I want to match a small mains adaptor to a small hand-held whisk.
Normally the whisk is battery powered (AA x 2) and has a variable speed. At its max I would like to run the whisk a little bit faster than the internal batteries permit. So I figure I could replace the two AA cells with a mains adaptor feeding approx 4V.
I came across the basic Nokia mobile phone mains adaptor (which used to be supplied as standard with Nokia phones). It's nothing fancy: no switched mode or high speed charging or any of that. This is Nokia model ACP-7X (X for the UK where I am) with a spec of 230 V, 50 Hz, 4.8 VA. Output 3.7 V, 355 mA.
HOWEVER ... when I measure the voltage across the output of the PSU it measures about 9V with no load. Don't know a whole lot about regulated/unregulated PSU's but I guess this is pretty unregulated if it goes from 9V to 3.7V.
Would it be LIKELY that the voltage would come down to about 4 V when I attach my whisk? The whisk has a resistence of about 250 ohms. When I measure the resistence of the Nokia when it's not attached to the mains, I get infinity.
So would this ACP-7 be safe to use? Or would it deliver well above 4v and blow the motor in my whisk?