"Franc Zabkar" wrote in message
...

| I've encountered a Sansui amp where the main bridge rectifier was
| constructed using four parallel pairs of 1A rectifier diodes rather
| than four individual 2A or 3A diodes. Placing diodes in parallel is
| bad practice because their sharp I-V characteristic almost guarantees
| that one will work harder then the other, so my only conclusion is
| that the manufacturer wanted to save money by making use of an
| existing stock of 1N4004s. Maybe that's what happened in this case???

There is a way to wire them so as to equalize the current somewhat. Also, if
they only needed 1.1 A say, the design might get by.

N

DaveC wrote:
Panasonic 2.4v screwdriver battery pack consists of 2x sub-C cells in series.
Pack has (+) and (-) terminals, and a 3rd terminal (charge sense?).

This 3rd terminal connects the charge circuit to the pack's (-) terminal
through 2 diodes and 2 resistors, all in series. The diodes are glass with a
yellow band. When I hook it up to the charger, the diodes each drop 0.535v.

What are these diodes? Germanium would drop 0.3v or less, and silicon would
drop more than this 0.5, no?

I want to make more battery packs for this screwdriver and need to identify
these diodes.

Thanks,

This is almost certainly a diode temperature sensor operating in
switched mode. In this mode, temperature is sensed based upon the diode
voltage differential at two separate currents: delta Vd= KT/q x Ln(
I1/I2), and this also explains why your readings are so low- the meter
is averaging- and the sensing may be operating in burst mode. The
resistors may serve any number of purposes- cheap current limiting or
simply to raise the input voltage level. Two diodes will double the
differential- but two resistors?- don't know.

Various manufactures may use their own particular designs to match up to
whatever they want in correspondence to their chosen designs.

Sometimes they use a diode coming from the battery pack to give a one way
isolation to the battery pack for their load testing circuit in their
charger. This blocks the load test circuit from feeding back in to the
battery pack. They sometimes use a resistor, or combination of resistors
with the diode for current limitation of some type, depending again, on what
they specifically want to do accomplish in their design.

Sometimes, they may also use a diode that is thermo sensitive, thus being
able to also determine if the temperature of the battery pack is going too
high. In this case the diode can be serving for several purposes.

If you are replacing this diode you will have to be sure of its
specifications before simply using any diode off the shelf. There may be
some safety and performance issues here. This is why I prefer to go out and
get the original battery packs for my equipment rather than jeopardizing
safety and performance for a few dollars saved.

--

Jerry G.
=====

"DaveC" wrote in message
al.net...
Panasonic 2.4v screwdriver battery pack consists of 2x sub-C cells in
series.
Pack has (+) and (-) terminals, and a 3rd terminal (charge sense?).

This 3rd terminal connects the charge circuit to the pack's (-) terminal
through 2 diodes and 2 resistors, all in series. The diodes are glass with a
yellow band. When I hook it up to the charger, the diodes each drop 0.535v.

What are these diodes? Germanium would drop 0.3v or less, and silicon would
drop more than this 0.5, no?

I want to make more battery packs for this screwdriver and need to identify
these diodes.

Thanks,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC

This is an invalid return address
Please reply in the news group

On Fri, 14 Jan 2005 09:34:35 -0800, DaveC wrote:

On Fri, 14 Jan 2005 07:32:34 -0800, Jerry G. wrote
(in article ):

If you are replacing this diode you will have to be sure of its
specifications before simply using any diode off the shelf. There may be
some safety and performance issues here. This is why I prefer to go out and
get the original battery packs for my equipment rather than jeopardizing
safety and performance for a few dollars saved.

Yes, you're right, I feel.

In this Panasonic pack, I simply replaced the cells with new ones, and the
pack seems to charge and perform as it used to when new.

Another pack, by another manufacturer (Milwaukee), fits this charger, but was
never meant to be used with it. This pack has one "diode" and one "resistor"
(in quotes, because we're making assumptions, of course). It never performed
similarly, because it never charged fully.

In a case like this, where you would have to toss it anyway, it might have
been worthwhile to slap a diode in series with the D & R in that one, and
see what happens.

Cheers!
Rich

"DaveC" wrote in message
al.net...

| The resistors are all light blue, which remind me of flameproof types. How
do
| you identify it as a NTC resistor if it is such?

It wouldn't usually look like a normal resistor.

N

DaveC wrote:
On Fri, 14 Jan 2005 09:43:25 -0800, Rich Grise wrote
(in article ):


How do
you identify it as a NTC resistor if it is such?

You put an ohm meter on it and change the temperature.
mike


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"DaveC" wrote in message
al.net...
| On Sat, 15 Jan 2005 03:05:58 -0800, mike wrote
| (in article ):
|
| How do you identify it as a NTC resistor if it is such?
|
| You put an ohm meter on it and change the temperature.
|
| No markings or other visual indication that it is an NTC resistor?

If you've seen enough of these you would spot it at once, but there's no
standard appearance. You can probably find pictures on the web.

N

On Fri, 14 Jan 2005 22:48:03 -0800, DaveC wrote:

On Fri, 14 Jan 2005 09:43:25 -0800, Rich Grise wrote
(in article ):

In a case like this, where you would have to toss it anyway, it might have
been worthwhile to slap a diode in series with the D & R in that one, and
see what happens.

I still might. I'm the curious type.

The Panasonic pack (the one that always worked with this Panasonic charger)
has 2 diodes and 2 resistors (240 ohm and 120 ohm). The Milwaukee pack (that
never really fully charged, and never lit the "charging" LED) has one diode
and one resistor (200 ohm).

Add a diode and 160 ohms of resistance to the Milwaukee pack?

The resistors are all light blue, which remind me of flameproof types. How do
you identify it as a NTC resistor if it is such?

Do you mean, completely light blue, without any bands? Do they have any
printing or any kind of identification at all? And I'm afraid I don't know
what an NTC resistor looks like anyway, sorry.

But I think what you've said - add one diode and 160 ohms, will probably
do no harm - you'll hear it before it smokes! If your meters go way out
of spec, pull the plug and call the experiment a success - you learned
that _that_ didn't work! ;-)

Good Luck!
Rich

On Sat, 15 Jan 2005 12:15:52 -0800, DaveC wrote:

On Sat, 15 Jan 2005 12:09:56 -0800, Rich Grise wrote
(in article ):

Do you mean, completely light blue, without any bands? Do they have any
printing or any kind of identification at all?

It looks like a 1/8W flame-proof resistor: light blue body with resistor
color-code bands.

Oh, then, sure - go for it. It's clearly either a temp sensor or some kind
of offset compensation in the current sense line. Even if it doesn't work
like we all want it to ( ;-) ), you're very probably not going to do any
damage, and you'll have your meters on it, so you'll know if it's way
off-base, in which case, just pull the plug.

Good Luck!
Rich