First Build, Battery Decisions Are HARD

[akrenits]

Hi ES,

Posted once before, but have since simplified my parts list immensely. Just want to make sure these parts are logical together.

I am definitely getting cyclone's 3 chainwheel 3kw middrive: http://www.cyclone-tw.com/order-3chain.htm

I plan on using it on some steep uphills for mountain biking. I don't need it to go fast on those, just more than walking pace. I weigh 160 lbs. That being said, I hear Amps is more important than volts to achieve torque. That also being said, I hear amps heats everything up more. So go for big volts and higher gearing? The controller that comes with the kit is rated for 40 amps. So my main question revolves around batteries. I definitely need a commute range of at least 10 miles total, flatish ground. Which of my options below should I go with? I definitely want to do this on as little a budget as possible which is why alibaba batteries are below (I know capacity can be overstated a bit, but for the price how bad can they really be? plus they include the charger ).


48V option: http://www.aliexpress.com/item/e-bike-battery-pack-48V-20Ah-high-capacity-li-ion-battery-48-volt-battery-with-charger/32620271416.html?spm=2114.10010108.100009.1.ek8bu1
72V option: http://www.aliexpress.com/item/72V-battery-pack-10AH-72V-li-ion-battery-18650-battery-with-charger-72V-battery-for-e/32630563034.html?spm=2114.01010208.3.1.2nd2dj&ws_ab_test=searchweb201556_10,searchweb201602_5_10017_10005_10006_10034_10021_507_10022_10009_10020_10008_10018_10019,searchweb201603_2&btsid=27d5aaee-22f5-48cc-971c-3f41813d0ceb

For the alibaba batteries, they say they can alter the continuous amp rating. Is this true/worthwhile/cost effective? Does the cost and included charger make either worth the risk of sketchy vendors to you?

36V option (can I get away with these few volts and still get decent performance?): http://lunacycle.com/batteries/packs/36v/36v-18650-20ah-samsung-26f-ebike-battery-pack/
52V option, maybe 2x in parallel?: http://lunacycle.com/batteries/packs/52v/52v-mighty-mini-cube-ebike-battery-pack-panasonic-pf-6ah-affordable/

Which option makes the most sense for me? Do you think I could get away with as little as 6 AH for what I'm looking for?

Other Questions
Do I absolutely need the brake cutoff switches? Can't I just be smart and not throttle while braking?
As far as matching connectors between battery and controller, can I just solder them straight together and plug my whole bike into the wall, or do I go through the trouble of replacing the connectors? (If so, link to some good, cheap options please)
Also, I plan on taking some pretty big jumps/drops. Anyone have any brilliant suggestions for protecting components in the event of a crash?

 

[USAEBIKECO]

I would not recommend keeping the battery permanently connect to the controller. It can slowly drain. Also, if someone steals your bike, they have the battery too.

The battery on my bike is removable and I keep it stored inside my house. I think its better that way.

 

[dogman dan]

A lot to cover here.

Firstly, I decided to take a flyer on one of those 48v 20 ah, Under $400 shipped, batteries on Alibaba last fall.

Well, I certainly got what I paid for. Sure, it still works, but brand new it dished out 20% less capacity than it should have. At least one cell in there is bad. Now, six months later, it's closer to 16 ah capacity.

It's crap, I could have gotten lucky, but I didn't. It may work as a 16 ah size for the next few years though. But the catch 22 is the bike I wanted to run with needs all 20 ah of capacity, or the motor will kill the battery. Now I have to run it on a smaller motor bike. BTW, this pack never did run the big motor, I didn't put that motor on the bike till this spring. I bought other new battery to run the big bike this spring.


Now, on to your needs. NO, very few batteries that are very small will run a bike that goes more than 15 mph. If you are going to run 3kw,, assuming you mean 72v for that, you will still need batteries that can handle 40 amps without strain.

This means 20 ah size of very good 18650's, or 40 ah of cheap shit, as I learned the hard way. Mine started croaking pulling only 20 amps, for 20 ah battery.

Or, you need to go to the dark side, running the more hazardous RC packs. The 30c type can easily pull 40 amps, in a 10 ah pack size.

Study lipo (lithium cobalt) before you decide on that stuff. Never store or charge lipo where you would not willingly build a fire.

Lots of good connectors for the battery plug out there, mostly from the RC world. RC style bullets, Anderson Powerpoles, etc. Lots of folks prefer the bullets, and it's what comes on the lipo from hobby king.

Battery in some kind of metal box for the crashes. Some kind of inner box still needed too. I like to make the inner box from old political or house for sale signs..

If inconvenient to install, just leave the brake cutoffs off the bike. Laws don't matter, your bike will be illegal anyway.

 

[akrenits]

I guess I'm still a little fuzzy on how to know if a battery will support the draw I ask of it. It's not all about its continuous rating? Could you share your rule of thumb? If I was going to let my dream of 3kw die, are any of those other options going to fit my needs almost as well (will they pull 40 amps decently?) It's worth noting that it would be a rare occasion to use all that power, just want it on tap in case.

What is your best guess of the max continuous and peak amps I could realistically pull from that 72v alibaba battery? its so tempting...

 

[Wheazel]

Expect the worst from alistuff until you know whats in it. Hard to say anything without knowing what cells we got on our hands.

 

[Tats]

I'd be looking at the highest C rating safest battery myself. Lipo gives the high C but too much hassle for me to manage the safety side of it. Headway 15AH cells might be worth looking at, still high C, much safer but bulky.