Test a relay?
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Lexus Test Driver
Joined: Mar 2002
Posts: 812
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From: Wisconsin
Test a relay?
How can you test relays? Someone said something about having to apply current to the relay itself and then test it again with a multimeter.
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CL Community Team
Joined: Apr 2001
Posts: 16,559
Likes: 1,385
From: Austin, TX
Not knowing exactly what type of relay you want to test ...
First task is to identify the terminals for coil and contacts. With the ohm meter, car (12v) relay coils show a resistance of 10 ohm to 60 ohms typically.
Contacts can be single pole (switch 1 line .... like light switch at home) or double pole (switch 2 lines ... like ganged circuit breakers). You can think of double pole as having an additional single pole in a common housing. The contact discussion below is for single pole.
Contacts again come in various forms .... normally open (2 terminal), normally closed (2 term), and both (3 term).
Normally Open is the most common application where when energised, a noramlly open termials would contact ... like a door-bell push button at home, instead of holding the button one has to energise the coil.
Checking a normally open single pole (2 term contacts) relay:
Confirm that the coil is not burnt/open (not infinite resistance)
Energise the coil by 12v. You would hear a click (typ)
Confirm with the ohm meter that the contacts show 0 ohm
Disconnect 12v (should hear a click). The contacts should show infinite/open resistance on the ohm meter.
Typical relay problems (other than wiring)
Burnt coil
Bad / pitted contacts.
Largest realy on the car: Solenoid on the starter.
Salim
First task is to identify the terminals for coil and contacts. With the ohm meter, car (12v) relay coils show a resistance of 10 ohm to 60 ohms typically.
Contacts can be single pole (switch 1 line .... like light switch at home) or double pole (switch 2 lines ... like ganged circuit breakers). You can think of double pole as having an additional single pole in a common housing. The contact discussion below is for single pole.
Contacts again come in various forms .... normally open (2 terminal), normally closed (2 term), and both (3 term).
Normally Open is the most common application where when energised, a noramlly open termials would contact ... like a door-bell push button at home, instead of holding the button one has to energise the coil.
Checking a normally open single pole (2 term contacts) relay:
Confirm that the coil is not burnt/open (not infinite resistance)
Energise the coil by 12v. You would hear a click (typ)
Confirm with the ohm meter that the contacts show 0 ohm
Disconnect 12v (should hear a click). The contacts should show infinite/open resistance on the ohm meter.
Typical relay problems (other than wiring)
Burnt coil
Bad / pitted contacts.
Largest realy on the car: Solenoid on the starter.
Salim
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