Maker Pro
Maker Pro

Some questions for my Container Overheat Indicator

Lei Reyes

Jul 2, 2014
60
Joined
Jul 2, 2014
Messages
60
I have the following setup below for my project Container Overheat Indicator .

Materials:
1pc TC4-M1A temperature controller
1pc 12v 3PDT Relay
1pc 12v LED Warning Light

Algorithm:
1. The Temperature Controller will read and display the temp. of the environment
2. If the temp reading reaches 70 deg C, the temp controller will turn on the 3PDT relay through its own Relay Output
3. The 3PDT relay will turn on the 12v LED Warning Light as long as the temp reading is 70 deg C or above
4. The 3PDT (and the Light), will be turned off by the Temp Controller if the temp reading is already below 70 deg C.

Questions:
1. The datasheet does not indicate that the Relay Output of the Temp Controller may be used for DC loads ...
It only says:
"Relay Output: 3A/250V AC Capacity"

However:
I still tried connecting the 12v 3PDT Relay to the Temp Controller's Relay Output.
And everything works fine, and the algorithm was followed seamlessly .

Is it ok to continue doing that ? Is there going to be any problem if I continued doing that?

2. Do I need to use a flyback diode for the 3PDT relay?

I uploaded below my setup diagram and the Temp Controller's images and sheets .

Thanks !
 

Attachments

  • TCSerieIntelligent.pdf
    178.5 KB · Views: 272
  • Some Temp Controller Details.jpg
    Some Temp Controller Details.jpg
    159.7 KB · Views: 117
  • Diagram.jpg
    Diagram.jpg
    65.7 KB · Views: 96

Lei Reyes

Jul 2, 2014
60
Joined
Jul 2, 2014
Messages
60
I have the following setup below for my project Container Overheat Indicator .

Materials:
1pc TC4-M1A temperature controller
1pc 12v 3PDT Relay
1pc 12v LED Warning Light

Algorithm:
1. The Temperature Controller will read and display the temp. of the environment
2. If the temp reading reaches 70 deg C, the temp controller will turn on the 3PDT relay through its own Relay Output
3. The 3PDT relay will turn on the 12v LED Warning Light as long as the temp reading is 70 deg C or above
4. The 3PDT (and the Light), will be turned off by the Temp Controller if the temp reading is already below 70 deg C.

Questions:
1. The datasheet does not indicate that the Relay Output of the Temp Controller may be used for DC loads ...
It only says:
"Relay Output: 3A/250V AC Capacity"

However:
I still tried connecting the 12v 3PDT Relay to the Temp Controller's Relay Output.
And everything works fine, and the algorithm was followed seamlessly .

Is it ok to continue doing that ? Is there going to be any problem if I continued doing that?

2. Do I need to use a flyback diode for the 3PDT relay?

I uploaded below my setup diagram and the Temp Controller's images and sheets .

Thanks !
 

Attachments

  • TCSerieIntelligent.pdf
    178.5 KB · Views: 190
  • Some Temp Controller Details.jpg
    Some Temp Controller Details.jpg
    159.7 KB · Views: 133
  • Diagram.jpg
    Diagram.jpg
    65.7 KB · Views: 115

Bluejets

Oct 5, 2014
6,901
Joined
Oct 5, 2014
Messages
6,901
Should be ok...but just wondering why you don't use the set of n/o contacts 6 and 7 in the controller? (or the 3 and 4 you already have)
They (6&7) are marked AL (alarm I assume) so should close on high temp which is what you are doing with your setup now.
They look to be dead contacts so you should be able to wire your 12v supply through there ok.
Unless I'm missing something here.......
 

Lei Reyes

Jul 2, 2014
60
Joined
Jul 2, 2014
Messages
60
Those terminals you have mentioned are reserved for future purposes, we're still thinking about those. I'm just confused with this relay output because it says only 3A/250VAC from which I connect the external 12V 3PDT relay .
Just wondering if something might go wrong if I continued connecting it there ....
 

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,700
Joined
Nov 17, 2011
Messages
13,700
1. The datasheet does not indicate that the Relay Output of the Temp Controller may be used for DC loads ...
It only says:
"Relay Output: 3A/250V AC Capacity"
Knowing which relay actually is built into the controller might help locating a full datasheet.

Using the relay for 12V at currents below 1 A is probably not an issue at all. The problem with DC is that an electrical arc can develop when opening the contacts and this arc can burn the relay because at DC it can stay on. With AC there is the zero crossing of the current which helps to extinguish the arc. But at 12V and 1A there is little chance of a continuous arc.
To be on the extra safe side you can put a small capacitor across the relay output, e.g. 4.7nF with a rated voltage exceeding that of your working voltage (e.g. 25 V cap. at 12 V working voltage). This capacitor picks up the first current peak when the relay contact starts to open, thus relieving the contact from the current and reducing the risk for an arc even more.
 

Lei Reyes

Jul 2, 2014
60
Joined
Jul 2, 2014
Messages
60
Thanks ! I'm just wondering , isn't the purpose of connecting a capacitor across the relay output the Same as connecting a flyback diode across the 3PDT relay's power supply terminals ?
 

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,700
Joined
Nov 17, 2011
Messages
13,700
Not quite.
The flyback diode willl suppress the negative voltage spike from the back-induction when the relay is turned off.
Across the contacts there is no negaive voltage spike. Instead the capacitor works as a temporary short-circuit (until chraged) to lessen the current across the opening contacts..
 

Bluejets

Oct 5, 2014
6,901
Joined
Oct 5, 2014
Messages
6,901
ok on the first if you need to reserve contacts for later but in the setup you have you are operating a relay from a set of relay contacts.
All seems a bit unnecessary. The LED light...how much current does it draw because that is the deciding factor.
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
8,393
Joined
Nov 28, 2011
Messages
8,393
Yes, you should have a diode connected across the coil of your 3PDT relay to protect the relay driving output of the temperature controller from inductive kickback from the coil of the 3PDT relay when the temperature controller turns its output OFF.

This inductive kickback can easily damage a solid state relay (SSR) and will cause contact arcing in a standard relay, shortening its lifetime.

Connect a 1N400x (4001~4007) diode directly across the coil of the 3PDT relay with its cathode (stripe end) to the side that is positive when the relay is energised by the temperature controller.
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
8,393
Joined
Nov 28, 2011
Messages
8,393
You posted the same question to two different threads; one in General Electronics Chat and one in Electronic Projects. Predictably, this has caused confusion and duplication of effort. DO NOT do it!

I have merged the other thread into this one. This is not an ideal solution because posts from the two threads are now mixed up together. But it's probably the best option for fixing this mess.
 

Lei Reyes

Jul 2, 2014
60
Joined
Jul 2, 2014
Messages
60
Hi Everyone, forgot something, from this whole setup that I made, do you think a 3A fuse is enough to use across the main supply of the temperature controller itself?
 

BobK

Jan 5, 2010
7,682
Joined
Jan 5, 2010
Messages
7,682
Using a fuse across the mains supply is never a good idea. I would put it in series with the mains supply.

Bob
 
Top