# 26vac to 9vdc

I am making a sprinkler system from an arduino and my valves run off of a 26vac source but i still need to power my arduino nano does anyone know of a 26 vac to 9vdc converter.(I want a 9v source because that is the gate voltage of the triacs.)

Use an adjustable buck converter. link

The buck converter is only one half of the required parts. You first have to convert the AC to DC using a full wave bridge rectifier and an electrolytic filter capacitor.

The bridge can be anything above 100 volts piv rated and the cap should be at least 1,000 microfarads (uf), 50 volts DC rated.

instead of a buck converter can i use a linear voltage reg.

avr_fred: The buck converter is only one half of the required parts. You first have to convert the AC to DC using a full wave bridge rectifier and an electrolytic filter capacitor.

The bridge can be anything above 100 volts piv rated and the cap should be at least 1,000 microfarads (uf), 50 volts DC rated.

Lol, missed the AC part. I thought it was DC-DC conversion he was after.

MR-Turtle: instead of a buck converter can i use a linear voltage reg.

Yes, but buck converters are MUCH better than linear ones.

i looked into full wave rectifier and it looks like there is a lot of ripples in the dc wave.

MR-Turtle:
i looked into full wave rectifier and it looks like there is a lot of ripples in the dc wave.

Not if you have the correct RC time constant. It all depends on how good you design the circuit. Not to mention, you should have a buck converter after the rectification. This will definitely smooth out any ripples.

You might have to share triac "ground" with Arduino ground. Then you can only use half wave rectification (single diode). That will produce 36volt or more (AC peak). You need a (>=40volt) electrolytic buffer/smoothing cap. And a switching DC/DC converter, capable of >= 40volt in.

Post a link to the triacs. 9volt@gate seems odd. Leo..

whoops i didn't mean 9v i ment 5v(dont know were i got 9v) here is the data sheet-guess that solves my problem. http://mhtml.alldatasheet.com/html-pdf2/166269/ONSEMI/MAC97/214/1/MAC97.html?lang=en

The gate voltage is 5V maximum, with trigger voltage typically less than 1V. Be sure to use a series resistor between the Arduino and the gate, 220 Ohm minimum.

guess that solves my problem

Maybe yes, maybe no. As Wawa so wisely pointed out, you may have issues, depending upon how you connect/drive your triacs.

Do you have a schematic of the entire arrangement? If so, please post it. If not, how do you plan on triggering your triacs? Directly or via triac output onto-couplers?

I have wall plugs to USB that are 110V to 220 input. what would happen if you feed them with 24vac ? ?

If you are on the path to rolling your own, look into the simple switcher chips.
up to 40volt in.

if you do plan to roll your own, be aware that the AC will rectify into DC through your full wave bridge rectifier to 1.414 x AC voltage. so your 26v AC will rectify to over 36 volts DC.

if you want to buy, you can find a lot of AC in, 5vDC out, or adjustable output voltages in e-bay. takes some searching with different wording

My problem is that I need a converter with 26v in it's range they are all 85 to 220v. I would like to avoid a bridge rectifier if I can and go with something that can just be dropped in. As for the schematic I will work on that and get back to you.

Here is the basic schemati. minus the power part

Just use an adjustable DC/DC converter that can handle 40volt input. Plenty on ebay. Single diode (1N4004) from AC to +in. Cathode(ring) to the converter side. Add a cap (470uF/50volt) from DC/DC input to DC/DC ground. Other AC wire is common ground (supply, Arduino, cathode triac, etc.).

Remove the transistors in your diagram. Just use 220ohm resistors between Arduino pins and triac inputs. Leo..

Can you show a diagram of how you are setting up the diode and dc/dc converter. I will remove the transistors, I was basing my diagram off of the PCB that I salvaged these pieces from, they were set up like that.

Explained clearly, so YOU should be able to draw a diagram. A DC/DC converter only has three terminals. In, out, and ground (common to in and out). http://www.ebay.com/itm/Step-Down-3A-Buck-Converter-3-40V-Inverter-Voltage-Regulator-Power-Module-/262806048246?hash=item3d30760df6:g:vzIAAOSw2xRYeLIL Leo..