Another Quest M3 PID modification - Page 2

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afan (original poster)

#11: Post by afan (original poster) »

Dear Jim,

Thx for your message, you mean using a cheap SSR with an additional circuit instead of an expensive Phase Angle fire like Crydom MCPC. If you say the board watch for the main zero crossing, what is it different with a zero crossing SSR ?

Pls pm me for the information.

Alternatively, I found a cheap "phase control" SSR (linear control), it says, 4-20ma input and input resistance 1.2K. My question is 4-20ma at 1.2K input resistance = 4.8V --- 24V. How can I make use of the TC4 - IO3 to produce Vdc at this range ?

The specification of this cheap SSR is http://www.fotek.com.tw/pdf/etc_533.pdf


Alex
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JimG

#12: Post by JimG »

afan wrote:Alternatively, I found a cheap "phase control" SSR (linear control), it says, 4-20ma input and input resistance 1.2K. My question is 4-20ma at 1.2K input resistance = 4.8V --- 24V. How can I make use of the TC4 - IO3 to produce Vdc at this range ?

The specification of this cheap SSR is http://www.fotek.com.tw/pdf/etc_533.pdf
Yes, I think you could control this using PWM from the TC4's IO3 port. If I understand the data sheet correctly, it would require an external voltage source (at least 24VDC), an amplifier circuit to convert 0-5VDC voltage to 4-20mA DC current, and maybe an RC filter to smooth the IO3 PWM signal before it reaches the amplifier.

Does fotek offer a random-fire SSR? I like that solution better because it offers more flexibility through software, and you already have the AVR processor that is not really very busy.

Jim

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Carneiro

#13: Post by Carneiro »

This one (part number 84137200, random-fire, 10A, 3-32 VDC input) seems to cost around 40 USD in the USA, probably cheaper in Hong Kong:

www.crouzet-ssr.com/english/products/_gnip20.shtml

Could this resolve the fan control? I just have to PWM the controller and we are good to go? :mrgreen:

Márcio.

JimG

#14: Post by JimG »

Here's the system I'm using for bench tests right now:
  • Small PCB (25mm x 35mm) with isolated zero cross detector (ZCD) connected directly to mains
  • The ZCD outputs logic low approx. 500us before each AC cross
  • Connect arduino pin 2 (I/O2 on the TC4 version 5.20 board) to the external zero cross detector; this triggers interrupt 0 on falling signal from the ZCD
  • Created lookup table of values that maps requested duty cycle to phase angle delay (microseconds). My table is based on power output, i.e., the square of the area under the clipped wave.
  • Interrupt 0 handler function uses AVR timer1 to wait 500us plus the phase angle delay from the lookup table
  • After the delay, pulse the SSR (or TRIAC) long enough to latch it, again using timer1 to time the pulse.
I was lucky enough to find a supply of Crydom D2425-10 relays for a good price, so that is the SSR I'm using. The Crouzet you referenced should work just fine, too.

Since I don't have a Quest (yet), I'm doing my testing on a Poppery I, which also has an AC fan. So far, everything is working great.

It should be a very simple step to control the fan and heater directly from Artisan and the TC4 using this system. All you have to do is program the Artisan event buttons.

What's the level of interest in a mostly DIY system like this?

Jim

afan (original poster)

#15: Post by afan (original poster) »

Dear Jim,

Thx a lot for your detailed explaination. I am more inclined to go for a simple solution rely on phase control SSR and minimize the potential disruption on the Arduino and TC-4. I have using both Fuji PXR and TC-4 on Artisan, it seems to me that the Fuji is more stable. Below is the initial draft design:

[TC-4OT3] --> [RC filter ] --> [Isolated Amplifier 0-5V to 4-20ma ] --> [Phase control SSR] --> [Fan]

My question now is the value of "R" and "C" in the filter in response to the OT3 frequency, any recommendation?

The difficult part is to modify the M3 body by adding a SPDT switch on the shiney stainless steel cover to by pass the original dimmer FAN circuit. I want to keep the original manual operating mode even after the modification.

Appreciate if you can enlighten me on the RC part.


Alex
LMWDP #327
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JimG

#16: Post by JimG »

In the schematic below, I used a 47K resistor and 1uF capacitor in a similar application. That worked well.

Jim


afan (original poster)

#17: Post by afan (original poster) »

Thx Great!
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Carneiro

#18: Post by Carneiro »

I'm lost. :mrgreen:

Jim's explanation is to sync the pulses with the zero-crossing if I want to use a zero-crossing SSR to control the fan? And how about the random-fire, just pulse it and no worry about the zero, right?

Just to see if I'm understanding... To use a zero-crossing SSR with the heat element I don't need to worry about this, do I?

Márcio.

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Carneiro

#19: Post by Carneiro »

JimG wrote:What's the level of interest in a mostly DIY system like this?
I'm interested a lot! :mrgreen:

JimG

#20: Post by JimG »

Carneiro wrote:Jim's explanation is to sync the pulses with the zero-crossing if I want to use a zero-crossing SSR to control the fan? And how about the random-fire, just pulse it and no worry about the zero, right?

Just to see if I'm understanding... To use a zero-crossing SSR with the heat element I don't need to worry about this, do I?
Sorry about getting so far down into the weeds in that last post. TMI maybe. :D

To answer your questions, in most situations, powering a small AC fan using PWM pulses from a zero cross SSR will result in choppy operation of the motor. I suspect there is not enough mass in the rotor to mask the effect of completely skipping many of the little AC sine waves.

So to make the fan operation smoother, phase angle control doesn't actually skip any AC sine waves. It just uses a portion of each wave by waiting until part of the wave has gone by before turning on the SSR. For 60Hz mains, this means waiting to fire the SSR for between 0 and 8333 microseconds after the zero cross is detected, depending on how much power you've chosen to send to the fan. The arduino processor is easily fast enough to do this.

The heat element is not nearly as sensitive to the skipping of AC waves, so PWM with a zero cross SSR will work very well. You can use phase angle control for this too, but you would probably only consider this solution if you needed to reduce the effects of the pulsing on other things on the circuit (lights, for example).

Jim