Dynex 1200 mA Universal Adapter

[knserbrave]

Hi,

I bought two adapters today, one in which I returned to the store because the current wasn't strong enough to power the intended device. I bought the adapter that is in the title of this thread to power a Casio electric piano that requires 850mA and 9V DC. The only adapter I could find had a setting for 9V DC and could have a maximum current of 1200 mA, yet the piano is still not working. I'm not sure if the package did not come with the right tip or if the device is defective. Could anyone tell me if it is ok to use a 1200 mA current in something that requires 850 mA and if there is some other reason as to why this is not working? Thank you.

 

[TBennettcc]

Usually, the adjustable-voltage wall warts have a specific current rating at each voltage rating, such that the maximum power through the device is roughly the same at each setting.

From what I could find, the product spec says it's 3-12VDC at 1200mA or less. If it's 1200mA at 3 volts, that means it's approximately 3.6 watts. So, if the relationship is linear, that means at 9VDC, you'll only get about 400mA max.

 

[daddles]

Someone gave my daughter a Casio electric piano years ago and I used to power it from my HP lab power supply. This got old real quick when I wanted to do experiments, so I went to Radio Shack and bought a 12 volt wall wart. IIRC, it was around 1 to 1.5 A and powered the thing just fine.

I would recommend you look for a wall wart rated at the single voltage that is required (9 V, apparently) and has a current rating 20% or so more than the required current. It harms nothing to have more current capability; it just typically costs a little more.

There's another issue: regulation. What you (probably) really want is a wart that has good regulation. Your Casio may operate on a wart with poor regulation, but you don't know that without testing (and you probably don't have the equipment for it). So, look for a wart that claims it outputs a regulated 9 volts. If things still don't work, then you can buy a 12 volt wall wart and we can show you how to build a regulator from an LM317 IC. But that will take a little work on your part; it's more efficient to try to find the proper wart first.

You need to test the wart to see if it is actually outputting anything. A cheap $5 Harbor Freight digital multimeter will do this. Then, to be sure it works, you need to test it under load, but this will be harder unless you have e.g. a resistor of the proper value and power rating.

 

[poor mystic]

Hi
You also need to check polarity. Did anyone mention polarity?