Diode in NiCd pack - what is it?

"DaveC" schreef in bericht news: snipped-for-privacy@news.individual.net...

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

On Wed, 12 Jan 2005 15:30:28 -0800, mc wrote (in article ):

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?

On Wed, 12 Jan 2005 17:04:15 -0800, Rich Grise wrote (in article ):

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.)

On Wed, 12 Jan 2005 17:31:01 -0800, petrus bitbyter wrote (in article ):

Sorry: Resistors: 240 ohm and 120 ohm.

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

On Wed, 12 Jan 2005 17:30:21 -0800, budgie wrote (in article ):

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

| 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.

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

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

On Wed, 12 Jan 2005 18:03:02 -0800, NSM wrote (in article ):

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

| 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.

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.

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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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

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

or

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

On Wed, 12 Jan 2005 17:51:03 -0800, DaveC put finger to keyboard and composed:

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

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

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.

-- Tzortzakakis Dimitri?s major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr ? "DaveC" ?????? ??? ?????? news: snipped-for-privacy@news.individual.net...

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

-- Tzortzakakis Dimitri?s major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr ? "DaveC" ?????? ??? ?????? news: snipped-for-privacy@news.individual.net...

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