Step down converter help

Thread Starter

Tig5

Joined Mar 28, 2018
10
Sorry, total noob here.

I have this step down converter (attached) but I don't know which input and output pins/screws to use.

I'll be attaching this to the 2 output wires of a 220v humidity sensor, i then want to step down that voltage to 5v for my mini humidifier. If anyone could suggest which wires go where it would be appreciated!

20180328_230508_Tig5.jpg
 

Thread Starter

Tig5

Joined Mar 28, 2018
10
Hi, I won't pretend to know what the Logical thing is or how it might be different.
My humidity sensor/switch is this:
12V-220V Digital Humidity Control Controller Switch hygrostat Hygrometer Sensor R06 Drop Ship
http://s.aliexpress.com/7j2YjIJF?fromSns=Copy to Clipboard
And my humidifier is this:
Mini USB Air Humidifier Bottle Caps Humidifier Essential Outlet Aromatherapy Spray Machine Household Small Air Humidificador
http://s.aliexpress.com/ayEB77n6?fromSns=Copy to Clipboard

I'm hoping to run the sensor on 220v AC, then take the "direct output" to run the humidifier. It's for a small, indoor tropical plant growing tent I'm making :)

Thanks for the help.
 

dendad

Joined Feb 20, 2016
3,190
That sensor looks pretty scary if it is the one that runs on 240V!
If so, I would consider not using it as the mains isolation is non existent as far as I can see. At least be VERY careful, and if you don't know what you are doing, don't do it!
Your humidifier runs on 5V so, a 240V to 5V supply is needed. An old phone charger is the easiest way to go.

But if yours is the 12V one, go for it.
You feed the 12V out to a buck converter..
On Ebay or Aliexpress, search for "dc-dc buck converter 5v"
Find something like this..
3Amp Buck.jpg
If you get the adjustable version, set it to 5V before hooking it up to the load.
 

Thread Starter

Tig5

Joined Mar 28, 2018
10
Thanks for the advice. What is the worry with the 240v unit? Randomly bursting into flames? I considered a phone charger, could i utilise a usb wall plug that puts out 5v? Just connect the output wires to the 2 prongs and insulate well?
Cheers
 

Thread Starter

Tig5

Joined Mar 28, 2018
10
If I under volted the sensor unit with a voltage converter would that also be a bad move? If the unit expects 240v, less would be a mistake?
 

dendad

Joined Feb 20, 2016
3,190
Thanks for the advice. What is the worry with the 240v unit? Randomly bursting into flames? I considered a phone charger, could i utilise a usb wall plug that puts out 5v? Just connect the output wires to the 2 prongs and insulate well?
Cheers
I'm concerned with the mains driven unit as the picture of the PCB does not seem to have a real power supply so mains will be on all the cabling to some extent. A lot of cheap devices from places like that will not pass safety tests. It may be wise to use a 12V unit running off a "real" power supply in the interest of not electrocuting someone, and that is not to mention the real risk of fire.
 
Last edited:

dendad

Joined Feb 20, 2016
3,190
If I under volted the sensor unit with a voltage converter would that also be a bad move? If the unit expects 240v, less would be a mistake?
It is a bit hard to tell. Is there any power supply markings on your unit?
Is your unit the same as the photo? can you post a picture of the insides?
 

DickCappels

Joined Aug 21, 2008
6,015
Thanks for the advice. What is the worry with the 240v unit? Randomly bursting into flames? I considered a phone charger, could i utilise a usb wall plug that puts out 5v? Just connect the output wires to the 2 prongs and insulate well?
Cheers
The main concern with 240 VAC is it might hurt or kill somebody. Even if you insulated it well your humidifier which is likely to be wet in places may have 240 VAC on it, and wet or dry I wouldn't want something like that around.

If you "under volt" the humidity controller to a voltage that is safe for human contact (48V for example) it probably will not work.

The large gray cable is the humidity sensor. That leaves the Yellow-Black and Black-Red pairs. Maybe @ScottWang can read the labels for those pairs of wire.

upload_2018-3-29_14-3-16.png
upload_2018-3-29_14-10-55.png
It looks like the relay in the photograph ( https://ae01.alicdn.com/kf/HTB1Eshmfj3z9KJjy0Fmq6xiwXXaD.jpg )
is there to drive the output but the output is not isolated from the power source. As such you would need a relay (like the one in post #1 but with 220 VAC coil to isolate and switch the power to the humidifier. Then you can do as you suggest - put the second relay contacts in series with your wall wart and the humidifier cap.
 

DickCappels

Joined Aug 21, 2008
6,015
@ScottWang

That helps, thank you.

Can you tell us which of the two pairs of color wires is 220 VAC input and which is the output? There is some writing that most of us cannot read -it is very light colored.
 

ScottWang

Joined Aug 23, 2012
6,846

dendad

Joined Feb 20, 2016
3,190
I considered a phone charger, could i utilise a usb wall plug that puts out 5v? Just connect the output wires to the 2 prongs and insulate well?
Cheers
A phone charger or other 240V to 5V supply will work ok. But I think you need to make sure you use a good brand one and not a knockoff. One with minimal capacitive coupled mains bleed through is in order. Even going to the effort of connecting the mains earth wire to the 5V supply 0V line to protect users may be in order.
 

DickCappels

Joined Aug 21, 2008
6,015
Thank you Scott. Excellent detective work. The only thing left that puzzles me is why, on the label on the top of the box "12V/10A" is checked off. This would only make sense to if the output was relay contacts since from the photograph of the internals I can see a relay but no 10A power supply.
 

DickCappels

Joined Aug 21, 2008
6,015
It is now clear that on the AliExpress website the buyer can specify 12V, 24V, or 220V versions. So if @Tig5 buys the 220 VAC version he can connect the Yellow-Black pair to wires to the 220 VAC input of a 5V USB power supply (or phone charger) and then safely use the phone charger to power the humidifier cap.
 
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