Charging the 7.2 Volt Batteries

[roboticsguy1988]

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:

The 7.2V backup battery may be charged on or off the robot. When off the robot, the battery is to be charged with the provided 7.2V backup battery charger. When mounted on the robot, the backup battery may be charged from the EX18-12 primary battery by using the custom charging circuit available from Innovation FIRST Inc. (note: IFI will provide the design for this circuit on the IFI website, however teams must obtain the parts for this circuit and assemble it themselves)

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

[want2modmygt]

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

[roboticsguy1988]

Originally Posted by want2modmygt

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

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)

[Erics626]

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.

[devicenull]

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)

[DonRotolo]

Originally Posted by devicenull

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)

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

[roboticsguy1988]

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.

[Mike Betts]

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

[Kingofl337]

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.

[MikeDubreuil]

Originally Posted by roboticsguy1988

Now where is this design?

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:

Originally Posted by Tom Watson

The 2006 control system is basically the same as the 2005 system with the exception of the User processor on the RC. The new user processor is a PIC18F8722. The Operator Interface is exactly the same as the 2005 model.

If has not been determined if the charger circuit will be released.

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

[lukevanoort]

Originally Posted by Kingofl337

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.

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.

[Kingofl337]

Originally Posted by lukevanoort

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.

Thats a very good point.

[sanddrag]

Originally Posted by lukevanoort

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.

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.

[Al Skierkiewicz]

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.