123 vs D or C Equivalent?

[ResQTech]

Theoretically, how many 123's in parallel would I need to have the same runtime as 2 D's or 2 C's in series?

 

[Mark_Larson]

1x 123 = 1.3Ah (3V)
1x D (Rechargeable at least) = 8-9Ah (1.5V)

You do the math.

 

[Brock]

It depends on what you consider for a run time.

I just ran a test with a 2 D Mag and was really surprised to find out it was to 75% after about 30 min and 50% after only 2 hours. So if your talking to about 60% on a 2 D Mag compared to many of the 2 123 lights they are about the same. The catch is the alkaline 2 D will put out light for much longer about 12 hours, but again after only 2 your under 50%. While the lithium lights will put out about 80% for about 50-60 min, then die completely after about 75-90 min or so.

 

[EvilLithiumMan]

From what I know about alkaline C & D cells, my guess is 3 for a C cell and 6 for a D cell. Sounds like kind of an expensive proposition. I'd stick with the alkaline cells unless you really have a serious requirement for one or more of the advantages that primary lithium cells offer:

1 - Somewhat smaller and much lighter weight for the eqivalent Watt/Hour capacity.
2 - Very flat discharge curve through 90% of the cycle. A 1.5 volt alkaline cell will be at .9 volts at the end of it's rated capacity. (Your 3 volt bulb would have 1.8 volts at the end of the rated capacity for a 2 cell flashlight - pretty usless, in my opinion).
3 - Exceptional cold temperature performance. At freezing, I think alkaline cells only have 25% of their nominal capacity. They are basically useless at 0 degrees. Lithium cells retain 60% of their capacity at minus 40 degrees.

 

[Mark_Larson]

[ QUOTE ]
Brock said:
It depends on what you consider for a run time.

I just ran a test with a 2 D Mag and was really surprised to find out it was to 75% after about 30 min and 50% after only 2 hours.

[/ QUOTE ] But how does the brightness compare? For example, a BB400 is also supposed to last around 2 hours in regulation with a CR123A but it puts out a lot of light during these two hours and is much smaller package, be it with 2 AA or 1 123.

 

[Brock]

Check out my runtime chart either in htm or xls format.

http://www.uwgb.edu/nevermab/battery.htm
or
http://www.uwgb.edu/nevermab/battery.xls

You can see how alkaline fall off rather quickly, but live longer.

In a regulated light all bets are off, then your just looking at if the battery can supply the amperage, if so, then just the total wattage is in question.