High power conversion advice please. BMC V4 Motor Downhill bike.

[handmadematt]

Hi.
After successfully converting a hard tail mountain bike with a Chinese 500w 36v kit with lead acid batteries I have attracted lots of positive attention amongst my friends who now all want me to build an ebike for them! Happy days.
One friend has given me this bike as a base:

I'm super excited it's going to be awesome.
He wants it to be powerful and light.
He wants this kit:
http://www.ebay.co.uk/itm/THE-ULTIMATE-ELECTRIC-E-BIKE-CONVERSION-KIT-BMC-CYCLE-ANALYST-40MPH-/131280470702?pt=UK_SportGoods_CyclAcces_RL&hash=item1e90ed02ae

BMC V4 rear hub motor £450
BMC 50A Controller £130
14S 10Ah 58.8v lithium polymer 150A max discharge battery pack inc. 3.5A fan cooled charger £395
Cycle Analyst V3 handlebar mounted monitor £150
DNP 11-32T freewheel cassette £45
Alloy frame mounted battery box £40
36h 26" Sun Rhyno rim £35
36pcs 13G stainless steel spokes and brass nipples £25
Half twist or thumb throttle £10
Chain stay mounted kickstand £10
Handlebar kill switch £5

Total price plus shipping £1295.

Before I go ahead and order it I wanted to ask some opinions on here.
Is it the best option for him with this kind of budget?
I have a few concerns.

In the article about the the motor that the seller himself has linked it says this:

"WARNING: this motor is often misrepresented and advertised by dealers as 2-3KW motor capable of reaching speeds over 40mph. Our years of experience riding and repairing these and similar motors suggest that for reliable operation, it should not be used at more than 1500 watts and it’s best to keep speeds under 30mph (in 26″ wheel), that applies to all BMC geared hub motors. Sure, it will go 40 + mph at 2000 – 3000 Watts, but that is comparable to running an internal combustion engine constantly exceeding maximum rpm it is designed for. Our advise for riders who desire speeds over 30-35mph and reliable hub motor operation, is to use a direct drive hub motor."

Also in the ebay listing he misses some very important figures, any ideas? (I have emailed him.)
Power
Range
Charge time
etc.

How will this kit compare to the chinese 500w 36v kit that I've fitted previously?
Are there any other suppliers the forum recommend or who use this forum as a supply platform?

When I built my bike kit the total cost was just over £250 so I was less worried about making the "right choices." Now I'm taking it to the next level I want to invest even more research time.
Thanks.

 

[Deleted member 4366]

You know the power. He says 50A controller and 50V battery, so that's 2.5kW, which I think is too much. The motor's basically the same as a Bafang BPM or MAC. EM3ev modify their MACs to get them to run reliably up to 40A.

Whatever you do, think about the position of the battery. With a 50v battery hanging over the back wheel and a 50A controller, it's probably going to be unrideable.

I don't think you need charge time and range. Range is easy to calculate. If you use the maximum 50A, the 10ah battery will last 12 minutes, although, it would probably be a lot less at that current. Charger is 3.5A, so 3 hours to charge an empty battery.

How does it compare with your? It'll be a lot lighter and about three times the torque.

It should be great for trail riding, but for on the road and normal bike riding, I don't think it'll be very pleasant. Traction will be a problem, especially in the wet.

 

[handmadematt]

Hi mate thanks.
I hope to position everything on the underside of the frame. All the weight low and in the middle.
You're right about the figures, thanks and sorry I just wasn't thinking.
It is for trail riding only, it'll never be used as transport. Mainly to ride back to the top for the downhill and to help in some sections, it'd be nice to get a fair few hours of playing before she's empty..

When you say that you think 2500w is too much why is that? It will wear the motor out too fast? Or just drain the battery too fast? (Or both?)

He claims "All this power can be limited via the supplied Cycle Analyst handlebar mounted computer"

So is he marketing this at it's absolute top spec despite the impracticalities and the intended normal use is to "dial it down a bit." Do you think?

Thanks for the fast response (as ever.)
What do people think of the battery?

Am I barking up the right tree with this kit? Performance and value?
Ta.

 

[handmadematt]

(The other option for less than half the price is to buy a 1000w chinese hub motor kit similar to the 500w kit that I have already fitted but with a lithium battery.) However, I have a feeling that this would be vastly inferior to the above kit and he is prepared to pay for quality and performance.)

 

[jackhandy]

Are you sure it needs 2.5kw just to get back to the top of a downhill trail?
That's a hell of a lot of poke & it's going to soak up battry power like a black hole.
I've just fitted a 200rpm, 500w Bpm2 in the back wheel of my bouncer & it gallops up the fire road at my local trail centre.
If I were to use its full potential when the centre's busy, I'd definitely become Billy-no-mates quicksmart! No-one takes kindly to some smartarse belting past, motor whining, on a gut-busting uphill.

 

[handmadematt]

I'm building it for someone as a commission.
It's what they want. The power won't only be used to get to the top again.
Having the computer means that it can be dialed up and down as required I believe. With this guys budget he wants all the trimmings and the option to put down all the juice quickly if he wants. It's truly a toy. An awesome toy.

 

[Cyclezee]

An eZee kit would be much more sensible and economic choice, enough power for most, sourced from the UK, but that is my opinion

 

[handmadematt]

Having a quick look at your website John I can't see any comparable product, it seems to be a great but altogether different thing.

 

[handmadematt]

My associate has decided that he wants to go for this kit. It has been paid for and should be delivered after the weekend. I'm truly excited about building it.