Diode in NiCd pack - what is it?

[budgie]

The resistors and diodes are not in the path of the charge current. The (+)
and (-) cell terms are connected directly to the (+) and (-) terms of the
battery pack. The 3rd pack term connects to the (-) cell term via these
resistors and diodes.

It would have to be temperature sensing for charge termination purposes.

 

[petrus bitbyter]

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,
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DaveC
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You did neither tell the resistor values nor the voltage measured across
them. Should be of some help. Can only guess these are old 1N914 or similar.
Most likely used for temperature sensing. The temperature itself is not very
important. It is the changing of it (dT/dt) that is used to decide whether
the batteries are fully charged.

petrus bitbyter

 

[DaveC]

As others have pointed out, they could well be silicon diodes, but are they
temperature sensors? I'd expect to find temperature sensors in a battery
pack.

They could be used as sensors, but they look just like common glass diodes
(1n4xxx type), to me.

However, while the diodes and resistors run alongside the cells, they are
(well, were) in shrink tubing and the cells are in a thick cardboard tube
(like a T.P. roll). Doesn't this make, logistically, for a poor temp sensor
location?
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[DaveC]

If one is up against one cell, and the other is up against the other cell,
physically touching, then it's almost a sure thing that they're temp.
sensors.

I checked: the 2 diodes are alongside one cell, and the resistors are
alongside the other. (See one of my other posts in this thread about the
insulation between the diodes & resistors and the actual cells.)
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[DaveC]

You did neither tell the resistor values nor the voltage measured across
them. Should be of some help. Can only guess these are old 1N914 or similar.
Most likely used for temperature sensing. The temperature itself is not very
important. It is the changing of it (dT/dt) that is used to decide whether
the batteries are fully charged.

Sorry:
Resistors: 240 ohm and 120 ohm.

Pack is sealed up again. Forgot to measure. Sorry.
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[DaveC]

It would have to be temperature sensing for charge termination purposes.

So, what diodes should I use if I want to duplicate the pack's circuitry?
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[NSM]

| So, what diodes should I use if I want to duplicate the pack's circuitry?

Try a couple of 1N4001 and see how it works. You could try a trimmer in
place of the resistors and see how the charging is affected.

N

 

[NSM]

| Sorry:
| Resistors: 240 ohm and 120 ohm.

Don't assume that they are just the nominal values. They may have been
selected.

N

 

[DaveC]

Don't assume that they are just the nominal values. They may have been
selected.

Hmm... as in, depending on the vendor of the cells, the end-of-charge
detection circuit needs to be tailor-made?
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[NSM]

| Hmm... as in, depending on the vendor of the cells, the end-of-charge
| detection circuit needs to be tailor-made?

Not impossible. Cheaper than stocking a large number of precision resistors
with various values. There's no other good reason for two resistors, unless
this is a short production run.

N

 

[Jim Adney]

Actually a silicon diode drops 600mV, prettywell consistently
irrespective of type.

It IS independent of type, but it is completely dependent on current
and temp. If you check the data sheets, it varies from nearly zero
(for nearly zero current) to about 1V (at the device's full rated
current.) For typical current values, however, .5-.75V is a good
estimate.

-

 

[amdx]

Just to be different, Could the diodes and resistors be used to trickle
charge after the batteries are fully charged.
The charger output switches from the ( - ) neg of the battery to the
resistor diode string connected to ( - ) neg,
and allows for long times on the charger without cooking the batteries.
Mike

 

[Ken Weitzel]

Just to be different, Could the diodes and resistors be used to trickle
charge after the batteries are fully charged.
The charger output switches from the ( - ) neg of the battery to the
resistor diode string connected to ( - ) neg,
and allows for long times on the charger without cooking the batteries.
Mike

Yet one more "different"... how about if the voltage drop
across the resistor is compared to the breakdown voltage
of the diode to determine the state of charge?

Ken

 

[NSM]

| Just to be different, Could the diodes and resistors be used to trickle
| charge after the batteries are fully charged.
| The charger output switches from the ( - ) neg of the battery to the
| resistor diode string connected to ( - ) neg,
| and allows for long times on the charger without cooking the batteries.
| Mike

No point. Why put them in the battery? Makes more sense for either

1) Sensing

or

2) Calibrated compensation.

N

 

[none]

| Just to be different, Could the diodes and resistors be used to trickle
| charge after the batteries are fully charged.
| The charger output switches from the ( - ) neg of the battery to the
| resistor diode string connected to ( - ) neg,
| and allows for long times on the charger without cooking the batteries.
| Mike

No point. Why put them in the battery? Makes more sense for either

1) Sensing

or

2) Calibrated compensation.

N

Or it's there as a fuse.(thermally sensitive it blows when the battery
starts to overheat. Helps to prevent a battery exploding.)

 

[Franc Zabkar]

Sorry:
Resistors: 240 ohm and 120 ohm.

Pack is sealed up again. Forgot to measure. Sorry.

Does current flow into the third terminal or out of it, ie how are the
diodes oriented? Are the resistors really resistors? Do they have the
usual identifying bands? Does their resistnace change with
temperature? If you heat the components with a hair dryer during
charging, how does the charger respond? If you disconnect the third
terminal, what does the charger do? Is the charger designed to charge
battery packs of different voltages and, if so, do the resistors and
diodes somehow identify the number of cells???


- Franc Zabkar

 

[Airy R.Bean]

Almost certain to be used as a temperature sensor (relying
on the "Diode Equation"), the abrupt rise in temperature
indicating when charging is complete.

 

[Dimitrios Tzortzakakis]

These diodes are possibly needed to rectify the ac provided by the charging
transformer, so that the batteries recveive dc.Check with your multimeter if
the terminals of the charger supply ac.Usually the diodes are silicone, as
germanium is more expensive.Do you have a retailer of electronic gear in
vicinity that has experience in this kind of parts?The one I buy everything
can identify almost anything just with one look.

 

[Dimitrios Tzortzakakis]

There are 2 resistors rather than one of higher wattage.These were used
extenisevely withtube circuits (I mean high wattage resistors).

 

[repatch]

They could be used as sensors, but they look just like common glass diodes
(1n4xxx type), to me.

However, while the diodes and resistors run alongside the cells, they are
(well, were) in shrink tubing and the cells are in a thick cardboard tube
(like a T.P. roll). Doesn't this make, logistically, for a poor temp
sensor location?

Depends on what you're sensing. For something like a NiCad sometimes you
can get away with just measuring the gradiant of the temp, for that the
setup you have is enough. TTYL