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-   -   Back-up Battery question (http://www.chiefdelphi.com/forums/showthread.php?t=53821)

marccenter 16-02-2007 12:06
Re: Back-up Battery question
 
Confused,
Can someone knowledgeable summarize this thread for me to help me understand the collective conclusion?
In addition I am a trite confused on the terms
battery, back-up battery (equivalent to 7.2V NI-Cad
pack or second 12V battery)?

Thanks in advance,

petek 16-02-2007 12:13
Re: Back-up Battery question
 
Quote:
Originally Posted by marccenter (Post 579563)
Confused,
Can someone knowledgeable summarize this thread for me to help me understand the collective conclusion?
In addition I am a trite confused on the terms
battery, back-up battery (equivalent to 7.2V NI-Cad
pack or second 12V battery)?

Thanks in advance,
This thread is addressing issues with the 7.2 V backup battery, not the 12 V main. The gist of it is that the AC "wall wart" charger included in the KOP can overcharge the backup battery if left on too long. The optional (build it yourself) on-board charger circuit is the only FIRST-approved alternative for charging these batteries.

Note that FIRST does allow the use of other 7.2 V NiCad batteries (such as listed in an earlier post, or the Vex robot battery), but not other chargers - even ones included in previous year's KOP.

oddjob 16-02-2007 13:18
Re: Back-up Battery question
 
Quote:
Originally Posted by Alan Anderson (Post 579367)
QI'yaH!
....That settles it -- we're using the onboard charger. We'll also be pulling the breaker supplying it when the robot is not in use.

That's what we did. Pulling the breaker is a bit aggravating, but it's better than boiling the batteries overnight on the lame kit charger.

Mike Betts 21-02-2007 05:42
Re: Back-up Battery question
 
Quote:
Originally Posted by Mike Betts (Post 575918)
...from an engineering standpoint, there are many better solutions than the provided charger. This is particularly true of "smart" chargers which monitor the state of charge of the battery (they utilize an embedded microcontroller and look for the minus dv/dt "bump") and adjust the charging current accordingly...

I invite you to air your concerns on the FIRST Q&A. Only by airing these concerns to FIRST will we get the rules changed...
Please read Team Update #13...

Your posts to the FIRST Q&A have had a positive effect...

Regards,

Mike

dcbrown 21-02-2007 10:03
Re: Back-up Battery question
 
Quote:
We'll also be pulling the breaker supplying it when the robot is not in use
.

It is also best to disconnect the backup battery from the on-board charging circuit. Without an attached RC or connection on the 12V supply end the circuit still discharges through the charging circuit to ground. Granted we only measured 6-8ma, but why start off with a partially discharged battery. With supply side connected but without the main battery the discharge rate will be much higher (assuming things like victor fans, etc. are directly connected to breakers and not via spikes).

pheadxdll 21-02-2007 10:30
Re: Back-up Battery question
 
Quote:
Originally Posted by dcbrown (Post 583244)
.

It is also best to disconnect the backup battery from the on-board charging circuit. Without an attached RC or connection on the 12V supply end the circuit still discharges through the charging circuit to ground. Granted we only measured 6-8ma, but why start off with a partially discharged battery. With supply side connected but without the main battery the discharge rate will be much higher (assuming things like victor fans, etc. are directly connected to breakers and not via spikes).
That's why we added a diode to avoid back feeding the spikes and victors. Too bad we'll have to take it off at competetion.

RyanN 21-02-2007 12:45
Re: Back-up Battery question
 
Quote:
Originally Posted by Mike Betts (Post 583167)
Please read Team Update #13...

Your posts to the FIRST Q&A have had a positive effect...

Regards,

Mike
This will make many MANY teams happy because the KOP charger is very very slow and is also dangerous. I'll quote the update so other teams can directly view the change:
Quote:
THE GDC MEMBERS AND FIRST STAFF HAVE JUST BEEN MADE AWARE THAT THE
7.2V BATTERY CHARGER PROVIDED IN THE KIT OF PARTS IS A DC POWER
SUPPLY AND DOES NOT DROP BACK TO TRICKLE CHARGE WHEN THE BATTERY
REACHES FULL CHARGE. THIS CAN LEAD TO AN UNSAFE SITUATION. THIS
BATTERY CHARGER WILL CHARGE THE BATTERIES, BUT IT IS OUR
RECOMMENDATION THAT THE BATTERIES NOT BE LEFT UNATTENDED WHILE
BEING CHARGED. WE ARE CHANGING RULE <R56> TO ALLOW ANY 7.2 VOLT
BATTERY CHARGER TO BE USED.
Section 8 – The Robot, Rev G has been modified to include the following changes:
Rule <R56> has been updated to state that:
When off the ROBOT, the battery is to be charged with a 7.2V backup battery charger.
Robot Inspection Checklist, Rev C has been updated.


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