today i am trying to manually measure the Eneloop AAA discharge capacity on a new ;) (hehe.. ) nimh charger which does display discharge capacities. the displayed capacities are a bit on the low side —compared to specs and C9000 results (Refresh&Analyze, Break-In)—, that's why i am doing this exercise. the UT61E comes in handy particularly for its stable unfailing logging capability. the serial cable was included in the package but i also bought the original USB cable from DX.
another beautiful point about this particular model is, because of its popularity the device gets continuously improved through invisible internal hardware revisions and users all over the world write their own PC LINK software (for Windows, Python, Linux, ..). I am satisfied with the original old Win software v4.01 on the CD-ROM but for our information, these are alternative programs compatible with UT61E:
The wiki site does not list the best tho:
There is also an entertaining and impressive UNI-Trend 12min company video (English lang, 118MB, slow download, use D/L manager).
So how does the kreisl measure discharge capacity?
Simply by logging the current I(t) over the entire time t with HKJ's measurement method:
One ends up with a data column for I(t) and one for t in Excel. Mathematically the discharge capacity is the integral of I(t) over time t, that simple. In a RL experiment this must be approximated by the sum of I(t)×∆t where ∆t=const.=1/f=1/(2.00Hz)=0.5s, because the updating frequency of UT61E is exactly 2Hz.
[quote]
Discharge Capacity
= ∫ I(t) dt
≈ ∑ I(t)×∆t = ∑ I(t)*∆t = ∆t * ∑ I(t)
= 0.5s * 1h/(3600s) * 1000mA/(1A) * ∑ I(t)
where I(t) must be measured in the ampere "A"-setting, e.g. 0.201A
[/quote]
In other words, the amps just need to be added and this sum must be multiplied with that factor, e.g.
(0.201+0.200+0.200+0.197+0.199+0.202+…)*0.1388888…*1mAh
That doesn't sound too hard, does it? ;)
The discharge test is still going on, i'll post my result here when i am done with everything stay tuna.
EDIT:
test done. saved as *.XLS-file, opened with Excel, then simple Sum function:
So we get in 3h33min24s:
|Discharge capacity| = 5600.236 * 0.13888888… = 777.81055555… ≈ 777.8 ≈ 778mAh
The same cell (from brand-new 4-pack) discharged from the same starting condition (i.e. charged at 400mA in C9000 and after completion left in charger for 18hrs) gives the C9000 discharge result 795mAh (in 4h24min), which sounds realistic given the "Sanyo mAh-scale" and their "800mAh"-rating. That's a minor discrepancy of 17mAh.
Maybe HKJ's measurement method which certainly increases the resistance between plus and minus poles of the metal contact plates of the charger (contact resistance + battery + tin foil + multimeter with leads + tin foil + contact resistance = 479-880mΩ total, instead of ~48mΩ total) influenced the system and falsified the result. Therefore we're repeating the discharge test twice: without UT61E on the new charger, and with UT61E on the C9000. after these 2 tests we'll know which of the three devices are consistent with each other and which device is a poor product.
EDIT: tests done.
C9000 current measurement test failed, see below post.
the "without UT61E on the new charger"-test was very successful. I got the same low discharge capacity and time for completion was also the same: 3h33min30s, amazing! It means that my discharge capacity measurements on the new charger are valid in the sense that they do NOT influence or falsify the charger's behavior (although it does so on the C9000!). Furthermore, my UT61E measurements are also fairly accurate, after the Sanyo scale.
What's our take home message?
- C9000 is very accurate with mAh-readings but also very/too sensitive to non-Eneloop or 1yr+ old cells because the "HI6H" resistance threshold is very low whereas all other chargers on the market do not have any such threshold. Trying to read (charge/discharge) current of a C9000 channel on your DMM in series is a practically an insurmountable challenge! Just give it up already :P
- On other chargers, discharge capacity (amateur) measurements with an accurate logging meter such as the UT61E is possible, easy, and fairly accurate. If you own a battery analyzer, then it is a very instructive exercise to compare your own capacity measurements (from calculations with UT61E data) with the capacity readings of the battery analyzer.