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Is it Possible to Replace the Usage of Relay with Microcontrollers?

12/16/2011 2:19 AM

One of my colleague wants to replace/reduce the usage of relay with microcontroller in the circuit we are using for the project. This is one way he thinks that is able to cut the cost of the project. But I'm not sure if the idea is a good one. Can some suggest another method to reduce/replace relays?

P/s: I'm not sure if my question had been posted but I do hope someone will answer it.

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#1

Re: Is it possible to replace the usage of relay with microcontrollers?

12/16/2011 3:18 AM

It depends on how many relays you can replace with a single microcontroller having as many outputs as there were original relays. Price out both options to see which is better for your particular situation.

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#2

Re: Is it possible to replace the usage of relay with microcontrollers?

12/16/2011 4:11 AM

It depends what the relay is controlling.
I routinely use a microcontroller to switch an FET to drive DC motors.
A microcontroller on it's own will probably only sink/source say 25mA max so you would probably need an FET or or bridge driver arrangement.
It all depends on the specifics of the application.
Del

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#3

Re: Is it possible to replace the usage of relay with microcontrollers?

12/16/2011 6:28 AM

I don't know what your application is but these might work...It's hard to beat microcontrollers for price and reliability...Maybe a PLC..

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#4

Re: Is it Possible to Replace the Usage of Relay with Microcontrollers?

12/16/2011 12:15 PM

Many times you can, and really save a whole lot; but in many test equipments, where power sources and measuring instruments are to be commutated, that is absolutelly imposible in terms of electrical isolation, parasitic resistance and 4 wire (kelvin) connections, and will never be otherwise.

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#5

Re: Is it Possible to Replace the Usage of Relay with Microcontrollers?

12/17/2011 3:00 PM

It depend on the load, the logic to be performed, what happens when power is first applied and the timing with delays and such. You may not need a micro-controller at all, some old fashion logic gates have always worked fine and with a higher reliability. BTW I design micro-control circuits for a living and can tell you that they are probably an overkill for what you need.

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#6

Re: Is it Possible to Replace the Usage of Relay with Microcontrollers?

12/18/2011 7:23 AM

Did you consider the Schneider Zelio or comparable products from other manufacturers?

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#7

Re: Is it Possible to Replace the Usage of Relay with Microcontrollers?

12/19/2011 6:22 PM

It depends much on how many of the relays are switching other relays and not any output loads, that are just doing "logic".

If you have a design with ten "many-contact" relays and ten mains voltage loads of several amperes each, then ten relays will still be needed. Also, if you need many delay timers, these are bulky and expensive in timer-relay units, but easily provided in a microcontroller or PLC.

Normal logic gates have been mentioned, there are also various programmable logic gate chips. Sometimes, if the relation is "combinational" (only logic, no time delays), a memory chip can do the job - code conversions have been done that way - if the task is presented as an input versus output table, it is easily converted to a "memory" requirement.

But you have told us so little about your project that you will get an equivalent little answer.

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#8

Re: Is it Possible to Replace the Usage of Relay with Microcontrollers?

12/20/2011 8:47 AM

The rule of thumb I have been quoted is that, if 4 or more relays and or timers need to be replaced, it is cost effective to use a PLC.

Having said that you need to look at each application separately and determine if this is the case. Some installations use relays because of their larger current carrying capability.

We replace relay logic with PLCs mainly because of lower cost, ease of troubleshooting, and the ability to make lower cost and quicker changes in the future.

There are some small controllers that can be programmed off of the keypad on the front of the unit that may work for you if your staff isn't trained. If it's a larger project then it does requires an electrical staff capable of doing this type of work, for both installation and maintenance reasons.

Good Luck Elroy

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#9
In reply to #8

Re: Is it Possible to Replace the Usage of Relay with Microcontrollers?

12/20/2011 8:28 PM

Thank you for your reply

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#10
In reply to #9

Re: Is it Possible to Replace the Usage of Relay with Microcontrollers?

12/21/2011 7:55 AM

Looking at your other posts, it seems you have a student project. In that case, you probably get more "brownie points" for programming a microcontroller chip than using a PLC!

In industrial use, in small numbers of similar projects, a PLC usually wins.

The deciding factor, from my experience, was that one could draw the diagram for the panel builder as soon as the input/output requirements were known. They could then build the panel while I did the PLC software, test requirements etc.

Previously, with relays & timers, I had to design everything before the panel could be wired and any modifications were expensive if they delayed delivery or had to be done on site (my manager reckoned any site modification cost ten times as much as in the factory, modifications cost more anyhow). Sending out a new programme tape/memory or small modification to site was much quicker and easier than modifying and issuing circuit & wiring diagrams.

In my applications, relay type PLC "ladder" diagrams were much more acceptable to commissioning & maintenance people than logic or flow chart presentation - micro-controller programmes would have been unintelligible!

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#11
In reply to #10

Re: Is it Possible to Replace the Usage of Relay with Microcontrollers?

12/21/2011 8:28 PM

Erm I'm actually working for a company ^^ It's for a company project which is currently on-going. Well, it's actually my colleague's project. I'm currently assisting him. Basically, in the circuit, we use around 12 or more relays to control the function of the circuit but my colleague is thinking of replacing or reducing the number of relay to cut-down the cost of the project (The relay being used cost around $4 or so each and this is excluding the cost of the whole circuit + packaging). For this project, the circuit is used to check the functionality of the product. It's quite hard for me to explain but this is the best I can say.

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#12
In reply to #11

Re: Is it Possible to Replace the Usage of Relay with Microcontrollers?

12/22/2011 2:25 PM

Don"t just consider the building/manufacturing cost. Also consider maintenance - who will do it, what will their skills base be, how critical is the equipment, what spares will be available. I lived through a case where we leased PLC-based equipment, but the local mechanics and auto-electricians could not really get it. I shudder to think what would have happened if it operated with a microcontroller! Our new equipment are all controlled with discrete relays, but that was related to the power requirementts too.

In most cases PLCs can be changed more easily if that should ever be an issue (10 years down the line it may be easier for the new guy to figure out discrete relays or PLC logic as opposed to a microcontroller program that may be obsolete/unknown by then).

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