battery life

I'm looking to power a 6v 10w halogen bulb using a 6v lantern battery would anybody be able to give me some idea of how many hours of usage I can expect from it? Any help greatly appreciated

The average alkaline 6v lantern battery is rated at about 25,000 mAh, or 25 Ah. At 6v, that would give it a capacity of around 150 WH. A quick division says that should give a run time of 15 hrs. To be conservative, let's cut that in half and say 7 hrs, since the last few hours of output are going to be rather dim. Now if you could arrange for a nice boost/buck circuit in there to provide some regulation, I think you would me much happier with the setup. The regulation would allow the lamp to stay at full brightness until the battery is almost totally depleted. And from what I understand of the halogen cycle in bulbs, it would greatly extend the lifetime of the bulb as well.

An option to consider is replacing the halogen bulb with one of the LED equivalent bulbs available. That would greatly increase the run time of the lantern, and would lessen any advantage of adding a regulator circuit to the system. There are universal-style LED bulbs available to replace most of the common lantern bulbs in use.

Calculate as Timothybil states above but battery capacity depends on whether you mean a square spring-terminal lantern battery (e.g., Duracell MN908 = 12 Ah) or a rectangular screw-terminal lantern battery (e.g., Duracell MN918 = 27 Ah).

Actually there are 3 different kinds of 6v lantern batteries (with springs), one has essentially 4 heavy duty D cells in it, another has 4 alkaline D cells in it and the best has 4 alkaline F cells in it. The D cells are not full height vs the full height F cells meaning the F cells have considerably more capacity. At a 1.75A current the capacity will be considerably less than maximum especially using he heavy duty battery version. As has been said the higher the current drain the less runtime and the easier it it to drop from a nice white color output to orange. If the halogen bulb is actually rated at 6v then it won't stay bright long on a lantern battery as most bulbs for D cells lights and lanterns have lower voltage requirements than the batteries. For example common 2D incan bulbs are 2.4v instead of 3v with 3.6/3 cells and 4.8/4 cells.

Lynx_Arc said:

... The D cells are not full height vs the full height F cells meaning the F cells have considerably more capacity.

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AFAIK, the Energizer 529-4F is the last of the 4 x F type made by a major brand.

EDIT: You may have them in the USA but I don't recall seeing one in Canada for some time. BTW, Energizer spec sheets for the 529-4D and 529-4F show runtime graphs for lighting based on the resistance of the load so you should be able to measure the resistance of a bulb and compare it to the graphs to get a reasonable estimate.

Timothybil said:

An option to consider is replacing the halogen bulb with one of the LED equivalent bulbs available. That would greatly increase the run time of the lantern, and would lessen any advantage of adding a regulator circuit to the system. There are universal-style LED bulbs available to replace most of the common lantern bulbs in use.

Click to expand...

What runtime would i be looking at if i used an LED bulb?

Here's my math.
Given: 12 Ah for a standard alkaline 6V lantern battery
12 Ah * 6V = 72 Watt hours.
72 Watt hours / 10 watts = 7.2 hours for a 10 watt halogen bulb that will INITIALLY put out approx 120-140 lumens.

I looked at only a couple of D cell alkaline battery charts, but the companies rated the capacity with the batteries getting much more rest than use, IE they only ran them for a minute or two an hour for an eight hour day, for a month or more. If you run the light for 20 minutes at a time, you'll get much less than the rated capacity. Also the battery output will drop significantly in its first hour of use, and it will continue to decline to where the bulb just glows, but doesn't put out any appreciable amount of light.

I did a run-time test of a lantern with a single Cree XB-D LED. There was no driver, just a resistor to reduce the battery voltage to within tolerance of the emitter. Here are my results, with 3 D cell alkaline batteries.

Initially the lantern pulled 700 ma high, and 390 ma low. ~210 lumens, and 130 lumens.
At the end of the first hour it was down to about 175 lumens
And at the end of the fifth hour it was just above 120 lumens.
For the seventh through seventeenth hours it was between 100 and 110 lumens.
Hours 18-28 it was between 80-95 lumens.
Hours 29-40 were between 70-80 lumens.
Hours 40-55 were between 40-63 Lumens

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I hope this helps.