Power supply from 24V~ transformer

[suirammarius]

Hello!
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[tronitech]

Are you saying a dedicated 5V @ 1A supply would be too expensive?

 

[suirammarius]

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[tronitech]

A separate 5V SMPS is the obvious solution don't you think and can be picked up for as little as $14.00.

You've already voiced your safety concerns and the fact that the LM2576 is running near it's maximum (the LM2576HV would be a safer chioice) and it's the best way of isolating the 5V rail.

A solution to your problem?

 

[suirammarius]

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[alec_t]

Why do you have to use the PLC's 24V~ transformer? As suggested above, a totally independent mains-driven power source (e.g. a wall-wart) would be simpler than trying to drop down from a noisy 24V~ and filter out all the hash. It would probably also be a lot cheaper.

 

[be80be]

Its easy to do what you want you pull the power for your micro before your your 24 volts using half of the 24 volts. With good filtering you'll get clean 5 volts and the full-wave bridge for the 24 volt side well help stop emf on the half bridge side.

 

[suirammarius]

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[be80be]

I'll post the idea give me a sec

Like this View attachment 63999

 

[alec_t]

That circuit grounds one AC line, but the OP's 24VDC supply probably has the DC negative side grounded. Won't that cause a problem?

 

[JimB]

I agree with alec_t, the existing supply probably is grounded at the -ve side of the DC.
The connection proposed by be80be would cause problems.

To the OP, you have already stated that this circuit of yours has safety implications, so do the job properly, not some half hearted cheepo bodge-up!
Just get a decent power supply that can be dedicated to the task of supplying your circuit and ensure that everything is well screened and filtered.

JimB

 

[suirammarius]

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[alec_t]

I insist with the PLC's power supply because this one needs to be cheap, small and very stable!

It probably won't be cheap (with all the filtering necessary) or stable (because of the contactors kicking in and out)

 

[suirammarius]

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[be80be]

A PLC power supply only puts out 24 volt DC And the PLC takes that and uses it. Your noise is from improper handling of motors or relays. You can't make a power supply how you going handle the rest of this.

I didn't post a supply for you just a idea of how you could do this

But if you want to make a high quality supply its not using the 24 volt output side and dropping that to 5volts you pick up you feed for
the 5 volt side and the 24 volt side is off the end to isolate any switching noise.

You have two supply's and supper filtering on the logic side And yes common ground

But I not going to make it all for you I just posted the basic ideal. Not all the parts and sch to get you a A+

 

[suirammarius]

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[be80be]

Older then you and a lot smarter. I don't see me posting how to make a PLC power supply. And i sure don't ask people to design

On the other hand, it can't be very expansive because the profitability falls down, and the project will not pass the prototype level!

You should be able to design a power supply.

If your resetting

But this is not the biggest problem! When I disconnect the servo or the coil of contactor the chip stuck!!

And I'll say it again PLC power supply's are 24 volt DC there is no

rectifying the 24V~ I have about 37Vdc (without load, the transformer has 27Vac)

And out of the ten's of thousands of PLC that I worked on I never seen any fall that where wire right because of spikes.

And if your ask for help like this and no every thing why ask.

How is powered a PLC (the TTL level)?
If someone wants to help me and needs more informations, just ask!
Thank you!
Oh! It needs to supply 1A.

And the last thing I good supply for PLC is about $300.00 to $400.00

And this autoinduction Is not a electric term Its

a process in which continued administration of a drug leads to an increase in the rate at which the drug is metabolized.

Now if you mean EMF or back EMF improper parts "Like you use a relay that has no back EMF protection"
Or you ran your wiring with the mains and are picking up noise.

 

[be80be]

And I would of told you how to use a cheap Laptop replacement power supply that would of fit the bill to a T.

It a very well made switching supply that has both 3 to 27 volts DC and a nice clean 5 volts DC for your 5 volts stuff. And there cheap. But very usable.

 

[panic mode]

1. who uses DIY power supplies on a industrial automation project in this day and age?
2. if you do, make sure you get it right, 37V is not same as 24V, making basic power supply is easy (something you didn't manage so far). making really good one is not.
3. make sure you use appropriate suppressors on each and every inductive load. if you are using 24VDC to power up some solenoids, contactors or whatever (all of them are inductive loads), add diode in parallel to each.
4. Make sure suppressor (diode or MOV or whatever) is always installed in the right place - directly across the load (if you are installing suppressor but placing it away, you are doing big mistake).
5. Make sure suppressor is rated according to application.
6. what kind of power you need from this PSU? there are low cost versions, check Idec, Omron, etc.

 

[alec_t]

If you insist on using the 24VAC to get 5VDC at 1A from a linear regulator then the regulator will have to dissipate ~ 30W. It will get seriously hot unless it is fitted with a large heatsink and possibly a cooling fan. That will push up the cost and occupy a considerable space. Have you considered that?