See Petzl website for details of the problem and which of their lights it is or is not OK to use lithium cells in.
Petzl warning on Lithium batteries and LEDs
- Thread starter ChrisB
- Start date
D
darkplaces
Guest
Sounds like Petzl were already operating the LEDs on the edge with minimal heat displacement. Just ask yourself why do the Nova 3/5's have a friggin huge heat sink on them? Its because LEDs that give out any decent amount of light create a LOT of heat.
I wonder if they were relying on battery characteristics rather than electronics to regulate the power supplied to the light sources.
With bulbs, that could be understandable - they may be chosen to run efficiently on the expected power sources, and wouldn't be expected to have any controlling electronics.
For LEDs, if they were running at a constant current, a touch more battery voltage under load is just going to result in a touch more heat, whereas if there isn't much regulation, a little more battery voltage could result in a fair bit more current as well, and a consequently larger increase in heat.
With bulbs, that could be understandable - they may be chosen to run efficiently on the expected power sources, and wouldn't be expected to have any controlling electronics.
For LEDs, if they were running at a constant current, a touch more battery voltage under load is just going to result in a touch more heat, whereas if there isn't much regulation, a little more battery voltage could result in a fair bit more current as well, and a consequently larger increase in heat.
C
cucc Paul
Guest
Lazy people you would have thought petzl could plug together some circuitry to work on lithium as well... they put enough wirey bits in as it is
whitelackington
New member
My new Hilti drill is 36 volt Lithium, now Bosch and De-Walt also make them, as in the 18volt range, lots of interchangable tools will soon be available for these 36 volt lithium packs, it is the way to go, double the power for the same power but they all have protective circitry as the batteries are so very expensive. Also the chargers are all smart chargers, will take a battery in any state , annaylize it, then fully charge it from where it was charged to.
whitelackington
New member
That should have read double the power for the same weight but even though I straight away tried to rectify my statement IT WOULD NOT LET ME!
There are several different types of batteries in use which use Lithium. The rechargeables are typically Lithium ion, and deliver 3.6V. More information can be found in Wikipedia.
The AA size are Lithium-Iron ("iron" not "ion"
) and use iron sulphide - see Powerstream battery FAQ. They havea voltage of 1.5V under load, but 1.8V without a load. They last longer than alkaline cells in high current applications such as digital cameras, but have no additional life in continuous low current uses (such as LED caving lamps)
The AA size are Lithium-Iron ("iron" not "ion"
) and use iron sulphide - see Powerstream battery FAQ. They havea voltage of 1.5V under load, but 1.8V without a load. They last longer than alkaline cells in high current applications such as digital cameras, but have no additional life in continuous low current uses (such as LED caving lamps)
biffa
New member
If Petzl had no drive electronics on their LEDs they would only last a matter of minutes, due to a thermal run away effect. As the LED junction heats up more carriers are thermalised, increasing the carrier concentration and decreasing the junction resistance. Because there is still the same voltage there, the current increases, more heating, lower resistance ad nauseum till BANG.
Since this doesn't happen my guess is that they must have some form of constant current unit. Either this isn't rated to work with the slightly higher voltages (so power dissipation in the drive electronics cause them to stop working), or there is some form of voltage reference that depends on battery voltage so the drive electronics outputs too high a current.
But then I don't know exactly what the circuit inside is.....
Since this doesn't happen my guess is that they must have some form of constant current unit. Either this isn't rated to work with the slightly higher voltages (so power dissipation in the drive electronics cause them to stop working), or there is some form of voltage reference that depends on battery voltage so the drive electronics outputs too high a current.
But then I don't know exactly what the circuit inside is.....
If the power control was a simple resistor, a PWM circuit with resistor-limiting on the 'on' current, or a current-regulating circuit which depended on the battery voltage to determine the current, then the power control would be dependent on battery characteristics.
In the context of battery-powered devices, I'd tend to think of a constant current circuit as one that was largely independent of battery voltage, using some kind of absolute reference.
That's the context in which I made my comments earlier, and I apologise if I wasn't clear.
In the context of battery-powered devices, I'd tend to think of a constant current circuit as one that was largely independent of battery voltage, using some kind of absolute reference.
That's the context in which I made my comments earlier, and I apologise if I wasn't clear.
