Building a e-fatbike - need help!

[Snusmumrikken]

Hello, im trying to get out of my car and take my bike to work, and really wanted to convert it to an e-bike. The only bike i have is a fatbike, which i love, and i would love to use this as the base for the build. Might not be the most efficient, but might help out in winter time here in Norway.
Since i live in norway, the same EU restrictions apply, so max 250W and max 25km/h, which im fine with. I am however wondering if the 250w is enough? Also, ive been looking at listings on Aliexpress like this one: https://www.aliexpress.com/item/1005005747376342.html
here they have 2 different versions of the 250w motor. one 36v and one 48v? The seller said the 36 volt is more powerful, but i know nothing about this kind if stuff. This was one of the only listings ive found that sells all motors at all BB sizes.

I see the 500w and 750w are rated at 48v, and maybe a solution could be to start off with a 250w 48v, and a big 48v battery, then potentially switch out the motor for something more powerful if i need it. This would not be optimal though if the 36v 250w motor actually is more powerful with higher peak watt.
my bike is a Hardrocx Circo Gigante XL, linked is a picture of my BB, will have to double check the chainstay though...

Hopefully someone who knows abit more about this stuff could share their thoughts and opinions. i would like to stay within the law, but still want to get the most out of my setup!

 

[neptronix]

The 250w motor should be a bbs01 and has a smaller stator than the bbs02 ( 500-750w rated ).
You have tires that suck up energy like mad versus a regular bike... that's a big disadvantage for running legal power.

These particular mid drives have kinda low efficiency ( 80% or under ). Being able to shift the power through the gears will be helpful on hills, but if you don't live in a very hilly area, there exist some geared motors in the >85% efficiency range that will give you a bit more power and help offset the massive amount of friction - i'd go that way if you want to stay in legal limits & don't have large hills to conquer.

 

[docw009]

You do need a 100mm BB motor. Ask the seller which one of the choices are BBS01 and BBS02.

I would suggest the BBS02B because no matter what the power level says. I believe they're all the same motor. Power level is set by a current limit in the settings that a user can change with a programming cable.

The BBS02B is a different motor than the BBS01B. Bigger. A BBS02B has more headroom than a BBS01B to handle higher current if you want to do the above settings change.

You can also set your speed limits to conform with local laws.

 

[fill]

Overvolting a 36v hub drive with a suitable (48v) controller and 48v battery can provide upto 30% extra oomph for hills if needed and can be applied to a 250w rated motor perfectly legally within the eu

Much cheaper than a mid drive, easier to fit, simpler diagnosis and fix regimes.. (mid drives with internal control pcb's are less open to this 'hack')

IF your cycling the fjords with steep climbs round every corner a mid drive and the mechanical advantage of the bikes gears could be the best fit, but if your covering 'normal' cycling terrain without monster hills, perhaps not?

while a fat bike with the added mass of a motor and battery might be a pita to pedal without any assistance, even a basic 250w 36v hub kit should have no problem scooting you and your bike up to 25km/h on the flat with some WEEEEEE factor still.

A lot of the info i first found when looking at ebikes certainly led me to believe mid drive motors were the best option.. And depending on use case they can be. But Hub drives can suit most applications at a lower cost employing simpler mechanics.