AC/DC Power Converters - Does Amperage matter?

  • I have a question regarding AC/DC Power Adapters. I just purchased an LCD monitor w/out a power adapter. It officially needs a 12VDC, 3.5A to work. Will a power adapter that supplies 12VDC, 4.0A work correctly? Will power adapters rated w/ higher output AMPs work for applications that require less?


  • I feel amperage would matter if you were not supplying enough amperage for your application. Your 4.0A will work as long as your start up power is not a lot higher. An automotive battery could have 1000 amp hours capacity and yet when you turn on the interior light it only draws what it requires. The same light would not last long at 24v. What you are going to need to know is with DC your polarity will become very important, so you will have to get the info as to if the centre pin is + or -, don't connect until you have that right. Find a monitor with the adapter and get the info from there, or ask Google.


  • Potentially incorrect parity can damage the appliance (or monitor in your case). The variety of plug shapes and sizes is intended to largely prevent this however. Awhile back I had a mobile telephone I got at a deep discount because it was a discontinued model, and it lacked the power adapter. Radio Shack had an adapter that came with a variety of interchangeable plugs, to address the variety of parities and shapes. Basically they sold you a base adapter of the correct amperage (and voltage) and then you put the right "tip" on the end. They may be able to sort out the right plug for you, if you happen to live near one of their stores. Is Sylvania L151 the model number for the LCD monitor? regards, mathtalk-ga


  • You should note th polarity of th plug before trying; Some have center post negative, outside positive; others th opposite. Obviously, your device and power supply must match.


  • That answers my question perfectly. Unfortunately there are many types of small variations in the power input plug, and I'll have my work cut out for me (or maybe i'll get lucky) in finding the right diameter one (since I can't find any manufacturer specs: Sylvania L151). I'll check the polarity graphic as well before I attempt it. If the polarity is incorrect between the plug and the monitor, could I cause any damage or will it just not power?


  • Yes, a higher rated power supply means it will work in your application that requires less. In fact the spec for the appliance (LCD monitor in this case) is really an upper bound on current consumption; most of the time it may draw less current. The other compatibility issue is the DC plug, generally a recessed pin on the appliance that fits a round plug from the power adapter. There are a surprising number of variations. With the adapter unplugged, try the fit. If it slips into place with a convincingly snug touch, I'd say you're set! regards, mathtalk-ga


  • Spartagus gave good advice. Wrong polarity can destroy. Higher voltage can destroy. Often a 12 volt device will function with a 9 volt or 11 volt power cube if the amp rating is higher than recomended. Higher amps does not hurt, except the under loaded power cube will supply more than the name plate voltage. The non-fitting plugs do not always save you from distructive voltage or polarity. In the 2 to 10 amp range some new smaller technology is appearing which may make it even more difficult to use anything other than the factory replacement. I have cut the wire to put a compatable plug on an otherwise suitable power cube. Going from 3.5 amps to 4 amps is probably safe. 3 amps is also safe, but the power cube needs to be cooled if it seems unusually hot. Neil







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