Bamboo GT AT 50km Range Project

Guys

I am looking at a project to get Bamboo GT AT up to 50km range with better power/ride for the whole trip (and keep up with GT Carbon boards )

The stock Evolve battery gets me 20km max with the last 10km crappy with constant dropping from fast back to eco etc. due to voltage sag

The stock evolve battery is 6.5Ah with 10 cells in series using unbranded prismatic Li Ion batteries with BMS at end of pack.

The board is fairly new so I am looking at using the stock 6.5Ah battery with another battery added to extend the range .

Being an engineer I like to design things out properly so my basic user specification is defined as

* at least triple the Ah capacity - so approx. 19-20 Ah in total
* utilise existing 6.5 Ah battery so approx. 13 Ah to be added
* additional battery to be "plug in" so only added for longer trips
* utilise stock BMS to charge auxiliary battery as well as stock battery

This will drive a few things in the design process

So far have worked out
A) Aux. battery pack will need to be of same battery chemistry as stock battery ( Li Ion) and a 10S configuration to match stock battery
B) Have selected 18650 Li Ion as the right type/size of cells
C) Aux battery pack will need to be at least 13 Ah - so if use 4P configuration - leads to 3.25Ah for each cell . This is just within range of latest 18650 cells
D) To use stock BMS - I will need to connect each 4P pack in aux. battery in parallel with each (1P) pack in stock battery. Based on research this does not appear to be a problem and the packs will current share based on capacity. This means 11 wires from aux. battery to connect to stock battery in a plug!
E) Stock BMS will charge aux. battery as it is in parallel with stock battery will take a lot longer though) and the BMS cell balancing will work OK w
F) The aux. battery will need to sit under the existing bamboo GT battery box ( having AT wheels means a lot of clearance) and should have maximum depth of approx. 20mm
G) The flat section underneath board battery pack is approx. 150mm wide and 500mm long.
H) Basic configuration of the aux. 10S 4P battery is as on attached file ( not sure how to insert photo in a thread)
I ) With configuration as on picture -aux battery dimensions will be 140mm wide 400mm long and 20mm deep so should sit under stock battery case nicely.

Things I will need for this project are
40 Li Ion 18650 cells with 3.2Ah minimum
18650 cell holders
nickel strip
spot welder
heatshrink
in-line fuse holders
12 pin plug with 30/40 A rating
high temp silicon wire (12awg minimum)


Any comments/feedback/suggestions on initial thoughts would be welcomed

Cheers

 

Good luck with that. looks like a great project. I think you would need some tape as everyone who makes these cells use heaps of tape. also changing your wheels to some scooter wheels might take some load off and increase distance. even if its just the front

 

I see a couple problems,
Your battery setup does not have any flex points.
Adding a second battery underneath will mean you will only be able to run in AT which means you won't get 50kms.
Your going to have 11 high amp plugs which will take up a lot of room.
There probably isn't enough room in the stock case to cluster all 11 wires so your going to have them coming out everywhere.
I think you would also need 11 fuses not just one.
You could only join the packs when they were at the same voltage.


Maybe I'm not imagining the same thing you are.... or maybe you have already thought about it and I don't mean to shoot you down but I just don't think this is a good idea, don't try to patch up a crappy stock battery. If you want that type of range get a super long deck and 60 x 18650 cells.
You could even use the stock deck and have 30 cells on top and 30 cells underneath the deck

Edit: just had a thought. You only really need to hook up both end of both batteries then when you want to charge your extra pack just take it off and use a separate charger then you only need 2 wires to join. You will still need balance wires but you would not need to wire then to the stock BMS.

 

Hi Everyone,
I'm new to this forum but not to E-boards and had 6-7 e-boards over last few years.
I also had same project in mind but after some research realised it won't work:
1. You can't combine 18650 cells with stock battery. Those batteries have different internal resistance.
2. If you just use 18650 cells as 10s4p setup which will fit in stock case, you will have a big issues with flex. Your custom pack has to be flexible enough. A lot of work to get rid of tabs and use flex wires instead.
3. And last - killing point: discharge current curve.
Stock bamboo pack works pretty much like a lipo: 4.2 gradually discharging till it reaches 3.4v per cell - then control board and BMS will say it's 10-15% and you pretty much done.
If you use 18650 for example samsung25r cell which will give you 10ah (10s4p) capacity and 80a discharge rate has a very different discharge curve:
Fully charged 4.2v then almost straight drop to 3.8v and then gradual discharge till 2.5V.
Which means once battery reaches 3.4v per cell your controller will go into eco mode while you still have plenty of juice left in your battery.
So unless you reconfigure bms and controller you will be only using 30% of your new pack.
In case you think- ok fine, I'll change BMS to 18650 10S so it doesn't cut the battery once it reaches 3.4v. But keep in mind- evolve bms has uart interface connection with control board. Without it - your board will give you an error..
I hope my input for some people will save a lot time and money.
BTW: I think finding a correct size lipo in 10s congratulations and rebuilding it in flex flat pack will be cheaper and much easier project.
Cheers
Evgeniy

 

Good info, I would just add 10s4p does not fit in the stock pack you need to extend it, trust me I have done it. Also adding flex to a 10s4p isn't that hard. Also a good choice for 18650 is LG GH2 once they get to 3.4v they are pretty well spent.

 

Thanks for correcting. You are right. 40 cells won't fit in stock enclosure without extending it. I've mixed up dimensions with carbon deck.
Have you done it as 10s4p on bamboo? If yes, how is it ? Can you please give us some feedback on range, performance, voltage sag in comparison with a stock pack?
Cheers

 

This should have everything your after
How I built a 12ah Battery for my BGT

I get about 40km with a street setup, and voltage sag has been reduced to single didgest.

 

Excellent! Thanks mate. I'll check it out.
Cheers

 

Nickelberry has a build thread: How I built a 12ah Battery for my BGT

**You beat me to it lol

 

I've just checked Nickelberry thread - Respect man - Good job!
Looks like I've just got myself a new project ...
Stock Bamboo battery is quite bad, even in comparison with Carbon one. I have run Internal resistance tests on both packs using ICharger and 10S custom balancing plug/adapter. Battery from Carbon GT was averaging 3-4 IR while new bamboo 7-10 IR.
And I had Second Gen Bamboo in the past and replaced their battery once - pretty much all 3 bamboo packs (2 x Gen2 and 1 x GT) were pretty disappointing.
My Carbon GT on AT 8" wheels done at least 5 times more than Bamboo GT on street wheels and still good. While Bamboo drops to 50% just after 5-7km and than you have to babysit the rest. Carbon GT also starting to sag a bit - but it's still reasonable.

Just a thought: Have you seen these packs in complete enclosure? Apart from flex issue what are your thought?
SPACE CELL PRO4 Electric Skateboard Battery USA

Maybe cut of a battery section and push it towards the front as much as possible and shorten Evolve enclosure to keep control board separately?

 

lol

 

Thanks Mate,
Yeah I was looking at the space cell, the problems I could see was flex, mounting the evolve motor controller and I didn't like the switch and charging port being on the bottom, I would scrape them off for sure.

 

Sorry I meant to show enclosure:
SPACE CELL PRO ENCLOSURE
Or ready pack but ask to upgrade cells to LG GH2

 

Agree!

 

Still don't know how you are going to get around the flex issue.

 

What about cutting of a battery section - seal it and push it towards the front as much as possible and also shorten Evolve enclosure to keep control board separately?

 

Nick and Evgeniy

Thanks for your comments/suggestions - interesting -

My comments on your thoughts are

A) Intend to use standard Aust. 12 pin trailer sockets/plugs for power connection - these are generally weather/dirt proof with a cover and rated at 20A cont. for small pins and 35A for large pins. The socket from stock battery will fit on the back of board between the two motor cables. The aux battery will be fitted with a 12 pin plug to match. The 11 power/balancing wires from stock battery will come out in a single heat shrink bunch to the 12 pin socket at rear of board.

B) The aux battery will only be plugged in if SOC is identical to stock pack - easy to check and do - will probably only plug in at full charge ~ 4.1V per cell. Of course this only applies if aux battery is not charges through board BMS.

C) A 10S4P wont fit in stock battery case and this would be wasting the stock batteries pack which is practically brand new.

D) My idea is to parallel up all ten cell banks from stock and aux battery -so yes 11 power wires required - and will fit 10 x inline micro fuse holders in aux battery with 25A fuses. Doing it this way means I can use the BMS in the board for charging and cell balancing . I do intend to also make an external charger with BMS so I can charge aux battery independently as well.

E) Evgenity - Your comment 1. - Yes there will be a different internal resistance between the cells (banks) in stock batter to aux battery cells. Being in parallel the two banks of cells will effectively "current share" due to different internal resistance effectively proportion to Ah capacity which is exactly what you want.

F) Your comment 2 - 18650 10S4P wont fit in battery case and will not utilise stock battery as per C) above

G) Your comment 3 - Discharge Current Curve - I intend to use latest LG HG2 cells which are 3400 mAh capacity . I have checked quite a few times the B GT AT motor current on flat ground at my normal speed of max 25/30 kmh and it is approx. 3-5 A per motor or 6-10A in total. Even up a very steep incline accelerating is in only approx. 8A per motor.
Assuming current sharing of approx. 1/3 stock battery 2/3 aux battery , the aux battery should see approx. 5-7A.
Discharge curve of an earlier 3000 mAh LG HG2 is


I think that 0% on stock battery is approx. 3.1V ( somewhere on this forum I have seen a %/voltage graph but cant find it now)- from LG HG2 discharge graph at 3.1V and 5-7A the discharge capacity is approx. 2.6 Ah from a rated capacity of 3 Ah - approx. 87% - so yes there may be a bit left in aux battery when stock battery reads 0% but not a lot.
Note that the discharge curves cut off at 2.8V - so presumably if you absolutely want the full 100% Ah you will need to discharge to 2.5V which I know the stock BMS wont allow.

I do not intend fiddling with stock BMS

Appreciate any further feedback on my comments above

Cheers

 

You should really consider designing your battery around the maximum possible discharge rate which is 35A ish per motor, you can hit this pretty quickly on grass or sand.
Also I see why you want to reuse the stock battery but I just don't think it will be worth it.

 

Also you may find it hard to get genuine LG HG2 cells, do you have a link to this new 3400mAh type?

 

Nick

The nickel strips in the middle ( where is says B10 B8 B6 B4 B2) will fold over "butterfly " style so this will provide some flexibility between the two halves. For flexibility longitudinally ( eg when you jump on the middle of the board) I can put separate each bank of four cells and put copper flexible braid where there is a joint between two four cell banks. Do you think this will be OK.

If I need flexibility within a four cell bank - may revert to your idea of a spacer between cells.

Cheers