+ Post New Thread
Page 2 of 2 FirstFirst 1 2
Results 21 to 38 of 38
  1. #21
    Advanced Member level 5
    Points: 34,003, Level: 45
    Achievements:
    7 years registered

    Join Date
    Sep 2008
    Location
    cambridge
    Posts
    7,062
    Helped
    513 / 513
    Points
    34,003
    Level
    45

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    Interestingly, The following electric shower..
    https://www.mirashowers.co.uk/shower...or-dual-108kw/
    ..has an extremely fine resolution in its temperature setting, so it must be doing mains burst fire control…….there is pretty well no other economically feasible way to do fine adjustment temperature control in an electric shower.



  2. #22
    Super Moderator
    Points: 82,712, Level: 70
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    13,584
    Helped
    4519 / 4519
    Points
    82,712
    Level
    70

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    Not necessarily, it may work the same way as some 'thermostatic mixer taps' with a constant heat source but motorized mixer valve.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


    1 members found this post helpful.

  3. #23
    Advanced Member level 5
    Points: 34,003, Level: 45
    Achievements:
    7 years registered

    Join Date
    Sep 2008
    Location
    cambridge
    Posts
    7,062
    Helped
    513 / 513
    Points
    34,003
    Level
    45

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    sorry Betwixt, i should have made clear that i am only speaking of "electric showers" here.....you are kindly referring to whats known in shower company marketing departments as a "digital shower".
    (i only know this because i spent a few months in a shower co working on their "digital shower"...unfortunatley, i was not given access to their electric showers)



    •   AltAdvertisement

        
       

  4. #24
    Super Moderator
    Points: 263,617, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    46,057
    Helped
    14007 / 14007
    Points
    263,617
    Level
    100

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    No. The user manual suggests that there's no electronical temperature control at all. Two level power control and a mechanical temperature controller manipulating the water flow. Just the classical instant water heater way.

    http://resources.kohler.com/plumbing...user-guide.pdf


    1 members found this post helpful.

  5. #25
    Advanced Member level 5
    Points: 34,003, Level: 45
    Achievements:
    7 years registered

    Join Date
    Sep 2008
    Location
    cambridge
    Posts
    7,062
    Helped
    513 / 513
    Points
    34,003
    Level
    45

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    Thanks, I also read the manual.
    There are three flow settings. Then there’s the temperature dial for you to increase/decrease temperature with whatever flow setting. The temperature scale has fine gradataions, showing a lot of different temperature settings, and this can only be economically achieved with burst fire mains control. –Unless of course, the multiple graticule markings are just there for show….to fool the customer that it has fine resolution temperature control



  6. #26
    Super Moderator
    Points: 80,392, Level: 69
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster 3rd Helpful Member

    Join Date
    Apr 2014
    Posts
    16,308
    Helped
    3700 / 3700
    Points
    80,392
    Level
    69

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    Hi,

    Let's assume you have
    * 50Hz full wave regulation (smallest time step = 20ms)
    * a 1kW heating element
    * 1 liter of water

    Then from the physics the limit is to regulate the water temperature with a resolution of about 0.005°C.

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.


    1 members found this post helpful.

  7. #27
    Advanced Member level 5
    Points: 34,003, Level: 45
    Achievements:
    7 years registered

    Join Date
    Sep 2008
    Location
    cambridge
    Posts
    7,062
    Helped
    513 / 513
    Points
    34,003
    Level
    45

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    Having re-looked at the shower of post #21, I now agree with your words. It’s the flow rate that is being adjusted to give a wide range of temperature outputs.
    However, there is a very big problem with this. It means that people may end up using a very low flow rate, which is very bad because it results in scaling up of the shower system….also, if your shower is on high power and high flow rate, then you quickly adjust the flow rate down…it can result in significant scalding…as well as temporary thermal shut down of the shower.
    So this is why mains burst fire control, using a fixed flow rate, (or perhaps just two very similar flow rates) would actually be the best way to control an electric shower.
    Please see point 13 (page 3 ) of the “Mira Décor” shower……

    Mira décor shower manual (£400 electric shower)
    http://resources.kohler.com/plumbing...user-guide.pdf

    …this is diabolical “DO NOT switch the shower off and back on while standing in the water flow.
    ….when soaping up in an electric shower..it is essential to be able to switch the shower off….then back on again when you wish to rinse off the soap….
    Burst fire mains control is the way forward.



  8. #28
    Super Moderator
    Points: 263,617, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    46,057
    Helped
    14007 / 14007
    Points
    263,617
    Level
    100

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    Instant heaters with electronic temperature control are state-of-the-art (other products than that presented in post #21). According to power quality standards, they need to use full wave switching with not too fast modulation period.

    - - - Updated - - -

    I reviewed the specifications of some electronically controlled instant water heaters. Interestingly they are controlling the water flow by a motor valve, not the heater power.


    1 members found this post helpful.

    •   AltAdvertisement

        
       

  9. #29
    Advanced Member level 5
    Points: 34,003, Level: 45
    Achievements:
    7 years registered

    Join Date
    Sep 2008
    Location
    cambridge
    Posts
    7,062
    Helped
    513 / 513
    Points
    34,003
    Level
    45

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    I reviewed the specifications of some electronically controlled instant water heaters. Interestingly they are controlling the water flow by a motor valve, not the heater power.
    Thanks, yes you are right, controlling temperature by controlling the flow rate appears to be the main method....but it is a poor method....just cheaper....

    What I would add is, that I have lived in some 35 different rental accomodations, and in virtually all of them, the electric shower had been pranged by the landlord to always run on maximum flow.
    The reason for this is because adjusting the flow rate of an electric shower can lead to problems…..because if one restricts the flow rate too much, too suddenly, then the heater element overheats…and even though there is a thermal shutdown, it never really operates fast enough, and so cumulative damage is done to the heater element and other parts.
    Another point about slow flow rates is that it increases limescale build….more so than faster flow rates.
    This is why shower temperature adjustment by flow rate adjustment is a poor, el-cheapo solution to the problem.



  10. #30
    Newbie level 1
    Points: 13, Level: 1

    Join Date
    Jan 2020
    Posts
    1
    Helped
    1 / 1
    Points
    13
    Level
    1

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    I tried to understand this but did not get a single word. can anyone help me to understand this


    1 members found this post helpful.

  11. #31
    Super Moderator
    Points: 263,617, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    46,057
    Helped
    14007 / 14007
    Points
    263,617
    Level
    100

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    There are 29 posts in the thread, you should tell a bit more clearly what you mean with "this". Alternatively, what's your question related to the topic?


    1 members found this post helpful.

  12. #32
    Advanced Member level 5
    Points: 12,484, Level: 26

    Join Date
    Aug 2015
    Location
    Melbourne
    Posts
    2,040
    Helped
    749 / 749
    Points
    12,484
    Level
    26

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    Most 1st world countries require that the net average DC over a 24 hour period be 5mA or less - this to prevent earth stake corrosion

    If you draw too much pos cycle only power ( or neg ) you can saturate the local supply transformer and blow the pole fuses

    you will also upset any transformers on the same phase ( making them hum loudly ) and they can blow their fuses too ... this because you are unbalancing the volt seconds on each half cycle on the local mains ....


    1 members found this post helpful.

    •   AltAdvertisement

        
       

  13. #33
    Advanced Member level 5
    Points: 12,484, Level: 26

    Join Date
    Aug 2015
    Location
    Melbourne
    Posts
    2,040
    Helped
    749 / 749
    Points
    12,484
    Level
    26

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    So you want full cycles of control ( 20mS for 50Hz ) or multiples thereof, zero crossing detect opto coupler and a ckt that keep the firing on for 15mS - the SCR / triac will then turn off at 20mS all by itself ...



  14. #34
    Advanced Member level 5
    Points: 34,003, Level: 45
    Achievements:
    7 years registered

    Join Date
    Sep 2008
    Location
    cambridge
    Posts
    7,062
    Helped
    513 / 513
    Points
    34,003
    Level
    45

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    Thanks, we will end up using back-to-back power FETs with isolated drive due to the total 32A of current. We will parallel them.

    What worries us is that I can see that if our zero-cross isnt pin point accurate, then we could end up with a net DC even if we do it in 20ms mutiples...though we can mitigate by having 10ms "gaps" (or multiples therof) between the (20ms x n) bursts.



  15. #35
    Super Moderator
    Points: 82,712, Level: 70
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    13,584
    Helped
    4519 / 4519
    Points
    82,712
    Level
    70

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    The offset would only occur on the start of a conduction cycle, if you use SCR/Triac switching it will turn itself off accurately anyway.

    Why use back-to-back power FETs when a triac is so much cheaper and easier to control?

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



  16. #36
    Super Moderator
    Points: 263,617, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    46,057
    Helped
    14007 / 14007
    Points
    263,617
    Level
    100

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    Why use back-to-back power FETs when a triac is so much cheaper and easier to control?
    Apart from component costs, to reduce power dissipation at 32 A below triac level, you would need less than 18 mOhms Rdson for each of the two MOSFETs. Did you identify suitable transistors?



  17. #37
    Advanced Member level 5
    Points: 34,003, Level: 45
    Achievements:
    7 years registered

    Join Date
    Sep 2008
    Location
    cambridge
    Posts
    7,062
    Helped
    513 / 513
    Points
    34,003
    Level
    45

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    Apart from component costs, to reduce power dissipation at 32 A below triac level, you would need less than 18 mOhms Rdson for each of the two MOSFETs. Did you identify suitable transistors?
    Thanks, no we didnt, but we will parallel them.



  18. #38
    Super Moderator
    Points: 82,712, Level: 70
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    13,584
    Helped
    4519 / 4519
    Points
    82,712
    Level
    70

    Re: Regulating temperature of mains connected heating element: Skipping mains half cy

    This is getting rather complicated and expensive. My initial thoughts if burst control is to be used is a triac fired with a ZCD opto-coupler, in turn fed from a comparator with the setting control on one input and a thermistor from the outgoing water flow on the other. Not a FET in sight and very little costs.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



--[[ ]]--