A Tale of 3 BionX Packs: Self Balancing LiMn

I’ve worked with a lot of BionX battery packs over the past two years - stuff I’ve torn apart, stuff I’ve rebuilt.  The older packs are an interesting series of packs all built around the Sony US18650V 1600mAh LiMn cells, and these older packs stand out, in a way, by what they don’t have.

This is a companion discussion topic for the original entry at https://www.sevarg.net/2016/12/04/a-tale-of-3-bionx-packs-self-balancing/

(Comments from Blogger)

2016-12-03 by Robert Moser

Always a nice change to see when practice decides to play fair and co-operate with theory. :smiley:

I hadn’t realized the energy density was so low. That seems to be slightly worse than the low-self-discharge eneloops I use all around the house, and those are NiMH, not lithium-based. Do these cells still hold a weight advantage?

2016-12-04 by Anonymous

Russell, I was wondering if there is any way of veryfying that a rebuild with higher capacity cells will not damage the Bionx battery case electronics? I look forward to your upcoming post on the Bionx 48V battery. I have both the DV500 system (late 2015) and a 24V PL250 with an original nameplate 240 Wh system from 2006, both CANbus. The new 48V battery with 555 Wh can be used on the 24V system. The new system has significantly higher regen capacity. Very nice! Fred

2016-12-04 by Russell Graves

The cells originally used are around 2007-era technology - they’re ancient, relatively speaking. Even the newer ones I use (2250mAh) are low density compared to the state-of-the-art lithium chemistries.

The older BionX packs were NiMH - around 24V/8Ah. They appear to be the same size as the lithium packs, give or take, and the old lithium packs are 37V/9.6Ah - so a good bit more energy density than at least the BionX NiMH packs. I don’t know how full those packs are, though.

2016-12-04 by Russell Graves

Fred -

The electronics would be damaged by a higher voltage pack, but not higher capacity. The current and power coming out of the pack are limited by the motor controller, which remain exactly the same. The only difference is that the rebuilt pack can hold a given power output longer.

The battery gauge may or may not be accurate, though. Some of the systems just rely on pack voltage (which will be more or less accurate), but some do seem to count amp-hours, which will not be accurate with the larger pack. There should be a way to recalibrate them, but I can’t seem to figure out what it is. Future research projects, I suppose…

2016-12-04 by Robert Moser

Makes sense. I had completely forgotten to take in to account to voltage difference between the two chemistries (~1.2V/cell NiMH, ~3.6V/cell LiIon), and was suddenly second-guessing what I thought I’d known about lithium-based batteries.

2016-12-04 by Robert Moser

If you’re lucky, a simple counter with a carefully-chosen resistor, which would allow some alteration. I would bet it’s a magic number somewhere in the firmware though.

2017-04-15 by Unknown

Hey there bro good job anyways I have a bionx kit I believe is older it’s the 37 volt li ion and someone stole my display is it possible to make it work without it if not I have a old strommer display can I somehow use this money is quite tight right now and I can’t afford 50 bucks 4a used display

2017-04-15 by Russell Graves

No. The console is the core of the BionX system and controls everything else. There’s no way to make a BionX system function without the console - sorry.

2018-01-14 by Witham

What is the size of nickel-strip you’re using? (width & thickness)

2018-01-14 by Russell Graves

0.15mm thick, 10mm wide. Pure nickel, not the nickel coated steel nonsense.

2019-09-18 by Unknown

I just bought the 250 PL kit, 26v, with 466 miles for $ 100, and its battery has been discharged for years, 0.1v is what my voltmeter indicates. I opened the package and yes, I started looking for the balance circuit and I didn’t find it. Honestly, I didn’t know that Li-Mn batteries could be balanced like an acid lead would, but at the expense of …? Possibly the overload in some cells shortens its useful life or loss of significant capacity. Maybe Bionx knew it and had prepared its spare batteries at scandal prices. The package now indicates 28.9 constants and everything works as it should, but I’m going to put a balance circuit just to try to extend its life.

2019-09-19 by Russell Graves

Sorry, you what? You charged a lithium pack that’s been down at basically 0V for some unknown period of time?

EVERY BionX pack I’ve seen that has been fully drained like that has seen some voltage inversion on cells (where they’re charged backwards - positive voltage on the negative terminal). They handle the lack of balancing wonderfully when being cycled normally, but when they drain like that, it all goes to hell in a handbasket VERY quickly.

That pack is NOT SAFE TO USE. Period. You CANNOT safely recharge lithium from 0V like that. Please, drain it and build/buy a replacement pack. The cells have been stressed from being deeply discharged (and possibly reversed), and they will let go at some inconvenient point. If a cell lets go, the whole pack will runaway, which is something you don’t want to be anywhere near.

2019-09-19 by Unknown

I completely omitted that the batteries suffer a constant degradation and if they do not follow the rules of charge and discharge, they can be dangerous. It is not worth the risk.
I will follow your advice and discard them.
Thanks a lot.

2020-04-18 by mihaslo

Can you help me with some tips how to solve my charging problem with bionx e bike battery 250w motor, 37v. I have e bike for 10 years and battery was exausted so I buy new one ( just connected battery pack 5p12s as previous one). Original battery was 37V and 9,7Ah. Now I wanted bigger capacity so I purches 37V 21Ah. I disconnected old batery pack and connect with original BMS. Unfortunatelly now when charging it stops after 2h charging or sth like that… On the display it shows that battery is fully charged but when using ebike the performance is not as it should be so it is pretty much as the old 10years old battery…

What can be wrong and any idea how to solve it?

I am thinking that battery cells are unbalanced ot maybe that theBMS still think it is the old battery capacity