balance-storage#post45491231

https://youtu.be/wIbHLacozFo

I'm basic entry level when it comes to charging parallel groups while still in a full pack. I want to be safe vs. sorry so that I don't ruin my FREE battery.

 

[mickyd]

Thinking of using the method indicated by john61ct doing one group at a time using the '+/-' charger output with header pin leads connected to the appropriate BMS connector slots OR, can I use the 'balance socket' output to do both at the same time?

No need to buy a 1S charger unless for convenience

https://www.rcgroups.com/forums/showthread.php?3713527-iCharger-balance-storage#post45491231

https://youtu.be/wIbHLacozFo

I'm basic entry level when it comes to charging parallel groups while still in a full pack. I want to be safe vs. sorry so that I don't ruin my FREE battery.

I opted to try charging the 3.80V group 7 alone first and see if I can get it close to 4.10V. Used the header pin connector attached to the Hitek X1 AC Plus charger. Based on results, I'll do the next lower 3.98V group 5. Then a short ride to bring the pack voltage down and measure how each group discharges. Then slap it on the pack 48V charger and see if 5 and 7 stay closer to the other groups.

 

[E-HP]

Good luck, hopefully they all stay balanced.

 

[mickyd]

I opted to try charging the 3.80V group 7 alone first and see if I can get it close to 4.10V. Used the header pin connector attached to the Hitek X1 AC Plus charger. Based on results, I'll do the next lower 3.98V group 5. Then a short ride to bring the pack voltage down and measure how each group discharges. Then slap it on the pack 48V charger and see if 5 and 7 stay closer to the other groups.

Brought group 7 up from 3.80V to 4.10V @1A. Working on group 5 now.

Noticing something odd while multimeter monitoring the voltage at the BMS connector header pin comparing to the Hitek chargers voltage on the display. THEY DON'T AGREE. Charger voltage was showing 4.16V whereas the group voltage at the BMS connector showed only 4.05V. I continued to let the group charge until the charger reached 4.20V and the amperage started to decrease from 1.0A. At that point, the BMS was reading only 4.09V.

QUESTION.....Any explanation for the voltage difference between the charger display and the multimeter? I know that my multimeter ALWAYS agrees with my LiitoKala 4-bay charger display.

 

[mickyd]

I opted to try charging the 3.80V group 7 alone first and see if I can get it close to 4.10V. Used the header pin connector attached to the Hitek X1 AC Plus charger. Based on results, I'll do the next lower 3.98V group 5. Then a short ride to bring the pack voltage down and measure how each group discharges. Then slap it on the pack 48V charger and see if 5 and 7 stay closer to the other groups.

Positive results from manually balancing the two lowest cell groups then test riding and recharging!!! Rode the trike until the instantaneous low voltage cutoff (which started this thread) and gained 2 miles of range, from 10 to 12 miles.

Full charge group voltages before and after manual balancing groups 5 and 7.
1- 4.04, 4.05
2- 4.10, 4.10
3- 4.13, 4.16
4- 4.10, 4.13
5- 3.98, 4.07 manual balance improved group by +.09V after charging.
6- 4.11, 4.10
7- 3.80, 4.05 manual balance improved group by +.25V after charging.
8- 4.06, 4.14 ???no clue why this group improved +0.8V after charging.
9- 4.15, 4.17
10- 4.09, 4.11
11- 4.09, 4.11
12- 4.07, 4.09
13- 4.05, 4.06

I guess my next step will be discharging highest cell groups 3, 8, and 9 to around 4.10V . My rational is that the charger is shutting off when one of those cells groups hit 4.20V preventing other groups from further charging.

Let me know if I'm way off base.

I still have the unanswered question from previous post https://endless-sphere.com/forums/viewtopic.php?f=49&t=117741&start=25#p1737047
QUESTION WAS.....Any explanation for the voltage difference between the charger display and the multimeter? I know that my multimeter ALWAYS agrees with my LiitoKala 4-bay charger display.

 

[john61ct]

Those Amazon links are ridiculously long and prone to copy / paste errors

Just chop off the tracking cruft after the product URL before posting.

 

[john61ct]

afaic a "hobby charger" just means a balance charger

Obviously a regular one outputting pack-level voltage should not be used on a single cell/group

that needs 1S voltage appropriate for that battery.

 

[john61ct]

Never trust ANY voltage readings from circuitry of an OTS device like BMS chargers inverters converters etc.

An accurate known good DMM is essential, verify everything, and calibrate it at least annually.

 

[john61ct]

For battery work, only trust measured at the battery itself.

There may be bad connections.

At high current relative to thin gauge wire, there will be a normal voltage difference at the other end.

Precise chargers may have voltage sense feedback wires separate from those that carry the charge current.

If you cannot disconnect your BMS while doing manual work on your pack, basically ignore it until you are done hopefully it will not interfere.

 

[mickyd]

For battery work, only trust measured at the battery itself.

There may be bad connections.

At high current relative to thin gauge wire, there will be a normal voltage difference at the other end.

Precise chargers may have voltage sense feedback wires separate from those that carry the charge current.

If you cannot disconnect your BMS while doing manual work on your pack, basically ignore it until you are done hopefully it will not interfere.

Got it. Glad you explained voltage difference seen.

Final discharge readings for group 9 seen on various measuring methods. Group was initially at 4.17V at the BMS group connector with multimeter and I wanted to get it down to the entire pack group average of 4.10V.
- 3.76V charger display
- 4.02V multimeter measuring at the same BMS connector with charger running
- 4.10V turning the charger off, disconnecting the leads, and measuring the BMS group connector

Moving on to the next high group 3 and repeating process.

Appreciate the explanation / answers you provided.