V8 battery upgrade!!!

[Blueblade]

Just curious, what are most folks using for BMS?

I wouldn't want to cannibalize my stock pack for its BMS, as there is nothing wrong with it, and id rather have all new cells rather than mixing and matching new and ol together.

If you find a defective pack someone is selling for cheap, it would leave you wondering if its BMS is defective too.

I see 20s 3.7v BMSes for 18650 cells on AliExpress for around $30 USD, but saw commentary on here before about such BMSes potentially not being safe for EUC use, and not sure the right amp rating (35A maybe?) Here is one example: 

https://m.aliexpress.com/item/32945748386.html?trace=wwwdetail2mobilesitedetail&gps-id=platformRecommendH5&scm=1007.18499.134607.0&scm_id=1007.18499.134607.0&scm-url=1007.18499.134607.0&pvid=e06d2776-6f1a-490f-bc26-6e96e9457984&_t=gps-id:platformRecommendH5,scm-url:1007.18499.134607.0,pvid:e06d2776-6f1a-490f-bc26-6e96e9457984&spm=a2g0n.detail-amp.moretolove.32945748386&aff_trace_key=29581d08b7f74a818031f2320187c25d-1572816271494-07556-UneMJZVf&aff_platform=msite&m_page_id=9243amp-L82iiCN6Y5laBXclRK2P-g1572816363859

Edited November 4, 2019 by Blueblade

[alcatraz]

If you can find a way to charge through the BMS but take power out directly from the cells, it'd be safe while riding I think.

The one you linked to does not do any balancing. That could work if the cells are extremely well matched.

Edited November 4, 2019 by alcatraz

[Chriull]

23 minutes ago, Blueblade said:

see 20s 3.7v BMSes for 18650 cells on AliExpress for around $30 USD, but saw commentary on here before about such BMSes potentially not being safe for EUC use, and not sure the right amp rating (35A maybe?) Here is one example: 

Problem could be the the short circuit protection - if this is too low or too sensitive it could shut off while riding.

Second prob is the cell undervoltage protection - could lead to cut offs while riding, too.

20 minutes ago, alcatraz said:

If you can find a way to charge through the BMS but take power out directly from the cells, it'd be safe while riding I think.

Yes. Like "shunting" the discharge protection mosfets as with the early generation wheels.

Ps.: I assume not, but one should check if the V8 has some "special communication" abilities with the BMS.

 

Edited November 4, 2019 by Chriull

[Blueblade]

18 minutes ago, alcatraz said:

 

The one you linked to does not do any balancing. That could work if the cells are extremely well matched.

I thought it did, it says 4.18v balancing release voltage and 30mA +-5mA cell balancing current, and has ~20+ wires im assuming for each cell group.

But between you and @Chriull its obvious the main problem to worry about is drawing power through the BMS--- probably should be avoided. I'll have to look more at stock wiring. Could it be as simple as soldering a big (fused for short protection I would assume) wire to the first and last cell group.

Or maybe a sufficiently high current rating BMS well above the largest expected demand would be sufficiently insensitive to large current surges.

Good point about the communication, too.  Wheellog obviously knows total current and voltage but I have never seen any cell group info, so maybe that's all done at control board.

You're convincing me to just find a stock BMS somehow before proceeding to be safe though.

 Too bad they don't just sell inmotion branded BMSes separately, or a darn 20S3P pack for that matter.

 

[alcatraz]

My initial idea modifying the battery was to keep the BMS "modular". That could be a good first project. To simply open up the original and desolder it from the pack. (19 small wires and 2 nickel strips). Then with appropriately sized wires and connectors connect it back.

Then test.

Afterwards you can build a pack and plug it into the old bms, which you also heatshrink separately. Just leave 2-3mm of thickness/depth available so it fits in the v8 cavity.

[Nic]

12 minutes ago, alcatraz said:

My initial idea modifying the battery was to keep the BMS "modular". That could be a good first project. To simply open up the original and desolder it from the pack. (19 small wires and 2 nickel strips). Then with appropriately sized wires and connectors connect it back.

Then test.

Afterwards you can build a pack and plug it into the old bms, which you also heatshrink separately. Just leave 2-3mm of thickness/depth available so it fits in the v8 cavity.

That is exactly what I had in mind, but I decided not to bother as I had a hard time just getting the extra batteries to fit and I figured that more wires and connectors would just get in the way. It is also quite hard to find appropriate connectors that are compact enough. All the extra wrapping would also make it harder to fit two items (battery + BMS) back in the case. In the end I realised that I wasn't going to carry a spare battery around, so I will just reuse the BMS if I build a new battery when my pack wears out. Hopefully we will have much higher capacity cells available when that happens, assuming we get some breakthrough in battery technology.

[alcatraz]

When you don't use the original battery case there is quite a lot of room actually.

The simplest and cheapest upgrade would probably be to go from 18650 to 21700 cells. LG 21700 M50 ~5000mAh cells are priced around the same as the king SanyoPanasonic NCR18650GA ~3500mAh. So I'd suggest to just build a pack with 40x21700.

I belive it can all fit without stacking a cell group on the top which will leave plenty of depth room. The 21700 cells are however 5mm taller than the 18650 but as there is no case or stacked cell groups it comes out shallower.

40x5000mAh x 3.75V = 750Wh

[alcatraz]

If you want to go supercheap, which I don't recommend because you'll regret it, then get 20-22pcs of LG MH1 cells and build a 20s3p pack.

You'll regret it because mixing cells of different ages will require you to balance with a hobby charger from time to time, and building a 20s3p and have it fit a V8 is quite a lot of work. A lot of the work is getting as many batteries in there, finding the most efficient arrangement while always fearing that you won't be able to even insert the pack after all the hard work.

[Blueblade]

7 hours ago, alcatraz said:

My initial idea modifying the battery was to keep the BMS "modular". That could be a good first project. To simply open up the original and desolder it from the pack. (19 small wires and 2 nickel strips). Then with appropriately sized wires and connectors connect it back.

Then test.

Afterwards you can build a pack and plug it into the old bms, which you also heatshrink separately. Just leave 2-3mm of thickness/depth available so it fits in the v8 cavity.

That is a good idea, but as @Nic says, i do worry about how much extra space 19 connectors would take up, certainly wouldn't want to use automotive crimp style bullet connectors for example.  I was wondering about the 21700's too, since you can get >10A cell ratings and more capacity simultaneously, close to 3P benefits with 2P.  Wouldn't want to drop hundreds of $ on cells though without being able to test fit them first.

Shoot maybe it is best to just get a Nikola or 16x, and never worry about the v8 range again 😁

[alcatraz]

You could also solder a wire between bms and pack. Anything that later can be cut and soldered to the new pack relatively fast will be appreciated. But I don't think it'll be needed. Get two 11 pin 2.54jst-xh connectors and connect it that way. Use 22awg wire which is thin but thick enough to deal with the maximum balancing currents of 2-3 amps.

The V8 battery compartment has a little extra space in the upper two "corners" of the middle block. This is where the original cables go on one side. The other side is empty i believe 

The battery has a plastic shell around it. If you simply get rid of it and just put the pack in without it you can fit a ton of wires. Just find a way to wedge the pack in there so it doesn't move around.

[Nic]

11 hours ago, alcatraz said:

If you want to go supercheap, which I don't recommend because you'll regret it, then get 20-22pcs of LG MH1 cells and build a 20s3p pack.

You'll regret it because mixing cells of different ages will require you to balance with a hobby charger from time to time, and building a 20s3p and have it fit a V8 is quite a lot of work. A lot of the work is getting as many batteries in there, finding the most efficient arrangement while always fearing that you won't be able to even insert the pack after all the hard work.

I already went that route and it is safe to mix cells provided you match one new cell with two old cells in each group of three as then the groups are matched. Also, I fully charged all cells and checked the voltages before assembly so they will already be balanced once assembled. It was a very tight fit and I had to trim some plastic from the shell to get the pack in. I like the idea of using 21700, so that might be for a future project.

Edited November 6, 2019 by Nic

[Chriull]

5 hours ago, alcatraz said:

Get two 11 pin 2.54jst-xh connectors and connect it that way. Use 22awg wire which is thin but thick enough to deal with the maximum balancing currents of 2-3 amps.

Mentioning the following should be superfluous, but just to be secure: the "first" and "last" wires have to be thicker and need another connector, as they have to take the whole operating current!

For the accuracy of the BMS cell voltage meadurements one could try to provide both wires - the thick ones for the charge/discharge currents and the measurement wires.

[rado]

Hi All and thanks for all your info. Was wondering if the v8 can be fitted with the V8f battery and if so, what would be the change in weight and performance boost? Many thanks!

[Nic]

2 hours ago, rado said:

Hi All and thanks for all your info. Was wondering if the v8 can be fitted with the V8f battery and if so, what would be the change in weight and performance boost? Many thanks!

10% increase in range (~3km) due to higher capacity cells. That's it. The packs are likely identical, but you should check with your supplier before ordering, assuming you can even find a V8F battery for sale.

[v8nice]

is it possible to made battery with 21700 cell.+5mm lengh is ok ?

i see with 18650 ,is not possible to made 20s3p battery with all cell in parallel but if it s possible ta made 20s2p  with 21700 all aligned is more good for 10ah (+56%) .

[Unventor]

5 minutes ago, v8nice said:

is it possible to made battery with 21700 cell.+5mm lengh is ok ?

i see with 18650 ,is not possible to made 20s3p battery with all cell in parallel but if it s possible ta made 20s2p  with 21700 all aligned is more good for 10ah (+56%) .

I doubt it but I am not a battery builder expert. The thing is the V8 is so small in the area where the battery is. 

[v8nice]

just with all size of original battery is possible to see if it s possible.

 

 

 

[meepmeepmayer]

People made a 3p packs with 18650s for their V8 by removing the plastic box holding the original battery to make more space. So I think 2p with 21700s might fit. Not sure.

[alcatraz]

20s2p 21700 fits easily. It's a good upgrade.

The pain of building a V8 battery is the shape.

What I did was to tape some 1mm thick cardboard around the opening (to provide clearance) and then raise the bottom of the cavity to support the build near the opening. (There's more space inside than at the opening so you need to build it just inside the opening.) Then just hotglue the cells together by hand and after every few cells take the pack out, check that it's level and then hot gluing from the bottom aswell to reinforce. You just use a little glue to position the cells and then reinforce to make it permanent afterwards.

The tricky part is to glue it all nice and level. The last cell should be just as deep as the first, and the angle should be right. Otherwise you have no chance in hell of inserting or removing the battery.

After upgrading remember that even though the wheel feels great with less voltage drop, the unfortunate safety circuits will still be set for the weaker battery so you could see a cutout if you push the wheel over the standard limits. So please treat the upgrade as a range upgrade and not a performance upgrade. I made the mistake of thinking I had more power and it cut out on me at high speed. Nothing damaged whatsoever, just a simple protection circuit, wheel fired up normally afterwards but my shoulder hurts like hell.

Edited February 17, 2020 by alcatraz

[Chriull]

12 hours ago, v8nice said:

i see with 18650 ,is not possible to made 20s3p battery with all cell in parallel but if it s possible ta made 20s2p  with 21700 all aligned is more good for 10ah (+56%) .

Sorry - how do you come to this numbers? I can't follow them?

A 18650 3p set has either about 6Ah (with ~2000mAh cells) or 10.5Ah (with 3500mAh cells)

A 18650 2p (3500mAh cells) set would have 7Ah.

A 21700 2p set has either 10Ah (with 5000mAh cells) or accordingly lower Ah if lower mAh cells are used.

So a 18650 3500mAh 3p set has about the same Ah as a 21700 5000mAh 2p set!

The capacity theoretically differs just by the this 0.5Ah * 20 cells * 3.7V = 37 Wh.

Especially as this cell capacity values are given for most cells for about 0.2C discharges downto 2.5V.

In EUCs they are burdened totally different (up to 2-3C, downto 3.3V.)

5 hours ago, alcatraz said:

20s2p 21700 fits easily. It's a good upgrade.

Which cells did you use?

Is the range increase somewhere near the theoretical 5000mAh/3500mAh= 142%?

5 hours ago, alcatraz said:

After upgrading remember that even though the wheel feels great with less voltage drop, the unfortunate safety circuits will still be set for the weaker battery so you could see a cutout if you push the wheel over the standard limits.

That's no safety circuits, this is just "normal e-motor behaviour". With the same voltage the lift cut off speed (max no load speed) as max speed limit stays exactly the same.

By the lesser internal resistance of the 21700 cells this max speed limit line over burden "gets steeper". So at higher burdens they should provide a bit more max speed as the 18650. But most presumably just an neglectable amount for practical purposes.

5 hours ago, alcatraz said:

... but my shoulder hurts like hell.

Get well soon!

[alcatraz]

I'm pretty sure the EUC turned off. I wasn't accelerating when it happened. Had plenty of battery 4/5 bars. It was at 9 km into my 11km ride home.

A guy on an electric scooter stopped in front of me for a moment and then took off. He didn't look back. I theorized that the industrial area I passed by emitted some kind of EM pulse or something and we both got caught in it. I've watched too many movies... right?

I used the same kind of cells that the V8 comes with. LG MH1 so I effectively reduced the amperage by 33%. Had I gone with Sanyo/Panasonic GA cells I could have gotten an even better result but seeing as it was my first build I didn't want to invest too much. I paid less than 40usd for the cells to expand to 20s3p. The pack works fine and I still ride the V8 but I capped the speed to 25km/h.

The 21700 cells currently available in China are refurbished tesla automobile cells made by sanyo/panasonic. The capacity is really 5000mAh. You can recognize them by the three lines on the negative side. Other than that mark they look all different because they are packaged by the refurbisher. In the cars they don't have a standard positive pole but just a concave pole so that's attached as well as a spacer and shrinkwrap. Every refurbisher has a different design but the three small lines on the negative side is the mark to look for.

[v8nice]

for 21700 in 20s2p this cell is the best ,is "only" 4200 ah but 30 at 45a capable per cells !

https://www.facebook.com/batterymooch/posts/bench-test-results-early-samples-molicel-p42a-45a-4000mah-21700great-30a-battery/2225447571078150/

in french (i m french) one guy make 20s3p v5 and he say :

" 

Little feedback after a few weeks of using my V5 ++ on the commute :

- objective reached: after a round trip of 25km my battery remains charged at 30 - 35%, against practically 0 before.

- collateral effect # 1: the wheel is less difficult in the steep hills.

- collateral effect # 2: the tilt-back occurs a little later. Finally more exactly a little earlier, it's still a V5.

When you think about it a bit, the two collateral effects were predictable, the battery being now able to supply more current during a strong request its voltage remains higher, so there is more power available. "

 

for 10ah battery in 20s2p with the same A of original is this cells :

https://www.nkon.nl/fr/rechargeable/li-ion/21700-20700-size/samsung-inr21700-50e.html

 

normally with batteries with a better Ampere discharge rate, the voltage drops less during acceleration, with the same "bms" protection card

 

i need to know if it s possible 20s2p 21700 ,I think it takes less space than 20s3p 18650 but just the batteries are 0.5mm longer.

 

 

 

[v8nice]

or this is very small 20700 with 15A and 4250mah typical capacity

 

https://www.nkon.nl/fr/rechargeable/li-ion/21700-20700-size/sanyo-ncr20700b-lithium-battery.html

[alcatraz]

The original V8 cells are LG MH1 rated for 10A continuous.

If you go with 5000mAh 21700 cells they can do 15A continuous and 25A bursts. In any case that's 50% more than the original cells. (Referring to the cells mentioned below)

There are a ton of 5000mAh cells coming out of asia now. They don't look official but they are repackaged Tesla Motor cells from recycled battery packs made by Sanyo/Panasonic. Supposed to be insane good value. In china they cost 1.2usd a piece.

They look a bit shitty because tesla batteries don't use shrinkwrap or a "complete" positive pole. Those need to be added before selling them for consumer use.

Edited February 21, 2020 by alcatraz

[v8nice]

for unicycle ,i never drive with chinese cells .