I'm trying to use an IRLB8721 and Nano to run some high power resistors in order to heat up a small box to ~35 celsius. It's PID controlled, and was varying heat by turning the Fet on or off in different time segments.
My issue is that the high power resistors are low resistance (in order to get maximum heating) and result in a lot of current through the fets to the point where they get too hot to handle, even with a 1A PSU. I would add in a series resistor but they would remove the heating efficiency.
Any suggestions or better ways to go about this? Goal is just to heat up a small box (8x8x2") with as little space taken as possible.
Note: I tried to use the Qwiic Single Relay but it looks like something may be wrong with the onboard controller, and the board by itself cannot drive the relay from digital pins.
Can you provide some information?
Links so we know what parts you have
The spec of the PSU - 1A what voltage?
What value resistors (the resistance and power rating)
a schematic
It is not a good idea to limit your current to 1A by choosing a power supply that says 1A.
1 it will most probably deliver more
2 it may get damaged
3 it will not maintain its rated voltage
All this unless it is a lab power supply where you can control the current with a knob, or it is a constant current supply...(the latter would not be good for different reasons).
What is the ambient temperature, that is, outside the box ? Is the box insulated and, if so, on the inside or outside and of what material is it made and what is its weight? How rapidly must it heat up to the desired temperature ? I'm guessing that a few watts should be enough unless the requirements are extraordinary.
Can you please post a copy of your circuit, a picture of a hand drawn circuit in jpg, png?
Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, power supplies, component names and pin labels.
Post an annotated schematic as @TomGeorge suggested. I’ll make an educated guess: if you look at the IRLB8721 datasheet, you’ll see that it’s not well-suited for driving directly from a Nano port. You’ll need a gate driver to achieve a Vgs voltage of at least 8 volts, as it is not a logic-level FET. Another option is to choose a MOSFET that fully turns on at around 4 volts, rather than just starting to turn on. Remember, Vgs is the threshold voltage at which the MOSFET begins to turn on.
I think that's a typical graph for a logic level power FET.
Fig1 showing that it's usable from 3volt, and fig12 showing you that you really should drive it with more than 4.5volt at higher currents. The table also lists an 'on' resistance from 4.5volt, which is 5volt-logic.
Leo..
