water heater circuit

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

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 resistor. I used model TR-3025-S current transformers from Toroid Corporation of Maryland - see:

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:

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).

Thanks, Dave

snipped-for-privacy@bellatlantic.net wrote:

Dave,

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 safely.

Dave,

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.

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. Thoughts? Thanks, Dave

snipped-for-privacy@bellatlantic.net wrote:

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!

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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... Thoughts? Thanks, Dave

snipped-for-privacy@bellatlantic.net wrote:

Dave,

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