Are Capacitors Legal?

[mechanicalbrain]

FIRST Q&A is down so I wanted to double check this. Capacitors are in fact illegal right? Are they considered an alternate power source?

[ahecht]

I can't speak for the 2006 rules, but in the 2005 rules, as far as I can tell, capacitors are legal if they are not used as a power source (i.e. they follow all the rules pertaining to custom circuits). You should be fine using them in an RC filter circuit in custom electronics.

[mechanicalbrain]

Great I have a 54 Farad capacitor bank I wanted to use and I didn't want to go buy a couple and have it be illegal. I think on second thought though ill wait until kickoff to see what Dave Lavery pull out of his sleeve this year. :D I'm looking forward to it.

[ahecht]

Great I have a 54 Farad capacitor bank I wanted to use and I didn't want to go buy a couple and have it be illegal. I think on second thought though ill wait until kickoff to see what Dave Lavery pull out of his sleeve this year. :D I'm looking forward to it.

As per the custom circuit rules, you could use that capacitor bank, but you could never use that stored power on any sort of output device. In fact, the output has to be connected to the analog inputs, digital I/O, TTL Serial Port, or Program Port. So, if you want to use your bank to fry your RC, nothing is stopping you (well, except for the hazardous devices rules).

EDIT: A 54 farad bank would probably violate the cost limits as well.

[Rickertsen2]

I assume you mean using a capacitor just like you would in a car stereo install. This usage is in fact illegal.

54 farad capacitor!!!!! Thats just scary.

[mechanicalbrain]

Ok, then ill use then in one of my own robotics projects as a battery replacement. Yeah they are 1.1 pound 54 farad capacitor banks with auto balancing software. They are a brand of ultracapacitors made by maxwell. http://www.maxwell.com/ultracapacitors/products/modules.html

[Tristan Lall]

To add insult to injury, you would have to start the match with the capacitor discharged, per <R02>.

[sciguy125]

What are those things supposed to be used for!? What could you possibly do with a 430F cap at only 16V? They also have a 2.6kF for 2.5V. I couldn't find any price info though.

[Al Skierkiewicz]

Capacitors are not strictly illegal but they cannot be used for power filtering at the power input to the RC. As an inspector I would also need to see a valid method for discharging the capacitors at the end of the match. Something automatic and absolutely fool proof. Barring that, everything must be insulated.
Remember there is a lot of power locked up in a 54 Farad capacitor. Certainly enough to weld metal if it were to come in contact with something.

[mechanicalbrain]

I wanted to use it in conjunction with a CIM (before the speed controller). I couldn't find a rule that would flag it (I'm not sure the alternate power source rule would apply) but it would probably get flagged anyway. Yeah I know that 54 Farads is a lot but consider the power draw on a single CIM. These in particular are used as replacements for batteries. I might use it in an off season project to see what effect they have on the motors.

[Dave Flowerday]

I wanted to use it in conjunction with a CIM (before the speed controller). I couldn't find a rule that would flag it (I'm not sure the alternate power source rule would apply) but it would probably get flagged anyway.
A capacitor would be considered a custom circuit, subject to the custom electronics rules. Right off the bat, it would be in violation of these two rules from 2005:

All outputs from the custom circuits must be connected to the analog inputs, digital I/O, TTL Serial Port, or Program Port on the Robot Controller.
Custom Circuits may not: Directly affect any output devices on the robot, such as by providing power directly to a motor, supplying a PWM signal to a speed controller or supplying a control signal to a relay module. (Custom high impedance voltage monitoring or low impedance current monitoring circuitry connected to the robot’s electrical system is acceptable, because the effect on the robot outputs should be inconsequential.)

[Al Skierkiewicz]

Yeah, what Dave said! (Thanks Dave)
In that application it would be more of hindurance than you think.
That calculates out to 3888 Joules and by my guess would take almost 16 seconds to charge up during which it will look like a dead short across the battery for most of that. I calculate 240 amps will flow into the capacitor at the begninning of the charge cycle.

[mechanicalbrain]

A capacitor would be considered a custom circuit, subject to the custom electronics rules. Right off the bat, it would be in violation of these two rules from 2005:
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)?

[KenWittlief]

what is the price and weight of one of those units, and what exactly do you expect it to do for you on the robot?

The batteries supplied in the kit are able to put out 200 to 300 amp surges - I think if you pumped any more current through a Victor or through the motor you would see a cloud of smoke where your robot use to be!

What problem are you attempting to solve by adding these to the bot?

[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.

[KenWittlief]

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]

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.

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]

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]

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]

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]

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]

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]

...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]

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]

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]

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]

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.

http://www.maxwell.com/ultracapacitors/products/modules.html

[CJO]

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]

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]

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..

[Rickertsen2]

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.


Not with these you won't. To make acheive the energy discharge rates and rise times needed for these sorts of devices, you need voltages at least two orders of magnitude greater than what you will get out of one of these things. You could hook a bunchload of them in series but this is not a good idea either. The 5000A is an indication of that will happen when you short the terminals, not what kind of current they are designed to source. If you put enough of these in series, to get a high enough voltage, you would run into a number of problems. Firstly, there is a good chance they would implode internally due to the flux that would be generated by the high current spikes generated if they were used for a HV Pulse supply. Secondly, its not safe. If the dialectic on a single cell were to break down, it cold cause a catatrophic cascade that might cause the whole thing to explode! This is warned about in the data sheet. These caps simply arn't meant for HV or high frequency use. Maxwell makes a number of caps designed for these applications

[John Gutmann]

To add insult to injury, you would have to start the match with the capacitor discharged, per <R02>.

start with a spring wound watever and use it to charge the cap

[DonRotolo]

...or the noise emitting diode.
The only noise most of mine ever emitted was a tiny "tick". Then they stopped working.....

Don