DIY build

[pete mac]

Hi, I'm trying to put together a package to fit my (oldish) Boardman pro.
Rear hub 250w legal for 18mile commute each way across London rush hour. However, since I tend to cycle around the 15 - 20mph mark would like to have the pedal assist able to go to 20mph (I know this is not legal, just have fear of cutting in and out at that speed through the traffic) So if someone would be good enough to offer advice I have 2 questions:

Can I simply use a 48v battery and different controller to match to get the speed up and if so can anyone recommend a 250w motor that will deal with this (I have no steep hills so extra speed not torque necessary) I only need pedal assist, I still want the exercise just less tired when I get to work (I'm not looking for 'fast' just a little more than 15mph).

My bike at present has a 11gear cassette on - will I need to replace this with a smaller cassette?
I've read so much on the internet I've confused myself.

 

[Nealh]

You will find it hard to buy a geared hub marked 250w unless it is off an old bike or part of a kit. Most are sold marked as 350w or 500w.
For 20+ mph you need a dual voltage KT controller and lcd3.

Better option is to keep your current rear gearing and fit a 250w GSM (controller less version) crank drive from Woosh bikes with 17a dual voltage KT controller and lcd3. Controller will need siting in a small saddle type bag.

36v will do 20mph but 48v will do it and more better.

 

[pete mac]

Thanks, not what I was hoping to hear but very interesting advise. I'd rather have a direct drive so as to keep wear and tear down but maybe thats not practical after all. Will have a re-think. Thanks for your help.

 

[pete mac]

Nealh, if I went for the GSM (CD motor) set up what size 48v battery would I need for a 17mile flatish commute? 8ah or bigger do you think?

 

[Nealh]

48v 8ah would give you a nice 384wh battery, approx. 25 miles at a usage of 15wh per mille.
So anything of that capacity, choice of cell is the one to think about.
If going 2p 13s for lightness look at 15/20a rated cell so HG2 3000mah = 6ah / 288wh;
VTC6 3120mah = 6.240ah/299wh;
30Q 3000mah = 6ah/ 288wh;

Both VTC6 & 30Q are rated for 20a for short power spikes.

If going 3p 13s you have more choice of cells but increase in weight, other cells to consider.
GA 3.400mah 10a rated but however it appears this cell is under rated and independent testing appears to suggest it is a 12a rated cell.
MJI 3500mah 10a rated better cycle life then GA.
VTC5/A 2500/2600mah 20/25a rated.
25R 2500mah 20a rated.
HE2/HE4 2500mah 20a rated.

 

[Benjahmin]

So 'you can't get hub motors marked 250W'
I pray to differ:
http://wooshbikes.co.uk/?hubkits

Second kit down.

Although for more speed you may be better using a 36v motor with 48v controller and battery.
Or use a motor wound for a smaller wheel so the rpm is higher - but torque would suffer.

For me a hub is the better choice for commuting, there's less to go wrong. I shall now retreat into my bunker!

 

[pete mac]

Nealh, thanks for battery info, very good.
Benjahmin, food for thought - it does talk about not de - restricting it so it must be restricted, not sure how I would do that?

 

[Nealh]

Pete wasn't asking about a kit other wise I would have said Woosh SWXO2 48V straight away.
He asked about a hub and a controller to use with a lightweight battery.

 

[pete mac]

iIt's true, I was - I've mostly ignored kits so far as in my limited knowledge they still leave me with the original problem of more speed - the kit you mentioned would be perfect except I'm trying to get over 15mph and the SWX02 is still limited to that. If I could get past that I'd go for it otherwise I'm back to building along the lines of Nealhs idea - can the SWX02 be derestricted? If so, problem solved. Thanks for your help.

 

[pete mac]

Sorry, I meant to add the motor being 48v and the battery being the same means I simply cannot over volt to get the extra speed (I'm still hoping not to make it any heavier than need be).

 

[1boris]

Not a problem to buy a 250w marked legal hub motor and controller

 

[Nealh]

If you are happy to buy off Aliexpress you can buy Mxus (Bafang clones) 250w 48v, not everyone like's the idea of buying from this form of site. Aliexpress though are very good to deal with and I have not encountered any problems.
Other wise buying direct from manufacturer they may marked accordingly if you ask.

 

[Nealh]

High torque low speed off Aliexpress 25/28kmh so about 18.5mph.
Pete if you buy the 36v one and run it at 48v it will be quicker and should run to 22.5mph but ideally for your flat terrain needs you need a faster 25kmh wound hub to start with.

High torque low speed 28kmh winding.
https://www.aliexpress.com/item/Brand-24V-36V-48V-250W-BLDC-Brushless-Gear-Hub-Motor-For-26-28-Wheel-Drive-Electric/32895417685.html?spm=2114.search0204.3.21.47496a7fVGTwtp&ws_ab_test=searchweb0_0,searchweb201602_3_10152_10151_10065_10344_10068_10130_10324_10342_10547_10325_10343_10340_10548_10341_10696_10192_10190_10084_10083_5011815_10618_10307_10820_10301_10821_10303_5723615_5011715_10059_100031_10103_10624_10623_10622_10621_10620,searchweb201603_1,ppcSwitch_5_ppcChannel&algo_expid=a15ef71d-2b29-4563-91ad-0b0bc07b66d4-5&algo_pvid=a15ef71d-2b29-4563-91ad-0b0bc07b66d4&priceBeautifyAB=0

low torque high speed 40kmh winding.
https://www.aliexpress.com/item/MXUS-XF08C-24V-36V-48V-250W-Cassette-Motor-High-Speed-Brushless-Gear-Hub-Motor-For-16/32844159961.html?spm=2114.search0204.3.2.4b5478a0PlHktp&ws_ab_test=searchweb0_0,searchweb201602_3_10152_10151_10065_10344_10068_10130_10324_10342_10547_10325_10343_10340_10548_10341_10696_10192_10190_10084_10083_5011815_10618_10307_10820_10301_10821_10303_5723615_5011715_10059_100031_10103_10624_10623_10622_10621_10620,searchweb201603_1,ppcSwitch_5_ppcChannel&algo_expid=3c95b998-414a-42b2-a772-62d098d5f5db-0&algo_pvid=3c95b998-414a-42b2-a772-62d098d5f5db&priceBeautifyAB=0

 

[pete mac]

Thanks, Aliexpress is no problem so will look into the Mxus option. Thanks again for your help.