determining ac adapter specs

[kanakanaka77]

hi there,
new to the forum; new to electronics as a whole actually. I'm sure there's a formula, or some common sense approach but I lack both it seems. I'm wondering how to determine which ac adapter I might need if the unit in use does not provide me with any information: polarity, voltage, amps, etc. is it possible to determine any of this information if I know how many, and what type of batteries the device uses?
thanks for the help

 

[(*steve*)]

You need to know the approximate voltage, the maximum current, and preferably the polarity.

Most of the round power connectors have the centre or tip as positive.

If the device is battery powered, and does not have rechargeable batteries, then the DC voltage is typically similar to the battery voltage.

The manual will often tell you the power requirement even if it is not printed near the power socket.

There are other things you can do, but most assume some electronics knowledge.

The most important thing to remember is that the wrong power supply can kill your device. Get the correct voltage and polarity, and have the adapter rated for at least the current required by the device.

 

[kanakanaka77]

So without polarity and current there's nothing I can safely assess? I mean I know thte voltage has to be somewhere around 9 volts as there are 6 AA batteries, however there is no other information either marked, or listed from the manufacturer.

 

[(*steve*)]

If you can tell us what it is, that may help.

If it's powered from 6 AA batteries, it probably draws under a few hundred mA. So an adapter rated at between 5 and 7 volts at around 300mA or more would likely be acceptable.

The adapter obviously had to fit, and centre positive is a common standard.

If you have access to a multimeter and can measure (with the batteries removed) the resistance from the positive and negative end of the batteries to the connector. If you find connectivity between either end of the battery pack and either connection within the power connector then you can infer the polarity.