<div dir="ltr">Craig,<div><br></div><div>The optoisolators allow the microcontroller to switch AC connected loads while isolating the microcontroller from the AC lines. Your AC solid-state relay for the heater coil has the optoisolation built-in. Actually you could use a DC solid-state relay for controlling the cooling fan as well. The only other components you would need to add are the input current limiting diode and the reverse-biased kick-back diode across the motor terminals. The IXYS DC solid-state relay below is $3 in singles (and IXYS makes nice parts). The diagram I shared in my previous message is basically how you would build your own solid-state DC relay. </div><div><br></div><div><a href="https://www.digikey.com/product-detail/en/ixys-integrated-circuits-division/CPC1706Y/CPC1706Y-ND/3077519">https://www.digikey.com/product-detail/en/ixys-integrated-circuits-division/CPC1706Y/CPC1706Y-ND/3077519</a> <br></div><div><br></div><div>Shane</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Jan 2, 2020 at 7:00 PM Craig Cook via TriEmbed <<a href="mailto:triembed@triembed.org">triembed@triembed.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><div style="font-family:"Helvetica Neue",Helvetica,Arial,sans-serif;font-size:16px"><div></div><div>>I was actually talking about the
voltage rating of the optoisolator used to drive the FET gate. The image
below more fully describes what I meant. I expect your final circuit
for the fan would include most of the items shown below (I am not sure
that you would need D2). <br></div><div dir="ltr"><div><br></div></div><div dir="ltr">Ah, I was working off this tutorial.</div><div dir="ltr"><br></div><div dir="ltr"><a href="https://itp.nyu.edu/physcomp/labs/motors-and-transistors/using-a-transistor-to-control-high-current-loads-with-an-arduino/" rel="nofollow" target="_blank">https://itp.nyu.edu/physcomp/labs/motors-and-transistors/using-a-transistor-to-control-high-current-loads-with-an-arduino/</a></div><div dir="ltr"><br></div><div dir="ltr">Their example uses a 12V motor. Mine is ~20V. I thought I was "close enough" to make it work.</div><div dir="ltr"><br></div><div dir="ltr">You are suggesting I need more components, i.e. at least add an <span>optoisolator into the mix.</span></div></div><div><br></div><div><br></div><div dir="ltr"><div>> How many popcorn
makers have you been through on this project? :-) <br></div><div><br></div><div><div style="margin-bottom:0in;line-height:100%" dir="ltr">LOL. Two have died from natural causes. I fried the heater on the third by running without a fan.<br>
</div>
</div><div><br></div><div dir="ltr">> the heater might
just be overheating a little bit each
time, gradually weakening itself until it breaks.
<div>
</div><div><br></div><div dir="ltr">Yes, that sounds like a great theory as well. The wire on the coil breaks, close to where the windings start. It may be due to the number of heat and cool cycles it goes though.<br></div></div></div><div><br></div><div dir="ltr"><div>>Also bear in mind that
your $30-or-so popcorn popper simply isn't built for longevity. <br></div><div><br></div><div dir="ltr">Yes. It's supposed to last 12 months of popcorn usage. For most units it's probably rare to be used many times in a 12 month period.</div><div dir="ltr"><br></div><div dir="ltr">The system I design needs to be reasonably easy to swap out the failed parts, which so far seems to be the heating element.</div><div dir="ltr"><br></div><div dir="ltr">Thanks</div><div dir="ltr"><br></div><div dir="ltr">Craig<br></div></div></div>_______________________________________________<br>
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