I have a project to measure temperature of a fish tank using an external DS18B20 and send it to a MQTT server every minute. Everything is functioning correctly as expected.
However, I have notices there is a strange tingling effect on the metal surface of the sensor when I rub my finder over it. If I rub the sensor on my lip, then it's has a minor sting.
The sensor is powered from the 3.3V output from the ESP8266 board I'm using and can't see any shorts n the board anywhere.
I have a similar circuit for another project with the same sensor and doesn't have this issue.
Obviously, I don't want to put the sensor in a tank full of fish if it risks hurting them, so any help will be much appreciated.
The power supply is a standard mains to 12v wall wart power supply fed into a switching rectifier to reduce down to 5V. Have tried multiple power supplies - same issue. Have tried this power supply on pretty much the same circuit for a different project - no issue.
The whole thing in this instance is indepentant if the fish tank itself. i.e same issue when this thing in on my desk.
OK, get your multimeter, set it to AC voltage and measure between the ground on your ESP and a known ground such as the metal case of something plugged into a three pin outlet or the green terminal on your variable power supply.
If there is a significant voltage, connect a 1k resistor across the meter probes and make the measurement again - you will then be reading the current in milliamps.
I would suggest the wall
Wart is likely to be the problem, if it is a switch mode type or cheapo bought off the market type.
These do not provide galvanic isolation and if live and neutral
are connected wrongly this is the result .
Really as water is involved you want an isolated transformer type supply with RCD protection.
hammy:
Sounds like a problem with whatever you are using to power your Arduino. The tingling sounds(?) like mainsleakage through the power supply.
It could also be something else, such as the tank itself is not earhthed / isolated .
This needs sorting out !
Its probably SMPS leaking at the switching frequency due to inter-winding capacitance in
the transformer. Unless you earth the output side ground several 100uA of leakage at
switching frequency is normal.
If the supply isn't suitable certified as safe for mains use, it should be replaced with one that
is as a matter of safety.
Thanks all for the help. I've done a bit more diagnosing.
Measuring between the ESP GND and the earth in the mains socket, I measure about 94V AC. Havn't checked the current with a resistor yet, but will do that next.
Secondly, I notices the tingling effect on the negative terminal on the jack connected to the 12V power supply when disconnected from the rest of the circuit, suggesting, this is entirely an issue with the power supply. However, I don't understand when I plug the same PSU into another ESP project again with the same temperature sensor (along with some fans) - this tingling effect is either not there or significantly smaller.
apeng:
when I plug the same PSU into another ESP project again with the same temperature sensor (along with some fans) - this tingling effect is either not there or significantly smaller.
When you check the PSU with the other project, are you using the same mains power outlet?
Have you checked the mains outlet for gnd connection?
Tom...
I agree with the previous poster that the cause is leakage through the power supply. I will guess the difference in "tingling" with different boards is a mater of perhaps different connections to other devices.
In any case I would not use that supply. It is either cheaply made or partially failed. I personally would not use a power supply that is not UL approved. I have purchased some great and some questionable supplies from ebay suppliers. I have come tot he conclusion that the supplies with UL approval give one a better chance at getting a good one. After all, I'm sure you don't want a fish fry due to a failed power supply.
I specifically chose this one because the leads plug in =above= the rest of the meter. They will have up to 1kV on them, so I want them away from my hands when operating the meter.
I bought one of those - or very similar (on eBay) - but have yet to use it. Testing dodgy Chinese power supplies - neat idea!
OK, so it is the VC60B, not the "plus" - box is very dusty now! And not the genuine(?) "Victor" brand. The terminals are along the bottom, but still reasonably well away from the operating controls.
So new PSUs arrived today and I'm still seeing the same issue. In fact, I've been around the house and pretty much every 12V adapter I have (e.g. ones connected to my external hard drives) also has the same effect.
Could this indicate an issue with the home wiring ?
You will always measure some amount of voltage to ground, unless the adapter is grounded.
What is important is a measurement taken with a load. The Sencore Powerite PR57 is, among other things, a device to measure leakage voltage and current. When measuring leakage current, it loads it with about 15k. To protect the analog meter, it has a resistor in the probe that is bypassed if you press a button on the probe. Also, when the output is set to 117Vac, it provides a handy calibration check as it reads full scale when connected directly to the HOT line at 117Vac.
Here is the schematic for it, offered for your analysis:
Note on page 18 of the PDF (page number 16), the operation of the leakage test function begins. 500uA is the maximum allowed current with the button pressed.
This guide concurs, it mentions a max current of 0.5mA on page 12. It does not specify a resistive load, other than to say "The leakage current is then measured using a special circuit that simulates the impedance of the human body." https://www.psma.com/ul_files/forums/safety/estguide2.pdf
So... come right down to it, if you have a DMM that will measure AC current down to 200.0mA, you can check this. I'd put a 10k resistor in series with it, and add a probe with a resistor and momentary button across it. Size the resistor so the meter measures 200.0mA or thereabouts when connected directly across Hot to Neutral.
Then only press the button if the meter only measures minimal current, then see how high it goes with the larger resistor bypassed.
I think you are getting way above the OPs capability. The test you described is for a validation or production test, not really suitable for the end user.
I am unable to quantify "tingle" but I've learned it is not an expected condition with typical components. I've tried a handful of various AC adapters (mostly from old dustbusters and phones etc) not one gave me a tingle when I brushed my skin across the output. With me both ungrounded and grounded.
I believe there is more to the situation we have yet to learn / troubleshoot.
I pointed out how to do this check back in reply #3. AC current meters are not quite as common, use your basic meter on AC V and put a 1k resistor in parallel with it.
If the resistor starts smoking, you have a serious problem!
