Need some help,tired of pedalling!

A

Addicted

100 mW
Joined
Apr 21, 2008
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47
I have done nothing but research this topic for about 3 days straight,But i still seem to need the help from the experts.I have a Specialized stumpjumper FS i want to convert to electric,i would like to keep the 26 inch wheel also.I weigh 160 and do not want to pedal at all,and it should be fast too,say cruise at around 35.I know it will take some good batteries but i would like to get at least a 20 mile range,is this possible with a hub motor?If so what motor,controler and batteries would you recomend?

Please help i Can't figure this out on my own!

Jason.
 
35mph is a cakewalk for a Crystalyte hub.

Definately go with some sort of lithium. PingPack, A123, emolis, whatever.

Unless you're willing to mod one yourself, your best option is to use a Crystalyte coontroller.
 
Let's step through it...

35mph on a MTB might require 1200 watts at the wheel.

View attachment slopeVmph1b.gif


you want to go for 20 miles... that might take 40min @ 35mph.

If you were riding for 1 hr, you'd need 1200Wh of power at the wheel, but you only need 66% of that... 792Wh.

So far so good?

:D
 
You'll need a motor that can deliver 1.2Kw (power_out) continously...

You'll need a controller that can supply that motor... best if it can do it near full throttle, so you don't get switching losses from partial throttle.

You'll want enough battery power to supply 1.2KW continously... after losses from motor efficiency losses (~20%) and controller losses (~20%): 1.2 / .80 = 1.5KW / .80 = 1.875KW

So if you run at 72V.... 1875 / 72 = ~26A * .66 = 17.16Ah

17Ah is a fair amount, so lighter batteries are suggested... they cost more than lead.

Now, look at the power chart and figure how much you might need if you only went 25mph. 8)


'Zat help?
 
This is all greek to me,Could you just suggest a crystalye model,pre made battery pack and controler?
 
Sure!

You might try a 5304 motor, a 30A controller and four Ping 36V 10Ah* packs.

:D

* http://cgi.ebay.com/36V-10AH-LiFePO4-Electric-Scooter-E-Bike-Li-Fe-Battery_W0QQitemZ220224453507QQihZ012QQcategoryZ11332QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
 
You might try a 5304 motor, a 30A controller and four Ping 36V 10Ah* packs.
Click to expand...

Thanks!Any controlers i should avoid,Any high on the list as a quality unit i should buy?
 
Addicted said:
You might try a 5304 motor, a 30A controller and four Ping 36V 10Ah* packs.
Click to expand...

Thanks!Any controlers i should avoid,Any high on the list as a quality unit i should buy?
Click to expand...

Ebikes.ca will have the motors... the controller #C7248SI should be back in stock soon.

http://www.ebikes.ca/store/

:mrgreen:
 
Of course, I must warn you that a 5304 motor at 72v and 48a will have a little more performance than you specified. Just a little. :mrgreen:

You'll be able to get far, far more range if you stick to a stately 20-25mph. Assuming again 80% controller and motor efficiency, and assuming 90% depth of discharge (so 18ah), and using 500w at the wheel, you'll get somewhere between 30 and 35 miles, depending on hills and winds.

TD's recommendations are accurate. Order everything but the batteries from ebikes.ca, and consider a CycleAnalyst. (http://www.ebikes.ca/drainbrain.shtml) The 72v 48a 4110-based controller is the best choice.
 
TylerDurden said:
Sure!

You might try a 5304 motor, a 30A controller and four Ping 36V 10Ah* packs.

:D

* http://cgi.ebay.com/36V-10AH-LiFePO4-Electric-Scooter-E-Bike-Li-Fe-Battery_W0QQitemZ220224453507QQihZ012QQcategoryZ11332QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Click to expand...
Why not try two Ping 36V 20ah packs?
 
Or email Ping and just have him make one 20ah 72v pack... Or whatever...

Before buying, though, you'll want to consider how and where you'll mount the batteries.
 
lazarus2405 said:
Or email Ping and just have him make one 20ah 72v pack... Or whatever...
Click to expand...

I don't think he makes 72V packs. I've never seen one up. Probably to do with the FETs on the BMS?
 
I bet so. And I also suppose there'd be no reason to make a 72v pack, when he can just make 36v packs to sell to both those wanting to use them at 36v and 72v.

Either way, he can make them in custom dimensions.

Though, a better option might be the LiFePO4s that ebikes.ca has. They're 12ah in 24v, 36v, or 48v. Four of their 36v 12ah packs would work well, and give you even better range. You'll need to email them about them first, of course.

Of course, you haven't mentioned a budget.

I do think that TD is a little pessimistic about controller efficiency (I sure know mine isn't dissipating hundreds of watts), but in the end the number aren't far off, considering other losses. It's better to overestimate the necessary battery capacity than be stuck short. :mrgreen:
 
lazarus2405 said:
I do think that TD is a little pessimistic about controller efficiency (I sure know mine isn't dissipating hundreds of watts), but in the end the number aren't far off, considering other losses. It's better to overestimate the necessary battery capacity than be stuck short. :mrgreen:
Click to expand...

Yeah, me too. I'm usually seeing 97-98% efficiency on the controller spec sheets. And I know that it would be getting a lot hotter if the losses were particularly significant.

And more battery is always better. :D
 
TylerDurden said:
Sure!

You might try a 5304 motor, a 30A controller and four Ping 36V 10Ah* packs.

:D

* http://cgi.ebay.com/36V-10AH-LiFePO4-Electric-Scooter-E-Bike-Li-Fe-Battery_W0QQitemZ220224453507QQihZ012QQcategoryZ11332QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Click to expand...

Dear ghod ... that thing would fly. I assume your intention was wiring the batts as a 2x2 for 72 volts.

Wear a motorcycle helmet.
 
I'm guessing, since I don't have a good way to test yet.... but:

Specsheets show the optimal efficiency, at 100% duty cycle.

The way I understand how this stuff works, is that under partial-throttle or current limiting the reduction of duty cycle brings losses in the FETs plus losses in the motor from the rise and fall of voltage.

When I figure out a way to test this, I'll be sure to report.
 
TylerDurden said:
Specsheets show the optimal efficiency, at 100% duty cycle.

The way I understand how this stuff works, is that under partial-throttle or current limiting the reduction of duty cycle brings losses in the FETs plus losses in the motor from the rise and fall of voltage.
Click to expand...

Most of the loss comes from when the FETs are switching to on from off and vice-versa. In this transient state, they act like a resistor and dissipate a lot of heat. Since this only lasts for a minuscule fraction of a second, it doesn't really come to much, even when done thousands of times a second.

A good way to get a relativistic idea of how lossy your controller is would be to take a ride on an empty road where you can leave the throttle full out and check how warm the controller is. Let it cool down and then do the same thing for the same amount of time on partial throttle. It will be warmer, but it shouldn't be too hot to touch.
 
I always use 0.95 for controller efficiency (95%). The motor is quite a bit less. They always show the peak efficiency, but usually efficiency across rpms seem to fall somewhere between 60% and 85%, for brushless anyway. If you are using a chain driven system, and it works well, thats 0.98. If it doesn't, it's lower. Batteries are also shown with capacities at a 20hr rate. Since most of the time we drain them much quicker, their actual capacity is lower.
 
fitek said:
IIf you are using a chain driven system, and it works well, thats 0.98.
Click to expand...

That is a really optimistic number. I think the chain itself is barely that efficient.
 
No, really, its ~98%. There is a paper out there on that one. My copy of bicycle science 3rd ed however gives 60%-98% as the figure. 98% is for correct setup and clean, etc. Your typical road weary department store chain is on the lower end.

Bicycle Science also states that the efficiency drops with bike sprockets that have less than 21 teeth due to chain articulation. But the loss is not considerable. If I recall correctly, many gears are worse than a proper roller chain.

I was interested in this because of my pedal generator setup. It is not very efficient, but it's cool and not a whole lot worse than the dirt caked and rusty chains I salvage from junk bikes anyway.

In any case, your biggest losses on a bike are going to be in motor efficiency and aerodynamics. The apparent battery capacity will drop with high discharge rates too.

Here's efficiencies for different gears:
http://www.roymech.co.uk/Useful_Tables/Drive/Gear_Efficiency.html

A thread on chain efficiency:
http://www.eng-tips.com/viewthread.cfm?qid=125414&page=3
 
Great,Thanks guys!I'm pretty much all set for now,I'm going to start by buying the motor and putting on my bike,then controler,cycle analyst and lastly the batteries.One more question though,I can start by buying one pack at a time and then just buy another one and bump up the voltage when i get the money right?And can i run 96 volts on it if i want to go with 48 packs?

Thanks
Jason.
 
Ohhhhh.

The way you worded "chain driven system" made me think you meant the whole drivetrain including motor.
 
Addicted said:
Great,Thanks guys!I'm pretty much all set for now,I'm going to start by buying the motor and putting on my bike,then controler,cycle analyst and lastly the batteries.One more question though,I can start by buying one pack at a time and then just buy another one and bump up the voltage when i get the money right?And can i run 96 volts on it if i want to go with 48 packs?

Thanks
Jason.
Click to expand...

Depends on what batteries you use, but yes.

96V? How fast you looking to go again? You could, but you'd need a pretty pricy controller. And definately a high torque motor in a small wheel. Anything else will give you some crazy top speed.
 
I'd get the 36v 18ah nimh packs from ebikes.ca if you have the money if its your first ebike. You won't have to fool with duct tape and foil wrapped fragile type batteries from ebay. There still new and the hampsters in here are still testing them. (no long term real world experiences yet)
 
Yes, with a 4110 controller you can run at 96v. Several people have done so. Generally speaking, you should be fine, controller-wise, but if something goes wrong the entire controller will be fried, not just one or two FETs.

Regarding the ebikes.ca NiMH, I say screw that. Wanting to avoid dust tape and foil packs is a a good idea, but ebikes.ca has LiFePO4 packs for sale.

Yes, you can start small with batteries and add as you go. The minimum pack voltage that the controller will run on is 36v.

Remember that different voltages will make the motor want to rotate at different speeds. Check out the simulator (ebikes.ca/simulator) to see exactly. A 5304 in a 26" wheel at 96v should top out at a little above 45mph. This may or may not "give you some crazy top speed", depending on your point of view.
 
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