Hewlett Packard
Classic Calculator
USB Charger Cable
Fits the HP 35, 45, 55, 65, 67, HP70, and HP80
Model: HP-USB-Charge Circuit
F
its
the following Hewlett-Packard Calculators:
Classic Series Calculators
:
HP35, HP45, HP55, HP65, HP67, HP70 and HP80
Auction Deliverables:
USB 5-6-foot long Charging cable
with charging circuit and LED light notification
Recharging Cable:
Charging cable fits the terminals on the HP classic calculators.
The cable is well made with 0.81″ diameter brass tubing, very sturdy.  I used shrink tubing and the USB cable is 5-6 foot long.  Note that the tubing part is connected to the upper terminal and the other to the left side lower terminal.
For your reference, the middle pin is
negative.
The lower left pin is positive and is wired to
the battery pack and the third pin is wired to the calculator circuitry.
Note a gold clip connects the two lower pin
allowing the battery power to connect to the circuitry and run the calculator when the adaptor is not plugged in.
Voltage Output from the USB cable
Amazingly,
if you put a voltmeter across the battery end of the cable (plugged into your USB 5 volt source) the voltmeter will register nearly NO volts direct current.  This is ok, as the charging circuit within the USB cable adds current then a load is present.  The USB cable will not run the calculator alone… unless there is a battery in the
calculator
, as the cable itself will not give necessary voltage into the calculator unless there is a battery (a load across the charging circuit) installed.  The advantage of the charging circuit is that you will never overcharge the battery, and that is a big safety advantage.
Since the USB voltage is 5 volts DC you can directly connect
to the pack and it will charge the cells.
When the HP adapter is connected, there are two voltages 5 volts and 14
volts.
Second pin gets 5 volts and the
circuitry gets 15 volts. My design allows the two lower terminals to remain
connected and thus the 5 volts travels also to the calculator, you can turn it on when plugged in.
I tested how long it would take to recharge the 3000 BTY (45 minutes), 2800 Bonai maH pack (90 minutes).  I plugging it into an Apple cube at 2.1 Amps for these tests.  I tested the charging time for this battery pack with a voltmeter also attached to the charger and battery.  I have videos of the charging cycles.  What is so nice is that the circuit board LED flashes while charging then turns off when the voltage is 4.12 volts.  No over charging of the battery packs.
NIMH and NiCAD charging circuit:
This option is so much better than my previous design.  Set between the USB power plug and the calculator battery pack is a circuit board that regulates the amps delivered to the battery pack.  The circuit is designed to detect both NiMH and NICAD battery packs.  While charging the LED light flashes every one second.  Upon completed charging the circuit stops charging the battery pack, and the LED light goes off.
Battery Storage:
Please protect your beautiful HP calculator!  All battery cells will eventually leak a corrosive acid that may harm your calculator.   If your not using the calculator for a long time, please consider removing the battery from the calculator.  These devices are just too awesome to risk potential corrosion damage.
If you are unhappy with it, mail it back, and I’ll refund your money.
Shipping:
Shipping costs are listed below.  For multiple battery pack purchases contact me for actual shipping costs.
I will refund your extra shipping charges and only charge you actual shipping costs.
Also check my other HP calculator battery packs for sale especially for the Spice HP 33-34-35 calculators and for the larger HP 95-97 calculators.
Waterhosko
(Mark Hoskins) is also on the HP Calculator Museum site
Hope to add you to my list of satisfied customers.
Sincerely,
Mark Hoskins