Of Amps, Volts, and Watts! - RC Groups
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Apr 28, 2011, 12:10 PM
Registered User

Of Amps, Volts, and Watts!

I have the Protek 40 power supply which has 4 individually switched 16 amps outputs. (13.8 V, 40 amps, 520 Watts). On each of the four outputs I am plannig to hook up and charge the following batteries:

1. I am planning to use the Hyperion DUO, charging 2 6S 5 Amp LIPO batteries at 4 amps;
2. using a second charger, the Protek DUO again charging 2 6S 5amp LIPO batteres at 4 amps
3. using a single hyperion charger, again putting up one 6S 5amp LIPO at 3 amps
4. and exactly the same as (3) on the 4th output.

By my count, this should put a total load of 22 amps and slightly more than 300 watts on the power supply. Will that work or is that too much?

Any help would be greatly appreciated!
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Apr 28, 2011, 03:33 PM
Registered User
S9coldfire's Avatar
Keep in mind that Power (Watts) = Voltage (Volts) x Current (Amps). And 6S is not the 13.8V of your power supply, but ~25V when charged. By conservation of energy, the V & A can change, but the power has to be the same in the power supply as all of the power in the chargers. So your chargers take some of the current and convert it to a higher voltage (from 13.8V to 25V).

So using your current levels it would be 22A x 25V = 550W, which is greater than the 520W your supply is rated for. You might be able to get away with 3A on each batt (18A x 25V = 450W), but that doesn't account for the power required to run the chargers and the wasted heat. You could give it a try and if you're not reading 3A on each try reducing the current a little more or just don't plug in quite so much at one time.
Apr 28, 2011, 03:52 PM
Rocket Programmer
jasmine2501's Avatar
Also, you need to use the fully charged voltages, since you're charging them all the way up. Just before finishing, before it goes into constant-voltage charging stage, the battery is almost fully-charged, and still being hit with the amperage you selected. So, the total wattage input required by your charger goes up as the battery gets closer to being done.

With a 6S pack charging at 4 amps, it's possible to need (25.2V * 4A) = 100.8 watts (+ a little bit for efficiency losses)

Then you also want to have a little breathing room in your power supply, since running it at maximum output for a long time will definitely make it get hot, and the heat can build up and increase the wear rate, eventually causing a failure. The Hyperion chargers will shut down and beep at you, if the power supply starts to fail. So, you can run it up to the limit, wait for one of the chargers to fail, then back off the amperage.
Apr 28, 2011, 07:51 PM
Registered User

of volts, amps and watts

Thanks to both of your comments S9coldfire - and to Jasmine, as always, very useful. Of course, the batteries go beyond 22.2 when full - that simply didn't cross my mind.

Thanks again!!
Apr 28, 2011, 07:56 PM
Rocket Programmer
jasmine2501's Avatar
S9 mentioned it, but I missed it when reading because he put your 22 amps right next to the 25 volts, and I reversed it in my head. So I wanted to be sure to mention it. Since you already own your chargers it isn't a big deal, but it's something people often miss when they are choosing a new charger.
Apr 28, 2011, 10:15 PM
that's gonna leave a scar
KCinNC's Avatar
wooh...if charging lipos were easy.....it wouldn't be any fun

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