Battery Misconceptions?

[LimboJim]

I keep reading articles, posts etc. that refer to Samsung, LG, Panasonic etc. as the battery brand used on specific ebikes. But these are merely the cells used within the battery casing, no? Those companies don't actually build complete ebike batteries, do they?

A battery using such name-brand cells could also be using a cheap, generic controller and/or BMS, which makes the cell brand moot, does it not? It's the BMS that slows and then stops the charger as the battery "fills up," and if it fails, that's when things can get dangerous...

I've also seen folks refer to Hailong as a battery manufacturer, but don't they only make the casing? Again, can't a battery that says Hailong on it could have any variety of cells, BMSs and controllers inside?

Sorry, I know these are ignorant questions from someone who's gone through a lot of ebikes since 2015, but the majority use(d) Bosch, Shimano, Yamaha and Brose systems, which I'm confident wouldn't explode...

 

[fooferdoggie]

there are also different grades of batteries. the best ones are matched so they put out as close as possible the same amperage and have the same voltage.

 

[m@Robertson]

It doesn't make the cell brand moot. By using quality, name-brand cells you eliminate some causes for failure, and minimize if not eliminate the likelihood that the pack will age prematurely (i.e. cheapo cells can degrade fast).

As you say though, there are other issues that need to be covered to make for a top quality pack. Another one not mentioned yet is the pack design itself. What is done if anything to separate the cells? What strip material is used to connect them? All kinds of shoddy work can be done with the best cells and the best BMS and the best casing (although I would argue the best casing is none at all, at least two layers of thick rubber and a custom triangle pack).

Or something even more substantial.

It's the BMS that slows and then stops the charger as the battery "fills up," and if it fails, that's when things can get dangerous...

No, thats not correct. The charger itself does that via something known as "CC+CV Mode" CC= Constant Current and CV = Constant Voltage. The charger starts out providing a constant current - say... 2 amps. Then as the target voltage is approached, the charger switches instead to Constant Voltage. Thats when you see the amps slowly start tapering down so the voltage level (which is spiked up a bit thanks to the charger current) approaches but never exceeds the final target voltage set by the charger.

What the BMS does is shut down the battery's acceptance of current if the charge value of the pack exceeds some amount. That amount can be surprisingly high. I've seen packs - good ones with quality components - that should charge only to 58.8v reach 59.5 with a malfunctioning charger that didn't stop feeding current at the designated full charge value.

Thats why I always charge with an extra layer of protection: A mechanical cutoff timer, set to kill the power after a set amount of time (I know my volts-per-hour increase on a given charger/pack).

 

[LimboJim]

It doesn't make the cell brand moot. By using quality, name-brand cells you eliminate some causes for failure, and minimize if not eliminate the likelihood that the pack will age prematurely (i.e. cheapo cells can degrade fast).

As you say though, there are other issues that need to be covered to make for a top quality pack. Another one not mentioned yet is the pack design itself. What is done if anything to separate the cells? What strip material is used to connect them? All kinds of shoddy work can be done with the best cells and the best BMS and the best casing (although I would argue the best casing is none at all, at least two layers of thick rubber and a custom triangle pack).

Or something even more substantial.


View attachment 148657View attachment 148658

No, thats not correct. The charger itself does that via something known as "CC+CV Mode" CC= Constant Current and CV = Constant Voltage. The charger starts out providing a constant current - say... 2 amps. Then as the target voltage is approached, the charger switches instead to Constant Voltage. Thats when you see the amps slowly start tapering down so the voltage level (which is spiked up a bit thanks to the charger current) approaches but never exceeds the final target voltage set by the charger.

What the BMS does is shut down the battery's acceptance of current if the charge value of the pack exceeds some amount. That amount can be surprisingly high. I've seen packs - good ones with quality components - that should charge only to 58.8v reach 59.5 with a malfunctioning charger that didn't stop feeding current at the designated full charge value.

Thats why I always charge with an extra layer of protection: A mechanical cutoff timer, set to kill the power after a set amount of time (I know my volts-per-hour increase on a given charger/pack).

Thanks for the detail and corrections! I've been using this "overcharge prevention timer" for a few years now, but mostly so a nearly depleted battery won't fully charge. I'm loathe to leave a battery at 100%, even just for a couple of days. My oldest battery is a 2015 Bosch PowerPack 400 that still seems to have more than 80% of its original capacity...

 

[m@Robertson]

Thanks for the detail and corrections! I've been using this "overcharge prevention timer" for a few years now, but mostly so a nearly depleted battery won't fully charge.

Interesting they are marketing a simple cutoff timer as an overcharge prevention device. It works that way of course but I haven't seen that done. I use this one, which is mechanical and infinitely adjustable between a few minutes and 12 hours.

https://amzn.to/3mFr3EU

Amazon says I have bought five of them, spread out between two residences, office, and ... not entirely sure where they all are. The most recent was secreted in a frame bag on a cargo bike where I built in a weatherproof charger onboard and its a permanent resident.

I'm loathe to leave a battery at 100%, even just for a couple of days. My oldest battery is a 2015 Bosch PowerPack 400 that still seems to have more than 80% of its original capacity...

Thats the smart move. I would shorten that interval to 'even for just overnight'. Best practice is, if you are going to charge to 100%, do it just before a ride. Go to 80% the day before and plug in first thing in the morning to get that top-up before you hit the road for the office.

 

[PCeBiker]

What the BMS does is shut down the battery's acceptance of current if the charge value of the pack exceeds some amount. That amount can be surprisingly high. I've seen packs - good ones with quality components - that should charge only to 58.8v reach 59.5 with a malfunctioning charger that didn't stop feeding current at the designated full charge value.

What about cell balancing?
Isn't that a function of the BMS?

Is a properly balanced battery "safer" in any way, or does it just have more capacity?

Is there such a thing as a BMS that will limit the voltage of each cell group if the charger is putting out too high a voltage?

 

[tomjasz]

Is there such a thing as a BMS that will limit the voltage of each cell group if the charger is putting out too high a voltage?

Sure. But not on those packs selling for under $500. The devil is in the details.


Isn't that a function of the BMS?

If the BMS has that function. No budget battery pack does.

Brand name isn’t a good measure either. Some cells are appropriate for laptops but a disaster in an ebike pack.

 

[PCeBiker]

Brand name isn’t a good measure either. Some cells are appropriate for laptops but a disaster in an ebike pack.

Hmmm,..
I just purchased this battery with Samsung 50E 21700 cells.
I'm not sure about the BMS?

 

[tomjasz]

Their builds are decent. I had noted the BMS information and I remember I was satisfied. Where I filed it is a mystery at the moment. I have two 21700 packs from her. One Poly case and one shrink wrap

I'm certain Jenny would respond to any detailed questions you have. I

 

[PCeBiker]

Their builds are decent. I had noted the BMS information and I remember I was satisfied.

The part I like is that the BMS is proven to be reliable with no defective products.
I'd rather have a reliable one than a fancy one that could possibly fail in a bad way in a really bad place.

I have two 21700 packs from her. One Poly case and one shrink wrap

Well, if they are good enough for you, then I should certainly be happy with mine.

I'm certain Jenny would respond to any detailed questions you have. I

I will ask her.

 

[Gionnirocket]

Their builds are decent. I had noted the BMS information and I remember I was satisfied. Where I filed it is a mystery at the moment. I have two 21700 packs from her. One Poly case and one shrink wrap

I'm certain Jenny would respond to any detailed questions you have. I

Yeah I did the same... I've got the BMS info from Jenny somewhere. I'm sure if I take a few minutes I could find it, but this 2700 battery is drastically different than mine so I'm sure it would be different anyway.
This said I got into a pretty detailed discussion with Jenny on the BMS and I went with her suggestion for reliability. My BMS does not balance but the high quality matched Sanyo cells should charge/discharge equally keeping the pack in line.