Fully Regulated USB Charger for Classic HP Calculators HP35, 45, 55, 65, 67, 80

Description

Gold Plated Contacts
- just like the HP original charger
Fully Regulated Voltage
- just like the HP original charger
Fully Regulated Charging Current
- just like the HP original charger
Keep your calculator plugged in full time, if you choose
Protect your precious calculator from damage!
Don't EVER apply 5 volts to your calculator or battery.
All units tested using a dummy load to simulate an HP calculator
350 sold over the past 10 years. Shipped all over the world. Do you have a beloved HP Classic series calculator sitting the the drawer? Batteries shot? Lost or broken charger? You can buy replacement battery packs on eBay, but the power adapter is a different matter. Get in touch with your HP roots with this USB power / charger cable, featuring gold plated contacts (see photo of the contacts before manufacture). The original HP charger provides 4.2 volts to power the calculator, and a constant current of 50-60 milliamps to charge the battery. I made a cable that provides the same functions, with a few modern changes. These cables provide regulated 4.2 volts to power the calculator and a regulated current of 20 mA to charge the battery pack. The current lowers to 10mA when the batteries are fully charged. I reduced the current from the original HP spec (60 mA) since I use NiMH batteries, which have a higher capacity than the original NiCds, but are subject to overcharging. The final current of 10mA is a 'trickle' charge for the NiMH batteries. So the batteries charge more slowly, but more safely, too. I use these cables at home and at work. Very handy since USB ports are everywhere, and USB wall adapters are very cheap. My testing setup simulates the electrical load of the calculator. Each cable is checked for correct regulation of voltage supplied to the calculator, and current supplied to the batteries.
Fully regulated
voltage to safely power the calculator and current to safely charge the battery. Don't risk your precious vintage calculator, or ruin the battery pack!
Bring your old HP calculator back to life!
Unlike some sellers, I don't make any money on shipping. I've just changed to small envelope shipping to save the buyer some $$. I ship quickly, but if I'm on vacation, I'll notify the buyer of any delay.