Runtime test with ZLT+, luxeon, and 2AA nimh

I did some testing with the ZLT+ Wayne Yamaguchi (dat2zip) made for me.

You might be interested in the results? (Just in case, here they are)

These tests are with 2AA nimh.

During the first, they were pretty fresh (but not "fresh off the charger")

I had the ZLT+ pushing out a lot of current, too...

Starting voltage was 2.68V with 2nimh AA's

Runtime / Vin (under load) / Vout / Iout

0 / 2.38 / 3.13 / 390

10 / 2.32 / 3.12 / 365

20 / 2.32 / 3.13 / 370

30 / 2.32 / 3.14 / 380

40 / 2.31 / 3.13 / 375

50 / 2.27 / 3.12 / 370

60 / 2.23 / 3.12 / 360

70 / 2.10 / 3.10 / 320

80 / 1.50 / 2.95 / 180

As you can see, nimh offer a "cheap" form of regulation, huh?

I stopped the test after 80 min. b/c the dropoff there was pretty significant and I didn't want to damage the batteries.

I did another test with a lower current setting to get better battery life and less loss through heat:

Starting at around 330 - 340mA, and two fresh AA nimh, I got 2 hours of pretty flat output (immediately dropped to around 320mA but then stayed at ~310mA for about 1 1/2 hours and then dropped to around 300mA...then slowly to 290, 280, etc. and finally to 250mA after 2 hours....could have kept going for another 1/2 to 1 hour?

The first test was done with GE/Sanyo 1600mah AA nimh. The second test was done with green 1600 mah "no-name" brand. I could probably get three hours in the second test if I use the new 1800mah AA's?

I too have the green, generic 1600mAh NiMH AA cells.

With the cells fresh out of the charger, I can get three hours out of them before the pair voltage falls below 1.8, with an average LS current around 320mA.

Hmmm...yes, I'm thinking of lowering my starting current to around 320 or so? That way, maybe I can get a good 2 1/2 to 3 hours around 300mA?

OK, I got better results with a slightly lower current.
Minutes / Current

0 / 320
3 / 320
10 / 320
15 / 310
20 / 310
25 / 305
30 / 300
35 / 300
40 / 295
45 / 300
50 / 300
60 / 305
70 / 300
75 / 295
80 / 290
90 / 290
95 / 280
100 / 280
105 / 270
110 / 270
115 / 265
120 / 260

Got tired and went to bed after 2 hours...
But it seemed like maybe it could last another 30 min. at or above 250mA (still bright!)

Duggg, I'm wondering why I'm not getting the 3 hours you're getting at around 320mA average???
I guess my batteries are bad? They've only been charged <10x, though...
BTW, this time I used GE/Sanyo 1600mah batteries, not the green ones...Maybe the green ones are better, as I got almost 1 1/2 hours at a higher current before?

Hi JollyRoger,

I don't know about the Sanyo batteries, but I have been very happy with the generic green ones.

All my tests have been with batteries fresh from the charger. As you know, NiMH's lose 10-15% of their energy within the first 24 hours due to self-discharge.

Heat damages NiMH cells, so if your charger is cooking the batteries, that may also result in less capacity.

Also, I assume your circuit uses the same bead core inductor as mine does. If it doesn't, then your efficiency and run time will probably be less.

To truly test your cell's capacity, hook it to a 10-ohm resistor and see how long it takes the voltage to drop from 1.4 to 0.9. A 1600mAh cell should take about 12 hours.

Hi there again Jolly and Duggg,

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by JollyRoger:
I did some testing with the ZLT+ Wayne Yamaguchi (dat2zip) made for me.

You might be interested in the results?

As you can see, nimh offer a "cheap" form of regulation, huh?
<HR></BLOCKQUOTE>


Yes, the NiMH cells also have a flat discharge similar to NiCd's and
since the Zetex circuit is moderately sensitive to input voltage
you see what looks like better regulation then the circuit actually
can do with alkalines.

Also, i test my batteries similar to the way Duggg does, except i check
the current every 10 minutes and write it down. Then, when the voltage
reaches 0.75 volts, i add up all the average current values and then
divide the result by 6. This gives a pretty darn accurate idea of what
your battery can/cant do

For example:
At start of the test the current reads 0.14 amps, then at the end of
the first 10 mins the current reads 0.13 amps, then that would total
0.14 + 0.13, or 0.27 amps, divided by 2 gives 0.135.
To convert to ampere hours, just divide by 6 to get
0.135/6 = 0.0225 ampere hours, which means for the first 10 mins
that battery put out 0.0225 ampere hours.

Now lets say that 20 mins into the test the current reads 0.12 amps,
so the total current for the second 10 min interval is:
0.13+0.12=0.25 amps
and the average for the second 10 min interval is:
0.25/2=0.125 amps, and then converting to ampere hours:
0.125/6=0.0208333 ampere hours.

Note the ampere hours put out during the second 10 min interval is less
then the output during the first 10 min interval. This is usually true
for the succeeding intervals as well.

An easier way is to add up all the amps first though, except for the
first and the last entry. Then, add to that total the first
and last entries divided by 2. Finally, divide by 6 to get ampere hours.

In the example above, we had:
00 mins 0.14 amps
10 mins 0.13 amps
20 mins 0.12 amps

So, take 0.13, then add 0.14/2 then add 0.12/2
and this totals 0.26. Now just divide by 6 to get ampere hours:
0.26/6=0.0433333 ampere hours, which means the battery put out
0.0433333 ampere hours for the first 20 mins of operation.

Of course using a full battery you will have many more readings
by the time it gets down to 0.75 volts.

Here's an example with more entries:
000 mins 0.14 amps
010 mins 0.13 amps
020 mins 0.12 amps
030 mins 0.12 amps
040 mins 0.12 amps
050 mins 0.12 amps
060 mins 0.12 amps
070 mins 0.12 amps
080 mins 0.11 amps
090 mins 0.10 amps
100 mins 0.09 amps
110 mins 0.01 amps

For this set, again take all but the first and last entries:
0.13 + 0.12 + 0.12 + 0.12 + 0.12 + 0.12 + 0.12 + 0.11 + 0.10 + 0.09
and add them up. This totals
1.15 'amps'.
Now add to that half the first entry and half the last entry:
1.15 + 0.07 + 0.005
This totals
1.225 'amps'.
Now divide this by 6 to get ampere hours:
1.225/6=0.2042 ampere hours.
Of course this battery wasnt fully charged, or was old

Now there is the question of variation in apparent battery capacity
with load current, so to test a battery accurately for a given
application you really have to either know the theoretical factor
for a given battery type or you have to measure the capacity with
a load that draws close to the actual current that will flow in
the actual application. Since the latter is not only easier but
also more accurate, simply hook up your actual load and at the
same time measure the current through the battery and record it
every 10 mins. Then it's simply a matter of calculating the
ampere hour capacity using the method outlined above.

If you dont feel like checking the current every 10 mins, then
you can get away with checking every 20 mins if you want, with
a little reduced accuracy. When you do this however, you have to
divide by 3 instead of 6 to get the ampere hour capacity in
the last step of the computation.

I use a multimeter with a computer interface to check my batteries.
I set the meter software to take a reading every 10 seconds and
record it in a file. A few hours later, another program reads all
the entries and does the above calculations. Since there are
360 readings per hour, it has to divide by 360 instead of 6
in the final step.
Since it's certainly not hard to take readings manually every
10 mins, i dont always use the program, but rather set an
electronic timer to beep once every 10 mins, at which time
i write down the current reading. This is especially easy when
im checking more then one battery at a time.

Good luck with it,
Al

Thanks, MrAl! I'll take these into consideration....My main goal is to find a good balance of brightness and battery life. I'd like to get the 2 1/2 to 3 hours of "constant" 300-320mA that Duggg got.

But seriously, thanks for taking the time to write that explanation...