Maha C9000 & P3 Kill-A-Watt Meter

[NikonF5]

The C9K applies a charge at the end of every mode except the Discharge mode.
At the end of the charge, once the charger terminates and the Done message comes on the bottom of the slot, it is still actually applying a top-off charge for another two hours after which it proceeds with a trickle charge for as long as the battery remains in the slot.

Since the Done message comes before the start of the top-off charge, there is no clear-cut indication on the C9K display itself as to when the top-off charge has been finished.
The exception to this is the Charge mode where it is easy to determine when this 2-hr period is over.
If you recorded the time the battery was inserted into the unit and you add the elapsed time it took to charge the battery [part of the info on the C9K while it says Done], you can do the math and know when you the top-off charge will terminate.

This still leaves the R&A & Cycle modes where a Charge is applied as the final stage of the process but the long times taken by the whole process can make it hard to predict when the Done message comes up.
There is no top-off charge applied at the end of the Break-In mode.

It is known that the C9K uses the same topoff charge current for the same duration regardless of the:
Mode you have the battery in [R&A, BI, Cycle or Charge]
Charge & discharge currents you programmed for that mode.
Capacity and size of battery you have in the slot, [LSD vs regular, AA vs AAA, 2000mAH vs 800mAH]

Thus, if there was a non-DMM cheaper method that anyone could use to measure the current being used by the C9K charger during the top-off phase, the number of populated slots would be the only variable.
There are only 4 permutations of how many slots can be populated on the C9K at any one time so by going through all 4 permutations, 4 measurements of current are all thats required to create a simple lookup table which can be used to determine whether all the slots have been topped off.

There is a product made specifically for checking the AC power [current or volts] usage of anything connected to it.
You connect the wall wart to the front and the 3-power prongs in the back of the unit [not seen in pic] connect to your power source making the P3 sit between the C9K and the power source.
It draws its power from the power source and no batteries are required, not that having batteries is a problem for the users in this forum.

Here is a link to the mfr website for the P3.

I have done some testing and I believe the following method will do the trick as long as you are NOT running a Discharge on any slot and ALL slots show Done.
You can use this method for the Charge mode as well if you forget to write down the time you put the battery in or you just find this easier.

Testing was done using OOTB Eneloop AAA's and a C9K [0J0FA = Jun 2010, NewEgg Canada / Sep 2010].
Measurements were taken using the P3 Kill-A-Watt meter in Amp mode where it shows the AC RMS current being used by the attached device.

There were 10 separate AAA's used for the 4 tests required
Test 1 - Only Slot 1 populated
Test 2 - Slots 1 and 4 populated
Test 3 - Slots 1, 2 and 4 populated
Test 4 - All slots populated

Eneloop AAA's were used because

• I had just ordered 36 of them so I had more than the required 10 to do this test.
• Since they are AAA's, a lesser time was required to top them up then it would have if I had used AA's, thus getting a Done message come up faster.
• Since these were Eneloops manufactured a little over six months ago, I wasnt expecting the need for much of a Charge before the Done message showed up thus making the measurements a lot faster for each batch.

Caveats

• Since the C9K uses a pulse charging technique, the current draw alternates between a base value [0.03] and its actual value with every refresh taking place just under a second.
• The moment the battery starts Charging, at the beginning a high current is applied for a short time so one has to wait for this to finish and stabilise to where the base value is as above before taking a reading.

Testing Methodology for each permutation

1. Note down the time
2. In an empty C9K, insert the required number of batteries for the test, one at a time and set them to Charge mode with charge current set at 400mA.
3. Wait for the current to stabilise as per the second caveat above.
4. Take a current reading for charging current.
5. Keep checking to see when the Done message comes up and, once it appears on all the slots, note down the elapsed time [and other stats].
6. Use the largest elapsed time for any slot together with the initial insertion time to calculate the exact time the C9K said Done for the last slot it finished, add 2 hours to this, and come back and check the C9K at this time.
7. Before you walk away for 2 hours, take a current reading for the top-off charging current.
8. At the time calculated two steps above, check the P3 to see if the current has changed from the top-off charging current reading noted in the previous step to the trickle=charging current.
9. Take a current reading for the trickle-charging current
10. Pull out the batteries

Full Test Results

1 Battery
Charging current used = 400mA
Amps used during charging = 0.03 / 0.07-0.08
Slot 1 - Charge done in 16min and put in 98mAh
Amps used during top-off charge = 0.03 / 0.04
Amps used during trickle charge = 0.03

2 Batteries
Charging current used = 400mA
Amps used during charging = 0.03 / 0.12-0.13
Slot 1 - Charge done in 20min and put in 121mAh
Slot 4 - Charge done in 18min and put in 108mAh
Amps used during top-off charge = 0.03 / 0.06-0.07
Amps used during trickle charge = 0.03

3 Batteries
Charging current used = 400mA
Amps used during charging = 0.03 / 0.17-0.18
Slot 1 - Charge done in 20min and put in 118mAh
Slot 2 - Charge done in 22min and put in 131mAh
Slot 4 - Charge done in 20min and put in 121mAh
Amps used during top-off charge = 0.03 / 0.09
Amps used during trickle charge = 0.03 - There is an infrequent switch over to 0.04

4 Batteries
Charging current used = 400mA
Amps used during charging = 0.03 / 0.22-0.23
Slot 1 - Charge done in 19min and put in 113mAh
Slot 1 - Charge done in 22min and put in 131mAh
Slot 1 - Charge done in 22min and put in 132mAh
Slot 1 - Charge done in 21min and put in 126mAh
Amps used during top-off charge = 0.03 / 0.11-0.12
Amps used during trickle charge = 0.03 / 0.04 - varies almost every second


Summarised Test Results

• All the populated slots must say Done before the measurements are taken.
• After the top-off charge is done, the P3 shows 0.03 for 1-2 batteries or varies between 0.03 and 0.04 for 3-4 batteries.

Quick pic of the last test with the top-off charge in progress

 

[more_vampires]

Brilliant! I'd considered doing this myself. Well done!

 

[magellan]

Awesomely informative post, thanks.

Also welcome to the forum!

 

[StandardBattery]

Not a bad idea. I don't use the C9000 much, but I should use the kill-a-watt on a few of my newer chargers.

 

[SilverFox]

Hello NikonF5,

Welcome to CPF.

A small correction... There is no top off charge associated with the Break In function.

Interesting project.

Another way to know when the top off charge is complete is to monitor the voltage of the cell. When Done is displayed the voltage of the cell will continue to climb until the top off charge has completed, then it will drop off.

Tom

 

[MidnightDistortions]

I'm curious (unless i missed it), did you figure out how many watts (or Amps) the C9000 takes during the discharge cycle?

 

[NikonF5]

Brilliant! I'd considered doing this myself. Well done!

Awesomely informative post, thanks. Also welcome to the forum!

:thanks:

Not a bad idea. I don't use the C9000 much, but I should use the kill-a-watt on a few of my newer chargers.

If the measurement of its electrical input would help in determining something that the device normally keeps hidden, then you can use the same principles to any device connected to the P3

I'm curious (unless i missed it), did you figure out how many watts (or Amps) the C9000 takes during the discharge cycle?

Never actually explicitly tested for this as the Discharge mode is the only one where a charge is not involved at the end.
That being said, there was one time between tests that I discharged a NiMH and the current setting read 0.03 and guess what, that is what it always reads when its not doing anything but the LCD is on because at least one of the slots is populated.

 

[NikonF5]

Hello NikonF5,

Welcome to CPF.

A small correction... There is no top off charge associated with the Break In function.

Interesting project.

Another way to know when the top off charge is complete is to monitor the voltage of the cell. When Done is displayed the voltage of the cell will continue to climb until the top off charge has completed, then it will drop off.

Tom

:sweat:Currently suffering from 1stSilverFoxReplyToOneOfMyThreads-itis:sweat:OK, its finally over.

Thx for the correction, will edit post after I post this one.
I was aware of the second point but I just figured the target audience of people who werent able to closely monitor the LCD panel would already know that or it wouldnt help them if they like this method which caters to the ADD.

Thanks for taking the time to read my post and for your comment :bow:

 

[NoNotAgain]

I use the Kill-A-Watt power strip which displays a little more information than the P3. Also using the Maha C9000 charger.

My use wasn't so much to determine charge completion, but to see how much current was being sucked by various wall-warts that I usually kept plugged in.

 

[MidnightDistortions]

Never actually explicitly tested for this as the Discharge mode is the only one where a charge is not involved at the end.
That being said, there was one time between tests that I discharged a NiMH and the current setting read 0.03 and guess what, that is what it always reads when its not doing anything but the LCD is on because at least one of the slots is populated.

The reason i'm curious is whether the discharging battery powers the unit but it appears the energy must be dissipated somehow. Thought it would be sent to something like a capacitor to supplement power to the device.

 

[NikonF5]

The reason i'm curious is whether the discharging battery powers the unit but it appears the energy must be dissipated somehow. Thought it would be sent to something like a capacitor to supplement power to the device.

I believe discharging has always traditionally been done through a resistor.
I also believe it was mentioned somewhere in the disassembly thread for the charger, that there were resistors found on the board for just this purpose.

 

[MidnightDistortions]

Ah, ok that would make sense