pros and cons of BMS with 18650 scooter pack

Hi
recently bought a Mercane Wide Wheel (and really liking it), however while I have yet to pull it apart, I feel a little concerned about having 13 bundles of 4 parallel cells in the pack and keeping them all "reasonably" aligned in charge.

So I'm interested in starting my learning curve on charging that many cells in a healthy way.

I understand that I can find 52V BMS's on ebay for not much money, which if I understand things would at least mean that each bundle of 4 cells would then be managed, but how to then find if one of these is falling behind the others? Or doesn't that happen?

I also understand that making a pack that does not heat up significantly under load (or charge) is a good thing. I'm intending to do some "thermal camera" looks at my pack after some time on "full load" to see if things are heating up (or not). I anticipate that's a good start (if not please let me know).

Thanks for reading.

You don't need a thermal camera just a finger.

You can balance the pack however you want: manually, with a bms, with a rc charger however many cells at a time. If the cells are good quality and from same time they will hold a balance very well throughout the working life and should rarely need balance.

If you discharge the pack too far (too close to empty) the cells will go out of balance much faster and more easily.

If you do get a BMS make sure it's programmable so you can have a good termination voltage (~4.1v / cell) and good cutoff voltage (3.2 chemistry depending)

The main reason to use a BMS is to protect the pack from voltage extremes which could result in fire or pack damage. The fancier ones can display all the cell voltages which would help you find a weak group.

Good morning

flat tire said:

You don't need a thermal camera just a finger.

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for sure, but as I have a thermal camera (for other home heating and insulation projects) its no harm to use it

You can balance the pack however you want: manually, with a bms, with a rc charger however many cells at a time. If the cells are good quality and from same time they will hold a balance very well throughout the working life and should rarely need balance.

Click to expand...

that's good to know. The bulk of my personal experience (as a tech) was on older NiCD systems which irrespective of the quality of the (Panasonic) cells we used in our remote gear a sufficiently large array of cells always went out of whack. However its very encouraging to hear.

Typically I charge my pack (13 bundles of 4 parallel 18650) to 52V and discharge no further than 46V. Now for clarity that's 52V when the cells have been removed from the charger and allowed to settle for about 5min and 46V when load is removed and 5min settle too. I've observed under load (like up a hill) the voltmeter is reporting 44.5V (which is when I start kick assisting

If you discharge the pack too far (too close to empty) the cells will go out of balance much faster and more easily.

Click to expand...

yes, I've read this (don't see the need to do any experiments to verify it and that makes sense.

If you do get a BMS make sure it's programmable so you can have a good termination voltage (~4.1v / cell) and good cutoff voltage (3.2 chemistry depending)

Click to expand...

sage ... thanks!

fechter said:

The fancier ones can display all the cell voltages which would help you find a weak group.

Click to expand...

good to know ... hadn't seen that, so thanks