45/70
Flashlight Enthusiast
This is an experiment, not a recommendation! 
A while back, in post #35 of Mr Happy's Ultralast NiZn thread, I brought up the idea of using a hobby charger to charge NiZn cells in series. Well, since having recently obtained 8 PowerGenix AA cells, I thought I'd give it a try, just to see what happened.
For my initial test, I used two AA NiZn cells that had been basically discharged, their rested OC voltages measuring 1.56 and 1.57 Volts. I set up my Dynam Supermate DC6 (link from Dynam-RC) hobby charger to "LIPo Storage". This is the setting used to either charge, or discharge a single (or multiple cells, with balancing leads, depending on the setting) Li-Ion cell, to about 3.80 Volts, when preparing LiPo, or modern LiCo cells for long term storage. When charging, a CC/CV algorithm is used. With the charge rate set at 2 Amps, this provides a 2A/3.8V CC/CV charge, with a 200mA cutoff current (0.1C). This is of course, meant for charging a Li-Ion cell, but I substituted two NiZn cells in series, in place of a Li-Ion cell, for this experiment.
The charge process appeared to work exactly the same as if there were a single Li-Ion cell being charged. The current started at 2A, and the circuit voltage around 3.3 Volts. When the voltage reached 3.80 Volts, the CV stage commenced and the current began to drop, as expected. When the current eventually dropped to 200mA (0.1C), the charge terminated.
During the charging process, I periodically checked the individual cell voltages with an accurate DMM. While the cell voltages were rarely exactly the same, they were always within 0.02-0.03 Volts, or so. The OC cell voltages (removed from the circuit) at charge termination, were within 0.01 Volt, reading 1.83 and 1.84 Volt. This may seem a little low, but I attribute this to the fact that the charge was terminated at 200mA, as opposed to the recommended 90mA, due to the 0.1C cutoff of the Supermate. At no time during the charging process did either of the cells become detectably (with my hand) warmer than ambient temperature, nor did either cell's voltage read over 1.92 Volts within the circuit, during the charge.
I repeated this test with cells that were initially 1.54 volt and 1.63 Volt, and observed similar results. Again, while cell voltages were never exactly the same during charge, the measured OC voltages off the charger after termination of charge, were within 0.01 Volt.
My next "test" will be with two cells that are significantly (but not extremely) different in SOC, as the previous two pairs of cells were in a basically discharged state. If there is going to be a problem charging NiZn cells in series, this is where it will show up, and I'm almost certain it will.
Possibly a slow charge rate such as is used with NiCd/NiMH will work in this situation.
If the results look promising, I will try charging 4 cells in series, without balancing leads (as NiCd and NiMH cells are series charged), and if that is successful, I'll try 6 and 8 cells. Keep in mind that two NiZn cells in series = one Li-Ion, in this experiment.
It would appear, admittedly in the early stages, that this is possibly a viable solution for charging NiZn cells, at least from what I've seen so far. Results suggest that it may at the very least, work for cells that are initially close in SOC.
I haven't been able to spend a lot of time with these NiZn cells, as I have other responsibilities to attend to, as well as other light projects. I'd also like to point out that I'm aware that this particular endeavor lacks any resemblance to having been performed in a "laboratory environment", with data logging of voltage, current, temperature etc. Expectations should be based more along the lines of what one might expect from someone who is the product of a Hillbilly and a Hoosier, with a bit of Cherokee Indian thrown in, more of a "hands on approach". At any rate, any comments, or suggestions are welcome.
Dave
A while back, in post #35 of Mr Happy's Ultralast NiZn thread, I brought up the idea of using a hobby charger to charge NiZn cells in series. Well, since having recently obtained 8 PowerGenix AA cells, I thought I'd give it a try, just to see what happened.
For my initial test, I used two AA NiZn cells that had been basically discharged, their rested OC voltages measuring 1.56 and 1.57 Volts. I set up my Dynam Supermate DC6 (link from Dynam-RC) hobby charger to "LIPo Storage". This is the setting used to either charge, or discharge a single (or multiple cells, with balancing leads, depending on the setting) Li-Ion cell, to about 3.80 Volts, when preparing LiPo, or modern LiCo cells for long term storage. When charging, a CC/CV algorithm is used. With the charge rate set at 2 Amps, this provides a 2A/3.8V CC/CV charge, with a 200mA cutoff current (0.1C). This is of course, meant for charging a Li-Ion cell, but I substituted two NiZn cells in series, in place of a Li-Ion cell, for this experiment.
The charge process appeared to work exactly the same as if there were a single Li-Ion cell being charged. The current started at 2A, and the circuit voltage around 3.3 Volts. When the voltage reached 3.80 Volts, the CV stage commenced and the current began to drop, as expected. When the current eventually dropped to 200mA (0.1C), the charge terminated.
During the charging process, I periodically checked the individual cell voltages with an accurate DMM. While the cell voltages were rarely exactly the same, they were always within 0.02-0.03 Volts, or so. The OC cell voltages (removed from the circuit) at charge termination, were within 0.01 Volt, reading 1.83 and 1.84 Volt. This may seem a little low, but I attribute this to the fact that the charge was terminated at 200mA, as opposed to the recommended 90mA, due to the 0.1C cutoff of the Supermate. At no time during the charging process did either of the cells become detectably (with my hand) warmer than ambient temperature, nor did either cell's voltage read over 1.92 Volts within the circuit, during the charge.
I repeated this test with cells that were initially 1.54 volt and 1.63 Volt, and observed similar results. Again, while cell voltages were never exactly the same during charge, the measured OC voltages off the charger after termination of charge, were within 0.01 Volt.
My next "test" will be with two cells that are significantly (but not extremely) different in SOC, as the previous two pairs of cells were in a basically discharged state. If there is going to be a problem charging NiZn cells in series, this is where it will show up, and I'm almost certain it will.
Possibly a slow charge rate such as is used with NiCd/NiMH will work in this situation.If the results look promising, I will try charging 4 cells in series, without balancing leads (as NiCd and NiMH cells are series charged), and if that is successful, I'll try 6 and 8 cells. Keep in mind that two NiZn cells in series = one Li-Ion, in this experiment.
It would appear, admittedly in the early stages, that this is possibly a viable solution for charging NiZn cells, at least from what I've seen so far. Results suggest that it may at the very least, work for cells that are initially close in SOC.
I haven't been able to spend a lot of time with these NiZn cells, as I have other responsibilities to attend to, as well as other light projects. I'd also like to point out that I'm aware that this particular endeavor lacks any resemblance to having been performed in a "laboratory environment", with data logging of voltage, current, temperature etc. Expectations should be based more along the lines of what one might expect from someone who is the product of a Hillbilly and a Hoosier, with a bit of Cherokee Indian thrown in, more of a "hands on approach". At any rate, any comments, or suggestions are welcome.
Dave
