Re: Custom Chargers for backup battery
 

For me, D1 is the real fly in the ointment. It's hard for me to tell what it is doing to the current coming directly from the 12V battery.

If the regulator voltage is at 8.3V and the battery is below this, then I guess D1 is reverse biased, and has no effect. The only way D1 comes into play is if you disconnect the backup battery.... If this happens it shunts the 12V to the regulator output... which is innecessary since the D2 would shunt it to ground anyway.

IMHO D1 would be much better served protecting the backup battery from being discharged when the 12V breaker is off.

Phil.

Re: Custom Chargers for backup battery
 

Modified schematic now posted on IFI: http://www.ifirobotics.com/docs/firs...up-charger.pdf

I've posted a layout at: http://www.chiefdelphi.com/forums/sh...ad.php?t=52541

Re: Custom Chargers for backup battery
 

This circuit is improved!
But I feel there should be a current steering diode in the path from the 12v main battery to the backup battery. Without that, when the main is shut off, there is still current leakage back to all of the 12v circuitry.

Ray M.
Team 1138

Re: Custom Chargers for backup battery
 

Your link didn't come out... Here it is in full.

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

Yeah, the addition of that connector makes a HUGE difference!!!!

And now that I've seen this schematic... it looks familar, as if I've seen it before. Maybe we've all been pointing at an old schematic.

Phil.

Re: Custom Chargers for backup battery
 

I agree that an additional diode would help this circuit and prevent back feeding the rest of the robot.
The diode in the schematic is a Schottky diode with a 0.4 volt drop instead of the 0.6 volt drop of normal diodes.
What we all need to realize is the 317 regulator will provide all the power needed by the 7.2 volt buss (at 8.5 volts) until the main battery falls to about 9.5 voltsor less. When this occurs, the output of the regulator will fall and when the output is less than about 7 volts, the backup battery will begin to supply current to the backup buss at 0.4 volts less the terminal voltage of the 7.2 volt battery. The resistor in parallel with the diode will also pass some current in each direction. The effect is that servos will not be running on 6.8 volts or less so teams should not be surprised if there servo operated devices run slower at lower main battery voltage.
There is still no substitute for a fully chargd backup battery working alone.

Re: Custom Chargers for backup battery
 

So this might belong in a discussion of off robot charging, but I'll put here too. Last year we used VEX bats and VEX intelligent charger for our backup bat on FRC robot. Looks like we can still use the bats, but maybe not the charger, which seems far superior in regard to life expectancy of backup batteries.

If we are really forced to use the supplied wall wart to charge our backup bat, we probably won't risk ruining a VEX bat in the process. Seems like a step backwards - and I'm pretty sure DLavery wouldn't use the wall wart on his second car - (on Mars). :)

Re: Custom Chargers for backup battery
 

Now that we have actually built this circuit, and placed it on our machine, I am more convinced that it needs an input current steering diode.
When the main power breaker is turned off, the RC, Victors ,and such stay alive. Within a few seconds, the RC starts to indicate low voltage, but keeps on going.

Is this really what IFI had in mind?

Ray
Team 1138 Eagle Engineering

Re: Custom Chargers for backup battery
 

Ray, connect it through a spike. Power the robot off, the spike disconnects.

Can you put an ammeter on the backup battery and measure the charge rate? I get about 100mA even with a fully charged backup battery. If we use the charger, I will probably use a timer to turn the spike on and off to prevent overcharging.

Even without the charger, our RC will stay energized after the main breaker is turned off, until you hit the reset button.

Re: Custom Chargers for backup battery
 

We built a couple (one for a spare) and measured ~98ma charge current with a fully charged backup battery (~7.4v). Disconnecting the 12v and the RC we measured a ~5-6ma discharge current back through the charger circuit. We haven't pulled the 43ohm resistor, but the next one we build we leave out this resistor to measure how much charge is coming through the regulator and how much is unregulated through the 43ohm resistor.

Bud

Re: Custom Chargers for backup battery
 

That is a design feature. The IFI manual says it will shutdown in about four minutes if you forget.

Re: Custom Chargers for backup battery
 

The manual describes the behavior with the 2004 master code. In 2005, the timeout changed to something more like ten seconds.

Re: Custom Chargers for backup battery
 

This from the RC reference guide 6/13/06
The Robot Controller cannot start running from Battery Backup power only. It requires Main Power connected at the required voltage to initially power on. If Main is lost and a link with an OI connected to an Arena Controller had been established, the RC will continue to operate with only Battery Backup power for approximately 4 minutes before it automatically turns itself off. If Main Power is lost under any other condition, the RC will continue to operate with only Battery Backup power for approximately 4 seconds or until the RESET button is pressed. This is to ensure maximum Backup Battery life.

Re: Custom Chargers for backup battery
 

Hey, One question is anyone making the backup battery custom charger for sale??
just wondering!
natalia

Re: Custom Chargers for backup battery
 

Actually, if you're attending the San Deigo or LA Reagonal our team, 1388 will be handing out the boards and materals for them (some assembly required) and you can make them for your bot.