Converting a tandem with 500w Bufang Rear Hub Motor - powerful enough?

[Barefoot_Wanderer]

Hi All,
I'm in a bit of a quandary with this. I have a 26" wheel Dawes tandem and want to know your thoughts about a THIS Bufang conversion kit. I have been told the 250w won't do any good on hills and wondered if this might have a chance. We just want something to get us up steep hills etc. My wife and I combined weigh about 320lb (not sure what the tandem weighs). I realise the 500w is not legal but visually is less suspicious than the big 1000w which I originally wanted. I realise I put my licence at risk (6pts) and a fine but honestly, this kit does look inconspicuous and my main concern is power - would I be wasting my money with this kit - would 1000w be required? If so, are they any small 1000w motors? something which won't look suspicious? Your thoughts and any recommendations/ advice would be warmly received.

 

[thelarkbox]

Not a tandem rider, but the legal restriction of a 250w rated motor can be 'navigated' legally. And provide ample power/oomph for most situations.

Watts the unit of power is the product off Volts and amps applied, (remember VxA = W) So simply applying more volts and amps with suitable batteries and controllers a 250w rated motor can run with over 1000w of power for short durations with no detrimental effects.

Can you provide details of the 'steep' hills you want to conquer?? length, gradient, etc..

And how much effort would you and your Mrs contribute to the climb? do you want to roll up with no effort or are you happy pumping legs while comfortable in the saddle?

I suspect that a 'slow' 250w 36v hub motor when supplied with a 48v battery and a 22a controller capable of applying over 1000w of power to climb will suit you while remaining the right side of the regs.
(upto 54v X 22a = 1180w potential climbing power)

 

[saneagle]

It looks OK, but it didn't show the controller current, which is the thing that determines how much power you get, neither does it show the motor's speed, which is another important characteristic. It's probably OK, but without that information, you can't be sure.

You could get a completely legal and more certain solution by buying a 250w motor the same size as that one, then get a 20A KT controller and a 48v battery. The motor needs to be around 260 rpm at 48v or 201 rpm at 36v. A 201 rpm 36v becomes a 260rpm one when you run it at 48v. Motor's don't care about voltage. The voltage only affects the speed.

Woosh sell a ready-made 48v kit that's legal and would work very well in a Tandem. Personally, I'd prefer a KT controller, but most people would be happy with the Woosh one in their ignorance.

Woosh hub kits | Electric Bike Conversion Kits from Woosh

Woosh range of hub kits with choice of front or rear hub motors. Convert your bike into an electric bike.

wooshbikes.co.uk

 

[Barefoot_Wanderer]

Thank you guys this is priceless. One of our concerns is the weight of the tandem after the conversion (lifting onto roof rack etc).

I already have THIS from Yasco which is 48v 15ah so, if I understand correctly, would I buy a 20a KT controller and 250w hub and this will provide the required power?

The 'steep hills' vary but occasionally can be extreme (unsure of the gradient but v.steep and up to 3/4 miles long sometimes - this isn't typical but something we come across near where we live (Bacup, Lancs.) If we head for Todmorden. Not something we can get up with pedals alone. We are prepared to put some leg work in just not enough for long steep climes.

If you are aware of a 250w hub kit which inc. 20a KT controller let me know.

Will my battery be suitable for this project?

BFW

 

[Nealh]

That Bafang kit has a std 15a max rated controller.
For the tandem I would opt for a KT T09S 22a controller , 48v battery and AKM hub.
All KT controllers have the option to reduce current /amps out put so no need to worry about the 22a max rating as one can reduce to 11a max or anywhere between if needed.
T09S differs from T06S, by being slightly larger in size and having better heat management with 9 mosfets instead of 6 and the larger size acts better as a heat sink.

T09S 36V/48V500W 22A KT Sine Wave Controller with Julet Waterproof connector [T09S controller waterproof plug] - $32.55 : Zen Cart!, The Art of E-commerce (topbikekit.com)

T09S 36V/48V500W 22A KT Sine Wave Controller For ebike [T09S KT 9Mosfers Controller] - $26.04 : Zen Cart!, The Art of E-commerce (topbikekit.com)

AKM-100 36V250W EBike Rear Driving Hub Motor [AKM-100SX Rear motor] - $79.05 : Zen Cart!, The Art of E-commerce (topbikekit.com)

AKM-100CST Cassette 36V250W EBike Rear Driving Hub Motor 32/36 holes [AKM100CST EBike 36V250W motor] - $97.65 : Zen Cart!, The Art of E-commerce (topbikekit.com)

Keep the AKM to 18a for longevity.

 

[Nealh]

If not bothered by the 250w limit then
AKM-128CST 48V500W Rear Driving Hub Motor Cassette motor For ebike [AKM 128CST 48V500W motor] - $116.25 : Zen Cart!, The Art of E-commerce (topbikekit.com)

Looks the same and is visually smaller then most 250w hubs.

 

[saneagle]

That Bafang kit has a std 15a max rated controller.
For the tandem I would opt for a KT T09S 22a controller , 48v battery and AKM hub.
All KT controllers have the option to reduce current /amps out put so no need to worry about the 22a max rating as one can reduce to 11a max or anywhere between if needed.
T09S differs from T06S, by being slightly larger in size and having better heat management with 9 mosfets instead of 6 and the larger size acts better as a heat sink.

T09S 36V/48V500W 22A KT Sine Wave Controller with Julet Waterproof connector [T09S controller waterproof plug] - $32.55 : Zen Cart!, The Art of E-commerce (topbikekit.com)

T09S 36V/48V500W 22A KT Sine Wave Controller For ebike [T09S KT 9Mosfers Controller] - $26.04 : Zen Cart!, The Art of E-commerce (topbikekit.com)

AKM-100 36V250W EBike Rear Driving Hub Motor [AKM-100SX Rear motor] - $79.05 : Zen Cart!, The Art of E-commerce (topbikekit.com)

AKM-100CST Cassette 36V250W EBike Rear Driving Hub Motor 32/36 holes [AKM100CST EBike 36V250W motor] - $97.65 : Zen Cart!, The Art of E-commerce (topbikekit.com)

Keep the AKM to 18a for longevity.

AKM100 can't run at 48v and 20A because it wears the gears too fast even for a light rider on a light bike. 15A is the maximum. Even then, it wouldn't be the best motor to drive two riders and a tandem up a hill. AKM 128 would be fine, but it's not really legal. Any medium sized motor would be OK as long as you run it at 48v.

 

[Nealh]

Tasco battery is 30a rated so 20/22a controller is fine , it all boils down to the hub used . In most cases one would be a bit conservative and limit current to 17/18a which is plenty of power at 48v.
At 18a 48a will produce approx. 650w of power to the motor.

 

[thelarkbox]

Max Constant Discharge Current:30A( BMS)

from your link, so yes that has ample headroom to provide full power to a 20a controller with no concerns.


As long as your not pumping excessive power into the motor for long durations over a 5-10mile climb it shouldn't overheat. Excess heat is the enemy when over-volting/over amping a motor under load.

But short bursts to climb a mile or so with supporting input in the correct gear should be no problem.

select one with a modest rpm at 36v, you will have to dive a little deeper into specs than the usual ad will display at the top of the page, but the info should be available.

over-volting a 36v motor with a nominal 48v supply will increase its speed and torque by circa 30% so based on the motors optimum rpm and wheel size you can determine the optimum running speed for the bike.
Aim for a speed as close to the regulated limit as possible for the maximum torque to climb with.

the closer to optimum speed the motor runs at the more efficient it is..

Yes there is more to it, i hope my potted synopsis is clear and correct..

 

[Az.]

if I understand correctly, would I buy a 20a KT controller and 250w hub and this will provide the required power?

Fully charged 48V battery has around 54V

54V * 20A = 960W

 

[saneagle]

Fully charged 48V battery has around 54V

54V * 20A = 960W

From the battery, not output power.

 

[Barefoot_Wanderer]

If not bothered by the 250w limit then
AKM-128CST 48V500W Rear Driving Hub Motor Cassette motor For ebike [AKM 128CST 48V500W motor] - $116.25 : Zen Cart!, The Art of E-commerce (topbikekit.com)

Looks the same and is visually smaller then most 250w hubs.

Think I'd be really tempted to go with 500w as this one is inconspicuous - how much of an advantage is 500w to 250w then. Avoids over-heating issue with 250w hub. Would I be able to apply power (more power?) and for longer/ steeper distances? Getting quite overwhelmed at mo, but in a good way - lots of info to digest but if I can do it legally might go that way.

If I thread my own spokes this also provides more options, but prefer a ready-made wheel if I can find one.

 

[thelarkbox]

Grin ebikes.ca has a good deal of info including a motor simulator you can use to compare different motors..

And while very few people have reported ever being stopped by police on an ebike, That could change.
But more importantly if in the case of an RTA a 500w motor comes to light on your bike, any insurance cover will disappear and you may even be found liable by default?..... making a bad day worse.

If you need that extra power.. (personal experience with an X who would in all likely hood sit looking at her phone ghost pedalling down hill on a tandem..) wink wink.. there are cases of motors stamped with one rating for one market and another for less restricted markets.. Hub drives meeting this criteria are like hens teeth, but woosh sell a mid drive that has a 750w ratting in international markets while receiving a legit UK 250w rating through woosh as a distributor

edit though looking at your bike pic above? would fitting a mid drive at the front crank work ok??

 

[saneagle]

Think I'd be really tempted to go with 500w as this one is inconspicuous - how much of an advantage is 500w to 250w then. Avoids over-heating issue with 250w hub. Would I be able to apply power (more power?) and for longer/ steeper distances? Getting quite overwhelmed at mo, but in a good way - lots of info to digest but if I can do it legally might go that way.

If I thread my own spokes this also provides more options, but prefer a ready-made wheel if I can find one.

The power comes from the controller, not the motor. If the controller gives the motor 1000w, you'd get about 700w maximum output power and about 500w when climbing. That would be the same for all the normalebike hub-motors regardless of what their designation is. The only question is whether the motor can handle that power. The small ones, like Q100 wear out quickly with that much power, but any medium sized one should be OK.

If you want to go for a motor that's designated as more than 500w, one that's embossed with it is going to be a bit awkward. The Q128 from BMSbattery had an easy-peal label on it. I'm not sure if it still does. Those labels have a nasty tendancy to fall off after a bit of weathering.

 

[Nealh]

AKM nylon gears are readily available from TBK , the AKM100 doesn't have to be run at 18 -20a , one can run it at a lower setting.
My 1.6kg G370 mini small front hub coped fine with my pre surgery 82.5kg weight + towing a trailer with 90kg payloads.
I have yet found the need to use more then PAS 2 towing which is a meagre 4.4a or approx .140-160w, my terrain is pretty much flat.
Post surgery I'm now 75.5 kg and waitng for when I'm allowed to ride again.

 

[Az.]

Think I'd be really tempted to go with 500w

Yep, you are definitely tempted by 500W. You keep coming back to this inconspicuous 500W

how much of an advantage is 500w to 250w then. Avoids over-heating issue with 250w hub.

Unfortunately there is no simple answer to that. Best answer would be "it depends".
I understand why you might be confused. After all 500 is more than 250. 500 is 2*250, so it must be better and stronger, right? Unfortunately in this case 250W motor can be more powerful than 500W.

In my humble opinion right 250W is more than enough for practically every AEPC application you can think of.

 

[Az.]

In UK Woosh is where you can buy very powerful and legal motors. Woosh is not cheap, but they have motors others don't. After you decide which motor to buy please make sure you buy right battery too. If you buy powerful motor and don't pair it with right battery, your bike and your house might end up in big ball of fire.

Woosh Bikes

Woosh Bikes Ltd Electric bikes and kits assembled in Southend-On-Sea. Affordable and comfortable e-bikes to suit every pocket.

wooshbikes.co.uk

 

[jimriley]

Just to contribute my two penn'orth, from the other side of the hill in Littleborough. We have a recumbent tandem (because wife can't ride an ordinary bike, she'd fall off). It came with a crystallite front hub motor with knackered controller and battery pack originally fitted pre 2016. I fitted a KT 24a 36/48v controller and screen and upped the settings to 20a immsmr. I use the 36v 17ah battery of my converted hybrid, just bought an extra battery cradle. We've had to push up really steep hills but although I haven't ridden that way I reckon it would get us up over Deerplay between Tod and Bacup. Because of the age of the original motor I have a legal throttle.

 

[guerney]

Just to contribute my two penn'orth, from the other side of the hill in Littleborough. We have a recumbent tandem (because wife can't ride an ordinary bike, she'd fall off). It came with a crystallite front hub motor with knackered controller and battery pack originally fitted pre 2016. I fitted a KT 24a 36/48v controller and screen and upped the settings to 20a immsmr. I use the 36v 17ah battery of my converted hybrid, just bought an extra battery cradle. We've had to push up really steep hills but although I haven't ridden that way I reckon it would get us up over Deerplay between Tod and Bacup. Because of the age of the original motor I have a legal throttle.

Good to hear your eTandem restoration is fulfilling it's intended brief. Did you have to push it up very steep hills because of too much battery voltage sag?

 

[jimriley]

Good to hear your eTandem restoration is fulfilling it's intended brief. Did you have to push it up very steep hills because of too much battery voltage sag?

Not quite, Noreen suffers from Cataplexy, a full body muscle weakness/paralysis triggered by all sorts of things, a woodpecker in the garden, getting 3/4 of the way across a busy road, or the power kicking in and taking the effort off her feet so she can no longer pedal. Life is such fun!
I can keep going myself+motor but prefer not to. We are talking a really short steep hill on N Wales Cycleway near Rhos on Sea. Possibly 1 in 4. I know the road the OP is talking about and reckon that wouldn't be a problem. Not tried it because she doesn't like roads with cars.