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water heater circuit

Discussion in 'Electrical Engineering' started by Dave, Apr 12, 2004.

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  1. Dave

    Dave Guest

    I am new here and have a question. Normally (at least here) a 220 volt
    hot water heater is wired using 10/2 with ground. I have a timer box
    connected and it works fine and has for years now. In order to connect a
    110-120v circuit to operate a 110v timer (one that increments time in
    units when the heater is actually using energy), one would initially
    think seeing that the ground is there that you could connect to either
    the red or black wire and the ground to get 110-120v. I guess it would
    work but I want to do it correct according to code. My Intermatic Timer
    box has a lug for the nuetral (if it exists) and also the ground. My
    current setup uses only the ground, red and black. Am I correct that I
    could run a new 10/3 with ground and connect all 4 wires to my timer box
    and then use the nuetral, ground ,and one of the 120v wires to have a
    correctly wired circuit to add my 110v intermittent timer to??
    Thanks in advance,
  2. Dave

    Dave Guest

    Hi again,
    I already got it figured out and am going to do as I planned.
    Thanks anyhow,
  3. Blue Crown

    Blue Crown Guest

    Those time clocks come with 220 volt clock motors to use with water
    heaters, that way you don't need the insulated neutral.
  4. Dave

    Dave Guest

    I guess I didn't make that clear enough now that I read it again. I am
    connecting a solar batch heater to preheat my water going into the hot
    water heater and using an idea from another guy, I was going to connect
    an analog 110 volt "clock" or 110 volt counter (here is where I used the
    word timer incorrectly) to the circuit to move the clocks hands only
    when the heater element was using current. This way I could see how many
    minutes a day my hot water heater was costing me $$. I have a "Little
    Gray Box" Intermatic water heater timer box and I thought it would be
    more professional if I added a duplex outlet to plug my analog clock
    into. So if I used a duplex outlet and used the ground and either the
    red or black wire, it wouldn't pass code. So I thought I would rerun the
    wire with a 10/3 with ground to add the nuetral and connect the duplex
    outlet to the nuetral and either the red or black to run my clock. Then
    I remembered the thermostats would give me some problems as if I
    connected as I just said, it would run my clock as long as the
    Intermatic timer "allowed" current to the "thermostats".
    So plan "B" is to use a current sensing relay so it energizes
    only when the heater is actually on. I am guessing I can get away with
    one if I put it in the right spot on my 2 thermostat hot water heater.
  5. Guest

    You can do that. One possibility: a current transformer
    with a diode in series and a (properly chosen) resistor
    in parallel, feeding an optoisolator in series with a
    1K resistor. The other end of the optoisolator actuates
    a relay via a transistor. You'll need a power supply at
    the relay circuit end. Physically, the current transformer
    is installed at the water heater, and you connect it to
    the diode, parallel resistor, series resistor and
    opto-isolator with a run of thermostat wire. I'll try a
    diagram of the sensor side of the circuit:
    Diode 1K
    AC ----+----|>|---/\/\/\-----+
    / |
    \ burden v Opto
    / resistor -
    \ |
    AC ----+---------------------+

    The lines labeled AC are the two wires from the current
    transformer. With power off, disconnect one of the
    power wires to the heater, pass it through the center
    of the transformer, then reconnect the power wire.
    The burden resistor is REQUIRED for safety. I used a 33
    ohm, 50 watt resistor in my circuit, which reacts (lights
    an led) to 5 amps in the primary. I wanted huge reliability
    in my burden resistors, so I used a pretty high wattage
    I used model TR-3025-S current transformers from
    Toroid Corporation of Maryland - see:
    and click on current sensing transformers on the
    right side of the screen roughly 1/2 way down.

    For a schematic of an opto-isolator relay driver
    circuit, see:
  6. Dave

    Dave Guest

    Ok, thanks for the detailed info. On the Toroid slection they offer 15,
    30, 60, or 90 am for the current transformer. Which one is best? I
    checked the website for the opto-isolator relay driver circuit and the
    image doesn't come up.. I also am curious if being that the heater has 2
    elements and 2 thermostats, if I need to make 2 of these for accurate
    readings as the heaters can operate independent of each other. That
    being said, I also found a nifty little already made device that may
    work and its about $35 already made. Check this out and let me know if
    it would work ok, (other than its somewhat bulky size).

  7. Guest


    I looked at the site and I can see the relay, but
    I don't see any details on it, so I can't say for sure
    if it would work. My guess - and it's only a guess - is
    that it is not a good choice. It is for a humidifier, which
    probably draws a lot less current than your hot water heater.

    If you build your own, I'd use the 30 amp toroid. Your
    heater will draw less than 30, but more than 15 amps, most
    likely, so the 30 amp one is best.

    Regarding accuracy:
    You are looking for an on-off indicator, not a measurement.
    Your clock can only measure time, not how much power was
    used. Your water heater will draw current and operate
    the circuit, regardless of which thermostat in the water
    heater turns on.

    I don't know why you couldn't open the site I posted:

    I'll describe it - you can draw a schematic from the
    description. The emitter of the 4N25 optoisolator
    connects to a 4.7K resistor. The resistor connects
    to the base of an NPN transistor. (A 2N2222 would be a
    good choice - the schematic shows a BC547B). The emitter
    of the transistor goes to ground. The collector goes to
    the relay coil. The other lead from the relay coil goes
    to plus 12 volts, and to the collector of the 4N25.
    Also there is a 1n4001 diode in parallel with the
    relay coil with the banded end connected to the plus 12
    volt side.

    If any of this is new to you, you might want to get
    some help. My concern is the use of the current
    transformer. You need to disconnect a wire feeding
    the hot water heater, run it through the transformer
    and reconnect it. You can't afford a loose connection
    to the water heater - and you can't afford sloppy
    wiring to the current transformer. It MUST have the
    burden resistor connected when the heater is powered
    on, so you need to be sure of your wiring. The output
    side of the optoisolator is non critical, as long as
    you wire up the relay contacts to your duplex receptacle
  8. Dave

    Dave Guest

    Thanks for the info. I got the schematic with a different browser and
    then rebooted my pc and all is well. Check out the link below as it has
    more info. As far as the device I gave you the link to, the current draw
    sensed can be changed by the amount of turns of the wire in the pickup.
    The output is 110 volt so I am guessing the output could surely run a
    clock and even a night light for instance if I wanted a visual. I am
    capable of doing the connections, and I have made some circuit boards in
    the past and have soldering equipment etc...but I was just thinking if
    the relay I can buy will work and is cheaper then it would be the way to
    go...What I do like about your idea though, is the possibility it is
    smaller to connect the toroid where I need to put it. As far as accuracy
    I know I have 2 4500 watt elements so if I know how long each one is
    "on" I can do the math and come up with a pretty accurate estimate.
    Thanks again,
  9. Guest


    Thanks for the link - it worked well. My guess is that
    it will work for you, now that I've seen it. You could
    call the company to make sure, and ask them if it will
    work to detect a current of up to 30 amps. I didn't see
    a spec for the maximum current it will work with. Your
    heater will definitely draw more than the 4 amp minimum
    they specify.

    If the company says the model 51 will work with up to
    30 amps, you can install it anywhere you have access
    to the branch circuit wiring. It does not have to be
    installed in the water heater. What you would need to
    do is install a junction box where you want to put
    the relay. You would need to cut the wires that go
    from the circuit breaker panel to the water heater,
    and route them through the junction box, splicing
    them inside the box with wire nuts. The relay bracket
    would go over one of the hot wires. Generally speaking,
    there is not enough slack in the existing wiring
    to allow you to do that. But say you can install
    a j-box within reasonable distance to the breaker box.
    You could disconnect the cable from the breaker panel,
    pull it out and route it into a j-box, than add a
    new piece of cable from the J-box to the breaker
    panel. If the wiring is exposed in the basement,
    that is a good option. You could run a 110 volt
    circuit into that same j-box, and install the relay
    and the duplex receptacle in the same box with the
    240 volt heater circuit and the 110 volt circuit.
  10. Dave

    Dave Guest

    I was going to connect a junction box onto the Intermatic Timer Box that
    is currently allowing my hot water heater to come on only twice a day
    for 2 hours in the AM and PM. First I was going to rerun the 10/2 with
    ground to a 10.3 with ground to make available the correct 120v circuit
    for a duplex outlet. Being I already have a breakpoint in the wiring
    thanks to the Timer Box, I can connect the relay to the red or black
    thats lengthened and pulled into my added junction-box. I can connect
    the releay to either the red or black, and the now available white wire
    (nuetral) to complete the 120v circuit correctly to a duplex outlet.
    When the existing Timer Box allows the current to flow, if it does
    indeed flow, the amps sensed by the relay should complete the circuit to
    the outlet(s). The little "timer motor" I am hoping doesn't draw the 1/4
    amp or 30 watts or the relay would energize when the timer allows
    current flow and give me false readings (basically show me the unit used
    current 4 hours a day as set by the 2 hrs AM and 3 hrs PM). That all
    said and thought about, I checked my Timex brand electric clock I bought
    with my Kill A Watt Meter and it doesn't draw the specified current on
    the load end of the relay! Arrghh. So I guess I need to find 3 watt
    clock or add a night light to the outlet, or hunt down a cheap hour
    meter in 110v. I found a Cramer brand that would have worked but it is
    not available from the Surplus Center as it was in their old catalog and
    not their new one...Anyhow, it looks like I am almost there unless the
    relay, by NOT seeing the correct current IE: too little doesn't cause
    damage to itself which I am assuming it just won't switch.
  11. Guest

    If the sensing part of the relay "sees" less than
    the rating, no problem - it just won't switch on.
    There will be no damage.

    On the other side of the relay, the instructions
    call for a minimum load of 3 watts and a maximum load
    of 50 watts. Your idea of adding a nite light to
    meet the minimum is great.

    Your timer motor will draw very little current -
    no where near enough to activate the relay.
    Sounds like you are in great shape!
  12. Dave

    Dave Guest

    Thanks for all of your input into my project. I will let you know how it
    goes when it all comes together. Maybe off topic but I am using two
    tanks to make this batch heater and one is from a gas hot water heater.
    In the 2 tank system, once the water is hot and moving, the primary tank
    will preheat the water going into the secondary tank before it goes into
    my in house hot water heater. Do you see an advantage to putting the
    tank from the "gas" hot water heater as the primary over the secondary
    (or vise versa) as the design has a 4" hole down the center for the
    flue? I know when the hot water rises due to stratification, it will go
    to the top. But the area and the hole in the center must make some
    difference as to its best position as far as a preheater, or the tank
    getting the preheated water...
  13. Guest


    Sorry, I don't know which one should be first, or if
    there would be any difference.
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