120VAC -> 12VDC -> Converter Needed

Thread Starter


Joined Dec 25, 2016
Hey folks,

Sorry about the noob question but I'm fairly new to circuits and wiring.

I noticed that my component below needs 12 VDC and I can either use the 2.1mm wire from adapter, which I don't want to do, or wire it directly into the board. My questions are,

1. Where does a consumer get power adapters like this (not ones that plug into recepticles but in-line/commercial grade)
2. I don't see the Wattage/Amperage requirements anywhere on the component datasheet...how do we know what to use?

Thanks for helping the noob.

You might like this http://www.mouser.com/ProductDetail/RECOM-Power/RAC03-12SER-277 supply. The picture is all messed up, so use the datasheet instead. I flagged the error at mouser. It's a hock puck sort of power supply with wire leads which is designed to fit in an electrical box.
At 3W at 12V is 250 mA and I think that's probably plenty.

In your case, I didn't see the power required either. Ask. It's probably pretty small.

A power supply that you select has a lot to do with the intended use. The DIN rail is a standard method of constructing control systems and this a DIN rail mounted supply would be useful. See http://www.trcelectronics.com/Meanwell/din-rail-power-supply-mdr20.shtml

The DIN rail is the backbone of an electrical erector set. The case is usually wall mounted, has a door and an aluminum plate in the bottom.
The rails are screwed into tapped holes in the plate with plastic wiring duct surrounding the "components". Things like terminal blocks, motor starters etc can be clipped to the rail.

it's wise to make a set of terminals for the I/O and then wire the board from there.

What I don't immediately like is the I2C bus connectors and I don;t exactly know what they are. Usually you want the wire insulation rating to be the same as the other wires in the box or have enforced physical separation.

Thread Starter


Joined Dec 25, 2016
Awesome! So many good notes here.

First, awesome that Mouser is where you pointed me to as that was where I was playing around with filters trying to see what I could find.
Second, Yeah I will ask and report back as to what the requirements are in case anyone else ever finds this thread.
Third, The DIN rail looks cool and very commercial but is definitely overkill for my project.
Fourth, the I2C connectors are typically low voltage connectors to power devices (such as IoT devices) and send data along the bus. This is typically a 5V DC plus some data wires. That being said, is there still a concern here? Why?

Basically I am going to put some little board device inside the circuit breaker box and I need 12VDC to power the initial board with the resulting board(s) being powered over I2C. These will be mounted inside the box and since I'm already next to all the power, it seems very stupid to get power from anywhere outside the box...Based on what you sent and my research here's the plan...thoughts?

Create a new circuit (with a breaker) for internal box power (or I could add the wire to a circuit like "kitchen outlets")...either way, get the hot wire from the circuit breaker fuse and the neutral wire from inside the box and wire them to the "in" side of the converter. Then take two much smaller gauge wires (18 gauge or so) and wire those from the "out" on the converter to the "in" on the board.

The part I'm missing is, based on the image (I know you said it's messed up but can't tell how), what's the correct way to get the wires to the converter box? I suspect these are the "terminal blocks" you were referring to. Never seen them before. Obviously I can't plug a wire (male) into a pin (male)...so how to get the connection?

Thanks again.
The datasheet http://www.mouser.com/ds/2/468/RAC03-SER_277-958338.pdf is right, the pic is wrong on mouser's website. So, it's just wires and wirenuts for power.

Fourth, the I2C connectors are typically low voltage connectors to power devices (such as IoT devices) and send data along the bus. This is typically a 5V DC plus some data wires. That being said, is there still a concern here? Why?
What I'm saying is that you can't use automotive wire inside the box. I "think" your going to bring the I2C connections outside, but I could be wrong here.

There's two .jpgs at the end of this thread http://www.plctalk.net/qanda/archive/index.php/t-33722.html which basically says the wiring insulation has to be rated for the highest rating in the box. e.g. ribbon cable won't cut it.

Just to persuade you again, see http://www.winford.com/products/cat_din.php for some DIN rail and clips. It's a lot easier to driil/tap two holes than 4 or 6.

I kinda wished the company that makes the current monitor had posts for a barrier around the low voltage parts. You can probably still do it with some male/female standoffs.

Romex cable specs: http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheetOEM10 600 V. 300 V should be OK in the US, but I can't vouch for it. This http://www.mouser.com/ds/2/18/843-135series-10203.pdf one anyway, has a UL rating and for 300 V.

Not sure if an isolation interface https://shop.mikroe.com/click/interface/i2c-isolator is appropriate either.

I wasn't caught in this type of system. One thing I did in a system I made, was I never allowed a box in another room with a panel indicator lamp to be fed from a power source 100 ft away. I always fed the lamp locally via a relay. Why? The I/O was virtually segregated inside the box and if I pulled power for one box, it was virtually independent. This system interfaced with the fire alarm panel. It sent and received signals from it.
There was a mix of 24 VAC and 120 VAC power in it. All wiring was 18 AWG.

Note that this http://ieeexplore.ieee.org/document/138183/?reload=true system uses optical fiber.

I found this https://www.ia.omron.com/products/family/3123/download/catalog.html for fun a giggles. I know it's not appropriate, but the BIG difference is the use of "protected" terminals. It's difficult for different voltages to see each other.

This https://boredomprojects.net/index.php/projects/home-energy-monitor could be interesting for you.

This https://www.google.com/search?client=ubuntu&channel=fs&q=individual+circuit+energy+monitor&ie=utf-8&oe=utf-8#q=individual+circuit+energy+monitor&channel=fs&start=10 search should also help.
In any event, I think I would do something like the following assuming:
a) You want to get the I2C bus or something out of the box.
b) Your mounting at least two of the current sensor boards on each side of the breakers.

1. I'd use DIN rail

2. I'd make some sort of protection for the boards. Simple version is a piece of PCB material on the component side where all of the chips are and cover the solder side too. With standoffs and spacers, you should be able to do this. Use the PCB support and connect to the DIN rail clips.
Your "cover" could be removed easily, say with thumbscrews. There are plastic pieces that you can buy that convert a socket head cap screw to a thumbscrew. The base might contain a way to secure a plastic corrogated tube or spiral wrap.

3. Enclose your I2C and power within this duct. Use wire rated for 300 V minimum and preferably 600 V.

4. Use a dual "wire ferrules" for power, since they didn't allow daisy chaining. Wire ferrules are extremely useful. Here http://www.mouser.com/ProductDetail/Panduit/FTD77-10-D is a two wire ferrule.

5. Bring the I2C into the box with a cable gland and jacketed cable and also fit with tubing or a spiral wrap.

6. Your not allowed to put two wires on a breaker, but I THINK you can pigtail with a wirenut. I think a separate breaker makes sense.

7. Measuring power can be a real pain in the butt. Your numbers likely won't add up. You have real power, reactive power and apparent power and the power factor. The current waveform is likely to be distorted and not sinusoidal. In a home, it's not likely to be a major problem with few motors. You should monitor both sides of a 240 V circuit. Each "phase" can be different. Neutral handles the difference in current and can be "negative" with respect to phase.

Remember: When using sites like mouser, pictures are only representative. Always check the datasheets. One easy example is ribbon cable. the same pic is shown for a 2 and a 100 conductor cable or a light lens may not be the color in the spec sheet.

Thread Starter


Joined Dec 25, 2016
Wow, again, thanks so much for all the info.

Still processing but based on what you said and looking into the codes it looks like some revisions to the plan would be good. I am now thinking about installing the DIN Rail system (even though it's overkill...it's a why not at this point)...in my crawl space. I already have a coduit from the box to the crawl space for electrical wiring so I will just utilize the same hole...providing...the Din RAIL system can be in an environment like a crawl space. It's not climate controlled but I do live in a modest climate and there would be no moisture other than humidity...ok to do this? Running wires in an already-built house is tough...so trying to keep it as close to the box as possible.

I have attached a proposed diagram. I know it's crude but hopefully it will help us in talking about the same thing. I am now planning to also put the I2C bus and logic board outside of the breaker box but leaving the monitoring control board inside the box. Ok? See diagram, hopefully it will help.

Thanks again for all the info!


I know I gave you a lot to process. The current required for the sensor systems is listed in the Datasheet as 100 mA BTW. https://www.controleverything.com/content/Current?sku=I2CCMAC1215A_DLCT03C20

Kitchen breakers are usually 20A.

I was thinking of the Hockey Puck power supply inside the box.

I don't know what your DIN rail plan is for the crawl space, but it does come in different varieties. Solid anodized is also available. Some companies groove a centerline. There are brackets than can raise the rail significantly off the base.

I will tell you this though: Do not mount the DIN rail directly to a rafter. I found out the hard way. I use this system to mount a fair bit of networking stuff that doesn't have exposed power. I had a water leak from an upstairs toilet tank and the water traveled along the rail which isn't good. I then mounted the rail on 1/8" very large aluminum washers, so it's difficult to create a water channel between the rail and the wood rafter.

I can tell you the way that I managed to get a large amount of cables to the enclosure at work which had a bunch of knobs and indicators as well/
I ran a large conduit to above the ceiling tile to a large J-box. The J-box had the strain reliefs for the individual CAT 2 PTFE fire alarm rated cables. It worked out well. I used the same method to penetrate a firewall too.