[BC-900 / C9000] SELECTED Charge Rate vs DISPLAYED Charge Rate

[TakeTheActive]

• Have you ever checked the DISPLAYED Charge Rate on your SMART 'Adjustable Charge Rate' Charger/Analyzer and compared it to your SELECTED Charge Rate?
  .
• Were they close (within ±1-2%), or WAY OFF (>5%)?
  .
• Did you wonder WHY?

Resistance!

There's:

1. Charger Internal Resistance
2. Charger Contacts Resistance
3. Cell Contacts Resistance
4. Cell Internal Resistance

I've observed this phenomenon on my La crosse BC-900 before, but since it was usually on *CRAP* cells, I didn't put much thought into to. Today I grabbed a pair of NON-*CRAP*Rayovac I-C³ 2000mAh AAs to cycle into one of my MANY Multi-Readout (i.e. 3 Remotes) Thermometers / Weather Forcasters, popped them into the BC-900 @ 1800mA to 'Top Them Off' and lo-and-behold, A1 is Charging @ 1640mA while A2 is Charging @ 1810mA. :thinking:

I rotated them, in place, several times (Charger Contacts to Cell Resistance) and only gained a few mA so I pulled them out to check their C9000 Impedance Check Voltage. While A2 only went from 1.54VDC to 1.58VDC, A1 *JUMPED* from 1.54VDC to 1.78VDC! A3 and A4 faired better (see table below), but gave uneven results when 'Topping Off' - A3 tripped the I-C³ 'Internal DONE Switch' after 887mAh while A4 terminated normally after only 402mAh.

Charger circuitry also seems to play a BIG role in this scenario :thinking: - where the BC-900 SELECTED vs DISPLAYED Charge Rate dropped 160mA (~9%), the C9000 only dropped 24mA (~1%). *AND*, comparing A1 to A2, the spread on the BC-900 is 170mA, while on the C9000 it's only 10mA.

A1 is now off to several cycles of 45/70's Deep Discharge Technique to see if I can get that 1.78VDC Impedance Check Voltage back down where it was.

That's what I get for letting them sit for almost 3 months!

Rayovac I-C³ 2000mAh AA      [A] |   #1    #2    #3    #4
---------------------------------+---------------------------

12/02/09 BC900 Discharge:  100   |    x     x
12/02/09 C9000 Discharge:  100   |    x     7
12/02/09 C9000 Discharge: 1000   |    x   321   n/a   n/a mAh
12/02/09 BC900 Charge: 1800      |  n/a   n/a  +887t +402 mAh Top Off
12/02/09 C9000 Charge: 1800      | 1776  1786  1791  1787 mAh Actual CHARGE RATE
12/02/09 BC900 Charge: 1800      | 1640  1810  1804  1804 mAh Actual CHARGE RATE
12/02/09 C9000 Impedance Check:  | 1.78  1.58  1.47  1.51 VDC

09/18/09 C9000 Break-In          | 1721  1707  1684  1672 mAh#
09/16/09 C9000 Impedance Check:  | 1.54  1.54  1.52  1.54 VDC
09/16/09 C9000 Discharge:  400   | 1457  1467  1571  1570 mAh
09/15/09 BC900 Charge:  1800     |  n/a   n/a +1995t+2040 mAh (1:06/1:08, 111°F)
09/15/09 BC900 Charge:  1800     |+1860t+1882   n/a   n/a mAh (1:02/1:02, 110°F)
09/15/09 BC900 Discharge:  100   |  108   153   147   142 mAh
09/14/09 C9000 Discharge:  100   |    0     0    24    51 mAh
09/14/09 C9000 Discharge:  400   |  111   218  1322  1424 mAh
09/14/09 C9000 Impedance Check:  | 1.54  1.56  1.51  1.54 VDC
[Bought: mm/dd/yy - HP Camera, GPS, RS Thermometer]

Legend: '+' = ACCUMULATED CAPACITY; no sign = DISCHARGE CAPACITY; 't' = TRIPPED.

On a more positive note, today's "Discovery"

has now established, for me at least, a 'previously undiscussed' RELATIONSHIP between BC-900 'SELECTED vs DISPLAYED Charge Rate mA Difference' and Cell INTERNAL RESISTANCE.

I'm going to start tracking the 'SELECTED vs DISPLAYED Charge Rate mA Difference' on cells with high C9000 Impedance Check Voltage / INTERNAL RESISTANCE and see if this theory 'holds water'.

Any other CPF members who own both chargers interested in comparing results?

 

[PeAK]

• Have you ever checked the DISPLAYED Charge Rate on your SMART 'Adjustable Charge Rate' Charger/Analyzer and compared it to your SELECTED Charge Rate?
  .
• Were they close (within ±1-2%), or WAY OFF (>5%)?
  .
• Did you wonder WHY?

Resistance!

​

There's:

1. Charger Internal Resistance
2. Charger Contacts Resistance
3. Cell Contacts Resistance
4. Cell Internal Resistance

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Charger circuitry also seems to play a BIG role in this scenario :thinking: - where the BC-900 SELECTED vs DISPLAYED Charge Rate dropped 160mA (~9%), the C9000 only dropped 24mA (~1%). *AND*, comparing A1 to A2, the spread on the BC-900 is 170mA, while on the C9000 it's only 10mA.

\/
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On a more positive note, today's "Discovery"

has now established, for me at least, a 'previously undiscussed' RELATIONSHIP between BC-900 'SELECTED vs DISPLAYED Charge Rate mA Difference' and Cell INTERNAL RESISTANCE.

I'm going to start tracking the 'SELECTED vs DISPLAYED Charge Rate mA Difference' on cells with high C9000 Impedance Check Voltage / INTERNAL RESISTANCE and see if this theory 'holds water'.

Any other CPF members who own both chargers interested in comparing results?

Hi TTA, as Einstein discovered, the "lab" can be your universe. By definition, a proper current source will account for resistances in the charging path by increasing the voltage appropriately to maintain the overall current. If for example, you charge at 1 amp and add an additional series resistance of 0.1 ohm, the current source should increase the overall voltage by 0.1V (1amp x 0.1 ohm).

Ideal Current Source: Will put out whatever voltage is needed to put out a specific current.
​

With regard to your observations of the Maha behaving "better" than the Lacrosse, most chargers behave as ideal current sources within a certain voltage range (usually to a maximum voltage). As the voltage nears this limit, the current source behaves more like a non-ideal current source and the current is a strong function of the resistances in the path.

Thanks for those interesting observations.

 

[Mr Happy]

I thought this was going to be about a different topic. But since it is related, I will mention that the C9000 is not supplying exactly the current the display is showing: if the display shows 500 mA, the average current is actually 450 mA (90% of the display reading). The accumulated mAh is accurate, however, which is how you can tell the difference between the displayed and actual current.