Diode in NiCd pack - what is it?

They are in series with a combined resistance of 360 Ohms, which is far too high to charge 'C' cells. It would require a charger at 43V to get a charge current of 120mA, and it's only a 2.4V battery pack.

In any case, it has already been established that the circuit in question is connected between the negative terminal and the sense terminal on the battery pack, so it is obviously not carrying the charging current.

To quote the OP-

"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."

Dave

The first thing I'd do is take measurements at different temperatures so you can characterize what's happening with the original.

Jeff

Ah you're over here too.. :)

The circuit in the pack is designed to match the charger. If you can measure the forward voltage under a known current, and match that to some common diode, then you're ok. They probably used cheap diodes, try

1n4001's and see where that gets you. Measure the voltage across the resistors when it's in use, and that will tell you what test current to set up.

| Nah, who am I kidding. I'm certain the diodes are not diodes at all. | They're put there just to add to confusion in internet newsgroups. | Leave them out. Bummer, I think I got something on my finger... ;-)

Actually, you're right. They're extra parts from the flying saucer used by Kang and Kodos. They were going to build a rectal probe for Homer J, but, as explained in "Treehouse of Horror VII" (1996) - The Halloween episode, they decided against it. "I suppose you want to probe me," says Homer on board the flying saucer and dropping his pants. "Well, you might as well get it over with."

Kang replies, raising a tentacle, and shuddering: "Stop! We have reached the limit of what rectal probing can teach us!"

I suspect we have reached the limit on what speculation on this battery can teach us!

GW

(Always laugh at that one)

On Thu, 13 Jan 2005 16:52:42 +0200, "Dimitrios Tzortzakakis" put finger to keyboard and composed:

That doesn't explain why the two resistors aren't identical. I would think that 2 x 180 makes more sense than 120 + 240. Could they be NTC resistors?

- Franc Zabkar

| That doesn't explain why the two resistors aren't identical. I would | think that 2 x 180 makes more sense than 120 + 240. Could they be NTC | resistors?

Because they are hand picked 5% resistors, matched to the battery pack.

N

The price difference between 5% &1% resistors in production volumes is zero. The cost of 'hand picked 5% resistors to match the battery pack' - whatever the latter means- is astronomic even in India or China.

| The price difference between 5% &1% resistors in production volumes is zero. | The cost of 'hand picked 5% resistors to match the battery pack' - whatever | the latter means- is astronomic even in India or China.

I've worked in production. Using two resistors in series is a dead give away that they are tweaking the system. The other way is to use a 10 turn trimmer. They didn't.

N

On Thu, 13 Jan 2005 23:29:53 GMT, "NSM" put finger to keyboard and composed:

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???

- Franc Zabkar

| 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

the diodes are probably mass produced to panasonics specs and you may or may not find the exact one...

by the way you say they are configured into the circuit i'd say they're trickle diodes and maintain the proper polarity and current going to the batteries from the wallpack... Like clipping and clamping the wave to suit the recharge needs of the battery pack.

is the arranged lead off the center tap of both series batteries?

A Japanese friend of mine has one of those, to open alarm/cctv panels., I'll ask him what he has on it.

I use the DeWalt power screwdriver, that "mickey mouse" };-) (Yellow & Blk) panasonic is good for small delicate work but not to handy when working on heavier equipment.

I'd just register the current and match it's polarity and drain towards the battery pack while charging with anything i can get or have at hand.

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.

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

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.

I'll go buy another Panasonic pack and when time comes, replace the cells to extend its life.

Thanks for all the comments and suggestions.

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

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

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?

On Fri, 14 Jan 2005 02:27:36 -0800, Roy Q.T. wrote (in article ):

This isn't a "wall pack", but a full charging circuit consisting of battery condition sense and end-of-charge sense, I'm concluding.

No. (+) and (-) terms of the series cell string connects directly to the (+) and (-) external terms of the pack. The 3rd external term connects to the (-) term of the series cell string via these diodes and resistors.

Thanks,

| 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

How do

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