JDH: CB750 Conversion - The World's LIGHTEST Batteries!
Battery and Motor Layouts
The following pictures show my trial layouts using 55Ah batteries and an ADC motor (6.75" diameter, 11 inch length). The box for the batteries includes the terminal height and is also oversized by 1/4 inch (the internal measurment is the external measurement of the battery).
My design is now at 84V - which requires seven 12 volt batteries. When I researched my options I found out that a 96V capable speed controller was going to cost me about $1200. I found that Kelly Controllers do an 84V model for $389 - I need an extra DC-DC convertor in their circuit (the control voltage needs to be 24V).
Now, if I could manufacture real batteries which were this light I'd be a VERY rich man and I could use a Zilla (which is closer to $2000).
|This is my favorite layout. It packages 5 batteries within the frame rails in a simple to implement box. Two other batteries would go as saddlebags/paniers - I will probably make larger paniers so that I can mount 7 seperate 12 volt battery chargers on the bike (not sure about this yet). I feel comfortable that the weight distribution is appropriate (the batteries are 38.5lbs each and the gas motor was over 180lbs (I broke my bathroom scale trying to weigh the motor!). So the majority of the weight is where it "belongs" - in the engine bay and as close to center and as low down as possible. Also, no changes to any of the foot pegs or rear brake lever is needed - so ergonomics aren't affected.
The downside of this design is that I can't run a chain directly from the motor (mounted where the battery and oil tank used to be) to the rear sprocket. The swing arm gets in the way - and there's no way I want to modify that. So, I'd need to use a jack shaft - and I'd need to figure out where to mount it.
Next up, layout number two, places the ADC motor so that the output shaft is approximately where the output drive of the gas motor was. Above it are the two side by side batteries which were on the bottom before. The fifth battery is where the ADC motor was in layout number one.
This still keeps the weight centered, and the ADC motor is 65lbs so the weight of shifting two batteries higher vs. bringing the motor lower pretty much cancels out. The battery placement is more tricky now - but not too bad.
However, this design is "tight" - until I get the real batteries I'm not confident I can make this all fit. In the photos the fifth battery is resting on the rear tire - however, in real life it will mount an inch or so higher. That gives some clearance but not enough. To make this design work I need to shift all the batteries forward slightly - to do this I'd need to grind away the "back side" of a bracket up by the front of the gas tank. I'm pretty sure that won't affect strength - but I'm still not sure I'd end up with enough clearance for the rear wheel (I can also put the rear wheel towards the back of the chain adjustment slot (and sacrifice adjustability).
Another area where this design is "tight" is around the right foot peg and brake pedal. I will need to bend the brake pedal out - I might be able to leave the foot peg alone - or I might not. I don't think either of these are a deal breaker.
Layout three addresses the concerns of not having rear wheel clearance for the fifth battery in layout two. I've mounted one battery on top of the ADC and between the frame rails and then I've mounted two batteries outside the frame rails next to the front stack of two batteries. As I look at these photos I realize that I should move those outside batteries lower to get the weight lower down. I'm also a little concerned about putting too much weight too far foward on the bike - however, it's still within the profile of where the original gas motor was.
Obviously this design sitll suffers from the "tightness" around the right foot area.
This last picture shows the front profile of the bike. It's for layout #1. Note that the ADC sticks out "a little bit but not too much" (hey, I never said I was an automotive engineer - this is as accurate as I get at this stage!).
So there you have it - three contenders. Any thoughts on which are best? Or a completely different set up? Feel free to leave comments or send me an email or PM (both can be done through links on this site). At the moment I'm thinking layout number three - but we'll see.
Finally, I'm trying to decide whether to look more at batteries to see if I can find something with higher Ah that I can still get to fit. I should probably do some more checking on the specs of my chosen Universal Battery UB12550 to see if they're up to the job...
The Universal Battery UB12750 (75Ah AGM) is the same height but 1.2 inches longer and 1.2 inches wider. I can fit them in the same basic layout as layout three above with the battery "on top of the motor" extending further back into the battery box compartment.