Power supply drop problem

  • Thread starter Prasanna S Venkatesan
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Prasanna S Venkatesan

I am facing a voltage drop problem while switching a 24VDC relay by an another 24VDC relay. (ie)
Coil of my remote relay is connected to contactor of my panel relay with a 5mts wire. Not a single relay is connected so but a group of such relays are wired through a D-type 25 pin connector. Once any of the relay is switched ON the voltage drops from 24V to 18V. The more no.of relays turned ON the more drop occurs. The voltage observed is almost 11V when all 16 relays are switched ON. All the relays are of the same type and rating (Coil current = 80mA). Can any one help me ?


Zan Von Flue

Have you tried Optocouplers. Most relay types can be replaced with optocouplers. Optocouplers have a very low switching current. You just have to watchout for the out voltage direction. Special opto's have to be used for a AC output.

Alan Rimmington

It sounds as though the return leg is common to all the relays, and that the resistance of this leg is causing the volts drop. You are drawing 1.28amps with all the relays on, to give your voltage drop of 13v (24-11) you only need 10 ohms resistance in the common leg to cause this. This resistance is probably occuring in the plug, in which case the plug probably gets warm because you are generating 16 watts of heat !!!!

First, you should check to see if the voltage drop is ocurring after the
wires or before. In other words, is your power supply capable of supplying
24V if all the relays are on? Or is the voltage at the supply drooping
progressively? five meters of wire seems very short to me, to be causing
this type of problem.

Hope this isn't too obvious!


Willy Smith
Please check the amp rating of the 24 v dc power supply U are using.If the rating is not adequate, get one more 24 v power supply and connect in parallel to augment existing power supply.