Barrel connectors and Power Supplies

[Bruce Cloutier]

What is everyone's opinion of the use of barrel connectors with power supplies in cinema installations?

My concern with them is that they can be accidentally disconnected. I am about equally concerned with supply leads wired to phoenix type screw terminal connectors. In that case wires are not stress relieved and can be easily broken after repeated disturbance. The screws too back off with the temperature cycles over time.

JNIOR supplies are wired to a 4-pos screw terminal connector. This was done originally as the majority of early product went into control systems with 12V generally already available. Prior to COVID we would source power supplies already tinned. These came at a premium and with lead times. Since COVID we just don't have that option. Power supplies (we are talking wall warts) are readily available with barrel or USB connectors.

We have in the past cut those off and tinned the leads ourselves. But we have run into too much variability in wire gauges, strand counts, and copper making the stripping and tinning processes difficult and potentially unreliable. I am uncomfortable with that.

So we started sourcing a barrel to tinned-lead adapter. This allows us to purchase available power supplies. It allows customers to more easily purchase their own power supplies (a majority do). The JNIOR standard connector kit now contains the 5 separate screw terminal connectors and this barrel adapter (already connected to the 4-pos connector). These adapters are pre-tinned and because that is the intention the wire gauge and type is guaranteed suitable for that kind of connection. But now you have a barrel connection that can be yanked apart.

A simple solution to the concern about the barrel connector is shrink tubing. Using a 1-3/4" piece of 1/2" marine quality shrink tubing you can apply the adapter to the barrel and affix it permanently. The marine shrink tubing includes a layer of adhesive (hot glue) inside. This then won't (ever) come apart and it is sealed preventing the environment from degrading the connection. It is easy to do too.

I have a thought about including a loose piece of the tubing in the connector kit. Without instructions though that is kind of odd. I don't know... what do you think?

Um... I can post photos of this if any of you want to see.

The day when we move to Series 5 is coming. There is discussion about a barrel jack power supply input. So... now would be a good time to complain about that.

[Marcel Birgelen]

The good thing about barrel connectors is that they're cheap and abundant, but that's about the only good thing I have to say about them. Depending on how much friction is on them, they can easily slip. I've also seen many terminals coming loose from the board, especially in mobile equipment like notebooks. I've seen Cisco switching from some obscure power connectors with retaining mechanism to standard barrel plugs, but they usually do allow for some stress relief in some of their rack-mount contraptions.

Maybe I'm old-fashioned, but when I think of professional equipment, I'm still somewhat biased towards screwed connections, even though pluggable connectors are usually quicker to install...

But if you're talking Series 5, what about putting an USB-C connector on there for power? Not any better than a barrel plug, but more universal. (And you could still sell it as a mobile phone in Europe.)
Or maybe a feature that would be actually useful: Support for Power over Ethernet? If your switch supports it, you could get rid of at least another external power supply this way.

[Harold Hallikainen]

I was thinking USB, but the POE is a great idea. Low cost "passive" injectors are available if there is not a POE switch available. The LSS-100 was originally powered over USB. In the LSS-200, we moved to POE. There is more complexity with POE. We used a Maxim PD chip in an interesting configuration to get isolated 5V. The chip is designed for non-isolated loads and is a buck converter. We substituted a transformer for the inductor in the buck converter. The chip regulates the buck converter output to +5V. When the chip pulls its output low, it puts 5V across the inductor or, in our case, the transformer primary. That put isolated 5V across the transformer secondary which was then rectified and sent to a filter capacitor.


Harold

[Bruce Cloutier]

We changed our approach to include the barrel plug as I described and are getting some push back That is why I brought this up. It is an issue right now with the existing product. You guys can all play with me when we get into Series 5 later.

The question now is whether or not barrel plugs are at all an issue in your current installs?

[Carsten Kurz]

I think for the typical JNIOR use scenario, the original Phoenix screw wire on method is better. Barrel plugs make more sense for consumers, and yes, they may become unreliable.

I don't think JNIORs are moved around so much that useful wire gouges break easily. What I like about the screw on also is that with the voltage and polariity flexibility of the JNIORs, you can easily get a replacement power supply and just screw it on after a quick basic check. Try to find a a supply with fitting barrel connector. Also, it's easy to parallel the supply voltage to other circuits from these terminals, e.g. to a relay block or another module. If you let clients source their own power supplies with barrel connectors, it will happen that they come up with one of those 'nearly' fitting ones that will cause contact problems - even WITH shrink tube applied.

[Marcel Birgelen]

The question now is whether or not barrel plugs are at all an issue in your current installs?

In reality, the impact switching from a screwed Phoenix connector to a barrel-style plug would be pretty minimal, even for a drop-in replacement. There even are barrel plugs with phoenix-style screw-on connectors in place for common widths:

dc-hohlstecker-mit-schraubanschluss-2polig-fur-gerate-mit-5-5-2-5-e-34KB7YJgA1LX5h2_600x600.jpg


Still, back in my mind I'm of the opinion that barrel plugs are for amateurs, real pro's screw their stuff...

[Carsten Kurz]

Yeah, real pro's screw it...

[Bruce Cloutier]

If you were at the helm of a large chain would you outlaw barrel plugs and, maybe, refuse power supplies that have them?

[Fraser Falconer]

Hi Bruce,
I'm not a fan of the DC Barrel Plugs, They aren't a terribly reliable connector. I know the way you are planning to implement these will be fine. But an extra connector is just another potential point of failure.

My thoughts for a dollar.
Cheers Fraser

[Bruce Cloutier]

I am just trying to make it easier for folks to use off-the-shelf power supplies and not have to cut and strip wires. It is hard to believe that a molded production assembled barrel plug would be any less reliable than random wire stripping. A large alphabetically prominent theater chain is telling us that. It doesn't make sense.

When you do strip wires do you tin them? Or do you use some crimp pin? How would you make the screw terminal connection so you would bet your house on it outlasting a barrel connector?

Not arguing for or against. I am just trying to understand and maybe develop (or alter) my own bias one way or another. We had thought that the decision to support the barrel connector was a good move.

We don't manufacture the supplies for the JNIOR. I don't (yet) have a long term contract for any one power supply. We encourage customers to source their own supplies. Many, and I would say the majority, do that. But when faced with lengthy lead times, price increases and tariffs you end up scrounging for a better deal. I think over time we've supplied a dozen different power supplies with JNIOR. There haven't been complaints or concerns until now.

Previously, other than making sure that a supply met its published specs, we were more concerned about selecting a physical form that would make better use of a power strip.

[Carsten Kurz]

But Bruce - the relay contacts are wire-on as well. Anyone being able to setup a JNIOR should have no problem to connect the two power supply wires.
They would not even have to be tinned for the phoenix terminal.
For a JNIOR, I use isolated wire ferrules. If the wire is thick enough, I even skip ferrules.

One exception of course, that is, if a power supply fails, and a replacement has to be connected on site by untrained staff. That would be a clear case for a barrel connector.


The trouble, again is, if you use a barrel connector in order to have people source their own supplies, these will turn up with all sorts of barrel dimensions. Also it will make it very easy to fry electronics by just plugging in 'some' supply. Admittedly, the JNIOR can hardly be hit with it's power supply specs. However, one of our employees recently turned up with an electronic gadget and asked me wether I would have a look for repair. Turned out quickly, that the device was spec'd for 5VDC, and she innocently had plugged in a laptop power supply running at 19VDC. Just because the barrel plug fit. She had a hard time to understand that identical barrel connectors are allowed to carry different voltages.

From my perspective - barrel connectors in a cinema installation environment are like RCA plugs. If someone want's to use them, HE has to take responsibility, that means, he would have to create adaptors, the device manufacturer should not force barrel connectors upon the installer.

[Bruce Cloutier]

Yep. We standardized on the 5.5MM O.D. and 2.1MM I.D barrel. The length matters but the adapter seems to be good with the range.

The JNIOR also can be powered with anything from 10V up to 24V either AC or DC. That does not even need to be regulated. So the power input (even when DC is used as is standard) goes through a full rectifier bridge. The resulting DC rail is limited to 40VDC. That feeds a 5V switching regulator (which now TI fails to supply) which feeds a 3.3V LDO.

There are only 2 cautions. If you use AC you need to pay attention to peak and RMS voltage with concern for the 40V limitation. If you trigger the MOV the JNIOR shuts down. And running at a higher voltage is less efficient. So 12VDC is recommended. Oh... and.... the GND pin on the DB9 serial ports is not exactly the same as the negative (-) power connection. It floats in-between.

With the JNIOR models (except the 412DMX) you can miswire (+) and (-) and the thing will still work. Where you then have a problem is if you tap of the (+) to power an input through an external relay as that will seemingly inexplicably not work. Check the polarity of the power leads. It is confusing because, hey, the JNIOR is up and running.

The JNIOR was originally designed to work with 24VAC HVAC wiring. But there we found out what 24VAC really meant. Those unloaded transformers put out a lot more voltage and, so, that didn't work out for us.

With relay and input wiring you can choose to use a good wire gauge and even solid copper. These power supplies are coming with really really fine wire strands and some seem to not be all copper. So when you strip the insulation you end up ripping strands. Then when you tin, even with good flux, the result is not gratifying. They don't define the wire used in the specs. It has been a problem. Sometimes the positive lean is not easily identified either.

[John Thomas]

99% of barrel receptacles are only physically held to the device by their own solder joints. They can be pushed in too hard, and heavy things can be set onto the inserted connector, wearing and breaking the solder joints necessary to power the device, usually resulting in intermittent failure. Something like an IEC receptacle, in contrast, is often physically screwed to the chassis and is immune to this type of wear and tear. That's not to say that IEC's are ideal either, but at least more robust.

Barrel connectors can be easily pulled out if someone is moving a device in a rack and isn't careful about the cables they're jostling. I always ziptie a strain-relief loop or something to mitigate this, and appreciate devices that have the little hook thing on the chassis meant for this purpose. I've also seen plenty of perfectly good power supplies that end up being flaky because the wire was pulled and bent so tightly that it wore down the strain relief on the cable/connector.

Different barrel connector sizes, while not terribly complicated, are not commonly memorized or understood by most technicians, nor are they immediately easy to identify at a glance. So looking around the booth for a quick-fix spare power supply or ordering third party can end up with a connector that "fits" but is loose and intermittent, or an incorrect purchase that just won't fit.



The more options you provide to power a product, the better, even to the point of having a phoenix receptacle and barrel receptacle alongside each other, and supporting PoE, as long as you've built in the protection that will keep the device from malfunctioning when multiple power supplies are connected. Installers generally don't have a good track record for reading the fine (or bold) print that says not to connect an external power supply at the same time as PoE.

[Bruce Cloutier]

Of course I am not even talking about a jack in the box. We went to using this and including that in the standard connector kit. I am also considering including the short piece of shrink tubing (also pictured) so you can lock the power supply to the adapter (assuming you have a heat source).

But there is an objection even to this?!

PXL_20220621_180047297~2.jpg

That is a 1-3/4" piece of 1/2" marine shrink tubing that includes an inner layer of adhesive (hot glue) so you ain't getting it off. Electrical tape (and even duct tape) works too.

Now, I assume, folks realize that using the adapter is optional. It comes off the 4-pos connector.

[John Thomas]

Prewired to the phoenix like that? I'm into it. You'll never please everyone though. "It's another point of failure!"