Average Energy per match

[Al Skierkiewicz]

Stephen,
I think that the greatest potential for these caps lie in DC/DC convertors which is the implied application in devices like UPS and rail backup systems. As yet, that application is not available for use on our robots under robot rules (other than in the PD) at present.

[DonRotolo]

Originally Posted by Al Skierkiewicz

The battery fully charged is capable of 600+ amps (albeit for short periods of time) and yes teams do approach that figure.

Interpolate that data as you might and a two minute match of average 200 amps will deplete the battery and shorten it's life.

Of course, teams do have that 120A main breaker to limit the actual currents to somewhat lower values on a competition robot.

[EricVanWyk]

Originally Posted by Don Rotolo

Of course, teams do have that 120A main breaker to limit the actual currents to somewhat lower values on a competition robot.

Not necessarily. If you look at the current vs time curves for the breaker, you can draw significantly more than 120A sustained. I haven't seen the breaker's curve in a year, so I won't falsely quote specifics on it.

If you look at PTC curves (which I spent way too much time looking at a month ago), a X amp PTC is spec-ed as "Never trip at under X amps, guaranteed to trip eventually at 2X amps". Pulse currents can be several times X. When you do the full tolerance stack up, you really need a 3x margin between the normal operational current and the fault current with a PTC.

Breakers require less margin, as they have better tolerances. Thermal breakers still have huge time effects, but some breakers use magnetic effects to counteract this.

[EricVanWyk]

In preparation for launching the PD, our interns created a battery monitor. It logged the battery voltage and current a couple times per second to an SD card. I have the information gathered at Mayhem In Merrimack. It is either 2meg zip of .pngs or a 2gig folder of raw data. If you PM me your email address I'll forward it along.

I was hoping that CrossTheRoad or AndyMark or other would sell the devices, but there wasn't much interest. All it is is a pic, a hall effect sensor and a microSD connector.

[Andrew Schreiber]

Originally Posted by EricVanWyk

In preparation for launching the PD, our interns created a battery monitor. It logged the battery voltage and current a couple times per second to an SD card. I have the information gathered at Mayhem In Merrimack. It is either 2meg zip of .pngs or a 2gig folder of raw data. If you PM me your email address I'll forward it along.

I was hoping that CrossTheRoad or AndyMark or other would sell the devices, but there wasn't much interest. All it is is a pic, a hall effect sensor and a microSD connector.

Any chance plans and code for this device could be published?

[EricVanWyk]

Originally Posted by Andrew Schreiber

Any chance plans and code for this device could be published?

Sure. It is just a lab tool - it isn't cleaned up or productized, and finding where the source went might take a few hours. I could email them or publish them somewhere. How do you want them?

[MrForbes]

Originally Posted by Stephen Kowski

To lose 20% capacity in 6 months by only sitting on a shelf makes me wonder about the impedance growth rate associated with these batteries.

It makes me wonder why we don't take more effort to make sure we keep ours charged up and in use all year

Energy use per match depends on a lot of things, and the game has a lot to do with it...we used up most of the capacity of the battery during matches in 2007...this year the batteries lasted quite a while.

You should be able to figure that on average, roughly one quarter to one half the capacity of the battery in each robot will be used in a match. So figure two batteries worth of charge per match (6 robots) as a starting guess.