Timer control of mixing vessel

Thread Starter

MztrRobot

Joined Oct 28, 2020
4
Hi Guys
I am looking for some input on some machine control. I installed a timer onto a mixing machine a few weeks back. The timer is basically running the machine automatically so that it can be set and the guys walk away from it and it runs for the preset time instead of the guys having to time it themselves and sometimes it gets forgotten about or over mixed. All fine. There is a start button pressed the timer begins to count which gives an output to a 24vac relay which is then turning on the main controls of the machine so when the timer ends the machine stops and if any safeties are activated the machine stops etc so it is all safe and fine in that regard.

The issue is that the relay which the output of the clock is switching on has burned out after about 8 weeks and I replaced it today and it worked again, but I noticed that when the start button is pressed the 24vac relay chatters a couple of times then kicks in and the machine runs ok. Obviously this is not correct and I am guessing that there is not enough power perhaps inside the panel or a volt drop when the start button is pressed to now cope with the clock or addition of the relay? All of the control inside the panel is 24vac as too are the relay and clock I fitted. All connections are fine and the panel is supplied with 3 phase 400vac which is going into a 0.160kva transformer primary side with a 24vac single output secondary side. I am wondering should I get a slightly bigger transformer with a 2 output option or something else which would stop this chattering or any other advice would be appreciated. Oh and if i take the clock and relay back out and run the machine it all works fine. I amusing a basic Omron SPDT realy and Omron timer too
 

AlbertHall

Joined Jun 4, 2014
10,575
What is the current drawn by the mixer at start-up (not just the run time current) and what rating is the relay contact?
Also I presume the mixer is an inductive load (motor of some sort) and so you need to have a suppressor across the relay contacts to reduce arcing.
 

AlbertHall

Joined Jun 4, 2014
10,575
Yes that's the sort of thing. I wouldn't know which one to suggest for a 5A circuit though. Does the 24VAC also power the motor(s)?
 

Thread Starter

MztrRobot

Joined Oct 28, 2020
4
Yeah the 24vac is switching the coils on on the 3 phase motor contactors. Would fitting the correct suppressor be enough or should I look at additional options too?
 

mcardoso

Joined May 19, 2020
176
I'm not 100% sure on what your system looks like based on your initial post. Let me summarize and see if I can get it correct. There is a 400VAC/24VAC 0.16kVA transformer which steps down the 3 phase mains to single phase control voltage. There is a timing relay operating at 24VAC which turns on its output immediately and begins timing when a push button is pressed (I assume the relay "seals in" on itself so it continues timing after the button was released).

The output of this relay energizes a second relay which in turn energizes the main load (two 5A 400VAC 3P motors). The issue is that the second load relay burns out after a short time and the coil chatters. Did I get it correct?

The first thing I'd check is if both of your relays are rated for AC voltage (many are DC only) and that they are rated for 24VAC. I'd make sure the transformer is large enough to supply sufficient current to pull in the load relay coil. I'd also verify the load relay is rated for the motor amperage you are drawing.

Can you provide part numbers for reference?
 
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