Should i be worried about an IRL520 overheating if i put it in small enclosure and fill it with hard pcb epoxy. I would be fully saturating the gate and pulling 8A @ 12v for ablut 5 hours continiously?
If yes, then is there a mosfet more suitable for this. Im worried about thermal runaway. I want to protect them from the rain so i was thinking about resin printing an enclosure and filling it with epoxy.
The easier solution is to use a different MOSFET with a lower RDSon (more amps). The extra cost will be less then a heat sink or other solution. Be sure to watch the VGS.
Can you think of a mosfet that would be more suitable for this. Sorry to sound lazy, i know there are soo many to choose from. The mosfet will always be fully saturated. Need to be logic level 5v or 3.3v and rated for atleast 12-14v 8A.
How about the IRLB3034PBF? It appesrs to have a lower RDSon at 1.7mohm
Any device that dissipates a few 10s of mW of heat will probably fail if enclosed in epoxy.
You need to place the MOSFET on a metal plate that is exposed to the outside but you also need to find another MOSFET with a lower Rds(on).
MOSFET power dissipation not only depends on the static Rds(on) but how fast you turn it on and off.
Will you be using PWM with this MOSFET?
No i would simply just turn it fully on with the arduino output. The gate would be fully saturated. Im using it just as a switch for an 8 amp load from an led strip.
Im trying to stay away from using a relay because i want to save as much space as possible. Im going to put the enclosure on my bike and want it to be water resistant, thats where i got the idea to resin print an enclosure and fill it with epoxy. I've never used the epoxy before so i didn't know what to expect.
I found some cheap aluminum fin heatsinks that i could partialy expose the fins through the epoxy but they still wouldn't get much airflow if any. I was hoping to find a mosfet i could just use in the epoxy filled enclosure without it thermally running away.
These are the cheap heatsink i speak of,
60 Pcs 20x15x10mm Black Aluminum Heatsink for TO-220 Transistor https://a.co/d/eHma4B3
I could see how the epoxy could insulate the heat around the mosfet.
This is the epoxy i was looking at
Epoxyseal 9000 Electronic Grade Potting Epoxy, Epoxy Resin PCB Coating, Electronic Potting Epoxy, Casting Epoxy - 48oz KIT. https://a.co/d/htm8qlW
Make one side of your enclosure metal and mount the MOSFET on the metal. Then you can pot the entire inside of the enclosure. With the IRLB3034PBF that should be enough of a heat sink.
That should be fine assuming you will be driving the gate with 5V. Do not forget the pull down resistor (10K) between the port pin and ground. I am assuming an UNO as you did not tell us. If you are worried add a small piece of metal to the tab but be sure to use heatsink grease before epoxying it. The metal would be enclosed in the epoxy. The epoxy we used years ago conducted heat but I could not find that information on this product. Be careful of your lead dress when assembling.
I was just reading about using an insulator and thermal compound on the the heatsink. Still not sure if the insulator is going to be required but im thinking about skipping the insulator since the bike frame is not grounded or part of any circuits.
If you use a metal plate like I suggested, then you will need and insulator, otherwise you run the risk of shorting 12V to ground
LEt me help you with this. My company used to build control boxes for motorcycles. They were similar to what you are doing.
The first thing is the epoxy is like water in that it will find ANY joint or opening to run out of. Second is ANY stranded wire going into the enclosure will wick water into the enclosure and your epoxy.
Third thing is air bubbles. When adding epoxy, do it slowly and move the enclosure around and turn is every way possible to let air escape. Then add more epoxy, and repeat. Let it set a while and repeat, until you have filled the enclosure and all the air bubbles have escaped.
Third, If possible place the completed project in a heated enclosure to speed up the setting of the epoxy.
The term saturation is not used with MOSFETs, that's for BJT transistors.
In case of a MOSFET, as you will see from the datasheet, the higher the voltage at the gate (until it reaches the limit, typically around 20V), the lower the on resistance.
So when you said "gate fully saturated" I was guessing you're driving it with a higher voltage, like the 12V of the circuit you're switching. But that's not the case, it's just 5V that you apply to the gate.
Are you sure about that? The term saturated in MOSFETS refers to operating the mosfet in its fully on region. It refers to somthing different in BJT terminologies. But it still applies to MOSFETS..
This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.