Hover Board Battery Autopsy

[Bikes4two]

• I think it was around last Christmas time and bored with it all I ordered up a supposed 68,000mAh 36v battery for ...... wait for it ..... £28 inc p&p
• Now, I had no idea what I'd get for the money but I knew that I would NOT get anything other than complete rubbish, but (a) I was curious and bored with winter, and (b) the physical size/form factor appealed as it would fit into the side pocket of one of my Carradice saddle bags.
• 2 months later it arrived but I didn't get to load test it until April time and when I did I got a whole 1,500mAh out of it.
• So after another boring few days, I eventually dissected the beast to see what cr*p was inside and actually I really quite liked the way it'd been constructed, with some obvious shortcomings like the lack of any physical impact protection as the only wrapping was the blue shrink wrap - just bits of foam on the corners but no other protection from dropping etc.
• However, the batteries where in holders and the only wires where the two for the XT60 connector. All the balance wires where in the main baseboard in a layered sandwich construction with of course the batteries interconnected with nickel strip (I didn't measure the thickness or test if steel coated or pure - durgh, but I doubt at that price point that it was pure nickel and probably only 0.1mm).
• The BMS - looked to me to barely minimal. It was same port charging but no means of switching off power. TBH I was suprised to even see bleed resistors for balancing (simple top balancing I guess?).
• During one discharge test I inadvertantly let them discharge below my normal test voltage of 3.0v per cell and they went down to 2 point something - so clearly no meaningful LVC on the BMS.
• The cells - no idea - no labelling!
• Anyway, I liked the form factor and physical layout of the batteries and I'm considering a similar construction method for a 10s2p build of my own.
• Below are some pics for those amongst the more curious readers - any comments/observations?

 

[saneagle]

When they share the charge port with the discharge one, they normally have a lower LVC because they need to allow for cell charging from 2.5v, which is what most BMSs with separate charge allow so that you can still charge when there was a bit of self-discharge after you let the battery run flat and forgot to charge it.

 

[StuartsProjects]

Those batteries are available from UK distributors for around £50.

I have been testing one on eBrompton and they are sort of OK in that they do provide enough capacity for short local trips.

I did try to find similar batteries but using higher quality cells, but no luck.

10S2P is OK on the Brompton, but if you want\need better quality cells then maybe you would need to get a custom build.

 

[Nealh]

I'm quite surprised you are still a live tbh !!!

 

[Bikes4two]

@saneagle - thanks for that. Clearly you've seen many bms in your time so looking at the pic of the one above, I was thinking of reusing it and rebuilding as per the initial design but using fresh cells.

I do have another standard bms available but it would be nice to re-use the original as all the connection pads on the board would lead to a neat solution. And whilst I at least can't tell from looking, there doesn't seem to be many components on the board.

The settings on my TSDZ2 controller can look after the lvc side of things and of course I could fit an in-line fuse and my charger would look after the max charge voltage aspect.

All I really need is that board to keep the cells in balance - any thoughts on this please?

Obviously this is all at my own risk of course.

 

[Bikes4two]

I'm quite surprised you are still a live tbh !!!

A jest? If not, why do you think that.

 

[saneagle]

@saneagle - thanks for that. Clearly you've seen many bms in your time so looking at the pic of the one above, I was thinking of reusing it and rebuilding as per the initial design but using fresh cells.

I do have another standard bms available but it would be nice to re-use the original as all the connection pads on the board would lead to a neat solution. And whilst I at least can't tell from looking, there doesn't seem to be many components on the board.

The settings on my TSDZ2 controller can look after the lvc side of things and of course I could fit an in-line fuse and my charger would look after the max charge voltage aspect.

All I really need is that board to keep the cells in balance - any thoughts on this please?

Obviously this is all at my own risk of course.

Yes, go ahead. It'll be a nice little project. If you want to be really clever, you can double up the sense wires with an additional connector so that you can check the cell voltages whenever you want. With two 5S connectors, you can even charge with a lipo charger if anything goes wrong with the BMS.

 

[Bikes4two]

Hmm, the notion of adding a couple of 2x 5-way JST connectors has its appeal as I already have an imax B6 doing not a lot.

Although adding additional (sensing) wires theoretically increases the risk of wire chaffing etc.

Some thought needed but thanks for the idea @saneagle

 

[saneagle]

Hmm, the notion of adding a couple of 2x 5-way JST connectors has its appeal as I already have an imax B6 doing not a lot.

Although adding additional (sensing) wires theoretically increases the risk of wire chaffing etc.

Some thought needed but thanks for the idea @saneagle

It depends how you do it. If you're aware of the risk, I'm sure tou can come up with a way to mitigate it. I've seen some commercially made batteries that already have an extra multipin connector sitting there unused inside the case.