Battery Consumptions

#1

During the season I began to wonder about the life cycle and utilization of the batteries that the robots use current.

As Dean spoke both this year and last about the importance of the environment and the need to plan for the future. I thought back to the time I was in Scouting and all the program taught be about being conservation minded. For that reason I am beginning to investigate the batteries we use and would like anyones help that can.

Thus, I am examining the life cycle of the batteries we used this year for power. I am looking for either decrease in power returns and increase in charge cycles or other issues over the course of useage.

If any teams did research on their battery useage, or the life cycle of the batteries I would greatly appreciate them sharing the information. To help me.

I will share any data I gather for the betterment of all teams next year.

With Respects,

#2

i do know that as the batteries age and are recharged more and more, they seem to get lighter, and hold a slightly smaller charge. i recall hearing somewhere (probably right here on CD), that this happens because the stuff inside the batteries slowly evaporates, a little bit with each charge. beyond this, all i know is that having one lighter battery is always good, especially if your robot is exactly 130 lbs. :wink:

#3

All I know about the batteries is when we drove our Robot in this years memorial day parade it made it over a miles worth of travel with the drill motors on high! Near the end we decided to change the battery to give a good finale’ but then the darn transmission started slipping! Oh well!! We had the crowd cheering as we ran and carried it the last 200 yards. The 200 yard robot dash!!!

#4

Jnatt,
The competition docs have a good sheet on battery from the manufacturer. The expected life cycle graphs show distinct functions of battery charge current, load current, and depth of discharge vs. life expectancy. In general, most teams will not deeply discharge the battery since robot controllers reset below 8 volts, so as the battery becomes discharged to the 8 volt level, current demands will cease in normal robot modes. In gelled lead acid batteries, the acid (the gelled part) is heated during charge and discharge and that heat does tend to evaporate the water in the gell with time. The amount of current available from the battery is determined by the surface area of lead plate in contact with the gelled acid. As the acid decreases less current is available and/or less time to discharge. Lead acid batteries also produce conductive particles as part of the charge discharge cycle. In your car battery there is space at the bottom of the battery for this matierial to collect. (gravity carries these particles to the bottom.) When enough of it collects on the bottom, it eventually shorts out the plates and you have a dead battery. In gelled batteries the particles cannot migrate to the bottom and so are held in suspension. When a conductive path finally occurs, you short out the plates. The batteries we use, like your car battery are multi-cell, i.e. 6 cells @ 2 volts=12 volts. A shorted cell will result in a 10 volt battery charged battery instead of 12 volts. Unfortunatelly this is kind of a domino effect. When you have a shorted cell during charging, more current flows in the other cells, raising the internal heat, evaporating more water, producing more particulates, causing more shorted cells.
The bottom line is use old batteries for practice and when they won’t hold a charge or have an obvious shorted cell then recycle. Most battery stores will take back batteries to recycle, the lead is recoverable and best not left to accumulate in the environment.
Hope you are still in scouting and working towards Eagle, good luck.

#5

*Originally posted by Al Skierkiewicz *
**Jnatt,
The competition docs have a good sheet on battery from the manufacturer. The expected life cycle graphs show distinct functions of battery charge current, load current, and depth of discharge vs. life expectancy. **

What the manufacturer states and what really occurs are normally different. I know within Motorola we site battery life at Point A, but find batteries developed by organizations like our ESG group last longer than batteries developed by select other vendors. But all that aside, the more a team uses the batter the short the life cycle of the batter. Hence my orginal question.

  • Did any team track their battery useage life this past year? (i.e. Length of Charge and duration of life)*

**Hope you are still in scouting and working towards Eagle, good luck. **

Eagle Scout Class of 1992

Among the reasons I am seeking this is to research the possibility of lighter, better batteries that are more environmentally friendly.

With Respects,
Joel

#6

While I agree that charge/discharge cycles do impact the life of a battery, I’d argue that how you charge and discharge the cells matters more.

If you charge too fast (or too long on a charger that doesn’t know when to stop), you’ll boil off the water in them. Once that happens, the battery, she is dead. Unsealed Lead-Acid batteries are cooler (pun not intended) in this regard. You simply add more distilled water, and the battery works again (I own an electric car with 16 deep-cycle unsealed Lead-Acids).

The documentation on the battery should list the maximum charge power, and the chargers that FIRST gives us charge at a reasonable rate (IMO). In terms of envrionmental concerns, I believe that Lead-Acids have wide-spread recycling programs. There are a number of threads on here that discuss at length all kinds of battery woe, you might want to check those out if you haven’t already.

In terms of lighter batteries, I think it would be hard to beat the Power VS Weight of the Lithium Ion type. I have no idea what recycling for these is like. Nickel Metal Hydride (NiMH) is also light, but takes a lot longer to charge than Li-Ion. Nickel-Cadmium batteries have been around forever, and are great if you want to get the power out of them in a HURRY. (Short across a small one with two wires, and watch them glow red). I think these are recycled, but people often complain about some kind of “memory effect”. FIRST used to use these. Anyways… just some ideas. Hope they are of some use.

#7

Jon:

You mentioned some excellent points. I agree that there are several different items that impact the life of the battery…

*Originally posted by Jon Lawton *
**While I agree that charge/discharge cycles do impact the life of a battery, I’d argue that how you charge and discharge the cells matters more.

…

In terms of lighter batteries, I think it would be hard to beat the Power VS Weight of the Lithium Ion type. I have no idea what recycling for these is like. Nickel Metal Hydride (NiMH) is also light, but takes a lot longer to charge than Li-Ion. Nickel-Cadmium batteries have been around forever, and are great if you want to get the power out of them in a HURRY… **

If we can find anything that will both help the robot and at the same time improve the Robots weight and performance. I believe would not only be a bonus, but would be improvement on other items too…

Thanks…

#8

Joel,
The sealed batteries we use are probably the best choice for our particular use. There are so many variables (users, temperature, mounting orientation and cost) that this battery fulfills most of the needs except weight. BUT… the weight restrictions on the competition are the same for everyone and really help adult advisors teach real world problem solving. The chargers are simple and if someone were to attach a a different charger, the results are not as nearly catastrophic as a lithium ion or nickle hydride under the same circumstances. The internal resistance of the battery has some saving grace in our competition since it will self limit how far you can discharge the battery. i.e. never being able to take it down to 1 volt per cell or less since the controller will not function that low. If you look at the life chart vs. discharged terminal voltage you will see a distinct relation between deep discharge and shortened life.
As to alternative power sources, silver cells would be a better choice for our use. They combine high current capacity, long life, and are slightly smaller and lighter than SLAs. They can be fast charged and used in any orientation. The down side is they are really expensive. $123/ampHour vs. $2.90/ampHour with the SLA.
Al
BTW My son is a ranger at Philmont this summer. (Alumni of Wildstang '96-'98)

#9

I think that the batteries that FIRST uses adequately serves our purpose. I especially like the internal breaker, one of the girls on our team connected the leads on the battery wrong and couldn’t figure out why it wouldn’t work. If i say too much more about the girls on our team I might bother some people in RCU… Also is everyone aware of the Co-ed section of boyscouts called Venturing? It’s mainly for high adventure camping and you are a youth until you are 20. Wish I could’ve gone to philmont…

#10

What “internal breaker”?

#11

I am not sure what he is talking about, but look at the kind of “internal breaking” our battery went through…
http://www.lar.cx/old/f/batterymelt.jpg

Apperently someone accidently brushed a cable away from the robot’s arm, and it started to smell like smoke in the room. I wish I would have been there to see it! :smiley:

So when FIRST yells at you do insulate those contacts… DO IT! :wink:

#12

Correct me if I’m wrong but isn’t there an auto-reseting breaker inside the battery casing to prevent short curcuits?

#13

No, there is no breaker internal to the battery. There are batteries available that have all kinds of protection built in but not these. That is why a protection device is needed to keep the battery from supreme damage, explosion, etc. Everyone should get a good look at the pic above. This is a mild example of what this battery could do. That burn mark could just as easily been a students arm.