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Aneta

Rockwheel GT16 battery configuration?

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Rockwheel GT16 (mine is a 1036Wh version) has 4 battery "packs" - two blue blocks on each side. I thought they were 20s1p each, connected in parallel, for a total of 20s4p made of Sanyo 18650 GA 3500mAh cells. However, I noticed that between two blocks on each side there's only one thick wire, and each block has only one thick (power) wire going to the controller (black from one block and red from the other). Black wire, connecting wire, and red wire - this suggests that the two blocks on each side are connected in series, not in parallel. So, each block is actually 10s2p? Two such blocks are connected in series on each side for the total of 20s2p for each side, and two sides are connected in parallel for the total of 20s4p. Is this correct?

If this is correct, press 1 any idea why they chose such a weird way of splitting the cells? 20s1p for each block would be more natural, wouldn't it? Why 10s2p (a 42V battery pack) instead?

And 2nd question: do you know if these packs have a proper balancing BMS? I'm asking this to know if leaving the charger on for several hours after a full charge (once a month or so) will balance the cells, or will do exactly nothing? (or worse, "cook" the cells, as trickle charging at 4.2V per cell for hours is not healthy for Li-ion)

Thanks for any insight!

Aneta

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Good job noticing that each pair makes up a single battery pack. I only figured that out when I had already taken every single cell apart. 😅There's a BMS by the way. 

The most obvious advantage of splitting up the batteries is space saving and lower centre of gravity. The batteries sit around the axle instead of above it.

This is why the GT16 is as small as the 14 inch MCM5. The insides of almost every other wheel are all annoyingly empty, making them much bigger than they have to be. 

The BMS:

HTB12IDAXvfsK1RjSszgq6yXzpXa0.jpg_q50.jp

This is what you will find in most Gotway wheels

The GT16 BMS is 95% identical to a Gotway BMS, the only two differences being Rockwheel's BMS having 4 Mosfets for output protection while Gotway Mosfet slots have been left blank ie no output protection.

The second difference is that Rockwheel had their BMS manufactured slightly differently so it could be split in two. The two nubs connecting the two halves of Gotway's BMS have been replaced by wires in Rockwheel's case.

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1 hour ago, Tinkererboi said:

Good job noticing that each pair makes up a single battery pack. I only figured that out when I had already taken every single cell apart. 😅There's a BMS by the way. 

The most obvious advantage of splitting up the batteries is space saving and lower centre of gravity. The batteries sit around the axle instead of above it.

This is why the GT16 is as small as the 14 inch MCM5. The insides of almost every other wheel are all annoyingly empty, making them much bigger than they have to be. 

The BMS:

HTB12IDAXvfsK1RjSszgq6yXzpXa0.jpg_q50.jp

This is what you will find in most Gotway wheels

The GT16 BMS is 95% identical to a Gotway BMS, the only two differences being Rockwheel's BMS having 4 Mosfets for output protection while Gotway Mosfet slots have been left blank ie no output protection.

The second difference is that Rockwheel had their BMS manufactured slightly differently so it could be split in two. The two nubs connecting the two halves of Gotway's BMS have been replaced by wires in Rockwheel's case.

Thank you very much, this is very interesting!

So, the reason for 10s2p in each pack, instead of 20s1p, is that the BMS wouldn't fit as a whole, so they split it in two halves, each capable of managing only 10 parallels, not 20, correct?

Sorry for repeating the 2nd question, but: does this BMS balance the cells?

And what does output protection do exactly?

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Don't worry too much about the battery specs, apart from its unusual look it is completely identical to what you would find on a gotway.

Yes, any BMS will balance the cells.

Output protection protects the batteries and prevents fires in the case of a short circuit. It has been phased out in most wheels by now as faceplants on early low-power wheels were caused by the BMS cutting off power when it deems the current draw too high for the cells to handle. However the GT16 battery is several times larger than those so I wouldn't worry about it.

There are ways to bypass it for heavier riders who need the peace of mind.

Always respect the beeps and you'll be safe.

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5 minutes ago, Tinkererboi said:

Don't worry too much about the battery specs, apart from its unusual look it is completely identical to what you would find on a gotway.

Yes, any BMS will balance the cells.

Output protection protects the batteries and prevents fires in the case of a short circuit. It has been phased out in most wheels by now as faceplants on early low-power wheels were caused by the BMS cutting off power when it deems the current draw too high for the cells to handle. However the GT16 battery is several times larger than those so I wouldn't worry about it.

There are ways to bypass it for heavier riders who need the peace of mind.

Always respect the beeps and you'll be safe.

Hmm... I'm pretty sure that not all BMS's have balancing function. In fact, many e-scooters don't have balancing BMS, only BMS with protection from overcharge/discharge, as well as current limiter.

If Rockwheel's BMS does have a current limiter, what that limit would be? I've seen battery currents of 50A when going up steep grades. Makes me wonder what the hard current limit is (if any).

I still would like to be 100% certain that leaving the battery on charger for several hours once in a while does balance the cells, or does nothing.

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On 10/31/2019 at 7:55 PM, Aneta said:

Hmm... I'm pretty sure that not all BMS's have balancing function. In fact, many e-scooters don't have balancing BMS, only BMS with protection from overcharge/discharge, as well as current limiter.

If Rockwheel's BMS does have a current limiter, what that limit would be? I've seen battery currents of 50A when going up steep grades. Makes me wonder what the hard current limit is (if any).

I still would like to be 100% certain that leaving the battery on charger for several hours once in a while does balance the cells, or does nothing.

My question has been most excellently answered here:

(To summarize: yes, it does appear from the photos of Gotway/Rockwheel BMS that it has balancing resistors.)

Thanks everyone for your help!

Edited by Aneta

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