Voltage oddity
Discussion
Just bought a new torch, and it takes 4x AA batteries (= 6V).
But on the torch, in the instructions and on the box, it says 'Rated voltage 4.2V/3A' and 'Rated power 11.1W'.
So not only are the batteries providing about 30% excess voltage, but according to Ohm's Law W = V x A, and 4.2V x 3A is 12.6W.
Are such discrepancies normal? Putting 6V into something designed for 4.2V isn't going to do it much good surely?
But on the torch, in the instructions and on the box, it says 'Rated voltage 4.2V/3A' and 'Rated power 11.1W'.
So not only are the batteries providing about 30% excess voltage, but according to Ohm's Law W = V x A, and 4.2V x 3A is 12.6W.
Are such discrepancies normal? Putting 6V into something designed for 4.2V isn't going to do it much good surely?
Since those are really 'design time' considerations, I wouldn't worry about it.
There is nothing that you, as an end user, can do to change the way it operates.
If it has a battery holder for 4 AA batteries, then it must operate with 4 AA batteries.
If it is an LED torch, then it will probably have a power circuit in there which changes the voltage before it actually reaches the LEDs. There may be some confusion in the documentation as to what is actually being referred to.
There is nothing that you, as an end user, can do to change the way it operates.
If it has a battery holder for 4 AA batteries, then it must operate with 4 AA batteries.
If it is an LED torch, then it will probably have a power circuit in there which changes the voltage before it actually reaches the LEDs. There may be some confusion in the documentation as to what is actually being referred to.
Thanks for the replies. It's an LED torch so as suggested maybe it has some gubbins to convert the 6V to 4.2 (I used Duracell alkalines so probably 1.7V = 6.8V in total).
The torch has one big LED behind a lens: https://www.amazon.co.uk/dp/B08BZNLF11
I thought it was actually dangerously bright - you wouldn't want to look close to the LED - but it can be dimmed a little which makes it nicer to use. I wouldn't leave it in a house with children.
Pulling 3 amps out of four AA batteries seemed very high though - LEDs are supposed to be efficient!
General question - why do most torches, even quite big ones, all use AAs? The bodies are big enough to take D cells. Maybe they need the extra voltage?
The torch has one big LED behind a lens: https://www.amazon.co.uk/dp/B08BZNLF11
I thought it was actually dangerously bright - you wouldn't want to look close to the LED - but it can be dimmed a little which makes it nicer to use. I wouldn't leave it in a house with children.
Pulling 3 amps out of four AA batteries seemed very high though - LEDs are supposed to be efficient!
General question - why do most torches, even quite big ones, all use AAs? The bodies are big enough to take D cells. Maybe they need the extra voltage?
It's Chinese.
All the numbers are questionable.
It runs for 30 hours on 4 AA cells.
A classic duracell Alkaline AA contains about 2Wh IIRC?
Go figure.
Thing is, numbers aside, it is probably fine.
I have a couple of smaller ones with comedy numbers, they've been great.
As for why AA cells, I try very hard not to buy anything which uses non-AA cells. I keep a stock at home and on the boat.
They are cheap and easy to buy.
One thing which is annoying with some LED torches is that they run at full power until the battery is low, then suddenly stop dead with no warning.
Hence I prefer to have two smaller torches!
All the numbers are questionable.
It runs for 30 hours on 4 AA cells.
A classic duracell Alkaline AA contains about 2Wh IIRC?
Go figure.
Thing is, numbers aside, it is probably fine.
I have a couple of smaller ones with comedy numbers, they've been great.
As for why AA cells, I try very hard not to buy anything which uses non-AA cells. I keep a stock at home and on the boat.
They are cheap and easy to buy.
One thing which is annoying with some LED torches is that they run at full power until the battery is low, then suddenly stop dead with no warning.
Hence I prefer to have two smaller torches!
They actually have a website! https://rehkittz.co.uk/
Voltage curiosities aside, the product is very well made.
Voltage curiosities aside, the product is very well made.
OutInTheShed said:
It's Chinese.
All the numbers are questionable.
It runs for 30 hours on 4 AA cells.
A classic duracell Alkaline AA contains about 2Wh IIRC?
Go figure.
Thing is, numbers aside, it is probably fine.
I have a couple of smaller ones with comedy numbers, they've been great.
As for why AA cells, I try very hard not to buy anything which uses non-AA cells. I keep a stock at home and on the boat.
They are cheap and easy to buy.
One thing which is annoying with some LED torches is that they run at full power until the battery is low, then suddenly stop dead with no warning.
Hence I prefer to have two smaller torches!
30 hours is on low, suspect on high it won’t last very long using aa batteriesAll the numbers are questionable.
It runs for 30 hours on 4 AA cells.
A classic duracell Alkaline AA contains about 2Wh IIRC?
Go figure.
Thing is, numbers aside, it is probably fine.
I have a couple of smaller ones with comedy numbers, they've been great.
As for why AA cells, I try very hard not to buy anything which uses non-AA cells. I keep a stock at home and on the boat.
They are cheap and easy to buy.
One thing which is annoying with some LED torches is that they run at full power until the battery is low, then suddenly stop dead with no warning.
Hence I prefer to have two smaller torches!
AA batteries are easy to get but it gets expensive if you need good batteries & have something that chews through them.
You can get li-ion rechargeable batteries on amazon that output at 1.5v rather than 1.2 of nimh, but for a torch I’d go for an 18650/26650 over aa for the runtime/form factor & output of the torch
Yabu said:
for a torch I d go for an 18650/26650 over aa for the runtime/form factor & output of the torch
Amusingly I put '18650/26650' into Google to see what you meant but got 0.69981238273 
The torch will only get occasional use and I'll turn it down a power setting so I think the current AAs will be fine.
Of course if it had D cells then much more of the volume of the handle would be filled with electrical storage than the current set up which is about 1/3 plastic and air.
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