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Topic: DC - DC isolation  (Read 551 times) previous topic - next topic

notsolowki

ive been searching for a way to isolate my arduino and all of its 5v sensors from my mains power. without doing this it makes it hard to measure any kind of conductance of water that has other electronics in it that are plugged into the main ac lines. for me to fully isolate the arduino i would need at least a 5v 3a power supply but i cant find anything. i bought a "isolated" switching power supply on ebay but measuring the ac line to the dc outputs revealed that its not. what are my options besides using a battery ???

notsolowki

can i connect 5 of these parallel to get 5 wats output isolated?

https://www.ebay.com/itm/B0505S-1W-5V-DC-DC-Convertor-Isolator/172221574668?hash=item281934ae0c:g:G4MAAOSwbWZagiAP

Wawa

ive been searching for a way to isolate my arduino and all of its 5v sensors from my mains power.
Which Arduino, what sensors.

without doing this it makes it hard to measure any kind of conductance of water that has other electronics in it that are plugged into the main ac lines.
So you have a groundloop problem.

for me to fully isolate the arduino i would need at least a 5v 3a power supply but i cant find anything.
That's quite a lot of current, and that can't be passed through the Arduino. So what are you powering.

i bought a "isolated" switching power supply on ebay but measuring the ac line to the dc outputs revealed that its not. what are my options besides using a battery ???
Modern switching supplies could have a small capacitor between primary and secondary.
It's possible that you measure some 'leakage'.

can i connect 5 of these parallel to get 5 wats output isolated?
Don't know how the modules will react.
It is generally a bad idea to connect switching supplies in parallel.
Leo..

larryd

No technical PMs.
The last thing you did is where you should start looking.

notsolowki

Which Arduino, what sensors.
So you have a groundloop problem.
That's quite a lot of current, and that can't be passed through the Arduino. So what are you powering.
Modern switching supplies could have a small capacitor between primary and secondary.
It's possible that you measure some 'leakage'.
Don't know how the modules will react.
It is generally a bad idea to connect switching supplies in parallel.
Leo..
the arduino don't power anything all of the power comes from a external 5v power supply. i have a few leds/relays/lcd and some other sensors that all use 5v. i didnt ask if i could connect switching power supplies parallel i was talking about the dc dc converter in the link i posted

notsolowki

Maybe isolate the signals.

http://www.ti.com/lit/ds/symlink/iso122.pdf




im not sure if isolating just the signal wire will do it. the ph senson im using has a series of opamps that do the conversion and send a 0 5v signal to the arduino through the analog port. im afraid since the ph sensors amplifier is powered by a non isolated psu then the ground on the ph probe will still loop?

notsolowki

i wonder if i could but an array of dc dc isolated converters with these untill i have the output current i need?

https://www.ebay.com/itm/B0505S-1W-5V-DC-DC-Convertor-Isolator/172221574668?hash=item281934ae0c:g:G4MAAOSwbWZagiAP

Wawa

#7
Apr 17, 2018, 07:28 am Last Edit: Apr 17, 2018, 07:31 am by Wawa
i didnt ask if i could connect switching power supplies parallel i was talking about the dc dc converter in the link i posted
But that IS a switching DC/DC converter, and you asked if you could put them in parallel.

I also see now that this is a continuation of your previous thread about pH sensors.
https://forum.arduino.cc/index.php?topic=540769.0
Leo..

larryd

im not sure if isolating just the signal wire will do it. the ph senson im using has a series of opamps that do the conversion and send a 0 5v signal to the arduino through the analog port. im afraid since the ph sensors amplifier is powered by a non isolated psu then the ground on the ph probe will still loop?
These are 'signal amplifiers' where the input to output is physically isolated from each other.
These isolated your transducer analog signals from a controller, PLC etc.

These are similar to what an optoisolator does for digital signals.




No technical PMs.
The last thing you did is where you should start looking.

notsolowki

it wouldn't make a lot of since to optically isolator the 5v analog signal from the ph sensor module if the module is still grounded at the same point as the arduino would i need to isolate the whole ph sensor module or jsut the signal wire? i dont know what to do anymore i have been searching for a solution for months as you can tell no body has anything to say. im surprised it seems like this would be a common thing

notsolowki

#10
Apr 17, 2018, 07:44 am Last Edit: Apr 17, 2018, 07:46 am by notsolowki
These are 'signal amplifiers' where the input to output is physically isolated from each other.
These isolated your transducer analog signals from a controller, PLC etc.

These are similar to what an optoisolator does for digital signals.





the really confusing part is that the ph sensor module is still grounded to the main psu wouldnt the probe get a ton of interference from the mains noise in the water even if the signal at the arduino was isolated? wouldnt i have to isolate everything? sorry im just really confused right now. besides what you showed me. the closest thing I found was this https://www.dfrobot.com/product-1621.html. i figured maybe i could power the whole ph sensor circuit with this and get isolated ground and signal?

outsider

How is Arduino powered? Have you tried powering it from a battery so it is isolated from mains? Post a detailed digram showing ALL components and how they are connected.

notsolowki

#12
Apr 17, 2018, 07:57 am Last Edit: Apr 17, 2018, 08:00 am by notsolowki
How is Arduino powered? Have you tried powering it from a battery so it is isolated from mains? Post a detailed digram showing ALL components and how they are connected.
man there is soo much stuff connected. let just say the arduino/esp/phsensor/relays/leds/lcds/ are all powered by a 5v samsung wall charger that i tore open and put inside the project box. the sensor reads fine if there are no other pumps/electronic in the water. its when a pump kicks on the reads go crazy. the closest cheapest band aid i found is to drop a earth ground into the water. connect the arduino and the ph probe to an earth via a 10kohm resistor. all of these sensor tie to the same grounds and vccs except the esp is connected to a buck converter. IF i connected it to a battery an eliminated the mains ac power then yes the problem is 100% resolved. except the fact that i cant / dont want to use a battery.  i would like to imagine not using a 120 to 12v transformer connected to a linear regulator just because of how big they are,

outsider

How are the pumps powered?

notsolowki

#14
Apr 17, 2018, 08:18 am Last Edit: Apr 17, 2018, 08:20 am by notsolowki
How are the pumps powered?
120v ac earth grounded. i think the phprobe is somewhere along the lines of 900m ohm so they are really sensitive to noise. the probe uses a double shielded bnc cable all the way back to the module. then the module plugs into 5vdc grn and analog input. its being powered by the 5v samsung brick too.

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