Voltage sag under load - Some figures

LED Flashlights – General Info
1

I thought I would note some voltage sag figures .. Used 4 batteries

Trustfire Flame 18650

Yezl 18650

Xtar 2200

Ultrafire BRC3600

I discharged at 1A - 500mA and 200mA to see battery voltage sag at various loads ..

Measurements were noted at 15 seconds , 30 seconds and 60 seconds ...

@ 1A the largest amount of battery sag noted was to 3.72v , that's almost half a volt [ 0.46v of sag ]

Brand Starting Voltage 1A Discharge
Trustfire 4.21 3.81v-15sec, 3.78v-30sec, 3.75v-60sec
Yezl 4.2 3.93v-15sec, 3.9v-30sec, 3.89v-60sec
BRC 3600 4.18 3.73v-15sec, 3.72v-30sec, 3.72v-60sec
Xtar 4.19 3.9v-15sec, 3.9v-30sec, 3.87v-60sec

Brand Starting Voltage 500mA Discharge
Trustfire 4.19 3.99v-15sec, 3.99v-30sec, 3.96v-60sec
Yezl 4.19 4.05v-15sec, 4.02v-30sec, 4.02v-60sec
BRC 3600 4.19 3.87v-15sec, 3.87v-30sec, 3.87v-60sec
Xtar 4.2 4.08v-15sec, 4.08v-30sec, 4.06v-60sec

Brand Starting Voltage 200mA Discharge
Trustfire 4.19 4.11v-15sec, 4.11v-30sec, 4.11v-60sec
Yezl 4.2 4.16v-15sec, 4.15v-30sec, 4.14v-60sec
BRC 3600 4.19 4.11v-15sec, 4.11v-30sec, 4.11v-60sec
Xtar 4.19 4.14v-15sec, 4.14v-30sec, 4.14v-60sec

Updated = Going the other way ...

Time to charge the batteries ...

Ive gone with the BRC3600 [ since this is time consuming ]

1A charge rate :

Batt resting Voltage = 3.62v [ after 1A discharge to 3v ]

Put on the charger , and after the charger reached 1A the voltage reading from the charger was 4.06v , if its the battery voltage , then thats a 0.44v increase .

[ There must be some voltage overhead - higher charge voltage than batt voltage , but what is it ? = will have to test for this as time permits ] [ buy data logging MM ]

500mA Charge

Batt resting Voltage = 3.64v [ after 1A discharge to 3v ]

Put on the charger , after charge current reached 500mA , the voltage reading from the charger was some 3.96/7volts , a 0.32v increase

200mA Charge

Batt resting Voltage = 3.66v

Put on the charger , after reaching 200mA , voltage reading was 3.85v , after 60 seconds 3.83v and after 90 seconds 3.82v [ well that was different , voltage actually dropping under charge , one possible reason comes to mind , = the battery had been rested after discharge - takes a long time to charge @ 200mA - so wanted to do most of it while I slept - so it may have initially resisted charging [ more than usual ] , but as the current flowed into the battery the resistance dissipated and the voltage dropped ] = I could be wrong ! [ so related to storing a discharged battery for several hours - Like 10 ]

Charge VS Discharge

1A - Discharge = - 0.46v , Charge = +0.44v

500mA - Discharge = -0.32v , Charge = +0.32v

200mA - Discharge = -0.08v , Charge = +0.16v

Hmmm , interesting .

2

Thanks, that's why the regulated lights would give higher current readings for some batteries.

3

Sag depends on internal resistance of cells mostly. If the discharge current exactly 1A, and you measure the sag whitin 1-2sec, you get the internal resistance. Sag= internal resistance.

I use 3-5 watt low value(2-5ohms) resistances for measuring internal resistance usualy. There are a couple of methods to calculate the internal resistance value, you have to use simply Kirchhoff and Ohm's law.

4

Unfortunately I cheap'ed out on the Hobby charger , 1A Max Discharge ...

ATM Im looking at spending money on a data logging Multimeter ... Maybe the last purchase for 2011 , Ive spent plenty in the last month or so .

5

Thanks for providing the test results, very helpful information. Would you happen to have 26650 batteries to compare?

-JH

6

Yeah, that would be nice.

7

No 26650 batteries [ in my collection ] , though there have been some tempting lights lately for that battery .

8

Time to charge the batteries ...

Ive gone with the BRC3600 [ since this is time consuming ]

1A charge rate :

Batt resting Voltage = 3.62v [ after 1A discharge to 3v ]

Put on the charger , and after the charger reached 1A the voltage reading from the charger was 4.06v , if its the battery voltage , then thats a 0.44v increase .

[ There must be some voltage overhead - higher charge voltage than batt voltage , but what is it ? = will have to test for this as time permits ] [ buy data logging MM ]

500mA Charge

Batt resting Voltage = 3.64v [ after 1A discharge to 3v ]

Put on the charger , after charge current reached 500mA , the voltage reading from the charger was some 3.96/7volts , a 0.32v increase

Charge VS Discharge

1A - Discharge = 0.46v , Charge = 0.44v

500mA - Discharge = 0.32v , Charge = 0.32v

Hmmm , interesting .

9

200mA Charge

Batt resting Voltage = 3.66v

Put on the charger , after reaching 200mA , voltage reading was 3.85v , after 60 seconds 3.83v and after 90 seconds 3.82v [ well that was different , voltage actually dropping under charge , one possible reason comes to mind , = the battery had been rested after discharge - takes a long time to charge @ 200mA - so wanted to do most of it while I slept - so it may have initially resisted charging [ more than usual ] , but as the current flowed into the battery the resistance dissipated and the voltage dropped ] = I could be wrong ! [ so related to storing a discharged battery for several hours - Like 10 ]

Charge VS Discharge

200mA - Discharge = 0.08v , Charge = 0.16v