Hero999
Banned
I've heard about it before but I've never tried it and after seeing this website I decided to have a go myself.
**broken link removed**
I used an ordinary slow NiCad battery charger, it's pretty old so I'm not bothered if the battery leaks and makes a mess.
I tried a 9V alkaline battery that I was using to power a multimeter, it wasn't completely dead as it read 7.4V but it was weak enough for the battery warning symbol to show.
The charger uses half wave rectified DC and the name plate says it puts out 20mA. I tested the peak open circuit by connecting a capacitor to the output and measuring it with a DVM, to my surprise it measured in excess of 30V!
I connected the battery and left it to charge for 8 hours in a safe place. When I took it off charge it measured 11.4V, I was surprised it hadn't leaked. I left it for a day to settle down and it still measured 10V.
Now here's where the fun really started, I put it in my multimeter and it worked well but it displayed the battery warning symbol when I activated the backlight and it was very dim. I thought "oh well it's obviously gone high impedance" but after playing around with it for a few miniutes I noticed I could get the back light to turn on at full brightness without the battery warning symbol displaying. I turned the meter off and on and I noticed the same thing again, at first the low battery warning symbol would come on when I activated the backlight but after several activations the black light would work at full brightness without the battery warning symbol.
I thought "this is wierd" and I decided to investigate further by measuring the battery voltage with another meter whilst it was turned on. It turns out that when there wasn't much load on the battery it would read 9.6V, then when I turned the backlight on it would drop to <4V but I noticed that after a few activations the voltage under load would creap up to about 8.6V when the light is on, then after turning the meter on and off this would happen again. I tried short circuiting the battery with a screw driver tip and the same thing happened again.
What do you think is causing this?
Perhaps the battery is somehow over voltaging itself and the excess voltage must be drained from the battery before it will carry a load; it could be just one of the cells that's causing this but it doesn't make much sense.
Maybe if I had limited the charge voltage to 9.6V this would have never had happend.
**broken link removed**
I used an ordinary slow NiCad battery charger, it's pretty old so I'm not bothered if the battery leaks and makes a mess.
I tried a 9V alkaline battery that I was using to power a multimeter, it wasn't completely dead as it read 7.4V but it was weak enough for the battery warning symbol to show.
The charger uses half wave rectified DC and the name plate says it puts out 20mA. I tested the peak open circuit by connecting a capacitor to the output and measuring it with a DVM, to my surprise it measured in excess of 30V!
I connected the battery and left it to charge for 8 hours in a safe place. When I took it off charge it measured 11.4V, I was surprised it hadn't leaked. I left it for a day to settle down and it still measured 10V.
Now here's where the fun really started, I put it in my multimeter and it worked well but it displayed the battery warning symbol when I activated the backlight and it was very dim. I thought "oh well it's obviously gone high impedance" but after playing around with it for a few miniutes I noticed I could get the back light to turn on at full brightness without the battery warning symbol displaying. I turned the meter off and on and I noticed the same thing again, at first the low battery warning symbol would come on when I activated the backlight but after several activations the black light would work at full brightness without the battery warning symbol.
I thought "this is wierd" and I decided to investigate further by measuring the battery voltage with another meter whilst it was turned on. It turns out that when there wasn't much load on the battery it would read 9.6V, then when I turned the backlight on it would drop to <4V but I noticed that after a few activations the voltage under load would creap up to about 8.6V when the light is on, then after turning the meter on and off this would happen again. I tried short circuiting the battery with a screw driver tip and the same thing happened again.
What do you think is causing this?
Perhaps the battery is somehow over voltaging itself and the excess voltage must be drained from the battery before it will carry a load; it could be just one of the cells that's causing this but it doesn't make much sense.
Maybe if I had limited the charge voltage to 9.6V this would have never had happend.