Can I use a higher current AC/AC adaptor?

--- The problem with small supplies is that they have poor regulation.

That is, with a 1000 mA load on it the output will likely be at 12V, but with a 500 mA load it surely won't. It'll be higher, and if it gets high enough could damage what it's driving.

One solution would be to put an extra load on the supply so that it supplies 500mA to your device and 500mA to the dummy load. For a

E 12V R = --- = ------ = 24 ohm resistor. I 0.5A

It would be dissipating:

P = IE = 0.5A * 12V = 6 watts

So I'd go for something like a 24 ohm 12 watt resistor, and that resistor's still going to get pretty hot.

Another way out would be to connect a 12V, 6 watt incandescent lamp across the supply.

But...

All of that'll be unimportant if the device you have now can take the higher voltage.

Do you have any specs for the device and can you measure the supply's voltager>

-- John Fields Professional Circuit Designer

Thanks for the very informative reply.

I think I'll be safe and buy a new 500ma adaptor. I know that the eqipment wont like a higher voltage.

Paul

John Fields wrote:

John Fields wrote:

But isn't a 12V AC power adaptor simply a transformer in a box? It seems to me his 1000ma adaptor should work fine.

Alan Nishioka

I'm still confused. I must be missing something. If it is just a transformer, shouldn't the output voltage be determined by the turns ratio alone?

I always thought that an AC wall wart rated 1000ma simply meant that the wires were thick enough to carry that much current.

Alan Nishioka

That determines the unloaded voltage. When load current passes through the secondary (and its transformed equivalent through the primary), those windings drop voltage proportional to their resistances and those currents. ] Small transformers are often made with intentionally high resistance windings, so that their current is limited in the event of a short circuit load, so that they do not reach dangerous temperature (catch fire). This causes them to have a lot of voltage droop as their load current reaches rated load. Their rated voltage applies at rated load current, so their output voltage will be higher at lighter loads.