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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 The two nubs connecting the two halves of Gotway's BMS have been replaced by wires in Rockwheel's case.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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@Aneta Where'd you find the Rockwheel BMS photos? I can't seem to find any, and I've been looking for a while.

 

On 11/1/2019 at 10:41 AM, 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.

Almost -- GT16 has 4x 10S2P BMSes, of which there is some communication going on between series packs (there seems to be a 3-wire connector for communication here), and potentially communication between the parallel packs (I've not been able to verify this as my vendor replaced the packs on one side with a third-party set after it shut down on me at 23km/h). Many wheels with parallel BMSes have a wire to synchronize the charge/discharge cutoff MOSFETs to mitigate the explosive rebalancing issue (one pack at 100% charges another pack at 0% explosively) documented in https://us.reddit.com/r/AskElectronics/wiki/batteries#wiki_increase_the_capacity_with_batteries_in_parallel. The KS18L, which has 2x 20S2P packs with independent BMSes, has this wire.

I think the GT16's battery packs are potentially one-of-a-kind, and I'm rather curious to see what the BMS looks like. Additionally, I don't see a charge-cutoff-sync wire connecting the parallel packs, so I've been slightly concerned that the issue mentioned above could happen to an aging GT16 battery pack.

On 11/1/2019 at 10:41 AM, Tinkererboi said:

Yes, any BMS will balance the cells.

No, some BMSes don't balance the cells, but simply stop the charging process when any one cell hits the max voltage of 4.2V. I left my Inmotion V8 battery plugged in for days (cumulatively, I unplugged it when I left the house), but the battery was pretty far out of balance and not fixing itself. Manually balancing that pack by charging up the low cells helped buy some cycles until the battery pack fell out of balance again.

On 11/1/2019 at 10:41 AM, Tinkererboi said:

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.

The Inmotion V5F, V8, and GT16 packs, at least, still cut power when cells dip below the minimum allowable voltage. I don't think output protection was current-based as much as it was a per-cell-voltage thing. The V5F and V8 packs at least had a smart connector that could signal errors to the motherboard so that it could enter deep tiltback instead of violently dropping the user.

On 11/1/2019 at 10:41 AM, Tinkererboi said:

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

The discharge-cutoff bypass (aka shunt) was a rather dangerous thing that exchanged the risk of a BMS cutoff for an increased fire risk, because that discharge cutoff MOSFET is the only thing preventing a battery pack from being over discharged to the point of voltage inversion. And you wouldn't even know you had a dead cell until you charged it up again and it set your house on fire instead. I wouldn't even be surprised if the e-scooter fires in Singapore were caused by something like this.

 

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11 hours ago, hyperair said:

@Aneta Where'd you find the Rockwheel BMS photos? I can't seem to find any, and I've been looking for a while.

I don't have RW BMS photos, I simply referred to @Tinkererboi's photos of Gotway's board, which, as he says, is almost identical, but in GT16 it's cut in half, and the halves are connected by those extra wires you can see between two sub-packs. There's no BMS communication between left and right sides, the two sides are simply paralleled (both discharge and charge ports).

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ae-1560708009876.jpg

ae-1560707999125.jpg

ae-1560708005274.jpg

My bad, I finally found the photos i took way back, and the board looks different than what i remembered. Did not take pics of the other side which had the 4 mosfets tho

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You Rock, @Tinkererboi! Were all those contacts B1, B2, ... actually connected to parallel groups?

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