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DC adapter vs Battery

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Njguy

Member
I wanna eventually use a 12 volt battery for my application, but while its in development I have no desire to be messing with one. Recharging it and such. So I figured I would get a 12v DC adapter that plugs into the wall. Like the one here. 12 Volt DC - 2 Amp Power Supply

My question is about the plug. If I were to cut off the plug/connector would there be two wires inside, like for positive and negative? Or if I could somehow buy the female end and save the connector.
 
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crutschow

Well-Known Member
Most Helpful Member
If the plug has two contacts, then the cable should have two wires.

Whether to cut the wire or use a connector depends upon what else you may want to use the adapter for.

It can be handy to be able to unplug the power supply during testing so I would recommend getting the matching socket if it isn't too difficult to find.

That also would allow you to easily change between the adapter and battery as a power source. You may find that your application doesn't always work the same under adapter power as it does under battery power so being able to readily change back and forth can be helpful.
 

Njguy

Member
This is a very noobish question. I bought this power jack- Alectron - ZC-2550A - Allied Electronics

As you can see from the picture it has 3 unmarked prongs. I cannot seem to figure out what the 3rd one does. I know with my multimeter, I will not get the full voltage unless the ground probe on the meter touches two of the prongs at once. Any help?
 

audioguru

Well-Known Member
Most Helpful Member
You bought the wrong jack. It is made to mate with a 2.1mm plug but the power supply has a 2.5mm plug.

The third terminal on the jack is the switched contact that would allow a battery to power the device then disconnects the battery when the power supply is plugged into it.
 

Njguy

Member
You bought the wrong jack. It is made to mate with a 2.1mm plug but the power supply has a 2.5mm plug.

The third terminal on the jack is the switched contact that would allow a battery to power the device then disconnects the battery when the power supply is plugged into it.
Ahh well it fits perfectly so I don't see how it can be the wrong one.
 

audioguru

Well-Known Member
Most Helpful Member
A 2.5mm plug does not fit in a 2.1mm jack. One of the numbers is wrong or the parts got mixed up if it fits perfectly.
 

Njguy

Member
A 2.5mm plug does not fit in a 2.1mm jack. One of the numbers is wrong or the parts got mixed up if it fits perfectly.
I think, that you're mixing up two sets of numbers. One is inner bore, and the other is outer bore. Both have an inner bore of 2.1 mm and an outer bore of 2.5 mm.
 

mneary

New Member
I think, that you're mixing up two sets of numbers. One is inner bore, and the other is outer bore. Both have an inner bore of 2.1 mm and an outer bore of 2.5 mm.
Both of you are almost right. In both cases the outer cylinder is 5.5mm. The 2.1mm jack appears to perfectly fit the 2.5mm inner bore, but there's 0.4mm of total clearance which will sometimes connect and sometimes not connect.
 
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