Circuit to indicate failure of a heating element

Perhaps overkill, but you could install two Cent-a-meter type power consumption devices on just the line supplying the heaters:

Dave.

rnatezone.com/eevblog/

Thanks Dave, I hadn't thought of this (though I was hoping to be able to do it with a handful of components rather than 2 x expensive pieces of kit. Oliver.

Don't know what you guys in the UK have available but this might get your brain juices flowing.

Do a search for a device that is called here across the pond as a "Current Sensing Relay".

You simply loop your wire lead to the heater thru the coil a couple of times and when there is current a relay is energized. The relay can turn on a bell or a light or what ever when the current drops out. Based on your use you would need a time delay relay so that you would only get the signal you wanted.

Saying it in other terms. Thermostat turns on heater and time delay. If current flows as it should the current relay triggers and now audible or light is lit. After a period of time the timer delay ends and all is checked ok. Now if the heater is burned out and the T-Stat turns the heater(which does not work) and the time delay. No current flows so the relay does not trigger and the audible sounds or the light turns on.

If you know how to draw a "ladder logic diagram" it will help with the wiring.

Hope that make some sense over there.

Good luck.

Les

Much like this one.

You could probably do it with a ferrite toroid, some fine enamelled wire, a diode and a LED. You would wind say 100 turns of wire on the toroid connect the led and diode in parallel, connect the pair across the toroid. Feed one leg of the heater through the core. You may need one or two turns. The diode is only there to prevent reverse voltage damaging the LED. You will need to play around a bit to get the turns ratio right, but as long as current flows through the heater the LED will glow.

Maybe just an incandecant lamp across each heating element, color to taste.

Would that not only just tell that power is available at the connection???? He needs to know if current is flowing thru the heating element.

Put them across each thermostat. Then they will light when the switch is open.

and the light will be out when the thermostat is on, the element is broken, or the ripple-control is off.

that's going to be confusing.

it's not a simple problem. water heating is often on a fairly complex circuit (ripple-control, meter, circuit breakers, switch, thermostat, heater)

also the heating element has two failure modes, one of which will blow the breaker and the other won't.

also in normal use the boost element is only runs when the tank is almost all cold.

Only to simple minds.

I used a similar design to monitor tower lights between two sites. The indicator at the manned site was light all day, and only went off, when all tower lights were on, including the flashing beacons. The FCC approved the design, along with the FAA.

Just like those tower lamps, the heating elements cycle on & off. If the indicators don't flash, you have problems.

If you can reach the contacts, you can (1) measure voltage across the heater, (2) connect (just for a second) a jumper across the thermostat, (3) have an associate (or a remote TV camera) monitor the power meter for the house.

If the heater has low voltage, that means its thermostat is OFF. Connect the jumper then, and if the spark doesn't convince you that it's heating, the confederate watching the meter can tell you that it spun faster for those few seconds. The same will work with clamp-type AC ammeters.

I think I have a circuit that will do what you ask, it still needs a few tweaks, use it at your own risk. If anyone on the group has any input on the circuit I'd like to hear it. Also please go over the logic and see if you think it will work.

Here I've added a couple extra labels,

site seems to be down.

I just tried it, it worked, Please try again. Mike

amdx Inscribed thus:

It seems very complicated just for a current indicator ! Yours seems more like a complete system.

The OP ask for a circuit: "to warn me when the element has failed." This circuit will do that ( I think). He didn't ask for a current indicator, he ask for a circuit that will indicate that the thermostat is on but no current is flowing. I'm open to a simpler design that meets his need. Mike Also this is pretty close to all electrical and very little electronic.

yeah, it's back.

it looks good. As it's safe to assume that the heating elements will never fail while unpowered it will detect failure. even where elements fail short-circuit and out the fuse on a load controlled circuit.

you can't power the bridge rectifier from the load controlled circuit

but if reset while the fuse on a load controlled circuit is blown it will not re-detect that, but a relay could be added to handle that

but if the short takes out the master fuse (killing all the power to the house) it it'll trigger it won't be obvious.