I'm not sure what a type B electrical outlet is. If the outlet is listed (by UL or others) and it is rated for AC only (no DC rating marked on the device) then the outlet should only be used on AC circuits.

And what happens when someone plugs one of your "DC" pigtails into a 120v receptacle? It may be spectacular for a moment.

Check out these receptacles designed for trolling motors, etc.

Here is a link that might be useful: DC plug/receptacle

The NEC does not cover test equipment and setups and even allows temporary setups required for experiments and testing for AC power. Every circuit breaker curve is verified as part of the design, motor ratings, heater ratings, etc. The test setup is not controlled by NEC rules since it is not part of utilization equipment.

You need a connection that is rated for DC use no matter what, the currents you intend to carry (regular AC type receptacles are not designed for low voltage high current service), and whatever you select needs to be INCOMPATABLE with other AC receptacles in use in the area.

If you want DC power out of an AC outlet
then you need a bridge rectifier for it.
And even then you won't get good clean DC power.
If you want clean power then you will need to filter it.

You need a device like a power supply unit in a computer.
But it needs to be rated for your voltage and current needs.

Pooh Bear

It's not clear to me what voltage you're using, and I also haven't a clue what a "type B electrical outlet" would be.

FWIW, I've read that folks with PV systems (solar energy) using 12 or 24 volts sometimes wire their houses for the lower voltage, and use some type of AC receptacle that isn't otherwise used (perhaps a twistlock). I don't think this method is to code, but regulation of systems using voltages under 48 is usually pretty minimal.

If you want to do it right, you might try Anderson connectors. They have a whole line of DC-rated connectors ranging from 30 amps to 350 amp capacity.

I think using an AC outlet for dc is a recipe for disaster. I would think the safer, smarter thing to do is to use conventional dc type connectors, if you're working on 12 - 13.8 vdc, a car cigarette lighter plug's the norm, or you could follow the film/tv industry norm for 12v power, a Cannon 4-pin plug/socket with pin 1 negative, and pin 4 positive - the others are not connected.

Pooh bear,

You really ought to read these things more carefully - he/she's not proposing to GET dc from a 110 outlet, he/she just (perhaps foolishly) wants to use mains-type plugs/sockets for DC (and there is a plethora of other connectors designed for dc use) - you can't just put a bridge rectifier directly on AC voltage, it's illegal (in most places I know) to directly rectify ac current.

What you are describing "a computer power supply" certainly is one way of obtaining a narrow range of dc power - 5 v and 12v and, I think sometimes 3.5v, but what it is, is a switchmode power supply - and I'm sure the original poster has a laboratory/bench power supply, they're designed to provide temporary power for repairs, design/development etc and offer a wide range of + and - dc voltages.

scott,

If you're using you're using a lab power supply, they usually offer a banana plug and wire terminal combination - surely that'd suit?

I think what you've been hearing above is that if you're using a standard duplex-style outlet there is a real danger of someone using it incorrectly. The old adage of you need to idiot-proof your test bench applies here: idiots are still allowed to roam freely. My suggestion is to use a non-standard receptacle, something that doesn't accept what is on the end of 99.9% of every electrical appliance out there. The link below is one possibility, the P&S 5371 style receptacle, there are others as well in the supply catalogs. These cost more that the run-of-the mill recepracles, but they will provide the security and safety that you need.

Here is a link that might be useful: Non-standard receptacle

we use bannana plugs on our benches. test cables are made to fit common devices we work on, and they just plug in the bannana plug on the benchs.

the major drawback to your idea is when you have a devices hooked up to the cord, then grab it and plug into a 110 outlet accidently. and believe me, that WILL happen. it may not be you, but someone will do it.

Found just what he needs on backwoods solar website. Took me a whole 30 seconds to type in "dc outlet" google. Outlets made for direct current. Fit into a standard electrical box. scroll down the page. About halfway down

Here is a link that might be useful: backwoods solar

I went back and re-read it. You were right.
I missed the part about already having a power converter.
This person is just looking for receptacles to use with it.
Sorry about that.

Don't understand the legalities of rectifying AC current.
I have a room full of home electronics and computers that
do it all day every day without a problem.
I used to own a 120vdc motor. Never did anything with it.
But why couldn't I have built a bridge rectifier to run that motor.
This mite should be a separate discussion??
Don't mean to hijack someone else's thread.

Pooh Bear

I don't know of any specific prohibition against rectifying AC directly. In almost every switching power supply and every compact fluorescent I've torn into, the first thing the incoming AC hits is a bridge rectifier.

The Backwoods Solar page is what I was talking about as far as using recepts not otherwise used (for AC) in the house.

OK well I was extrapolating, as I understood the rules in Australia, where I used to live, I actually stumbled across a rule stating that you must not attempt to directly rectify - as in, put a bridge rectifier across the ac current...

Davidr, if a switching power supply performs as you said, I'm mystified as to why this rule existed, I assumed it was because - my knowledge of electronics doesn't extend to knowing how this'd work - stuff/interference/induction or whatever would or could travel back up the ac lines.

Poohbear, except/unless the appliances you speak of work as Davidr is saying you are again missing one little bit of information (I'm not picking on you, honest, although I guess I am nitpicking) - that is, most of those appliances are ISOLATED from the mains supply, by virtue of a transformer. A transformer (so clever, wish I'd invented it, but that Stanley guy beat me to it) works like a generator by virtue of it being alternating current, so the electricity in the primary side (the mains side) 'induces' a current in the secondary side, so the mains is actually physically not connected to the dc side of the appliance at all - they are completely isolated, hence the "isolating transformer" the safety predecessor of the GFCI.

Directly rectifying the AC line is not a problem and is done i many small universal motor appliances that have variable speed control. An SCR (only conducts in one direction) is cheaper than a triac (conducts in both directions) and easier to control. The pulsing DC waveform at the output of a full wave bridge rectifier is perfect for SCR speed control of a universal type motor.

A certain amount of 'hash' is produced back into the supply lines by dimmers and switching power supplies. In the US commercial itmas must comly with FCC rules about their radiated emissions, and radiation from the supply cables is included in the measurment. How many monitors have you seen with a heavy ferrite slug inside a plastc case on a computer monitor or other electronic gizmo? They are there to prevent EMI (Electro Magnetic Interferance) from travelling olng the cable and radiating.
Early dimmers produced so much noise you could not use an AM radio wthin many feet of them. Newer dimmers have some filter capacitors installed to reduce the noise to manageable levels. Many small supplies for undercabinet lights are still pretty noisy, and an AM radio in the kitchen may not work at all. Some low value ceramic capacotrs across the output of the supply can significantly reduce the radiation from the output wires.

Hi pjb999,
Don't worry about picking on me, I know you are not.
I learned long ago that I gotta have really thick fur
to come over here and post the code violations I have done.
But I can't learn if I don't ask questions.

I thought it mite have something to do with an isolation transformer. Usually when building a rectifier circuit the first thing the AC power line encounters is a transformer to change the voltage to the correct levels.

A certain amount of 'hash' is produced back into the supply lines by dimmers and switching power supplies.

Could you elaborate on this statement a bit more.
I have never encountered the term 'hash' in electrical terminology.
And what effect is being caused in the supply lines.

I do understand the RF emmittance and interference.
(I have been told that) Sound engineers have to be careful in setting up large rock concerts because if they leave a power supply cord coiled anywhere it acts as an antennae and reeks havoc with local radio stations.

Pooh Bear

'Hash' is simply an poold term for EMI that appeared as noise in audio circuits.
Dimmers (or any device that switches the current quickly) place harmonics on the power line. A typical triac dimmer takes the normal sinusoid of current and delays the current flow until further into the voltage waveform. The front edge of the current sineusoid is chopped off, and the curernt actually starts to flow when the absolute voltage is well above zero volts. These sharp jumps in the current flow create electrical noise that is radiated by the inductance of the wires feeding the circuit. It is at multiples of 120 Hz (twice the base power frequency of 60 Hz) and can extend for many harmonics depending on how big the jump in current is.
This is refered to in EMI design as 'conducted emissions'.
These conducted emissions will also radiate from the cable and produce 'radiated emissions'.
Switching power supplies produce similar noise since they turn on and off very quickly (compared to the 60 Hz power line) at anywhere form kHz to MHz. This noise can be shunted to ground using a capacitor that can use the inducatnce of the cables to force the noise to ground. If the inducatnace is not high enough, coils or ferrite beads can be used to help the capacitor shunt the current by raising the impedance of the power cord at the desirted frequency, while having almost no affect at the power line frequency.

Good explanation. And it actually makes sense to me.
Switching the current off somewhere mid cycle causes the
electric field to start collapsing, then switching it back
on at another point in the cycle rebuilds the field, and
both of these changes cause the emission an EM pulse.
If it is done fast enough the EM pulse hasn't had time to
dissipate before the power comes back on and it effects
the new field as it builds, throwing the harmonics off.
Sounds like a reactive inductance problem to me.

Pooh Bear (aka Fluff For Brains)

Usually when building a rectifier circuit the first thing the AC power line encounters is a transformer to change the voltage to the correct levels.

In a linear supply, yes. But more and more equipment is now fitted with switching supplies. One of their virtues is that they eliminate the large expensive 60 Hz transformer.

They rectify the AC as it enters. Then they chop the DC into a high frequency square wave. A transformer for higher frequencies can be smaller and lighter, so this saves on materials cost and weight.

I hear that some of the power supplies for LV undercabinet lights and such are neither transformers nor switchers, but rather little more than regulated light dimmers. I would think some of these would have a series inductance to smooth out the waveform, but maybe not. I've never taken one apart because I don't generally have much truck with LV lights.

This subject of sockets for DC wiring has been discussed endlessly for years.

Onc question to be answered first is do you need a three pole (grounded) system or are two poles enough.

The most common usage among "off the grid" folks is the "cigarette lighter" format. This is a very poor design because the center terminal just pushes against the contact--there is no wiping action. I think people use it because it is cheap and familiar.

There are lots of NEMA plug/socket formats that are seldom if ever used in residences. I think most of these are usable if you stay within the current limits. I like the 277 volt "crowfoot" pattern, because this voltage is never found in residences. The problem is, these are low-volume and tend to be expensive.

The Anderson connector is a excellent design but does not really lend itself to us as a wall or chassis outlet.

am

I hadn't heard of a coiled cord causing radio interference, but i know that with heavy loads, having a coiled cord exacerbates voltage loss and makes the cable heat up, they call it the "transformer effect" since the coils work like a transformer. Power cables can generally be adjacent to audio cables, provided they cross at right angles, rather than run parallel.

I wonder about those specialist non-domestic plugs, some of them look as if you could still plug a normal plug into them, and a lot of appliances wouldn't like dc.

I still say, don't use ANYTHING that normally carries AC. Having said that, you want something completely different, you use Australia/NZ/China plugs, active and neutral are sloping and the ground is a vertical flat pin. It's a good system, looks like this:

/ \
l

"I hear that some of the power supplies for LV undercabinet lights and such are neither transformers nor switchers..."

They are a particular type of switcher called a buck switcher.
They aer connected therough a switching device (FET or BJT) with a coil directly across teh line. By switching very quickly they prevnet the coil current from ever getting to high, and then as the magnetic field collapses generate a lower output voltage.
Switch on, current starts to rise, switch off, magnetic field supplies current into load. Since the switching frequency is in the kHz range (a few into MHz) the inductor value and filter capacitors on the output to smooth the voltage can be much smaller. The switching device takes a beating, but as long as the actual swtiching time is samll it alternates between high voltage (off) and low voltage and moderate current (on, but off before the current gets to high).