| Author | Message | ||
     Reepicheep |
Just for fun over lunch today, I decided to see what it would cost to convert an old dual sport into an e-bike. I thought I'd share... From ebay... a decent electric motor / controller / solenoid combo... 9HP continuous. Not great, but maybe enough for commuting. $1361 to your door, available now. Also from ebay. A nice looking LiPo battery with built in charge controller. $160 for a 12AH 12V battery. Err, but that battery would (in best case theory) power that motor at full power for... uh... 1.1 minutes. Erp. So how many batteries would you need (theoretically) to make a 60 mile commute (figure 1 hour at 60 MPH)? 53 batteries. At $160 each. $8510 in batteries. So you are pushing $10k, and you have a 10 HP bike, and you don't even have a bike part yet... Makes that Brammo look like a Bargain at $10.5k... And when looking at costs for EBikes... . The math for the rest works. | ||
| Teeps |
Don't confuse me with the facts... | ||
| Glitch |
How much for a transmission? | ||
| Nik |
I did some numbers for a ninja 250. A 3kWH pack (~25-30 miles range for a motor with more power than the 250 ICE unit), in: LiFePO4: ~$2000 Turnigy LiPo : $1500 Lead Acid: ~$800 So; it can be done right for a lot cheaper. | ||
| Nik |
elmoto.net has a lot of good info. | ||
| Reepicheep |
Somebody there is doing "green math"... which is another term for "lying". Or maybe I am missing something... There are 745 watts in 1 HP. Watts is volts times amps. 3kWH battery can deliver 3000 watts for an hour (or 6,000 watts for half an hour, etc). 3000 watts / 748 watts in 1 HP. So that would be 4 HP for 1 hour, or 8 HP for 30 minutes, 16 HP for 15 minutes. A 15 HP bike would need about 11kWHr battery to run for an hour. Thats still better though, using your LiPo cost, that's down to $5587 in batteries. Of course now you also have to add to the cost a charger that can balance and charge all those LiPo cells... | ||
| Nik |
charging is really the problem with those LiPo packs. What a lot of the tinkerer's do is charge them with the turnigy chargers, but you can't do a whole pack with that. You also need to make sure they don't explode.... You're making the assumption that power is being consumed at the full rate of the motor all the time. At a constant speed the motor is only outputting as much power as it needs to sustain that speed. My 9hp Vespa could do a GPS verified 70mph. So your 8HP for 30 minutes puts me at 70mph * .5 h = 35 miles, which is even more than what I would expect to get since its not 100% efficient. So in one respect you're right. With a 40 hp (peak) motor I could kill the battery in 6 minutes at WOT. But in normal commuting it would last much longer. The Zero S gets 43 (commuting) - 76 (EPA) miles of range on 6kWH batteries and their new long range 63-114 miles packs are 9kWH. The motor I was planning on using has very similar specs to theirs (same manufacture) but differed in that its a DC brushed, as opposed to PMAC. | ||
| Reepicheep |
Good discussion, thanks! As a datapoint, I'm using my old KLR-250, which I suspect was about 17 RWHP or so peak. It would do 70mph, but you were wringing it's neck to get and stay there. I have a 45 mile, mostly 60 MPH round trip commute. So my bar is pretty high for an EBike. I'd love to do a conversion though... | ||
| Glitch |
http://www.electricmotion.org/ | ||
| Sifo |
With a 40 hp (peak) motor I could kill the battery in 6 minutes at WOT. But in normal commuting it would last much longer. I can guarantee you that with a 40 hp motor I'm going to have more than 6 minutes at WOT in a 20 mile round trip commute around town. That doesn't leave anything left for the cruise portion.  | ||
| Nik |
That 40 hp motor has more torque than my xb9 btw. WOT = wheelie time! You just need more batteries. I did the math for 3kWH because that's how much lead acid I could fit to start. | ||
| Sifo |
Just wondering. Did you happen to do the math on the weight of lead acid batteries? That's been one of the huge stepping stones of electrics. By the time you add enough batteries, they either weigh too much or cost too much. | ||
| Blake |
>>> That 40 hp motor has more torque than my xb9 btw. WOT = wheelie time! Torque is relatively feckless if the motor or rear wheel isn't turning fast enough to translate that torque into power. | ||
| Nik |
Isn't that same argument used to discredit Buell's vs japanese inline-4s? My CBR revs twice as high and makes more power than my XB9, but half the torque. The CBR is faster, and obviously the superior motorcycle by this metric. But guess which I prefer? Torque = acceleration. Yeah, that 40hp isn't able to achieve the same top speed of the XB9, but it could zip around town at commuting speeds in a similar manner. | ||
| Sifo |
Torque is relatively feckless if the motor or rear wheel isn't turning fast enough to translate that torque into power. You still haven't answered the question I poised a while back. 50 foot pounds of torque at zero RPM is zero HP, correct? So how does an electric motor even begin to move a vehicle with zero HP? How can it even begin to turn itself? Torque matters, even at zero RPM. | ||
| Fast1075 |
The problem with understanding an electric motor at zero rpm is the formula for horsepower requires a time element to define the amount of work being done. At zero rpm, under full continuous power, the electric motor delivers full torque. At zero rpm, it is effectively potential energy. Once it moves at any speed, the formula for horsepower applies. In an IC spark ignition engine, which uses a throttle plate and consequently varies the intake vacuum depending on throttle position, rpm, and load the effective pumping efficiency can vary widely. That is why part throttle steady state cruise is far more fuel efficient at the same rpm as compared to the engine at WOT. The volumetric efficiency changes. An electric vehicle such as the ones discussed in this thread use pulse width modulation to vary motor output and inversely vary the rate of power consumption. Just like an IC engine, the power consumption is directly related to load and throttle position. My electric scooter that uses a 3kw wheel hub motor draws the full 50 amp limit designed into the controller at full throttle while getting up to speed. Once at speed the cruise can be maintained at part "throttle" and the current draw drops of dramatically at steady cruise. With the throttle closed, there is no parasitic loss from chains or "drivetrain" parts. "Coast" consumes no power. The controller at zero throttle consumes milliamps. At rest, the largest power draw is from the required lighting. I have it set up with selective regenerative braking. The regen is commanded by a momentary switch when desired. I use "coast" a lot. There is no need to waste power getting to the stop sign ahead. Careful use of coast limits wasted momentum. The regen is "first stage brakes". I only use the mechanical brakes when I need to. Of course, with the limits of the 60 volt lead/acid batteries (5 twelve volt 35 AH), it has a relatively short range and longish recharge times. That is why I also bought a new IC scooter for those longer errands that would not be possible on the electric. | ||
| Reepicheep |
We have beat this to death in the past. I can *literally* make 100 foot pounds of torque with a dremel tool, if I run it through a transmission. What matters isn't torque, it is torque (which is how hard you can push) multiplied by speed (how quickly you are turning when you can make that torque). There is a term for torque times velocity. It's horsepower. 40 HP can be a ***HARD ACCLERATING*** bike at lower street speeds. What people mean when they say "high torque makes a great streetbike" is to really say that making good power at lower RPM's is better street bike than making good power at high RPM's. For a race bike, you don't care, just drop down several gears, wind that motor out, and it's all about peak horsepower. For a street bike, having to wind the RPM's out high to get decent power is just tedious. That's why a Uly or an M2 is such a nice street bike. That'll be true of bikes with better torque. With an electric bike, many of which don't have transmissions, just quoting torque is useless. A 100 foot pound torque motor that is only turning at 10 RPM is going to be a total dog. A 10 foot pound motor that can turn at 10000 RPM is going to be blindingly fast. The unit that combines torque for a particular rotational speed is horsepower, and it's ultimately what matters. | ||
| Reepicheep |
Fast posted while I was typing, so don't interpret my post as arguing with anything he said. I agree with all of it. | ||
| Glitch |
I can *literally* make 100 foot pounds of torque with a dremel tool, if I run it through a transmission. Blake is happy with this statement  I love this thread! | ||
| Reepicheep |
It would be an exceedingly dull 100 foot pound motor though... because it has very little horsepower (100 foot pounds, making .001 horsepower, because it turns one revolution per hour maximum). | ||
| Sifo |
Of course we are assuming the little motor has enough torque to overcome the parasitic drag of the transmission.  | ||
| Glitch |
One word. Bigger magnets | ||
| Nik |
I can *literally* make 100 foot pounds of torque with a dremel tool, if I run it through a transmission. You can also do the opposite. The fact remains that the motor I'm detailing specs of is the Motenergy me1003. 72 ft-lb at 500A and 5000 rpm (@100V) max. With a controller able to dump 500A at 100V it's capable of 68.5 hp peak for 10 seconds, before risk of overheating according to the manufactures specs. This power can be sustained longer with better cooling. And this is a motor that's sold as a 30-40hp motor depending on who's selling. The guys racing these just dump even more amps in and get even more power. They also reinforce them and spin them faster. It's all about the controller and handling the heat. You can't compare ICE and Electric motor power ratings side by side at face value. And that 72 ft-lb is basically available anywhere in the entire rev range, as long as the controller can dump in 500A and the batteries can handle the discharge rate. And the controller is a big part of why factory e-bikes have sucked. They limit the current at lower speeds to increase the range.} | ||
| Nik |
Need more torque or power, reliably? You can probably add another motor for less weight (the me1003 is a bit of a porker at 39lbs) than a transmission, but you have to have a controller and batteries that can handle dumping 1000A in. | ||
| Reepicheep |
So what is the street price of the motor and a controller? 60HP peak for 10 seconds is a recipe for fun! | ||
| Nik |
$1500-3000, most of which is the controller. The motor is only ~$600. The Zilla 1k controller is $1975, but it can handle 1000A and can 'shift' two motors between series and parallel, effectively creating a high and low 'gear.' | ||
| Blake |
>>> You can't compare ICE and Electric motor power ratings side by side at face value. Okay, then how about at the rear wheel? Any direct drive electric is going to be a slow-poke when it comes to acceleration at low speed. Put a transmission on it however and the world of high performance opens wide.  | ||
| Nik |
Name one high performance racing e-bike with transmission. Many run dual motors though. | ||
| Reepicheep |
The Brammo Engage. Water cooled, transmission, and definitely on my short list. | ||
| Nik |
Racing bike (aka FIM E-power or TTXGP). Engage is a vaporware consumer product. (Message edited by Nik on April 24, 2012) |
