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Old December 8th, 2017, 02:23 PM   #1
dev67
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24V to 5V DC Buck Transformer on the same rail as inputs, is that bad?

I've had only rudimentary education in EE so I'm not sure about this setup. I've had 24V discreet I/O have problems in the past when a relay was added due to the inductive load screwing with signals.

Will this buck transformer give me similar issues if I have other 24 Volt DC components on the same rail? I assume it will act kind of like an inductive load while converting down to 5 volts DC but I'm really just guessing. I think it might just be power for photo eyes and proximity switches but I'm not positive. I'm looking to get some Pis in the mix and need a power source!

Here's the device in question.
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Old December 8th, 2017, 02:42 PM   #2
jrwb4gbm
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1st of all, let me say I am just guessing here. The best answer I have is try it and see. Since the device is powered with DC in, I would think that there would be very little or no inductive load reflected back to the rail due to internal filtering of the DC/DC converter. Personally I would suggest using a separate 5 volt power supply connected ahead of the 24 volt rail supply source. That "should" isolate the two.

Last edited by jrwb4gbm; December 8th, 2017 at 02:48 PM.
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Old December 8th, 2017, 03:18 PM   #3
GaryS
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First there is no thing as a DC Buck transformer
Transformers work only with AC power the device you show is a DC to Dc converter.
I will convert either 12VDC or 24VDC to 5 VDC out
if you are having trouble with a 24v relay on an output the there are other problems
the relay will need the full 24VDC to turn on reducing it down to 5 v will not work to give you a better answer we will need more details
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Old December 8th, 2017, 03:38 PM   #4
Mickey
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Unfortunately GaryS, that is what the vendor is calling it.

Quote:
KNACRO
KNACRO Waterproof Voltage Converter Regulator DC/DC DC 12V/24V (10-30v) Step-down to DC 5V 15A 75W Power Buck Transformer
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

It is most likely constructed like..see link.

http://www.radio-electronics.com/inf...ter-basics.php
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Old December 8th, 2017, 03:45 PM   #5
GaryS
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It's most likely a 3 point regulator with a power transistor output very common arrangement.
I would question the vender basis electric transformers only work with AC power
unless you are talking about the movie cars / robots but the even label the wrong they are automaton's
Venders should really get it right I find it all the time we know more then they do
But what is the actual problem I still don't have enough information
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Old December 8th, 2017, 04:08 PM   #6
dev67
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No outright problem yet, I was just asking to see if there was an obvious mistake in my logic for placing a 24V to 5V DC converter on the same rail as a bunch of photoeyes and proxes. When I had a 24V relay hooked up in a similar situation in the past, the inductive load screwed up my discreet signaling. I just wanted to be sure there wasn't an obvious problem with having this converter on the same level as my PE and PXs. jrwb4gbm mentioned that he thinks the converter should have some filtering to keep any electrical back noise out of my 24V rail, but yea as a rule of thumb it'd probably be better to have a 120AC to 5V on a separate rail entirely. I'll probably try it out from the 24V first but with some attention to my 24V I/O just in case. The fact that this vendor mislabeled the product on amazon doesn't instill much confidence.
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Old December 8th, 2017, 04:22 PM   #7
GaryS
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I would go with the separate 5 volt power supply it will give you less problems
I have put relays on the same rails ad I/O and never had any problems
I think there is something else going on there if a simple relay can cause that kind of problem then motors will be a real big problem. I would be looking at other things.
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Old December 8th, 2017, 10:21 PM   #8
keithkyll
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You should not be using automotive products for industrial control. It expects a battery input. Doubt if it has anything to prevent noise on the input line.
75 Watts for 15 bucks is scary just by itself.
Use an industrial type. Here's one that's close from Automation Direct.

The issue you had in the past with a relay was probably because someone forgot to add a snubber (AKA Flyback) diode. See this recent thread for more info.
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