How much power would i theoretically need?

[flik9999]

Hey so I currently run a 250w fronthub cyclotrocity. Its ok gets me about 20 mph on flat but I want a bit more.

Would 350w or 500w be enough to get me 30 mph if I peddle hard?

Also whats the problem with direct drive? Do they stop you peddling then or is cycling them fibe on power mode 1?

 

[danielrlee]

There are five ways to increase your top speed:

1) Increase voltage.

2) Swap the motor for a faster wind.

3) Swap the controller for one that features field weakening.

4) Increase your gearing (larger wheel size with a hub motor).

5) Pedal harder.

The first four methods will increase the load put on the rest of your system, so may require further upgrades.

Simply increasing wattage (by increasing amperage) will not increase your top speed unless there was insufficient power to reach your top speed previously. It will however give you greater speed while travelling uphill and better acceleration all-round.

EDIT: You need a minimum of 900W to overcome the air resistance to reach 30mph, but more specifically, you need to be running sufficient voltage for your motor to reach this speed.

 

[Wheel-E]

Hey so I currently run a 250w fronthub cyclotrocity. Its ok gets me about 20 mph on flat but I want a bit more.
Would 350w or 500w be enough to get me 30 mph if I peddle hard?

I'm running a 500W Cyclotricity Stealth - same parts as the 500W kit. With and without the shunt mod adding more current it naturally wants to sit around 23MPH - 25MPH if I pedal reasonably hard on the flat.
Even lifting the wheel off the ground it maxes out at 27.5MPH.
Looks like you may need 1000W and moving to a 48V system which will mean you'll need to replace your current battery.

 

[Deleted member 4366]

Forget about these 350w/500w designations. tThey're pretty well meaningless. In simple terms, power is volts times amps. You need around 900w to do 30 mph. That's at the wheel, so something like 1200w from the battery. At 36v, that's about 30A, At 48v, it's about 22A. That's the starting point. Then you need a motor that will spin to about 35 mph without load to get meaningful power at 30 mph. Additionally, it needs to be able to run at that power without over-heating during all your riding conditions.

It's not really something you can do by numbers because you have to juggle all sorts of parameters at the same time. You can use the Ebikes.ca/simulator to see what happens under different conditions, but you only see one set at a time. Really, you need to have quite a bit of experience riding bikes with all the different motors to get a feel of what will work and what won't.

For an MTB type bike without pedalling too hard, you need something like a 1000w direct drive motor kit with 48v battery and 25A controller or a Bafang BBSHD at with a suitable 48v battery.

For a light-weight slim bike with 700c wheels and moderate pedalling, a BBS02 at 48v would probably be enough or a Q128C at 52v and 20A

For a road bike, very hard pedalling and streamlined clothing you could get there with a high speed 36v geared hub-motor at 48v and 17A.

 

[anotherkiwi]

Hey so I currently run a 250w fronthub cyclotrocity. Its ok gets me about 20 mph on flat but I want a bit more.

Would 350w or 500w be enough to get me 30 mph if I peddle hard?

Also whats the problem with direct drive? Do they stop you peddling then or is cycling them fibe on power mode 1?

The easy way to get high speed on flat roads is the correct gearing and a crank drive - I get 45 km/h tops from a "250 W" GSM so a 350 or 500 W BBS02 should be enough. I have an all up bike + rider weight of just a bit over 100 kg.

http://bikecalculator.com/index.html

This says you need about 500 W total so definitely doable with a motor providing 350 W through the pedals.

 

[flik9999]

On another note. Im not sure if im doing my maths correct but would I be able to get some more power out of my current fronthub if I switched to a 48v battery or would I just fry my controller or motor?

If im correct my motor would go up by 33% to 333 Watts. Or am I incorrect and this would not be the case?

Could I also get a bit more power out my current system if I went and bought the 500W controller from cyclotricity?

 

[flik9999]

Looking at the website my current controller (250w) has a max amp rating of 14 (Maybe that would be 14amps X 36v for 504 watts. The 500w version has max amps of 22 amp current (22x 36 for 792 watts).

What im unsure of is if this has any relevance to the size of the battery I can run. So if I was goign to switch to a 48v battery would I need to get a small one (10 amps 48v battery is 480 watts, comparable to a 14ah 36v battery)

 

[anotherkiwi]

On another note. Im not sure if im doing my maths correct but would I be able to get some more power out of my current fronthub if I switched to a 48v battery or would I just fry my controller or motor?

If im correct my motor would go up by 33% to 333 Watts. Or am I incorrect and this would not be the case?

Could I also get a bit more power out my current system if I went and bought the 500W controller from cyclotricity?

Your controller would need to be a 48v one or a 36/48v one. You risk blowing a component in your 36v controller the motor isn't at risk.

No your motor will be 250 W nominative as it is now.

Controllers are rated in Amps not Watts.

 

[anotherkiwi]

Looking at the website my current controller (250w) has a max amp rating of 14 (Maybe that would be 14amps X 36v for 504 watts. The 500w version has max amps of 22 amp current (22x 36 for 792 watts).

What im unsure of is if this has any relevance to the size of the battery I can run. So if I was goign to switch to a 48v battery would I need to get a small one (10 amps 48v battery is 480 watts, comparable to a 14ah 36v battery)

Your controller is a 14 Amp controller, your motor is a 250 W nominative motor.

The important part of any battery is the cells that are inside. If they are low Amp cells they will not be able to provide enough Amps to a 22 Amp controller. The only way that would be possible is to have very many of them in each parallel group.

 

[flik9999]

Is there a way to check if its 36/48 compatable? On the website they sell 250w/500w controlers that are 36v and a 1000w 48v controller. So assuming my current controller is 36v only would buying the 1000w controller be the correct next step?

 

[Nealh]

Open the controller and have a look at the voltage rating of the large capacitor adj to the shunt, if it says 60v you should be ok. If the controller fries then simply upgrade it.

 

[anotherkiwi]

Please! Controllers are rated in volts - input, and Amps - output. Motors are rated in Watts. It is very important that you use the correct terms so that every one understands.

The 500 W kit they sell seems to be a direct drive motor, not the same as your 250 W geared motor. Is the 21 A controller compatible with the 250 W motor? That is the question you need to ask them.

 

[Deleted member 4366]

You can't take as much power as you like out of the battery. The battery, controller and motor all need the same ratings, i.e. if you want to use a 22 amp controller, the battery has to be able to supply that current continuously, so you need one rated at about 30 or 40 amps max. Then, the motor needs to be able to handle that current, which a small motor with a heavy rider won't.

Basically, you need a new motor, battery and controller. The 1000w kits with the big direct drive motors can just about manage 30 mph, but the batteries are always cheap and not up to the job, so they don't last long and don't give you much range (10 to 15 miles).

It would be nice if we could all get extra power for nothing, but that's not possible. 30 mph is a lot more expensive than 15 mph.

There is one way you can get your bike over 30 mph, which doesn't cost much. Take it to Beachy Head and chuck it off. It should get over 100 mph before it hits the rocks.

 

[Woosh]

Hey so I currently run a 250w fronthub cyclotrocity. Its ok gets me about 20 mph on flat but I want a bit more.

Would 350w or 500w be enough to get me 30 mph if I peddle hard?

Also whats the problem with direct drive? Do they stop you peddling then or is cycling them fibe on power mode 1?

You need about 1000W mechanical power to maintain 30mph on flat roads.
Try to work out how fast you can pedal without motor, then go to http://www.ebikes.ca/tools/simulator.html?axis=mph to look up (on the load curve) how much your legs produced. The electrical system will need to produce the difference for you to maintain the desired speed. From that, you work out how many Amps you need, typically 36V x 25Amps.
You'll need to wear a helmet and buy insurance if you ride your e-bike over 16 mph.