Capacitor feedback needed for acceleration project

1379 Views 4 Replies 3 Participants Last post by Duncan, Dec 5, 2010

ElectriCar

Discussion Starter · Dec 4, 2010

I am pondering adding another bank of caps to my S10. I added 10,000uf on advice of an engineer a while back. If any of you have any comments or suggestions on this I would greatly appreciate it because I know many of you can give me some good info.

The reason I'm looking to do this is that if I accelerate normally I draw 250-350 amps for about 5-7 seconds off my 144V pack. I know this EATS battery capacity , due to P (peukert) losses so usually I poke along and accelerate slowly, pissing people off along the way, which I don't care for.

OTOH I don't like wasting power and shortening my range as well!

I was wondering how much capacitance I would need to split the current between the caps and the pack. This also would do the same thing climbing all these hills along my 11 mile commute that increases my amp draw from about 50A on level ground to 200-250A up a typical hill in the area.

I'm hoping to eventually power an EV with Supercaps if they ever become reality but for now I am planning on using conventional caps due to their voltage capacity. OTOH, I could parallel a super cap with each of my 24 batteries if I could get some rated at 8V or so.

Any comments or suggestions welcome!

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major

· #2 · Dec 4, 2010

ElectriCar said:
I am pondering adding another bank of caps to my S10. I added 10,000uf on advice of an engineer a while back. ............Any comments or suggestions welcome!

Hi Electric,

10,000uf isn't going to do much. You might find some info to help you in this thread.

http://www.diyelectriccar.com/forum...apacitor-eye-candy-25994.html?highlight=candy

major

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ElectriCar

Discussion Starter · #3 · Dec 5, 2010

Took a trip to town tonight and on two hills I was pulling 250 amps or so for 20-35 seconds. I'm not sure the current cap technology can handle 125A for 20-30 seconds. Though any help would be better than nothing I guess. Just hate to spend a bunch of money for not very much benefit.

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major

· #4 · Dec 5, 2010

ElectriCar said:
Took a trip to town tonight and on two hills I was pulling 250 amps or so for 20-35 seconds. I'm not sure the current cap technology can handle 125A for 20-30 seconds. Though any help would be better than nothing I guess. Just hate to spend a bunch of money for not very much benefit.

Ultracaps could do that much energy. They would be large and expensive. But could fit into your truck. And could be made to work well. But to give you some idea:

144V * 125A * 25s = 450,000Ws (or 450 kiloJoules). About 1/3 of what I used for that bus for the ultracap. In comparison, that 10,000uf cap stores 103Ws.

For the money, a lithium battery would be a wiser choice by far. Unless you plan to climb a million hills with truck

major

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Duncan

· #5 · Dec 5, 2010

Hi Electricar

You want 125 amps for 20 seconds while your pack may sag 10 volts

125 x 20 = 2500 divide by 10 = 250 Farads

you have - 10,000 micro farads = 0.01 Farads - your current capacitors can only give you 1 / 25,000 of what you want

ie 1/10th of an amp for second

Ultracaps are measured in Farads - unfortunately you need to put them in series to get the voltage

if you need 10 ultracaps to get your pack voltage the capacity of the string is reduced,

10 off 250 Farad ultracaps in series have a capacity of 25 Farads so to achieve your 250 Farads you would need 10 off strings of 10 250 Farad capacitors

100 - 250 Farad capacitors!

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