Battery construction 5,8kwh 72V


Sash

Member
Location
Switzerland
Hi all, i hope im in the right thread.

Im Sascha from Switzerland and im on convertign a KXF to electric. A lot of parts are ordered and now im on constructing the battery on paper.

Im new to this, and i absolutley know that this is not a easy thing and pretty dangerous as well.

But i want to share my ideas and hope for some advise to get safe battery with good performance.

The datas are following:

I want to get 72V and 5,8Kwh
so i need around 510 panasonic 18650 Cells.

I made some drawings to be shore that the cells-layout fits the kawasaki frame.

I also play with the thing in my mind to use the tesla model S style cooling tubes to internal liquid cooling the battery. But i dont have any practical experience, so i dont know if its neccesary. I just now that my performance goal is to run around 30minutes on hard pushing the bike.

I think its possible to do that, but dont know if its worth.
I now Alta did a lot of engeneering to air cool the battery in the redshift. But for me is that too much away from my skillevel, to construct somthing like this.

For the cell-holders i want to 3d print the parts.
For the connections i want to wire fuse the cells.
And maybe laser a (i dont now the right word) "connection plates" out of aluminum.

Next question is what BMS i shoud use.

Maybe someone have a few answers.

BTW sorry for my bad english,

greetz from switzerland, Sash
 

DonCox

Well-known member
Hi all, i hope im in the right thread.

Im Sascha from Switzerland and im on convertign a KXF to electric. A lot of parts are ordered and now im on constructing the battery on paper.

Im new to this, and i absolutley know that this is not a easy thing and pretty dangerous as well.

But i want to share my ideas and hope for some advise to get safe battery with good performance.

The datas are following:

I want to get 72V and 5,8Kwh
so i need around 510 panasonic 18650 Cells.

I made some drawings to be shore that the cells-layout fits the kawasaki frame.

I also play with the thing in my mind to use the tesla model S style cooling tubes to internal liquid cooling the battery. But i dont have any practical experience, so i dont know if its neccesary. I just now that my performance goal is to run around 30minutes on hard pushing the bike.

I think its possible to do that, but dont know if its worth.
I now Alta did a lot of engeneering to air cool the battery in the redshift. But for me is that too much away from my skillevel, to construct somthing like this.

For the cell-holders i want to 3d print the parts.
For the connections i want to wire fuse the cells.
And maybe laser a (i dont now the right word) "connection plates" out of aluminum.

Next question is what BMS i shoud use.

Maybe someone have a few answers.

BTW sorry for my bad english,

greetz from switzerland, Sash
Sascha,
Lets start from a better spot. What kind of performance do you want out of this dirt What level do you ride. These are the starting blocks. Alta built a 260+lbsbike with 40HP (using I think Panasonic cells). When they went to the Sony VTC6 cells they were able to get 50HP. These are pretty true numbers, @phillip has his Alta dyno info on this forum.
The type cell you use and quantity determine the available max current, times your Voltage give you your HP. Then you must decide how much weight you want for how long you can ride.
In my recent builds I have been using the 21700 type cell, similar to Stark, the energy density per weight is better, less connections.
Cost is also a factor, at least for some of us, The Sony VTC6 and VTC6A seem to be the most expensive. I have 420 Sony VTC6 cells (18650) in one of my bikes. That gives me a theoretical 630A, but I actually only measure 570A. But very reliable. . Now if you could put 570A at 72V to a 100% efficient motor, you could get 41KW or about 54HP. Is that the power you want? I have not got all of that to the motor, because of the Controller in my bike . I am changing that now.
The engineering of the cooling is important, looking both at the Alta battery and the Stark sale info. If you are going to wire bond, you can do it like Alta and I think tesla with both leads on the one end and mount them on a heat sink like Stark did. I haven't figured out how they isolated all the heatsink end of the cells in the Stark yet. But go thru the Stark promotional info and gather as much info as you can from them about the battery. Here is a link to the tearing apart of the Alta battery.
Possibly think about a higher voltage motor also. Less current needs and smaller wire components. But higher voltage can be more dangerous. Commercial products mostly run up to 120VDC, but lower voltages are more common for the DoItYourself group.
Here is a link to the Stark, and at about 1:57 min in they have some info on the battery.
I hope this info helps.
Don
 

Sash

Member
Location
Switzerland
Hi Don, thank you very much for your answer.

To answer your questions: My goal is to get a dirt bike wich gets around 40hp, around the same weight like a stock 250 4-stroke bike and around 3o minutes of riding on a mx-track.
In other words: it has to be the same as a 250 4-stroke bike only in electric version. And it has to be able to compete on a race in our swiss champipnchip, wich goes normally 20minutes + 2 laps. after that you normally have around 2-hours of break till the next race.

the motor is a qs138/90h with a reduction shaft from 2:1 and then goes to via 13t sprocket to the rearwheel.

I alreaddy saw both videos, and the alta battery seems like pretty complicate for a diy project with cooling.
 

testus191

Member
Location
Poteau, OK
510 cells is pretty ambitious to fit in a conversion in my opinion. Alta and Stark are barley fitting that much energy in a frame specifically designed for the application. Also, you're looking at 23kgs (51lbs) of cell weight and the Alta and KTM packs are around 1.4 for pack to cell weight ratio. So your looking at around 32.5kgs (71.5lbs) of weight for the full pack; roughly on par with the Alta pack, pretty obvious as its relatively the same amount of energy. You're chassis weight is going to be right around 68kgs (150lbs), which is about what the weight of my '07 KX250F and '03 YZ250 rollers are stripped down to only what will be left for a conversion. Motor weight of the popular QS138 90H is 12.7kgs (28lbs), same motor I am using and have in my possession. Add in weight for mounts and gearing reduction if going that route. Controller weight is going to be around 2kgs (4.4lbs) at the lightest for anything with enough power. I am using a Sevcon Dragon8 (96v nominal (26s) and 300-350a dc), the Gen4 Size4 or 6 are other good options, ASI BAC8000 if you can figure out the overcurrent issue, Curtis, Silixcon, and some others out there that will get close to 40HP electrically. I don't think any of them actually will give that much other than the Sevcon Gen4 Size6, as far as rear wheel hp that is. Add water cooling for any of the powertrain and there's I'm guessing another 2.5kgs (5.5lbs). So in total you're looking at 115kgs (253lbs) before including motor mounts, cabling, throttle, and all the other little things that add up. It will easily add up to over 118kgs (260lbs), likely over 123kgs (270lbs).

Here's a rough idea of playing around with 18650 sized cells and how many can fit in my YZ frame with QS138 90H and a reduction shaft. Mounting locations all taken from a CMM or probing system on a CNC mill. The two "groupings" boxed together below equate to 144 cells, and with two sides, so 288 cells in total. Running 26s I could run 11p26s in that space, so 286 cells. Needing 300a at 11p I need a cell capable of 27a. So something like the Molicel P26A or P28A would give around 2.8kWh of energy. The Alta at 36kW peak power seems to use around 270kWh/mi, the KTM Freeride at 18kW peak power used about 200kWh/mi, these are just findings from as many anecdotal reviews, results, etc that I can find on the internet. Being these are much higher voltage and more efficient systems, I thinking I will be around 250kWh/mi with a 30kW peak system.
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