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Electrical question

Post in 'DIY and General non-hearth advice' started by Eric Johnson, Jul 30, 2007.

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  1. Eric Johnson

    Eric Johnson Mod Emeritus

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    I'm trying to make a regular room thermostat break the electrical connection when it hits the (low temp) set point, instead of making the connection, which is what most thermostats do. So when the temp drops to 40 or 50 degrees, in other words, I want the current to be interrupted. Can I wire it through some magic box that would do that?

    I have SPDT switched aquastats that will "go either way" depending on how you wire them up, but nothing that goes that low, temp-wise.

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  2. jqgs214

    jqgs214 Minister of Fire

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    Sounds like ya need to tear apart and old fridge and find out what makes the compressors on them stop when they are cold enough

    Edit: Or an air conditioner for that matter.
  3. nshif

    nshif New Member

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    How about a duel mode stat, heat or air, In the air mode that should give you what you want
  4. jqgs214

    jqgs214 Minister of Fire

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    yeah thats what i was aiming at!
  5. keyman512us

    keyman512us Member

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    Eric,
    ...If you have a supply house close by...or even a radio shack get 24 volt relay. About $10. Wire through the thermostat to the coil of the relay. When the temp drops below the whatever the set point is (thermostat will close the circuit to the coil of the relay). Most 'decent' relays have two sets of contacts usually rated at 10 amps or better. They also have normally open and normally closed contacts so you can wire it to your specific requirements. "Industrial relays" available through any supply house have a "base block" for easy wiring. Easy way to do what you need to.

    http://www1.mscdirect.com/CGI/N2DRVSH?SISECT=0002000746&SIS0NO=00000305788
  6. GVA

    GVA Minister of Fire

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    Eric.
    It depends on what you are trying to switch
    If you are trying to switch a high inductive load, then yes a relay will work or a line voltage thermostat for cooling as shown below on the link.

    http://www.mcmaster.com/
    page 603
    item 1846k26
    If you just want this to make or break power to say a blower it is ideal.

    the relay requires a transformer since a standard T-stat doesn't generate power it only controls it up to a certain rating.
    Unless you are using a t-stat that is allready hooked up to a furnace or something.


    I have something similar in the plant where in 1 room when the room gets to a high setpoint it kicks on the exhast fans, or in other rooms it turns them off when they reach a low setpoint. It depends on what I need it for and I only have to keep one type on the parts shelf.
    the one shown I believe one would find on a walk-in cooler. down to -30*

    The beauty of these are it is just a switch the only wires are, one in one out, no control wires etc.
  7. GVA

    GVA Minister of Fire

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    And for you guys that want your distribution blower to turn on at a certain temp check out the one above it....
    Simple to plug in.

    1940k8
  8. Eric Johnson

    Eric Johnson Mod Emeritus

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    Thanks, guys. I'll look this over and learn something in the process.

    I'm just trying to power (or rather, de-power) a zone valve.

    Keyman, you'll like this:

    I need a power-out gravity-feed dump zone for my new gasifying wood boiler (arriving any day now). I have a 30-gallon steel pressure tank that I'm going to put in the barn attic right over the boiler. One line goes to the boiler supply and the other one to the return. The zone valve, an Automag, opens up when the power is cut, allowing hot boiler water to be replaced with cooler water from the tank, thanks to convection, in the event of a power failure. My problem is that instead of glycol in the boiler, I'm going to run straight water, so the tank in the attic would freeze on cold days. My thought is to wire the zone valve through a thermostat on the tank, which will be located in a well-insulated wodden box. So when the tank temp gets down to, say 40 degrees, the Automag open up long enough to warm it back up. Why don't I put the tank in the boiler room? Well, for one thing, there's no room. For another thing, I already have a similar system piped into a couple of cast iron radiators in the attic, which contained glycol from my previous boiler. So it should be easy to swap the tank for the ci rads, which I have other use for, anyway. Finally, I think 40-degree water for this application is preferable to 100+ degree water, which is what a tank in the boiler room would yield.

    An old water heater would work just as well, I guess. But the tank is what I happen to have handy.

    If you want to take it a bit further, I will also have a pumped dump zone on this system, which will activate the greenhouse zone pump when the boiler temp exceeds, say, 200 degrees. An aquastat would simply power up the pump. If I also ran a line from the aquastat to the same relay or other gizmo hooked up to the stat on the tank, I could cut the power to the Automag and make the gravity dump open up at the same time, for a little extra insurance. And I will have a transformer right there, because the Automag is a 24-volt part.
  9. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    For stove blowers nothing beats the Stove Stat.

    Enter "Stove Stat" in the search box on the main page.

    http://www.northlineexpress.com/
  10. begreen

    begreen Mooderator Staff Member

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    Eric, sounds like a Grainger special. Would a remote bulb thermostat work? There are several White Rodgers and Honeywell controls that do this. I'll see if I can dig up some part numbers.

    Later -
    Try this one. It has a SPDT contact so you can wire it to open on temp fall. 0-100 degrees F, 3-10 degree adjust. differential:
    http://www.grainger.com/Grainger/items/3UC72

    This was a real inflation awareness moment for me. I have the 1995 Grainger catalog at home. These controls were in about the $35-50 range 12 years ago.
  11. Eric Johnson

    Eric Johnson Mod Emeritus

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    You can still get new, standard Honeywell SPDT and SPST aquastats on Ebay for around $20 if you shop around and are patient. Sometimes these oddball parts, like the link you posted, appear and go for next to nothing. But you gotta be patient and know what you're looking for. Thanks for the help, BG!
  12. begreen

    begreen Mooderator Staff Member

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    May be your lucky day. I see the Honeywell T991A 1426 on eBay for $11.99 (with outrageous $30 shipping). From what I can tell that is a 0-100F controller.

    http://tinyurl.com/2w242s
  13. keyman512us

    keyman512us Member

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    Eric...
    I see you are learning the "finer side" of what makes a boiler fun... controls are great! Some wire, a couple relays this, a few aquastats that and a rainy sunday afternoon is complete...lol

    I checked "the ace in the hole" scrapyard for more of those forklift LP tanks for a mainfold setup tank for ya to play with but he hasn't gotten in since the last batch....but I'm gonna be stopping in there more often. ;)

    You're gonna love this one:

    A short while back I had some scrap metal to get rid of, and a buddy of mine did too...so I help him load up the truck we grab a couple of coffee's over at Dunkins' and head on over... While I'm singlehandedly throwing old dryers etc off the truck I spot some old Oil boilers off to the side... That still had fairly new TACO 007 cartridge circulators attached ;)

    Needless to say my buddy doesn't carry much for tools on his truck... so the knuckles got a little bloody scavenging...those 007's were mine! YUP...'Dawg Boy' went to work on them old boilers allright...lol Smashed the BX whips clean off with a 'Vin Bahh' (old axle shaft...I plead the fifth..not even gonna tell ya the charachter that coined the Vinn Bahh...lol) and spun the rusty black iron apart...only snapped two flanges, total haul 7 circulators...

    I decided it's in my best interest (with the money I had just saved) to spend $20 bucks or so to put together a small tool bag of cheap tools for the next occassion. Even though I'm far from having "bankers hands" I'm getting a little too old to tear flesh...lol

    If I "come across" a honeywell 84XX triple acting aquastat or two in the pile I'll save one for you to "experiment with" ;)

    You wanna check out a sharp thermostat:
    http://www.hoffmanonline.com/produc...at_2=2383&cat_3=92663&catID=92663&itemID=3572

    That thermostat is the size of a 35MM film tube!
  14. Eric Johnson

    Eric Johnson Mod Emeritus

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    It's true, you can have lots of fun with aquastats and pumps. I always try to get SPDT-switched stats, because they go either way. I'm also putting a three-way zone valve in this system, which should also be a fun project.

    I buy my 007s on Ebay new for around $35, but the free ones you take off old boilers are even better. I have a couple that are shot, so if you need the castings, let me know.

    I'm going to be using an old cast iron radiator for the manifold in my greenhouse. It's got 1" tapping, so I figure I can hang a few accessories like an air scoop, pressure tank, pressure relief valve, etc. off of there.

    Let me ask you this: Most of my greenhouse heat is going to come from some 10-foot hot water baseboard units that I picked up new a few years ago. I'm going to be installing three or four of them, stacked up along the wall, downstream from the ci rad. (I know, you're not supposed to mix the two, but this is a greenhouse, not a living room). I'm thinking it makes the most sense to run them in series, after the water passes through the cast iron "manifold" so that the return water coming out of the top one has has most of the heat wrung out of it. Since the greenhouse system is glycol and the main system is water, I figure the bigger Delta T I get across the (shell and tube) heat exchanger, the better. I've never done a monoflo tee setup, but I don't think it makes much sense in this application.

    Any thoughts on that?
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