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receiver battery charging

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Old 01-17-2019, 01:15 PM
  #1  
zzdruid
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Default receiver battery charging

I am flying a nitro plane with a 850ma 2c lipo receiver battery. There are 4 standard servos and a voltage regulator with a set output of 5.7 volts. There is also a battery check port on the side of the plane which I can connect to a volt meter (the one shown or a std multimeter). The plane is new to me.

When I check the battery after about five 10 min flights the reading is 7.8 volts at the balance plug and the same at the volt meter connection. I also have an old "Voltwatch" monitor attached to the receiver and the fully charged light ( far right one) is lit!. I am assuming that this monitor is for 4 AA cell packs and should show a warning at 4.8 volts.

Since I can still recharge the lipo at > or =3.3v /cell or 6.6 volts and the regulator is set to put out 5.7 volts I am wondering at what voltage I should recharge the lipo.
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Old 01-17-2019, 08:58 PM
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Use of the "voltwatch" may be useless. Nominal voltage for ni-cads was 4.8, and they would stay at that level for a large part of their life. So depending on design, it may not show "low voltage" until they got to 4.6, or even lower (in some brands of voltage checkers). That means showing 2.3 v per LiPo cell (or lower) when they indicate. A ruined pack.
Measuring the voltage at the regulator is also not very useful. Depending on design, it could very well maintain 5.7 volts until the pack reaches 2.8v per cell, at which point the pack is ruined.
All lithiums are noted for maintaining very consistent voltage right up to the end. You would be very lucky to catch it right at the point where it starts to sag to below nominal voltage, but before it hits the "bad" zone. They can fall off the cliff very, very quickly. Electric flyers have the advantage here, as their ESC's are constantly monitoring, and most will signal (usually cut the motor) when the voltage starts to drop.
Depending on the radio gear, some brands have meters that stay plugged in that show total milliamps used, others have telemetry add-ons that can send the same back to the transmitter. Easiest - just fly your normal 5 10min. flights, and then put the battery on the charger, and read how many milliamps it puts back. A little math will then tell you about how many flights you can fly before the battery is considered discharged. Of course, be conservative so you have a healthy margin for error.
Since these are LiPo's, never, ever charge them when installed in the plane. And give them a bit of access to cool air (they won't get real hot, like ones that run electric motors can, but burying them deep inside tons of foam is not good for them, either).
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Old 01-18-2019, 06:19 AM
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zzdruid
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thanks
when measuring voltage at the plug on the side of the plane I am actually getting the lipo voltage. I do understand that the voltwatch is showing regulator voltage since it is plugged into the receiver.
so i reckon the bottom line is to use a balance plug meter and fly until that meter says 30 to 40% or around 3.4-3.5 volts per cell>
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Old 01-21-2019, 03:39 PM
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Rule of thumb, it is not wise to run the pack below 3.7v/cell under load. At 7.8 volts on a 2s pack, I would be recharging before flying again. There's no telling what kind of voltage sag the airplane is seeing either, it's always better to play it safe than sorry.
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