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Super capacitors to capture regenerated power.


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Given that I am riding mostly in urban situations among pedestrians during day time, I often have to start and stop a lot, crossing roads, cars etc... Sometimes the battery is noticeably drops in these conditions.  I wonder if having a super capacitor in parallel would help me extend range, and keep the unicycle responsive in acceleration/breaking even when the voltage is lower.

I am seeing on Aliexpress v16 500F super capacitors for about USD165.  I've not seen anything at 84V, but want to find out if anyone has done this and how did it go?

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In general. Capacitors become more expensive the higher the voltage.
I have been thinking the same, but it will be expensive. And probably not worth it.

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Yes, or simply putting them in series to reach the desired voltage adds.... but even with what I list above it would only be 6 x US$165. The problem is that it would be bulky so we need one or of 84V or 48V with lower farads.... can't I can't seem find anything.

I did the calculation and the 16V 500F can store 18Whr....

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I have considered it before. Those 500f super capacitors are rated for 2.7 volts each so you would need something like 40 individual ones for a 100v wheel and with each super cap being 40mm diameter and 60mm high, space becomes an issue. They should technically be able to fit in an Rs if you put some sort of external enclosure on the outside of the wheel. I have done the math on the power gains and I can post them tomorrow if I find the paper.

There is also the issue of what happens when the super caps are charging. You could connect them permanently in parallel to the batteries, but then they will slowly drain the battery since capacitors lose their charge over time. Then you risk over discharging your battery. You could have a switch to connect/disconnect them, so they can drain without draining the battery, but then you are essentially shorting the battery until they are charged (which would be several seconds). That is not good. You could put a resistor, but it would have to be rated for a ton of power and it would defeat the purpose of having a supercapacitor. The solution I came up with is to charge the battery and super capacitor separately and then use a high current switch to connect the two when they are at the same state of charge. This would be a pain in the butt and you wouldn't be able to just grab the wheel and go. Of course even when you are riding and you have drained the capacitors due to an acceleration or something, the battery now has to charge them back up in addition to powering the wheel. Overall I think it would just be a pain in the butt and an extra stress on the batteries.

I have been toying with the idea of using the smaller 100f super caps instead, which only really solves the space problem, but then I only have 20% of the gains (actually the same power gain for 20% of the time). I think an additional cell group in parallel would be better, but now we are playing with lithium batteries, which is a fire hazard if you don't know what you're doing and is also more expensive so I think I'd rather just save for a more powerful long range wheel.

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  • 2 weeks later...

what if we replace one or two cells with a one or two super capacitors, and then wire them in parallel....

it would always be the super cap charging and discharging first.... as it has the lowest resistance.... so you would have a bit of hybrid system....

what you think?

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When capacitors fail, do they short circuit or open circuit?

I'm guessing they short circuit and that's a bit scary. You would add another failure mode to the wheel.

If they're oversized then it would be safe I guess. Maybe a special brand that works fine under harsh environments etc. Vibrations, temperatures...

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Posted (edited)
48 minutes ago, alcatraz said:

When capacitors fail, do they short circuit or open circuit?

They fail both short and open but when they fail short circuit, they can burst (heat boils the electrolyte—probably not a thing with a supercap) and that open circuits them. There are little score marks in the part's 'can' so it'll split open in a more predictable manner when this happens... it's typically fail short unless the lead breaks off or has a solder joint problem (usually stress from vibration or thermal cycling or no-lead solder or bad soldering)

Edited by Tawpie
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If you are adding 2 super capacitors per series... maybe you can sneak them in....

 

I think we should be discussing how a super capacitor can charge and discharge faster than all other cells... and improve the batteries performance.... extend range, and life time.

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