|04-12-2006, 09:28 PM||#11|
RCC Supreme Contributor
I am: Wayne MIller
Join Date: Aug 2004
Location: Kitchener/Drumbo, On
Radio of choice:
Hitec A9 JR 9303
# of RCs: 19
Feedback: 11 / 100%
Total Props: 8
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I won't get too technical with this and will try and simplify it as best I can.
The following is good for NiCd (Nickle Cadium) and NiMh (Nickle Metal Hydride - spelling?) batteries. If the manufacturer doesn't list the "C" rating for charge or discharge, then usually it is safe to fast charge at 1C (whatever the battery pack is rated at) but this should only be done on an intelligent charger that knows when to stop charging. The standard wall charger that comes with your radio (typically nicknamed "wallwart"), usually charges at 1/10C (one tenth the rating of the battery pack) and usually requires 10 to 16 hours for a full charge. Charging at 1/10C is usually considered a "trickle" charge, this means it won't hurt the battery if it is left on too long - this would be the safest charge rate.
To charge a NiCd or NiMh, from fully discharge, you need to put in approximately 1.5 its mah rating. Note, most batteries are never fully discharged, so it will usually take less mah in for a full charge.
To give you some examples. If your battery is rated at 500mah, it will need 750ma to bring it to a fully charge state form a fully discharged state. Therefore, you would have to put in 50ma for 15hrs = 750ma or 75ma for 10 hrs = 750ma - again, you must remember that most of the time your batteries are never fully discharged and it will charge in less time. However, if you charge at 1/10C, you could leave it on without damage.
I have an article I wrote for the KWFD (Kitchener Waterloo Flying Dutchmen) newsletter that you may find interesting. I'll copy it below, you may want to go to the KWFD site, we post our new newsletter there each month and you may find some interesting articles.
"Hints and Tips:
Most people in our hobby have a need to check batteries or calculate wattage for electric fliers etc. Below is a brief review of the most used formulae and what each term needs. Hope you find it useful.
P= Power in Watts
E=Voltage in volts
I=Current in Amps
R=Resistance in Ohms
The Following Describes Basic Battery Information
NiCd (Nickel Cadium) or NiMh (Nickel Metal Hydride) Battery Voltages:
Fully charge voltage will be 1.35 volts per cell.
A fully charged battery pack quickly goes down to 1.26 volts per cell when in use.
When in use it will stay between 1.26 to 1.2 volts per cell for a long time (safe working voltage), we can safely to fly down to 1.2 volts per cell
RC flyers consider batteries to to be discharged, or lose ability to provide proper current, or amps (milliamps in our case) at 1.1 volts per cell, and we consider the time between 1.2 to 1.1 volts per cell a safety margin. You should NOT start a flight if your battery is below 1.2 volts per cell.
Capacity ( C )
We usually reference our battery charge and discharge capacities by “C”. You will see such things as “Charge at 1/10 C”, what this means is the charge rate should be 1/10 of the capacity. So, if your battery is 500mah, and the stated charge rate is 1/10 C, then it should be charged at 500mah/10 = 50mah. “C” can also refer to the safe discharge rate, and you see this mostly in LiPo’s (which this article does not cover). If you see “Safe discharge max 10 C”, this would mean that you could safely discharge this battery at 10 times its capacity. Example: A 500mah pack that is rated at a safe continuous discharge of 10 C, would be able to safely supply 500mah X 10 = 5000mah (or 5 amps) until it is discharged.
Battery discharge by time:
A battery capacity will be measured in mah (milliamps per hour), or 1/1000 of an amp, the larger the mah rating, the longer the battery will take to drop voltage (discharge) for the same application. If a battery had a constant current draw, and the full cycle time was divided into fifths, the time battery pack will stay in a given voltage range would be:
It takes 1/5 th of the battery total cycle time to go from 1.35 volts to 1.26 volts per cell
It takes 2/5 th of the battery total cycle time will be spent going from 1.26 to 1.2 volts per cell
It takes 2/5 th of the battery total cycle time to go from 1.2 volts to 1.1 volts per cell
For Full Charge:
To charge a NiCd or NiMh battery from full discharge, you will require to put in 1.6 times its capacity (remember, this would only be if it was completely discharged. Typically our batteries are not fully discharged.) It will take longer to charge batteries at a lower mah setting on the charger.
If you have a 500mah battery, you will need to put in 1.6 X 500mah = 800mah for a full charge from a discharge state.
Therefore if your charger puts out 50 mah, you would have to charge for 800mah/50mah = 16 hrs.
If your charger puts out 80mah, then it would take 800mah/80mah = 10 hrs.
A 4 cell pack (4.8 volts) will:
Be considered full charge above 5.4 volts
Working voltage between 5.04 to 4.8 volts, will stay within this range for a long time
Safety margin - stop flying at 4.8 volts or lower
Batteries will not supply any current below 4.4 volts
A 5 cell pack (6 volts) will:
Be considered full charge above 6.75 volts
Working voltage between 6.3to 6.0 volts, will stay within this range for a long time
Safety margin, stop flying at 6.0 volts or lower
Batteries will not supply any current below 5.5 volts
A 8 cell pack (9.6 volts) will:
Be considered full charge above 10.8 volts
Working voltage between 10.08 to 9.6 volts, will stay within this range for a long time
Safety margin, stop flying at 9.6 volts or lower
Batteries will not supply any current below 8.8 volts"
Hope the above helps.
|04-12-2006, 11:23 PM||#12|
RCC Master Contributor
I am: Ralph B
Join Date: May 2003
Location: StoneyCreek Ontario
Feedback: 9 / 100%
Total Props: 0
That's great info Wayne.Lots of knowledge there.I will read this over a few times so it sinks in.I hope your fingers aren't sore.
I refuse to join any club that would have me as a member.
Maac # 60449
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