[ QUOTE ] MTFD17 said:
So is there a resistor you can put in to get the current down to acceptable levels? Will the resistor waste a lot of power?
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Let's assume the battery voltage drops to a total of 5.2V under a 1A load. Thus, you would want about 1.5 ohms, giving around 1A. At that load, the L3 will be dissipating 3W, while the resistor will be dissipating 1.5W, or 33% of the total power. You'd want at least a 2W resistor to handle this.
3D's DD seems to be a good combo, as I would imagine 3C's would also be.
My 3D TWAK DD is awesome! With fresh batteries, I measured 3.8v at the LS and it was pulling 1.8A!!! /ubbthreads/images/graemlins/eek.gif That's nearly 7 Watts! /ubbthreads/images/graemlins/ooo.gif This didn't last for too long though. After about 10 minutes, it was down to 3.7v and 1.4A (5.2 Watts).
Now that the batteries have a bit more time on them (probably about an hour and a half), things have settled into a more reasonable level. 3.6v at the LS and 1.2A draw (4.3 Watts). Still awesome! I don't think that this combo should really do too much harm to the LS, as the Vf doesn't go much above what it should on fresh batts.
BTW, to make the battery capacities clearer, here is what is listed at data.energizer.com for standard alkaline batts:
D --- 18,000mAh
C ---- 8,350mAh
AA --- 2,850mAh
AAA -- 1,250mAh
These need to be taken with a grain of salt however, as all of these are quoted down to a cut-off voltage of 0.8v with only small continuous current draw (25mA). For higher current draws, say at 1A (like we do things), things are a bit different (based off of my interpolation of the graphs):
D --- 7,000mAh (appx) - 39% of quoted capacity
C --- 2,300mAh (appx) - 28% of quoted capacity
AA -- 1,200mAh (appx) - 42% of quoted capacity
AAA --- 300mAh (appx) - 24% of quoted capacity
and quoted for the popular lithiums:
123 (3volt) - 1,300mAh (with 100 Ohm load to 2.0v)
L91 (1.5volt) - 2,900mAh (Lithium AA, rated at 200mA draw to 1.0v)
but at say 1A draw (again from the graphs):
123 - 850mAh to 2.0v - 65% of quoted capacity
L91 - about 2,600mAh to 1.0v - 90% of quoted capacity (I believe this is a bit too high)
So there you have it. I hope this makes things a bit clearer for some. This is all quoted for continuous operation, so battery resting periods aren't taken into account. As we all know, if you allow the batts. some time to rest, they recover some lost voltage. For real-world mAh ratings the way we do things, I would speculate they're nearer the 1A capacities, but maybe 25%-30% better. /ubbthreads/images/graemlins/icon3.gif
If you look at the L91 spec sheet, check the Constant Current Disacharge graph to the right of the battery dimension drawing (remember this is a log scaled graph). Also look at digital camera line in the graph at the bottom right of the 2nd page. Both graphs show a capacity about 2,600 - 2,700mAh at 1A current draw down to 0.8v.
Now if you look at the E91 spec sheet, check the Constant Current Disacharge graph at the lower right of the battery dimension drawing (remember this is also a log scaled graph). Again look at digital camera line in the graph at the bottom right of the 2nd page. Both graphs show a capacity about 1,000 - 1,200mAh at 1A current draw down to 0.8v.
I hope this clarifies things a bit. /ubbthreads/images/graemlins/smile.gif
[ QUOTE ] Klaus said:
with only 850ma remaining at 1A draw I think we wouldn´t see i.e. an E2(e) run for 75 minutes under around 1A load.
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I said that I thought it appeared to have 850mAh capacity at 1A load down to 2v. Is this how you understood me?
I got my comparison data in real numbers out of the old L91 application manual which isn´t available anymore online it seems - I could email it to you though - there the numbers are in writing and not just a graph. regarding the 123 - yes this is how I understood you - and I see that the current datasheet of the 123´s from the energizer site does claim so (850ma) but I somehow still doubt that based on mine an dothers experience with i.e. the E2s.