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Batteries & Chargers Discuss Li-P, Li-Ion, NiMh, Nicad battery technology and the chargers that juice 'em up!

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Old 12-07-2012, 04:58 PM   #1
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Default No Load Walll Charger voltage is Not Correct right?

The typical voltage from a rc wall charger is not really the charge voltage without a load right? All the ones I have read output volts below what a fully charged pack would normally peak at so...

The load activates the charger? how?
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Old 12-07-2012, 05:27 PM   #2
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LiPo chargers are amp limited. The voltage varies to whatever is required to push the pre set amps into the battery.
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Old 12-07-2012, 05:29 PM   #3
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I'm thinking RC wall chargers are not generally for lipos.
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Old 12-07-2012, 05:36 PM   #4
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Originally Posted by Henry Sistrunk View Post
I'm thinking RC wall chargers are not generally for lipos.
Henry
You can get LiPo 'wall wart' type chargers. Many budget price RTF kits come with them.

But the OP didnt specify what type of charger, so fair point...
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Old 12-07-2012, 07:00 PM   #5
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It would indeed be interesting to know exactly what chargers the OP is talking about.

Every standard NiCd/NiMH wall charger I've seen measures way MORE than the battery charged voltage e..g. the standard TX 9.6V (about 11.5V charged) charger typically measures around 18V with no load.

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Old 12-07-2012, 08:33 PM   #6
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Most all wall warts used for Nixx type batteries will read a much higher voltage than what is to be charged. They depend on the internal resistance of the charger to drop the voltage down to a proper level to charge the battery that is connected to it. Most of these will read open an open circuit voltage of at least 3 or more volts above the voltage of the battery that you will charge with it. If it reads less, it will not charge the battery at all, in fact may even discharge it depending in what caused the fault in the charger. An extreme example of this is some of the early vintage (1950"s versions) would read 115 volts open circuit as the charger was just an isolation transformer with a rectifier diode and a current limiting resistor in series with the output. The voltage drop across the resistor would then drop the voltage to the required level.
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Old 12-08-2012, 12:41 AM   #7
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Its the charger that came with all my radios. The no load output is 6.15 volts and this goes to the nicad 8 cell transmitter. Works fine tho somehow..Got a full charge..
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Old 12-08-2012, 01:46 PM   #8
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In every case I've used, the charger follows the battery's voltage albeit will be higher to charge.
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Old 12-08-2012, 04:21 PM   #9
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To see what is really happening you need to measure the voltage with either a peak reading meter or use an oscilloscope. The conventional VOM will not give you an accurate measurement as this is usually not a nice clean constant voltage, it is usually either a full or half wave rectified sign wave. It is just a natural physical fact, the voltage of the charger must be higher than the voltage of the battery being charged or you will not get any charging current. You can approximate a peak reading voltmeter by putting a capacitor on the output while you are measuring the voltage with a typical VOM.
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