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DIY Controller Question

edited April 26 in Usage

Hi all, i had a question from a customer i don't know the answer to and thought there may well be someone here who does.

Your SSR controller kit has a dial indicator from 0 -> 100. Would this mean, when the dial is at 50, your only heating at half speed? I query this because my understanding is, the SSR controls the voltage applied to the heating element, not the output wattage. Therefore, to heat at half speed the knob would need to be at 70/71, not 50?

Hoping someone can help, my electronics training was many beers ago.

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Comments

  • You certainly need both the voltage and current to figure the wattage. While i have one i never use it and am sure someone with more knowledge will come in. I did buy a couple of power meters on he-bay but as yet not set them up. Only something like $20 with a little CT for the output line.

    So if you halve the voltage you 1/4 the power and yes if you want to 1/2 the power you need to go 70% of the voltage like you suggested ( assuming constant resistance ). All depends on what the scale represents and if its linear etc. That requires instruments or experience to know.

  • edited April 26

    The element wattage is determined by the resistance of the element which never changes (unless it blows up ;)) eg at 240v, a 2400W element draws 10A (P=VI). it's resistance = 24 ohms (R=V^2/P)

    My understanding is the SD controller is a phase angle controller, so assuming a linear pot, at 50%, only half the waveform is being passed to the element. Like you I can't recall all the AC theory, so can't work out what that equates to in RMS terms. However i have come up with this quick spreadsheet based on R=24ohms & using P=V^2/R

      %       V     P  
    ===================
      4.17   10     4.2  
      8.33   20    16.7  
     12.50   30    37.5  
     16.67   40    66.7  
     20.83   50   104.2  
     25.00   60   150.0
     29.17   70   204.2
     33.33   80   266.7
     37.50   90   337.5
     41.67  100   416.7
     45.83  110   504.2
     50.00  120   600.0
     54.17  130   704.2
     58.33  140   816.7
     62.50  150   937.5
     66.67  160  1066.7
     70.83  170  1204.2
     75.00  180  1350.0
     79.17  190  1504.2
     83.33  200  1666.7
     87.50  210  1837.5
     91.67  220  2016.7
     95.83  230  2204.2
    100.00  240  2400.0
    

    Based on the above at 50% on the dial assuming 50% of the waveform equates to 50% of the voltage being output, the power being input to the wash is 600w. This aligns to your customers comment that 70% on the dial equates to half the element power.

    However In practice it does not matter.

    What is important is that there is a scale reference so that each time it's used, the dial can be turned to the same setting and the system will behave in the same way.

  • edited April 26

    My thought exactly and if one was dead set on knowing the amps being supplied it's easy to add an ammeter and pretty sure it is in the instruction thread. The thing is we don't know exactly how many volts our supply is at any stage either without a volt meter.

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  • I'm not so sure. I may be wrong about how these controllers work, but if you are cutting the wave form with a linear potentiometer and the wave form is cut at 50% of each peak then 50% on the potentiometer equals 50% power as the area under the cut waveform is exactly half. The non-linearity comes in either side of the 50% point because of the sinusoidal wave form.

    image

    Full Half Power.jpg
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  • Ed, I was thinking along those terms but then the assumption that at 50% the voltage is also halved kicked in & the brain applied the maths & I ended up where I did......

    I still think my comment about using the scale for repeat ability is important as is monitoring your rig and adjusting it as required (whether that's via power or cooling). I don't have a voltmeter or a power meter to measure and prove your thought (but thinking about it I reckon you're right) and simply adjust the pot to the same point each run.

  • I am 99% sure the SSR is NOT supplying half the voltage... it is time based, it is supplying the full voltage for half the time.

    Additionally, I am 98% sure it is NOT messing with individual waveform cycles, it is "zero-crossing', that is it turns on and off only when the voltage is at zero, if you are at 50%, it is FULL ON for 50% of the time...

    There is another thread on here titled "DIY Controller" with LOTS of information.

  • A customer sent me this pic this morning. Solves all the problems too.

    image

    diycustomer1.jpg
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  • @punkin Do you know the model number of that ammeter? It looks really sharp!!

  • I sent the builder a link so hopefully he'll chip in. If not i'll ask him for the info.

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • He said he'll pass on the info next week.

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • I use the same meter got them off ebay. I never use the dial position. I step in amps eg up 1 amp at a time or down 1. Repeat the same setting next time. I use 2 by 2400 watt elements one on full all the time and the other adjustable as required.

  • edited April 27

    @trebor. Does the energy value reset anyway ie reset on power off ? I wonder what @punkin's customer was running there as it has a power factor of 0.9 so either a motor or the power controller introduces a pf as an element is,by nature, resistive. That meter is the way to go.

  • I dont believe that it is very accurate but i only use current value as a reference. I adjust power up or down in amps from 0 to 10.

  • Would be interesting to hook up an osci and look at the wave forms.

    My meter results look similar to @punkin 's customer pic, even though I only have U & I. My understanding of the operation of the SSR from SD is the same as @CothermanDistilling . That means your resolution would be 100-120 steps based on your local supply

  • edited April 27

    My understanding is ssr's can be any of the above i.e. On off zero crossing or phase control so basically on/off or clipping sections of the waveform out. It all comes down to measurement or repeatable skill to get what you want when you want it. But a CRO would be good for the technofiles. Again even the measurements are only approximations when dealing with a shonkie waveform and in the end it doesn't matter how as long as it does consistently

  • edited May 7

    Hi guys, customer passed on this link to the power meters;

    AC 80-260V LCD Digital 100A Volt Watt Power Meter Ammeter Voltmeter 110V 220V @ eBay

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  • @punkin better check that link. 1 hr 15 min in phone to Telstra sorting internet so sitting on computer testing

  • Give it a whirl now.

    Thinking i may include these in the large controller kit.

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  • edited May 3

    Thats better. What a price - @ $10 a pop including shipping . A real steal. Just bought three.

    I asked a question back a few posts if the energy value can be reset . It can very easily.

    @Clotherman I think we came to the conclusion some time ago that you could run say three elements active wire thru the CT and it would read the correct total ( same phase ). Agree ? ( assuming same voltage on each element ) It is rated at 100 A.

  • Yeah, my customer is updating the wiring diagram for me and writing some simple instructions. Maybe we can get someone knowledgeable to add them to the DIY kit thread.

    I think it will be a good addition to the larger kit. He said he had some trouble fitting them in the small boxes and had to cut the heatsink away a little.

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • Unfortunately we can not purchase on EBay. Country excluded.

  • Thats what mates are for. If needed i will buy and reship.

  • This weekend I installed a SPDT cam switch in my simple one element controller. The switch has 3 positions. 0 - bypasses the SSVR, 1 - breaks the circuit and 2 - routes the power via the controller. I figured why involve the SSVR when I just want to run the element flat out. I think it is better to have a switch to cut the power on the controller when shit happens mostly in the form of cooling water spraying everywhere. Next bit of controller bling will be one of those pretty meters from ebay; I ordered mine from an "Aussie" vendor promising quicker delivery

    LCD AC 80-260V 0-100A Digital Voltage Volt Current Meter Panel Power Energy YA @ eBay

  • @richard said: Unfortunately we can not purchase on EBay. Country excluded.

    Pretty common item on most eBay country sites e.g.

    AC 80-260V LCD Digital 0-100A Volt Watt Power Meter Ammeter Voltmeter 110V 220V

  • Today I put the multi-parameter meter on my controller box. This pic shows switch set to bypass the controller - out of control.

    image

    1.jpg
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  • Second pic shows switch set to controller with potentiometer set to total control

    image

    2.jpg
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  • Final pic shows switch set to control (2) with the potentiometer set to lack of control

    image

    3.jpg
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  • @kimbodious have that setup put it to 50% and also 70 % for us to confirm another series of posts. My meters arrived today as well but it will take a while. Nice setup you made.

  • That looks really sharp, nice.

  • @GD50 said: kimbodious have that setup put it to 50% and also 70 % for us to confirm another series of posts. My meters arrived today as well but it will take a while. Nice setup you made.

    cheers GD50! I don't have a scale marker for the potentiometer, but I'll give it a crack anyway!

    I'd always felt the SSVR used extra power at flat out hence the device heating up, That was the theory behind justifying installing the bypass switch.

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