Since I am new in this forum, first Hello to everybody 
I am looking into interfacing my newly bought BotBoard II with some Kondo KRS HV servos.
These servos are using 10.8V (max 12V) and I have quite a few batteries left from my previous robot at that voltage.
I wonder if I can plug a 10.8V into VS without any problem.
Additionally could I plug it into VL ? (If not I don’t mind using a 9V battery)
The LM2937 seems to support up to 26V and going from 9V to 10.8V shouldnt be that big difference in terms of heat dissipation I would think.
Thanks
Laurent.
The voltage regulator is de-rated to only handle 250ma on the 5v bus. The 9v limit said in the documents is the max you should use before needing a heatsink. So, theoretically you could use 10.8 but something might melt! Also, your batteries wouldn’t last as long since your are losing more to heat. I would separate your supplies and use a 9v or less for the VL and your 10.8 on the VS. Hope this helps.
I’m fairly new myself so I’m happy to help another new guy!
Understood. I will do that.
And since at first I won’t be using the servos, I might as well not stress the board unnecessarily.
I am sure that I have some heatsink lying around so I could add one if needed but better be on the safe side for now.
Thanks.
All true but honestly unless you’re connecting a lot of extra stuff to the 5vdc output there shouldn’t be a problem using 10.8. The limit is in place to prevent the regulator getting too hot. Connect it and test to see if the regulator heats up. If not then you are good.
For example with the Vin at 9vdc
Vin = 9vdc
Vout = 5vdc
Vdrop = 4vdc
volts * amps = power in watts
power dissipated at 500mA = 2.00W
power dissipation at 250mA = 1.00W
power dissipation at 60mA = 240mW
Now change the Vin to 10.8vdc
Vin = 10.8vdc
Vout = 5vdc
Vdrop = 5.8vdc
volts * amps = power in watts
power dissipated at 500mA = 2.90W
power dissipation at 250mA = 1.45W
power dissipation at 60mA = 348mW
Now change the Vin to 12vdc
Vin = 12vdc
Vout = 5vdc
Vdrop = 7vdc
volts * amps = power in watts
power dissipated at 500mA = 3.5W
power dissipation at 250mA = 1.75W
power dissipation at 60mA = 720mW
That’s as far as I can take it. Not sure how to calculate the temperature the device will reach given the power dissipation. Perhaps Eddieb can shed some light on this?
Great,
I will try. At first I won’t have a lot more than the 3 sensors that comes with the A4WD1 so it should not need that much power.
The good thing is that I have a few batteries in 10.8V and being able to use them will just save me the pain (and money) of ordering another one.
I might well switch for a stronger 6V battery later but at least for now the ones I have should do. (10.8V 300mAh, 800mAh and a 7.4V 720mAh )
I have just finished assembling the kit and will do some tests this week-end.
Thanks.
