Is 750W too much?

J

judson

New Member
Hey all I have way more questions than I have answers at this point but I bought an old Specialized Rockhopper in decent condition with the idea of converting it into an ebike. If that goes well I will likely upgrade the bike (perhaps to a cargo bike) and switch the ebike kit over. My goal was to tinker with this project all summer and be ready in the fall to commute daily on this bike.

I have two essential questions. First, is the 750W the right size for the job. I live in Seattle and my commute is 10 miles long with one short and steep hill, and two 1-mile long shallow hills. The ride will be very urban with much stopping and going. Eventually I would like to use this kit (perhaps on the cargo frame) to haul kids and/or groceries over the milder hills within my immediate neighborhood. I weight about 175 lbs for what its worth. I aiming towards the 750W mostly for torque, not speed (max 25!)

Second question is about battery size. I really would prefer the ones that mount to the bottle monuts of the frame. I plan on not mounting a throttle and using only pedal assist. I can charge at work. Is there a rule of thumb for Ah or Wh per mile?

Thanks everyone!
 
Hi Judson,

I have recently built a bike with the BaFang 750W and a frame-mounted 10Ah battery.

The BaFang 750W has got plenty of torque. Speed is easily set on the display with 3, 5, 7 or 9 steps, your choice.
The motor will accelerate you to target speed and then wait if you can either maintain it yourself or "get you up to speed" again whenever you slow down (while pedaling).

With a lot of stop and go you need to consider to shift down before you accelerate again. Despite the torque you'd probably fry the controller sooner or later by demanding too much power on initial start-up. A dérailleur shifter get's you stuck in too high a gear too often in city traffic for that. So I'd recommend an IHG which allows you to shift without turning the cranks/wheels.

In regard of battery size: it all so depends! Total weight, how much power you generate yourself, the terrain, ...
I'd estimate 5Ah minimum. My 10 Ah battery lasts me for about 40-50 km without asking too much of it.
I guess you'd rather want some spare Amps waiting for you than run out of power too soon also.

Hope this helps,

Happy building and riding,
Cheers, Go-Coo
 
You`re right about finding yourself in too high a gear too often - so are we talking NuVinci or what?

They`re a bit pricy, and how do they hold up to the 48v/750w torque?
 
Hi RoyL,

Yep, I run a NiVinci 360.
Pricey? What ain't? Got mine for about US$ 350,- all in all on Amazon and other online dealers.
A steal compared with a Rohloff IGH (I'll get 3 NuVincis for one).

I haven't really run up any substantial milage yet (200 km only so far), ask Spotty Dog how many miles he's run with his kit yet.
I simply love the combo so far! (Got the manual not the electronic harmony)
So easy to adjust, a plain joy to shift either way though shifting all the way while not moving cant be expected, but no need to.

I'm sure one could wreck the NuVinci with an adequately aggressive driving style pretty fast but with moderate use I expect it to outlive the battery at least if not the motor.
 
I don't think that you'll ever be sorry by over sizing the motor and battery, and 750w is by no means too much power. Add the most powerful battery that will fit with the motor and you'll be happy. If you under size these items you will have regrets, in my lame azz opinion. I have 500W, 48v 8ah, and there are many times I wish I had more power on hills and longer battery life, etc., but then again I'm a fat azz, lol.
 
I have a 48 volt Bafang bbso2 500 watt, I weight 220lb and I have not found a hill it won't pull me up in low gear on pas level 1. My battery pack is 10.4 Amps and uses
Samsung 18650 26 F cells.
That being said the 750 watt bafang would be a good choice. Plenty of reserve power, better resale value, especially for a cargo bike. Using pas 1 you should get 20 to40 miles per charge with a 10 amp battery.
WARNING, The 750 watt bafang does need a battery pack with significant discharge capabilities like one using samsung 18650 25R cells, You could ruin a battery pack that does not supply enough
discharge current with the bbs02 750 watt Bafang.
Check out; http://em3ev.com/store/index.php?route=common/home I have never used them but looking at their website they can build or sell you the right battery pack for your needs.
 
Last edited:
RoyL said:
Level 1 (ONE)

... are you sure??
Click to expand...
OK let me clarify that as a paved hill. The kind that cars drive on not off road. Level 1 is about 5mph and draws 300 to 500 watts, the lower level pas 1 is to keep the motor from overheating it's also easy to contribute some power from my legs. The use of the rear gears for varying terrain is what makes the middrive unit my choice.
 
Michael Moore said:
OK let me clarify that as a paved hill. The kind that cars drive on not off road. Level 1 is about 5mph and draws 300 to 500 watts, the lower level pas 1 is to keep the motor from overheating it's also easy to contribute some power from my legs. The use of the rear gears for varying terrain is what makes the middrive unit my choice.
Click to expand...

Rear gears are also very utilized with the rear hub motor while pedaling, though I don't think they play a part when in throttle only mode, but who uses that anyway. I use all PAS levels for hills and different gears and haven't found a hill yet that I couldn't climb, although I'm not that aggressive of a rider. It's all fun and keep pedaling!
 
judson said:
Hey all I have way more questions than I have answers at this point but I bought an old Specialized Rockhopper in decent condition with the idea of converting it into an ebike. If that goes well I will likely upgrade the bike (perhaps to a cargo bike) and switch the ebike kit over. My goal was to tinker with this project all summer and be ready in the fall to commute daily on this bike.

I have two essential questions. First, is the 750W the right size for the job. I live in Seattle and my commute is 10 miles long with one short and steep hill, and two 1-mile long shallow hills. The ride will be very urban with much stopping and going. Eventually I would like to use this kit (perhaps on the cargo frame) to haul kids and/or groceries over the milder hills within my immediate neighborhood. I weight about 175 lbs for what its worth. I aiming towards the 750W mostly for torque, not speed (max 25!)

Second question is about battery size. I really would prefer the ones that mount to the bottle monuts of the frame. I plan on not mounting a throttle and using only pedal assist. I can charge at work. Is there a rule of thumb for Ah or Wh per mile?

Thanks everyone!
Click to expand...
Hi I recently joined this site and finished up with conversion not too long ago what is the 750 watt Bafang BBS02(unlocked). The battery I chose was a tube style and is 48v 13ah.
I don't want to jinx myself but so far so good and I've definitely done some modifications. If you have any specific questions please let me know and I'd be glad to help. Thank you, Jason
 
Mike,

the rear gears are not used by the motor. they are used in a mid drive as the way they are used on a a car w/a transmission . The motor dose not see any difference with a DD hub. your legs do though and the amount of input your legs do depends on the rear gears all other things being equal. Using PAS or Throttle makes no difference to a rear DD hub.
 
I live in a hilly area and have built a 350w and a 750w both use Nu Vinchi N360 and Harmony electric shift.
My girlfriend loves her 350w bike it does the job, had I not been able to do a direct comparison the BBS01 is adequate especially if your riding is fairly flat.
The BBS02 has the extra power to pretty much eliminate personal effort on your part pedaling.
If I choose to use the extra power the BBS02 simply leaves the BBS01 in the dust.
The bike can hussle along suprisingly fast I upgraded my brakes to cope with what is a fairly large and heavy machine by bicycle standards able to hit 30 mph on flat and 40mph down hill.
As Go-Coo says ride with mechanical awareness and avoid brutal use of throttle, you can break anything if u drive it hard enough, im up to about 400 miles now with no problems.
 
Hi Spotty, i live in a very hilly area myself, what gear ratios are you using with your NuVinci?
 
Hi RoyL,
I run 42t x 16t my tyres are big apples 2.35 on 26" rim.
You can work out the gear inches on sheldon browns calculator I find they mean more to me than percentages.
My bottom underdrive gear would be too high for me without motor assist but my full overdrive gives me a good top speed for my mostly road riding.
I would say it was a shade on the tall side, If I was off road more I would lower it with larger sprocket but probably only an 18t.
 
Hey folks thanks for the good info. Sorry for not checking back sooner, I got caught up in a weeks worth of family drama. But I am back and I just had a chance to review the posts. I am not hearing anyone say that the 750W is too much power. It does sound like I am might need to upgrade my brakes we will just see what feels safe on that front I suppose. Certainly if I upgrade to a cargo bike then I am aiming towards some beefy disc brakes.

Regarding battery sizing, I still am not sure how to decide. I am likely going to get one directly from em3ev.com where I am also sourcing the 8fun. Seems easiest to just get it all from one super reliable source.

Does anyone have data on how many Ah they are using per mile for their rides? I know every rider and every ride is different but I am really just looking to get in the ballpark. Thanks!!
 
Hello All,
I just got a rear hub, integrated wheel, 750 watt Bafang (Moton M-70). It's an awesome fat tire bike, and comes with a 48v, 14.5 amp battery. I love everything about the bike except the speed cap of 20 mph. I've spent that last month trying to figure out what I can do to modify this. The display allows you to set speeds up to 40 kph. I've read all about ways to modify mid drive bbs02 and bbshd, but nothing on this rear hub. I've swapped out the front chainring from 48 to 52 teeth (may even go to 56) in an effort to be able to pedal at top PA, which helped, but i'm still capped at 22. Will a 52 volt battery work, and where can I source that? Or is there any way to reprogram like the bbs02?
TIA,
Mike
 
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