Large Scale Central

Ni-CD battery replacement with Ni-MH

Electronics
#1

Ok … I need someone thats a lot more savvy at this then I am…

Here’s the deal… I have a Dremel battery powered tool. Its got a 7.2Vdc removable clip in battery pack… 6 ea 1.2 V AA Ni-CD cells rated at 700mh. To recharge, the snap in battery pack is put into a charger base, that plugs into a standard wall outlet ( 110 AC US ). This pack is dying ( won’t hold a charge, short run time etc.) Time to replace it.

I can get Ni-MN AA cells with 1500mh rating w/tabs to replace the batteries, not difficult.

But… Will the charger work to re-charge the new NI-MN pack as is? If it can great… IF NOT, Then how would I go about re-charging the new pack? Or should I just go back to some higher mh NI-CDs? And would the charger handle the added load?

Thanks ahead of time…

Dave

#2

Dave,

The charger will work, but its insufficient; as NiCd chargers are not as sensitive as required to detect the peak of NiMH technology. Not to mention its likely anemic as in provides less than the desired current for a 1500mAh battery to properly charge. That said, your existing charger is likely a trickle only device…

I assume 700mAh Ni-Cd is not available? Larger capacity cells would likely work, but again they will charge at a lower than specified rate.

Perhaps purchasing a new charger that is capable of charging modern battery technologies would work for you, they can be had very reasonably IMO.

Michael

#3

That’s a pretty old tool if it is using ni-cads. Maybe its time for a tool tool. You can get a small Dremel 7700 kit for about $45.00 that comes with Li-ion batteries and a charger. Just a thought.

#4

That’s a pretty old tool if it is using ni-cads. Maybe its time for a tool tool. You can get a small Dremel 7700 kit for about $45.00 that comes with Li-ion batteries and a charger. Just a thought.

#5

@Paul… Thanks for the reply… It is a 7700 03 model. Ni-CDs… Replacement packs are listed as NI-CD 700mh…

@ Michael… So a Replacement build of 1000mh battery pack would recharge with the plugged into charger, only it would take longer to re-charge… Correct? This is a encased Snap in pack… I have a high end charger for loose batteries.

Your thoughts?

#6

Dave

If it were I, I’d use the 1000mAh cells mentioned and trickle charge the battery as usual with an occasional topping charge with a NiMH peak charger. Are you able to ascertain the charge value of the existing wall wart/charger power supply? Looks like current NiMH cells can trickle charge at less than 0.1C of rated capacity. Does your charger support NiMH peak charging?

NiMH cells benefit from an initial charge regimen coined as a form charge. Basically peak charge and discharge fully for at least three complete cycles, each discharge will garner higher discharge current totals until such time you realize the rated capacity of said cells.

Michael

#7

@ Michael… The charger that the pack drops into is rated

INPUT: AC 120V 60Hz 6W

OUTPUT: DC 9V 0.20A

This Dremel pack charger will not take loose cells, only the battery pack…

I’m leaning to using 1000mh NiCd replacement cells w/tabs. Should do the job, just take longer to charge to 1000mh cells?

Stop me if this is wrong thinking.

Dave

#8

Dave,

Yes, I’d go with the 1000mAh Ni-Cd cells. The charger @ .20A will be fine. I’d limit charge cycles to 24 hours or so. That said if possible an occasional topping charge with a peak charger is highly recommended IMO.

Michael

#9

1000mh NiCd it is…

Thanks Guys… I can always count on LSC to keep me from looking too stupid…

Dave