# Low voltage plug sizes



## AntAltMike (Nov 21, 2004)

Is there any kind of a jig available to determine the size of push-in connectors used on external power supplies, similar to the way we check screw sizes at the hardware store? I have to acquire a lot of 5.5 VDC wall power supplies and will favor the purchase of those with plugs that match the product that I need them for. I will therefore favor the purchase of plug compatible ones and splice the rest.


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## P Smith (Jul 25, 2002)

Using caliper would tell you, don't forget - such plugs defined by two diameters - external and internal.


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## SayWhat? (Jun 7, 2009)

The center pin diameter is just as critical as the outer barrel diameter. The other factor is polarity. I'm not sure how many variations there are, but we're talking 'few', not dozens.

Try searching for 'power plug configurations' or something similar.


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## Rich (Feb 22, 2007)

AntAltMike said:


> Is there any kind of a jig available to determine the size of push-in connectors used on external power supplies, similar to the way we check screw sizes at the hardware store? I have to acquire a lot of 5.5 VDC wall power supplies and will favor the purchase of those with plugs that match te product that I need them for. I will therefore favor the purchase of plug compatible ones and splice the rest.


How do you plan to do that? If you're gonna do what I think I'm reading in your OP, you're gonna have problems.

I don't have any real expertise in the sizing of the plugs themselves. I always thought it depended on the voltage, in other words wouldn't all 5.5VDC plugs be the same size? I know when I misplace a cord for a device, I look on the device and see what the voltage is and root thru a bin and find an external power supply that matches the voltage and they always fit. Admittedly, I don't do this often, so I might have been just lucky each time.

Rich


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## P Smith (Jul 25, 2002)

*No, rich, no ! Don't do that !*

Totally different cases - all manufacturers attemting to protect their investment and produce those brick in many variations, include a most dangerous for _your_ investment - with inverted polarity. Same phys sizes and PUFF (!) - your device :burned in flames".


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## AntAltMike (Nov 21, 2004)

Maybe I should have mentioned in my opening post that I'm a repair technician. :eek2:


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## P Smith (Jul 25, 2002)

Would you limit posters here by certain level of professionalism ? Likes say - only EE who have experience with design/manufacturing/testing/etc external power supplies could answer here !


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## AntAltMike (Nov 21, 2004)

In another thread where I have queried similarly, I have been told that Radio Shack stores have a set of size-labeled plugs that they use to assist in matching replacement plugs but it is not for sale, and what I am looking for is a set or panel of labeled jacks.


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## Rich (Feb 22, 2007)

P Smith said:


> *No, rich, no ! Don't do that !*
> 
> Totally different cases - all manufacturers attemting to protect their investment and produce those brick in many variations, include a most dangerous for _your_ investment - with inverted polarity. Same phys sizes and PUFF (!) - your device :burned in flames".


You didn't read my post correctly. I do check to see if the voltages are the same. There's usually not anything else on the devices themselves except the voltage required. Thankfully, a lot of manufacturers are putting the names of the devices on the power cords. Roku is a good example of this. All their external power supplies have "Roku" on them.

Rich


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## Rich (Feb 22, 2007)

AntAltMike said:


> In another thread where I have queried similarly, I have been told that Radio Shack stores have a set of size-labeled plugs that they use to assist in matching replacement plugs but it is not for sale, and what I am looking for is a set or panel of labeled jacks.


So, a 5.5VDC plug can vary in size? I know when you go to 120VAC and above, the plugs are all the same size with regard to voltage. In other words, a 220VAC plug is configured differently than a 120VAC plug or a 480VAC plug. Just so you cannot (that's not an absolute) mix them up.

Rich


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## Rich (Feb 22, 2007)

AntAltMike said:


> Maybe I should have mentioned in my opening post that I'm a repair technician. :eek2:


Yup, I think most of us know that by now.

Rich


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## Rich (Feb 22, 2007)

AntAltMike said:


> In another thread where I have queried similarly, I have been told that Radio Shack stores have a set of size-labeled plugs that they use to assist in matching replacement plugs but it is not for sale, and what I am looking for is a set or panel of labeled jacks.


I guess I'm just confused. If they have that device, doesn't that mean that a 5.5VDC will be the same size as every other 5.5VDC plug? How else would you know the voltage the plug is designed for?

Rich


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## AntAltMike (Nov 21, 2004)

The ones I've examined usually specify maximum output current and they indicate polarity with a labeled arc and center pin drawing.

Now that most of these "wallwarts" are switching supples rather than linear regulators, they can withstand shorts. Linear regulator wallwarts commonly had pigtail fuses in them that blew when shorted.


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## P Smith (Jul 25, 2002)

rich584 said:


> You didn't read my post correctly. I do check to see if the voltages are the same. There's usually not anything else on the devices themselves *except the voltage required*. Thankfully, a lot of manufacturers are putting the names of the devices on the power cords. Roku is a good example of this. All their external power supplies have "Roku" on them.
> 
> Rich


Ooops. You missed other very important parameter - max load or sustaining load: mA or A (amperes).


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## harsh (Jun 15, 2003)

Some of the outfits that retail adapters have what is often called a "cat o' nine tails" that is essentially a bundle of cable ends that are marked with a reference number. The idea is that you try each until you find one that fits.

As for the insistence that plug inside diameter is somehow different from jack pin diameter, that's just silly.

For future reference, the jack is the "port" on the device to be powered and the plug in on the end of the cable and inserts into the jack.


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## Rich (Feb 22, 2007)

AntAltMike said:


> The ones I've examined usually specify maximum output current and they indicate polarity with a labeled arc and center pin drawing.
> 
> Now that most of these "wallwarts" are switching supples rather than linear regulators, they can withstand shorts. Linear regulator wallwarts commonly had pigtail fuses in them that blew when shorted.


I've got a Roku switching adapter in front of me and it says "Output +5V (I'm assuming DC, is that correct?) and the current is 2.5 amps. Doesn't really give you much more info than that except for the input voltage which is 100 to 240VAC at either 50 or 60Hz. There is a polarity symbol.

Rich


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## Rich (Feb 22, 2007)

P Smith said:


> Ooops. You missed other very important parameter - max load or sustaining load: mA or A (amperes).


On the Roku, the device itself does say 5V, 2.5A. But the amperage is dependent on the device not the power supplied. In other words as long as you supply 5V, the Roku is gonna pull 2.5A.

Rich


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## Rich (Feb 22, 2007)

P Smith said:


> Ooops. You missed other very important parameter - max load or sustaining load: mA or A (amperes).


I gotta look at some other devices. I don't think they all give the amperage.

Rich


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## P Smith (Jul 25, 2002)

rich584 said:


> I gotta look at some other devices. I don't think they all give the amperage.
> 
> Rich


Yes, they are must have it, by a standard.


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## P Smith (Jul 25, 2002)

rich584 said:


> On the Roku, the device itself does say 5V, 2.5A. But the amperage is dependent on the device not the power supplied. In other words as long as you supply 5V, the Roku is gonna pull 2.5A.
> 
> Rich


Ummm, lets not go in that direction ... 
I did state "max" and "sustain" current of each PS. 
It's a critical parameter of the power supply - do not mix with a particular load [Roku box].


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## Rich (Feb 22, 2007)

P Smith said:


> Ummm, lets not go in that direction ...
> I did state "max" and "sustain" current of each PS.
> It's a critical parameter of the power supply - do not mix with a particular load [Roku box].


Max to me means the inrush current of any electrical device. Sustained current is the current it pulls when the inrush current subsides and the device runs as it should. The device is still the governing factor when it comes to amperage.

Just ran around the house looking at devices with wallwarts (always wondered what they were called, learned something today) on them and only found one that doesn't have the amperage on it. Variable speed screwdriver that just says "6V" on it. Guess it's because it's a variable speed device, but there is no amperage rating on the driver itself.

This is really making me wonder how many plug sizes actually exist. Never gave it much thought since I've always worked with much higher voltages. Very interesting.

Rich


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## Rich (Feb 22, 2007)

P Smith said:


> Yes, they are must have it, by a standard.


Is that an NEC standard?

Rich


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## P Smith (Jul 25, 2002)

No, not inrush current - modern switching PS handle it different way. 
Max is mean the PS will work certain amount time, could become hot but will handle the load. Sustain will be for indefinite amount of time.

No, not NEC.


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## houskamp (Sep 14, 2006)

biggest problem is there is no standard for small stuff.. they use whatever voltage, current, plug size/type they want to.. they are required to be marked in some way.


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## Rich (Feb 22, 2007)

houskamp said:


> biggest problem is there is no standard for small stuff.. they use whatever voltage, current, plug size/type they want to.. they are required to be marked in some way.


Considering how everything over 110VAC is regulated, I find that rather amazing. No regulation whatsoever? This is turning into a real "eye-opener" for me.

Rich


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## Rich (Feb 22, 2007)

P Smith said:


> No, not inrush current - modern switching PS handle it different way.
> Max is mean the PS will work certain amount time, could become hot but will handle the load. Sustain will be for indefinite amount of time.
> 
> No, not NEC.


Max means you can run it at an amperage that will eventually cause it to ignite? Please tell me they have thermal protection built into them.

I can find no devices in my home that have "Max Amperage" and "Sustainable Amperage" on them.

Rich


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## AntAltMike (Nov 21, 2004)

I'm not an electrician, but I think that everything over 60 volts is regulated as a certain classes of wiring that professional licensing for service. I think under 60 volts is "Class B" wiring and there is little regulation of it. That has resulted in some regulatory "gray areas", like with 70,7 volt ceiling speaker wiring, and now, 90 volt AV cable TV trunkline powering.

I once had to get a "Class B" wiring license for a C-band satellite installation. The local electrical inspector actually came out to confirm that the mast and coax were grounded according to the 1987 NEC. The code said that "the mast" had to be grounded, and he wouldn't allow me to satisfy that requirement by grounding the mast mounting bracket. I had to drill and tap a threaded hole for a grounding wire connection screw.

The code also said that the outer conductor of the coax downlead had to be grounded with a wire "approximately equal in current carrying capability to the coax outer conductor". Unfortunately, there are no published specs for that, and since high frequency current flows on the outside of the conductor, one could plausibly ague that I would need a copper ground wire equal in diameter to the coax, which would have ben about 0000. He did say that since an auxiliary ground rod could be bonded with 6 gauge wire, it would make no sense for a system to require ground wire any larger than that because the ground path capacity would be limited by its weakest link, so he OK-ed the use of 6 gauge ground wire for that purpose.

The Code regulations are for fire and shock prevention. They don't care about damage to components or suitable performance.

One reason that many 110 volt line powered devices use wallwart and desktop supplies is so that the manufacturers will not have to get UL approval for each variation of the product. They only need to get the external power supply approved.


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## Rich (Feb 22, 2007)

AntAltMike said:


> I'm not an electrician, but I think that everything over 60 volts is regulated as a certain classes of wiring that professional licensing for service. I think under 60 volts is "Class B" wiring and there is little regulation of it. That has resulted in some regulatory "gray areas", like with 70,7 volt ceiling speaker wiring, and now, 90 volt AV cable TV trunkline powering.
> 
> I once had to get a "Class B" wiring license for a C-band satellite installation. The local electrical inspector actually came out to confirm that the mast and coax were grounded according to the 1987 NEC. The code said that "the mast" had to be grounded, and he wouldn't allow me to satisfy that requirement by grounding the mast mounting bracket. I had to drill and tap a threaded hole for a grounding wire connection screw.
> 
> ...


I am an electrician and I'm having a hard time with this, but I find it very interesting. Grounding, as you've found out, is a royal PITA, open to differing opinions in different jurisdictions by different officials.

In industrial environments, low voltage is considered anything under 600VAC. Voltages above that are really just plain scary. I was qualified to work on 4160 and I avoided that as much as possible. Any devices that were under 110VAC were installed and serviced by our "Instrument Men". A group that knew little about electricity. We had a strong union that kept the various crafts well separated and I rarely had anything to do with those very low voltages. Which made me happy, because, as I've mentioned many times, I'm very lazy....:lol:

I really find this discussion about "wallwarts" very interesting. I hope it continues.

Rich


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## P Smith (Jul 25, 2002)

rich584 said:


> Max means you can run it at an amperage that will eventually cause it to ignite? Please tell me they have thermal protection built into them.
> 
> I can find no devices in my home that have "Max Amperage" and "Sustainable Amperage" on them.
> 
> Rich


You could find them in UL docs.


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## houskamp (Sep 14, 2006)

One of the main reason for wallworts it that the regulations end at the wallwort.. much easier to get devices approved..


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## Rich (Feb 22, 2007)

P Smith said:


> You could find them in UL docs.


You don't think I'm actually gonna search for UL documents, do you, Pete? You gotta keep in mind how LAZY I am!

Rich


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## Rich (Feb 22, 2007)

houskamp said:


> One of the main reason for wallworts it that the regulations end at the wallwort.. much easier to get devices approved..


So, the only way to be sure you're not gonna incinerate the WW is to use one that has a higher amperage rating than the device requires? If the plug fits. I really find all this rather unbelievable (I don't doubt anyone, just kinda surprised). No one regulates these things?

You can actually stick a 7V WW on a device that calls for 2Vs if the plug fits? Wouldn't that be like putting 220VAC into a 120VAC motor (which will promptly burn, if the thermal device in it fails)?

Rich


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## AntAltMike (Nov 21, 2004)

Any wall power supply will have a non-replaceable fuse on its input size -typically under 0.5 amps - which makes it impossible for it to draw enough current to start a fire. On the output side, a primitive linear supply will have its output voltage drop to near nothing when shorted, as it's theoretical maximum output current would be limited by the impedance of the secondary coil, whereas with switching supplies, I shorted a two amp one recently without damaging it, so whether it had a thermal sensor or some kind of current draw sensor, I don't know, but it didn't fry anything.


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## AntAltMike (Nov 21, 2004)

rich584 said:


> So, the only way to be sure you're not gonna incinerate the WW is to use one that has a higher amperage rating than the device requires? If the plug fits. I really find all this rather unbelievable (I don't doubt anyone, just kinda surprised). No one regulates these things?
> 
> You can actually stick a 7V WW on a device that calls for 2Vs if the plug fits? Wouldn't that be like putting 220VAC into a 120VAC motor (which will promptly burn, if the thermal device in it fails)?
> 
> Rich


You've go it! When these push-in plugs came into common use in the 1990s, I really expected some industry group to do something to standardize them, but no one did.


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## Rich (Feb 22, 2007)

AntAltMike said:


> Any wall power supply will have a non-replaceable fuse on its input size -typically under 0.5 amps - which makes it impossible for it to draw enough current to start a fire. On the output side, a primitive linear supply will have its output voltage drop to near nothing when shorted, as it's theoretical maximum output current would be limited by the impedance of the secondary coil, whereas with switching supplies, I shorted a two amp one recently without damaging it, so whether it had a thermal sensor or some kind of current draw sensor, I don't know, but it didn't fry anything.


Don't understand. If you're drawing 2 amps, how does a .5 fuse not blow? I really don't understand how these things work.

Rich


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## AntAltMike (Nov 21, 2004)

V x A = W


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## P Smith (Jul 25, 2002)

rich584 said:


> Don't understand. If you're drawing 2 amps, how does a .5 fuse not blow? I really don't understand how these things work.
> 
> Rich


input: 110Vx0.5A (max) = 55W (max)
output: 5Vx2A = 10W


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## TBoneit (Jul 27, 2006)

P Smith beat me to it


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## Rich (Feb 22, 2007)

P Smith said:


> input: 110Vx0.5A (max) = 55W (max)
> output: 5Vx2A = 10W


OK, formulas I have no problem with, but what's the load that the .5 fuse is protecting, physically, I mean?

Rich


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## P Smith (Jul 25, 2002)

in case of input over-voltage (240VAC) and other possible shorts inside of the PS what would over-load first contour (AC), include second contour (DC)


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## Rich (Feb 22, 2007)

P Smith said:


> in case of input over-voltage (240VAC) and other possible shorts inside of the PS what would over-load first contour (AC), include second contour (DC)


What does go on inside those things? How does the AC become DC?

Rich


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## armophob (Nov 13, 2006)

rich584 said:


> What does go on inside those things? How does the AC become DC?
> 
> Rich


inductive coils that form transformers, they are not robots in disguise


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## P Smith (Jul 25, 2002)

present time - switched power supplies
you can start here http://www.smpstech.com/tutorial/t03top.htm#SWITCHINGMODE


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## AntAltMike (Nov 21, 2004)

rich584 said:


> What does go on inside those things? How does the AC become DC?
> 
> Rich


The inductive coils transform voltage levels, as do switching intervals, but it is diodes that limit the current flow to one-way, or _direct_, current


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## PokerJoker (Apr 12, 2008)

There is a fairly good list of DC Coaxial Power Plug types and dimensions on Wikipedia. It cross references to the Radio Shack letter code.

And there is indeed no standardization and no protection from plugging in a wall wart that fits the socket but will blow up your device. There was an effort from the EIAJ a while back to come up with a "standard" but it has had limited adoption.

Thankfully nearly 100% of all modern wall wart plugs have the positive pole on the inside pin. That was not always the case, and older devices should be carefully examined.

So, to make a non-original DC wall wart or power supply work - the voltage has to be right - the DC current rating has to be sufficient - the plug has to match, both inside and outside diameters - and the polarity has to be correct. All of this matching is up to YOU - you cannot assume that anything is standardized.

(And don't get me started on the identical-appearing supplies with the same plugs that put out low voltage AC. :eek2: )

Keith


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## AntAltMike (Nov 21, 2004)

PokerJoker said:


> Thankfully nearly 100% of all modern wall wart plugs have the positive pole on the inside pin. That was not always the case, and older devices should be carefully examined...


Yeah, the Drake TSM1000 terrestrial field strength meter used a plug with the sleeve hot, and when the jack needed to be replaced, they'd actually cut about a 1" diameter hole in the grounded metal back panel and rivot a piece of fiberboard to it, so that an ordinary jack could then be used as a replacement without creating a short.


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