48v battery pack full charge voltage?

[Gionnirocket]

AliExpress doesn't 'sell' products, they are more like a marketplace of sellers from China, much like Amazon. And you're right - it's a crap shoot on what you get coming out of china - some of it is really good, some of it not so much.

My extensive experience with batteries is with12V lead acid for cars boats and RV's, and Lithium Polymer packs - these from playing with RC crawlers, or 'tiny trucks'. "LiPo", as they are referred to, are considerably more volatile than lithium-ion, like we have in our ebikes. For lipo cells, each cell has a sensor wire that the charger uses to balance all of the cells in the pack. These packs are generally 2 to 6 or so cells, 2 or 3 being most popular for crawlers - low power - and more for high speed surface and aircraft models, like racing cars and boats, and electric powered aircraft. AFAIK the only way to get proper cell balancing is with this sensor wire that actually measures the voltage of each individual cell. Obviously our bike batteries don't do this, and there are a lot more cells, like 50 or so. So as I understand it, our very basic chargers and battery management systems (BMS) only measure for whole-pack voltage, min and max for shut off. There isn't really any true balancing going on there. And why simply charging up to 100%, or 'peaking' out the pack, is the best way to keep all cells balanced. If too many are failing, or are of lower capacity - measured by voltage - then the whole pack suffers, those bad cells will drag the rest of them down. Also why it's valuable to charge the pack fully - the best chance of peaking up all the individual cells.

Same way a lead-acid fails - if one set of plates, or 'cell' fails, it drags the others down to it's level, the whole battery fails. And why you don't mix old and new deepcycle batteries in an array, like in RV's and boats and such. I've seen charge systems destroy a good battery paired with a bad one - starting batteries for a marine engine. It literally cooks the juice out of the good battery, trying to get the bad one to take up charge.

Anyway, that's how I understand it, and these are kind of low-tech packs for our ebikes, much like you find in any cordless appliance, but just a lot more of them, and why you just charge and go like your dust-buster. The charging system is just a very basic process of adding charge amps to the pack. All the BMS does is shut it down at low voltage, and stop charging at high voltage - there isn't really anything else going on there.

Yes I understand how Aliexpress works... but it was a general statement meaning that most sellers don't care about matching products through manufacturers specification... They sell what ever they can and it's up to the end user to know what they are doing/buying.
On the subject of balancing, I too have extensive battery experience from the RC hobby to Data Center UPS Systems with rooms full of lead acid and you are misinformed on the balancing of the common ebike battery. Even the most basic of BMS's are doing true balancing and it is accomplished at the end of the charge cycle. A 48v pack will have 14 balancing leads, one for each series string and a common wire which works in the same fashion as your hobby charger. Since the parallel cells will self balance each series string is approached as a single cell. So though I agree that these are low tech, there is a little more going on than just high/low voltage protection.

 

[Browneye]

So, 14 'cells', but not all of the individual cells. Sounds good.
What happens if a few of the actual 18650 cells are bad in one of the 14 sensed cells?

Evidently the technology for Li-ion doesn't have custom cell pack configurations like Li-Po, with various sizes and styles. They're still using the old round like a AA - 18650 cells. My guess is we'll see some new battery pack technology in the near future. I wonder if they'll ever move to Lipo.

 

[Gionnirocket]

So, 14 'cells', but not all of the individual cells. Sounds good.
What happens if a few of the actual 18650 cells are bad in one of the 14 sensed cells?

Evidently the technology for Li-ion doesn't have custom cell pack configurations like Li-Po, with various sizes and styles. They're still using the old round like a AA - 18650 cells. My guess is we'll see some new battery pack technology in the near future. I wonder if they'll ever move to Lipo.

13 cells in the example, a 48v pack is a 13SxP
In any series circuit if you have an open cell you will loose it. If it's a degradated cell as in your lead acid battery plate example it will drag it down. I don't think they'll move to Lipo's as they are more volatile and there isn't a need for such a high discharge rate