On Jan 7, 4:05 pm, wrote:
Hi JF
I would have been happy to report that my 5V-24V switch worked with
the solenoid.
And it did...Until later that night that I discovered that my solenoid
must have gotten warm and melted in the middle and now the metal thing
is stuck in there. (that's what I deduce at least. After pulling out
the metal shaft, I can see brown discoloration in the inside of the
solenoid).
So I'm pretty sure I fried it with some sort of exhaustion. So now I
have the following questions:
- Is is possible that the diode can break it... I was wondering about
this befo If the magnetic field colapses and force current in the
opposite direction, does that mean the duty cycle extends further than
the amount of time that it is ON? So it is on for 0.5 seconds at 24V.
Then it colapses for 0.1 second at -200V. Should I add the power of
these together to calculate the duty cycle?
- Is is AT ALL possible that the MOSFET will allow some current
through if I have nothing connected to it (not necessarily negative
but just nothing).
- How does the mosfet 'decide' how much current to get through? Will
it just bridge the gap between the source and drain? Or will it put a
multiplier on the voltage or current of the gate? And then the
question that goes with this is: does is matter what size resister I
put in between my 5V pic and the gate?
One comment: I thought in the begginning that the gate is the middle
pin (like the base of a transistor). So I had my gate and drain the
wrong way around for about 10 iterations (and of course I was
scratching my head as to why the stupid thing didn't work). After that
it worked when I swopped it but maybe that introduced the timebomb
slow death for my solenoid.
-The final question I have is about my powersupply. Now it says it is
a 24V, 800mA, regulated power supply. (http://www.maplin.co.uk/
module.aspx?ModuleNo=48484&doy=7m1 --- the 24V one) This is a
switched mode PSU. Now, the bizarre thing is that despite all this 24V
talk theres a sticker on the power supply that say 24V and then also
"Typical voltage 21-35V" ---WTF?!?
I thought its 24 and that's it. Why would it be 35V sometimes?
Thanks again for your support and HAPPY NEW YEAR!
Ok, I read up on a few things so some of my questions are answered. I
know now that the gate never draws current becuase it is a FET. It
works with a field, the gate is insulated so no current flows through
it.
I think I find out why things went all wrong the other day. I realised
yesterday that I had the polarities of the 24V reversed. So I had 24V
at the source and 0V at the drain. In addition to mistaken the drain
with the gate pin, I think I had more than enough reason and flaws in
my little system to even break the MOSFET. I can confirm that the
MOSFET is not working now. Or at least: I THINK the MOSFET is not
working. Which brings me to another question: Is there an easy test
for a MOSFET to see if it's functioning properly?