36V 500W rear hub motor folding spare bike - supercap experiment???

bakaneko

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Nov 16, 2015
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guys, i know im not done with other build yet but i have this spare 500w rear hub motor just sitting there and i had 2 issues with my 72v 3kw cyclone that is making me think i should make a spare bike incase something breaks in my main bike. i would just use one of the batteries to power the spare bike. and, i am thinking of a 26" folding bike in case weather is bad and i need to be dropped off or if i want to go far to bike. but, you know i need to tinker... and, i think i also found a 1000w 38a 36v controller for cheap.

i want to try to integrate a supercapacitor setup with the 36v lithium battery where the battery will charge the supercap and then the supercap will dump the amps to get up to speed fast and then the battery will take over at speed. ive seen supercaps 15-16v for $20 but if they can be wired in series that is 45-48v and will my 33-42v lithium battery will be able to charge that or i need some type of converter?

here is what im thinking...
- 26" folding bike
- 36v 16ah or 24ah lithium battery from main bike (when main is in service)
- 45-48v supercap with 5-8 wh
- upgraded 38A controller to go about 30 mph max, 20-24 cruise

what do u think? feel free to tell me this is stupid. i am fine doing it without the supercaps; i figure i am not gonna craiglist the motor for peanuts when i could use a spare bike.
 


FurryOnTheInside

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Sep 23, 2013
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I've never heard of the things but I assume it charges up at extremely high current as soon as you plug in, so I'm sure you'll need a pre-charge resistor to prevent the sparking as you plug in your battery.

(That is about as far as my knowledge of Ebikes goes at this point and you probably knew about pre-charge resistors already, but I have to assume it's worth stating just in case (lots of people will see this thread in the future and many of them won't know).)
 

JerboaJohn

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Jul 29, 2018
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caps in series add their capacity together in milli amp hours, like just a fatter cap. in parallel, they directly add each capacity. voltage discharge stays the same as it's built in. you'd have to get a 36v rated cap.
tho I havn't did ebikes, I played with electronics. caps can let go of their charge like RIGHT NOW and you have to limit the current to the motor or possibly burn it out. you can do it, just need a resistance between cap -> resistor ->throttle (controller)-> motor
sounds very expensive! but that's relative I guess. the cap and the resistor block (500W + rated)
 

bike4life

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Mar 19, 2018
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caps in series add their capacity together in milli amp hours, like just a fatter cap. in parallel, they directly add each capacity. voltage discharge stays the same as it's built in. you'd have to get a 36v rated cap.
tho I havn't did ebikes, I played with electronics. caps can let go of their charge like RIGHT NOW and you have to limit the current to the motor or possibly burn it out. you can do it, just need a resistance between cap -> resistor ->throttle (controller)-> motor
sounds very expensive! but that's relative I guess. the cap and the resistor block (500W + rated)
well just curious i dont know much about electronics but if u have a resistor, how would that limit current, it only creates voltage drop thats all. Plus with a resistor u are wasting 500w of energy as heat and your battery is 1000wh so it would drain fast.
 

bakaneko

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thanks for the comment. guys, yeah, i mean part of this experiment for learning is my own understanding of supercaps and applications to electric vehicles (EVs) beyond just bikes and into cars. best case scenario is that the supercaps with their large cycle life take the brunt of the large amps needed to accelerate from a stop and then deplete and the lithium batteries take over once at speed, which require much less power and stress. and then when slowing down the lithium batteries charge the supercaps at low-moderate amps. and cycle repeats.

i talk with an endless sphere and ive seen literally no threads actually trying it out more just talking about it. i think this might be one of those horrible ideas. but, i am not defeated yet. i will ask some youtubers that made supercap/lithium car starter crank builds what they think.
 

JerboaJohn

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you'll be the test case haha everyone will base configuration off your initial results and improve,, supercaps are kinda scary. not many mess withem.
controller limits some current, it'll fry first but as long as it's rated for the motor you're using and you don't go over volting, you'll be ok. 36v are lighter duty and don't pull godawful amps. most ppl into upgrading go 48v + setups since 1000w isn't scary fast and the controllers are more beefy n handle some over-volting
 

bakaneko

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Nov 16, 2015
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Well, Tesla just bought Maxwell Technologies, a major manufacturer of supercapacitors. I guess I will have to race Tesla now in getting this done~! :oops: Jeez I hope Tesla doesn't corner the market and prevent Maxwell capacitors to market for the common person.
 
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