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Old 05-24-2006, 04:39 PM   #11
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cool

good luck, that is a great project idea. I'll watch every step of the way!
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Old 05-24-2006, 05:33 PM   #12
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Originally Posted by DaX
Krousdb or anyone for that matter - if you know someone FRIENDLY that knows a lot about this type of thing (electronics) that would be willing to talk to me about capacitors and stuff, please let me know. Maybe you know someone who knows a lot about this stuff through hybrids.

I hope all you guys will stay along for the ride (no pun intended), as there will be pictures and videos as we progress through the summer. Thanks in advance to anyone who helps out!
Actually I have played around with capacitors in my Prius. The Prius II comes standard with three 1900 uF capacitors located near the inverter. I thought that if 5700 uF was good, then 42000uF more would be even better! Well after finding the caps on Ebay and carefully placing them in parallel with the OEM traction battery and my aux batteries, I found that they made very little difference at all in EV distance. So I took them out and the capacitor pack sits in my garage collecting dust.

Now the question that I have for you is where the he double toothpicks are you gonna get your hands on one Farad of capacitors? I know that there are ultracapacitors being developed but they arent ready for prime time. To get one Farad of standard can type caps you could add 300-400 lbs to your recumbant bike. True, you will get lots of regen going down the hills but I would hate to be pedaling uphill.

If you can give me more detail on the caps you plan on using, I can start looking through some old emails for a contact for you. I know a real nice guy in Minnesota who might be of some help to you.
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Old 05-25-2006, 11:18 AM   #13
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Originally Posted by krousdb
Now the question that I have for you is where the he double toothpicks are you gonna get your hands on one Farad of capacitors? I know that there are ultracapacitors being developed but they arent ready for prime time. To get one Farad of standard can type caps you could add 300-400 lbs to your recumbant bike. True, you will get lots of regen going down the hills but I would hate to be pedaling uphill.

If you can give me more detail on the caps you plan on using, I can start looking through some old emails for a contact for you. I know a real nice guy in Minnesota who might be of some help to you.
Dan,

I was thinking of using a standard single 1 Farad capacitor, typically the type found in car audio systems. They are about 3" in diameter and 10" long. I have seen for sale up to and beyon 20 farad digital capacitors, but I highly doubt I'll need this much charge storage. I'm looking for a canister type anyhow, so that I can mount it where the water bottle would mount on a bicycle. HERE is an auction on eBay for a 1.2 Farad capacitor (only $40). Is this not what I'm looking for? I don't know what the other numbers in the description mean. Is this type of capacitor only having a large capacitance but not some other property that I need?

Thanks for the help!
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Old 05-25-2006, 12:00 PM   #14
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This could be an interesting project. In a way, the use of a capacitor for energy storage is much more elegant than using a battery. You aren't converting to and from chemical energy, which looks like a plus from the perspective of efficiency. Capacitors tend to lose their charge over time, but I don't suppose that really matters if you just want to make a rider's life easier over the course of a single journey. On paper I really like it!

Then comes the problem of energy storage. I'm a little rusty on this so I just used this little tool on the web:
http://hyperphysics.phy-astr.gsu.edu...ic/capeng.html

If you plug in 1,000,000uF (1 farad) and 12V, you get a total energy storage of something like 72J. If you idealize in a major way and pretend like you can convert it all to work, you are looking at 72N*m. For perspective, that's enough to lift my heavy 825N (190lb) rear end about 8cm vertically.

So let's say you want to build a system that can get you up a 10m hill unassisted and work backward. Working strictly from PE, that's 86kg*9.81m/s^2*10m = ~8400J. (Obviously, this is BS because I'm assuming 100% system efficiency.) By fiddling blindly with that calculator, it looks like a 1F capacitor at something like 130V will store the 8400J.

Yeah, I guess that passes a sanity test. You could achieve that voltage through some kind of transformer, and you would have to make sure that your capacitor is rated for that kind of voltage. But it should be feasible, I think. Yeah? Somebody should confirm that the calculation makes sense because it's been a while since I have worked with silly things like numbers and units.
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Old 05-25-2006, 02:00 PM   #15
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I don't think finding a capacitor that can handle the voltage is a problem... I think the problems are:

*gettng a capacitor to discharge slowly and not all at once
*stepping down the DC voltage from the capacitor to something useful by the motor

I don't think you can use a transformer on DC, can you? What is the DC equivalent of a transformer?
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Old 05-25-2006, 04:50 PM   #16
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Dax, I was using 450V capacitors. I never looked at 12V caps. Caps in the Prius are used to absorb power spikes that the batteries cannot. And as you said, they let go of thier stored energy very, very fast and I know of no way to slow that down to something that you can use.

Sorry I couldn't be of much help. I will PM you with an email address of someone who might be able to steer you in the right direction. Just tell him I sent you.
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Old 07-20-2006, 05:22 AM   #17
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Well, I know I haven't said much on this lately, but we're actually in the process of prototyping! I think we're going to have a working prototype and be testing our regenerative braking abilities this weekend. I'm VERY excited!
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Old 07-20-2006, 09:48 AM   #18
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Dax: Do you have any way you can get some picture's to post. I'd be interested in seeing what you guy's have been able to do.
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Old 07-20-2006, 12:05 PM   #19
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Sure, I'll try to take some pictures tonight. For now here are some drawings of what we're working on. Below are two drawings of the crank assembly for the bike - one is an exploded view and the other is a cutaway. We had to rebuild the crank assembly because we wanted to drive the system from the front sprocket set and thus we needed to remove the one-way clutch from the rear and build our own in the front.

The white/grey disc is the stock drive sprocket on the bike. The purple sprocket is the one that will be driven by the motor at a reduction rate of 1:8. Both sprockets are to be fastened to the turquoise hollow shaft. The crankshaft (blue) will be welded to the pedals and fit into one-way clutch bearings (red) which are fixed to the inside of the sprocket shaft (turquoise). This setup allows the user to pedal forward (locking the clutch bearings) and spin the back wheel, or to pedal backwards and spin the pedals independent of the sprockets.

We're still fighting with the machine shop over the bracket for the motor, and McMaster-Carr still hasn't sent me my chain. I think we'll have it all together in time though.



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Old 07-20-2006, 03:03 PM   #20
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machine shop, on time? McMaster, on time? Good real world experience!
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