Fluctuating voltage

A capacitor is not going to help with an AC circuit.

There are 2 options open to you.

1. Upgrade the supply so that it does not drop when the line is started. This might be accomplished by using a separate supply, or increasing the capacity of the current supply.

2. Change all relays to dc, and use a stabilised power supply. You can then use capacitors to keep the relays energised when the voltage drips. Rule of thumb is about 1000uF per amp required on the output. I like to add one extra 1000uf above this for peace of mind.

Regards

John

DC contactors/relays are less prone to dropouts.

If you cannot change to DC, try a CVT (constant voltage transformer) in your control circuit.

Good luck.

You might look into relays with a lower dropout voltage.

In addition, you might stagger electric motor startups on your production line. Starting current for any motor (or for any other inductive load, for that matter) is much greater than running current.

You should really have someone who knows something about electric services, controls, motors, etc. to take a look at your system. It is just possible that keeping those relays energized during a big power sag might result in greater problems, like motors cooking their windings because they can't start.

It might be a good idea to find out why you have a fluctuating voltage. The relays dropping out when you start the process line indicates a heavy start current, or conversely your fluctuating voltage has dropped too low to maintain the relays in the closed position . Try and stagger the current build up of the process line, like a soft start and then see what happens.

Guest,

I agree with the suggestions of others that you should check further to see why you have a fluctuating voltage. Particularly if this is a recent change. If this is a new installation, then staggering the starting of loads is good because the inrush current of the relay and contactor coils can overload the available power from the power supply.

In one case, I was called to solve a similar-sounding problem, in which the system would drop out the Master Control Relay whenever the Start button was pushed. When I found an over-sized replacement control transformer fuse, I checked further and found a conduit apart with a wire from the Start button shorted to ground. Each time the button was pressed it shorted the transformer just long enough to drop its output voltage below the seal-in voltage of the MCR. Then when the MCR dropped out it opened the circuit which was shorted.

You may want to look for something wrong with a sensor, or control device, or wiring at a distance from the control panel.

--JMM

Dear Sir,

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Hence, we will be able to suggest you a suitable capacitor to improve upon the fluctuating voltage.Please send us the electrical circuit diagram(in pdf file) used in your control panel so as to select a suitable capacitor for your application.

Injineri.RC

Marketing Dept.

Trishala Electrolytics Pvt.Ltd.,

A-111,Rajajinagar Industrial Estate,

Rajajinagar,

Bangalore-560 044

I have two options for you:

1. If this happens only at stating up then you can use a delay timer i.e.your control power must on after a few seconds so that the voltage dip may be eliminated.
2. If your voltages are consistently fluctuating then it it is better to supply control power through UPS.

You should use an UPS to feed relay board.

Plenty to choose from.

If this problem is a problem that first appeared perhaps months or a year ago and progressively got worse to the point of being very irritating, then "perhaps" one or more of the equipment is getting bad.

Might be motor capacitors are getting bad (not providing enough of a kick to start or wrong starting motor capacitors installed when recently replaced or repaired), or motors might be getting worn out, or perhaps oiling and lubricating the equipment and driveshafts so that the starting current isn't so high as it is when equipment is old and bearings and other frictional areas are worn.

You will need to know for each machine on your line: motor voltage, and amps, and what is the capacitor that is installed now. Sometimes many machines in same line have similar or same type capacitors in motor start scenarios .

You could try to buy one new capacitor to save money (or replace all $$) and start changing the new one with the old ones one at a time to 'find' the weak/bad one. Hopefully there is not two or more bad ones.

You can try simply increasing the capacitance while keeping voltage the same. IF this solves the problem then you can stop looking.

Look for bad connections, recent repair items, new load added without your knowledge, has a new machine recently been added to the line?

I agree with "staggered" starting also to reduce the "drain" on the system when it starts.

Dropouts like this are all too common if the original design was not up to scratch. A frequent cause of trouble is voltage drop in the neutral or common leg. Adding a couple of extra cables to loop the neutral and / or supply the biggest coils directly can make a huge difference. Take some current readings to give yourself a fighting chance. It is not always system voltage drop that is the culprit.

Capacitors. Oddly enough some help can be gained with their use in an AC circuit by improving the power factor. To help your problem the capacitors need to be connected close to the largest coils. To guage their effectiveness keep measuring the current at the control fuse after each change. Make sure you use AC rated capacitors for the job, flourescent light power factor correction capacitors are a good place to start.

I would only play around with caps after correcting the expected wiring defects, especially since you say it is only one control panel.