72V 40AH, 150 amp capable battery build

[From-A-To-B]

Where did you get those honeycomb style 21700 cell spacers from?

An Aliexpress store, ages ago, that has since closed. I no longer have a source for these style cell holders and am also on the lookout for some. They are conducive to some battery shapes, but are not any easier to use than the square ones. And I’ve gotten square cell holders with much higher quality plastic than these particular honeycomb cell holders.

 

[From-A-To-B]

I hope your project battery pack works out for you. Bummer that the cells you got are underperforming.

My main issue with 21700 cells is the same as with 18650 cells. If you have to massively parallel them to get relevant capacity (and we do), you limit the cells to the capacity of the interconnects, and you multiply the opportunities to have a fault or failure somewhere.

I have never seen a nickel strip that was good for 30 amps. Though such a thing is clearly plausible, I don't think many of us could weld one without harming the cell we're welding to.

Using cells sized for pocket devices to power traction motors is a little like using Bird scooters to carry heavy freight. I mean, yeah sure, you could hypothetically gang up a bunch of them on some kind of common frame that can handle the load, but wouldn't it be more expedient to use a truck? Even if there are so many Bird scooters lying around that we're literally tripping over them?

This tracks, and I agree. Copper sheet bussing opens up more options, but it’s MUCH more work to use, requires a kweld or similar, and is easier to goof up. I’ve blown through a few cell cans while trying to affix copper because it takes so much energy to assure a good weld with a resistance welder. What a mess.

Building with pouch cells often requires the messy and tedious job of affixing the tabs and insulating all the connections. Then, pack compression is a whole new project.

It’s way easier to build with round cells for projects that require less than 30 amps. But the pouch cell and prismatic batteries I’ve built are better performers than round cell packs. The difference is especially clearly with big loads, but shows up even in small LEVs.

I have an OEM Samsung module from Battery Hookup - 12S47AH, IIRC. In summertime temps, voltage sag is something like 0.2V at 20Amp pedicab draw. I’m working from memory here, so I could be wrong on those figures, but the point is, the pack barely flinches. Of course, mounting that lunchbox is it’s own fun game…

I built a 20S75AH battery from 2017 ford prismatic cells that drops 1.5V at 110 amp draw. Round cells can’t keep up in that application.

Tesla has figured something out in their ganging of a gajillion 18650 Panasonic cells into an EV battery, but this is something I cannot reproduce.

 

[From-A-To-B]

Using cells sized for pocket devices to power traction motors is a little like using Bird scooters to carry heavy freight. I mean, yeah sure, you could hypothetically gang up a bunch of them on some kind of common frame that can handle the load, but wouldn't it be more expedient to use a truck? Even if there are so many Bird scooters lying around that we're literally tripping over them?

Chalo, I know you use prismatic or pouch batteries on your commuter. Have you ever posted photos of your mounting on the bike? If you have a moment, could you share a link?

 

[From-A-To-B]

I like 20ah pouch cells for a 20ah pack as fewer interactions. But the question will it fit in a triangle.
So Chalo how would you get 72v, 20-24ah battery @ 80amps in a large mtb triangle.

The next problem is mounting said 25 pound battery to the frame, using more than than the water bottle eyelets. I’m not comfortable with my own 48V20AH batteries on my bike, and I’ve added two more mounting points with Rivnuts. The battery still wiggles and that wiggle makes me squirm. GRIN’s Bob mounts may be better, but I haven’t trip them. Tying into the top tube seems like a must-do for large batteries.

 

[999zip999]

I had my Samsung 40t 21700 20s6p pack to fit a em3ev triangle battery. The bag was made for 18650 cells. I couldn't get it to zip close. So I went down to the shoe repair guy to put in some leather sides to expand it. Then I mounted it into the bike it fit great but was so heavy for the velcro ties. I had to make a bottom support for it for off-road. I've had to put the bottom support back in place twice since installed. Because of off-road biking. These 72 volt battery packs are big and bulky no matter what. I did have an A123 20ah split pack bigger and heavier.
I would sure like to find a 72 volt battery 20 ah that could fit on a bike comfortably.
I found that velcro straps also help.

 

[amberwolf]

Even if you do nothing besides crank a cargo strap around the tubes and pack with some carpet tape on the tube where the strap grips it (to keep it from sliding and loosening), it would be better than nothing to keep the wiggle to a minimum. (just don't crank the straps down enough to deform the tubes. )


I am pretty sure I've seen a pic of Chalo's bike with the battery on it but I couldn't find it in a search--it might be one of the pics that the old forum software "lost" over the years.

 

[Chalo]

Chalo, I know you use prismatic or pouch batteries on your commuter. Have you ever posted photos of your mounting on the bike? If you have a moment, could you share a link?

Here's a picture with one of my e-bikes with a 44V 20Ah Mercedes-Benz module attached to the Racktime rear rack with their Snapit 1.0 adapter. The bike behind it has a compatible rack but with no battery attached in this picture.

Here are three packs, from to to bottom a 44V 47Ah pack, a 44V 20Ah pack, and a 48V 25Ah pack, all with Racktime Snapit 1.0 mounting plates. The lower pack shown here has heavy duty stainless steel mounting plates, while the other two have the default adapter with a lower weight rating.

And here's a photo of one of the big 47Ah pack snapped onto a spare rack:


I have one more smaller hard cased pack without a mounting plate, which I just toss into a cargo box or pannier for more capacity as needed.

My knees pass close enough to the bike frame when I pedal that it would not make sense to use a triangle battery unless it were mounted low near the cranks. I've used both front and rear mounted battery packs, but lately I prefer to keep my front boxes available for carrying stuff.

 

[999zip999]

I far does one go with 92ah of 44v's of battery. I guess in theory. Or have you ever been able to use all your 92ah of battery?

 

[Chalo]

I far does one go with 92ah of 44v's of battery. I guess in theory. Or have you ever been able to use all your 92ah of battery?

I usually only have one battery with me. I've never used up the 44V/47Ah pack, and I've only run down the 48V/25Ah pack to cutoff once. The smaller ones I use when I know my circuit will be relatively short, so I've never run those down to cutoff.

I get about 40Wh/mi when I'm flogging my bike mercilessly, and about 25Wh/mi when I'm trying to conserve, but not pedaling hard. So by extension, my 4.5kWh of batteries would take me 110 to 180 miles depending. Probably a little less, if I were dragging all those heavy packs along at one time.

 

[From-A-To-B]

Here's a picture with one of my e-bikes with a 44V 20Ah Mercedes-Benz module attached to the Racktime rear rack with their Snapit 1.0 adapter. The bike behind it has a compatible rack but with no battery attached in this picture...

WOW. Those rack-mount batteries, cases, and clips are all awesome. I know you've put a lot of miles on your bikes, so your use of the Snapit adapters is a big endorsement in my book.

Also - that is QUITE a bike you ride. IGH on the back end, small front wheel with a front hub motor, that handle for picking up the bike... such a tailor-made affair.

Thanks very much for sharing.