Recommanded NiMh battery cells for HP82162A

[Dieter]

(09-25-2017 10:48 AM)Neve Wrote:  Where do you get your 12V and your other figures? The charger is supposed to be delivering 8VAC (at least that’s what written on it). Although mine does deliver 12VAC!

The "charger" (actually a simple AC-adapter) provides about 8 V under full load at 375 mA, but significantly more with no or no substantial load applied, like in our case (we are talking about ~20 mA here). So an open circuit voltage of 12 V or even more is normal. This has been discussed several times here, even back in 1999.

Edit: I just found a 2011 post by myself, saying that both of my 82066B provide 11,5 V AC with no load. Others have reported values between 11 and 12,5 V, so your 12 Volts are perfectly OK.

Take a look at the circuit diagram. The input provided by the 82059/82066 is first rectified by the four diodes D1...D4. Assuming 12 V AC, due to C1 the output should be somewhere near 16 V DC or a bit more (√2 · 12V). This is fed to a 78L12 regulator which delivers exactly 12 V. Diode D6 reduces this by approx. 0,7 V. So the voltage between the 78L12's output and GND is 0,7 V + the voltage across R1 + Vbat (or the Zener, if the battery is not connected). This leads to 11,3 V – Vbat for R1. If we assume a battery voltage of 5,3 V during charge this means about 6 V across R1 and thus 6 V / 365 Ohm ≈ 16 mA charging current. Or, as Sadsilence already said, near 20 mA for a completely empty pack and about 15 mA as it approaches full charge.

But... if you have opened the pack and installed new NiMH cells, why don't you just use your meter and see what you get ?-) You could directly measure the input voltage of the 78L12, confirm its output to be exactly 12 V, and you could measure the voltage across R1 as well as the actual charging current.

Dieter