Can this actually work?


I came across this TAS Auction which includes a so-called "USB Power Adapter" that directly connects the calculator AC adapter pins to a computer USB port. Since this is a Classic series calculator, its AC adapter has two separate outputs to operate the calculator, approximately 5 vdc, and to charge the battery, approximately 17 vdc. So I don't see how a USB cord could do this. Also, I don't see how a USB port could provide sufficient power for these tasks. So I ask, can this device actually work, and if so how?


This looks like a straight USB cable with no molded-in voltage conversion circuit, however.....

A USB port can supply at least 500ma, so powering the calculator is certainly possible. 5 volts is also fine, I power all my classic calculators from 3 x AAA Energizer lithium cells which works out to be 5.1 volts when they are new.

Charging the 3 nicad cells in a classic from a 5V DC source will work fine as well. Nicads are fully charged at 1.45 volts per cell, so 5 volts will do it.

The high voltage that you measure from the standard HP chargers/adapter is an open circuit voltage, it drops considerably when loaded. Also as long as the voltage across the nicads cells being charged is greater than 1.45 per cell they will fully charge. The current flowing determines how fast they charge.



Old threads about these cables: 1 and 2



Hi there,

I've been using a USB to HP-41 cable (connected to an empty port) to run my 41's for the last copule of years or so, and they work like a charm from 5v.

Due to its internal design, Halfnuts show the BAT annunciator on, however they also work without problems.

Best from Spain.


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