Gear

I heard a while ago that Petzl are doing a new head-mounted electric stove.

Jon Doran wrote (see)

That's interesting. I'll contact Petzl and see if there are any implications for UK users.

I guess the implications are that they might get burnt!

Lol that the 'remedy' is to stop using rechargeables and Petzl will send you....  a label! Ah well, that's the potential litigation dealt with.

Princeton Tec - the way, the truth and the LIGHT!

That's pretty irritating. 

As mine will munch a set of batteries every fortnight that increases my running costs from virtually zero to £6 a month or £72 a year.  Since the use of rechargeable batteries was a key decision in buying this I would argue that this is not fit for purpose.

I have reported this to Trading Standards.  Petzl can't seriously be selling a lamp that is safe and won't catch fire...much.

Of course these will now be allowed on planes will they?

Brand Trust now equals ZERO.

Petzy MYO?  Petzl MYARSE...

Craig Porter wrote (see)

The warning notice very short on details but why does the problem only happen with rechargeable batteries?

Off the top of my head.....

Rechargable batteries are a lower voltage that non-rechargable alkalines (an alkaline AA battery is 1.5V, a Ni-MH AA is 1.2V). As the lamp for the Myo has a set wattage (power) you can look at the equation:

Power = Current x Voltage

As the voltage is lower in rechargables the current must increase to deliver the same power. It may be that the Petzl wiring is designed for the current delived by 1.5V alkalines not the higher current delivered by 1.2V Ni-MH's. The LED's themselves will have a current-limiting resistor built into or next to them.

Ok! Class over, go and run around the school yard!

Apparently Lyon are accepting returns as long as they are within the 3 year warranty.  That's fine for me then but not sure about the older ones... still not really ideal...

LYON EQUIPMENT LTD
Dent
Sedbergh
LA10 5QL CUMBRIA
United Kingdom

UNITED KINGDOM / IRELAND

Tel : 44-(0)15396-25493
Fax : 44-(0)15396-25454
E-mail : info@lyon.co.uk
Web : www.lyon.co.uk

Good point, Mike. The cable rating might not be up to the job. Sounds like they're cutting things a bit too fine in their calculations and tolerances to me but there you go.

Toxic, soldering in a 5p resistor might be cheaper than using alkaline batteries. You'd void any warranty you might have of course.

I also saw this warning note, but I'm going to ignore it.

Reason?

1: It is a 99,9996% chance that nothing will happen. There is much greater risk in crossing a normal road in any town in the world.

2: I have found the Eneloop batteries to be so good even in cold weather, so I'll use them this winter as I did last.

> It may be that the Petzl wiring is designed for the current delived by 1.5V alkalines not the higher current delivered by 1.2V Ni-MH's

As you point out, P = IV.  So, for a fixed P, and varying V, I must change.

However, this change isn't dramatic:

P = I1V1, so I1=P/V1

P = I2V2, so I2=P/V2

So I2/I1 = (P/V2)/(P/V1) = V1/V2

With V1 =1.5 and V2 = 1.2, I2/I1 = 1.5/1.2 = 1.25

i.e. the current has increased by 25%.

The resistive loss in the wiring = I^2R.

With fixed R, the power in the wiring increases by 1.25^2, i.e. by 56%.

If they've not allowed for a 50% margin on resistive heating in the wires in normal operating conditions, it's a pretty poor show.

However, my suspicion is that the problem is in the event of a fault condition in the lamp causing excessive current draw from the batteries.  Rechargeable batteries can usually provide a significantly higher current than alkalines.

A fuse, or fuse-like device sounds like an appropriate fix...  Or fix the problem that causes the fault condition...

Think the problem is that rechargeables have a lower internal resistance than alkaline cells, so the current increases and overdrives the light. Whether its the LED, cable or what that overheats, who knows ...

Judy