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-   -   Charging the 7.2 Volt Batteries (http://www.chiefdelphi.com/forums/showthread.php?t=41781)

MikeDubreuil 12-01-2006 15:02
Re: Charging 7.2V Backup Battery
 
Quote:
Originally Posted by Al Skierkiewicz
3. Many of you seem to be fully on board with a 12 volt charging circuit operated from the main battery. I am not, as it adds weight to your robot and steals power from the main battery. Simple buy two backup batteries and charge one while you use the other on the robot. If you find that you require higher current (due to multiple servos in your design) Digikey or other vendors can assemble battery packs in any current or package size you might desire.
I guess I'm on board with the idea for a couple reasons.
  • I think adding the charging circuit will more fit the notion that the 7.2V battery is a true backup. I think it was a great mistake for IFI to power external devices through the 7.2V battery. I do like how the backup keeps the RC alive during brownouts. By adding the power charging circuit it makes the RC more the way I wished it was.
  • I think the added weight will be negligible.
  • The backup battery does not have to be easily accessible with a sturdier mounting system.
Either way you look at it there are engineering trade offs. I just feel the benefits of never having to manually charge the backup are worth the added weight.

lukevanoort 12-01-2006 22:14
Re: Charging 7.2V Backup Battery
 
Quote:
Originally Posted by sanddrag
I own at least 8 NiCd batteries and I've never had a single one cause harm to me or the environment. Are you talking about when they are disposed of? If so, what can 1100 little batterypacks, that are each at a minimum of a few miles apart, do to a whole world of an environment? If we are talking about ALL NiCd batteries (not just in FIRST), then you may have a point if there are studies to back it up.
I am talking about all NiCds and cadmium in general. FIRST may not be affecting the environment on it's own, but neither does a car. However, if you use cars for lots of things you get tons of pollution. For cadmium's toxicity:

http://en.wikipedia.org/wiki/Cadmium
http://risk.lsd.ornl.gov/tox/profiles/cadmium.shtml
http://www.epa.gov/ttn/atw/hlthef/cadmium.html

DonRotolo 12-01-2006 22:50
Re: Charging 7.2V Backup Battery
 
Quote:
Originally Posted by Al Skierkiewicz
<snip>If you find that you require higher current (due to multiple servos in your design) Digikey or other vendors can assemble battery packs in any current or package size you might desire.
I don't see anywhere in the rules where it states you can use an alternative 7.2 volt backup battery. As I interpret the rules this year, you must use the one supplied. EDIT: My interpretation is indeed wrong, <R68> is clear that any 7.2 volt battery can be used. Sorry for the bad info (and thanks, Alan A.)

Quote:
Originally Posted by roboticsguy1988
Well it would actually be simple to come up with a circuit that charges it anyway. As long as it went along with all the rules.
I agree, but teams designing such a charging circuit MUST consider the safety aspects of such a device, specifically that it really must be a charger and not just a voltage source. A simple voltage source runs the risk of overcharging the battery.

A good choice for such a charger circuit would be the MAX 713 which is available from almost everyone, and also comes in a 16-pin DIP package (so you don't have to mess with surface mount stuff).

Don

Alan Anderson 12-01-2006 22:57
Re: Charging 7.2V Backup Battery
 
Quote:
Originally Posted by Don Rotolo
I don't see anywhere in the rules where it states you can use an alternative 7.2 volt backup battery. As I interpret the rules this year, you must use the one supplied.
You'll find it in the Control System Rules.
Quote:
<R68>The 7.2V Robot Control backup battery must be connected to the Controller as described in the Controller’s manual. The 7.2v battery should be charged to at least 7.0v before entering a match. As a replacement for the FIRST supplied battery, any other 7.2V NiCad battery pack may be used.

roboticsguy1988 12-01-2006 23:02
Re: Charging 7.2V Backup Battery
 
After reading through the rules i don't really see anything that would violate them as far as creating a custom charger circuit for the 7.2V battery.

As far as weight goes.... we are talking about a circuit board with some components on it. It shouldn't weigh that much.

I just mainly wish i could get the IFI design. That way there would be no worry at all of the inspectors saying "you can't have that".

DonRotolo 12-01-2006 23:22
Re: Charging 7.2V Backup Battery
 
Quote:
Originally Posted by Alan Anderson
You'll find it in the Control System Rules.
Yes, I stand corrected. R68 is quite clear. Next time I'll read further along...

Don

fowlerm 13-01-2006 11:58
Re: Charging 7.2V Backup Battery
 
IFI charger schematic is online here.

roboticsguy1988 13-01-2006 13:49
Re: Charging 7.2V Backup Battery
 
Quote:
Originally Posted by fowlerm
IFI charger schematic is online here.
Yeah i know i found it today. There was link at the bottom of the homepage. I wonder if it as there the whole time.... If so, that was my bad :-p

fowlerm 13-01-2006 14:13
Re: Charging 7.2V Backup Battery
 
Quote:
Originally Posted by roboticsguy1988
I wonder if it as there the whole time.... If so, that was my bad :-p
It wasn't there the whole time, they added it yesterday evening.

roboticsguy1988 13-01-2006 14:23
Re: Charging 7.2V Backup Battery
 
Yeah i realized that after i printed it out. It got added yesterday on 01/12/06. So it wasn't there in the beginning but it got here in time. :D

Alan Anderson 13-01-2006 14:25
Re: Charging 7.2V Backup Battery
 
Quote:
Originally Posted by fowlerm
IFI charger schematic is online here.
That's a very odd looking circuit. I don't understand the point of the regulator, and I see nothing to prevent the backup battery from powering anything else that's connected to the main battery input.

Al Skierkiewicz 13-01-2006 14:47
Re: Charging 7.2V Backup Battery
 
Quote:
Originally Posted by Alan Anderson
That's a very odd looking circuit. I don't understand the point of the regulator, and I see nothing to prevent the backup battery from powering anything else that's connected to the main battery input.
Alan,
I agree, the only limiting factor is the big resistor between the main and backup battery. According to my calculations, the regulator is set for 8.26 volts output which at full charge will still attempt to pump about 45 ma into the battery with the controller turned off. With everything up and running, the zener will be turned on at 8.7 volts.

Makubesu 13-01-2006 16:13
Charging the 7.2 Volt Batteries
 
We're trying to charge the 7.2 volt backup batteries you use for the control system, and we can't figure out how to do that. We looked through the kit of parts, and it seems that there is a charger for them, but closest thing we could find was a 9v charger. Is that alright to use? Or should we look through the parts again?

BrianBSL 13-01-2006 16:16
Re: Charging 7.2V Backup Battery
 
I also see some weirdness in this circuit, but for anyone that wants to build it, I already put together the list of parts from Mouser. Sorry for the horrid formatting (this is a paste straight from their cart). The Tantalum cap's can probably be substituted for ceramics if you have them laying around or for cost reasons. Here are the part #'s that I chose:

Code:
610-CZ5345B            CZ5345B          Central Semi Diodes - Zener
DO-201 8.7V 5.0W
        $ 0.520       

511-LM317T        LM317T        ST Voltage Regulators
TO-220AB 1.2-37V Adj Positive - RoHS COMPLIANT per producer documentation
        $ 0.460       

625-1N5820        1N5820        Vishay Semiconductor Schottky Rectifiers
DO-204AL Vr/20V Io/3A BULK
        $ 0.290       

271-221-RC        271-221-RC        Xicon 1/4W 1% Metal Film Resistors
221ohms 1% 50PPM - RoHS/Pb-FREE per producer documentation
        $ 0.090       

271-1.24K-RC        271-1.24K-RC        Xicon 1/4W 1% Metal Film Resistors
1.24Kohms 1% 50PPM - RoHS/Pb-FREE per producer documentation
        $ 0.090       

294-43-RC        294-43-RC        Xicon 1W 5% Carbon Film Resistors
43ohms 5% - RoHS/Pb-FREE per producer documentation
        $ 0.140       

294-22-RC        294-22-RC        Xicon 1W 5% Carbon Film Resistors
22ohms 5% - RoHS/Pb-FREE per producer documentation
        $ 0.140       

80-T350A104K035        T350A104K035AS        Kemet Dipped Radial Tantalum Capacitors
35V 0.1uF 10% - RoHS non-compliant/CONTAINS Pb
        $ 0.300

MikeDubreuil 13-01-2006 16:17
Re: Charging the 7.2 Volt Batteries
 
Quote:
Originally Posted by Makubesu
We're trying to charge the 7.2 volt backup batteries you use for the control system, and we can't figure out how to do that. We looked through the kit of parts, and it seems that there is a charger for them, but closest thing we could find was a 9v charger. Is that alright to use? Or should we look through the parts again?
If you look in the box from Innovation First you should see a 7.2V battery charger.


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