Where to find low-voltage, manual reset relay?

[Clarkbug]

Hey Everyone.

Still on hold for my install, but thats just giving me more time to think about things.

We lost power here the other day, and as it was coming back on, it blinked in and out a few times. Why I thought of this is due to my overheat loop. I currently have a 24v transformer powered from the same feed going to the wood boiler. If the power goes out, it opens the valve to the dump zone.

Whats worrying me is that if the power goes out for just a few minutes after I have loaded the boiler up and left for the day, and then comes back, I still have plenty of heat in the boiler that I need to dump, but the valve will be closed. My thought was to install a manual reset relay (like a murphy switch on a tractor) that would open on a power outage, and then have to be reset just like my boiler would be.

Does anyone know if such a thing exists, and where I could get one?

Or I guess more importantly, am I over thinking this?

 

[timbrjackrussel]

Hi, you need to make a latching relay, that if there is a very short power outage it will stop power to your dump valve and even if the power returns it will stay off until a normally open push switch is pushed for a second.
Get a relay with a 24VAC coil and at least a single normally open set of contacts. Connect one side of the relay coil to the 24V transformer and the other side of the relay coil to one of the normally open contacts. Connect the other side of the normally open contacts to the other transformer terminal. Now connect a normally open, push to close switch across the relay normally open contacts. Move your dump valve wires to connect to the latching relay coil. When power is turned on the relay and the dump valve will not get power until the push switch is closed for a second. This puts power to the relay coil (and the dump valve) and the relay closes the normally open contacts and this contact keeps power to the relay coil (and the dump valve) after the push button is released. If the power is lost for a very short time to the latching relay, the closed contact opens (dump valve has no power and opens) and even if the power comes back on the relay (and the dump valve) will not get power until the push button is pushed to latch the relay on.
A UPS for power to the boiler system may be a very good safety item as well.

 

[maple1]

What is your system contingency for an overheat that doesn't involve a power outage? Something like the fan not shutting off for some reason when the boiler gets up to temp?

My relic here has a separate aquastat that when the boiler gets above a certain point (200 I think), it will open one of my regular zone valves & start the circ - just the same as a thermostat would - and dump heat to one of my house zones. I'd think that between something like that and your current setup, the bases would be pretty well covered.

EDIT: That wasn't quite right, when it gets hits the 200 it cuts power to the NO dump valve - creates a power outage. I've been living with this thing for 15 years and still don't have all the circuitry straight in my head.

 

[Clarkbug]

timbrjack, thanks for that great explanation. Any idea where I can get that stuff?

maple, you bring up a good point, that if the power comes back on, my zones can still pull water from my storage. I also will have an aquastat in the top of the boiler set up to run my biggest zone, similar to what you have going. The issue will be that my laddomat/charging pump is interlocked with my boiler. On the Varmebaronen when you start the fan, it also starts the loading valve. I think that on power loss, the fan will turn off, and the pump would as well. Im not positive on that, since the shut off is normally based on flue gas temp, but Ill know better when I finally get it hooked up....

 

[maple1]

Looking forward to your future 'up & running' thread.

I'm thinking when it loses power, the loading valve internally opens a direct flow from bottom of storage to boiler - allowing natural convection flow and draining of heat. How much of that it will do though depends also on having a flow circuit out the top that will be conducive to good convection flow. The straighter & higher up it can go the better. I think I saw a slideshow on that on the Smokeless site - I should go poke around there some more.

 

[Clarkbug]

I think that Ill be the happiest one of all... The gauge on my oil tank keeps going down, just like the mercury in the thermometer....

You are right, it is supposed to allow for that sort of thing, I just dont know how well it works, or how worried I should be. I know the Varm has internal overheat protection, but that only kills the fan and keeps the loading valve running. Just too much time to think about it I suppose....

 

[jebatty]

You can find manual reset electronic limit controllers on eBay for reasonable prices. These include digital readouts and most handle the various kinds of typical temperature sensors.