Charging 7.2V Backup Battery
 

Ok, everyone knows the common way fo charging the 7.2 Volt Backup Battery, taking it out and connecting it to the charger. Although while reading through the 2006 FIRST Encyclopedia (Rule Book) I noticed Rule R53 in Section 5 on page 16. It States:

Now where is this design? I spent about a half hour looking through IFI's website. :ahh: :confused:

Re: Charging 7.2V Backup Battery
 

i dont know, but is it that hard to take off the battery? lol. :)

Re: Charging 7.2V Backup Battery
 

Well..... lol last year we kind of had the battery squeezzed in there so it was hard to switch. This year it shouldb't be though. But Still think about it. If your backup batt doesn't get charged before you go out on the field at least it would be getting charged while your waiting in queing (if thats how its spelled :-p)

Re: Charging 7.2V Backup Battery
 

That is a good point. For us at least, the backup battery seems to be one piece that is easily overlooked, no matter how hard I try to remember or write it down, I always get sidetracked. If this is acutally possible, it could be a nice backup in case it is not charged.

Re: Charging 7.2V Backup Battery
 

Quick question, what is constant charging going to do to the battery? I would be worried about the "memory effect" (not fully discharging the batteries makes them not able to hold a charge as long)

Re: Charging 7.2V Backup Battery
 

It will have a negligible effect on the battery over the course of a season. It may have some impact over a timeframe of many years, but I do not see this as a cause for serious concern. Also note the memory effect of NiCd batteries does not manifest itself quickly, it takes considerable time.

Don

Re: Charging 7.2V Backup Battery
 

As far as the battery being charged constantly i don't think you will have to worry about it for one season.

But back to the main question, has anyone seen the diagram yet? I STILL cannot find it.

Re: Charging 7.2V Backup Battery
 

A couple of references have been made to the "memory effect" of Ni-Cad batteries. I did a lot of research into this in the late 80's and can state that it simply does not exist.

Now before someone ups and quotes a university, technical or other "knowledgeable" source, I would ask you to read the sidebar article, Memory effect? No, voltage depression, in this article from EDN magazine. It does as good of a job of explaining the phenomenon in (almost) layman's terms.

The "memory effect" has been bantered about for so long (over 40 years) that it is accepted as fact by many very smart scientists and engineers. I had a devil of a time trying to explain this to my to management... But that's another story...

Regards,

Mike

Re: Charging 7.2V Backup Battery
 

The memory effect is very real. Constant charging will shorten the life of the batteries. But, for the amount of use the batteries would see it shouldn't be much of an issue. You could also build a pack with NiMH cells that do not have a memory effect.

Re: Charging 7.2V Backup Battery
 

I was wondering where the design for the charger circuit was and 2006 reference guides for the RC and OI. I asked IFI and received this response:

Re: Charging 7.2V Backup Battery
 

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 will read over the electrical and custom circuit rules and see if i can find anything that wouldn't allow that.

Re: Charging 7.2V Backup Battery
 

I don't really care about memory effects in this app, but I wish they'd switch to NiMH due to the damage to people and the environment that Cadmium causes.

Re: Charging 7.2V Backup Battery
 

Thats a very good point.

Re: Charging 7.2V Backup Battery
 

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.

Re: Charging 7.2V Backup Battery
 

I feel the need to chime in here on a few points.
1. The charging circuit that IFI is likely to publish will include charge current limiting and diode protection so that the backup battery is not able to supply current to the 12 volt circuitry on the robot. There are several usable designs that can accomplish this, just be patient.
2. Mike, I have to disagree on the NiCad memory issue. It does exist, particularly in inexpensive cell technologies and older batteries (we make extensive use of rechargeable packs in camera, VCR and light applications for the field). New designs have managed to overcome the chemical issues that led to this problem. (much of the problem occurred with internal construction and material choice.) It is unlikely that any of the newer, high charge current or extended use NiCad cells will exhibit the problem. As a team, you should not consider it to be a factor in your battery choice.
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.

Re: Charging 7.2V Backup Battery
 

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.

Re: Charging 7.2V Backup Battery
 

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

Re: Charging 7.2V Backup Battery
 

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.)

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

Re: Charging 7.2V Backup Battery
 

You'll find it in the Control System Rules.

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".

Re: Charging 7.2V Backup Battery
 

Yes, I stand corrected. R68 is quite clear. Next time I'll read further along...

Don

Re: Charging 7.2V Backup Battery
 

IFI charger schematic is online here.

Re: Charging 7.2V Backup Battery
 

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

Re: Charging 7.2V Backup Battery
 

It wasn't there the whole time, they added it yesterday evening.

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

Re: Charging 7.2V Backup Battery
 

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.

Re: Charging 7.2V Backup Battery
 

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.

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?

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:

Re: Charging the 7.2 Volt Batteries
 

If you look in the box from Innovation First you should see a 7.2V battery charger.

Re: Charging the 7.2 Volt Batteries
 

I believe the standard IFI battery charger says 9.0V on the outside of it, as it likely uses that as the charging voltage. If the connectors match, then that's probably the charger you have.

Re: Charging the 7.2 Volt Batteries
 

The charger we received in the Kit of Parts is approximately half as wide as the OI power adapter, and has a connector matching the backup battery pack. It came in its own little white cardboard box. A red/green LED on it indicates that the battery is charging/charged.

I think the voltage listed on it was 8.something, which is perfectly appropriate for charging a 7.2 volt NiCd pack.

Re: Charging 7.2V Backup Battery
 

Historically there have been many matches lost due to a weak/drained 12v battery. I would not want to add ANY un-necessary load on my primary power source. It shouldn't be that difficult to design-in easy access for replacement of your 7.2v.

Re: Charging the 7.2 Volt Batteries
 

thread merged with other backup battery thread to reduce clutter.

Re: Charging the 7.2 Volt Batteries
 

For one to stop backfeed just simply add another diode.

Two, why waste time taking the backup battery out and putting new ones in, and buying extra ones, when you can just put this little circuit together and it will keep it charged enough to do what is was ment to do. Which is provide power for a short amount of time like when a motor sraws to much current or something.

If you think about it the normal use of the servos and camera which draw there power off of i wouldn't really be coming from the battery anymore as much as it would the little charger.

The backup battery is a major part since the servo's and the camera depend on it. It also help the OI and radio modem, out in case there was a real small cutout in the power.

So in fact its not just for the purpose of not wanting to take it out and charge it. It's also for the fact that there will be times that it won't be fully charged and having the little charger on the robot will help in those situations.

Besdies, its a good learning experience for the students, isn't that what FIRST is about? :confused:

Re: Charging the 7.2 Volt Batteries
 

Our charger (makubesu, I and our team) is as big as the IO converter and says 9.0 volts. Is this safe tpo charge a 7.2 volts battery with?

Cory, this is a different subject than this other thread you merged it with.

Re: Charging the 7.2 Volt Batteries
 

The 9V charger is the charger IFI has been shipping for years for the 7.2V batteries, so it's fine to charge them with it.

Re: Charging 7.2V Backup Battery
 

In case you haven't found it yet:

http://www.ifirobotics.com/docs/firs...up-charger.pdf

This is all they had posted - it's a link in the small print at the bottom of the ifirobotics home page.

Craig Roys

Re: Charging the 7.2 Volt Batteries
 

Thanks for your help, the 9v one worked perfectly.

Re: Charging the 7.2 Volt Batteries
 

It is important to remember that when a robot is involved in pushing or is running with motors near stall, the main battery gets down to 7 volts or even lower. We have observed conditions on robots where they regularly drain the main battery down to 4 or 5 volts. It is for these reasons IFI began using the backup battery. Remember that the backup keeps the main proc alive and keeps the radio modems talking, no matter what voltage the main battery has fallen to. If you are on my alliance, I hope you are using a charged backup battery with no ties to the main battery and no attempt to compete with the bachup battery disabled.

Re: Charging 7.2V Backup Battery
 

Yes, Mike. It is more appropriately called voltage depression, but it is widely known as memory effect and the early quit of the equipment that sees the voltage drop is what matters. Putting those sleepy NiCds through a couple of cycles of a charger that conditions them through a proper discharge, watching the voltage, will usually get good performance out of a battery. Using such a charger, as opposed to a trickle charger, is a good idea to avoid these problems.

The notion that NiMh batteries dont suffer from these problems is also incorrect, on top of all of this. Their problems are not as severe, but NiMh also can get a bit sleepy after storage and a couple of cycles from a good conditioning charger will wake them up.

The Maha MH-C777PLUS charger, or its equivalent, will allow you to keep on top of this, and will tell you what your battery capacity is.

Please recycle batteries properly when they die...

At our first regional with a back up battery, I think two years ago, the tech inspector did not allow a larger radio shack battery and insisted on the IFI backup battery, in spite of the written rules. We compiled...

Re: Charging the 7.2 Volt Batteries
 

If it's such a problem removing the battery from the robot.. charge it on the robot. I'm sure you can set up some sort of circuit/mechanical device that will disconnect the battery from the RC when you plug the charger into it. Then just mount a battery socket somewhere easily accessible on the robot, and when you get back to the pit, plug the charger into it.

Or, mount a robot battery with this circuit on your cart, and when you put the robot on your cart, plug the charger in. No drained battery during the match, but you also don't have to switch the battery out. Because it doesn't seem to be that much of a load.. you should be able to replace the cart battery once a day, and be fine.

It also seems to me that to use this circuit, you would have to have your robot powered on in the pits.. which doesn't exactly seem like a good idea. No one should be using radio's there, but what if someone has a misconfigured OI, and it manages to link up to your active robot? If you don't have the robot on in the pits, your battery gets charged for what? 3-6 minutes at the most (set up for match, match, clean up from match). And it would be a bad idea to have the robot on in the pits, because, at least from my experience, you are always working on the robot.

Re: Charging the 7.2 Volt Batteries
 

Well i don't think its as much of the fact of a full recharge as make sure that the camera and the servo's and other stuff don't take most the batteries energy when ther may come a time where you need that extra boost.

Besides if it is charging all throughout a match wouldn't that mean a faster recharge in the pits?

Besides in a way this also would help (according to how you wired it) if like a team member forgot to put a new backup battery in there at least the servo's and the camera could run off of the circuit..... or purhaps it comes disconnected suring a game.

There are several advantages especial for a little circuit that take a VERY SMALL amount of weigth and space.

Re: Charging 7.2V Backup Battery
 

Spoken like a true software guy...

BTW, the best tool I have found for really testing the condition of your battery (main or backup) is this. I have one and it is very cool.

Don