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Max Blower Power

Bryan Mayland edited this page Mar 27, 2019 · 1 revision

What is the maximum allowed power draw of the HeaterMeter blower?

Up to 250mA

The first limitation of blower output power is going to be the input power supply. With the suggested 12V 1A power supply, along with a Pi 3B+ (with wifi) and servo damper, the maximum blower power is 12V 250mA / 3W. The suggested blower can easily support all size BGE Big Green Eggs (up to XXL), WSM Weber Smokey Mountains (up to 22"), UDS Ugly Drum Smokers (~55 gallon), and may offset smokers.

Up to 1000mA / 1A

The HeaterMeter 4.2 and 4.3 boards are designed with for a maximum of 1A through the blower step-down circuit. Therefore, a 12V 2A power supply should be able to drive a blower up to 1A without any modifications to the HeaterMeter. A properly selected 1A (12W) blower can probably support smokers up to the size of a large sofa.

Beyond 1A

If a larger blower beyond 1A is desired, the limiting factors (in addition to the power supply) are:

  • Max current (DC Current rating) through inductor L1
  • Max current (Forward Current rating) through freewheeling diode D2
  • Max current (Ripple Current rating) on the AC portion of the voltage at C12
  • Max current (Continuous Drain Current rating) on the power MOSFET Q2 -- this should be fine up to 9A
  • Max power dissipation on the power MOSFET Q2 -- should be somewhere around 3.5A but might require more cooling
  • Current through the power traces (16mil thickness, 1oz copper) -- somewhere around 0.95A for 10C rise
  • Max power through the RJ45 jack 1.5A
  • Max power through the 2.1mm barrel jack 1.5A

So in short, you'd definitely need to upgrade the inductor L1 to something with a larger current rating, and most likely D2 as well. Then almost certainly change C2 to something with a higher ripple current rating. Q2 might need a heatsink. You may want to augment all the PCB trace connections with small wires. And finally, the barrel jack and RJ45 jacks are not well suited to the higher current application and will need to be replaced with a different style connector.

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