Automotive Relay Make and Break Current Explanation

Thread Starter

Surya1234

Joined Apr 23, 2021
16
Hi Everyone,

I appreciate if someone can answer the following questions that I have about this relay:

1. What exactly make and break currents do mean?
2. Why they are different for resistive and inductive loads?
3. How much current the coil would need to close the relay contact? This current will be delivered by the electronic control module and the other end of the coil is connected to chassis ground.
4. When this relay contact opens?
 

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MaxHeadRoom

Joined Jul 18, 2013
23,779
1 The break current is usually more stressful on relay contacts due to arcing, acerbated when inductive load is switched. Which can result in plasma arc, destroying or welding contacts
2 A resistive load, if DC is essentially the voltage/current requirement of the device. An inductive load stores energy which can cause excessive contact arcing, particularly at switch off.
3 The relay coil current will depend on its rated voltage and the resistance of the coil, applies to DC only.
4 see above
IP67 rating means it can withstand/sealed to outside atmosphere, can be immersed.
 

Thread Starter

Surya1234

Joined Apr 23, 2021
16
Thanks for the prompt response. This relay has 10A of break current rating for a resistive load, whereas 75A of break current rating for an inductive load. Does it mean 1. To turn off power to the DC resistive load, the relay contact/load current shouldn't be more than 10A and 2. to turn off power to the DC inductive load, the relay contact/load current shouldn't be more than 75A i.e. relay can be opened by de-energized the coil ckt, provided the load current is not more than 75A
 

Thread Starter

Surya1234

Joined Apr 23, 2021
16
Thanks for the prompt response. This relay has 10A of break current rating for a resistive load, whereas 75A of break current rating for an inductive load. Does it mean 1. To turn off power to the DC resistive load, the relay contact/load current shouldn't be more than 10A and 2. to turn off power to the DC inductive load, the relay contact/load current shouldn't be more than 75A i.e. relay can be opened by de-energized the coil ckt, provided the load current is not more than 75A
 

MaxHeadRoom

Joined Jul 18, 2013
23,779
I don't think I would want to break a 75a inductive load with a 0.3mm contact gap, where do you see those ratings?
Typically the inductive load rating is much less than the resistive load.
 

Thread Starter

Surya1234

Joined Apr 23, 2021
16
Before de-energizing the relay, the appliance (could be a heater or cooler) will be turned off manually using its switch. Once the appliance is turned off, the relay will be de-energized to break the circuit.
 

MaxHeadRoom

Joined Jul 18, 2013
23,779
Before de-energizing the relay, the appliance (could be a heater or cooler) will be turned off manually using its switch. Once the appliance is turned off, the relay will be de-energized to break the circuit.
Commonly known as 'Dry Contact' switch rating.
IOW, it is not breaking the load.
 
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