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# HVAC project need to convert 24v AC to DC for an arduino sensor project

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#### Tony Cape

##### New Member
What is an inexpensive way to take 24vac and convert to DC. I've looked on amazon and looks like the cheapest thing is about 10 bucks.
Just curious if there are any creative ways to do this. Would not need more amperage than an arduino could provide.

You have a source of 24vac like a door bell transformer?
You wan to have dc voltage.
Would not need more amperage than an arduino could provide.
Are you powering the Arduino with the DC?

Here is a circuit that changes 25Vac to 33Vdc. Is this what you want?

I was planning to use the 24v transformer on an existing Gas(LP) hot air furnace and tap the 24v and convert to DC so I can hook up an arduino and create a propane gas leak sensor. Your schematic could work , but would have any affect on a furnace control board that uses 24v AC and I'm pretty sure it converts to DC on the board.
I've also been entertaining the though of a 110 AC to DC 5v buck converter to eliminate the potential of frying a furnace control board.

Is the DC to power the arduino, or merely be an input signal that is active when the furnace is in heat mode?

ak

To power the arduino

DC DC 5V 1A
The link takes you to a board what bucks a high voltage to a low voltage. (1A max output) DC to DC
If the voltage drops from 30 to 5 then the current will increase 160mA in to 1000mA out.
I do not know how much current the computer board needs but less than 1A!. So the current from the 24Vac will be less than 160mA.

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The recommended external DC voltage input to an Arduino Due Millie Nova, Arduino Uno or Arduino Mega is 7 ~ 12 VDC. While I have seen some run with higher input voltage I can pretty much assure you that if you apply an external 24 VDC the on board little voltage regulator will get real hot real fast and game over in several seconds. Keep the external voltage in the recommended range.

The current draw will be a function of what the processor is doing but under average loads under normal use the Arduino Uno for example will draw about 200 mA but if I am running an application using several digital out pins sourcing 40 mA each then obviously more current will be drawn. So it all depends on the task at hand. Your application using a gas sniffer won't be very demanding.

I would just use the suggestion by ronsimpson:
DC DC 5V 1A
The link takes you to a board what bucks a high voltage to a low voltage. (1A max output) DC to DC
If the voltage drops from 30 to 5 then the current will increase 160mA in to 1000mA out.
I do not know how much current the computer board needs but less than 1A!. So the current from the 24Vac will be less than 160mA.
View attachment 122550
I would just use a full wave bridge on your AC supply to rectify it. Then add a buck converter as a simple economical solution affording 5 V at 1 Amp and you should never need that much.

Ron

Just use a cell phone charger any newer one will work fine

Less than 1 amp. I appreciate all the responses, thanks!

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