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Choosing power supply, how to get the voltage and current ratings?

I have a device (a Geneva XS portable Bluetooth speaker) which is supplied with a power adapter that specifies the output as DC 5.5V and 2A with a concentric barrel output plug. Before I bought it, many of the reviews I read of this speaker commented that it was a shame that the device did not use a USB port for charging. I certainly agree with the sentiment, as I already carry around a charger for my various "iDevices" and other things, and it would be nice to simply use the existing adapter and cables that I already carry to charge the Geneva when I travel. To that end, I resolved that I would see whether I could buy a cable with USB to concentric barrel plug to see if I could indeed only add an extra cable to my load, rather than have to carry an entirely new charger. Anyway, I have found such cables on ebay, but before I buy, I am wondering if my 5.1V 2.3A iPad charger will actually manage to pass any charge to the 5.5V 2.0A hungry Bluetooth speaker...or am I just wasting my time? Cheers, Harry.


marked as duplicate by Leon Heller, Olin Lathrop, Nick Alexeev, Brian Carlton, W5VO Nov 6 '12 at 4:31

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While the actual answer would be "You won't know until you try", the following might be useful to know:

A couple of products I have destructively analyzed (i.e. broken apart and was unable to reassemble) which were specified for a 5.5 V or 6 V charger, had internal circuitry including in one case a "original brand charger identification circuit", driven at 5 volts off an LDO that requires typically at least 0.5 Volt headroom to work.

Similarly, I have found devices running at 4.x Volts (no, not 3.3 V specified parts) with a diode bridge bringing the voltage down from the charger's 5.x volts - evidently to avoid concern about reversed supply polarity.

Either of these designs would either not work, or work unreliably, off 5.1 Volt supplies.


I have tried a 5 volt wall adapter with a remote control car that needed 5.5 volt charger and it did not work. The charging light came on but the car would never charge up.

(this should have been a comment not an answer, I know)


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