Re: Two different designs of the 82120A rechargeable battery pack Message #2 Posted by Randy Sloyer on 21 Nov 2003, 8:40 p.m., in response to message #1 by Jon
Jon, good detective work. The 3-pin version is similar to the classics circuit. Perhaps after the failure lessons of the Woodstocks, they went back to what worked. But, I suspect the kapton film that acted as both an insulator and conductor had reliability, manufacturing or cost issues. So, out goes the safe circuit for a lower cost, easier to manufacture 2-pin unit.
But, unlike the Woodstocks, the 2-pin version 82120A has a 6.4 volt zener diode across the battery so that should be the maximum voltage the calculator will ever see. The only problem with the design is that there is no series current limiting device. When the batteries begin to fail and no longer present a low impedance to the source, the zener diode alone provides the load. Yes, it prevents the calculator from frying but leave it on charge long enough and the diode will fail due to overheating. Ask me how I know... At least they short when they fail and you have a dead battery pack but the calculator survives.
Charging times for both versions are the same.
Edited: 21 Nov 2003, 8:41 p.m.
|