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-   -   (Earlier version of) Backup onboard charger not correct (http://www.chiefdelphi.com/forums/showthread.php?t=51566)

Dad1279 23-01-2007 08:50
Re: Backup onboard charger not correct
 
Quote:
Originally Posted by dcbrown (Post 558853)
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 23-01-2007 09:43
Re: Backup onboard charger not correct
 
Quote:
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 23-01-2007 22:41
Re: Backup onboard charger not correct
 
Quote:
Originally Posted by Al Skierkiewicz (Post 558215)
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 23-01-2007 22:57
Re: Backup onboard charger not correct
 
Quote:
Originally Posted by RyanN (Post 563852)
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 23-01-2007 23:10
Re: Backup onboard charger not correct
 
Quote:
Originally Posted by jgannon (Post 563870)
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 :D. I have 2 things that I'm not sure about, this, and the radio problem.

Al Skierkiewicz 24-01-2007 07:58
Re: Backup onboard charger not correct
 
Quote:
Originally Posted by RyanN (Post 563852)
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 24-01-2007 08:06
Re: Backup onboard charger not correct
 
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 24-01-2007 08:17
Re: Backup onboard charger not correct
 
Quote:
Originally Posted by jskene (Post 564049)
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 24-01-2007 08:18
Re: Backup onboard charger not correct
 
Quote:
Originally Posted by jskene (Post 564049)
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 24-01-2007 08:34
Re: Backup onboard charger not correct
 
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 24-01-2007 08:46
Re: Backup onboard charger not correct
 
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 24-01-2007 09:26
Re: Backup onboard charger not correct
 
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 24-01-2007 09:41
Re: Backup onboard charger not correct
 
We might be getting a new schematic... I can't find it on the IFI web site.

robind 24-01-2007 23:36
Re: Backup onboard charger not correct
 
Quote:
Originally Posted by MikeDubreuil (Post 564096)
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 24-01-2007 23:44
Re: Backup onboard charger not correct
 
Quote:
Originally Posted by robind (Post 564673)
Second that. The links in this thread are 404ing.
Oh geez... right after I built the old defective one :D.


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