Cordless Tool Battery Charging Question

My wife & I each have coldless drills, which we use intermitently for household repairs & projects. The only way to make sure we have a charged
battery handy for emergencies is to leave one in the chargers. Even though these are reasonably high quality chargers (Ryobi & DeWalt), I'm sure we are shortening the life of the batteries.
It occured to me that one option might be to put the chargers on a timer, so that they are on for half an hour a day. That should top them off, without cooking them. The catch is that I'm not sure what sort of load the charger presents when it is off. I could just end up discharging the battery through (at a minimum) diode leakage. As long as the leakage is low, that might actually be OK, or it could produce a nasty memory effect in the NiCd's.
Any thoughts or comments?
Thanks!
Doug White
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Doug White wrote:

The DeWalt chargers I've used automatically go to a float or maintain charge state when the battery is fully charged , and I suspect most others do too . I found that completely discharging NiCad batteries between chargings was the best way to prevent a less-than-full-charge memory situation . I've had DeWalt batteries last up to 5 years while coworkers that recharged as soon as the drill slowed usually got less than a year ...
--
Snag
"90 FLHTCU "Strider"
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The battery in my DeWalt charger stays noticeably warm, so _something_ is going on, even when it fully charged. The charger is about 5 or 6 years old, so maybe the newer ones are better.
There also seems to be a lot of disagreement about discharge levels. If you only discharge it a little, you can get memory issues, but if you discharge it too much, you can end up reverse charging a cell, which definitely wrecks the battery.
Doug White
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I'd go with running them flat before storing them - they seem to whisker (and go short circuit) if you leave them to the notorious self-discharge.
In the black & Decker drills, 1 or more shorted cells burns out the current limiting resistor in the charger.
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wrote:

The instructions for my Black and Decker 24 volts lawnmower advise to leave the charger plugged in when the mower is not in used. I leave it in all winter also.
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I thought most of the mowers wre lead acid, but I'm not sure.
Doug White
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You are correct, That does make a different. I haven't open this one but my older one was open and it is a sealed acid battery
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You are correct, That does make a different. I haven't open this one but my older one was open and it is a sealed acid battery
You'd probably be better off taking the SLA battery out and leaving it on an Optimate over winter, if it's 6V Honda do a similar charger with switchable voltage.
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wrote:

Read The Friendly Manual for the tool.
The daily hour works for some things, the ones that use a fixed rate trickle charge at all times, and then it tapers off to a maintenance charge at full voltage. I use it for a lot of my small tools that I never know when I'll need it in a hurry, like the combustible gas detector.
But the high rate chargers for tool batteries, probably not such a good idea - they try to do a full fast-charge cycle that is current limited (note that the battery gets hot, they sense that as to when they're "cooked") and only switch full-off or to trickle after that.
You'll be forcing a full charge on an almost-full battery every day with the daily timer setup.
If it switches to trickle automatically, LEAVE IT PLUGGED IN. The cost of the power for a "vampire load" of the trickle charge is far less than the cost of a new battery pack - killed by cooking the battery with an unnecessary charge cycle every day. Mine are $90 each. (Dewalt 18V XLR)
I need to set up a second plugstrip with a Skipper-Dial timer to charge things like that without a trickle function, so it only comes on once a week.
--<< Bruce >>--
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The best scheme I've found for long term float charging is temperature controlled.
Set the limit no higher than 40C.
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<snip>
Reading this thread I though I should look at my two chargers. I used the Kill-a-watt to measure current (yes, I know it is on the "wrong" side) and a IR thermometer to measure the battery housing temp. Here are the results. I hope the table posts OK.
Hitachi NiCd 14.4V (EB1414S) - 4 years old. Pretty much useless due to high rate of self discharge which developed about 6 months after purchase. Can be used if charged just before the job:
Charger Current Temp Ambient temp
No battery 0.05A
Start 0.71A
15min 0.81A
fullcharge 0.06A 36C 12C
1h50min 0.07A 29C
3h15min 0.07A 22C
7h05min 0.06A 19C
19h21min 0.07A 19C 9C
21h14min 0.07A 18C 10C
Mastercraft NiCd 18V 54-3064-2 - 4years old. Both batteries still going strong
No battery 0.03A 11C 9C
start 0.16A
1hr 0.1A 13C 13C
1h40min (full charge) 0.04A 19C 13C
2h53min 0.04A 14C 13C
4h53min 0.04A 15C 14C
disconnect 0.03A
Clearly there are many limitations to these observations but the trend would suggest that the Hitachi fast charger cooked the batteries - the battery never reached the ambient temperature while still in the charger. Note that I never left the batteries in the charger, stored them discharged and in the coldest room in the house.
It also suggests that the cheaper technology is not always inferior. One thing to look at when buying IMHO is to look at the battery warranty. The Hitachis were only 90 days! With good reason! Some companies now offer 10 year and even "life-time" warranties, presumably if used with their (more intelligent) chargers.
--
Michael Koblic,
Campbell River, BC
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Doug White wrote:

I have 12v and 9.6v Ryobi drills. The instructions say to avoid over charging. But the charger doesn't indicate anything but On and Dead Cell. Leaving the battery in the charger will kill it rapidly.
The Timer idea might work. I've thought to try it myself, but haven't yet.
--

Richard Lamb
http://www.home.earthlink.net/~cavelamb /
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Check out what Bruce Bergman said below. He's right. I know for a fact - because I own both a Ryobi and a Dewalt set - that the chargers will not overcharge or "dry out" a battery if left on charge. The DeWalt I have switches to a trickle when the thermostat in the battery kicks out. The Ryobi just turns off; and I've never seen it turn back on except during a power failure/restore situation. The worst thing you can do is re-charge an almost-full battery over and over. You'll just evaporate the electrolyte eventually, because they only stop charging after a certain temperature (determined by a thermostat IN the battery) is reached, declaring them fully charged. (BTW... that's why there are three terminals on the batteries instead of two. A "smart" peak-charger wouldn't need that third "thermostat" link.)
LLoyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in

Both the Ryobi & the Dewalt _I_ have keep the batteries warm. Both units never turn off. If they are trickle charging the batteries, they are doing it at a current level high enough to raise the battery temperature considerably above ambient.
These may be older or cheaper chargers than what you have. I'll have to double check the manuals, but I believe both tell you not to leave the batteries in the charger. That's fine as long as you use the tool often enough that the batteries don't self discharge. That is often not the case for us.
Doug White
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Generally, as long as the battery pack doesn't get hot, the charger probably isn't causing any damage to the cells.
When the charge is completed, if the battery pack was warm, it should cool down to ambient after it's been on a trickle charge rate/cycle for a while. If the battery remains much warmer than ambient while trickle charging (an hour after a full charging cycle), the trickle current is probably a bit excessive. Trouble is, ya can't do much about it, as far as modifying most sophisticated chargers.
The trickle charge level only needs to be high enough to cancel/eliminate the self-discharge rate of the cells (both NICAD and NIMH), although some new NIMH cells claim to have zero or very low self-discharge rates.
See the Maintenance Charge section http://www.ka7oei.com/nicds.html
There are many different grades of high quality cells, and some are designed to withstand a constant, but reduced charging current, rapid charging and/or rapid discharging. Trouble is, ya don't know for sure which grade of cells are in a battery pack unless you selected and installed them yourself from a quality manufacurer such as Panasonic or Sanyo. Some high quality cells can cost over $24 per cell (1.2V per cell x 10 cells for a 12V pack), so you can understand why so many folks experience rechargeable battery problems.
Poorly designed chargers and low grade cells result in short battery pack lifetimes, even if the batteries are neglected and/or abused. Trouble is, when most cells get weak, there isn't any way to rejuvenate them, so replacement is the only practical option to fully restore the battery pack's capacity. Since many new battery packs cost almost as much as a brand new tool with new batteries, landfills continue to fill up with discarded tools, and groundwater-contaminating/poisoning battery packs. Some chemistries of battery packs, such as cell phone and laptop batteries can be restored with the proper, really expensive equipment (Cadex).
Most consumers don't have any way to gauge the condition of their battery packs. Most battery tester/checkers with a meter, or a few LEDs don't show the condition of the internal cells. Batteries that test good on these types of testers can go dead in a matter of seconds.
Some chargers made for the Remote Control hobby users are somewhat sophisticated, in being able to show mAh capacity during a controlled discharge. Some models allow the user to select charging rates, etc. I have one model that does these functions, the MRC Super Brain 977. There are more advanced analyzers that connect to a PC and plot charging and discharging rates.
Rebuilding battery packs isn't complicated for handy-type users with soldering skills, if they're willing to buy good cells with tabs, to avoid soldering directly to the cell terminals. There are usually several nearby places where bad cells can be dropped off, so they can be recycled or disposed of properly (incinerated?).
Many universal chargers switch from the charge rate, to a trickle rate when a delta/volt level is sensed, so many models can be used for NICAD or NIMH.
There is always the possibility that battery packs can be overcharged or undercharged, and most users won't know.
--
WB
.........


"Doug White" < snipped-for-privacy@alum.mit.edu> wrote in message
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Wild_Bill wrote:

I had my 9.6 volt packs rebuilt by Interstate batteries. They did it while I watched and the price was quite reasonable.
But the charger is still the brute simple Ryobi thing. HAVE to watch the times.
--

Richard Lamb
http://www.home.earthlink.net/~cavelamb /
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