A beginners question about voltage vs. brightness

[YellowstoneYeti]

I have an old Petzl Arctic headlamp that is great for night skiing. It was quite bright with its halogen bulb. Unfortunately, it uses a 4.5 volt flat battery that is really hard to find unless ordered online. I have been thinking of converting to 3 AA nimh rechargeable batteries by using a battery holder. I have several technical questions about this or possibly going to a 4 AA nimh setup with a different, or possibly same bulb.

1.Nimh batteries put out 1.2v instead of the 1.5v rating on alkalines. Could I get by with the 4.5v bulb with 4 AA nimh's? Or will I greatly shorten the bulbs life?
2.Assuming the wattage ratings on the bulbs are the same, if I used the 4 AA nimh setup and changed to a 6v bulb, will the light be brighter than with 3 AA and a 4.5v bulb?
3.Of the 2 setups listed in #2, which one will have longer battery life?
4.Would heat be a factor if I went to the 4 AA/6v combo?
5.Does anyone know of an LED conversion for this headlamp? If so, does it provide more light/battery life?

Thanks in advance for any help. Let me know if you need any more info.

 

[turbodog]

First, just buy a new light with a modern battery pack (AA cells).


The 4.5v bulb is rated for peak voltage. Alkalines "settle down" and usually provide about 1.2v under load, which is what your rechargeable cells will produce. It should work fine.


Bulbs with the same watt output, especially at similar voltages, properly supplied with electricity, should produce about the same amount of light. Problem is, you're NOT supplying the 6v bulb with the proper voltage. You said you were considering 4 nimh cells @ 1.2v each, which is only 4.8v.


It's hard to say. One setup is alkaline cells and the other is nimh. But IF they were both the same chemistry (alkaline or nimh) the one with the higher # of cells would run longer. With the same load (# of watts) the higher number of cells has more total energy available, and would run longer.


Heat should not be a factor if your bulb is the same watt rating.



One thing. For a given wattage, the bulbs with the lower voltage rating will be tougher. The filament is thicker and more robust. That's one reason car headlights still use 12v bulbs.

 

[cave dave]

Bring your old artic to your nearest outdoor retailer and compare it to some of the newer LED lights on the market. (PT Apex, EOS, etc) I think you will be impressed. Try to find a dark room and bring some fresh charged batteries with you. Gosh knows whats in the display model.

 

[lctorana]

Answer 1
Your "flat battery" has 3 size "B" cells in series for a nominal 4.5V, but that is the no-load voltage.

When brand new, an alkaline battery might be good for 4.2v under load, but will deliver power at about 3.75 volts or so for most of its useful life.

A zinc-carbon battery will also deliver about 4.2v under load when fresh, and progresssively tail off until at about 2.7v when you give up on it.

Your bulb is therefore not rated at 4.5v. It should be rated at between 3.6 and 4.0V.

I'm lucky. A B&M store only half a mile away still stocks these batteries!

THREE rechargable batteries (3.75v, falling to 3.6v under load) will power it to the same brightness as either the zinc-carbon or the alkaline primary, believe it or not.
FOUR recharageables (5.0v, falling to 4.8v under load) will make the bulb go . Or, at least, it will have a short and merry life.


Here's my recommendation.

Open up one of your old flat "flat" batteries, and take the cells out.
Buy three size "A" (17mm diam x 50mm) rechargeables, solder them together and reassemble. There will be heaps of room. Voila - a rechargeable "flat" battery.

Answer 2
With 4 rechagables, please use a 4.8v globe.
A 6v globe is for 5 cells.
And yes, 4 cells & 4.8V will indeed be brighter than 3 cells & 3.6V and so on.

Answer 3
If you use the same type of globe when you change to a higher voltage, then battery life will remain exactly the same.
However, if you swap to a bulb that draws more current, be prepared for brighter light at the expense of runtime. At any voltage.

Answer 4
Heat will not be a factor.

Answer 5
I agree with the other posters. Keep your old headlamp standard, and buy yourself a new LED headlamp as well. Easier, and probably not much dearer.

 

[YellowstoneYeti]

Thanks for all the replies everyone. Lots of good info and I got my ?s answered. I have an LED headlamp already. I'm just kind of attached to the old Arctic. It has a great beam for skiing and has a separate battery pack so it works great in the subzero temps that we often get here in MT.