I think we may be being very, very nice to Batteroo by avoiding some of the basic tests.
We keep testing single batteries - but most devices use more then one battery cell. As far as I know, no one has even done one of the most basic important checks - a reverse diode test across the output to see if it acts like a diode. Absolutely unbelievable!
When a Batteriser shuts down due to low voltage, what does it do? A really important questions as the other Batterisers are still producing 1.5V at this point.
If it goes open:
The shutdown cell will get a reverse voltage across it - so it has to be able to be an open circuit with a reverse voltage of up to 10.5V (for a device that uses 8 AA cells - such as many old handheld walkie talkies). It could be tested non-destructively by applying the reverse voltage via a 10K resistor. See what the maximum voltage it can take. Perhaps short out the battery contacts to simulate a flat battery. 10.5V does not sound like much, but the batteriser IC is optimised for high currents and 1.5V operation - it may use devices with a 5V maximum rating.
The big thing if it behaves this way is that if there is one weak battery cell in a multi battery cell device, the Batteriser will draw more current from the weak cell then all the other cells and so it speeds up the discharge of that weakest cell. When the device shuts down, you chuck out all the cells (it is the Batteriser right? Uses every drop of power from a cell.) The trouble is those other cells you are chucking out may have more remaining charge in them then if you had no Batteriser - so the Batteriser, even if 100% efficient, may be wasting more batteries!
Lots of people buy AA/AAA cells in bulk so by the time they are used, they may be years old. Or they grab whatever mixed batteries they have on hand. It is easy to end up with a set of batteries with very different available capacities.
If it looks like a diode junction with a reverse voltage:
This opens up a whole nest of questions.
For a start, the device can still draw current from the other 3 battery cells (in a 4 battery device) and so in a high current device, there can be a lot of heat in this reverse diode junction - probably much more then when the Batteriser is in switching mode. Could easily cuase the Batteriser IC to fuse (ie become a short across the battery). This could be the factor that decides the maximum current rating of the Batteriser.
The second point that I have raised several times is that if the IC acts like a diode with a reverse applied voltage, the device may be susceptible to latch up. To test non-destructively (hopefully), apply a reverse current through the output of say 100mA with no battery and then connect 1.6V via 100 ohms to the battery terminals. Then switch off the 100mA through the output. Is the batteriser dragging down the 1.6V to a lower voltage such as 1.2V? If it has this inherent weakness, then it is possible for the Batteriser to latch up during the insertion of the last battery into a switched-on device or a device that has a capacitor permanently across the batteries. If it can latch up, this could easily cause enough heat in the switching IC to make it fuse and short the battery out. It is possible to design latch-up resistant IC's, but most switching regulator IC's probably were not designed at the start to have to cope with working in series with other regulators.
If the Batteriser behaves in some different way:
The least likely, but say when it shuts down, it somehow connects the flat battery to the outputs. Really unlikely.
Richard
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