Abandoned_Trolley wrote:
=======================

Out of interest, you may like to note that I have a couple of Uniross
NiCD PP3 cells, which must be at least 10 years old, but seem to still
work ok - the downside is that the capacity is only 120mAH, but thats
enough for a few hours service on wireless microphone system.


** The only common application for 9V batts I know of which has both high discharge ( ie 50mA) AND regular use is a radio mic.
I doubt the OP has any of them.....

What else are are high capacity , rechargeable 9V batts good for?

The self discharge rate ruins them for most jobs.

Well, I have a couple of wireless guitar belt pack things, but I guess
they must use the same sort of technology as wireless microphones ?

** Of course, just no actual mic capsule.

The spec for the Trantec model I have quotes a battery drain of 50mA -
so you were spot on with your figure.


** I have dealt with a few of the beasts .....

A while ago I bought a new battery operated doorbell - one of those
"ding dong - Avon calling" things, which has a single solenoid which
moves out to hit one chime and then gets the other one on the way back.

I was astonished to see that its powered by a 9v battery, and yet more
astonished when I discovered that the 120mAH NiCD will deliver the surge
current required to shift the thing, whereas a 300mAH NiMH will simply
not do the job. I have tried this out with 3 different NiCDs and a
couple of the NiMH cells and the results are consistent.

** What a POS design !

A fresh 9V alkaline will deliver about 8 amps into a short as will a NiMh.

Have you tried adding a 2,200uF 10V cap in parallel with the batt?
Good for about 0.1 Joules


Out of curiosity I am going to try out with Li-ion cells to see if the
story is any different. Maybe theres more to this lark than meets the
eye, and its not just about capacity.

** Some items draw very high currents, small digital cameras for example.
Alkaline AAs give poor life times, NiMh are far better - but need regular topping up.
Same goes for camera flash guns using AAs.


...... Phil