The Museum of HP Calculators

HP Forum Archive 12

 AC adaptorMessage #1 Posted by Michel Beaulieu on 2 May 2003, 11:29 p.m. I have a lot of wall adaptor for calculators and other appliance. If i test them i get a LOT more thatn it is written on the adaptor, why? I read that this is an idle voltage that needs a load to get the written voltage but my question will be : will the level of the load affect the "final" voltage of the adaptor? Is a witten 8 volt adaptor will be 8 volt on all calculator? thanks Michel

 Re: AC adaptorMessage #2 Posted by Chris Catotti (Florida) on 3 May 2003, 12:34 a.m.,in response to message #1 by Michel Beaulieu Probably not. The stated voltage is for a given load, i.e. current. Let's review Ohms law: V=I*R V: Voltage I: Current R: Resistance P: Power V=I*R I=V/R R=V/I P=V*I P=V^2/R P=I^2*R Anyhow, most of thwe wall module chargers are not regulated poer supplies, and therefore you should try to match both the Voltage rating (volts [V]) and the Current rating (milliamperes [mA]). If your power supply is signigficantly undersized, you may cause it to overheat and melt or catch fire. If it is signigficantly oversized, you will probably supply to great a voltage to the calculator, and can damage the calculator.

 Re: AC adaptorMessage #3 Posted by David Smith on 4 May 2003, 5:39 p.m.,in response to message #1 by Michel Beaulieu I don't think I have ever seen an unregulated adapter put out its stated voltage or less even under a proper load. They always seem to be a bit on the high side.

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