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Old 07-16-2012, 11:58 AM   #1
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relay switching.......


I want to set up a relay based switching control for a dehumidifer. I'm looking for help on this project.

The dehumidifer sits in the basement and the condensate it creates is pumped outside by use of a condensate pump. The condensate pump has a low voltage safty switch built-in so that in case of a pump faliure (overflow) the switch will open.

What I'd like to do is shut down the dehumidifer if the safty switch on the pump is activated. I belive I will need a realy to achive this. Unfortunitly thats about where my knowledge to set-up such a system ends.

The low-voltage of the pump switch would need to shut-down the line voltage to the dehumidifer.

What kind of relay do I need? Where would a get a relay like this?

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Old 07-16-2012, 12:23 PM   #2
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You will need a relay with contacts rated for 120V AC and 15A, or whatever the dehumidifier requires. It will need to have a low voltage coil, probably 12 or 24V AC. You will also need a transformer to supply your control power, 12 or 24V AC. A standard furnace control transformer would be fine.

You'd wire the relay's normally open contacts in series with the hot wire to the dehumidifier, so that the relay needs to be closed for the dehumidifier to run. You'll wire low voltage power from the control transformer to the relay coil, with the condensate pump's safety switch in series with one of the low voltage wires.

Wired in this way, power will normally flow from the transformer, through the float switch, and to the relay coil, closing the relay and allowing the dehumidifier to run. If the float switch opens due to a pump overflow, the power will be interrupted, the relay will open, and the dehumidifier will shut off.

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Old 07-16-2012, 12:34 PM   #3
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Thanks for the quick reply. I didn't know that the pump side would need a source of power. Is there anyway to eliminate the need for adding that transformer?

Can youu give me an example of a relay that would work for what you described. The number of diffrent relays available is mind-blowing. If I go to a catalog that lists relays there are 100's if not 1000's of choices!!!
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Old 07-16-2012, 12:46 PM   #4
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I would recommend maybe using something like a contactor, used in central air units to switch the compressor on and off. I'm afraid I can't really help you with any specific part numbers.

There might be another, more elegant way accomplish your goal. I assume we're talking about a standalone, plug-in dehumidifier here, yeah? One that can be drained into it's own tank or through a hose?

Is the hose fitting part of the tank? If your pump stopped, wouldn't the water just back up into the dehumidifier's tank, filling it and tripping it's internal float switch?
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Old 07-16-2012, 12:54 PM   #5
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Yes, a portable dehumidifer with tank, 120 VAC. Mine has a hose attached to the tank. The condensate pump will need to be lower than the dehumidifer so it will drain by gravity. I would assume that with a pump failure the condensate pump resivor would simply overflow. There's nothing to stop the flow of water at that point. There's no way for the float in the dehumidifer to rise/trip.

Last edited by sorethumber; 07-16-2012 at 03:12 PM. Reason: better explaination
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Old 07-16-2012, 01:14 PM   #6
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relay switching.......


I found this on Amazon.......Would it work?

http://www.amazon.com/SSR-25DA-Tempe...rds=hvac+relay
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Old 07-16-2012, 05:59 PM   #7
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Quote:
Originally Posted by sorethumber View Post
I found this on Amazon.......Would it work?

http://www.amazon.com/SSR-25DA-Tempe...rds=hvac+relay
It probably needs a heat sink. I'd get an electromechanical relay instead.
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Old 07-16-2012, 06:16 PM   #8
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http://www.ebay.com/itm/Furman-MP-15...8167%26ps%3D54



Im not 100% sure if you can de energize the receptacle with NC contacts like in your condensate pump, but this is worth looking into... just do your homework before you order one.

Last edited by stickboy1375; 07-16-2012 at 06:25 PM.
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Old 07-16-2012, 07:15 PM   #9
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To get the right relay,
we need to know more about the load ?
What is the power draw of the unit you wish to control ?
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Old 07-16-2012, 07:15 PM   #10
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Originally Posted by dmxtothemax View Post
To get the right relay,
we need to know more about the load ?
What is the power draw of the unit you wish to control ?
Its a dehumidifier... 15 amp max.
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Old 07-16-2012, 07:20 PM   #11
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Use one of these and you won't need a power supply. It is looking for a dry contact switch to control it. The device is UL listed so you won't be violating NEC using it. Also due to nature of dry contacts it is well isolated from the 120VAC side so you can use class 2 wiring for the dry contact side. Just be sure you wire it into a float switch that is not powered by other means.... i.e. don't cross connect the dry contact leads with power switching within the condensate pump. That could damage one or both devices.


http://www.functionaldevices.com/bui...model=RIB01BDC
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Old 07-16-2012, 07:24 PM   #12
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Use one of these and you won't need a power supply. It is looking for a dry contact switch to control it. The device is UL listed so you won't be violating NEC using it. Also due to nature of dry contacts it is well isolated from the 120VAC side so you can use class 2 wiring for the dry contact side. Just be sure you wire it into a float switch that is not powered by other means.... i.e. don't cross connect the dry contact leads with power switching within the condensate pump. That could damage one or both devices.


http://www.functionaldevices.com/bui...model=RIB01BDC
I was going to recommend one of those, I didn't realize they did make them with internal power supplies, I should have known better, its still a bit of work to setup with what I posted though.... he still needs a pre made cord, a box, and a receptacle with the RIB relay and the knowledge to make this all up.
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Old 07-16-2012, 07:40 PM   #13
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Quote:
Originally Posted by stickboy1375 View Post
I was going to recommend one of those, I didn't realize they did make them with internal power supplies, I should have known better, its still a bit of work to setup with what I posted though.... he still needs a pre made cord, a box, and a receptacle with the RIB relay and the knowledge to make this all up.
All true. This company has an interesting line of relays of all types and flavors, dry contact, delay, 24VAC coil, wireless, .... I just ordered one of their catalogs, I estimate they have 100+ SKUs. The good thing is they are all UL listed where a simple relay from and electronics store may not be. Also the knockout mounting scheme is pretty flexible.

Not sure how ambitious the OP is here. Also depending on how much space there is in the wiring end of the dehumidifier he may be able to mount it on dehumidifier using a knockout hole.

Not sure I understand the need though as I though all dehumidifiers had shut off switches for this very purpose (when the tank is full it shuts off to prevent spilling water all over the floor).
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Old 07-16-2012, 07:44 PM   #14
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Quote:
Originally Posted by curiousB View Post
All true. This company has an interesting line of relays of all types and flavors, dry contact, delay, 24VAC coil, wireless, .... I just ordered one of their catalogs, I estimate they have 100+ SKUs. The good thing is they are all UL listed where a simple relay from and electronics store may not be. Also the knockout mounting scheme is pretty flexible.
I have the catalog already... I use these relays frequently, just not the one you posted.



Quote:
Originally Posted by curiousB View Post
Not sure I understand the need though as I though all dehumidifiers had shut off switches for this very purpose (when the tank is full it shuts off to prevent spilling water all over the floor).
He is dumping the water directly into a condensate pump, there is no shut off feature when you do this, hence the utilization of the safety switch built into the condensate pump. Its really not a bad idea, and I'm surprised a product does not exist already for this need.... I suppose most people install these on concrete floors, and who really cares at that point.

Last edited by stickboy1375; 07-16-2012 at 07:46 PM.
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Old 07-16-2012, 08:53 PM   #15
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relay switching.......


how much 'low voltage' is this? I would personally use an ice cube style plug in relay. You would need your dehumidifier power to pass through the relay contacts and the coil to interact with the condensate pump. Either that or wire up your own float switch as to 'shut off' coil voltage when normally closed float switch opens.

The problem is not knowing anything really about the safety switch and how it interacts with the condensate pump. I would just say hook up the coil in series with the switch. When the switch opens, coil voltage is cut, and the closed contacts open to shut the dehumidifier off. It's impossible to say if that would work though without knowing the wiring.

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