Drill Charging.

[mhannah]

I found an old 'Power Devil' cordless drill/driver at the back of my cupboard yesterday.

The reason that it got to the back of the cupboard is that the battery does not hold a charge for very long...a few days at the most. So, the battery is always flat when I need it.

Since another drill/driver is always really usefull to have (even if it is a cheapo!) I was thinking about leaving the battery plugged into the charger via one of those mechanical timers that you use to turn your table lamps on and off when you're away on holiday, to fool the burglars.
That way I could let it charge for an hour each day, hopefully resulting it being juiced up and ready to go when I next need it.

What do folk think?

Thanks,
Mark.

 

[Charley]

Good idea Mark. In theory it should work, just depends how quickly the battery lasts while in use.

 

[Aragorn]

Only problem I can think of is that rechargeable batteries like to be completey discharged before you recharge them. This way they keep a better charge and you get more life out of them. If you're "topping" it up for an hour everyday you may find that it doesn't hold a good enough charge to get through even the smallest task with any torque, especially being a Power Devil. :wink:

 

[Adam]

Hmm, I'm not sure about this, some rechargable batteries should be run down completely before charging, otherwise they start to loose capacity. Most DIY drills etc suffer from this caused by them being used infrequently, but charged too frequenctly.
You could try and restore some of its capability by putting a resistor across the battery and discharging it completely. Some one I know at work has been using the same drill for 20 years, and completely discharges the battery between uses.

I clipped this from the internet - this phenomenon is frequenctly called the "memory-effect" but it's a bit of a myth

The NiCd memory effect business is an urban myth, but it still keeps coming up. In summary, if you overcharge a NiCd battery, it develops a voltage depression which makes the battery appear to go flat earlier than you would expect. Since the discharge curve is so steep, sensitive devices which rely on battery voltage to detect when it is almost flat, will report that it is almost flat early due to the voltage depression, when in fact the cell still has significant charge. The voltage depression can be rectified by discharging the cell to its full discharge level.

Many people misinterpret this phenomemon and conclude that the battery somehow remebers its last discharge level on the next charging cycle. This is not the case. The only effect that the current charge level has on the next charging cycle is that it's much easier to overcharge a NiCd cell whose current charge state is unknown, than it is to overcharge one which is known to be flat.

The so-called "memory effect" is a simple case of user error in overcharging the cell. If you don't ever overcharge a NiCd cell, there's no need to discharge it before recharging it again.

 

[Adam]

Ah, Aragorn beat me too it!

Adam

 

[mhannah]

So, how would one go about dis-charging with a resistor?

What value would be suitable?
10Mohms?

How long would the discharge take?

Thanks,
Mark.

 

[Aragorn]

You can discharge by running the machine! Hold the trigger down with some tape and just leave it somewhere safe.
Once it's flat, up the trigger, wait for a while and do it again. Repeat once or twice more until there's no power left.

 

[Anonymous]

It's in that state every time I pick it up!

Mark.

 

[Aragorn]

Hmmm :? :? :?
Perhaps it's time for a new drill! :roll:

 

[Midnight]

you ummmmmmm... could buy a replacement battery....

 

[Aragorn]

Mike -- this is an excellent opportunity for a new tool. Can't pass these things up. :wink:

 

[DaveL]

This site http://www.eurobatteries.com does replacement batteries, my brother inlaw had one of his 20 year old Makita drill batteries re-celled by them. Cost £25 and the drill is like new again. Power devil are not listed but it may be worth calling or emailing them.

 

[Anonymous]

Only problem I can think of is that rechargeable batteries like to be completey discharged before you recharge them. This way they keep a better charge and you get more life out of them. If you're "topping" it up for an hour everyday you may find that it doesn't hold a good enough charge to get through even the smallest task with any torque, especially being a Power Devil. :wink:

This is true for NiCads but not for Lithium Ion or Nickel Metal Hydrid

Cheaper tools use Nicad

We use Nicads at work and the 'memory effect' is clearly exhibited there.

 

[Signal]

Power devil do replacment batteries for about 20 quid,

but seings as you could get a new power devil or equivelent for that is it really worth the hassle?

Signal

 

[Bean]

Getting the Battery Re-Celled sound like a good idea, with the capacity of rechargables going up all the time.....I recently purchased some 2.3A 'AA' cells :shock: So you could increase the usable time of the power tool by increasing the capacity of the battery.

Ohh I wouuld also look at changing the cells to NiMH's as well.

Bean