Ni-Cad vs Lithium batteries

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Robert Green wrote:

    If you can give me an estimate of the current drawn by screw driver, I can measure the battery voltage while drawing that current.
    Does the screw driver draw approximately 1/2, 1 or 2 AMPS while driving a screw (under load)? I can how much the 4.0 volts drops under load.
Thanks, Dave_s

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Unfortunately, I can't answer that question for you other than to say the batteries, when new, can power the motor continuously for at least two hours. It's just too hard to clip the motor and battery contacts in such a way that you can take a current reading.
I don't know whether this helps, but you can get the motor to run (slowly) even though one of the three cells is dead.
Put a bit inside the tip and twist it around a few times with a pair of vise-grips to make sure the red sliding collet lock isn't engaged and to break any "stiction" that has occurred from a long period of non-use.
My money's still on corroded contacts if the battery hasn't been left on charge for too long.
-- Bobby G.
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Robert Green wrote:

    If you can give me an estimate of the current drawn by screw driver, I can measure the battery voltage while drawing that current.
    Does the screw driver draw approximately 1/2, 1 or 2 AMPS while driving a screw (under load)? I can measure how much the 4.0 volts drops under load.
Thanks, Dave_s

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Bobby G. repair info has resulted in a Successful repair!!!!! After removing corrosion from internal contacts, the SKIL Driver now runs again. As Bobby predicted, the Battery Pack was still charged and OK.
Many Thanks, Dave_s
Dave_s wrote:

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All Right! Thanks for the report. Just make sure you don't overcharge that sucker because that WILL kill it for sure. We may not have solved the problem of the OP and his edger, but at least something good came out of this thread. Although I have not tried it yet, a friend suggested I coat the contacts with a thin film of vaseline next time I clean them to keep them from re-corroding. You'll probably have to reclean them in a year or so. )-: But at least you saved $ by not replacing a perfectly good pack.
Happy screwing! (I couldn't resist!)
-- Bobby G.
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<stuff snipped>

I have done that with the B&D Firestorm drill power packs, not the Skil. The drill is designed so that cutting the pack open and removing the batteries gives you a good platform to attach a 12V gel cell and doesn't change the balance of the drill much.
I suppose you could do the same with the Skil powerdriver, but it would make it pretty awkward to use.
I rebuilt the NiCad pack *once* only to discover that the center battery kept failing because it would overheat during charging. Instead of wasting my time rebuilding it again, I cut away the batteries, saved the good ones and attached the 12V gel cell to the remaining bottom plate of the old NiCad pack. Cost a lot less than buying a new pack (about 25% of the cost of a new pack) and have lasted way longer. I first used Velcro to attach the battery to the battery pack plate until one fell off and hit my foot. Now I strap them to the platform with large hose clamps. (-:
The design of the Firestorm battery pack (and many other drill packs that bury a cell inside ring of cells) is faulty so there was no point in continuing to try to rebuild packs that would only last through a few chargings. The drills come with fast chargers that really heat up the pack. I suspect a slow charger wouldn't kill the center cell as quickly because it would be able to shed charging heat a little better.
It's a great way to use up what's left of a UPS battery that's not really dead, but "rejected" by the UPS for being slightly too low in voltage. The Firestorms run on 9.6V but have a variable power trigger so you can run them from 12V without motor damage if you don't bear down all the way on the trigger switch.
-- Bobby G.
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Anthona wrote:

NiCads last for far more discharge cycles than other batteries and are more tolerant to high discharge currents and overcharging.
The problem is crystal growth. It reduces capacity and eventually shorts the cell. Leaving the cell on a charger causes the fastest growth. They also grow when a cell sits.
Once a month, exercising a cell by discharging it down to 1 V will dissolve crystals and increase life expectancy by about ten times. If it has been more than 3 months, slowly discharging from 1 V down to 0.6 V may help.
Having 15 cells in a sealed battery pack complicates maintenance.
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Re "dead" NiCds. There is a kill or cure it solution. As someone else said the problem is with whiskers of metallic cadmium inside the cells. The answer MIGHT be to "flash 2 the dud battery across an automobile battery. (ie a momentary connection) to blast the whiskers away. Sometimes it works (for a while anyway). You need to wrap the NiCd in a bundle of rag, they can burst open & ideally do it with a long wire (so you can be well clear). Afterwards try to charge as normal.
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Drain a Nicad pack and you can easily reverse a cells polarity and ruin the whole pack, 1.2v is considered discharged, I wonder if 1v is bad for a single cell V. I have 20 yr old packs that still get me some use and I never drain them past when the tool slows down or excersise them.
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wrote:

You can safely discharge a single cell NiCd down to zero. The problem is reverse charging a cell by discharging a multi-cell battery pack too far. Cell reversal is cause by mismatched capacity, so with perfectly matched cells one could discharge a multi-cell battery to zero safely but cells are never perfectly matched. It's generally safe to discharge a multi-cell battery down to about 1.1V or even 1.0V per cell. Limiting discharge to 1.2V/cell throws away a significant fraction of the useful capacity.
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That many cells, packed in a ring, are designed to fail because the internal cells can't dissipate the heat from charging as well as the outer ones and eventually fail quite prematurely. I have taken apart six Firestorm B&D battery packs that were carefully charged on a fast charger that dropped down to a trickle charge once the batteries were full. In each and every one, the center (tower)cells in the cluster were bad. And that was only a 9.6V drill.
Fortunately, it was very easy to cut the plastic battery case open, and instead of replacing the bad NiCads, (which are almost always tacked and not soldered together and I find a bitch to work with) I just mounted a holder made out of plastic and velcro straps for a 12V SLA gel cell battery and use them. You can get an SLA 12V 3AH battery pack that costs about $9 compared to B&D's insane price of $45 which is more than I paid for the new drill and two packs in a case with a fast charger.
I was able to preserve the locking mechanism on the original battery case so I could switch out my modified packs just as easily as I could the original NiCad. I also wired up the charger to a gel cell float charger and a DPDT switch so I could charge either type of battery.
It's almost as good as the original, it's much cheaper and much more powerful. The only issue is that it's a little more unwieldy than the original NiCad pack in really tight spaces. But it's always ready (gel cells hold their charge for a year) and it's always got plenty of power.
-- Bobby G.
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Anthona wrote:

If it has a cheap slow charger that doesn't tell you when it's charged and stop the charging itself, then after a couple hours when the battery appears charged, I put the charger on a timer so it charges 15 minutes every day. Works great for me, even on a crappy B&D batteries.
Don't do that every day for a fast charger, maybe a 15 minute charge every 2 weeks to 1 month. The worst things for NiCads are leaving them sit without being charged, using them until they are way too discharged or overcharging them. The memory problem is pretty much cured these days and using the tool until it starts to loose power is as low as they need to be before a full charge. This doesn't mean run them dead, run them low not dead.
I've read that lithium batteries prefer to be stored in a discharged state. That doesn't work so well with me unless I bought an extra battery on sale that I don't need to use yet. It would suck to have to charge a Li-Ion before each use!
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I have a Dewalt 12V drill which I bought so long ago I can hardly remember. I made sure that I discharged the ni-cad batteries all the way and I would only charge it a few hours before I needed it. It still works btw but the charge does not last long. There is nothing wrong with ni-cads imo you just have to be careful with them.
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