Omaha, NE
Quoted from Moonbus:Not meaning to be like a dog with a bone but anyone got opinions on the Squawk and Talk board and how happy it will be with the GI input running at 7.4v and the 12v running at 18.5 ?
I see from the schematic that the Squawk board has a voltage rectifier setup similar to the solenoid driver board and almost the same TO-3. the solenoid driver board however has a proper heatsink whereas the Squawk has a tiny heatsink that heats up real quick.
The GI input I gather goes through a 7905 that does not have a heatsink. Given the increased voltage from spec do you think it would be prudent to add a heatsink or sail with it as is?
Can calculate if the 5V heat sink is sufficient or not. But first, does anybody know the actual current going into the S&T board?
If the existing board's heat sink is getting hot fast then an input voltage going from 12V to 18.5V will make it even hotter.
Not knowing what the current consumption is for the S&T board - so let's use 1 amp for simplicity sake. Probably higher since they spec'd a 78H05 for this part.
Using a 1 amp load:
If the input voltage was 12V then the power dissipated by the regulator would be approx [(12vin - 5vout) x 1 amp] = 7 watts.
If the input voltage was 18.5V then the power dissipated by the regulator would be approx [(18.5vin - 5vout) x 1 amp] = 13.5 watts.
Guestimating the existing heat sink has a thermal resistance of approx 7C/W:
For a 7W load -- it would climb by 49C. Add in ambient and the temp would be 76C.
For a 13.5W load -- it would climb by 95C. Add in ambient and the temp would be 120C. OUCH!
Going higher in current load will dramatically increase the temperatures.
