My new camera is much more particular about the quality of the batteries and will shut down with some sets even when they are fully charged. Some as a result of many recharge cycles/age but also some newish high capacity sets show this behaviour.
The 2-battery Canon A580 draws more power/current and is more particular about batteries than the older A60 it replaced. This led me to devise a way to grade my collection of rechargeable batteries using "On Resistance" R_on and a inexpensive tester costing about $2.
1 Loaded Voltage Measurements
I received this tester bundled with a package of disposable batteries from Camelion called the "slim battery tester".
I traced the circuit topology of this $2 tester and found that it operates by placing the battery under a 2 ohm load (0.3C roughly for 2000mAh cell ~= 650mA) and simultaneously driving an orange bulb. The brighter the bulb, the healthier the battery. Below are shots of two batteries differing in voltage by 150mV (1.32V and 1.17V) where you can see both the bulb brightness and the meter reading (FSD=0.25V).
2 On-resistance Calculation
for most batteries the voltage will hover around 1.3V and the corresponding current will be roughly 0.650A (See Equation 2 ). You can use this information with the difference between the loaded voltage (above) and unload voltage (no load) to estimate the on resistance "R_on":
I have found that a few of my worst performing high capacity Duracells (2650mAh) to have high values of on resistance (0.250 ohms) compared to some of the generation (and lower capacity) Energizers (0.04 ohms). This amounts to my modern two cell digital camera being able to take far less pictures with the higher capacity due to voltage drops being sensed by the camera low voltage circuit and prematurely shutting it down.
A low "R_on" value meanas low voltage drop when the batteries are driving current/power into electronics thus maintaining the "open circuit"/unloaded voltage (which tends to be fairly constant at about 1.25V for most NiMh batteries). This tester produces a condition to determine these drops and present them visually down to a level of about 100mV resolution.
EDIT: Results on about 50 batteries can be found here
PeAK
The 2-battery Canon A580 draws more power/current and is more particular about batteries than the older A60 it replaced. This led me to devise a way to grade my collection of rechargeable batteries using "On Resistance" R_on and a inexpensive tester costing about $2.
1 Loaded Voltage Measurements
I received this tester bundled with a package of disposable batteries from Camelion called the "slim battery tester".
I traced the circuit topology of this $2 tester and found that it operates by placing the battery under a 2 ohm load (0.3C roughly for 2000mAh cell ~= 650mA) and simultaneously driving an orange bulb. The brighter the bulb, the healthier the battery. Below are shots of two batteries differing in voltage by 150mV (1.32V and 1.17V) where you can see both the bulb brightness and the meter reading (FSD=0.25V).
2 On-resistance Calculation
for most batteries the voltage will hover around 1.3V and the corresponding current will be roughly 0.650A (See Equation 2 ). You can use this information with the difference between the loaded voltage (above) and unload voltage (no load) to estimate the on resistance "R_on":
R_on = (V_unload - V_loaded ) / 0.65
Here are some voltage differences and their corresponding R_on values:
HTML:
Voltage_delta Ron
_50 mV 0.077 ohm
100 mV 0.144 ohm
150 mV 0.231 ohm
200 mV 0.308 ohmA low "R_on" value meanas low voltage drop when the batteries are driving current/power into electronics thus maintaining the "open circuit"/unloaded voltage (which tends to be fairly constant at about 1.25V for most NiMh batteries). This tester produces a condition to determine these drops and present them visually down to a level of about 100mV resolution.
EDIT: Results on about 50 batteries can be found here
PeAK
Last edited:
