Gadget_Guru
Newly Enlightened
Soshine CR123A 3V Li-Ion cells and Ultrafire WF-138 LITTSVIK charger from DX
I bought four of these Soshine 3V RCR132A lithium-ion cells from Deal Extreme for my Fenix P1D CE. They work very well in the Fenix, allowing all the five modes to work with a fully charged cell.
I was quite curious as to what method these cells use to drop voltage, so I sacrificed one to "science". After hacking one open (they're very well made) I discovered that they use a pair of diodes:
The diodes are installed in a PCB module under the positive end of the battery in a side by side configuration, with the negative ends of each diode opposite from the other, to allow two-way current flow (necessary to allow charging). There are two types of diodes: one is a S2M, the other a SS12. The reason for using two types is to allow more voltage to be dropped under discharge than during charge. Using my DMM's diode test function, I get 556mV drop in the discharge direction, and 197mV drop in the charge direction. These voltage drops will change somewhat at higher or lower current than whatever current my DMM uses to test diodes.
With the 200mV drop during charging, a 4.4V charge voltage is required to fully charge these. I use my UltraFire WF-138 3.0V/3.6V CR123A charger, set to "3.6V" mode. DON'T use the "3.0V" mode of this charger, as it's intended for a different type of 3V cell, and will not fully charge these Soshine 3V cells. Like all the other cheap Li-Ion chargers I've tried, the WF-138 uses an (almost) constant current (CC) charge profile, simply terminating charge when a certain voltage is reached. Because of this improper charge profile, it must charge to a higher than recommended voltage to fully charge a normal 3.6V Li-Ion cell. My WF-138 charges to 4.45V before terminating, instead of the recommended 4.20V.
I am sure it is quite harmful to the long-term cycle life of a normal 3.6V cell to be charged to 4.45V every time. 3.6V cells will settle quickly to around 4.20V after the charger terminates. If all you test is the cell voltage hot off the charger, you'll gain the illusion that the charger is doing a proper job. I used thin metal strips between the charger terminals and cell, connected to my computer-connected DMM to capture the brief 4.45V peak of my WF-138.
Since these Soshine 3V cells have the diodes inside, they never "see" over 4.25V or so while being charged from the WF-138, and don't get quite a full charge, since they are only at 4.20V very briefly.
A proper Li-Ion charger uses the constant current, constant voltage profile, which means that current is held constant until the cell reaches full charge voltage (usually 4.20V), then voltage is held at that level while the current tapers off to a certain fraction of the initial charge current, then charging terminates. To give these Soshine cells a true full charge safely, a CC/CV charge that holds at 4.40V until the charge current tapers to perhaps 1/10 of full current, then switches off would be ideal. I will charge manually using this method soon, to determine true capacity in mAh.
I've been getting a little under 500mAh tested capacity so far when charging with the WF-138 and discharging down to 2.5V at a 500mA rate. I use a Triton charger to do the discharge test. I don't use the Triton to charge, since although it is a true CC/CV charger, it can only be set to 4.10V or 4.20V charge voltage. The Triton actually charges to only 4.18V when in the 3.7V/4.20V mode.
I bought four of these Soshine 3V RCR132A lithium-ion cells from Deal Extreme for my Fenix P1D CE. They work very well in the Fenix, allowing all the five modes to work with a fully charged cell.
I was quite curious as to what method these cells use to drop voltage, so I sacrificed one to "science". After hacking one open (they're very well made) I discovered that they use a pair of diodes:
The diodes are installed in a PCB module under the positive end of the battery in a side by side configuration, with the negative ends of each diode opposite from the other, to allow two-way current flow (necessary to allow charging). There are two types of diodes: one is a S2M, the other a SS12. The reason for using two types is to allow more voltage to be dropped under discharge than during charge. Using my DMM's diode test function, I get 556mV drop in the discharge direction, and 197mV drop in the charge direction. These voltage drops will change somewhat at higher or lower current than whatever current my DMM uses to test diodes.
With the 200mV drop during charging, a 4.4V charge voltage is required to fully charge these. I use my UltraFire WF-138 3.0V/3.6V CR123A charger, set to "3.6V" mode. DON'T use the "3.0V" mode of this charger, as it's intended for a different type of 3V cell, and will not fully charge these Soshine 3V cells. Like all the other cheap Li-Ion chargers I've tried, the WF-138 uses an (almost) constant current (CC) charge profile, simply terminating charge when a certain voltage is reached. Because of this improper charge profile, it must charge to a higher than recommended voltage to fully charge a normal 3.6V Li-Ion cell. My WF-138 charges to 4.45V before terminating, instead of the recommended 4.20V.
I am sure it is quite harmful to the long-term cycle life of a normal 3.6V cell to be charged to 4.45V every time. 3.6V cells will settle quickly to around 4.20V after the charger terminates. If all you test is the cell voltage hot off the charger, you'll gain the illusion that the charger is doing a proper job. I used thin metal strips between the charger terminals and cell, connected to my computer-connected DMM to capture the brief 4.45V peak of my WF-138.
Since these Soshine 3V cells have the diodes inside, they never "see" over 4.25V or so while being charged from the WF-138, and don't get quite a full charge, since they are only at 4.20V very briefly.
A proper Li-Ion charger uses the constant current, constant voltage profile, which means that current is held constant until the cell reaches full charge voltage (usually 4.20V), then voltage is held at that level while the current tapers off to a certain fraction of the initial charge current, then charging terminates. To give these Soshine cells a true full charge safely, a CC/CV charge that holds at 4.40V until the charge current tapers to perhaps 1/10 of full current, then switches off would be ideal. I will charge manually using this method soon, to determine true capacity in mAh.
I've been getting a little under 500mAh tested capacity so far when charging with the WF-138 and discharging down to 2.5V at a 500mA rate. I use a Triton charger to do the discharge test. I don't use the Triton to charge, since although it is a true CC/CV charger, it can only be set to 4.10V or 4.20V charge voltage. The Triton actually charges to only 4.18V when in the 3.7V/4.20V mode.
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