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Line Voltage drop (110v AC - 60v AC) causing relay to drop out

Hi Hope you can help. I currently have an application where I am using a 110v AC Relay for an alarm circuit. An upstream panel has had an A/B 24v power supply fitted. Everytime the panel with the PSU is switched on it drops the line voltage, to my relay, from 110v AC to about 60v AC and the realy drops out. Can anyone recommend a solution that will compensate for this drop say for 2 seconds? I am assuming the inrush current to the PSU is causing the voltdrop.

Thank you 

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April 23, 2018 10:38

Nice detective work...

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April 23, 2018 09:36

Further investigation - supply transformer only 50 VA !!! - no wonder it was saturating LOL !!!!

April 17, 2018 10:03

Just spoken to Omron - they don't recommend capacitors across coils - looking at changing the supply transformer now for a CVT !

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[Comment was deleted]

April 17, 2018 08:08

Hi Boss - thank you for your reply. Problem is this installation is an upgrade from 110v control to 24v DC on 2 of the control panels, the third panel has remained the same at 110v AC (which is also the last in the looped feed). The supply voltage to all panels has stayed on its original wiring and is still at 110v AC. I believe the inrush current is probably momentarily saturating the transformer which is causing the volt drop - I wondered if a capacitor across the coil of the 110v relay would momentarily hold up the voltage to smooth this dip? Or if there is some other device available to hold the supply voltage up ?

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April 17, 2018 08:08

That sounds like a big voltage drop! Could you reduce the cable length or use a higher rated cable (lower impedance) to the PSU?
What is the power cable route to the relay? Is it sharing i.e. in series with the problem PSU if so can it be commoned to the 110V power further along, i.e. removing as much of the shared power cable as possible.
The closest I have experienced to this was a lift motor in an old building causing a huge drop out affecting our instrument, we could not get the lift or supply changed so had to redesign our instrument to be less sensitve to mains fluctuations.