Power plug - positive or negative on center pin?

Scavenger

Joined Jan 5, 2005
15
I have a trail camera that eats AA batteries. It has a plug the supports an external power source. I bought a plug that fits but I'm not sure if the center pin should be connected to + or - on my new power source. Common sense is telling me the center is + and outside is negative but I'd like to know for sure. The camera plug has a nomenclature I don't recognize. See photo. Thanks in advance. Richard

Attachments

• 118.2 KB Views: 82

Joined Jan 15, 2015
4,521
Normally but not always the inner pin is the Positive (+) and outer shell the Negative (-) as shown below. The bottom of the text in the rectangle. Most times it is clearly marked on the mating connector of the device to be powered. Your image looks to have a negative shell. That is purely a guess on my part.

Ron

paulktreg

Joined Jun 2, 2008
771
How many AA batteries does it take?

If you have a multimeter you could try measuring the resistance from the terminals on the batteries to the power input socket and see if you can determine the polarity?

Dodgydave

Joined Jun 22, 2012
8,413
Easily checked with an ohm meter on the Outer Terminal to battery Negative, should be a shot circuit zero ohms, this will prove Centre pin Positive.

jpanhalt

Joined Jan 18, 2008
7,939
What brand and model trail camera. Some of us may have something similar. Mine is a Victure HC400 and center pin is positive. There is a chance you can use an ohmmeter to test continuity between the battery negative and the barrel side.

rambomhtri

Joined Nov 9, 2015
295
Center pin should be the positive, hands down. If not, the camera design, specially electric designer, doesn't know what he's doing. There are special cases where this doesn't apply, like guitar pedals, although I don't know why, really. It is to preserve battery live, but I believe you can totally design something to preserve what is more correct in protection terms.

Last edited:

jpanhalt

Joined Jan 18, 2008
7,939
Center pin should be the positive, hands on. If not, the camera design, specially electric designer, doesn't know what he's doing.
That is way over simplified and wrong.

Here's one explanation for why some designs use center-negative.
Source: https://neunaber.net/blogs/neunaber-audio-blog/13849473-pedal-power-basics
Most electronic devices and their power supplies have center-positive polarity, so why do pedals have center-negative polarity? Because many pedals work with either a battery or a power supply; and, to preserve the life of the battery, it is disconnected from the circuit when either (1) a power plug is inserted or (2) the input plug is removed. This is accomplished by connecting the battery's negative terminal to the input jack's ring contact and the battery's positive terminal to the sleeve shunt on the power jack. When the input plug is inserted, it completes the circuit for the negative battery terminal. When a power plug is inserted, it breaks the circuit to the positive terminal of the battery. Power jacks do not have a shunt for the center (pin) contact, so a center-positive power supply would not work in this type of circuit.
JR radio used center-negative. Some others quickly found on Google are Casio and Boss -- I did not confirm either.

Albeit, a lot of equipment has built-in protection from reverse polarity by using diodes or mosfets, but there is no guarantee that the TS's field camera is so protected.

rambomhtri

Joined Nov 9, 2015
295
That is way over simplified and wrong.

Here's one explanation for why some designs use center-negative.

JR radio used center-negative. Some others quickly found on Google are Casio and Boss -- I did not confirm either.

Albeit, a lot of equipment has built-in protection from reverse polarity by using diodes or mosfets, but there is no guarantee that the TS's field camera is so protected.
Thank you so much, I'll never stop learning. I thought about protection, and if I were to design that, positive in the middle all the way. If not, you would be touching the positive, which is never a good idea, doesn't matter if it does no harm to humans. Positive should always be protected. Funny enough, I own an electric guitar and I just checked my pedal and that's right, the negative is in them middle.

Anyways, isn't any way to do what pedals do, but still preserving the positive in the middle?

Scavenger

Joined Jan 5, 2005
15
Thanks for all the replies.

The camera is an older Bushnell, model 119678. I'll try the suggestions tonight and report back.

Richard

MrChips

Joined Oct 2, 2009
19,280
Do you have a barrel plug or compatible cable that will fit into the power jack?

Plug in and measure the polarity of the voltage at the plug while the batteries are still installed.
You may be able to sense how the batteries are wired.

Scavenger

Joined Jan 5, 2005
15
I tried the route of putting the barrel plug into the camera, which gave me electrical access to the outer ring. I had zero resistance when I tested between the outer ring wire harness and the negative battery terminal, so outer ring is negative. Thanks for all the suggestions.

rambomhtri

Joined Nov 9, 2015
295
I tried the route of putting the barrel plug into the camera, which gave me electrical access to the outer ring. I had zero resistance when I tested between the outer ring wire harness and the negative battery terminal, so outer ring is negative. Thanks for all the suggestions.
As we all expected, I guess.

MisterBill2

Joined Jan 23, 2018
3,888
Center pin should be the positive, hands down. If not, the camera design, specially electric designer, doesn't know what he's doing. There are special cases where this doesn't apply, like guitar pedals, although I don't know why, really. It is to preserve battery live, but I believe you can totally design something to preserve what is more correct in protection terms.
There are many companies of questionable integrity, which have the center pin negative. My solution would be to refuse to let their products be sold in the USA, or any place else. But since that is not possible to enforce, there is a need to check. But not continuity fron the barrel side to the negative, since inserting a plug shifts the internal switch. Check the continuity from the pin to the battery pack positive terminal, with the batteries removed, of course.

thedoc8

Joined Nov 28, 2012
128
Look for the reverse polarity diode with your meter across the power input, that is if it has one.

bassbindevil

Joined Jan 23, 2014
30
Handheld 2-way radios seem to be a frequent offender. I have a Radio Shack 2M handheld that uses one polarity on the rechargeable battery pack, and the opposite on the radio itself, and I've run into CB and VHF marine radios that were cooked by the wrong power cord.
And then there's the devices that use AC wall warts... like my Cambridge Audio DacMagic. 12V AC on the exact same plug that many 12V DC things use. It had a MSRP of $449 back in 2009 (now worth$20 at a yard sale in 2019); surely there was room in the budget for, if not a custom connector, then some unpopular but off-the-shelf connector. And this is a device that includes a USB input, so it would not be unreasonable for it to be plugged into the same power bar as the 12V DC wall warts for external USB hard drives.
Until some meddling authority like the EU enforces standards for DC power connections, our best bet is to design products (or projects) than are protected from incorrect polarity and voltage, if at all possible.

MisterBill2

Joined Jan 23, 2018
3,888
Look for the reverse polarity diode with your meter across the power input, that is if it has one.
A series protection diode might be a challenge to protect, and a shunt protection diode is a bit less common in the really cheap stuff. And physically looking for the diode requires a fair amount of experience.