Melted Relay in Greenhouse

powerplay

Senior Member
In an Agriculture Research Station where lights are being turned on 4 times a day, the 24volt furnace Relays that were installed by the lighting control people from "Argus" are melting and brittle. Facility Manager, Electricians are telling me go with a bigger box to handle the heat, but I was saying why is it getting that hot in the first place?

- greenhouse is hot and humid
- CO2 is present and oxidizes most metals in an arc?
- lights switched on 4 times a day in experiments (I assume the plants on farms are left on longer and not switched as frequently?
- definite purpose lighting contractor is rugged, but if connection expands, gets loose, oxidizes and hot enough to melt insulation, it would not as likely destroy Compactor but still pose a hazard if melted.

My observation was that the "Argus Relay Box had a gasket, but no sealed cable connections.
- the crimps being used were made of inexpensive material ( I had some stronger nickel crimps for high heat, which with penatrox would make a better connection)

Is it a good idea to put bigger Contactors into a bigger box? ... Or will the same problem occur?

My suggestion was just use nickel crimps, use antioxidant, seal the box from humidity and co2, and possibly get a sealed metal pipe toenter and exit the box as a heat sink with a computer fan to circulate the air.
 

gar

Senior Member
160706-0854 EDT

You have not mentioned the type of load or load current.

If the load is within the ratings of a GE RR relay, then I suggest that you look at the RR as a possibility.

A GE RR relay is a mechanically bistable unit that has no continuous internal power dissipation other than the loss in the contacts. I will assume 20 millivolts at 20 A as power dissipated. This is 0.4 W and you won't detect the temperature rise.

Assuming your present relay requires continuous coil excitation, then to use the RR relay would require a change in your control logic. The coil is nominal 24 VDC and can not be continuously excited.

.
 

mgookin

Senior Member
Location
Fort Myers, FL
In an Agriculture Research Station where lights are being turned on 4 times a day, the 24volt furnace Relays that were installed by the lighting control people from "Argus" are melting and brittle. Facility Manager, Electricians are telling me go with a bigger box to handle the heat, but I was saying why is it getting that hot in the first place?
I don't have any history with Argus but they look like any other LED company to me. All LED companies have to be approached with caution.
What is the manufacturer's name & part number on the relay?
How many are we talking about?
What are the loads on the relay?
Is the relay in an environment where fertilizer is getting to it, either as fumes or liquid?

...

- greenhouse is hot and humid
- CO2 is present and oxidizes most metals in an arc?
- lights switched on 4 times a day in experiments (I assume the plants on farms are left on longer and not switched as frequently?
- definite purpose lighting contractor is rugged, but if connection expands, gets loose, oxidizes and hot enough to melt insulation, it would not as likely destroy Compactor but still pose a hazard if melted.

...
Hot & humid should not be a concern. The heat probably isn't over 105F and humidity is not a concern, unless it's condensing.
Plants consume CO2. The formula is CO2 + H2O = O2 + C6,H12,O6. (CO2 and water make oxygen and sugar). Plants give off oxygen. You may be in an oxygen rich environment.
Switching any light 4x/ day is not of concern. If a relay can't handle it, it's the wrong relay.
Definite purpose and Lighting are different. Which is it?


...

My observation was that the "Argus Relay Box had a gasket, but no sealed cable connections.
- the crimps being used were made of inexpensive material ( I had some stronger nickel crimps for high heat, which with penatrox would make a better connection)

Is it a good idea to put bigger Contactors into a bigger box? ... Or will the same problem occur?

My suggestion was just use nickel crimps, use antioxidant, seal the box from humidity and co2, and possibly get a sealed metal pipe toenter and exit the box as a heat sink with a computer fan to circulate the air.
Can you locate these relays outside the greenhouse? My main concern is the fertilizer which can be corrosive to metals, deteriorate plastics, etc.
Do they have other problems?
 

GoldDigger

Moderator
Staff member
A "definite purpose" relay or contactor is the absolute minimum design for normal conditions. A general purpose unit will run cooler and last longer.
And in the long run may cost you less than periodic replacements.
 

dfmischler

Senior Member
Location
Western NY
Plants give off oxygen. You may be in an oxygen rich environment.
CO2 is generally considered a nutrient for greenhouse production purposes. CO2 is probably being purposely added, either by releasing it from tanks or by burning fuel (e.g. natural gas). Burning is in some ways simpler because you don't have to keep swapping tanks, but it also adds humidity which can be undesirable.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
This is likely Argus Controls, who make furnace management systems. The "relays" I have seen from them are really more like PLC output modules, 4 outputs on a "brick" that snaps onto DIN rail. Those little contacts are rated for something like 3A and 24V AC or DC. That's not much, so it depends on what you are trying to switch.

But really, this is all just speculation because you didn't provide anywhere near enough info to be useful in trying to help you. You seem to have decided its environmental contamination and are looking for validation of that. You might be right, but again, not enough data to offer any meaningful support.

I don't know where you got the info that CO2 is detrimental to contacts by the way. I've been working with controls for 40 years now, that would be the first time that has ever been suggested. Moisture, absolutely, but CO2? I don't see how that would make one iota of difference.
 

powerplay

Senior Member
This is likely Argus Controls, who make furnace management systems. The "relays" I have seen from them are really more like PLC output modules, 4 outputs on a "brick" that snaps onto DIN rail. Those little contacts are rated for something like 3A and 24V AC or DC. That's not much, so it depends on what you are trying to switch.

But really, this is all just speculation because you didn't provide anywhere near enough info to be useful in trying to help you. You seem to have decided its environmental contamination and are looking for validation of that. You might be right, but again, not enough data to offer any meaningful support.

I don't know where you got the info that CO2 is detrimental to contacts by the way. I've been working with controls for 40 years now, that would be the first time that has ever been suggested. Moisture, absolutely, but CO2? I don't see how that would make one iota of difference.
http://www.clihouston.com/knowledge-base/co2-corrosion.html
 

powerplay

Senior Member
160706-0854 EDT

You have not mentioned the type of load or load current.

If the load is within the ratings of a GE RR relay, then I suggest that you look at the RR as a possibility.

A GE RR relay is a mechanically bistable unit that has no continuous internal power dissipation other than the loss in the contacts. I will assume 20 millivolts at 20 A as power dissipated. This is 0.4 W and you won't detect the temperature rise.

Assuming your present relay requires continuous coil excitation, then to use the RR relay would require a change in your control logic. The coil is nominal 24 VDC and can not be continuously excited.

.
Existing Lighting Contactor... was told to replace part with supplied, but in process of identifying part... and I figures there should not be substantial heat created
 

Ingenieur

Senior Member
Location
Earth
What is the load in amps
what is the voltage
what are the relay ratings (cut sheet)
without this key basic info it's all speculation

for something like this I would use a latching 3 wire contactor
 

powerplay

Senior Member
Hot & humid should not be a concern. The heat probably isn't over 105F and humidity is not a concern, unless it's condensing.
Plants consume CO2. The formula is CO2 + H2O = O2 + C6,H12,O6. (CO2 and water make oxygen and sugar). Plants give off oxygen. You may be in an oxygen rich environment.
Switching any light 4x/ day is not of concern. If a relay can't handle it, it's the wrong relay.
Definite purpose and Lighting are different. Which is it?




Can you locate these relays outside the greenhouse? My main concern is the fertilizer which can be corrosive to metals, deteriorate plastics, etc.
Do they have other problems?
I would have thought 4x switching would not be a concern...

my mistake, I was thinking the Square D Magnetic Contactor was a lighting one, but I guess the lighting one looks and sounds like it sends Morse code... so I guess definite Purpose was what I was thinking

The relays are separated from the separate Greenhouses by doors, but it is in a shared "hallway" adjoining the separate greenhouses... humid but not directly in with the Plants.
 
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