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PubInv / moonrat

Moonrat: A second-generation portable incubator
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Maximum Heater Current, Control Assembly, Build of 2023, IRF520NPbF, Future Use IRF540NPBF? #189

Closed ForrestErickson closed 8 months ago

ForrestErickson commented 9 months ago

During the team discussion of 20240116, we spoke about the maximum current into the heaters which the Control Assembly might provide into the incubator heaters. Each of the heating pads (Sparkfun COM-11288) will draw about 2.5 A at 12V.

The 2023 Control Assemblies

The maximum current into the heater will be limited by the current carrying capability of Q1. For the assemblies build in late 2023, here is part of the schematic and is an IFR520N. image

Under some test conditions, this part is rated at 6.8 Amps. And in the MoonRat II will have to be operated at less than that because our gate voltage is about 5V not the 10V for which the part is rated. image

So the 2023 Control assemblies should be able to provide current for two heating pads because 5A < 6.8 A.

Opportunity forward

If next time we build we change the schematic and BOM to call out IRF540NPBF, (JLCPCB part number: C2566) the Control assemblies may be able to provide more current. Under some test conditions, this part is rated at 23 Amps. And in the MoonRat II will have to be operated at less than that because our gate voltage is about 5V not the 10V for which the part is rated. image

Assemblies which user this part may be able to provide current for as many as 9 heating pads.

Other Design Constraints

We will want to consider adding additional screw terminals on the Heater Assembly PCB to make assembly within the incubator easier. We must review the current caring capability of our connectors, especially the IDC connectors.

CC: @SilviaKarbid @HJGV05 @kant

ForrestErickson commented 9 months ago

@RobertLRead Should have tagged you to Robert.