From: James T. <ja...@al...> - 2008-11-14 20:18:00
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RussellMorin wrote: > I measured the current while the stack was booting up and it fluctuated > between 0.35 and 0.5 amps. The voltage regulator should be able to handle > 1.5 amps. It made it as far as the login screen before cutting out this > time. Do you think adding a fan to convection cool the voltage regulator > might stop it from cutting out? Do I need a larger battery? > > -Russell > Yes, it has to be thermal limiting given those numbers. The device does not have the capability to deliver 1.5A in all configurations, and as such will go into thermal limiting. Lets take a quick look at some more numbers, since you have given current readings: Voltage drop across the regulator is 9.4V (14.4-5). Thermal impedance, junction to ambient is 50 degC/W (for TO-220). Max junction temperature 150degC Ambient temp 20degC (150-20)/50 = 2.6W, this is the amount of power disspated by the regulator that will put the junction temp at 150degC. 2.6/9.4 = 276mA This is the amount of current that will cause 2.6W to be dissipated by your regulator. So, it _IS_ thermal limiting. You can try a heatsink, but your best bet is going to be a switching regulator (or drop the battery voltage as was also suggested). James |