Hi Craig,
Paul's going to be out of town next month and we should carry on his
"problem of the month" theme. Perhaps you'd like to bring some of your
hardware to the February meeting and we could chat about it at after
announcements but before Charles Lord's talk? Brian's done a wonderful
job of moving your design in the direction of safe closure and it would
be great to see faces behind the email.
Folks on the list should know that Craig was responsible for most of the
video recordings of past TriEmbed meetings (Charley West did the others).
-Pete
On 1/10/20 10:33 AM, Brian via TriEmbed wrote:
On 1/9/20 9:08 PM, Craig Cook via TriEmbed wrote:
I appreciate everyone's advice. I think I added to the confusion of
what I am playing with.
We aim to please and/or confound! XD
<snip>
For the Fan I was basing my ideas off this:
https://itp.nyu.edu/physcomp/labs/motors-and-transistors/using-a-transistor-to-control-high-current-loads-with-an-arduino/
It seems to control a 12 VDC motor using a FQP30N06L 60V LOGIC
N-Channel MOSFET
The fan I am using seems to be running from 20 VAC with a bridge
rectifier.
Plan A
Use an external 19 VDC, 2A power supply with a FQP30N06L to do PWM to
control fan speed. Based on my understanding of the nyu tutorial, I
think that should work. The onboard 20 VAC supply will not be used.
This is definitely the best approach if you have the external DC power
available. Much simpler and safer.
Plan B
Use the built in 20 VAC supply with something else to do PWM control
for fan speed.
I believe the consensus for Plan B is to use an AC Solid-State relay.
Given that I know 20 VAC and 58.3 ohms are involved with the inner
coil, I believe that means there is 0.34305 amps involved.
Not quite. You need to add up the impedance of the inner coil AND the
motor, and then divide that into 120 VAC to get your current. Also
note that AC impedance isn't quite the same as DC resistance, but for
heavily inductive loads (like motors and coils), the actual impedance
is higher, so your DC math will give you a good "worst case" cushion
around the actual AC current. Then double that to spec your parts.
If I want to use the existing AC line, I could use one of these to
control it
https://www.digikey.com/product-detail/en/ixys-integrated-circuits-division/CPC1706Y/CPC1706Y-ND/3077519
(along with resistors to drop the ardunio digital control into the
1.2 VDC range)
Actually, no. That SSR is rated for a load voltage of maximum 60 V.
But when your fan circuit is turned off, no current is flowing through
the inner heater coil, so no voltage is dropped across it; therefore
your switching element will see the full 120 VACrms (~170V pk) when it
is in the "off" state. I'm sorry to say I've forgotten who mentioned
it first; someone did a few layers back in the thread.
For both Plan A and B I was planning to leave the bridge rectifier in
place.
No harm in that.
-B
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