On Demand Water Heater

Discussion in 'General Electronics Chat' started by R!f@@, Oct 19, 2010.

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  1. R!f@@

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    Apr 2, 2009
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    First of all the item

    [​IMG]

    Now the story.

    We have these..hell, ya ..they are every where, here.
    My concern is this thing refused to heat water with in weeks of purchase.

    This one is used by one of my cousin. She has a baby, so she need's water and yadi yadi yada ..etc.

    So now she says the guy who installed it said to short that thing in there and it will work... and yes when u short the thing water his indeed heated :eek:...What thing...:confused:

    And yet he cannot do tht. He showed but he won't do it. too scared.
    Of what? :confused: who knows.

    Any ways. It came my way..so now I am thinking of making it coooooool!!!! :D

    By the way....see the inside

    [​IMG]
     
  2. R!f@@

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    So any ideas on how to crank it up..

    I'm working on the schematic right now......will upload it later
     
  3. hgmjr

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    Jan 28, 2005
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    I will wait for your schematic before providing any definite response. I would be looking for a blown fuse or tripped circuit breaker somewhere.

    The sensor that you have pictured is a thermally tripped sensor (pictured in the upper right) mounted to the top of the small holding tank. It may have failed open so that the signal it sends back to the monitoring circuit is telling the circuit that the water has reached the upper temperature limit and so the heating system is turned off.

    hgmjr
     
  4. R!f@@

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    I though of that two. It seems by shorting the triac, heater is working.

    Got tangled up in Riot last night with political parteeeeys.

    I too can say anything further after the schema.
     
    Last edited: Oct 21, 2010
  5. R!f@@

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    Here's a rough sketch of the wiring.

    The only thing tht makes me :confused: is the one marked ???.

    From the photo it is marked as another sensor. Meter shows an open circuit. So I just dropped a symbol for it. Problem is tht there is nothing written on the bloody thing.
    It looks like a thermistor, but it is not a thermistor, this I am sure.
    What I thing is tht it is a fuse to cutoff the gate drive if the triac faulted.

    Other than tht there is no other fault.

    Their may be some mistakes on the diagram, but nothing I could find.

    I like Sgt to Spice this circuit for me and tell me or show me the power and Voltage that is applied to the heater when the VR is turned.

    Heater is 3.5KW 13Ω one.

    Even though I can fix this, I donno how much or how well the circuit regulates the heater voltage. cause I am not too good with triac as u know. I am still learning this part as I go.

    This is why I am humbly requesting Sgt to Spice the circuit and show me the V, I scope traces at different temp settings.

    What I like to do is make this one better. Built a more reliable and efficient controller now tht it is on my bench. I like to learn this thing for once and get it over with.
     
  6. debe

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    Sep 21, 2010
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    Hi R!f@@, is the ??? part the sensor on the water inlet. If it is it should switch on when water is flowing through the system (thats how my Rinnai instant HWS works) just a sugestion. Daryl
     
  7. R!f@@

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    I am way ahead u mate :cool:

    I checked it, it's just sealed like a thermistor. Only two wires coming out.
    Nothing else. It is mount on the water inlet, I really donno why it is there.

    Another option is tht it could be a reed relay type of switch thingy.
    When water is there it switches on. But for tht pressure sensor might be used, and this one is not a pressure sensor.

    It has nothing written on it, only the fact that it is open circuit and is sealed and is mounted on the inlet valve. But has no influence from anything around it from what I can see.

    Only thing I can say is, is there a switch that can sense water flow just by being near the water. something like hall effect sensor.

    Is this a new component that is now being made?
     
  8. SgtWookie

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    Gee, I don't have ANY models for TRIACs nor DIACs (you are showing a DIAC below the TRIAC, but have not provided a part number for it.)

    Do an Erc in Eagle to find the places where you are missing junctions.

    I don't know what the "Another sensor" might be, either. [eta] OTOH, it might be a thermistor that they send current through; if there is no water in there to keep the thermistor cool it's resistance will change.

    Can you find the owners' manual for it? It might have a schematic in there.

    If that doesn't work, why not write to the company and get a schematic diagram from them, or have them honor the warranty on it?
     
  9. R!f@@

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    Bummer Sgt.
    Ur spice has no triacs. The diac is just a standard one. But if u do not have the model there is nothing anybody can do.

    As for manual and contacting service...I am better off with u guys.

    Hmmm..I think I will try the thermistor approach u said, it did not cross my mind cause they are all plastic. If it is a NTC, then it should be thermally coupled, right?
    With plastic, thermal coupling isn't enuf.
     
  10. SgtWookie

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    Wait a minute - I think it might be a float or a flow switch.

    You wouldn't want the heater to come on unless there was water in the tank, and water flowing through the device.

    Right?

    Or, it might be a solenoid valve, like in a washing machine.

    I don't know, can you try to determine what type of part it is by looking in the openings using a bright light?
     
  11. R!f@@

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    Naaa....It is sealed.

    Let me get a shot of tht.


    Now where did I put my camera...........
     
  12. SgtWookie

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    I mean look in the openings where the water comes into the thing and out of it.
     
  13. marshallf3

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    Jul 26, 2010
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    Most of these operate by sensing a pressure drop across the input and output to indicate demand and the actual presence of pressure to indicate that water is available.
     
  14. R!f@@

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    Here are the photos of that "thing" Zoom in
    I have attached them for ur convenience.

    [​IMG]

    [​IMG]

    [​IMG]

    so what is it.
     
  15. bertus

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    Apr 5, 2008
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    Hello,

    The black part in the middle of the second picture is a reed switch.
    The switch probably reacts on a magnet moved by the waterflow inside the tubing.

    Bertus
     
  16. BillB3857

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    Feb 28, 2009
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    I would have to agree with Bertus about the reed switch. As for the schematic, it appears that the variable resistor would control the output wattage, therefore the rate at which the water is heated. If the flow rate is low, the water will come out at a higher temp than if the flow rate was high. Other than the high temp cutout, I don't see any feedback sensor to compensate for various flow rates.
     
  17. hgmjr

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    I too agree with bertus that the black rectangular sensor is a reed switch activated by a magnet.

    hgmjr
     
  18. debe

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    Sep 21, 2010
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    Hi Ri!f@@, I would check if there is any continuity on what looks like a black reed sw when a magnet is close to it. If it does then i would dismantle the inlet fitting (apears to be held together by 2 screws) & check if there is a magnetic asssembly in side that moves with water flow, may be stuck? It hasto sense water flow before it will heat. Daryl
     
  19. hgmjr

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    I wonder if small ferrous metal particles in the water have adhered to the magnet in the water stream and degraded the magnet to the point that it no longer is strong enough trigger the reed switch. If this is the case then you should be able to replace the plastic inlet assembly and fix the problem.

    Or you may be able to disassemble the plastic inlet assembly and flush the contamination off of the magnet.

    hgmjr
     
  20. R!f@@

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    I will try the magnet approach.

    Will get back
     
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