Charging a NiCd battery pack

Do what I do. Stick an analog meter in series and charge at a reasonable rate while watching the current.

Does it have to be analog? Can I use digital? I only have digital meters.

Will putting a digital meter on the + and - output of the power supply and setting the meter for the correct DC range read the current being supplied from the power supply? Or do I have to have a load on as well? I would think the latter since the current has be being drawn by a load yes? (i know next to nothing about electronics/electricity as you can see)

b.

Sure, but some DMMs turn off after a period.

No. You need to put the meter in series to read current. And you'll need a little more voltage with a DMM because they usually drop more volts than an analog meter.

from another poster here.

NiCd batteries should be charged at constant current (approx). Set your power supply to about 18 volts and 150mA checking the latter with your meter in series with the battery. Using the C/10 rate will recharge the cells in about 14 hours and no damage will be done if you charge for longer so no need to stay up all night watching the meter!

IF you want to charge quicker then by all means raise the current but DONT leave it charging for more than 2Ahrs or use more than 500mA otherwise the cells could overheat.

Bob

NiCad cells are best charged at constant current. It might be possible to use the current limit on your bench supply but on some it's only intended as a safety feature and it will overheat if used in limiting mode for very long.

You could try...

Setting the current limit on the bench supply to 0.3-0.5A then connect the battery and increase the voltage until the current limit just kicks in. Look for signs that the supply is running too hot. If you see the current fall increase the voltage slighty to keep the supply just in current limiting mode. Monitor the battery temperature and stop charging when it starts to warm up. If you know it's flat then just stop charging after the required ammount of time. Do not leave it on charge overnight.

analog meters typically cost less to run.

stick it in series with the batteries. use the 10A range.

without the load the meter onb the amps scale behaves like a short circuit and something will possibly be damaged.

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Bye.
   Jasen

I tried this. I put the meter between the + output of the power supply and the battery and the DMM read nothing. I also tried connecting the device to the power supply with the DMM between the + of the power supply and the + of the device and turned on the device. The device didn't work and the DMM read nothing. The device works on the power supply without the DMM in series.

I also tried putting the DMM between a charged battery and the device so that the DMM was between the + terminal of the battery and the device and again the device didn't work an the DMM read 0 while the device was on.

I feel like I am missing something fundamental.

b.

Did you switch the DMM to a current range AND plug the probe into the current socket on the DMM?

Sure did.

Black lead to COM, red lead to the non-10A input.

Set the DMM to read DC current (in the range labeled with an "A" with a solid and dashed line above it) on the "200m" setting (200 milli-apms IIUC).

Now wait. I just tried the red lead in the 10A plug and setting the

10A selector on the DMM and when I set the bench supply to .15 (amps) I do read 0.15 on the DMM. I wonder why it reads 0.00 with the red lead in the (up to 200mA) socket and the 200m selected on the DMM but fine in the 10A plug. Strange.

Looks like I am charging now. I'm assuming the DMM continues to conduct the current when it's switched off.

Not an assumption I would make although it may be true. That's why I prefer an analog meter for this.

Sounds like you blew the fuse in the meter's 200mA input circuit.

--
Peter Bennett VE7CEI 
email: peterbb4 (at) interchange.ubc.ca        
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Very easy to do. Set it up to measure the voltage of a power source then switch it a current range. Been there done that.