I've a Skil Mod 2375 3/8" cordless drill (9.6v) thats nearly an antique.
The old wall wart outputs dc 11v, 250 mA when functional. It now has a slight bulge and outputs 0v.
I rumble thru my box of WW's, find one at rated output of dc 12v, 300 mA, splice the wires, plug it in to see if it will charge. It will, but it heats up a bunch, enough to burn my fingers a little.
Are there any guidelines for substituting these things? I'd like to keep the drill, but can hardly afford to burn the house down. :-)
Thx, P
"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
To charge a 9.6V battery (which would be eight 1.2V NiCd sub-C cells in series) I'd consider 150 mA for eight hours. So, connect a series resistor to the 12V supply that chokes the charge current down to that level (measure with ammeter into a part-charged battery).
The purpose here is to DEFEAT THE REGULATION of that 12V power supply, it oughtn't drive its maximum current just because its load is intended to be 9.6V instead of 12V...
At a guess, the original power was unfiltered but rectified, and the replacement is rectified, filtered, and regulated. The filtering doesn't hurt, but that voltage regulation is your enemy here.
**Agreed with the above, but for a few cents more, you could use an LM317 as a current source (see the Natsemi application notes), set for the appropriate current. You may need an unregulated 12 Volt wall wart, or, perhaps, a 15 Volt one.
The reply from whit is a good suggestion, but I suspect that the cells in the drill are shorted, which will damage a charging power supply. It seems that the old supply became overheated and failed, which will happen if the cells are shorted. I believe this is the reason for the substitute wall wart getting hot.
To find out if the cells are shorted, the cells need to be accessed, and individually checked with an ohm meter or an instrument capable of measuring battery cell impedance or ESR. Also, a reading for individual cells with voltmeter reading of zero volts generally indicates shorted cells.
Replacing all of the cells is the most effective solution, and cells with tabs can be soldered together in the original order, and restore full (or even better) operation of the drill (or most cordless tools).
If you have the ability to make good solder connections, replacement is usually less costly than paying someone else to do the work.
There are numerous online sellers with reasonable prices for replacement cells.
I shoulda mentioned, I'm not an electronics guy, just a tinker. Limited (make that -very- limited) skills, eqpt.
I might've charged with the new supply 20 min. before I noticed the heat. The drill worked a little thereafter.
The drill still works a little. I measure about 4v aggregate from the battery pack.
The usual case, not practical. Wierd cell shapes, very old unit.
If I can't tinker-fix it, it goes in the trash. Any replacement parts either won't fit or are too expensive or both. I hate to throw potentially useful tools away, but ...
Thanks, P
"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
If the pack didn't consist of 8 AA-sized NiCds I would be muchly surprised. Anybody who can plug new AAs into a remote control, and knows which end of a soldering pencil to hold, likely has the skill level to rebuild a battery pack.
The charger was involved in a safety recall. I have a similar model with the same problem. The xformer will overheat when trying to charge a dead battery. If you call the 800 number, you might get a free charger.
However, if it's a later replacement, then all you did is blow the thermal fuse inside the charger. You can crack it open and replace it, but my guess(tm) is you also have some very dead batteries.
drill,
Not without knowing where the charge controller (probably just a resistor) is located. If it's inside the wall wart, you'll need to add an identical resistor. If it's inside the drill, you can probably get away with your 12VDC substitute. Measure the current drain at the charger output. My guess(tm) is you should have a mess of AA size NiCd batteries inside the drill, which are usually rated at 750ma-hr. Using the 0.1C rule, that would be a charging current of about 75ma max.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
They have no replacement parts for the 2375. They say that they'll send paperwork so, if I send 'em the charger, they'll send more paperwork so, if I buy a new Skil drill, they'll refund $25 or somesuch -if- I send 'em the UPC code -and- the orig. receipt, etc, etc ad nauseum. I don't think they really wanna honor the recall.
drill,
Lost me there. Measure the *drain* at the charger output? But I'm pretty sure it is inside the buggered charger.
It's evidently all original: charger is 92950, power pack is 92955, and is a *sealed* unit. I see no way to take it apart.
Am I missing something here?
Thx, P
"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
Looks like the $25 rebate is all that they are offering.
Maybe calling them back and asking for the name of the company attorney and whether this recall is defacto admission of their responsibility if your garage burns down, might get their attention.
drill,
I guess it might be difficult to measure the current if the charger is dead.
The problem is that we don't really know how the charging system works without tearing it apart. If the blown charger has a resistor in series with the output, there's no way to know at this point without cracking it open, or comparing it with another working unit.
Start by using an ohms-guesser on the charger base. Cut the cord. Is there DC continuity between the two wires and the contacts on the charger base? If there's a measurable resistance, then the charger base has either a resistor, or complexicated charge controller in the base. I would therefore guess(tm) that the wall wart is just a simple wall wart with nothing more complex than a thermal fuse inside. However, if there is DC continuity between the leads and the battery terminal connections, then the charge controller is inside the wall wart, and a simple replacement isn't going to work.
Since the power supply is obviously blown and useless, tearing it apart should reveal if there's anything inside. You'll probably find a thermal fuse. If it's blown, just replace it with a similar thermal fuse, glue the case back together, and continue charging. However, if there's a series resistor inside (which is what I suspect), then use the 12V adapter, add a similar resistor in series, measure the charging current, and see if it's reasonable 0.1C. If not, adjust the resistor value for 0.1C charging current.
Most chargers and charging bases are solvent welded together. They can usually be cracked open with brute force. Place a masons chisel along the glue line, and beat on it with a hammer. The glue line should crack as the plastic bends. If not, just use a hack saw to saw along the glue line. Do the repair, and then glue the case back together.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Overnight in a freezer helps. It makes the plastic brittle. If you have a deep freezer (0F or colder) use it instead of a refigerator freezer (around 10F).
Geoff.
--
Geoffrey S. Mendelson N3OWJ/4X1GM
It's amazing how many people have no clue what the word "contiguous" means. :-(
But the OP needs to know that none of the cells are shorted before he goes any further, that requires trying to charge the cells for a few minutes and then measuring the voltage at the drill. The voltage should be 8x1.2V =3D 9.6V or slightly higher. If the voltage is not at that level, then one or more cells in the drill are shorted and no charger is going to fix that. You can blast the shorted cell by putting it across a very large charged capacitor if you take the drill apart and measure each cell individually, but even then the cell is likely to redevelop a short unless it is kept on a charger almost continually.
Ok. There may be a diode inside the base. Try reversing the leads on the ohms-guesser and see if it acts like a diode.
Learn by Destroying(tm). If you haven't destroyed it and fixed it, you don't understand it.
Yech. I can't see anything in there. Fix the focus. Is there any manner of diode, resitor, charge controller, PCB, pilot lamp (current regulator), or thermal fuse inside? If not, it's an ordinary AC xformer. Also, no points for covering the xformer with the burned insulating material, so I can't see anything.
If AC only, then there's the usual problem of what voltage to get. Peak voltage on a single diode is 1.414 * AC voltage. If there's no series resistor, and just a diode in the base unit, then my guess(tm) is that you should be looking for a 7.5VAC wall wart. Again, you'll need to measure the charging current and check for 0.1C current to be sure you got it right. Of course, make sure you don't have a shorted battery pack.
--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS
You've done the right thing, substituting one of a slightly higher spec. The fact that you've had one burn out and its replacement gets hot suggests there may be something wrong with the charging circuit in the drill or the battery.
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