Better Battaries for Driver Pratice

[MaxMax161]

This post is asking about robot battery alternatives for driver practice not for competition. When doing driver practice we will kill a battery in about 6-8 minutes maximum. We only have so many batteries and thus it limits the amount of time we can do driver practice. Does anyone know of an alternative way of powering a robot for longer? Possibly a battery that is not competition legal but will last longer for practice?

[Chris is me]

Buy more batteries. Not only do you get more drive practice, you get more at competition too!

8 batteries gets you 45 minutes of continuous practice time. Add in a bit of a break and then you can start practicing again. Plus you get to use one battery per match in eliminations, which is really nice.

[MaxMax161]

It takes about 3 hours for us to charge a battery. Is that because we have bad chargers? Would plugging multiple chargers in to the same strip slow them down that much?

[Chris is me]

Originally Posted by MaxMax161

It takes about 3 hours for us to charge a battery. Is that because we have bad chargers? Would plugging multiple chargers in to the same strip slow them down that much?

Okay, so "a bit" is a little longer than I remember... Still - consider upping to about 12 batteries. That will give you 90 minutes continuous, so about 2 hours of practice at a time, which is pretty dang good.

You want to practice with your competition batteries, so everything behaves as expected on the field.

[Chris Mormile]

Hi, I am the battery guy (aka Battman) for team 1676.
We have 10 good batteries and 6 chargers. Each battery is 18Ah. Each charger can charge at up to 6 amps. By basic math it takes a battery that is 1Ah (in capacity) that is being charged at 1 amp, 1 hour to charge. So our FIRST robot batteries will take 3 hours to charge because they are 18Ah and are being charged at 6 amps.

If we were to purchase chargers that could charge batteries at, lets say 8-10 amps (which would result in faster charge times). There is always the possibility that we could blow the batteries up. And if we didn't blow the batteries up we would wear out the batteries faster then if we charged them at a slower rate. Basically we would have to replace batteries every year rather than every 2-3 years. And that would cost teams a lot of money. As a set of 2 batteries from ANDYMARK are $83.00.

Also we could purchase non-competition legal batteries that were the same physical size or larger and use those during driver practice. But on the other hand you don't want to be driving around with a 40lb marine battery running your robot. you may get exceptional run-time but it will cut into the robot's performance. Batteries that are the same physical size but have a higher capacity would be ideal for use, but they would cost teams even more money, and could possibly run teams $100+ per battery.

Also there is another aspect to charging times. This applies to all batteries. As batteries become more charged they will start accepting less and less voltage. therefore it will take longer to charge. The first 75% of a battery charge will take approx. as long as the last 25%.

And finally the last factor in run-times is the heat that you generate. As you run your robot more and more electronics start to heat up naturally. But the parts that heat up the most are the connections from the battery terminals to the PDB. Also the motors Heat up quite nicely to the point that they will burn you. And finally if you have a compressor (we have had the past 2 years) your battery life will go out the drain (plus that heats up quite well too). Parts like the C-RIO and ESCs wont heat up as much for one of two reasons. 1) they have a fan or 2) they dont have as much power flowing through them.

I think i have covered all of the bases of run-time and charging time. Please let me know if you still have questions...

[Bill_B]

I'm not trying to put words into Chris Picone's post, but here's what I think he means. Suppose you got a 12v marine deep discharge battery and hitched up an Anderson connector to its terminals. It might then power your robot for a significantly longer time than the regulation batteries. However, the increased size and weight of that battery would significantly change the driving characteristics of your robot by traction, turning momentum, geometry of gripper arm's motion due to its size and alternate placement, etc.

The consensus seems to be invest in more of the same batteries and practice with them. You'll also get practice changing the batteries on the robot so you'll realize how important easy access is to the power source. To this I'll add: look around CD and other places for ideas about how to make a combination battery cart and charging station. Ride herd on your energy sources. It's also interesting to note that many teams have named their batteries for easier and more effective handling. It's much better to say "I'm going to use Delta now." than to wonder if an anonymous battery has a proper charge.

[bensherman]

Originally Posted by Chris Mormile

Hi, I am the battery guy (aka Battman) for team 1676.
We have 10 good batteries and 6 chargers. Each battery is 18Ah. Each charger can charge at up to 6 amps. By basic math it takes a battery that is 1Ah (in capacity) that is being charged at 1 amp, 1 hour to charge. So our FIRST robot batteries will take 3 hours to charge because they are 18Ah and are being charged at 6 amps.

If we were to purchase chargers that could charge batteries at, lets say 8-10 amps (which would result in faster charge times). There is always the possibility that we could blow the batteries up. And if we didn't blow the batteries up we would wear out the batteries faster then if we charged them at a slower rate. Basically we would have to replace batteries every year rather than every 2-3 years. And that would cost teams a lot of money. As a set of 2 batteries from ANDYMARK are $83.00.

Also we could purchase non-competition legal batteries that were the same physical size or larger and use those during driver practice. But on the other hand you don't want to be driving around with a 40lb marine battery running your robot. you may get exceptional run-time but it will cut into the robot's performance. Batteries that are the same physical size but have a higher capacity would be ideal for use, but they would cost teams even more money, and could possibly run teams $100+ per battery.

Also there is another aspect to charging times. This applies to all batteries. As batteries become more charged they will start accepting less and less voltage. therefore it will take longer to charge. The first 75% of a battery charge will take approx. as long as the last 25%.

And finally the last factor in run-times is the heat that you generate. As you run your robot more and more electronics start to heat up naturally. But the parts that heat up the most are the connections from the battery terminals to the PDB. Also the motors Heat up quite nicely to the point that they will burn you. And finally if you have a compressor (we have had the past 2 years) your battery life will go out the drain (plus that heats up quite well too). Parts like the C-RIO and ESCs wont heat up as much for one of two reasons. 1) they have a fan or 2) they dont have as much power flowing through them.

I think i have covered all of the bases of run-time and charging time. Please let me know if you still have questions...

Chris, since FRC batteries never get down to 0v during competition (or practice), there's always some charge left on it, so it shouldn't take 3 hours to charge a battery that was normally used.

[MaxMax161]

Originally Posted by bensherman

Chris, since FRC batteries never get down to 0v during competition (or practice), there's always some charge left on it, so it shouldn't take 3 hours to charge a battery that was normally used.

Batteries don't need to go down to 0v to be empty. Also by the same logic a half full 12v battery doesn't put out 6v. This isn't for the batteries we use but look at this chart for a conceptual example http://joe.lagrecafamily.com/wp-cont...voltchart1.gif .

[Chris Mormile]

Hi. Ben Sherman,
i know that batteries never go down to 0V. but they still take 3 hours to charge. if you had read my whole post you would have seen that i said "the first 75% of a battery's charge will take just as long as the last 25%, as it starts accepting less and less voltage."
Because of the characteristics of the battery it will take the 3 hours to charge.

Ask Mr. Don Rotolo if you dont believe me. I got my information from him.

[Ether]

Originally Posted by Chris Mormile

Each battery is 18Ah. Each charger can charge at up to 6 amps. By basic math it takes a battery that is 1Ah (in capacity) that is being charged at 1 amp, 1 hour to charge. So our FIRST robot batteries will take 3 hours to charge because they are 18Ah and are being charged at 6 amps.

Just to clarify: 18Ah is a measure of the energy stored in the battery, not the energy required to charge it. The charging process is not 100% efficient.

[bensherman]

That's true, chris. I believe it's called the absorption/float charging (I'm not sure of the name)

[MrForbes]

You might try scheduling more practice sessions, and have them be of shorter duration. I don't know how many hours a day you practice, but it must be more than an hour at a time if you're not able to get it done with 10 batteries that each last 6 minutes.

If you have to spend more than an hour practicing, then you might try using the batteries when they're only about 75% charged, and limit them to 4 minutes of operation.

Or schedule a five minute cooling off period after each five minutes of driving.

[akoscielski3]

Get a new charger...Ours do not take 3 hours to charge ... usually close to 20-30 minutes. Our charger can charge a battery at up to 15 but we usually charge them at 10 or 5. It can also choose what to charge it at, somtimes it chargers at 0.2, but this takes FOREVER to charge them fully.

http://www.canadiantire.ca/AST/brows....jsp?locale=en

Here is the link to our new chargers ^^ ... i dont think america has Canadian Tire though :$

[Chris Mormile]

Originally Posted by Ether

Just to clarify: 18Ah is a measure of the energy stored in the battery, not the energy required to charge it. The charging process is not 100% efficient.

Thank you. I forgot to state that "Ah" (amp hour) is a measure of capacity.

And Ben Sherman. The type of charging we use is called absorption. Most laptops and mobile devices will use this type of charging as well.
Float charging is more commonly known as trickle charging. It is used on High Performance NICD, NIMH, LIPO, and A123 batteries to keep them from self discharging. This method doesn't hurt or damage the battery. where as if you did that with a lead-acid battery it would start to damage it after a while.

Get a new charger...Ours do not take 3 hours to charge ... usually close to 20-30 minutes. Our charger can charge a battery at up to 15 but we usually charge them at 10 or 5. It can also choose what to charge it at, somtimes it chargers at 0.2, but this takes FOREVER to charge them fully.

http://www.canadiantire.ca/AST/brows....jsp?locale=en

Here is the link to our new chargers ^^ ... i dont think america has Canadian Tire though :$

The reason that you can charge your batteries so quickly is because you have the ability to charge at 2A, 10A, and 15A. When you charge a battery at 15A, it may charge really quickly but it also increases the chance of blowing up your batteries. Plus they are not competition legal. but for driver practice they are probally great.

[pfreivald]

We always have a minimum of ten "good" batteries on hand -- it's something I got caught off-guard with as a rookie mentor in 2001, and not something I intend to ever do again.

Budget for extra batteries and chargers, and build a battery charging cart. Number or name all of your batteries, and include them on your pit checklist between matches. (Keeping track of the voltage going on and voltage coming off each match can help keep you ahead of cells that are dying for one reason or another, in addition to keeping your 'bot from dying in the middle of a match.)