what are these?

[Dave G]

i bought a job lot of ebay old skool kit that just arrived,in it was some of these,they are definately old skool stuff..i think they are dischargers,cant remember seeing any of these before?

[AEyokomo]

yes they are dischargers i have one of them they are very old they are just an led which is used to drain the power.

[Custard]

Just the LED would take an age to discharge at ~20ma.

I reckon there must be a resistor in there with a couple of diodes to make sure it doesn't completely flatten the cells.

I remember the bad old days when we used an old car headlight bulb as a discharger.

[Mark Christopher]

Just the LED would take an age to discharge at ~20ma.

I reckon there must be a resistor in there with a couple of diodes to make sure it doesn't completely flatten the cells.

I remember the bad old days when we used an old car headlight bulb as a discharger.

so why would a diode stop the cells going flat?

[Dave G]

if i recall mark,a diode will only be open circuit upto a certain voltage then it shuts off.. ?

[Steve Cann]

Was a range of products sold thru' Helger...

'Keep it simple!' was where idea of branding came from...

[Steve Cann]

I remember the bad old days when we used an old car headlight bulb as a discharger.



"The bad old days".... They were the GOOD old days :):)...

[Mark Christopher]

if i remeber from my electronics lessons, a diode will only allow volts/current to flow in one direction
so a resistor will work no matter which way round you put it a diode will only let the electrons flow one way

[simonc]

Zener diode maybe?

[Skiddins]

"The bad old days".... They were the GOOD old days :):)...

Quite right Steve, you could leave the batteries indefinitely on bulbs and people used to store with resistors across the terminals.
None of this 'cut-off' voltage crap :D

Skiddins

[terry.sc]

so why would a diode stop the cells going flat?The point was to completely discharge the nicad pack to zero volts, after you had used a discharger. The LED was to show you when it was flat. Somewhere I've got a stack of resistors on battery plugs designed to be left connected across the nicad pack until the next weeks racing to keep the voltage at zero and prevent any cells from reversing. It made sure you never had any memory effect problems.

[Mark Christopher]

The point was to completely discharge the nicad pack to zero volts, after you had used a discharger. The LED was to show you when it was flat. Somewhere I've got a stack of resistors on battery plugs designed to be left connected across the nicad pack until the next weeks racing to keep the voltage at zero and prevent any cells from reversing. It made sure you never had any memory effect problems.

yes but the diode does not stop em going flat, it prevents reverse polarity!

[mlitton]

A diode will not conduct in the reverse direction unless you exceed its reverse breakdown voltage which is extremely likely to kill it.

A diode will only conduct in the forward direction if the voltage exceeds the forward voltage rating - this is normally about 0.6 volts but will vary depending on the type of diode chosen.

So yes - a diode will prevent "complete" discharge of cells as it will not allow the pack to fall below the diodes forward voltage. This is exectly how crude equalisers worked before we got the likes of Novak's smart tray.

A collection of diodes in series will allow you to add the collective forward voltages together to provide a higher "cut off" voltage.

Having said all that - I don't recognise the above device and have absolutely no idea what is in it!

HTH

Matt.