Re: Driver station power
 

What is the above comment referring to?

Re: Driver station power
 

Or a supercap can produce a surge, as in the story that was recently told here about getting zapped by capacitors in a speaker. Similar concerns with lipos -- there are hard and fast rules for good reasons, such as safety. The rules are abundantly clear and these rules have been in effect every season I've been involved: no external energy sources (there are a few very strict exceptions) and no extra parts in the power system (again, very specific exceptions such as small filtering capacitors for motors).

There are good ways to solve problems such as these within the rules, but within the rules is where to stay. Even though the rules do not apply to things like carts and driver station power, the safety concerns remain valid.

Re: Driver station power
 

The topic has digressed a bit, but it has never been about what is legal on a competition robot. That has & will continue to be controlled by rule.

Our motivation for a Li ion battery is for our tee shirt cannon which is going through about 3 comp batteries in a typical football game. We were originally going to use a deep cycle lead acid battery. One of our sponsors offered to build the Li ion battery which he says is better technology for the application. I expect cost & safety will prevent this technology from being adopted by FRC for competition in the foreseeable future.

Re: Driver station power
 

Ah, fond memories...

Back in the 60's I got knocked out by an electrolytic cap in the power supply of a Hi Fi audio power amp I was designing and building with 6L6GC vacuum tubes in push-pull configuration.

I unplugged the amp to re-solder some wires going to the 5Y3GT full-wave rectifier and forgot to discharge the caps.

That thing was a beast when connected to the triaxial 12" speaker in my home-built speaker cabinet. The cabinet was 12 cubic feet and weighed over a hundred pounds. 1.5" thick plywood internally reinforced with two-by-fours.

Re: Driver station power
 

If you guys are scared of lipos, try lithium ferrophosphate (life bateries). They don't hold as much, (by barely), but are mucho safer than lipos which explode and catch on fire veery easily::ouch:: ::ouch:: ::ouch:: ::ouch::

Re: Driver station power
 

I have to hear this one, please...

Re: Driver station power
 

That reminds me of the 5000F supercap bank that I want to fit in my room. Power inverter for AC power, and solar panels to charge up the caps. Use it to power electrical tools that require craploads of energy to function. BTW, how do you guys thing of the safety of a 12000 watt inverter?

Re: Driver station power
 

Just worked on an RCA BA6 leveling amp ca 1948. Our local AV guys found this on the shelf and had used it as a movie prop recently. They were thinking of dumping it until they looked one up on the boards and found they are going for $6K. I went over to their shop and plugged it in. I noticed that the OO3/VR150 wasn't lighting up very much and as I looked further I noticed that the the filaments on the 5R4 weren't very bright. (thinking that the transformer had shorted the filament winding) When I touched the envelope (lightly) the filaments went out. I told them they needed to get a 5R4 and call me if they couldn't get any audio through it. The 5R4 is connected to a center tapped 640 volt winding on the power transformer. The caps have bleeders in this design though. I suggested that they put the unit on a variac and run the voltage up slowly over a few hours to form the caps. They reported that worked fine and it is now making some nice sounding audio. This unit uses a pair of 6SK7s feeding a pair of 6J7s feeding a pair of 6V6s on the output, each stage is balanced during the setup. I of course told them to touch the 6SK7s lightly after turning it on to see if they were warm. I once fixed the Clarion Bells at Bradley University when a 6SK7 turned up cold during an onsite check in the bell tower of Bradley Hall. But that was 40+ years ago.

Re: Driver station power
 

Here's the story I was thinking of: "SoC Power".

Incidentally, I wasn't saying there aren't ways to do things for a cart, off-season demo robot, etc. that are outside the rules for a robot but still reasonable and acceptable, but some things that get brought up here are probably not wise paths for students to take without an abundance of caution that isn't a universal trait, because there are many more ways to get this sort of thing wrong than right and learning by experience can sometimes come at a very high cost. Better safe than sorry!

FWIW, capacitor banks power railguns and some very powerful lasers.

Re: Driver station power
 

Let us not confuse voltage with current.

At the voltages involved with FIRST it is unlikely anyone will ionize the air significantly enough to move any meaningful current.
Regardless of what is storing or producing that potential.
Physically shorting either a battery or capacitor would be unpleasant.
The capacitor will be unlikely to literally explode however a battery might pop from boiling.

Also 'supercapacitors' generally have a low voltage rating.
They also tend to have more internal resistance than what most FIRST people would consider normal for a battery.
Finally 'supercapacitors' have a much greater leakage which means that they will self-discharge much faster than your average battery.

Comparing an audio amplifier say for PA application potentially with 70V outputs to a 13.8VDC charged 'supercap' is not a good comparison.
It would be like unplugging and opening a tube computer monitor and poking around in the 15,000V+ section.
People who frequently poke around in electronic repairs learn about these risks (some the hard way).

A high voltage and capacitance bank would be much larger physically.
'Supercapacitors' are not typically suitable for rail guns or generally powerful lasers.

The real lesson for anyone doing repairs from the referenced post is to carefully consider what might store power when things are allegedly powered off. All of those things present an elevated risk.

Re: Driver station power
 

I concede the point. However, even a 5V supercap has a fair amount of stored energy that can be released quite quickly under the right (wrong?) conditions, internal resistance notwithstanding. Same goes for some batteries. I wasn't trying to imply that these scenarios were the same in all respects, only that there is danger here and these components should be treated with respect.

If anyone accidentally succeeds in making a rail gun that fits in the space / weight restrictions of an FRC 'bot (or cart, or driver station, or t-shirt cannon robot, ...), I'm sure the DoD will beat a path to their door! But I'm much more concerned that someone might get hurt because they don't appreciate what they are dealing with. If this happens, it will have been a preventable tragedy and therefore will be doubly tragic. I was just trying to sound a note of caution and also bring up some interesting devices that illustrate how much energy can be stored in capacitors.

Re: Driver station power
 

The moto is lighter, almost 2 pounds, so it's easier to carry

Re: Driver station power
 

I agree caution is always warranted.

You should qualify what sort of performance you want from the railgun because I have built such an item and it would fit within the dimensions of FRC robots. Course the projectile only achieves a velocity comparable to a air rifle. So it's more amusement than useful for the DoD. ::safety::

The capacitor bank (these were not 'supercapacitors') on that unit was actually in a box that would fit on an FRC chassis and it did at any one time contain sufficient energy to be a very real threat to human safety. It was rigged with a bleed down load specifically so that when not in operation it eventually was safe to do repairs.

An interesting project but not safe for students. Do not attempt it. Way more than enough stored energy to melt metal.

Re: Driver station power
 

Don't you need a high voltage to ionize the air? Also, used properly, a supercapacitor can be a great invention. I am designing a mini car right now and I might use the fast energy storage of supercaps to allow regenerative braking. Their low internal resistance will allow the brakes to have a significant effect while not getting as hot or exploding if I were to simply feed back into the 200 amp lipo.

Re: Driver station power
 

By the way, do any of you know the regulations for large lipos? I want to buy 4 200AH Howell (Chinese) lipos to power my electric are that I want to build These weigh six kilos a piece. I want to make sure it is legal before I order them. I am expecting them to be expensive

BTW, sorry for the confusion, but they are actually Lithium Ferro Phosphate (LiFePO4 Batteries)

Here is Howell's page:
http://www.howellenergy.com/
http://www.howellenergy.com/index/view.php?aid=4 (HW-F200Ah)