Hi All!
I hope this note finds all of you well & enjoying today!

In our home we have a battery powered stick vacuum broom gizmo. It is used perhaps once a month.
We run it until the motor slows noticeably, then put it on the charger for about 16 hours before unplugging it. But, when one of us decides to use it, the battery pack is depleted. I believe this is due to NiCad battery characteristic self-discharging.

I replaced the cells recently & have a question about proper charging procedure for a seldom used item. From my general on-line research, much conflicting information was read.

The cells are:
Quantity of (5) 2200 mAh 1.2 volt Nickel Cadmium sub-c cells wired in series.
The charger is:
9 volt DC 1t 150 mA. It is a plain "wall wart" looking charger. I do not believe it has any specific charge level sensing circuitry, as there are only two wires to the battery pack.

My best guess of how to properly treat these cells and still have the machine available when needed is to:
1) Run the machine until the motor slows noticeably, but not totally off.
2) Charge for about 16 hours
3) Then move the charger to a timer which will charge for 1 to 2 hours a day (In order to replace what depletes from the battery)

But, for convenience, will it be OK to simply leave the machine connected to the trickle charger constantly?

What do you all think is the best way to treat these cells?
Thank You For Helping & Educating!
Paul

 

But, for convenience, will it be OK to simply leave the machine connected to the trickle charger constantly?

As long as the trickle charge is 0.1C or less.
https://batteryuniversity.com/learn/article/charging_nickel_based_batteries

 

This is a pretty good read on the subject of charging NiCd batteries. You have 5 cells and a typical NiCd is about 1.2 volts so a 6.0 volt system. Here is what I see as a problem. NiCd batteries are typically charged at 1.55 Volts under temperature and current control. All covered in the link. THe problem is a 9.0 Volt wall wart which over time will just cook the batteries. Not unusual as most home appliances like vacuums, brooms and such that came with NiCd batteries came with a simple cheap wall wart charger. People just keep replacing batteries.

Ron

 

All of the above.
I have yet to find a working regimen that keeps NiCds in working order for a reasonable number of years.
However, here are the general guidelines.

1) Deplete NiCd battery energy before recharging in order to mitigate the memory effect.
2) Keep charging current below 1C.
3) Stop charging when full charge voltage is reached.
4) Monitor temperature while charging and discontinue charging if max temperature exceeded.
5) Trickle charge at 0.1C no more than 2 hours then disconnect from charger.
6) Trickle charge regularly to maintain battery voltage.

Caveat emptor: Take everything that I said with a grain of salt. If you wish to dispute any of the above, go ahead but it's no skin off my nose.

 

Thank You All for taking time to reply & to educate. The article was informative, and lead to further reading.
Since the charging current is ca. 0.68C we're safe in that respect. (Assuming the label on the charger is correct)

I'll try what you said MrChips and stop when the voltage is reached- monitoring temperature for the first few charge cycles.
Then, after use & a full charge, we will trickle charge for 2 hours or less periodically to maintain the charge.

I remembered that I replaced the cells in a screw-drill driver motor with cells from the same batch as the vacuum.
When I assembled the pack (8 cells @ 2200 mAh for 9.6 volts) I made a temporary slow charger at 0.005 c and charged it very slowly so the cells could equalize. Next I used it to near depletion & repeated.
Then I used it to near depletion and re-charged it with its normal charger (which has a voltage sensing circuit).
It has been sitting idle for about 7 months. I was surprised that the battery still provides good torque today. It seems that the cells didn't deplete themselves very much.

Thanks Again Everyone!
Paul