(Earlier version of) Backup onboard charger not correct

[Dad1279]

Originally Posted by dcbrown

I wonder if just adding a switch into the circuit at the 12v + point would violate R56. At least then we'd have a manual method of disabling the circuit rather than physically unwiring it if there were issues we wanted to isolate.

As currently written, it would appear that adding a switch would be a violation of R56 though.

Bud

You can switch the power (12v) with a spike. Then when the robot is shut down, the charger is off. Drain to the backup battery in this case would be through r3/r2, about 5ma.

[dcbrown]

You can switch the power (12v) with a spike. Then when the robot is shut down, the charger is off. Drain to the backup battery in this case would be through r3/r2, about 5ma.

Excellent idea. I'm sure there is spike already in the mix somewhere that is on if not on all the time, then most the time. The better idea would be a steering diode below the 'batt' point in the schematic... but the schematic isn't likely to change at this point so the spike at least addresses 1/2 the discharge/back power issue with the current charger design.

thanks!

[RyanN]

Originally Posted by Al Skierkiewicz

Paul,
If you use the IFI charging circuit, then IFI makes it mandatory to use it as it is drawn with no mods. If the RC should fail and they determine the cause relates to backup battery it may void the warranty.

<R56> 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.

There is no other provision beyond these two.

Where in the rules or on Innovation First does it say that we cannot modify this circuit to work the way we need it to work? I found nothing so we took it as a chance and modified it a bit. Added a steering diode to prevent the back feed, and we are going to add a 1 AMP fuse to it as well.

[jgannon]

Originally Posted by RyanN

Where in the rules or on Innovation First does it say that we cannot modify this circuit to work the way we need it to work? I found nothing so we took it as a chance and modified it a bit. Added a steering diode to prevent the back feed, and we are going to add a 1 AMP fuse to it as well.

The general feeling around here about <R56> is that the backup battery may only be charged by the circuit from IFI, and not from a custom circuit. I could have sworn there was a Q&A that backed up this interpretation, but I'm not seeing it under section 8.3.

[RyanN]

Originally Posted by jgannon

The general feeling around here about <R56> is that the backup battery may only be charged by the circuit from IFI, and not from a custom circuit. I could have sworn there was a Q&A that backed up this interpretation, but I'm not seeing it under section 8.3.

Maybe this will be clarified in Team Update #6 . I have 2 things that I'm not sure about, this, and the radio problem.

[Al Skierkiewicz]

Originally Posted by RyanN

Where in the rules or on Innovation First does it say that we cannot modify this circuit to work the way we need it to work? I found nothing so we took it as a chance and modified it a bit. Added a steering diode to prevent the back feed, and we are going to add a 1 AMP fuse to it as well.

Ryan,
I could see how it might be interpreted that way but the rules simply state the IFI suppied circuit design must be used. I read that (and the inspectors last year were interpreting it) that it is and must remain unmodified.

[jskene]

The rules say:

<R56> 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 use of this circuit is strongly encouraged.

This rule does not say that it MUST be charged with the IFI circuit. This wording appears to allow an alternate, on-robot charger. We should get an official ruling from USFIRST on this.

[Dave Flowerday]

Originally Posted by jskene

This rule does not say that it MUST be charged with the IFI circuit. This wording appears to allow an alternate, on-robot charger. We should get an official ruling from USFIRST on this.

I have already submitted a Q&A to the official FIRST forums. We should have our answer in a few days.

[Al Skierkiewicz]

Originally Posted by jskene

The rules say:

<R56> 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 use of this circuit is strongly encouraged.

This rule does not say that it MUST be charged with the IFI circuit. This wording appears to allow an alternate, on-robot charger. We should get an official ruling from USFIRST on this.

Jerry,
Read that rule as "if you charge it on the robot it must use the IFI charger. If you charge it off the robot then you must use the supplied charger". There is no other alternative.

[jskene]

Certainly that is the safest way to read the rule, but USFIRST has in the past been very specific in their choice between the words "may" and "must". If this rule specifically, definitively, was intended to disallow an alternate on-robot charger, is should use the word "must".

A poorly designed charger could lead to overheating of the batteries, so a specific charger design should be used here.

I'll be interested in their comments on this.

[intellec7]

I might be wrong...
I am assuming they are enforcing the use of the IFI circuit for safety reasons, but if they truely want to be safe, they should include something prebuilt in the kit because there is no guarantee that whoever builds the circuit will build it correctly.

[Dad1279]

We have just built one, and will post some voltage and current measurements in the next few days.

I would not be concerned about overcharging, the current is limited by the resistors, it is only on for a few minutes at a time, and you should only be using this circuit if you have servos & cameras drawing power.

[MikeDubreuil]

We might be getting a new schematic... I can't find it on the IFI web site.

[robind]

Originally Posted by MikeDubreuil

We might be getting a new schematic... I can't find it on the IFI web site.

Second that. The links in this thread are 404ing.

[RyanN]

Originally Posted by robind

Second that. The links in this thread are 404ing.

Oh geez... right after I built the old defective one .