What would cause a N channel MOSFET FQP33N10 to short between the Gate and Source? Im trying to control 12V 2A power to an electromagnet through the MOSFET but cant seem to get the Gate to work. I test the MOSFET prior to using with a multi meter and all is well, but when I turn on the power it shorts. Ive gone through 3 so far and would really like to know what is causing this.
Thanks
Not sure but that transistor may not be a logic MOS FET and may not be saturating.
Also, your snubbing diode may be bad.
.
To turn really hard on the FQP33N10 needs a bit more than 5v on the gate ..
perhaps you could post a circuit diagram so we can help
regards
Allan
The fact that it "shorts" after you have turned on the power, strongly suggests you don't have a snubbing diode across that inductor (electromagnet) you are driving and the inductive kick is probably breaking down the transistor with a large spike. Any inductor like that needs a diode across the coil in the opposite direction of the current flow. Without that, you can get a spike of 100 volts or more.
Hi,
Welcome to the forum.
OPs Circuit;
The resistance of the coil is 4.5R, if you are PWM to 255, or digitalWrite HIGH, then you have 12V across it.
12/4.5= 2.66Amps.
Your N-Ch MOSFET is not a logic level type so it will not be turning fully ON.
What is your 12V supply and do you have a fuse in the positive line to protect the circuit?
Is your 12V supply gnd connected to the Arduino gnd?
Is the BackEMF diode the correct way round?
Place a 470R resisitor in series between pin D11 and the gate of the MOSFET.
If you are shorting gate to source then you need this resistor to protect your Arduino.
You need to test if pinD11 is still working.
Place a 10K resistor from gate to source to ensure that open gate circuit will keep MOSFET OFF.
Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html then look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.
Thanks.. Tom.. 
Nikoli:
What would cause a N channel MOSFET FQP33N10 to short between the Gate and Source? Im trying to control 12V 2A power to an electromagnet through the MOSFET but cant seem to get the Gate to work. I test the MOSFET prior to using with a multi meter and all is well, but when I turn on the power it shorts. Ive gone through 3 so far and would really like to know what is causing this.Thanks
No idea why its shorting, it shouldn't.
But it won't work as that's not a logic FET - it could be overheating, but you've have noticed that.
Reasons for a MOSFET failing are gate-source overvoltage or static damage, or burning out through
too much dissipation, or overvoltage on the drain (failed free-wheel diode possibly?).
[ One last thought - were the MOSFETs from a reputable supplier - might they be factory rejects from eBay? ]
latchup?
While that may not be a true logic level FET, the datasheet shows that 5V of gate drive should result in about 10A of drain current (unless I'm tragically misreading it). Figure 2 (Transfer Characteristics):
http://www.mouser.com/ds/2/149/FQP33N10-1009544.pdf
My guess is that it's getting pounded for lack of a clamping diode on the coil. (EDIT2 Ooops, I see he has one. hmmmmm)
EDIT: Also, that 2A 12V supply is a tad weak considering the 2.7A load on it.
I'm not sure if I agree that a gate pull-down resistor is absolutely necessary unless the coil is hot all the time. With the Arduino pin set to output, the gate is going to be driven one way or the other (not floating) pretty much at all times excepting when the Arduino is booting up. It wouldn't hurt anything to add one, though I might personally choose a larger value (100K+).
I'd appreciate some feedback (or brow beating if I need it 
from MarkT. I'm pretty rusty these days.
It's usual to use a resistor of 100 ohms or so in series with gate of a power MOSFET, partly to prevent parasitic oscillations. Unusual, but it can happen. Very layout dependant. And here because you're not fully turning the fet on.
Try it
Allan
Thank you all.. After reading your posts, I found that I had not placed D2, a NTE116 standard power Diode in reverse bias mode, and the power supply was not grounded to the Arduino. I have checked Pin 11 and it works, the electromagnet, when connected directly to the power source, works as well, heats up after a bit, but works. I have ordered 5 more MOSFETs that should arrive in 4 days.. just in case. The power supply Im using is a 12V 2.0A max FSP024-1ADA21 that I had lying around... any suggestions on a better one?
Something like an IRL1104 might be a better choice - with 5v on the gate a much lower d-s resistance, and wouldn't get so hot
Allan
allanhurst:
It's usual to use a resistor of 100 ohms or so in series with gate of a power MOSFET, partly to prevent parasitic oscillations. Unusual, but it can happen. Very layout dependant. And here because you're not fully turning the fet on.Try it
Allan
Such parasitics are only a problem in paralleled MOSFETs, not single MOSFETs. Early MOSFETs had
such high on-resistances they were very often paralleled and thus gate resistors used. A gate resistor
for a single MOSFET can be used to control the switching speed (slow it down for less EMI), or to protect
the driving circuit from overload.
Also use of gate resistors in paralleled MOSFETs helps dynamic current sharing during switching when
device threshold/plateau voltages are badly matched.
Nikoli:
What would cause a N channel MOSFET FQP33N10 to short between the Gate and Source? Im trying to control 12V 2A power to an electromagnet through the MOSFET but cant seem to get the Gate to work. I test the MOSFET prior to using with a multi meter and all is well, but when I turn on the power it shorts. Ive gone through 3 so far and would really like to know what is causing this.Thanks
Your diagram shows a coil of 4.5 ohms. At 12 volts, that's 2.67 amperes. According to the data sheet for your mosfet, the Vgs required at that current is around 4.5 volts. I'm guessing that the mosfet is barely turning on and being killed by heat.
Does it get hot, or does it "just not work" the moment you try it?
gpsmikey:
The fact that it "shorts" after you have turned on the power, strongly suggests you don't have a snubbing diode across that inductor (electromagnet) you are driving and the inductive kick is probably breaking down the transistor with a large spike. Any inductor like that needs a diode across the coil in the opposite direction of the current flow. Without that, you can get a spike of 100 volts or more.
Did you look at the OP's diagram? There's a diode in there.
tinman13kup:
latchup?
Seriously?
tinman13kup:
latchup?
Latchup is a feature of CMOS circuits where the n-wells can form parasitic BJT action. Single MOSFETs
don't have n-wells. Latch-up - Wikipedia
MarkT:
Latchup is a feature of CMOS circuits where the n-wells can form parasitic BJT action. Single MOSFETs
don't have n-wells. Latch-up - Wikipedia
I know that. That's why I asked "Seriously?"
I haven't observed the MOSFET while its been on (heat buildup)... adding that to my list of things to do when my new MOSFETs arrive, hopefully sometime today or tomorrow. The first time I tried this, the MOSFET melted the breadboard around the three leads, but this hasn't happened since then when I have used different MOSFETs. When I turn the Arduino on, I dont see any change in electromagnet, it doesnt turn "on", and when I turn everything off, the MOSFET has a short. So far the short has been between the source and drain(magnet was "on" constantly) , and the last two times between the source and gate (magnet didn't turn on at all). I'm hoping having the diode in reverse bias will help, along with grounding the power to the Arduino.
Krupski:
Your diagram shows a coil of 4.5 ohms. At 12 volts, that's 2.67 amperes. According to the data sheet for your mosfet, the Vgs required at that current is around 4.5 volts. I'm guessing that the mosfet is barely turning on and being killed by heat.Does it get hot, or does it "just not work" the moment you try it?
The FQP33N10 is not a logic level MOSFET and requires 10V or more to operate as a switch
according to its specs. The graph you refer to is for Vds=40V, it is nothing to do with operating
the MOSFET as a switch(*). It is also a "typical behaviour" graph, and the process variation in gate
voltages for MOSFETs is substantial, often +/- 1V or so.
(*) That graph shows that for 2.6A at 40V the device has a resistance of 15 ohm and is dissipating > 100W (if a 40V supply was available).
When the device is switched on it has a resistance of 0.04ohms and dissipates about 0.1W.
Problem(s) solved! Thank you to everyone who responded to my question! I believe my main problem was not having the power supply grounded to the Ardruino. To solve this, I connected my 12V 2A DC power supply to the DC power input, then used the VIN pin on the Ardruino to power the magnet and the negative lead of the magnet to a ground pin on the Ardruino, worked the first time out! Again.. thank you all for your help.
