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