Need to simulate an induction motor load

Thread Starter


Joined Oct 15, 2013

I have to demonstrate the functioning of relays to someone. Now these relays would be used to switch the supply to an induction motor. I want to check/show that the relays can be turned on-off repeatedly under such a load without getting damaged. However its not possible to use an actual induction motor for the purpose. I was wondering if I could instead use inductors and resistances to simulate the load of a motor in a single phase circuit, and maybe blink an led instead of turning on the motor. The purpose is to roughly estimate the load of a real motor and not to get an accurate judgement.

Can anyone help me with any references on deciding the values of resistances and inductances for testing purpose - maybe there is a typical range for induction motors' equivalent resistances and inductances - I tried finding one but with no luck.


Joined Jul 9, 2011
I don't have those values. But depending on the relay contact rating I would tend to believe that they can be damaged over time if you repeatedly open / close them with current flowing through them. There are also different contact materials...


Joined Oct 15, 2009
What is the purpose of this test and how do you intend to "prove" if a relay is suitable or not?
Normally you would just choose a relay/contactor with a contact design rated to switch inductive loads..

Have you looked into solid state relays/snubbers


Joined Sep 17, 2013
I want to check/show that the relays can be turned on-off repeatedly under such a load without getting damaged.
All mechanical relays will suffer contact damage in time. Mcgyvr has the answer.


Joined Jul 18, 2013
You could use an inductance such as a large transformer with a rectifier and large capacitors and a high lighting load on the secondary to simulate an induction motor.
An induction motor at switch on actually represents a transformer with a shorted turn secondary.
For applications that switch motors or similar loads very frequently such as HVAC etc, a specially made relay is used call a 'Special Purpose Contactor' type, this posses heavy duty contacts and arc Chutes etc.
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Joined Mar 14, 2008
Because it's difficult to simulate the large starting current of an induction motor I agree with mcgyvr, use a real motor.


Joined Jul 18, 2013
I find the whole exercise somewhat a little pointless, all relays and are typically chosen or selected to suit their respective loads, if you undersize a relay contact rating, especially for an inductive load, the life of the relay is going to be shortened, whatever the application?
No different for motor loads, this is why as I previously pointed out the use of Special Purpose for repeated inductive motor load switching.
It may be more enlightening to use undersized relays on a high inductive DC load and show the results that can occur when the selection is wrong?
Once those being demonstrated to observe a plasma arc that continues on a miss-selected relay to the point of melting the contact. The observer usually does not forget it.
Also an opportunity to get into Magnetic arc-blowout.
Much more enlightening!