While I could tell idiots to go away, they never realize they are being idiots… Around these chargers they might maim or kill themselves, hence the warning. Ppeople with presence of mind and know to excercise cautions, should have no issues. These chargers are not isolated from mains current, as the Reverse Current Charger text indicates. The safety margins are only those you excercise. This information is presented for educational and informational purposes. If you build one you are accepting the risks completely. Even though I have built and tested mine, since I have zero control of anything you do in making or charging with these, the liability is your own and only your own.
As with anything electrical in nature, you can kill yourself quite easily.
Voltage measurements should never be taken while chargers are plugged in unless you are measuring voltage drop across portions of the active the circuit. Measurement of each cell should be done with unit unplugged for accuracy.
I have been able to charge cells reliably to 1.7 and 1.8 volts if they are capable of it. Consider a fully charged cell comparable to new to be any of those that measure above 1.6 volts. Not every cell is going to give these results. Some cells will peak at 1.4 volts. Most of the older cells that do not charge above 1.6 volts will usually charge to 1.5 volts and stay at that point even when left on charge for an additional amount of time relative to cell size.
These cells at the lower voltage end that I have encountered are typically older cells that I have been accumulating, and can be considered to have lost some water out of the electrolyte, and hence at the limit of charged voltage potential for that cell.
While charging alkalines, check the temps periodically. Those that may be prone to failure will be notably warmer than the other cells. If one is encountered, unplug charger and test the voltage of that particular cell- it may be fully charged, but in any event it should be taken out of the charger and another discharged cell slipped in.
So far I have not seen evidence of “memory” like Nicads notoriously develop, so interupting the charge cycle is not an issue. Putting a discharged cell back in it’s stead will not disrupt anything, nor cause problems.
These chargers are built around US/North American standards of 120 Volts AC at 60 Hertz, and the battery sizes are US standard, they go by other designations in other parts of the world. many commercial cells are labelled internationally already, so I will use the US designations here.
When charging, do not exceed 12 cells, with 9 volt batteries, do not charge more than 2 at a time in series. With 6 volt lantern batteries do not charge more than 3 at a time in series.
Once a cell has reached 1.6 volts, or higher, consider it fully charged and remove from charger. Insert discharged cells in their place. If the discharged cells are not fully charged at the end of the cycle of maximum time indicated below, put them in the next batch, and pull them out when they either have reached the 1.6 volt point, or the maximum time indicated. Further time on the charger will not improve them.
Lantern batteries have 4 cells and 9 volt batteries have 6 internally.
When checking temps, assuming insulating label is intact, you can safely touch the side of the cell to determine if it is warming excessively.
Check temps at 30 minutes, voltages at first 45 minutes. After that point, check voltage every 20 to 30 minutes while also checking temps. The charging cells that are healthy will be nominally above room temperature, the potentially failing cells, which do not fail if you catch them early enough are always warmer than the other cells under charge. If cells do not improve after 70 minutes total charging time, they are as charged as they are going to get.
Check temps and voltages at 45 minutes. After that point check voltage and temps every 20 to 30 minutes. If they do not show any additional charge after 90 to 100 minutes of charging time- they are charged as well as they are going to get.
These are inferred, I did not have any to charge at this time to determine expected charge times.
Check temps and voltages at 1 hour. After that, check voltage check temps at about 30 to 45 minutes. If after 150 minutes, there is no addition voltage gain, the cell is as charged as it is going to get. Most cells will be recharged within the first 90 minutes.
D Cells and standard lantern battery sized 6 volt batteries
These can charge in as little as 1 hour, so temps should be checked every 1/2 half hour and voltage checked after 1 hour. If cells do not achieve the expected target voltage of 1.6 volts after 3 hours under charge- they are as charged as they are going to get. After that first hour of charge, temps should be checked each half hour, and voltage checked each 45 minutes to an hour.
9 Volt batteries
These are difficult to check for temps but should be checked after 20 minutes. Voltage should be checked after 30 minutes. After that every 15 minutes. A battery not improving after 75 minutes on charge should be considered as charged as they are going to get.
The matrix above will give you the highest yield of useful batteries with the least amount of failures. Mark the cells that heat so you can monitor them closely when next charged.
Just because a voltage may be only 1.5 volts or 1.4 volts after charging times indicated, they are as charged as they are going to get and should perform adequately well.