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80 volt Minibike Build

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  • #16
    Totally lovin that! Now the Miata?
    I make Stuff....shiny,Metal Stuff.


    • #17
      This is completely *****in' - and top notch work. I wonder if there's a market for a retrofit kit like this- and a profit in it now that you've done all the engineering...?
      | 90 Miata | Turbocharged Stock Mazda FE-dohc 2.0L engine swap | 302whp 281ftlbs |


      • #18
        Originally posted by FE3tMX5 View Post
        This is completely *****in' - and top notch work. I wonder if there's a market for a retrofit kit like this- and a profit in it now that you've done all the engineering...?
        that means a lot, thank you! I'm sure there's no market for it, the cost is simply too high for most people to be interested in!


        • #19

          and again - 7 months away. I have a Hummer carcass but I'm not an (active) member of any hackerspaces for the moment..


          • #20
            A build like this is on my bucket list... thanks so much for sharing.
            The only thing that oughta be hella flushed is a toilet.


            • #21
              I went to RA yesterday and seeing peoples pit bikes and James' scooter made me start itching to revive this thing...

              First of all, I've learned a LOT since I made this. Looking at this thread knowing what I know now, I see several things I'd do differently.

              Also, the bike currently does not function. The rear tire is flat (too many electric burnouts, sorry) and both batteries are DEAD.

              The story with the batteries is... they are like glass. Being 80 volt lithium ion batteries, the company that built them was very cautious.. if the circuit board on the battery pack detects an issue, it will permanently disable the battery pack and they have to be sent back to the manufacturer for refurbishing. I'm not exactly sure how it functions because the circuit board is completely covered in conformal coating and I'm not that talented with that side of things.

              I started off with 2 packs. The first one was destroyed when someone looped the bike and the battery came out. He put the battery back in (but didn't seat it fully) and as soon as he hit the throttle the pack disabled itself. Then I decided to open the pack up and see what kind of cells and circuitry were inside, thus it can't be sent back.

              The second pack was destroyed when me and a few people were doing some pretty intense hill climbs with the bike. We found the steepest hill we could, and then flew up it wide open throttle. After doing quite a few runs flawlessly, a bigger guy got on and made it alllllmost all the way up the hill and then the internal battery fuse blew. Then, a friend and I took the pack apart to solder in a new fuse, aaaaaand somebody shorted the battery pack with a pair of pliers (unintentionally) and the pack disabled itself again.

              Then the thing just kind of sat in my house until now... because the price on the battery packs went up 50% (from $80 each to $120 each) and I decided I'm not willing to spend that kind of cash on packs that will just disable themselves. I want to be the one making that call.

              One of my close friends just got a spot welder in the past couple of weeks, so building a legit battery pack for this thing is in the cards. I started to do a bit of looking into that and realized that these Greenworks packs are terribly optimized for space, so I should be able to fit 2x the cells in the space one of these packs takes up. Which means I can get twice the range without taking up any more space (and only adding 2 pounds) on the bike, and also put less stress on each individual cell since I'll be pulling the same amount of current out of twice as many batteries.

              I've ALSO been tossing around the idea of selling this bike and building another (I'd use the exact same chassis because it's very fun and easy to ride) but with a completely different design philosophy. I think the way I built this one is great (chain is short and out of the way, no danger of catching clothes or anything, the entire bottom section can be used for battery etc) but I realize not everyone has a welder and I could totally design this so it could be 100% bolt on.

              But not only 100% bolt on on this particular mini bike. What I'm envisioning is creating a completely enclosed box that shares the same mounting holes as a Predator 212/Honda GX200 small engine as well as the same location for the motor shaft/output sprocket. Basically a bolt in power unit that can be used on pretty much any go kart/mini bike with no more modification required than a Predator 212 (which is an extremely common engine, because of its low cost and availability). This power unit would contain the motor, controller, main fuse, key switch, etc. The only *required* external components would be the throttle and battery. And actually, I'm fairly sure I could make it work with a throttle cable from the host vehicle.

              Anyway, just thinking out loud here. If anyone has any thoughts/input let me know!


              • #22
                Sooo, I went to my friends house this weekend to use his spot welder... unfortunately I forgot my security torx drivers, and the Greenworks packs use security torx screws. So, of course, I decided to drill them out...

                Drill slipped, oops.

                So, in my eyes, that basically means that entire set of batteries is scrapped. I don't want to order a single battery and have a mismatched set. With that said, I decided to forge on and instead just use the other 20 cells in their own pack with the BMS I ordered. The plan is to use this as a practice run, then I'll buy a set of new, virgin cells and use the lessons learned from this to do that pack better.

                This is what happened with the power management circuit board. As you can see the internal fuse is not actually blown, but one of the mosfets actually blew up.

                This is what the full set of 40 cells would have looked like size wise compared to the original housing for the 20 cells.

                And then this is the 20 cell pack with fire extinguisher just in case.

                The extremely sketchy chinese charger I bought. Check out that google translate nightmare.


                Here's the actual spot welding process. (supposed to be a video/gif, hope it works)

                This is about as far as we got. Got the entire pack spot welded together, didn't get a chance to start soldering the balance leads from the BMS on. Neither of us could find our soldering guns and our soldering irons just aren't as powerful as they need to be to put in enough heat quickly enough.


                • #23
                  Getting after some CAD work tonight...

                  Going to throw together a quick design and then 3d print something tonight for test fitting. I think I want to have the battery housing have the following features:

                  1) active cooling. Of course even a 120mm fan is significantly larger than my entire battery pack.. a 40/60mm fan would be ideal.

                  2) channels inside for wiring to pass through

                  3) 3 piece design--middle section (includes fan mounting on one end and exit vents on other end), top section (basically just a lid), bottom section (also a lid, but contains the BMS and DC-DC converter? need to think more on this and actually buy the DC-DC converter so I can CAD it up and figure out where it will fit best) The 3 pieces will be held together by 4 through bolts and nuts, creating a sandwich. I think I might make the nuts captive. This also makes printing it much easier/better.

                  Perhaps this thread should get moved to off topic? Not sure what mods think.