When you get a new rechargeable lithium battery pack, does anyone know how long we should charge it the first time? 

Thanks,
Sonya


On Wed, Oct 20, 2010 at 10:37 PM, Andy Traiger <[log in to unmask]> wrote:

Hey Jude,

 

Be aware that alkaline batteries, which are the most common type of AA battery, may not be the best to use for your robot.  The reason is that the six alkaline batteries when fully charged will have a voltage of 9.6 Volts.  As you’re using the robot and the batteries discharge, the voltage will decrease fairly rapidly; even when the battery has a fair amount of capacity left the voltage can droop significantly.  The more they are discharged the lower the voltage gets.  Lithium batteries tend to hold their voltage more stable as the batteries discharge.  The Lithium batteries that are made for the NXT brick will be 8.4 volts when fully charged.  Comparing performance over the same amount of time, the voltage of the Lithium battery will stay stable while the alkaline voltage is drooping substantially.   

 

What does this mean to your robot performance?   If you’re using alkaline batteries, the motors will move faster than the Lithium when both are fully charged.  So, alkaline batteries can give your robot more power / speed when they are fresh.  However as the alkaline batteries discharge a bit the motor performance will slow down.  This will possibly lead to inconsistency in running your missions.  If the kids refined their missions when the voltage was low, the robot may perform completely differently when a new set of batteries is inserted.

 

My team uses the Lego lithium battery pack.  The kids on my team periodically check the battery voltage as they are developing missions, especially if they start seeing their missions failing.   Use the NXT window to view this while the brick is connected to the computer if using NXT_G.  Our team swaps the Lithium battery with a freshly charged one if the voltage drops to about 8.1 Volts.

 

All that being said, besides Alkaline there are other types of AA batteries being sold (including even lithium batteries which are pretty expensive).  Each battery type will have different discharge characteristics.

 

Andy

 


From: First Lego League in Virginia and DC [mailto:[log in to unmask]] On Behalf Of Jude Arulpragasam
Sent: Wednesday, October 20, 2010 9:48 AM


To: [log in to unmask]
Subject: Re: [VADCFLL-L] NXT batery warning

 

I would like to know if there is any advantage using re-chargeable battery pack over individual AA batteries'?
I just bought new re-chargeable DC battery pack (NXT Rechargeable DC Battery (W979693) from Lego website.
 
Please give me some pros and cons  on this
 
Thanks
 
Jude
 


Date: Tue, 19 Oct 2010 20:36:44 -0700
From: [log in to unmask]
Subject: Re: [VADCFLL-L] NXT batery warning
To: [log in to unmask]

Our team started using AA batteries instead of the rechargeable battery pack. But when they had to change the batteries, they had dismantle the robot to get to the battery compartment. I am worried that the kids will not put back the robot perfectly, if they have to do this just before the tournament to have fresh batteries in. Is that how it is normally done?

thanks
Gaja

 


From: Jerry Lorengo <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, October 8, 2010 3:28:54 PM
Subject: Re: [VADCFLL-L] NXT batery warning

Agreed - always use fresh AAs. 

 

The recharchable batter has a goofy memory and the voltage drop will make reproducibility for missions almost impossible. 

Sent from my iPhone


On Oct 8, 2010, at 12:48 PM, Lloyd O'Hara <[log in to unmask]> wrote:

We only use batteries and always make sure we have plenty on hand.

 

Also, I'm sure why you would take 2 sets of four AA batteries, the nxt takes six AA..

 

Lloyd

----- Original Message -----

From: Viquar Shaikh

Sent: Friday, October 08, 2010 10:50 AM

Subject: Re: [VADCFLL-L] NXT batery warning

 

To add to this --- no matter what - we always carry 2 sets of four AA batteries - one is a new packed set. This is a good backup for these 'just-in-case' scenarios.

 

Thanks

Viquar

On Fri, Oct 8, 2010 at 10:32 AM, Brandy bergenstock <[log in to unmask]> wrote:

This came across the Ga FLL yahoo group adn I thought it was important for everyone to realize:

The other day my team had taken one of their NXT bricks with them to a meeting.  When we got home, the battery was completely discharged. After recharging it, my  daughter discovered that the "Sleep" setting was at 60 minutes. The brick had  accidentally turned on during transport and since the sleep setting was so long,  it ran the battery down. We discovered that the 60 minute setting is the default for both the 1.26 and 1.31 firmware update. That is WAY too long!

If you have updated your firmware, you should check the sleep setting and change  it is a more reasonable time (perhaps in the 2-5 minute time frame). This way you won't accidentally run down your battery. I'd hate for someone to discover their battery was dead when they arrived at a competition.

To access the sleep setting on the NXT brick, go to:

Settings
Sleep
and then change the time with the arrow buttons

 


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