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-   -   Are Capacitors Legal? (http://www.chiefdelphi.com/forums/showthread.php?t=40236)

KenWittlief 28-10-2005 17:11
Re: Are Capacitors Legal?
 
Quote:
Originally Posted by Kyle Fenton
I would also think that it would be a safety issue. If someone touched that capacitor at the terminals it could seriously injure them. Also I don't think capacitors that big can handle that much vibration, which would make them impractical to use.
not if you touched it, its still only 12VDC if its charged from the battery

but if they were shorted (during a collision for example) there would be a huge arc - the caps might explode, frame metal or heavy cable would turn into a shower of sparks and molten metal.

Dave Scheck 28-10-2005 19:02
Re: Are Capacitors Legal?
 
Quote:
Originally Posted by mechanicalbrain
Yeah your right it violates the first one but the second one? It is not providing power directly to the motor but through the victor.
Yes, but I believe that the intent of that rule is that there is to be nothing but the correct gauge wire and a victor/spike between the RC and the motors. This is FIRST's way of drawing a line in the sand to avoid controversy later.

Quote:
could I possibly power the capacitors seperately and then apply power to motors? Maybe with a second connection and a switch to apply a physical connection (A switch would also allow my to disengage the capacitors from the motor if needed)?
I'm assuming you mean for a non-FIRST application since this definately violates the second rule that Dave quoted.

mechanicalbrain 28-10-2005 19:26
Re: Are Capacitors Legal?
 
Quote:
Originally Posted by Dave Scheck
I'm assuming you mean for a non-FIRST application since this definately violates the second rule that Dave quoted.
But of coarse. Ive been planning a solar robot for some time and I would rather use a capacitor over battery.

EricH 28-10-2005 20:10
Re: Are Capacitors Legal?
 
Quote:
Originally Posted by KenWittlief
not if you touched it, its still only 12VDC if its charged from the battery

but if they were shorted (during a collision for example) there would be a huge arc - the caps might explode, frame metal or heavy cable would turn into a shower of sparks and molten metal.
I've seen a robot battery get a short on the charger. The charger clips touched and eventually fused. Then that team went to take the battery off the charger. Can you say sparks all over? To make matters worse, the battery was supplying the power after the charger was unplugged. This went on until someone figured out how to get it off completely.

Al Skierkiewicz 29-10-2005 13:23
Re: Are Capacitors Legal?
 
Quote:
Originally Posted by mechanicalbrain
Yeah your right it violates the first one but the second one? It is not providing power directly to the motor but through the victor. But the point is mute since it violates the first rule. Oh well this is starting to look better suited for a private robot. Just another idea I had been throwing around. Oh Mr. Skierkiewicz could I possibly power the capacitors seperately and then apply power to motors? Maybe with a second connection and a switch to apply a physical connection (A switch would also allow my to disengage the capacitors from the motor if needed)?
There just isn't enough advantage to add capacitors in this application. Yes they store a large amount of energy but you need to look at how that energy ports out. the reason they are used in amplifier design is that the impedance of the power system just isn't low enough to give good regulation on power peaks. (Particularly those low rumbles in the sub woofer that people are so fond of.) If you were designing a robot where the power source was very far from the motor with a smaller guage wire and the motor only needed high current for very short periods of time, this might be a good alternative. For a common sized robot with normal wiring, it just isn't worth the weight.
For those skeptical few that still are wondering, try to visualize a 3800 joule discharge with a rise time of microseconds and a duration of 1 msec...

KenWittlief 29-10-2005 15:30
Re: Are Capacitors Legal?
 
ok, Im closing my eyes

trying to visualize one millisecond....

one thousand one, one... nope that was 1200 milliseconds

Ill have to get back to you on this :^)

CJO 29-10-2005 15:53
Re: Are Capacitors Legal?
 
I had a wicked smile on my face . . . 3888 J, 1ms, Rock and Roll!!

(Of course, your robot might well be a pile of goo afterwards, but it would be a cool pile of goo)

I think that these are really meant more to, for instance, store the power from regenative braking, than as an actual power source, they would certainly be no good in high voltage applications.

KenWittlief 29-10-2005 19:36
Re: Are Capacitors Legal?
 
Quote:
Originally Posted by CJO
...they would certainly be no good in high voltage applications.
one of the things you always remember, as an electrical engineer:

the first time a capacitor blows up in your face!

usually because it was connected backwards, or powered above its rated voltage.

They started putting pressure relief lines in the tops of electrolityic caps several years ago, so all the material will blow out the top

they use to go off in all directions.

Alan Anderson 29-10-2005 21:55
Re: Are Capacitors Legal?
 
Quote:
Originally Posted by KenWittlief
one of the things you always remember, as an electrical engineer:

the first time a capacitor blows up in your face!
Ah, yes, the electronic confetti generator. Not all that different from the flaming resistive element, or the noise emitting diode.

Al Skierkiewicz 29-10-2005 22:22
Re: Are Capacitors Legal?
 
Quote:
Originally Posted by KenWittlief
one of the things you always remember, as an electrical engineer:

the first time a capacitor blows up in your face!

usually because it was connected backwards, or powered above its rated voltage.

They started putting pressure relief lines in the tops of electrolityic caps several years ago, so all the material will blow out the top

they use to go off in all directions.
Too bad the valves leak juice sometimes and the smell, you never forget that do you? If the 54 farad were to leak I bet it would disolve a hole in your trunk big enough to drop the spare through.

ConKbot of Doom 30-10-2005 03:13
Re: Are Capacitors Legal?
 
The one thing that people aren't considering is the ESR of these huge capacitors. The super-capacitors have a high ESR, so massive discharge currents aren't really that big of a threat with them. The highest discharge current Ive seen with super capacitors was 100A, and that was a rather expensive, bulky, and weren't anywhere near the capacities you guys were talking about. Any links to datasheets for these 54F caps?

Oh, and car-audio caps arent super caps, they are just really friggin big electrolytics. That is why they work for car audio purposes.

sciguy125 30-10-2005 10:26
Re: Are Capacitors Legal?
 
Quote:
Originally Posted by ConKbot of Doom
The highest discharge current Ive seen with super capacitors was 100A, and that was a rather expensive, bulky, and weren't anywhere near the capacities you guys were talking about.
The datasheet for the 58F cap said it has a short circuit current of 1500A. The 430F said 5000A. I'm tempted to make a rail gun now. Or maybe one of those coin smashing things.

Quote:
Originally Posted by mechanicalbrain

CJO 31-10-2005 13:56
Re: Are Capacitors Legal?
 
I would love to make one of those coin smashing things, now all I need to do is convince the physics deprtment to fund me. ;}

Al Skierkiewicz 31-10-2005 14:19
Re: Are Capacitors Legal?
 
Quote:
Originally Posted by ConKbot of Doom
The one thing that people aren't considering is the ESR of these huge capacitors. The super-capacitors have a high ESR, so massive discharge currents aren't really that big of a threat with them. The highest discharge current Ive seen with super capacitors was 100A, and that was a rather expensive, bulky, and weren't anywhere near the capacities you guys were talking about. Any links to datasheets for these 54F caps?

Oh, and car-audio caps arent super caps, they are just really friggin big electrolytics. That is why they work for car audio purposes.
In looking to their website, ESR is about the same as the internal resistance of our battery, 11mohm.

ConKbot of Doom 31-10-2005 15:18
Re: Are Capacitors Legal?
 
Quote:
Originally Posted by Al Skierkiewicz
In looking to their website, ESR is about the same as the internal resistance of our battery, 11mohm.
Looking at the datasheet now... some pretty slick stuff. That definitely would be dangerous...

They really have improved on ultracapacitors lately :D

EDIT: bah I missed that link earlier..


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