Is this a good circuit to use as a air condition switch with a help of microcontrollers 5V? What relay to use in this situation?
What parameters should I take into consideration when choosing relay?
Answer
What parameters should I take into consideration when choosing relay?
There are three main categories to look at, coil specification, contact specification and general technical data. I will discuss some common parameters below.
Contact specification
Contact configuration - Do you need a contact that closes (NC / normally closed), opens (NO / normally open) or switches over (CO / change over)?
Rated current - The maximum rated DC current. You should stay well below this value for some safety margin.
Rated voltage - Maximum switching voltage.
Rated load according to Utilization categories - Some manufacturers specify a maximum load for specific conditions. For example AC-1 (Non-inductive or slightly inductive loads) or AC-15 (Control of A.C. electromagnetic loads).
Breaking capacity - Specifies the maximum current the relay can switch off without being destroyed or causing an electric arc with unacceptable duration.
Minimum switching load - A minimum voltage/current may be necessary to overcome the contact resistance.
Contact material - There are lots of different contact materials used. Gold plating is useful for switching light load due to low contact resistance. Some silver alloys are more resistant to arcing than others.
Coil specification
Nominal voltage - Normally the rated DC voltage. Most relays are available with several coil types like 5V, 9V 12V and so on. This is a trade off between what voltage you have available and the maximum current you want/can switch (may be limited by transistor for example).
Operating range - Specifies the minimum (relay won't switch on below that) and maximum coil voltage (above could cause excessive current and/or maybe mechanical damage).
Holding voltage - Once the coil is magnetized and the contact closed, the voltage to hold the contact is often even lower than the minimum specified operating voltage.
Drop-out voltage - The voltage where the relay is guaranteed to switch off.
Other technical data
- Mechanical life - Number of switching cycles (without load)
- Electrical life - Number of switching cycles at specified load
- Operate/release time - Self explanatory
- Insulation between coil and contacts - This is important if you have to design according to safety regulations. You may require 4 or even 8kV for example.
- Dielectric strength between open contacts - This may be of interest if you have to make sure that there is no arcing while the contact is open.
- Ambient temperature range - Self explanatory
- Environmental protection - If there the relay/device is going to be used in a harsh environment, this is worth looking at.
No comments:
Post a Comment