Hello,
I need to control with Arduino 6 resistive heaters of 30W 12V, 180W in total
I have some mosfet IRLZ44 with heatsink. Could I connect the six resistors with a single mosfet? How many mosfets would I need?
Thanks
One mosfet per heater, and controlled/switched with one Arduino pin per mosfet gives the lowest losses.
The mosfets should barely heat up, and almost all the power ends up in the heaters.
One mosfet to switch them all will have the highest losses.
Heater currents ^2 * Rds(on) = 15^2 * ~0.05(hot mosfet)= 10-12watt. Need big-ish heatsink.
PWM control will increase heat.
Leo..
One MOSFET for all of them is good, simpler, cheaper, but you'll need a better MOSFET than the lowly IRLZ44,
something that's logic-level with on-resistance of 6 milliohms or less and a small heatsink would be more like it.
Go for a 30V device, lower voltage is usually lower on-resistance for the same price.
If you want to use PWM, you'll have to carefully consider the gate drive current - an Arduino pin can't give
much drive current. Certainly if you powered 6 MOSFET gates from one Arduino pin PWM might lead to excessive
switching losses and overheating of the MOSFETs.
With PWM you have to allow for switching losses which depend on switching time times twice the PWM frequency.
For instance with 1kHz PWM, 10us switching time would mean 2% of the time the MOSFET is dissipating
about 25% of the load power (roughly, for resistive load). For 180W of load that's 45W x 0.02 = 0.9W
Higher PWM frequencies are more problematical.
But for simple on-off (which is more likely with a heater), slow switching isn't an issue.
Thank you for your answers.
MarkT:
One MOSFET for all of them is good, simpler, cheaper, but you'll need a better MOSFET than the lowly IRLZ44,
something that's logic-level with on-resistance of 6 milliohms or less and a small heatsink would be more like it.
Go for a 30V device, lower voltage is usually lower on-resistance for the same price.If you want to use PWM, you'll have to carefully consider the gate drive current - an Arduino pin can't give
much drive current. Certainly if you powered 6 MOSFET gates from one Arduino pin PWM might lead to excessive
switching losses and overheating of the MOSFETs.
...
But for simple on-off (which is more likely with a heater), slow switching isn't an issue.
My control is a simple on-off: they are 3D RepRap printer heaters, but I want to use them to heat an aluminum container to 200ºC.
MarkT, Could you tell me two or three mosfet models with these characteristics?
curro92,
I think the IRLZ44 will do fine and they have a low Gate to Source requirement which pairs well with the arduino output.
I don't know what you actually need for heaters but assuming you have more heater than you need, you can make the control loop more flexible if you used 3 Mosfets.
3 heaters on MosFet #1
2 heaters on MosFet #2
1 heaters on MosFet #3
Maybe all 6 to start from cold then 1 to 6 can be chosen to keep the temperature stable. This is unless the location of the heaters precludes such a configuration.
Good Luck
Thank you very much to all.
I tested connecting all the heaters to a 12V battery, the temperature rise is quite slow, but sufficient. The inertia is small: when I disconnect it keeps going up only 2-3 degrees. No problem.
I will connect the heaters to 2 mosfet, 3 + 3, and see if they heat up or not.