Well first , it can easily do 0-100% Power
0-1000% Power if you want .
Call 1000% your 5500w element and you can control 0-5500w in 1watts steps ...or any steps you you want .
The Math in the Aurduino sorts it and you can configure it how you like ....well thats the aim .
And theres the thing ...if you are not into micros ,then this isn't for you ...but iff'n you are , read on .
For years ,I've had a good old SSVR phase controller and its done it's job .But I have always liked the idea of the Auber controllers and being able to accurately dial in a percentage of power .
I now have an Auber DSPR1 controller .It has both Burstfire and Time proportional Modes of Power control and is part of their "easy Boil" range although it seems after the DSPR1, they dropped the Time Proportional Control in favour of Burst Fire and rightly so .
What is this Burstfire and Time Proportional Modes you ask?
First off , these controllers use an SSR .They conduct for a minimum of half a mains cycle .( thats 10mS for us 50Hz folk and 8.33mS for the 60Hz crew)
To be nice to the Power company , it's polite to use a full mains cycle .So if you want 0-100% control ,it will take 100 full mains cycles .
For us 50Hz folk ,thats 2seconds , but only 1.66 seconds for the 60Hz'ers
Well basically ,Time proportional is like a Pulse Width Modulator (PWM) with a period of 2seconds ( I'm gonna talk 50Hz from now on) .
That means that 50% power is on for 1 second and off for one second .
Burstfire is different . It spreads the power out more evenly over the 2 second period . So 50% power will be on for 20mS off for 20mS etc .
This Burstfire is the key here .
So say you want 0-100% ...OK 2 seconds is pushing it but still fine for cycling an element .
But if you want 0-1000% control , now you need a 20second time frame ......and thats just bad
But with Burstfire , you are spreading those 1000 pulses over the 20 seconds and its happy days in the boiler
This is what the difference looks like .This is 37% power shown in Burstfire and Time proportional Mode .
Sorry about the hand sketch . Creating a program to do Time proportional control is relatively easy and there are quite a few out there .
Burstfire on the other hand is a lot more involved . I have spent a lot of time thinking about it and I think I have reinvented the wheel so other DIY"ers can include it in thier controllers .
I spent quite a bit of time looking at the Oscilloscope looking at how Auber have done it and I'm pretty sure my program is good .
Here is a classic shot . 25% power . ...1 cycle on ...3 cycles off OK so thats a no brainer . But what about the other numbers ?
What I worked out was there are several patterns that are calculated and layered to make up a Burstfire .
Basically say you want 37% power .
First , Divide 100 /37 = 2.707 ....take the interger
so that is 2 . That is our first pattern .
Turn ONevery second cycle . ...That gives you 50 cycles ( out of 100)....but 50 is more that 37
Find the diffence . 50 - 37 = 13
So if you turned off 13 of the 50 cycles , you would get 27 .....but its ever that simple .
To spread the 13 Off cycles evenly , we divide it into 50 .
50 /13 = 3.846...again we take the integer ( as you can only get so many evenly into 50)
now we have our second pattern .....3
We Turn OFF every 3rd Cycle turned ON in the first Pattern , and we are getting closer to home .
Alas 50/ 3 = 16.66......again , we take the integer 16 .
And here we are again over shooting the mark .....16 was more that the 13 we needed .
We go again ...16 - 13 = 3
we need to add 3 cycles back to the 16 we just removed .
16/3 = 5 .33
5 is our 3rd Pattern . ..We will Turn back ON every 5th Cycle we turned Off in the second pattern
we now have 37 cycles out of 100 . 50-16+3 = 37
looking closer at the first pic , you can see how the patterns combine to create the final drive waveform to the SSR. There are another couple of adding and subtracting Patterns that will deal with several thousand .
Here's the Chaos . The Audiuno is connected to a LCD display .
Still in fun mode ,it shows the power % .the other 5 numbers are the ON/Off patterns ...all that will change .
The Rotary encoder is using External interupts to set the required power/percentage and will be used to enable menus .
The Small Mains transformer is half wave rectified and turns on a transister to trigger a Pin Change Interupt that Synconizes the Cycles and turns on?off the SSR each Cycle as required
A couple of CRO shots of the SSR drive signal . Heres the Code so far .Its no Bells and whistles ...just the bits that make it work .