So Travis (T2) has been busy this last week drawing the batteries and buss-bar in 3D since I lack experience. It turned out great and gives the clearances between cells so that we can mill the cell-holders out of UHMW. This week he’ll start to draw the holders and add on the Elithion cell-boards to the drawing (Elithion provides these on their website).
Once we get the pack drawn in CAD, I want to mill these parts out of fiberboard (probably HDF) and check fitment. Then I’ll build up a pack without buss-bar and refit and start to figure out how we would like to do the metal box. I’d like to build the box around the HDF prototype so if anything has to change, I’m not wasting $200 worth of UHMW plastic.
Here is a picture and 3D PDF of the pack. If you click on the pack within Adobe Reader, it will let you rotate/pan/zoom. It’s pretty slick.
I went to the shop last Thursday for a little bit and talked with Travis. I showed him the mockup and how well things seemed to fit inside the frame. We didn’t spend a ton of time on the bike that night, mostly just talked about the overall idea of what the project plan is.
I returned Saturday and cut the top area of the gas tank. This is where the original gas cap was. The pack as it is, just barely hits this on the inside of the tank. I figured we could cut it out and get another inch and fill it with fiberglass and epoxy later. I also cut some plastic out of the rear fender where the original battery holder for the 12V battery was located. There is a ton of room under the seat just above the rear shock and in front of the rear tire fender. I brought in my DeltaQ and it fits pretty much perfectly in that space now that the plastic is gone. I might have to modify the charger a bit, but It should fit in that space fairly well.
I compressed the front tire again and estimated how much room the front fender takes. I reinstalled the mockup, placed my charger, placed the controller and put the gas tank on. There a surprisinly large amount of room around the battery pack. The issue now, is how to design it such that the frame is properly supported, as the engine was a stressed member.
For now, Travis is going to help with some 3D CAD work and draw up the pack with the bussbar and BMS. Then hopefully we can get some pieces cut out of MDF that match the exact dimensions of the pack with all of it’s hardware. Until we really get that done, it’s just a rough estimate where things are at this point.
I’m not able to go this week (going out of town again), but Travis is going to do a little work and we’ll meet up next week and see where we’re at. That’s it for now, but things seem to be going along well.
I went down to the shop tonight to test-fit the battery pack mock-up. Since I oversized the pack, things seemed tight at first. Just to make sure everything fit OK, I used a tie-down and compressed the front forks as much as I could. This ensures that I’d have enough clearance under heavy braking. Add a little wiggle room for fork flex and fudge factor and things fit pretty well.
I put the side fairings and the Faux-tank back on and made sure it all fit. Even with all of the wiggle room I built into the mock-up, it fit just fine. There’s plenty of room for the charger inside and quite a bit of room underneath the pack for the controller and wiring.
It’s got a little bit of refinement left, but it’s a great start. I’ll be back down there tomorrow my buddy Travis to kind of finalize some things. Pretty happy with this setup.
So tonight I came home and worked a little on the battery pack mock-up. I printed out a full scale drawing of the 160-cell pack showing the right and left side to use as a pattern. I cut some foam-core board to the same size as the scale drawings and then glued it together with some hot glue. I over-sized it quite a bit just in case. I’d rather have a mockup too big and have extra room, than make it too small and find out too late that there’s not enough.
In the pictures, you can see the cardboard cutout that we made that hugs the inside of the frame, gas tank and motor. It fits pretty well within those constraints. The cardboard cutout is a little smaller than the room I actually have, and the foam-core mockup is a little big, so it should represent the pack fairly well.
I’m going to the shop on Wednesday to fit the mock-up inside the frame. We can take some overall measurements and see how well everything fits inside.
So this last week was great. The bike is in the shop with fairings on it. I spent some time with my buddy Travis and we cut out some cardboard that sort of hugged the inside of the frame/gas tank/motor so we could see how much room we had to play with. Dave took a few minutes and did a huge drawing using an array of the 38mm cells with a couple mm of separation between each cell. We used a printout of his drawing and overlaid it on the cardboard cutout and cut out the cells that didn’t fit inside the cardboard. Without much effort, and using only a single layer, we figured we could get 160 cells in a trapezoidal shape. I wanted at least 144cells, and thought that 180 cells would be too difficult to fit inside the bike on one layer without a difficult pack arrangement. With 160 cells, I can do 32 cells in series and put 5 in parallel. If you use 3.2V nominal and 10Ah to get 32wh/cell, that’s about 5.1kwh of battery, which is perfect.
So 32s5p puts me at 50Ah of batteries and sets me right at 102.4V nominal. The DeltaQ algorithm I’m using charges the battery pack up to ~116.8V, which would give a peak charge of about 3.65V per cell. Perfect! The controller allows me to go up to 130VDC before cutout, so even right off the charger, I should be just fine. 32S is also great for my Elithion, as each cell board can balance 2 cells. This means I only need 16 cell boards. I’ll likely split this into 2 groups of 8, so I’ll need 2 positive boards, 2 negative boards and 12 mid boards.
So after we did a layout, Travis and I drew the proposed pack in CAD. It looked beautiful. The pack is mostly square, but the front towards the wheel, is angled. The pack would mount at an angle so the front angled part is actually perpendicular to the ground. This arrangement also allows me to install my charger under the tank and put the controller under the bike with the heatsink sticking out from under the fairings. I’ve also got plenty of room to fit a box holding relays, the BMS and other controls.
I spent some time today at lunch designing the buss-bar layout. There’s 8 shapes of buss-bar that will get cut out of copper. The design is nice too, because the positive and negative exit on the same side of the pack, towards the top of the bike. The shapes are designed so that current flow from the positive of the previous 5 cells to the negative of the next cells provide a very large cross-sectional area for current to flow. Even if we have to slightly modify the shape of the pack, the buss-bar should stay fairly simple.
I’m going out of town this weekend, so no more work on the pack, but next Weds I should be back at the shop with a mocked up pack to see how things fit.
And now, for some pictures: