Thank you for such comments l.Almost certainly one or more cells are weak (typical reason for the owner to throw it out after a few years). It's easy to leave such appliances charging continually, although it's not great for the batteries.
A weak cell can be pushed into reverse polarity by the good cells.
You ought to test each cell voltage individually. Charge the pack overnight. (15 minutes is not enough time.) Since the cells are 1300 mAH, a reasonable charge rate is 130 mA. Check this with your meter because it's possible the charger is at fault.
See if each cell can hold a charge. You don't absolutely have to separate them all to do this. Peel away plastic to get at the terminals.
If any cell has much lower voltage than the others, you should remove it from the pack.
When you charge the battery pack your charger ought to reach a voltage of 1.5 V per cell. 12V is insufficient for 9 cells. You can wire two of your power supplies in series to produce sufficient total voltage, but one or both must be transformer-based.
It's important to limit charging current. The simplest way is to install a series resistor inline.
A problem cell can become faulty by developing very high internal resistance, or very low internal resistance.
If merely one cell becomes high impedance then it prevents the pack from carrying sufficient current. In that case you must disconnect the faulty cell.
Or a cell can become very low impedance like a short circuit. You can charge it forever but it never reads more than 0V. This is the reason you must install a safety resistor to limit charging current.
It's likely you'll find you must break up the pack.
1.2V is not enough voltage to push current into a cell, because it rises to 1.2V after a short time.another charger for Sayno 1400 twicell which gives 1.2v /550mA and that battery should be 1.2 v , 1100mAh, in this case charging time will be 2 hrs.
If its 1300mAh then charging time will be 2.5 hrs.
Dont you think I could use that charger just for single battery? It wont be a quick charger?
If you have time to kill I'd just use a power supply
in current-limited mode at the C/10 charge rate,
charge them one by one looking at cell voltage
and then discharge it hard (like into a 1 ohm
wirewound power resistor) watching the output
voltage again (full charge loaded current, and
how long it takes to drop to an unsuitable level -
like maybe 100mV below initial loaded voltage).
Log each cell and soon it will be evident which
one(s) are strong or weak.
1.2V is not enough voltage to push current into a cell, because it rises to 1.2V after a short time.
You need to apply enough voltage so that the cell goes up a few tenths of a volt higher than that during the charge sessison (say 1.6 to 1.8 V). This requires a power supply of 2 or more volts.
When I take a nicad/NIMH off the charger, its voltage normally reads 1.44V. After a few hours it settles to 1.38 V.
Don't try to quick charge a cell if you're not sure it's healthy. Quick charging heats up a cell which tends to shorten its useful life.
1/2 Ampere heats up a C or sub-C (which looks to be the size of your cells) making it noticeably warm. It's a reason to install a safety resistor.
dedicated for 1.2 v sanyo 1400 Twicell batery. Charger company said to use it 2.5 hrs. But somhow sanyo gets charge.
That is possible if there is no smoothing capacitor at the output. Evidently the raw waveform peaks higher than 1.2 V. In that case you can use it to charge one nicad/nimh.
A 1.2VAC sine wave has peaks of 1.7 V. (Assuming the unit contains a transformer.) When rectified it becomes pulsing DC with peaks around 1.6 V. A meter reads its average voltage which is 1.1 or 1.2.
To take a correct measurement requires an oscilloscope. (Although there are some meters with an Output jack which extracts just the AC component giving an idea of the shape of the waveform.)
If your unit were an everyday power supply then it would contain a smoothing capacitor so that the output is smooth DC with an average level at 1.2V. As a result we're not always certain whether we're talking about a battery charger specifically, or an everyday power supply.
Ni-Cads have 'memory' (crystalisation)that reduces its power delivery over time, even though they're fully charged - just replace the pack.
Some people say they've managed to recharge them by burning the crystalisation away with shorting the battery, then recharging.
But be carefull with this as shorting a battery is not a recommended practise.
/QUOTE]
Years ago when I still had some Ni-Cad cells, I tried charging a Ni-Cad AA cell and a Ni-MH AA cell in the same charger.
I can't remember which but one got warmer and the other got cooler while charging.
I found two old AA Ni-Cad cells (one says 2006 and the other says 2019). I will try charging them in series with some new AA Ni-MH cells later.
Since I have a complete product then transformer or AC components should not get priority now.
But, I checked with multimiter charging voltage is not stable it is moving from 1.2 v.
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