Battery pack questions

[Jiminyfixit]

As a new member, I have a few questions regarding a battery pack best suited for a Honda Reflex conversion, using a Golden 5K motor. I have modified the original crankshaft to utilize the original variator belt drive attaching it to the Golden motor. My current issue is with batteries. I plan on utilizing the space where the original gas tank was, but have limitations in accessing that space with one single pack,(using 18650 cells). If I split it in half, I could go in from each side, but was told I can't connect 2 packs in this manner.  Not sure why though. OR, I could use 21700 cells and not have to use up so much space.  I'm shooting for 72v 60Ah, in hopes of a 55MPH max speed with a 30-40 mile range.  I ordered the motor with 6000RPM, since the original ICE RPM's were 6000 @ 55 MPH. I will be using the heaviest Dr. Pulley sliders in the variator to get the RPM's down. So far I haven't had much luck finding a source for building or supplying the battery pack. Not sure if I trust any of the Chinese builders through Aibaba or DH Gate. All seem to be limited to the 18650 cells. I have made inquiries with several sources with NO response. Nobody seems professional enough to even email me back with a simple NO or, can't do it.

I'm not really excited about getting a spot welder, nickel strips, heat shrink wrap, 240+ batteries, etc to build my own pack. I'm more of a machinist/mechanical kind of DIY'er, who would greatly appreciate input from any of you who are willing to share your thoughts. I can supply photos of the working space if needed.  Thank you in advance, Jim

[Bikemad]

Hi Jim andto the forum.

It is possible to use two 36V battery packs wired in series to power the bike at 72V and even reconnect them in parallel for charging from a single 36V charger:



However, it would take ~24 hours to charge a 36V 120Ah pack from a 36V 5A charger. 

Also, if each 36v pack has its own BMS, you may need to add a couple of diodes to prevent damaging to the first BMS that cuts out:



They would need to be pretty big diodes to handle the sort of current you will be drawing.

Alternatively, you could build a single 72V battery in two sections and use a single 72V BMS, but the 21 balance leads would need to be connected to all parallelled cell groups spread across both halves of the pack.
This would also require a 72V charger, calibrated for 84.0V maximum charging voltage.

If you're building your own 72V pack from 18650 cells you will need 400 individual 3000mAh cells configured 20S20P (either 10S20P or 20S10P each side) to achieve your 60Ah capacity. 

Check out this handy battery configurator for help with pack shapes and sizes.

The cells and a BMS must be capable of producing at least 150 Amps if you are aiming for maximum torque, check out the 72V Dynamometer data for further information.

I don't suppose there is sufficient room to accomodate 10 of these Nissan Leaf battery modules:



Each module is 7.6V nominal and has a guaranteed 54Ah capacity. (Click on the above photo for more details.)

Anyway, it sounds like a very interesting conversion and it would be nice to see some pictures of your progress so far.

Alan
 
EDIT: Picture URL changed as hybridautocenter.com website is currently inaccessible.

[Jiminyfixit]

Hi Al,

I'll try again since my reply to you yesterday disappeared into the either. I attached 4 photos that seem to have caused a big problem.
I appreciate the thorough information you provided and will seriously take it under consideration.  I made a mock up of a leaf cell and couldn't get enough of them in the space I have, to get the desired voltage, without extensive frame mods. I've already removed one short, weird frame tube that was in the way, but shouldn't alter the integrity of the structure.

I first started this project 13 years ago and was disappointed by the advice I got from the guy that sold me the motor & controller. On my first, short test ride, the controller blew out the mosfets and did the same with a 2nd controller. I donated the motor to the UCLA engineering dept. and sold the prismatic batts on eBay. Interestingly enough, the Golden motor mounting holes fit my adapter plate perfectly and the motor shaft was the same diameter, but a bit longer. The old motor was an E-tech pancake motor. Perhaps Golden bought out E-Tech?

Yesterday I tried to send some photos of the space available, along with the cardboard mock up of the triangle batt pack. Not sure what I did wrong. 

I would love to find someone in the forum who would be interested in working with me on a battery pack for this project.

Cheers,
Jim

[Bikemad]

Yesterday I tried to send some photos of the space available, along with the cardboard mock up of the triangle batt pack. Not sure what I did wrong. 

I suspect the resolution of the photos was too large to upload as an attachment, as there is a 1000KB limit on the individual file size.
Check out this post for more details on posting pictures.

I would love to find someone in the forum who would be interested in working with me on a battery pack for this project.

I suspect you may have more luck posting for help on the Endless-Sphere forum when it comes to battery building.

Alan
 

[Jiminyfixit]

Thank you VERY much for the advice Alan. I'll be back to post some photos when I wrap this project up. You've been a big help!!!

Jim