Motor starting relay alternative

[Factoryspark]

I previously posted about having a single phase reversing motor which I thought had a centrifugal switch.

After looking into it more, it actually has a motor starting relay, Klixon 2CR4-243 (max pick-up 18.9A and min pick-up 15.6A).

These were superseded by the 4CR series however I'm struggling to source one.

So I have been thinking about whether it would be practicable to use a timer relay, specifically a N/C, timed open contact type.

Theory being, the start winding would be in circuit for 5 seconds once the relay coil is energised then switch to an open state taking the start winding out of circuit, the relay coil can just be put in parallel with the forward and reverse buttons and latched to hold the open state of the timed contact.

The issue I have is that, is 5 seconds adequate? its very guess work but I think the theory is okay.

 

[Lucien Nunes]

As I'm sure you're aware, the orignal relay senses the current in the main winding and energises the start winding when it exceeds the running current (indicating that the motor is not at speed). The length of time it remains energised depends on the mechanical load imposed on the motor. A light load with low inertia might allow the relay to open within a second, minimising the heat dissipated and maximising the number of starts possible per hour. A high-inertia load might take five seconds to reach speed.

Another advantage of a current'sensing relay in some applications is that it will restart the motor if it stalls due to overload, while a timer would be oblivious and leave the motor stalled. IIRC your application is for a blower and therefore this capability shouldn't be required.

So yes, a timer will work; you will need some knowledge of the behaviour of the unit and its operating duty to select the best runup time. OTOH I would be surprised if an equivalent relay can't be sourced, even if you have to go via e.g. a HVAC parts supplier.