my battery has died and no longer accepts a chrage. any ideas? i have read about and tried the deep freeze, thaw , charge thing and it did not work for me. can anyone tell me which terminals are postive and negative? i have also heard of "jump starting " the batteries by applying a short current across the terminals. it worked just fine until a few days ago
If you need your drill to be reliable, eg for your business, forget about trying to revive the battery pack. Even if you manage to get it to take a charge, it is likely worn out and will give poor running times and poor charge retention. Once one or more cells become weak, when a load is placed across the battery, ie your drill, the weakest cells take a reverse charge from the stronger cells which causes permanent damage to them. A DeWalt drill is likely to draw several Amps, and this high current reverse charge will kill cells very quickly indeed.
My advice is to buy a new pack, or if you are handy you could probably repack the old one with new and possibly higher capacity cells, which may or may not work out cheaper. Bear in mind all cells must be changed together, it's no good just replacing the obviously weak ones.
A common way of trying to get individual cells to take a charge after they have developed an internal short is to pass a substantial current through them to 'blow' the short. It can work but IME it is a short term measure at best. Just attaching a large current source across its terminals to zap shorts won't work, the shorted cell(s) have to be identified and zapped individually. I have used large capacitors charged from a bench power supply in the past to zap shorts, usually upwards of 2200uF, the bigger the cap the bigger the current pulse. However, too large a capacitor could cause the cell to fail completely or even explode.
You certainly shouldn't zap the entire battery by shorting it out- this will likely make things very much worse or even cause cells to explode.
Dave
Just to add to my last post- you might want to check that the internal thermal/current cutout inside the battery pack hasn't failed open circuit. If you are getting no reponse from the battery at all, ie drill not turning at all, zero volts across the battery terminal, that is a possible cause, and rather cheaper/easier to fix than failed cells. Bad cells would usually give increasingly poor performance up until its failure. The fact that it seems to have suddenly stopped working implies a component failure either inside the battery, the charger or the drill itself, rather than bad cells, but without further info I can't really speculate further.
Does the charge light (if any) come on when you try to charge the battery?
Dave
Agreed, a couple of bad cells will cause the max speed of the drill to be lower, but will not reduce the total running time all that much. It sounds like most of the cels have developed a short, or the protection device has opened so that no charging current is ever reaching the cells. The problem in the second case is that over time, most discharged NICAD cells will develop shorts when not on charge, whichj is why it is good to periodically recharge all NICDs, just to prevenbt shorts from developing.
The trick of blasting open the cells is one I learned at Bell Labs 45 years ago when we were experimenting with NICADs to power remote line equipment. Those old-days cells had a fracion of the capacity of current NICADS, but they were much less prone to shorting as they used thicker spacing between the plates. Technology wasn't as advanced, but the old cells lasted forever compared to the life of the newer cells available today.
H. R.(Bob) Hofmann
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