eneloop vs. Kodak Pre-Charged Voltage Maintenance

[UnknownVT]

Re: eneloop vs. Kodak-> R_int Calculation

The form (V2-V1)/(I2-I1) give the slope, so since
Rb=-slope, we get the equation that you have been using.
If you really want to capture the curvature, then you can use a quadratic equation that will fit a line through all the dots. A more complicated model

V=a * i^2+b * i+c
​

Compare that to V = Vo - Rb * i
Using higher currents to determine Rb will result generally in larger values of Rb

Thanks PeAK - we were basically using the same equation(s) I only listed them so that others can be sure what Mr Happy and I were calculating.

However I prefer the version without using the R(load) - as there is no way I can measure the resistance accurately - mine is only a cheapo DMM which seems to show 0.6ohms when the leads are shorted on the 200ohm scale (the lowest) - readings for both 1 ohm resistors show 1.6 ohms - so one could say they are 1 ohm allowing for the 0.6 ohm offset....
- but that is really crude. Also the package rating/specs are 1 ohm +/- 10% so strictly speaking the resistor(s) used could be 0.9 to 1.1ohm - too much margin of error to use in the calcuations - using actual measured voltages and current(s) drawn probably has a better resolution on that cheapo DMM - even then it was liken to hitting a moving target - I just took the "best" measurements I could - it would probably be slightly different on another day/hour.....

Nevertheless I ended up with 3 sets of results for 0.5, 1, 2 ohm loads plus the open-circuit (no load) voltage which allowed 6 calculations for the internal resistance - and the general trend, not surprisingly, was that the internal resistance increased with increasing current draw (decreasing resistance)
this was enough to give reasonable "confidence" in the figures -
although there were slight variences -
there did not seem to be anything that stuck out to show possible major errors.

The increments for the resistive load were 0.5,1, and 2 ohms so pretty close to approximate the "curve" and in the common/practical range for flashlight usage (ie: in the range of about 0.6 to 2.4 Amps)

So the calculated internal resistances probably are good enough for an indication for both eneloops and Kodak Pre-Charged.
Not forgetting, of course, this is strictly limited to the samples of one of each of the batteries I used.

 

[Mr Happy]

Re: eneloop vs. Kodak-> R_int Calculation

even then it was liken to hitting a moving target - I just took the "best" measurements I could - it would probably be slightly different on another day/hour

A way to deal with this is to alternate back and forth between the loaded and unloaded state about once a second or so until the readings stabilize.

 

[UnknownVT]

Re: eneloop vs. Kodak-> R_int Calculation

A way to deal with this is to alternate back and forth between the loaded and unloaded state about once a second or so until the readings stabilize.

Thanks, yes, I waited until the readings seemed to stabilize - but I only have the one DMM which meant making and breaking the circuit each time I changed from voltage to current - so it was still pretty crude.

Like I said the resultant calculations seemed good enough as an indication
- considering all the limitations - especially the sample size....

 

[PlayboyJoeShmoe]

Re: eneloop vs. Kodak-> R_int Calculation

One pair of Lenmar NoMEM Pro 2000mAh batteries failed miserably to run my GPS all day on monday.

Both pairs of Duracell Rechargeable ACCUs 2050mAh DID run the GPS just fine yesterday and today.

Both types are some of my earliest nimhs.

The Duracells may be the first of the Hybrid/Hybrio type batteries.

Shame I only have 4.

edit for INTERESTING fact: The Lenmars that died during the day on monday show 1.27 and 1.24. The Duracells that lasted until I shut the GPS down at home show 1.25ea for Wed and 1.23 and 1.24 for todays.

AHA! one of the monday lenmars has 3.5FA and the other 1.5. The Duracells are all over 4 except one almost 4.

That explains things nicely!

 

[UnknownVT]

I depleted a set of eneloops (my #1-4) in the Pentax K100D dSLR - the camera shut down during a test shoot - by turning it off and back on, the eneloops managed to shoot some more - but after about twice - even turning off then on failed to power the dSLR - so I consider this as low as one could drain the eneloops for all practical purposes. The final shot count for this set was 989 mostly without flash.

Since I now have a Maha C-9000 charger I thought I'd see how much charge was left in these eneloops - discharge current set at 0.2C = 400mA

eneloops -
#1 151mAh 25mins
#2 151mAh 25mins
#3 151mAh 25mins
#4 159mAh 27mins

pretty consistent with only #4 showing very slightly higher.

That's about 8% remaining charge - if the dSLR could actually take the batteries down to 0.9V (which it doesn't).

So this is pretty good considering how notorious the Pentax K100D dSLR is for being battery fussy and requiring higher operating voltage under load - my estimate is the DSLR is utilizing just over 90% of the eneloop capacity.