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RC Network to act as a battery for time delay

RC Network to act as a battery for time delay

RC Network to act as a battery for time delay

(OP)
Please help:

I have a 4160 V starter. I want to delay the starter from shutting down the motor by a 20 cycle delay.

I am trying to achieve this using an RC Network. (Basically I want the capacitor to act as a battery for 20/60 = .333 sec. longer)

The circuit is: starter coil connected in parallel w/ the motor contact.  I will place my RC circuit in parallel w/ the contact.

I have the values of coil resistance = 541 ohms
             My RC capacitor value is= 235 /microF/

How can I find the value of the RC Network "R" resistance needed to accomplish my task?

Are there any other things I need to consider?


                     

RE: RC Network to act as a battery for time delay

What's your control voltage?  AC or DC?

Mike Halloran
Pembroke Pines, FL, USA

RE: RC Network to act as a battery for time delay

(OP)
My control voltage is AC

RE: RC Network to act as a battery for time delay

Won't be easy then.

The RC only works as a DC "battery". And your coil is AC. I think that you shall drop that idea and use some other technology.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: RC Network to act as a battery for time delay

If it is a vacuum contactor, even though your control circuit is AC chances are that the actual coil on the contactor is DC with a small rectifier. You may be able to tap onto the DC side of the circuit with your RC circuit.

JRaef.com
"Engineers like to solve problems.  If there are no problems handily available, they will create their own problems."   Scott Adams  
For the best use of Eng-Tips, please click here -> FAQ731-376

RE: RC Network to act as a battery for time delay

(OP)
I apologize for not being clear or giving enough information.

There is an undervoltage relay connected to the motor, when it sees a 20% voltage dip, it will open,  killing the control ckt, where the starter is located, and motor starter coil (where I want to put the RC Network).  

By it opening, it will not supply any more ac to the control ckt therefore de-energizing the motor start coil.


So here is my scheme:  By no more AC power, this will now look as a DC ckt: The coil will behave as a 541 ohm resistance, and I want to parallel connect my RC Network to act as a battery, so the control will never see the relay open, nor the dip and therefore I do not have to go and start the motor over and over again.

I have the value of the motor coil resistance, and I have the RC cap value, but how do I go about and get the R value?

RE: RC Network to act as a battery for time delay

Sounds to me like an LRC network excited by an AC circuit and then the AC is turned off.  The L and the C will ring and you will continue to have AC.  Why not just buy the time delayed undervoltage relay and not try to reinvent the wheel?

RE: RC Network to act as a battery for time delay

It should be mentioned that a slowly decreasing voltage on a relay (capacitor time delay) not only provides a time delay, but also causes the contacts to open very slowly.  This is the last thing you want to do with a high voltage/current contact. Use a real time delay or at least an additional DC relay to put this capacitor on.

One manufacturer I worked with had to use a 20A analog supply (lots of big caps)to supply the coil of a main contactor to keep it from dropping out on a foreign voltage supply that would suffer from 1/4 second drop outs.

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