72V or 96V?

[wolf]

I'm planning on my next ebike, the last two were just 48v 1000w china kits. But now (as probably most people) i want to go for more power!
That means, I don't want to go any faster then 50kph. But I want as much torque as possible!
We have lots of hills here and I like riding in the forest.

I am going to weld the battery pack myself.
My question now is: 72V or 96V (or 84V)?

I want to use ~200pcs. 18650 10A discharge cells.
So i could have 20s10p or 26s8p

I have some kind of 9c clone right now, according to the motor simulator (ebikes.ca) it seems to be similar to the 3007. So i took that one for trying.

Generally more current means more torque, but it seems that the motor is limiting the current at 72V. So a higher current limit only affects the first part of acceleration.
So it seems to me that 96V is the better choice for me?

But this makes things more complicated and brings some questions:
- Is a standard 72V controller with 4110 suitable for this voltage? (maybe with a change of the resistors?)
- Where do i get a 26s BMS? Or two BMS in series?

Thanks in advance,
Wolfgang

p.s. I know that this battery can easily burn my motor, but I'm going to install a temp. sensor and I'll probably air vent it in the future.

 

[spinningmagnets]

Personally, I would recommend 20S as the max for using affordable components (charger. BMS, etc)

 

[bionx 1954]

I have a 9C MC3004 ( fast wind), and run a 20S 72V (83V Hot) lithium pack, with a 72V @ 40A controller and it has a lot of torque and peaks at about 2900 Watts. It does 50-60 KPH which is fast enough for me. It does well climbing hills also.

 

[Drunkskunk]

72V with that controller. the 4110 FET has a maximum voltage of 100V, and the capacitors used are generally rated for 100V. A 96V battery will reach 109 volts fully charged. more than enough to let the smoke out of the controller.

 

[999zip999]

Melted a couple 9c's at 72 volt 40 amp. Be careful save money for 35mm d.d motor like a leaf. The bigger muxus is heavy. Nice to have a back up motor. Unmelted.

 

[dogman dan]

Stick with 72v, you can really melt down that motor fast with more. Sure, you can temp sensor it and all, but the fact is, it does really shorten your ride too much to push more than 3000w through those motors.

But at 72v 40 amps, 3000 w peak, and pulls about 2500 at full gallop, you can get a nice ten mile ride out of it before hitting the danger zone temps. That's enough for a decent length ride in time, rather than 10-15 min and done. Cooling holes do help, for one, you can smell the motor starting to roast, and it will definitely cool down for another ride later much faster. Stop a really hot sealed motor, and it gets even hotter for the next 15 min. Cool down run at 15 mph is best!!

You do need a bigger motor, soon as you can afford it, if your battery can stand that kind of high rate drain in the first place.

If you want to keep going with 72v for a much much longer ride, limit amps to about 25. You will still have about 35 mph, but the heating will take a LOT longer. Acelleration will be very slow, but top speed still not too bad. I used to do this to mine every summer, or I'd melt a motor a week in the hot weather. Once it got below 80F in the day, then I'd crank er back up to 40 amps.

 

[wolf]

Thanks for the many replies!
Well i guess it's 72V then
It's true, it seems to be a lot easier and also safer.

Do you guys know where to get a decent 20s BMS?
The only things that I've found are aliexpress and bestech power. But bestech seems to be really expensive..
Can i trust the specs on aliexpress?
How much should i spend on the BMS?

 

[999zip999]

Where does the wolf live these days ?

 

[wolf]

Oh forgot about that.
In the Austrian mountains of course!

 

[eee291]

Oh forgot about that.
In the Austrian mountains of course!

I've got a 20s Bestech BMS rated at 55A 60€ sipping included 8)

 

[999zip999]

I'm happy with 72v get a good cell. So it can survive. Don't need to do it twice.

 

[wolf]

Thanks eee, but 55A seems a bit low for a 10p battery. Not for now, but if i want to get a bigger motor some day..

 

[999zip999]

72v 30amp for 9c 28mm stator. Still be careful. A leaf 1,500 watt is good for an ebike 35mm stator. As my muxus 3,000 watt 45mm is heavy. But handles 72v 90amp for slow 5t. 43mph. 35mph is fast enough for ebike.
More battery more better in ah.

 

[parajared]

72 volts for just 3000 kilowatts. Why?
-so you can use higher kv motors? (better weight per watt)
-so you can use thinner lighter wire? (same wattage for less wire weight)
-use a really low C rated battery?
-you can't find a proper motor/ voltage combo that meets the rpm you need so you use voltage instead of kv

Just for reference I personally fly an airplane that outputs 3 kilowatts and use just a 5s lipo (18 volts)

Golf carts are commonly 24 or 36 volts and carry around like four fat dudes and all their golfing gear.

 

[flat tire]

I was running my 1000W ebay hub on 72V around 3KW max with great results, I forget how much phase current I had programmed but the torque was good from a stop and it had no problem cruising 20-35 for 20+ miles.

I'd like to try higher voltage with one of these motors when I get the chance.