hot water heater monitor.

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dacflyer
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hot water heater monitor.

Post by dacflyer » Tue Mar 01, 2016 3:13 pm

i am planning to make a hot water heater monitor, this will have about 5 indicators.
1 for power to let me know the timer has turned on.

( water heater has 2 elements ) 2x
1 indicator for each element, so i know if the upper or lower element is in use.
and a load indicator that will light up, to let me know if a element is failed or not.

i am thinking to use 3 neon panel indicators 1 for power, and 1 for each element in use.
as for the load indicators i was thinking to use ( here is where i want advice ) a small current transformer to power a led.
or if simpler just wind a few turns of wire around the lead of a wire going to the element.
the elements are 5500 watts each. which comes to about 20 amps each element.
any ideas on how many turns i'd need to have enough power to drive a led directly ?
of course i know i'd need a diode and a cap for filtering the led.
or is a current transformer a better idea ?
i used to have some small ones around here somewhere..lol

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haklesup
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Re: hot water heater monitor.

Post by haklesup » Wed Mar 02, 2016 1:05 pm

easier to detect Voltage than current, there will be plenty of voltage drop across a heater coil and there won't be any when it is operating. The neon bulb with dropping resistor takes almost no current and can run off the same voltage as the core. Some configuration of the neon bulbs either across a heater coil or spanning both of them should get you indicators of activity without any circuitry

This may not indicate an open coil though, is the heater 220V, then you might have two hot and one neutral, this give you more combinations. a bulb between hot input to a coil and neutral will tell you it is on but a bulb across the coil will light brighter when the coil is open and the voltage drop is gone.

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Externet
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Re: hot water heater monitor.

Post by Externet » Wed Mar 02, 2016 1:12 pm

Hi dacflyer.
I did something similar to mine. Installed 230V panel green neons 'special order' from Digikey, in parallel to the thermostats. Showed me the 'temperature reached' condition (and element is off now)

Or, ----> http://www.crmagnetics.com/remote/cr2550
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dacflyer
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Re: hot water heater monitor.

Post by dacflyer » Thu Mar 03, 2016 6:51 am

mainly i am looking to have a open coil detection.. ( load sense )
the neons will be connected directly to the elements, so i know if the upper or lower is in operation, but i want to know that it is actually working and not burned out..
and yes i am operating off of 220V

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Externet
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Re: hot water heater monitor.

Post by Externet » Thu Mar 03, 2016 7:47 am

You did not open the link ?
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dacflyer
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Re: hot water heater monitor.

Post by dacflyer » Thu Mar 03, 2016 4:13 pm

sorry , i overlooked it earlier..
looks neat all in 1 package.
thanks.. i'll look into it more...

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Re: hot water heater monitor.

Post by dacflyer » Fri Mar 04, 2016 8:11 pm

i see them things are not cheap.. i found some cheap current transformers, but they have different rating, not sure what i should pick that will light up a led in the 18-22 amp load range.

plus i am curious as to how it works ( triggers on at a certain load )

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Re: hot water heater monitor.

Post by haklesup » Mon Mar 07, 2016 10:17 am

You would need a few dozen to a hundred or so turns to detect current with a powered circuit like a diode and op amp. However if you wanted to light a bidirectional LED with no powered circuits just off the energy harvested by the coil, you would need thousands of turns. To install such a coil, you would need some space.

Who remembers how to calculate current in a coil with N turns around a wire carrying 20 to 40A? Its basically an air core transformer with N to 1 ratio. How many turns to get 30mA to light an LED for example.

I'm not sure why detecting a coil open is important. It has got to be a very rare event taking years to occur and one normally notices this with a cold shower since when they break at 2AM, the Big Box store isn't open. If you are worried about a cold shower, you might get the same effect with a temperature monitor with low alarm (lower than the thermostat). In any case a LED would go unnoticed, a buzzer would be better if rapid detection is paramount.

I've always had a gas water heater, when they fail, its always tank rust thru. Tell me; does the coil or the tank generally fail first with no maintenance?

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Re: hot water heater monitor.

Post by dacflyer » Mon Mar 07, 2016 12:43 pm

usually the coils fail 1st, ( thinner metal ) but i make it a point to replace my anode rod every 5 yrs or so, the heater will last many years past the rated warranty..

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Lenp
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Re: hot water heater monitor.

Post by Lenp » Tue Mar 08, 2016 6:12 pm

Rambling comments about the CR Magnetics sensing products and other stuff!

The LED indicator sensors are small, and just hang on the wire. They work very well and probably last forever. The proper terminology refers to this as a CT, or Current Transformer. Many junk box coils might also work but may be larger.

A CT is just a simple transformer secondary, and the primary is the load wire looped through the coil. (Think soldering gun turned backwards!) If you can make the load wire loop through the coil, the turns ratio changes and the secondary output increases proportionately.

There are other CT coils with very exact ratios so that they can be used for instrumentation of AC currents remotely, like metering power consumption without requiring the ammeter to be capable of withstanding the actual load current. Perhaps the CT may provide something like 1volt on the secondary with 1 amp in the load circuit. It's DC equivalent would be a current shunt resistor, where the current is measured as a function of the voltage drop over the shunt resistance. Many CT's outputs also produce a reasonably similar waveform of the load current.

Three phase monitoring is also done to detect lost or unbalanced phases.

Applications.
I have a Weller soldering iron with all of its temperature controls in the iron handle. The tip has a slug of steel that operates a magnetic switch, based on the slug's Curie temperature, and different tips have different preset temperatures. So there's just low voltage AC to the iron. I used one of the CR units and an LED so I could monitor when the iron was cycling. It's been working for years.

Another of the CR Magnetic coils is connected through an opto-isolator to an Omron counter and an Omron elapsed timer. The Omron units are self powered so you just feed a wire through the coil and you can monitor how frequently, and how long, a load, like a pump or lighting circuit, was energized. It just doesn't get much simpler, or easier.

About water heaters. (And often these critters are called 'Hot Water Heaters' but we usually don't heat HOT water do we?)
Most all electric water heaters have an upper and a lower immersion heater. You will still get some hot water with a bad heater but the recovery and efficiency suffers. You'd be surprised how quick, and often, a dry heater can self destruct! Larger commercial heaters often use three phase power, have multiple heater banks, with staging controls All this can easily mask an open heater if it's current isn't being monitored.

Is all this a case of overkill for a home 'hot water heater'. Well maybe, but don't most of our projects cater to our sense of perceived need, in spite of logic, and we just call it fun.

Enough said :eek:
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)

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Re: hot water heater monitor.

Post by ShopRat » Wed Mar 09, 2016 7:09 am

Long ago and far away, my brother milked 70+/- cows. He had given up replacing the lower heater element in the 80 gallon water heater because it would fail within a few weeks. (He generally kept a replacement on hand, also stocked by the local hardware store) Every month or three, one of us would drain the heater, remove the lower element, and drag out the lime and scale with "coat hanger" wire. I think a half-gallon-size pile was common. He finally replaced it with an LP gas heater, but I don't recall how he addressed any buildup issues. My point is, it all depends on your water whether the tank rusts out or the heater elements burn out first. I've also heard of some localized conditions where the anode rod is removed, or a different material is used.

On a safety note, I vaguely recall from my substation training that a current transformer "open circuit" tends to "drift" up to the voltage of the conductor passing through it. Though not as dangerous at 230V as at 20kV or higher, safe practice would recommend closing the circuit if the transformer is left installed (say, between test runs).

Dale

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Lenp
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Re: hot water heater monitor.

Post by Lenp » Wed Mar 09, 2016 8:30 am

I guess the high voltage was more of a static or capacitive coupled charge, like holding one lead of a hi-z dmm and getting a reading. It's there...but it isn't. Energy, without the capacity to do useful work! But hey, we had some of those guys on a company payroll in the past! :sad:
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
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Re: hot water heater monitor.

Post by haklesup » Wed Mar 09, 2016 11:55 am

your milkman brother must have been pumping well water from limestone aquifer to be as hard as it sounds

Electricity is very expensive in CA, few people would have electric heat or water heaters here by choice but I know in other regions, electricity is far less expensive and that in rural areas you may not have natural gas and that Oil would be the only other alternative (and not so much for hot water). Not sure about MI but they practically give it away in WA where they have ample hydro power for example. I pay up to .36 per kWh. I'd like to dump my electric dryer, then I might get to what the power company calls an "efficient House" level. Abandoning electric cooking would force me to pay a plumber to upgrade my gas piping, that's probably not going to happen unless I dare to DIY (not out of the question). Electric rates should fall a but due to lower oil and gas prices and as more PV and other renewables come on line

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Re: hot water heater monitor.

Post by ShopRat » Thu Mar 10, 2016 9:47 am

To detect a failed heater element, how about tracking thermostat "ON" time?

It's been awhile since I worked on one (I currently have a tankless LP gas water heater), but I believe residential water heaters are effectively wired as two "shared neutral" 115V circuits within the heater. Each 115V heater element has its own thermostat wired in series. As you draw hot water off the top, cold water enters the bottom (via a drop tube from the top connection) and the lower thermostat turns on the lower element. If you draw enough hot water (shower, laundry, etc.) the upper thermostat also turns on the upper element. Shut off hot water and eventually the upper thermostat reaches its setpoint and shuts off its element, followed by the lower thermostat and element. Then, as heat is lost, probably only the lower element cycles on and off to maintain temperature.

Now, suppose the lower element fails open (shorted is rare and should trip the breaker). Wouldn't the lower thermostat be always ON, with the upper element cycling on and off to maintain temperature (slight temperature differential from top to bottom of the tank, due to "heat rises")? Upper element failure (less common?) should result in much longer "recovery" ON time of the lower thermostat. I'M ignoring the "cold shower" complaints here.

To monitor, the high-tech version would modify one of the microcontroller data-loggers from N & V, with suitable opto-isolators. Low-tech could be (after verifying 115V NOT 230V) the neon indicators mentioned, across (in parallel with) the heater element terminals, with eyeball monitoring. You could connect an old kitchen clock or an appliance timer (the low-tech type used to turn your Christmas lights on and off at preset times) in the same way as the neon, and note how much time it advances compared to "real" time.

I realize I've probably "over-explained" for the OP, but I hope it's helpful to others following this thread. (I'm rather new to this interweb thingie Al Gore invented, and brand-new to forums)

Haklesup: Yes, water softeners and other treatment systems are common in Michigan, with dissolved limestone, iron, and sulfur common. Conditions may be completely different just 25 miles away, but fortunately we don't usually have to drill too deep to find water.

Dale

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Re: hot water heater monitor.

Post by Lenp » Thu Mar 10, 2016 12:18 pm

All the water heaters I've seen that were 230 V used no neutral. The elements were rated at 230v. The power goes through the top thermostat and heater. When that thermostat is satisfied, power is switched to the lower thermostat and heater to heat the colder water at the bottom. The elements are not both in use at the same time. The top thermostat also has the high temp safety thermostat.
Sensing heat near the heater or the duty cycle is inaccurate since the element is immersed it will still be hot . The parameters will change with inlet water temperature and use. Monitoring the element's current is the easiest, and most reliable way to detect an element failure.
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)

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