*Q: What’s ‘cycling’ and why do I need to do it?




A: Battery‘cycling’ in it’s simple form is the two step process of charging and then discharging the battery under controlled conditions. Normally the purpose of the procedure is to ‘condition’ or ‘format’ a new pack or to verify the capacity or check the condition of a pack that’s been in service. ‘Routine’ cycling, or discharging before recharging a pack after every use is not necessary for either NiMH or Nicad packs, and discharging to ‘zero’ voltage under load is in fact harmful. A ‘cycler’ or controlled discharger will limit the discharge voltage level to prevent damage to the pack, whereas ‘leaving the switch on’ in your radio system to discharge a pack is very poor practice and may result in damage your radio system components or the battery.

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Most ‘hobby’ cyclers or dischargers operate at a predetermined load and cutoff level that is different than the cell mfg’s rating system. This leads to discrepancies that can be a high as 10-15% of rated capacity between the mfg’s rating and the rating presented by the cycler or discharger you are using. If your cycler or discharger system’s numbers are lower than the comfort zone described above then you need to verify the calibration of the cycler and check the charge rate and charge time to insure the pack did indeed get a full charge before the discharge function began. If the numbers are still uncomfortably low after re-running the test with your new pack, we suggest you contact the assembler or retailer for evaluation assistance in determining what the cause is before using the pack in a critical application. Any pack cycling more than 25% below the mfg's rating or the original numbers established for the pack with your equipment when it was new should be removed from critical application service.

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Q: How do I know if my pack is fully charged?

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Temperature is the key.. always, always, always! IF THE PACK AIN'T WARM AT THE END OF THE CHARGE ROUTINE, IT AIN'T CHARGED! Note I said 'warm'. Not HOT! Hot is NEVER GOOD at the end of the charge routine.. but warm is OK. If using a temp probe, set it for 10 degrees above AMBIENT. If it's a peak controlled charger and the charger shuts down before the pack is slightly warm to the touch.. IT AIN'T FULLY CHARGED. If it's a timer controlled charger and at the end of the charge period the pack is not warm.. it's NOT fully charged yet! By far and away the biggest reason for low capacity numbers is undercharging.. if you have a 5 gallon pail with only 3 gallons in it, your only gonna get 3 gallons out of it. Engage your brain.. check temperature at the end of the charge routine!

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Q: Temperature?? I thought voltage was how you could tell the pack was charged??

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A: More packs have been fried by guys looking for a 'number' instead of temperature on a charger than any other cause of premature battery failure. The 'finish' voltage of a pack will vary under an astounding number of variables.. but temperature rise ALWAYS signals that the cells are charged in a slow charge routine. Why? Because when the cells can no longer absorb the energy being shoved at them by the charger, they begin to give the unstored energy off as heat.

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Taking the Temperature story to the next level.. fast charging. Here we can generate even more heat. Some high-impedance cells like AA NiMH's can get warm when being charged at 'normal' 1C (fast) or even 10% (slow) rates. They can get warm BEFORE they get to full charge. Why? Because high-impedance cells don't absorb energy as efficiently at high current levels.. just like they don't give up energy efficiently at higher discharge rates. So.. before you crank up the current on your charger on your new NiMH Txpack.. check the pack label on our packs.. and set the charge rate recommended; which is often LESS than the 'industry standard' for NiMH cells.


Final word on temperature: Aside from being a key indicator for correct charge time, rate and final charge condition bear in mind that heat is the bitter enemy of NiMH Cells. Drive the pack into thermal overload (hot) on the charger and it's likely you'll ruin it. Pay attention to the temperature!



Taken from http://hangtimes.com/rcbattery_faq.html