Battery Charging Currents of Assorted HP-Calcs & Peripherals

[Sadsilence]

(02-12-2016 07:46 PM)Dieter Wrote:  In general I agree – especially if the charging circuit essentially consists of a simple resistor. ;-) But are you sure this also applies to the 82120A battery pack? It contains a PCB that is described here: There is a 78L12 voltage regulator and a resistor which should provide a (nearly) constant charging current. But I'm not at all an expert in electronics, so you or someone else may be able to say more about how constant the resulting charging current will be with this design. Please note the linked PDF at the bottom of the mentioned URL, here the last page says 16 mA.

On the other hand discussing about 1 mA more or less does not make much sense assuming components with ±5% or even ±10% tolerance... #-)

Fine. So let's make it 15 mA on average. ;-)

Dieter

Of course you are right. Around 15 mA is a perfect compromise ;-).

Just for info: Curcuit plan from that fabulous site tells the story. Current is limited by R1 resistor, which is given with 365 Ohm. So theoratical current depends on Battery voltage which increases during load time. Let assume a totally empty pack with 4V remains voltage. Icstart = (Usupply - Udiode - Ubatstart)/ R1 = (12V - 0.7V - 4V) / 365 Ohm = 20 mA. When completely loaded Ubat has around 1.5V/cell for NiCD and 1.6V/cell for NiMH, in total 6V or 6.4V. But battery voltage is limited by a 6.2V Zener diode. So worst case Icend = (Usupply - Udiode - Ubatend)/R1 = (12V-0.7V-6.2V)/365 Ohm = 14 mA. But as you mentioned. There are a lot of components with tolerances...

Best regards,

Werner