Diode in NiCd pack - what is it?

They could be silicon. What was the current? A 1N4148 drops about 0.5v at around 150 micro-amps.

Farnell sell Schottky diodes with forward voltage drops ranging from 0.2 to

1.2V.

diodes

silicon

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

Have you tried reverse supply through a resistor? They could be zeners.

Either way they are part of the charge sense or charging circuit. If the battery has three contacts, then you have +ve out, -ve out, and charge probably common to -ve. The diodes ensure polarity, the resistors control the charge current, simple as that.

-- Woody

harrogate2 at ntlworld dot com

Most likely a 1N4148, a silicon diode. They are as common as muck and very cheap.

You won't find germanium diodes in a battery pack, they're still used but only for specialised purposes.

Dave

On Wed, 12 Jan 2005 12:46:42 -0800, harrogate2 wrote (in article ):

So the diode specs aren't really important (as long as they handle the forward charge current, that is)?

But why 2 diodes and 2 resistors, if the designers weren't trying to get the v. drop precise?

And why are there 2 resistors rather than 1 360-ohm one?

According to the datasheet, the 1N4148 drops 1V at 10mA, which surprised me.

Diodes can be used as temperature sensors, and there's an outside chance that they monitor the battery temperature. It's unlikely but worth bearing in mind.

If they are 1N4148s and they are carrying the charge current it seems a bit of corner-cutting by the manufacturer. 1N400x would have been a better option IMO.

Dave

Yes, if they are passing the charge current, but given the new info you've provided, they aren't...

If the resistor really is 360 Ohms then the resistor and diode are not passing the charge current, the resistor value is far too high for an approx

120mA charge current a standard C cell expects. Even with a 12V charger, (very unlikely for a 2.4V battery pack) there would only be a 33mA charge current through a 360Ohm resistor, which would take over 50 Hours to charge!

You'd need a 43V charger to give a 120mA charge current through a 360Ohm resistor, and that's ignoring the drop across the NiCads and diodes.

The diodes and resistor have to be part of the sense circuit, so you'll need to do a little digging into how the charger works.

Dave

Could be a thermal resistor. That is, the charger senses when the battery pack is getting too hot (due to charging) and shuts down the charger.

Jeff

On Wed, 12 Jan 2005 13:27:15 -0800, Dave D wrote (in article ):

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.

Yes, I'm certainly inclined to think the devices are something to do with temperature monitoring.

Dave

While they could be standard pn junction silicon diodes, my guess would be they are schottky. TTYL

No. The voltage drop of a diode is VERY dependant on the current flowing through it, a 1N4001 diode can range in drop between ~0.3 and ~1.0 depending on the current flow. The 0.6 that is common is just a convinient number to use. TTYL

It's possibly how they tune the sense circuit to a particular battery pack. Two resistors may be more flexible.

N

Why?

Does the third terminal connect to the junction of the two nicads? You can check that by seeeing if it is at 1/2 voltage. Do the diodes make any connection to that?

Tam

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 both. Diodes can be used to sense temperature.

Dave

On Wed, 12 Jan 2005 20:46:42 GMT, "harrogate2" wroth:

Actually, a silicon diode drops (in the forward direction) any value from 0.0 volts to more than a volt depending on the current through it.

Take a look at some typical characteristic curves from the data sheets.

Jim

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.

Cheers! Rich

On Wed, 12 Jan 2005 15:24:45 -0800, Tam/WB2TT wrote (in article ):

No. One end of this series string (2 diodes, 2 resistors) connects to the (-) term of the cells, and the other to the 3rd term (external) of the pack. No other internal connections.