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[bertible]

I am using a UM506 as a continuous on/off switch for my millivolt pool heater.  The heater is in a shed, and I'd like to put an LED or other small indicator light on the outside of the shed, so I can see if the heater switch is on or off, from my house.

 Since the voltage being switched is very low (< 750 mV)  I cannot really use the Voltage going through the UM506 contacts to drive an indicator light so must find another solution.  Also, I want a 100% reliable hardwired indication, otherwise one solution would be to use an ActiveHome macro to turn a light on whenever the UM506 is turned on, or maybe to have a second UM506 on the same code to run a 12V indicator light. 

Since the UM506 has a built-in chime, which I assume runs from the 110V side of the device, it should be possible to open it up and tap into the chime circuit,  disconnect the chime, and attach an indicator light.  Has anyone done this?  Is there another way I could achieve the same thing?

[Jsnlong]

A hardwire for sure thing maybe to put a light on the power of the pool heater its self or off the relay that gives power to the heater.. That way you know for sure that the heater is on/heating and not just that the UM506 is telling it to come on.

[bertible]

Thanks, but won't work in this case.  A millivolt heater has no external power supply.  The slight voltage that operates the gas valve is created by the pilot light through some bimetal wizardry that generates voltage (actually millivoltage).   Many waterheaters, RV heaters, and gas fireplaces use the same technology.   Not sure if there are inexpensive relays or LED's that run on that low a voltage.  I thought tapping into the 110V side seemed a more viable option.

[steven r]

Is there any place/way that you could place temperature sensor to detect the water temperature? This would ideally be inline near the water output of the heater.

[bertible]

Yes, this is theoretically possible and I presume you mean that the temp switch would be set so that when it was hot, it would switch on, and a light would be wired to it.   There is already a temp sensor that drives the thermostat but I believe it is on the input side.   Your idea would  give me the secondary light that tells me that both the UM506 is on, and the thermostat is closed.  This might be neat, but doesn't achieve my primary objective of only indicating the UM506, not the thermostat.  You see, if I know the UM506 is off, then I know the heater can't come on, no matter what the thermostat tells it to do.  (the UM506 and thermostat are wired in series. Both have to be closed for the heater to be on.)

 Sorry I have to go into a bit of detail to describe some seemingly irrelevant background..only technos will want to read:

I have a hot tub with a high and low speed pump switch.  The pump speed must be on high whenever the heater cycles on.  This is because the heater is a 250K BTU one that is also used for the pool so it can create steam and pressure if the water is not moving at a certain speed.  The amount of water that pumps through the hot tub at low speed is simply not enough to release the amount of hot water created when the heater is on.  So, right now I have an airswitch to turn my pump from high to low. I have an X10 remote wallswitch near the hot tub to turn my UM506 (and therefore the heater) on and off.   The heater thermostat is enabled when the UM506 is in the on position, so of course the heater comes on only as it needs to, to keep the water hot.  After I use the hot tub, I turn the pump to low, and turn the UM506 off at the same time.   Due to the vagaries of X10, I'm worried that I'll turn the pump on low, but that the Heater won't actually be turned off.  Then the next time the thermostat cycles on, the heater will damage itself.   So,  to be extra cautious, I either listen for the barely discernible click that the UM506 makes, or I end up having to walk a few paces, barefeet in the snow, down to the pool shed, to see that the UM506 actually turned off.  (which totally wastes the need for the remote X10 switch in the first place)  A little LED light would be so much better!

So the end result of all that detail?  I don't really need to know if the heater is actually on at this very moment, I need to know if the UM506 is on, even if the thermostat is open, and the heater off.

I sure wish the UM506 had its own LED light.  Then I would simply splice in some extension wires and move the light to a location on the outside of the shed that I could see.

[HA Dave]

I sure wish the UM506 had its own LED light.  Then I would simply splice in some extension wires and move the light to a location on the outside of the shed that I could see.

Maybe we're over-thinking this. If all you need is to see if the UM506 is On simply add a wall-wart/transformer and a relay. Allow the multi-switch relay to close your heater circuit as well as the transformer powered light.

[Brian H]

I would not recommend any connections to the insides of a UM506. Like most X10 modules. It has a power line derived type power supply. Most times the LINE AC input is the common connection in the module. So it is very possible that the LED and all the rest of the internal electronics could be a shock hazard if run outside the case.
The external controlled  connections on the case are isolated by its relay inside the box.

[dave w]

bertible,

Another way to skin this cat is to use an appliance module instead of the Universal Module to control a DPDT 120V AC relay. 

Radio Shack or "All Electronics" carry them.   http://www.allelectronics.com/make-a-store/item/RLY-453/120-VAC-RELAY-DPDT-12-AMPS/-/1.html     

One pole of the relay controls the thermocouple line and the other pole could light your LED. Or since we are now using an Appliance Module, you could also plug a 120 V light in addition to the relay (night light, neon pilot light, flood light, 100W boom box, etc)  and use it to indicate heater status.

[steven r]

...I don't really need to know if the heater is actually on at this very moment, I need to know if the UM506 is on, even if the thermostat is open, and the heater off...

Ah. Now I get what you want. I assumed the goal was to make sure the heater was on not locked off.

Maybe we're over-thinking this. If all you need is to see if the UM506 is On simply add a wall-wart/transformer and a relay. Allow the multi-switch relay to close your heater circuit as well as the transformer powered light.

Yes it could work to have the UM506 trigger a DPDT that turned on the thermostat and a signal.

Now comes the caution: What happens if the UM506 fails ON? Could that happen? Well it is an X10 product. Do you ever need to turn on the heater remotely? If not, I'd recommend a latching relay as a fail safe approach.

Re the use of an appliance module: I'm concerned that local control might, in a worse case scenario, might trigger it on. Would definitely recommend a latching relay in this case.

The safest approach might be to rewire things so that the high speed pump always  comes on when the heater does. Of course since it's a gas heater you're kinda in a catch 22 that takes us back to square one of needing to detect when it's ON.

[Knightrider]

I use the appliance module to run relays (rat shack 275-217) in several of my applications.  Never had a problem with the local control thing.  In fact, this is how I disable the local control when switching high power (100 watt) strobes.

[steven r]

How about this? Connect a relay in parallel with the high speed pump and have the relay switch the thermostat on.
One relay and a bit of low voltage wire and you're guaranteed that the heater can not be turned on unless the high speed pump is on!

Now you can also add X10 controls and a display light if you like but the safety issue is addressed.

[bertible]

Wow!  thanks for all the ideas.  I'll see what my local Radio shack/Source has in the way of multiswitch relays.  It may be easier to drive a 110 relay from an appliance module, rather than using the UM506