Custom Chargers for backup battery

[roboticsguy1988]

Hate to bring up old conversation...

However at the Kokomo Workshops recently some members of other teams and i got into a discussion about wether custom charging circuits were legal.

We never really decided. However we did find that many teams had custom charging circuits on there robots and got through inspection with out a problem.

I just wanted to repost and remind every (incase i forget), that this should definitly be a question to ask this year... As it would be very beneficial to many teams.

Something a little off subject... but still partially related. I myself worked on a custom charging circuit and i do have to say that i learned a lot more by doing that then simply taking IFI's design... I think that we should see more custom circuitry in FIRST. Because right now the way it is you learn the very very very basics of DC electrical wiring. Unless you get into custom circuits you don't learn many things about electrical circuits and electricity as you should.

[Al Skierkiewicz]

Larry,
No other charging circuits were allowed under the robot rules this year. Although I didn't like the IFI design, teams who wanted the charger feature on the robot for the backup battery had to use the IFI circuit. I recommend purchasing an additional backup battery and a valid charger for off robot charging.
Inspectors can't find everything so it is possible that robots made it through with chargers of their own designs.

[Tristan Lall]

Originally Posted by Al Skierkiewicz

Larry,
No other charging circuits were allowed under the robot rules this year. Although I didn't like the IFI design, teams who wanted the charger feature on the robot for the backup battery had to use the IFI circuit. I recommend purchasing an additional backup battery and a valid charger for off robot charging.

You know, I'm still of two minds regarding this rule. And not just because I see it as being of limited utility.

Where it says "[w]hen off the robot, the battery is to be charged with the provided 7.2V backup battery charger", it specifies that if off-robot, a certain charger is the only one permitted. But when it says "[w]hen 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.", it specifies that when on-robot, the battery may be charged by that method, but doesn't specifically preclude another charger, as it would have if "may only" were substituted for "may" in that sentence. The implication is that this does not specify the IFI charger to the exclusion of all else, but rather that you may choose between the IFI charger or an unidentified alternative. (Steve and I argued about this during the season, and I believe that we agreed to disagree....) That would mean, that as long as the battery is "on" the robot (secured with Velcro, perhaps), it could be charged in any manner (including, obviously, the IFI charger). Maybe (indeed, probably) they meant something else, but that's not what was written, and I don't remember a Q&A response clarifying that intention.

As for the usefulness of the rule, it's not as if we're charging potentially-explosive lithium-ion batteries here; the Ni-Cd battery is a robust and relatively safe type. I'm not sure we need this rule, as written. Maybe it would be enough to require any COTS charger rated for use with the appropriate battery type and voltage.

[Al Skierkiewicz]

Tris,
I believe the "may" in the language is meant that you may or may not charge the battery in the robot. If you choose to charge in the robot then the IFI charger is to be used. The issue I have with the on robot charger is that a charger with no designed in safeguards will alllow the full charge of the main battery to be dumped into the backup battery. This is a dangerous condition as all additional current will be turned into heat at the backup battery. The other problem (the one that is more likely) is that the charger will allow a sneak path for the main battery to keep circuits on the robot energized at the full potential and current of the main battery or by the backup battery alone. In either case, it gives the team a false sense of security thinking that both batteries are fully charged when they are not.

[Tristan Lall]

Originally Posted by Al Skierkiewicz

Tris,
I believe the "may" in the language is meant that you may or may not charge the battery in the robot. If you choose to charge in the robot then the IFI charger is to be used.

Isn't that the first "may" in the rule? I'm considering the second one (i.e. the ninth word of the third sentence).

My point is simply that they failed to restrict alternatives (in the case of the on-robot charger) by only describing what's allowed, and not saying what's disallowed.

And of course, I'm pretty sure that they intended for teams to use only the IFI charge circuit for on-robot charging. It's just that in order to say that, they should have repeated "is to be" in place of "may", or qualified it with "only". Sure, it's lawyerlike to insist upon this point, but it's also crucial to consider all the possibilities when interpreting an engineering specification.

By the way, I should qualify what I said above about COTS chargers; I meant for that to refer to off-robot charging only....

[roboticsguy1988]

Well regardless of whether or not it was that way last year. It should be asked in Q and A this year.

I was taking it as you may use their design or one of your own. The reason being under any of the other rules relating to custom circuits it does not limit charging the backup battery.

Despite the way it was meant to be i seen teams with the IFI Circuit, and Teams without it, but still charging the battery on the bot, but there were also the teams that didn't use either.

Either way i think IFI needs to modify there circuit design there are a few problems with it. The design we used also had a few problems, which is why this year depending on the rules we hope to make a newly designed safer charger.

And i still stick by what i said earlier, in FIRST we need more circuit experience and we need to do more advanced electrical stuff. I mean after all FIRST is about learning and inspiring others to learn.

[Al Skierkiewicz]

From "The Robot Rev F"

<R53> 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 12VDC 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)

Please note: You may charge on or off the robot. If on the robot you must use the IFI charger connected to the main battery. If off the robot you must use the provided battery charger. There are no other possibilities listed.

[roboticsguy1988]

Originally Posted by Al Skierkiewicz

From "The Robot Rev F"

<R53> 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 12VDC 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)

Please note: You may charge on or off the robot. If on the robot you must use the IFI charger connected to the main battery. If off the robot you must use the provided battery charger. There are no other possibilities listed.

Al, you may want to double check your qoute....

The very last updated file which is revision F http://www2.usfirst.org/2006comp/Man...obot_Rev_F.pdf

says: "<R53> 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 12VDC 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)"

The other part is not mentioned, however you could have meant it to not be part of it and i not realized it.

[Al Skierkiewicz]

Larry,
That is copied and pasted and is identical to yours. The "please note" is my editorial.

[roboticsguy1988]

Originally Posted by Al Skierkiewicz

Larry,
That is copied and pasted and is identical to yours. The "please note" is my editorial.

lol, ok, i thought of that after i made the post... lol, thats why i edited it. I figured you probably added that as your own

[roboticsguy1988]

I contacted FIRST and they finally replied... this is what the rule was intended to mean

Hello Larry -

If the team is going to use the main battery to charge the backup battery then you can only use the schematics provided by IFI to design and build the circuit.

Thank you for your question.
FRC OPS SUPPORT

[Mike Schroeder]

except that may not even be the case/and or option this comming season......

[roboticsguy1988]

Originally Posted by Big Mike

except that may not even be the case/and or option this comming season......

True... I still go with the prediction that something is changing in the control system...

I wonder if they will provide a charer in the KOP.... lol, doubt it

[eugenebrooks]

Originally Posted by roboticsguy1988

I contacted FIRST and they finally replied... this is what the rule was intended to mean

Hello Larry -

If the team is going to use the main battery to charge the backup battery then you can only use the schematics provided by IFI to design and build the circuit.

Thank you for your question.
FRC OPS SUPPORT

So, you run two backup batteries and swap them every match, keeping the spare on the charger between matches. Prior to the competition you load test the batteries to make sure that neither is laying down on you. You should also consider changing out the connector on the battery to the powerpole unit used on model airplanes. The connector that comes on the battery can develop intermitent contacts and this can lead to spurious RC controller resets.

http://www.powerwerx.com/product.asp...015&CtgID=3014

Eugene

[roboticsguy1988]

Originally Posted by eugenebrooks

So, you run two backup batteries and swap them every match, keeping the spare on the charger between matches. Prior to the competition you load test the batteries to make sure that neither is laying down on you. You should also consider changing out the connector on the battery to the powerpole unit used on model airplanes. The connector that comes on the battery can develop intermitent contacts and this can lead to spurious RC controller resets.

http://www.powerwerx.com/product.asp...015&CtgID=3014

Eugene

Lol, well i think if that is the ruling for 2007 i'll stick with the IFI schematic and at least have some kind of charger on the robot. But i will probably wire a switch so i can turn the charger on or off then i could have a spot where i could test the battery without removing it... IDK, i am already thinking of my teams electrical board and i don't even know whats all going to be on it