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Correct Polarity?

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I bought this for 9 dollars and 9 cents.  

 

https://www.ebay.com/itm/Lind-Electronics-Mac-Powerbook-Battery-Charger-BC-4070/383690523212?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

 

Here is an identical one.  I did not want to pay so much so I took a chance on the other one.

 

https://www.ebay.com/itm/Vintage-Apple-Macintosh-Mac-PowerBook-140-180c-Battery-Charger-Conditioner/303690343628?hash=item46b55ae4cc:g:ESMAAOSw1a5fXpoL

 

No adapter is included.  Its only 1 amp so my generic universals I have at home should work.  But on the adapter in the second link it does not say polarity.  Nor anywhere on the device in the first or second link it does not say what polarity.  How can I tell which polarity is needed?

 

 

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according to the image, it does not have one:

 

It's an AC-AC transformer.  Not a DC transformer.

 

s-l1600.jpg

 

Since it is alternating current, it does not matter which is tip and which is lead.  You WILL however, need an AC-AC adapter that outputs 12vAC

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No, the one on Walmart converts high voltage AC from your wall jack to low voltage DC in the range 3-12V.

 

What you need is a transformer that outputs 12V AC. While it is true that many computers and video games designed for working with AC, just as well can be powered with DC because those got a rectifier and voltage regulator right inside the system, I'm not sure this battery charger works in the same way. You would need a schematic or taking it apart to tell for sure.

 

(Note: NEVER do the other way around, using an adapter that outputs AC to a system that expects DC. It will likely fry it within seconds)

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