seeking input on battery for fat bike build

[ravencroft]

Hi,

I'm building a custom atv-wheeled bike (the front end is from a Honda three-wheeler). The frame is steel, and the wheels and tires are fairly heavy...I would guess it weighs around 100lbs, plus motor, controller and rider, so I figure 300-350lbs. total. Use for the bike will be mostly short off-road sessions, probably never more than 20 miles as the crow flies, but spent in short bursts, like in heavy traffic.
I am looking to get around 30 mph top speed with vigorous (if not front-wheel-lofting) acceleration.
I have looked at the offerings from Motenergy, but aside from price, they seem like more than I need. I found a motor/controller combo from Golden Motor that looks like about the right size:

Motor:
HPM3000B -- High Power BLDC Motor
1. Voltages: 48/72V
2. Rated power: 2-3KW
3. Peak power: 6KW
4. Speed: 3000-5000rpm
5. Rated torque: 10 Nm
6. Peak torque: 25 Nm
7. Efficiency: >90%
8. Dimensions: 18cm dia. 12.5cm height
9. Weight: 8kgs
10. Cooling: air

Controller:
Brushless Motor Controller for 72 Volt 3 KW Motor
Model: VEC200
Voltage:72V
Rated continuous current:80A
Maximum phase current: 200A
Motor control mode:FOC
Driving methodirect torque control
Dimensions: 170mm(L) x 120mm(W) x 50mm(H)

I am tentatively looking at building a battery from 18650 cells using a spotwelder, as this seems like the best bang for the buck currently (pun intended). My only experience has been with lead acid and AGM deep cycle batteries, but weight and life expectancy has led me to look at lithium ion. Can anyone here help me determine how big a pack I need for this application, and where to source the best/cheapest cells. I have seen apparently successful salvage of used laptop cells, and I am willing to put the work in if I realistically get a reliable battery out of it. I would rather not spend a lot of time removing the battery and testing for dead cells down the road.

Also, I would love suggestions for a battery management system and a suitable charger.

Thanks,

Carl

 

[mikebikerad]

I would go with something off the shelf versus assembling an 18650 pack yourself on first go. Tab welding can be fun, once you get to that point, but pack building is repetitive, requires a tab welder (unless you already have), in which case go for it! Deffinately interesting and fun, but there is something to be said for getting a professionally fully built pack that is plug and play. Something like this would probably work well, or a few of them in parallel. http://em3ev.com/store/index.php?route=product/product&path=35_52&product_id=252

Good luck!

 

[Noq]

My recommendation for a hassle/worry-free battery would be to grab 10 Nissan Leaf modules from Hybrid Auto Center and wire them up in series. You'd get a 20S2P battery at about 60Ah at 74V nominal. These batteries stay so well-balanced "they're boring" and are very powerful. I've pulled over 600A out of them before in burst, and they're easily capable of 200A continuous. This is so much less of a chore than wiring tons of little cells together; you're literally just wiring ten modules and they're done. Hybrid Auto Center even ships you all the tabs and wires and mounts you need for free. It's what me, mistercrash, inedible, and others are using successfully.

 

[ravencroft]

Thanks for all the input. I was looking at 18650 cells because I can get used laptop batteries by the pound locally and at a good price. I don't mind putting some work in, and I don't really have the grand or so for something off the shelf. I'm now thinking that battery holders of some sort would be the way to go. It would make it easier to disassemble the pack if I need to replace cells, and I probably will, since they're used to begin with. If I can make a pack that will run the bike for an hour, I'll be happy. If I find I use it enough to justify more capacity, I'll buy more battery later.