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Topic: Mosfet (Read 5124 times) previous topic - next topic

ReverseEMF

ok im back because it didnt seem to be quite that.  It turns out when I touch the back of the mosfet is when it works.
Define "works".  
"It's a big galaxy, Mr. Scott"

Please DON'T Private Message to me, what should be part of the Public Conversation -- especially if it's to correct a mistake, or contradict a statement!  Let it ALL hang out!!

Marciokoko

Well the issue was that when I sent the signal to turn on the mosfet sometimes it would work and sometimes it wouldn't.

I noticed that every time it didn't work I would start trying out new mosfets and they would work during the same time and when I tried any one of them about 2 days later neither would work even though they did work a couple of days ago. 

So I've noticed that if I let the setup sit for a couple of days and try to turn it on they fail.  But if I touch the back plate slightly they work.

TomGeorge

Hi,
Can you please post a picture of  your project so we can see your component layout?

Thanks.. Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

Marciokoko

#78
Jun 12, 2018, 02:28 am Last Edit: Jun 12, 2018, 02:28 am by Marciokoko
Sure, here it is.  Sorry its from an old post but here it is:


ReverseEMF

Sure, here it is.  Sorry its from an old post but here it is:


Can't see all the connections -- how about a picture of the back.  
Also, this is a very strange problem, so you need to give us as much "help" seeing what's going on, as you possibly can.  No offense, but we have to assume you're making a simple "newbie" mistake, but we can't discover that mistake, unless we can see [and I mean really see] your setup.
"It's a big galaxy, Mr. Scott"

Please DON'T Private Message to me, what should be part of the Public Conversation -- especially if it's to correct a mistake, or contradict a statement!  Let it ALL hang out!!

allanhurst

It HAS to be a simple wiring  mistake - we've all made them.

Look very carefully at your diagrams - which ought to work with the 1k load -  and compare with your actual wiring.

Allan

Marciokoko

#81
Jun 12, 2018, 03:22 am Last Edit: Jun 12, 2018, 03:23 am by Marciokoko
Here:




TomGeorge

Hi,
Can you connect the two Nano gnds together, just in case the a gnd track has popped on the Nano and one is no longer giving adequate grounding.

Thanks.. Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

Marciokoko

How do you mean?  They are connected together by the black wire.

TomGeorge

#84
Jun 12, 2018, 04:59 am Last Edit: Jun 12, 2018, 05:00 am by TomGeorge
How do you mean?  They are connected together by the black wire.
The black wire connects one gnd pin to the MOSFET Source.

The other gnd pin  is connected to the 6k2 resistor you have going to the MOSFET gate.
Put a link between the two gnd pins, at the moment you are relying on the gnds being connected together on the Nano board.
Thanks.. Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

Marciokoko

Ok I put a connection between GND pins and I still get the issue.  I noticed a consistent, reproducible issue: the first time I set the pin-to-gate HIGH, the voltmeter doesnt move so I set it back to LOW.  The second time I set it to high, it starts slowly moving up to 0.90V then 1.0V (2-3 secs) then it jumps to 2, 5, and finally 8.7V (1 sec)(cause its a 9V) so Im guessing the channel forms but slowly?  But why would it never open up the first time around?

ted

#86
Jun 20, 2018, 04:58 am Last Edit: Jun 20, 2018, 04:59 am by ted
Put in parallel to diode a small 9V light bulb, disconnect wire from D5, apply 5V to gate - the results ?


Marciokoko

Ok you mean disconnect cable from D5 to mosfet Gate pin in order to apply 5V directly to Mosfet gate?  From where?


ReverseEMF

#88
Jun 21, 2018, 08:27 am Last Edit: Jun 21, 2018, 08:32 am by ReverseEMF












It sure sounds like the Drain is open [i.e. nothing is actually connected to it].  And  the Top Photo seems to corroborate that hypothesis.  But, because that section of the Bottom Photo is covered by the "HEADER DRAIN DIODE" label I can't tell for sure.

Also, from neither photo can I determine if anything is actually connected to the Gate.

Have you used a continuity tester to make sure all of the connections are correct, and actually made?  And, you must test from part pin to part pin.  Not from solder connection to solder connection.
"It's a big galaxy, Mr. Scott"

Please DON'T Private Message to me, what should be part of the Public Conversation -- especially if it's to correct a mistake, or contradict a statement!  Let it ALL hang out!!

Marciokoko

#89
Jun 21, 2018, 05:09 pm Last Edit: Jun 21, 2018, 05:09 pm by Marciokoko
Yes the Drain of the mosfet is connected to the female header pin1.  Here is the Drain connection in yellow, both to diode (in blue) and female header pin 1 (in fuscia):



As for the Gate, yes its also connected to D5 which activates it and to the GND pin thru the 6.2k R (all in light blue).


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