[sinobread]

I'm new to forum, just learning how to build EV - it is cheaper for me, because I'm living in China.

searching for batteries in Taobao.com, chinese ebay

What I found:

12v, 200Ah, 1088rmb (173$), other places similar power selling for 788RMB

http://item.taobao.com/item.htm?id=1...56e612ca809465

Lithium, 12b 50Ah, 2650rmb, (424$), weight 10kg

http://item.taobao.com/item.htm?id=1...3k1_1783564695

Chinese now using ultra-capacitors batteries, less expensive and more rechargeable, up to 100 000 times

http://english.chinabuses.com/news/2...icle_5505.html

I'm also searching for ultra-capacitors to build own batteries, it may be much less expensive

2.5v, 630F, 13RMB
http://item.taobao.com/item.htm?id=9..._u=nl7jn38e865
2,5v, 2000F, 60RMB
http://item.taobao.com/item.htm?id=1..._u=nl7jn38be21

http://www.alibaba.com/product-gs/51...capacitor.html
10000 F, 4 Ohms
2.7V3000F0.45 Oh, 63×140screw
any feedback will be greatly appreciated

Jan

[ricklearned]

Jan,
I envy you, being close to the battery resources. I don't know much about ultra capacitors but others might be able to help. This is a global forum and is a great way to share knowledge.

My installation uses an AC motor and controller that was programmed to work with it. I would be happy to share my limited knowledge of that motor/controller combination.

Rick

[sinobread]

Thanks Rick

not long time ago I was living in your area, Riverside-Ontario

Jan

[PStechPaul]

I can help with some of the technical details. For instance, from the weight of the vehicle and the inclines you need to climb and the speeds you need, and the gear ratios from the motor to the driving wheels (and their outside diameter), I can determine the motor torque and power. This translates to a certain size motor with a certain number of poles or nominal RPM. Then you need to determine your average driving needs in terms of watts/mile, and the maximum range you need before recharging.

From this you can find the total energy needed for your battery pack. There are pros and cons to lead-acid vs lithium and generally the LiPo is the best choice for long-term cost and performance.

You also have a choice as to what motor and controller you want to use. I prefer 3-phase standard induction motors which can be controlled with a standard industrial VFD, and require a battery voltage of at least 300 VDC. Or you can use a DC-DC converter to get the voltage from a smaller number of batteries. That is also my choice and I am working on a design that can do that economically and reliably.

The ultracapacitors can be very helpful for short-term surge power and efficient regeneration for braking. AFAIK this is not possible with series-wound brushed motors but other motors can also work as generators and dynamic brakes. The energy in ultracaps is determined by the formula:

E=0.5C*V^2

This is in watt-seconds, or joules. So your 2000F 2.5V capacitor can store 6250 W-seconds. or about 2 W-hrs. Generally about 300W-hr per mile is used, so to get a 30 mile range you need 9000 W-hrs. This would require 4500 of these capacitors and 60*4500=270,000 RMB = $46,000. You would need to connect them in banks of about 120 each for 300 VDC. This expense is probably 10 times that of LiPo, but they will last 20 times longer.

These are rough calculations. You need to factor in efficiencies and how much of the potential energy in the batteries and/or ultracaps you can extract. Batteries tend to have a fairly level voltage until maybe 50-60% of capacity has been used and then the voltage drops and impedance rises so you can't get much more out. Capacitors have a logarithmic discharge into constant power load so the voltage is 1/2 when 3/4 of the energy has been used. And most controllers will not operate below about 70% of their nominal input voltage, so a VFD that normally operates on 320 VDC will shut down below 200VDC.

You should be able to work out these calculations for your own needs, or there are spreadsheets and calculators that can help. Let me know more, and good luck!

[sinobread]

Thanks Paul.
Definitive, I will need help
What stopping me now?? Why conversion is soo expensive when on the markets are new electrical cars staring from very low, 3000-5000$? Of course, they may be completely different classes, but still. I also believe, that I can find more economical batteries, still don't know prices for 100 kF, even seen adv for 200 kF.

Chinese are having double pricing - one for international market mostly by traders, other for locals. Alibaba are for intentional market, I already found several product where prices are double what Chinese are paying.

Thanks for calculations, it is very helpful

Jan

[sinobread]

Ultra capacitors, it can be find for less

2000F, 2.3v, 36 RMB, $6.00+
http://item.taobao.com/item.htm?id=14860869766

other, Place of Origin: Zhejiang




Capacitance: 1/2-10hp

Part No.
Operation Voltage(VAC)
Recommended Range(HP)
Increase In Torque(%)
SPP*
90--277
1/2 to 10
250%
SPP5
90--277
1/2 to 10
300%
SPP6
90--277
1/2 to 10
500%