A 1.0 Ohm resistor should work. The Estes Igniter #302301 is about a 0.8 Ohm resistance and they normally fire these things with a 12 Volt lead acid battery.

I have used the MOSFET you are using with an Arduino and driving about a 0.5 Amp load, maybe only 400 mA as it was a RGB LED string but it worked fine using 5 Volts from an Arduino with a 10K gate resistor to ground. Pretty much as you drew it. This is also a good read from Estes if you haven't read it. Anyway while a 9 volt battery is not the best choice it should work as it did before for you. Something is not allowing enough current. You could try a fresh battery?

Ron

I think it was supposed to be a joke.

 

I think it was supposed to be a joke.

Slow on the uptake here.

Ron

 

Resistors have been used for igniters for model and high power rocketry for years, been there done that. The better choice is a 1/8 watt carbon film resistor. It generally takes about 14 watts of power for the resistor to burst into flames. Using a 9 volt battery with a 5.6 ohm resistor should be about right assuming the battery can deliver the required current.
SG

 

"Don't touch my uncle. You know? He's a genius of my family. He used to work for a big bomb factory. He used to make the tip of the bomb, the thing that finds, uh, New York or Washington, you know?"

​

 

OK I tried a fresh energizer battery. Still no go. The weird thing is that not only did it work before but also the estes igniter comes with a setup for a 9v battery.

 

The purpose is clear: It is to ignite the trigger fuse for an explosive device. They work very well in that application, being just slow enough to not detonate in response to noise spikes. The makers of IEDs are becoming more clever every day. And now there is some way for the arduino board to detect a passing truck while ignoring passenger cars.

Or instead of an IED, perhaps to ignite a model rocket engine. Or some fireworks.

My suspicion of a model rocket engine is confirmed by the TS reference to Estes, a model rocket supplier.

<edit> I missed @sghioto ’s reply.

 

OK I tried a fresh energizer battery. Still no go. The weird thing is that not only did it work before but also the estes igniter comes with a setup for a 9v battery.

Just for the heck of it manually gate the MOSFET, eliminate the Arduino and ditch the diode. This thing worked previously and if none of the wiring has changed it should continue to work.

Ron

 

Or instead of an IED, perhaps to ignite a model rocket engine. Or some fireworks.

My suspicion of a model rocket engine is confirmed by the TS reference to Estes, a model rocket supplier.

<edit> I missed @sghioto ’s reply.

An interesting and handy side-fact: I have re-used those Estes igniters by putting the used igniter in a new engine and then shaving the head of a paper match and gently packing the shavings into the engine opening behind the igniter. And it works every time. It does take some practice to get it just right, though.

 

Well the fet turn on at least somewhat because when I send high to the pin that the gate is connected to, header pins - multimeter goes from 0v to 9v.

Are you saying it might not be opening enough so I should apply 5v directly to its gate?

 

Hello,

As said before, change the fet to a logic gate version.
An IRL540 or similar will likely work better.

Bertus

 

Well the fet turn on at least somewhat because when I send high to the pin that the gate is connected to, header pins - multimeter goes from 0v to 9v.

Are you saying it might not be opening enough so I should apply 5v directly to its gate?

You know about resistive dividers, right? Well, a transistor when it's barely beginning to conduct acts like a high-value resistor. A digital voltmeter has a much larger input resistance, so all the voltage drops over the voltmeter. But what will happen if you replace the voltmeter with a 1 ohm resistor? Now all the voltage drops over the transistor, and none over the resistor. You can check that, just measure the voltage drop over the resistor. It's likely to be very small.
The mosfet you're using, when used as a switch, needs 10v at it's gate. For a mosfet that works as a switch with 5v at it's gate, you need a "logic level" mosfet, like the one bertus recommended.

 

I did it once before from a Nano that feeds a fqp30n06 mosfet that uses a 9v battery thru the resistor.

This may be of some interest. You mention the FQP30N06 and here is the Fairchild data sheet.

I have several FQP30N06L MOSFETS, take note of the L suffix in the part number. Here is another Fairchild Data Sheet.

Note that the second link has an L suffix and the data sheet reads in part: FQP30N06L 60V LOGIC N-Channel MOSFET with a reference to "Logic". The ones I have here are all L Suffix. However the data sheets, other than release dates are about the same. The L suffix doesn't seem to signify logic level on the gate.

I have used them, as I mentioned, with the 5 volt logic out of an Arduino driving loads and thinking about it loads as small as 125 to 150 mA. Additionally why would have your circuit previously worked and now not work? If you have the pin out correct and things connected correctly it should work just as before.

Ron

 

No place is it mentioned that this resistor has been verified as actually being a 1.0 ohm resistor. If it happens to be a 100 ohm resistor it will not even get very warm. So I am suggesting that measuring the resistor with an ohm meter makes sense. And then with the leads connected measuring the resistance at the other end of the leads. Consider that if it worked once, what has changed??? Has anything besides the resistor changed?? Back to basic diagnosis instead of redesigning the system.

 

The resistor is actually 0.7 ohm according to my meter. It was labeled as 1 ohm in the package.

I'll try and irl or irf when I get back home. I think I understand what you say about the resistance of the meter. Iow, I understand that the meter acts as a huge resistor compared to a 1 ohm resistor and therefore the voltage drops over the meter. I'm not sure why that means that this causes the meter not to read the voltage difference but I'll take it for granted.

I'll post back when I try the other fets

 

The resistor is actually 0.7 ohm according to my meter. It was labeled as 1 ohm in the package.

I'll try and irl or irf when I get back home. I think I understand what you say about the resistance of the meter. Iow, I understand that the meter acts as a huge resistor compared to a 1 ohm resistor and therefore the voltage drops over the meter. I'm not sure why that means that this causes the meter not to read the voltage difference but I'll take it for granted.

I'll post back when I try the other fets

You like;y have error in your meter and or the leads.

 

The point is that if you replace a 1 ohm resistor for a voltmeter, the circuit is not the same anymore. You basically replaced a 1 ohm resistor by an open circuit. That's as different as it gets. You need to measure with the 1 ohm resistor in place to know what is happening.

 

Hello,

The point is that if you replace a 1 ohm resistor for a voltmeter, the circuit is not the same anymore. You basically replaced a 1 ohm resistor by an open circuit. That's as different as it gets. You need to measure with the 1 ohm resistor in place to know what is happening.

That is why I suggested to put an 1K resistor parallel to the meter, in an earlier post.
Then there must be a current of about 9 mA (there is a 9 Volts battery) to see if the mosfet is conducting anything.

Bertus

 

Hello,


That is why I suggested to put an 1K resistor parallel to the meter, in an earlier post.
Then there must be a current of about 9 mA (there is a 9 Volts battery) to see if the mosfet is conducting anything.

Bertus

The whole purpose of the check is to see what voltage is developed across the one ohm resistor. What sort of voltmeter needs a 1000 ohm isolation resistor for a DC connection?? The cheapest VOM that I have seen was 5000 ohms input resistance. That would not make a readable difference for this check. So just connect the meter directly across the resistor leads.

 

You connected the voltmeter across the 1 ohm resistor? Ok, what voltage did it measure while "burning" the resistor?

 

Since the stated goal is to apply 9 volts across the resistor, and since there is no reason to not try it, connecting the circuit and reading the voltage across the resistor is the first step. Whatever voltage does appear will help to understand why enough voltage is not appearing. The causes could be an open connection, a failed mosfet, a weak battery, or even a high resistance in the test leads. We saw that problem in another post a while back. Those test leads with the cheap skinny conductors had a hundred ohms resistance. OR it could be a weak battery or the micro board may not be driving the transistor into saturation. But seeing just what does appear at the resistor connection will help discover where the problem lies.