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Wall Warts

P

Puddin' Man

Jan 1, 1970
0
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."
 
P

Phil Allison

Jan 1, 1970
0
"Puddin' Man"
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.

** Wall warts break up into THREE distinct groups:

1. AC output.

2. DC output.

3. Battery chargers.

You cannot exchange units from one group into another.

Those in group 3 are the most variable in design and are purpose built to
charge a specific type and number of cells.

The fact they all look much the same and often have the same plugs attached
is very misleading.


..... Phil
 
P

Puddin' Man

Jan 1, 1970
0
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.

Certainly possible, for all I know.

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.
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.

The drill still works a little. I measure about 4v aggregate from the
battery pack.
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).

The usual case, not practical. Wierd cell shapes, very old unit.
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.

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."
 
P

Puddin' Man

Jan 1, 1970
0
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.
<http://www.all-cordless.com/skilrecalls.html>
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.

Thanks. That was worth checking into.

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.
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.

Lost me there. Measure the *drain* at the charger output? But I'm
pretty sure it is inside the buggered charger.
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.

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."
 
G

Geoffrey S. Mendelson

Jan 1, 1970
0
Jeff said:
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.

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.
 
A

Archon

Jan 1, 1970
0
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."
Recall on the charger, though not much good if the battery is knackered.

http://store.boschpowertoolsource.com/skil9296vwar1.html

JC
 
P

Puddin' Man

Jan 1, 1970
0
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.

The + side measures 3 ohms.
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.

Thanks for this opportunity for taking revenge on the offending WW. :)

After freezing, it cracked open easily, but I see no fuse.
Apologies for lack of quality of pix:

http://imageshack.us/photo/my-images/231/skilwallwart1.jpg/
http://imageshack.us/photo/my-images/831/skilwallwart2.jpg/

Thanks,
P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
 
M

Mike Tomlinson

Jan 1, 1970
0
Puddin' Man said:
Are there any guidelines for substituting these things?

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.
 
P

Puddin' Man

Jan 1, 1970
0
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.

Measures infinite ohms when reversed.

...
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.

There's nothing else in there.
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.

I'm 'fraid you'll have to elaborate on this last. And, what is "C" in
..1C?
Of course, make sure you don't have a shorted
battery pack.

So I gotta crack the battery pack open. And test each cell individually?
How?

Thx,
P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
 
P

Puddin' Man

Jan 1, 1970
0
It's a diode, with no series resistor. That presents a problem.
Without some form of current limiting, the voltage of the xformer will
need to be VERY carefully controlled to keep from overcharging the
battery. I will swear there's a resistor or charge controller
somewhere in the system, but I can't tell where from here.

I dunno where it would be ...
Sorry. C is the current rating of the battery in ampere-hours. A
typical NiCd pack, full of AA cells will have a rating of about 750
ma-hr. NiMH would be around 1200 to 2200 ma-hr. The maximum charge
current of the charger should be about 0.1 times this value (i.e. 10%)
or 75ma for the NiCd pack.
Thanks.


You don't need to destroy the battery pack in order to test it.

Good! :)
First,
just measure the terminal voltage of the battery pack after it's been
sitting around for a day without being charged. Even if totally
discharged, it should have at least 1.1 volts per cell or about 7.7VDC
across the terminals. A fully charged NiCd will have about 1.45VDC
per cell or about 10.2VDC across the terminals.

I measure just under 4vdc for the pack. Your opinion is
solicited.
Now, if you really want to test you battery packs, I have a West Mtn
Radio CBA-IIv1:
<http://www.westmountainradio.com/product_info.php?products_id=cba3>

Only $150-300. Lordy mercy!

I rambled thru my WW box again and found the following:

ATLINKS USA
Telephone power supply
Input: AC120V 60hz 4.4w
Output: DC 9v 200 mA
Class 2 transformer
UL etc

but when I measure, I get about 20vdc from my meter.
Any idea why the drastic difference from spec?

Thx,
P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
 
G

Geoffrey S. Mendelson

Jan 1, 1970
0
Jeff said:
This was also for a brand new cell, as repeated
charge/discharge cycles would also decrease the cell capacity.

Funny, I've always read the opposite with Nimh cells, they need to go through
several charge/discharge cycles before they reach full capacity.

This is especially true of the long discharge ones, which come "pre-charged"
at about 80% and then at least in my experience take 5-10 cycles to come
up to a useable capacity. It also seems in my experience that the lower the
charge rate, the more cycles a cell needs.

BTW, if you have any info on charging an Azden HT, please let me know.

Thanks,

Geoff.
 
W

William Sommerwerck

Jan 1, 1970
0
Geoffrey S. Mendelson said:
Jeff Liebermann wrote:
Funny, I've always read the opposite with NiMH cells. They need
to go through several charge/discharge cycles before they reach
full capacity.

This has always been the "conventional wisdom" about nicads, as well.

I wish I knew what the "truth" about rechargeables was. Contrary to the
common belief, I've never had problems with rapid self-discharge with NiMHs.
 
P

Puddin' Man

Jan 1, 1970
0
Many thanks.

S'long,
P

Your battery pack is dead, kaput, eWaste, gone, shorted, etc. That's
what probably killed the wall wart and inspired the recall. Charging
a shorted cell is a great way to overheat an unprotected transformer.
If you simply replace the transformer, you're likely to fry it again.


The requisite computer is not included in the price. I use it to
characterize Li-Ion mutations for model airplanes, robotics, cell
phones, and general havoc. The energy available is basically the area
under the discharge curve.


Sure. You're measuring the voltage without a load. If you load the
xformer with a 200ma load:
R = 9V / 0.2A = 45 ohms (47 ohms is close enough)
and
Power = E*I = 9v * 0.2A = 1.8 Watts (so use 5 watt resistor)
you should get around 9V DC.

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."
 
W

William Sommerwerck

Jan 1, 1970
0
Had these cells been "formed" properly prior to your test (via several
slow-charge / slow-discharge cycles)? There seems to be a general
agreement that NiMH cells don't achieve their maximum storage capacity
unless they've gone through several cycles like this, and that many
manufacturers don't take the time to do this during the manufacturing
process.

Why should they, when it would add to the cells' cost? Given the relatively
low price of uP-controlleed chargers, there's no point.
 
W

William Sommerwerck

Jan 1, 1970
0
There seems to be a real tradeoff. In general, the very-high-
capacity NiMH cells seem to have a more rapid rate of self-discharge;
they're good for "use immediately after charge" applications, but not
so good for "charge and store" standby uses.

That hasn't been my experience. My 2200mAh and 2700mAh MAHAs hold up very
well -- months, in fact. I've never made a study of the actual capacity, but
they /do not/ "fall flat" shortly after being put into use.
 
W

William Sommerwerck

Jan 1, 1970
0
I also use NiMH batteries in my various cameras (Canon S5IS etc) all
of which use AA cells. I'm seeing the typical 1%/day self-discharge
rate. I keep two sets of batteries in the bag. It's not unusual for
me to find the spares to be nearly dead after about 2 months.
Your NiMH milage may vary, but mine sucks.

Weird. Which brands do you use? I use mostly MAHA (PowerEx).
 
J

josephkk

Jan 1, 1970
0
the internal impedance of the transformer itself may be the current
limiter. That's the way it was in a B&D VersaPack NiCd charger I have.



Just a FYI,I have some Everready NiMH AA cells rated at 2350 mAH(bought at
Wal-Mart),and saw some no-name 2800 mAH AA cells for sale on Ebay.

I see stuff like that as well. Though i am starting to wonder if it is
just printing higher and higher numbers for the capacity without any
difference in the cells themselves.
 
G

Geoffrey S. Mendelson

Jan 1, 1970
0
josephkk said:
I see stuff like that as well. Though i am starting to wonder if it is
just printing higher and higher numbers for the capacity without any
difference in the cells themselves.

All I can say is that I have several AA battery cases for ham radios. The ICOM
ones take all AA batteries that I have every put in them, the one off brand one
I have that was made in the 1980's won't. It will take AA alkeline batteries
and up to 1600mah Nimh batteries, but not the 2500 ones. They really are
wider. :-(

Geoff.
 
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