I am using a Mega and I need to control a circuit that draws up to 8.4v 300w 36amp. The circuit will only pulse 2-5 seconds, once every couple minutes. The switch could be momentary or alternate.
I can rig a normal momentary switch and control it with a linear actuator, but I would rather do it electronically than physically.
I am new to electronics and any help you can offer would be greatly appreciated. Thank you
Please post schematics and links to datasheets to the external devices.
What, specifically, are you hoping to control?
Not sure I am understanding you. Let me tell you what I think you mean in MCU terms.
You want a timer to go off every 'couple minutes' that will trigger the gate of a MOSFET for '2 to 5' seconds at a frequency of ????.
The MOSFET must be a logic-level MOSFET able to control 36A at 8.4V.
If that sounds right, you will need to decide on 'every couple of minutes' or make it variable controlled by a pot or Bluetooth or WiFi. You will need a similar setup for the 2 to 5 secs and the frequency.
I am looking for the switch, not the timer. I can program the MEGA to do what I need it to do. I may resort to a second MEGA as well, because of the number of circuits I am trying to control, though I haven't finished the exact number of circuits yet.
I need a switch the MEGA can control that can handle 8.4v 300w
Sorry for the confusion.
The electronics I am trying to control currently has a physical momentary switch that turns on the 8.4v 300w component. I am trying to replace it with a electronic switch
The switch is the MOSFET unless you are planning to use a mechanical switch.
You mentioned at least two timer, 2-5 secs every couple minutes.
ok
so then I am looking for a mosfet that can handle 36 amps.
All I have been able to find is a max of 15 amps or lower
The popular IRLZ44N might be ok as long as it isn't on too long and has a heatsink, but if that is too sketchy, the STP55NF06Lcan handle 50A, and the IRL3705 can handle 75A.
Good luck.
thank you for your help 
So is post 10 the solution?
Probably
I will have to order it and see if it works or overloads
Like I said before, the most it needs to run is less than 5 seconds, several minutes apart, depending on input. I will set a software clock to prevent over usage or if there is no input. It should not over heat as the project box will have a fan directly blowing across the MOSFET and it's lack of usage. I believe I found a MOSFET board with it preinstalled and screw connectors for easy testing.
Swithing high current DC with a mechanical switch is much harder than switching AC.
If the load is inductive then you have another thing to consider. 36Amp of back EMF.
Please tell us what you're switching, so you don't get a pile of useless information.
An IRLZ44N could 'loose" 1volt @ 36A. Is this acceptable.
Leo..
Hopefully not the common boards with an IRF520.
Leo..
It is a micro heating element. I am not concerned about the loss of voltage. It can heat down to about 3.4v 125w. I do not intend to run it at 8.4v 300w but it is possible. Of course, at bottom end that is approximately 34amp vs 36amp at high end. Basically, it is instant on element at 93c-220c for seconds at a time. the element is liquid cool to prevent burn out. it will boil small amounts of liquid instantly, creating steam. I don't think EMF will effect the heater but it could the electronics. That is why I am placing the controller for the heater and the arduino out of range of the MOSFET just incase.
And no, not the cheap little asian board with the twin IRF520.
I think I am just going to get a STP55NF06L and a IRL3705 and wire them direct without a breadboard and test which works best. Of course, with a heatsink...
Using a solder PCB board
The control board for the heater came preinstalled with a mechanical momentary switch.
Trying to remove it so that I can control it without an actuator to push the button.
A really big heatsink with a lot of thermal grease and a fan.
Both MOSFETs will produce a lot of heat
Yes and the power may not be specified...
36 Amp is a lot of current, and you should be aware of how to handle that, and the safety risks. Be aware of the possible need for fuses (with sand) and what might happen if something short circuit.
The IRL3705 is produced in a lot of versions and from different manufacturers. I saw one that did not specify RdsOn at 4.5 V or 5 V Vgs. And you need to know that to be sure to limit the power loss of this power switch.
I would suggest a mosfet from Texas Instruments, CSD18510KCS. It have a specified Rds On of 2 mOhm (2.6 max) at 4.5 Vgs. At 36 A it is a power of 2.6 W. I saw it from Mouser for about 2 Euro.