Recondition cordless batteries?

Agreed that you should replace all the cells at one time for reduced effort. The 2600 mha batteries are physically a bit larger than the

-Red

Based on my one experience, a complete discharge is not advisable.

-- Oren

"I don't have anything against work. I just figure, why deprive somebody who really loves it."

As I understand it, if you're going to discharge this way, you want to stop discharge just as the voltage across *the lowest cell* is around

snipped-for-privacy@nortelnetworks.com (Chris Lewis) wrote in news: snipped-for-privacy@corp.supernews.com:

Good way to start a fire. NiCds can source a LOT of current in a short time. NiMH too.

On the outside of the pack? Or do you have to open it up first?

the DeWalts I've seen have the same flat contacts as other brands,that prevent accidental shorting

:Dan_Musicant wrote in :news: snipped-for-privacy@4ax.com: : :> On 22 Apr 2007 10:37:27 -0700, Red wrote: :> :>:On Apr 22, 10:44 am, Dan_Musicant wrote: :>: :>:>

:>:> I wish there was a way (I'm sure there is) that I could discharge :>:> them without using the motor, but maybe it's not a problem. If I :>:> knew how, I would build a discharge device, but my electronics savvy :>:> isn't great. I'm cross posting this post to :>:> sci.chem.electrochem.battery in hopes for some expert advice. :) :>: :>:There is. Solder a short pair of leads with alligator clips to a 12v :>:light bulb and clip it across the battery leads. Use a smaller bulb, :>:like a dome light, parking light, or tail light. :>: :>:Red :>: :>: :> Hey, that's a smart idea. It would need to be a DC lamp, I suppose, :> and most auto lights would probably work, I'd think. Thanks. :> : :Incandescent lamps don't care whether it's DC or AC applied to them. :I have a 12W,12V auto bulb that's used in a Tensor hi-intensity lamp that :applies AC volts to it,works just the same.

Good to know. I have a couple of tensor lamps. Thanks!

Dan

:On 23 Apr 2007 14:47:05 -0700, Red wrote: : :>On Apr 23, 4:05 pm, Oren wrote: :>

:>> >As I understand it, if you're going to discharge this way, you want :>> >to stop discharge just as the voltage across each cell is around :>> >1V. Which for an 18V battery is 15V. The lamp should be noticably :>> >dimmer at that point. :>>

:>> So leaving the flash light switched on over night is not best... no :>> lamp flicker, light, nada...too much drain on the battery? :>>

:>I've heard that if you completely discharge a battery it is "possible" :>that it can recharge with a reverse polarity. May be possible with a :>single cell, but I don't think that is possible in a battery pack. :>There may be other new reasons for not completely discharging battery :>packs, but that used to be the way to prevent ni-cad memory problems. :>-Red : :Based on my one experience, a complete discharge is not advisable.

I believe it is possible to reverse polarize one of the cells in a battery pack such as a cordless drill's. I seem to have read that in a post somewhere. Anyway, the manuals for the tools always seem to counsel not draining the pack too far before recharging. It's always possible that one of the cells is a lot weaker than the average and that would cause trouble. It's something that would be hard to know unless you could disassemble the cell pack, which I'm not about to do.

I haven't gotten too far in my experiment (busy today), but will get back at it tomorrow and this time keep careful records and try to determine if I'm making real progress in reconditioning my 4 cordless battery packs.

I don't think I'll bother using a slow discharge method this time. The batteries don't seem to be getting very hot while I drain them by having the drills set on low and rubber bands around the switch. I'm careful not to have the switch partially depressed. The Dewalt's instructions actually said it was bad for the drill to use very slow speed. I have no idea why. The drill itself seems to be getting a lot hotter during discharge than the battery pack, but not alarmingly so.

Dan

:Chris Lewis wrote: :> As I understand it, if you're going to discharge this way, you want :> to stop discharge just as the voltage across each cell is around :> 1V. : :As I understand it, if you're going to discharge this way, you want :to stop discharge just as the voltage across *the lowest cell* is around :1V. By the time you discharge until the average cell is around 1V, or :until the pack voltage is about 1V per cell, or worse, until all cells :but one are below 1V, chances are good that you will be able to measure :reversed polarity across the weakest cells. That's an indication that :those cells are no longer cells.

I agree.

Sure they would fit. At least well enough. Very little difference in size and so what if the case doesn't close properly. The battery pack just hangs there, it is not important that it have any structural integrity. The diameter is the same, but the length is different and altho a tight fit, mine fit and the case screwed together just fine.

I went ahead and bought some NiMh 3300 mah batteries for the next device I have in the house that craps out so am anxious for something else to fail. I may go find that hand vacuum I tossed in the garage.

According to Jim Yanik :

I wasn't referring to putting a single wire across the contacts, tho, I can see how it could be read that way.

Oops.

I was trying to say that the ends of the wires connected to the load (eg: lightbulb) can be taped to the contacts, and it will be good enough for a couple of hours of discharge as long as you don't yank on anything. Or rubber bands.

Outside.

Take a look at the 12V versions. There's a rectangular opening in the upper end of the battery housing. Inside the opening, there's two male spade lugs separated by a plastic divider. When you drop the battery into the charger or tool, the spade lugs go into a split female connectors.

You could just about plug those lugs into female automotive spade connectors. Perhaps slightly more heavy duty ones.

It's easy to connect to the lugs with alligator clips.

No, that's a *really bad* idea, unless you continuously watch the bulb and disconnect it when it starts to get dim.

The problem is that the cells in the battery pack are in series, and some are always stronger (higher capacity) than others. When you discharge the battery into a load, one of the cells always goes dead first, while the rest still have some energy left. If the load remains connected, current keeps flowing, and the weak cell starts *charging in reverse polarity*. That will soon permanently damage it.

In normal use, you hear the drop in motor speed caused by that first cell's voltage suddenly dropping, and you switch battery packs. Automated battery cyclers also shut off when the voltage drops to a preset level. But the 12 V light bulb won't stop until the net voltage across the battery pack is zero, and that doesn't happen until one or more cells are already reverse charged.

You can safely discharge *one single cell* with a light bulb or a resistor, but not a battery consisting of several series-connected cells.

The usual "safe stopping point" voltage is 1 V per cell. A 12 V battery is actually 10 cells of 1.2 V each, so it can safely be drained until the voltage drops to 10 V. For 9.6 V battery, stop at 8 V, and so on.

Dave

As I understand it, you can safely discharge NiCd down to zero volts, but no further. If you had some way of measuring each cell's voltage individually in a battery pack, you could discharge the pack until one cell reached 0 V. But you generally can't do this, so the "1 V per cell" rule of thumb is an approximate way of finding a point where one cell's voltage is diving fast.

For example, a 4-cell pack is 4.8 V (4 * 1.2 V) nominal. When its voltage drops to 4 V, there are *probably* still 3 cells putting out almost 1.2 V, while the weak cell has dropped to 0.4 V. Time to stop discharging.

Unfortunately, this doesn't work so well with larger packs. When a

Also, NiMH cells don't like being taken all the way to 0 V.

Dave

I've had exactly zero luck with any cell that ever went as low as 0.8V for more than a second or two. I've read articles by others who've had the same experience you claim, but I've been completely and utterly unable to duplicate it under any circumstances.

Safest way I've found with packs is to watch for a sudden small drop in voltage. When the weakest cell gives way, it'll drop from 1.1V or thereabouts over a few seconds to less than a volt. That'd take the

Amen! Been there, done that.

As I read the literature, good multiple cell batteries are made up from uniform cells all from the same production batch. Then you hope they stay uniform. Best to quit using the battery as soon as you detect a slowing speed. But my wife would take a half discharged device and run it till it stopped. Hard to recover from that.

I now keep small appliances like hand vacs and grass clippers on chargers modified to trickle charge (added resistance). For frequently used tools, the slow charge might not be at all convenient but for occasional use devices, the resulting full charge adds a large margin of safety. My old Dustbuster has 10-year old cells used this way and still does its job.

SJF

"SJF" wrote in news:jfm1i.12116$% snipped-for-privacy@newsfe07.phx:

the cells in the Dustbuster are designed to be left on charge continuously. digi-Key sell s NiCd cells expressly designed for continuous charge. And the transformer already trickle-charges the cells.(C/10 rate)

My first DB pack lasted 10 yrs,then had the pack replaced at a Dewalt service center.