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  • These cells use diodes to reduce voltage

    posted by darronb on 08/05/2007

    Involvement:Expert (understands the inner workings) - Ownership:more than 1 month


    I was quite curious as to what these cells contain, so I sacrificed one to "science".
    These cells use a pair of diodes to drop voltage.
    The diodes are installed 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 my DMM uses to test diodes.


    A 4.4V charge voltage is required to fully charge these. I use the UltraFire 3.0V/3.6V CR123A charger (LITTSVIK), 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. Like all the other inexpensive Li-Ion chargers I’ve tried, The LITTSVIK uses a constant current charge profile, terminating charge when a certain voltage is reached. A proper Li-Ion charger uses a constant current, constant voltage (CC/CV) profile, which means that current is held constant until the cell reaches full charge voltage (usually 4.2V), then voltage is held at that level while the current tapers off to a certain fraction of the initial charge current, then charging terminates. The LITTSVIK simply terminates the charge at 4.45V, without holding at that level (to do so would NOT be good for a normal 3.6V Li-Ion cell). A normal 3.6V Li-Ion cell will get pretty close to a full charge, despite the less than ideal charge profile of the LITTSVIK. Since these Soshine 3V cells have the diodes inside, they never “see” over 4.25V or so while being charged from the LITTSVIK, and don’t get quite a full charge, since they are only at 4.2V very briefly. To give these cells a true full charge safely, a CC/CV charge that holds at 4.4V 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 posted two photos of the diode module.


    If you use the LITTSVIK charger, these work quite well, though you may not be getting quite full capacity out of them, and certainly not 650mAh. I can't hold the lack of stated capacity against them, since NONE of the RCR123A cells I've seen will test anywhere near rated capacity.

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