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Shower power control

Discussion in 'Electronic Basics' started by [email protected], Feb 26, 2007.

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  1. Guest

    I am looking for a way to control the power (the water temperature if
    you prefer so) of my shower.

    Specifications:
    Tension: 220V
    Resistance: 11 ohms
    Nominal current: 20A

    I found solutions using Google but they are some problems on them:
    - generates a lot of harmonics
    - wastes much power on control circuit

    I would like a circuit to analyse/think not a ready product.
    I appreciate any idea.

    $ flames >> /dev/null

    Thanks you,
    Pedro Henrique
     
  2. Europe? Why not increase the water flow?


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  3. Guest

    Brazil. I would like to control the power/temperature, dear Homer.

    PH
     
  4. Phil Allison

    Phil Allison Guest

    ** Groper Folly Alert !


    ** Phase control always does that.

    Why should YOU care ?


    ** A triac will drop maybe 1.5 to 2 volts at 20 amps - not much compared
    to a 4.4 kW load.

    Use a hefty AC power relay if you cannot tolerate a bit of heat.


    ** Getting a clue first would be a good start.




    ...... Phil
     
  5. The general choices are phase control or integral cycle
    control. Phase control is finer grained, smoothly variable
    and faster responding, but is electrically noisy, ans you
    mention. Integral cycle pulse control is a lot quieter as
    far as harmonics goes, but creates sub harmonics that can
    cause annoying flicker of lights and picture distortions on
    televisions. I guess a fast motorized variable transformer
    would be the quietest and smoothest as far as the AC line is
    concerned.

    No particular need to worry about waste heat, since that is
    what you are producing. Just heat sink the control elements
    to the cold water upstream of the heater.

    A PID feedback controller with feed forward (power
    predicting feature) capability on either water flow rate or
    unheated water temperature or both, would help speed up the
    control. Stabilizing such a controller is also easier if
    the heater mass is lower (less heat storage inside the
    heating element) and the water volume being heated is better
    mixed (some backward mixing of heated and unheated water)
    and larger.
     
  6. Guest

    Why folly, hehehe?
    Why not?
    Sometimes, the circuits in a house are not installed/separated
    adequately. So it could be a serious problem to others equipments
    connected in the shower circuit. Don't you think?
    The problem will be the cost and the harmonics. Anyway, It seems to be
    the best solution really.

    What relay type do you refer?

    Thank you,
    PH
     
  7. Guest

    Can you explain better about integral cycle pulse control please?
    Maybe, some book.
    :) I will study officially power electronics this year.

    The motorized variable transformer will be very much expensive to me.
    The water could damage other circuit components. I would like to put
    the control circuit in a plastic box with a little opening to a
    possible potenciometer.
    You have reason.
    Anyway, the control speed isn't so important preoccupation to me. I
    just would like to adapt the temperature control to common showers
    (when there isn't a mixing between heated and unheated water) in the
    best way possible and, of course, viable economically.

    Thank you,
    PH
     
  8. You can't make the water hotter except by reducing the water flow. To make
    it cooler, you need a 20 amp dimmer control which is safe to use on 220 V.
    You will have to adjust it before using the shower - it would be very
    dangerous to use one while in the shower.


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  9. Gareth

    Gareth Guest

    First, think very carefully about safety before actually doing anything.
    Water and electricity can be a dangerous mix, but since you just want
    to think about it..

    A simple solution would be to have a number of different heater elements
    in the shower. If these elements had a suitable power ratings you could
    get a large number of different levels with only a few elements and no
    additional electrical noise or wasted power. e.g. if you had four
    elements you could get 15 power levels by selecting different
    combinations (2^4 - 1)

    Perhaps not as elegant as a solid state PWM system but I think it would
    work.

    --
     
  10. (snip)

    Phase control involves turning on a latching device, like an
    SCR or TRIAC at the same fraction of each half cycle, and
    the device remains on till the next current zero crossing.
    Power is varied by changing the timing of where in each half
    cycle that power is switched on.

    Integral cycle control involves turning on the switching
    device just after a voltage zero crossing, so that an entire
    half cycle of line voltage is passed, so that there are no
    fast voltage rises in the waveform. Power is controlled by
    changing the number of complete cycles, in some time
    interval, that are passed to the load and the remainder that
    are blocked. Usually, the cycles that are passed are all
    together in a group, and the ones blocked are also together
    in a group, but the power control is smoother if the
    groupings are eliminated and the ratio of passed and blocked
    cycles are mixed as well as possible. With a microprocessor
    that has a line cycle input, to synchronize the timing to
    the line zero crossings, this process can be done almost
    entirely in software, as can the feedback PIC control
    function, whose output decides the fraction of power cycles
    passed.

    While it is not so important that each positive half cycle
    delivered is immediately followed by the negative half
    cycle, it is important that it is impossible for the
    controller to supply only positive or only negative half
    cycles, because this would put a DC component back into the
    line power source, and that isn't good for the transformers
    in the distribution system.

    See:
    http://www.athenacontrols.com/pages/fund.html
    http://www.ccipower.com/support/control_modes.php
    http://www.patentstorm.us/patents/6849834-description.html

    There are also special purpose solid state relays that
    accept a control voltage and generate the variable duty
    cycle burst of line cycles in proportion to the control voltage.
    http://www.crydom.com//userResources/productFamilies/50/crydom_pcv.pdf
     
  11. The UK ones work like that. You have a high / low switch, and further
    adjustment is done by adjusting the flow rate.


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  12. Guest


    There is a similar switch here also but the switch isn't very useful
    because:

    - that is above the shower, so it is height
    - I would like to have a better temperature control. The climate in my
    region is very volatile.

    thanks you,
    PH
     
  13. Does this unit have a pump?


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  14. jasen

    jasen Guest

    bolt the heatsink to the water pipe (with apropriate insulation)
    look at some datasheets.
     
  15. JeffM

    JeffM Guest

  16. Guest

    No, it doesn't have.

    Are you european, no? What is used there, handshower or headshower?

    PH
     
  17. No, Canadian but I travelled in the UK for work. Most of theirs have pumps.
    In N America, we have high pressure hot water gas fired so plenty of hot
    shower water.

    You could build a triac type dimmer but you'll need a big triac - 20 or 25
    amperes 400 volts.

    I'd use a neon lamp to fire it - you don't need to go down to a very low
    setting.

    http://www.aaroncake.net/circuits/dimmer.htm is a circuit using a neon for
    117 VAC. You will need to add resistance to the circuit for 220 volts.

    http://www.epanorama.net/documents/lights/lightdimmer.html#1kw230v is a
    circuit for 230 VAC. It uses a diac instead of a neon.

    Assume 2 VAC across the triac (it'll be a little less than that). At 20 amps
    that's 40 W which is HOT. You'll need to be able to get rid of that heat.

    Search for (neon lamp triac dimmer 220 volt) for more info.
     
  18. Works in the USA. Not in many other countries.


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