Hey there /diy/
I am working on putting together an electric booster pack for a bicycle, but I want to use a capacitor instead of batteries.
Planning on using a 24 V, 350W hub motor and a 2F capacitor from car audio thats 12v, 24v surge rating.
I want to charge it using my motor going downhill, and boost uphill.
Could I use the 24v surge capacitor and assume I can charge it to sustain 24v for an extended period of time?
Don't wanna blow my knee off - ty for response.
Pic related
>>964449
Not a good idea. Generally speaking, one should de-rate capacitors based on the nominal rating, i.e. use a >24V nominal cap if you expect a 24V input. Trying to use a cap based on its surge voltage would be terrible for the health of the capacitor, assuming it didn't blow up on you.
>>964449
Also, according to this guide, "Rated surge voltage is the maximum DC overvoltage to which the capacitor may be subjected at 25 ºC for short periods not exceeding approximately 30 s at infrequent intervals of not less than 5 min."
http: //www.cde.com/resources/catalogs/AEappGUIDE
>>964453
>>964452
Shit ... ty anons - here is a pic of a bike hub motor
>>964449
>extended period of time?
Unless I'm doing the math wrong, you're going to get like three seconds of run time out of that capacitor, overcharged, for your motor.
>>964457
Yeah i think you are right - do you think I could play with charging in parrallel vs discharging in series to increase run time - 10 - 15 secs, I could live with - 30 secs would be ideal
Video somewhat related https://youtu.be/z3x_kYq3mHM
>>964449
1. Why not use a supercapacitor instead? They're designed for this sort of duty, regenerative braking that is. Of course I don't think the motor type you're referring to can be used for braking? It's brushless, right? The controller for the motor itself would have to specifically support regenerative braking, and there would have to be somewhere to attach a storage device (like a supercapacitor) to store the braking energy.
2. For all the trouble you're going to, you may as well get a moped, scooter, or small motorcycle. Then you'd have a full set of lights and signals, and brakes that are intended to stop you quickly from higher speeds than typical for a bicycle.
3. Or maybe stop being lazy and pedal your bike instead of bolting all this heavy stuff to a frame not designed for it in the first place? None of these 'conversion' kits have safety in mind, just getting your money. There's a dozen reasons it's a bad idea.
>>964600
>1. Why not use a supercapacitor instead?
He said he wanted to use a capacitor storing 2 farads. I'd qualify that as a supercapacitor.
>2. For all the trouble you're going to, you may as well get a moped, scooter, or small motorcycle.
E-bikes are subject to the same laws as regular bicycles, mopeds and scooters are much more strict and often require licenses.
>3. Or maybe stop being lazy and pedal your bike instead of bolting all this heavy stuff to a frame not designed for it in the first place?
I take it you don't ride a bike very often, or very far. I used to commute to work on an e-bike, and a regular bike before that, and riding the regular bike up hills, especially after a long ride, made me want to kill myself.
>>964449
Use batteries faggot. Laptop batteries usually hold 6-8 high quality 18650 cells that you can hook up into a pack.
>>964449
>>capacitor instead of batteries
bad idea m8 here's why
that capacitor stores:
0.5 * 2 farads * (24 volts)^2= 576 joules
which is enough to power the motor for:
576 joules/ 350 watts = 1.6 seconds.
You need more energy storage. Do the math. If you tell me the combined weight of you and your bike and can show you why you need more.
>>964610
2 farads for something that big ain't great. Pic related is 1 farad.
Get some ultracapacitors on ebay. For just a bit more than the price of that shitty audio cap, you can get an ultracapacitor bank
>>964619
Op here
Ty for response - its been a while since I ran the number so I forgot how to ... lets assume 250 lbs for me with bike
>>964600 it is brushless - how hard is it to make my own controller? The ones online are bulky and have useless shit I don't need.
I am going through this trouble because its an interesting project. I already have a motorcycle.
>>964610
I don't want to deal with plugging my bike in/swapping batteries. If I use capacitors, I'll be able to charge up relatively quickly the first downhill I encounter.
>>964707
Making your own brushless controller, while not impossible, would be a lot more pain than it's worth, IMO, especially when it inevitably shits the bed due to vibration/rain halfway between point A and B.
>>964449
>>964619
>1.6 seconds
That's a pretty conservative estimate too.
As the capacitor discharges, it's voltage will drop. If you're actually serious about this you'll probably want to charge the capacitors to value higher than 24V (V_c) and then hook them into the input of a driver that provides a steady 24V output for any input in the range 24-V_c.
>>964707
> it is brushless - how hard is it to make my own controller?
If you need to ask how, it's too hard.
Basically, you need to generate three-phase AC with variable current and frequency as determined by the operating conditions. For regenerative braking, you also need to make the circuit able to run in reverse.
>>964707
250 lbs = 1112.06 N
Energy = Force * Distance
In an ideal world that capacitor will take you uphill by:
576 joules/ 1112.06 N= 51.8 cm.
i feel like a brushless motor on something like this, having no gear ratio. wouldn't provide enough torque to be of any help
