mAh charging questions for the electronic novice

[Hello82]

Hello

Can someone explain the basics of mAh rates and charging please?

I see so many different charger rates and battery rates I starting to get confused. I know that it stands for milli amps per hour, but for example I have a dual wall charger that puts out 110 mAh for both the tx and rc...but I have another wall charger that puts out 50 mAh for tx and rc...both say charge batteries for 16 hrs .

Someone told me that you would need to charge twice as long is you used the 50 mHa vs the 110mAh...but when I charge and check the volts they both seems to be full after 16 hrs?

...and does the charger mAh out rate basically have to meet the battery mAh out rate

Also, are flight batteries with higher mAh basically just better, than lower ones...do you get more power does it just last longer between charges?


thanks for any tips

M

[Sparky Paul]

Usually the full charge time refers to a completely discharged battery.
Unless you fly to that point, you'll find your batteries get back to full in less time.

[slipstick]

1. Charging rate is not measured in mAh. That's a measure of capacity not current/charge rate. And it doesn't stand for milliamps per hour it stands for milliamps TIMES hours. A 2000mAh capacity battery will deliver 2000mA for 1 hour, or 200mA for 10 hours etc.

2. Charging rate is measured in mA (no "h" on the end). To get the same amount of charge takes a bit over twice as long at 50mA as at 110mA.

3. Batteries with the same voltage but higher capacity (mAh remember ;)) give the same power but for longer.

4. How long you need to charge depends on both the charge rate (mA) and the capacity (mAh). Roughly speaking if you divide capacity by charge rate you get the charging time in hours (that's where the "h" comes in). So 1100mAh capacity at 50mA charge rate = 22h (hours) charging. 1100mAh at 110mA = 10 hours. Because charging isn't 100% efficient you always add a bit so call it 28 hours at 50mA and about 14 hours at 100mA.

Steve

[Hello82]

Hey, thanks sparky and slipstick for clearing some stuff up.

So, no matter how long I charge them...if my volt reader reads the right voltage on them ...they are fully charged? Or is possible they are the right volts but the capacity is way down and still need to be charged for another 12 hrs??

...cause if I'm working in the shop on the plane and switch radio on and off for a number of days etc, the volts come down maybe .5 to 1 from the max. So if I want to fly the next day, be safe and plug it in for 16 hrs ...or plug it in for a few hrs to top it off....I 'm under the impression the trickle charge for 16 hrs won't burn it out and or harm it in any way, so just leave it on way longer to be safe?

thanks
M

[slipstick]

The unloaded voltage of NiCd/NiMH batteries isn't a very good indicator of how fully charged they are. The difference in voltage between a 100% charge and a 50% charge can be hardly anything. It also depends what you think "the right voltage" is. If you measure the nominal voltage i.e. if a 4.8V (4 cell) battery reads 4.8V it is probably almost empty. A fully charged one is more likely to be somewhere around 5.2V-5.6V

At low charge rates, like the typical RC charger, it is safe to leave the battery on charge for longer than strictly necessary. If you want to be certain to have a full charge that's what you need to do.

Steve

[Sparky Paul]

I charge 9 of my transmitters for 5 hours every day.
They're usually ready to go.
The planes which have receiver batteries usually get an overnight charge.
I use an "Expanded range volt meter" to check the receiver batteries under load.

[Hello82]

Hi

So what does expanded mean in this sense then exactly? Will it show you the capacity at which it is at, and not just the volts?

So charging 5 hrs everyday is because you fly every day, or just because it keeps them topped off? For example I wanted to go flying today but it was too gusty, batteries were charged over night for 16 hrs. If I don't turn anything on at all today, can I fly tomorrow worry free, or should I charge over night again, or maybe just for 5 hrs?

thanks...it's all becoming clearer

M

[Sparky Paul]

An expanded scale voltmeter places a load on the battery similar to what a plane would.
If the needle doesn't plummet off the scale, :), and it's up in the green band, it's safe to fly.
An overnight charge should be good the day after, but check the voltage before you go to the field.
A quick field charger can bring a low battery up to par on the way to the field, or at the field.
You should monitor your battery levels as a matter of course.