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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › How do you figure wattage on charging?
03-24-2015 10:07 PM  4 years ago
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McKrackin

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Lucasville,Ohio

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How do you figure wattage on charging?
How many watts does it take to charge two 6S packs at 25 amps?
I literally never use the word literally right.
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03-24-2015 10:23 PM  4 years ago
Eury

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Dover NH USA

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Whatever the final voltage of your pack is x desired charge rate will give you your max. It won't be exact, but close. I cheat and just start charging and my charger says what it's pulling from the PS.Nick Crego

Citizen #0168
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03-24-2015 10:23 PM  4 years ago
ssmith512

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Indianapolis, IN USA

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Watts = Volts x Amps.Steve
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03-24-2015 10:27 PM  4 years ago
Fauropitotto

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Tampa, FL

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Watts = Amps * Voltage

So say you have a single 6S 2200 mAH pack. Each cell is 3.7V, so 3.7*6 = 22.2 V at nominal charge. However, fully charged it will be 4.2V per cell, so 25.2V when fully charged.

Next, we need to know the charge rate. C= AH * amp, so 1C on a 2200mAH pack is 2.2 amps. 3C is 6.6 amps and so on.

So a single 6S 2200mAh pack charging at 3C will require 6.6 Amps.
A pair of 6S 2200mAh packs charging in parallel at 3C will require 13.2 amps.

Watts = Amps * Voltage

For a single 6S 2200 mAH pack charging at 3C:

Watts = 6.6A * 25.2V

Watts = 166.3

For a pair of 6S 2200 mAH packs charging at 3C in parallel

Watts = 13.2A * 25.2V

Watts = 332.64

If you need help calculating what sort of power supply you need, let me know.
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03-24-2015 10:50 PM  4 years ago
michael88997

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Lewisville,Tx

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I charger duo... it will tell you how many watts your using
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03-24-2015 10:55 PM  4 years ago
McKrackin

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Lucasville,Ohio

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I charger duo... it will tell you how many watts your using
Well duh...My power supply will too. Thanks
I literally never use the word literally right.
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03-24-2015 10:57 PM  4 years ago
McKrackin

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Lucasville,Ohio

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I was just wondering if I could get more than 40 amps worth of charging going on if I used two chargers at a time.

My power supply can only do 1200W though.
I literally never use the word literally right.
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03-24-2015 11:10 PM  4 years ago
Aaron29

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USA

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I've also heard use a fudge factor for inefficiencies in power supply / charger design. Expect about 2/3rd the watts at the battery for every watt of power supply, when all is said and done, due to power supply inefficiency and charger inefficiency.

So for your situation, 1200W power supply, losses between PS and battery I'd assume you have about 800W to give the battery. 800W/25.2V (for a 6S, it'd be 25.2V, don't use nominal, use end charge voltage to determine max amps). I get about 30amps.

I'm not seeing 40 AMPS unless you get a better PS. Don't push it.
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03-24-2015 11:21 PM  4 years ago
michael88997

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Lewisville,Tx

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I have HP 1200 power supplies in series and I have pulled 40 amps at 24v without any issue from them... might depend on the psu and how efficient they are.
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03-24-2015 11:25 PM  4 years ago
Aaron29

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USA

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It may push that, but the charger has inefficiencies as well. They are listed in specs, but if you assume 80% PS efficiency and 80% charger you can't go wrong with specs. They will do better than 80% and you will have a little headroom for component longevity. I see no reason to push for 40A to get 4C when 30A will do a 3C charge. It won't save but a few minutes.

Edit: a 1200 PS that no kidding does 1200 W probably sucks 1500 from the wall. The efficiency factors in at some point. I like to play it safe.
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03-24-2015 11:28 PM  4 years ago
McKrackin

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Lucasville,Ohio

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30 amps is not 3C with four 6S 5000mA packs but I see what you mean.I literally never use the word literally right.
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03-24-2015 11:30 PM  4 years ago
McKrackin

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Lucasville,Ohio

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I have HP 1200 power supplies in series and I have pulled 40 amps at 24v
My old 24V server supplies also hit 40 amps with my PL6.
I literally never use the word literally right.
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03-24-2015 11:30 PM  4 years ago
Aaron29

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USA

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Yeah I was saying a pair. If you are doing 4 expect 1.5C.

I only charge one pair at a time, the other is in the bird! I pop the battery on charge, while it's charging, I load the new battery in the heli, power up, servo checks and beepy noises check, fly, shootthesh1t, and the charger's done before I'm even ready to go back up. Wash rinse repeat.

Edit: Mine's a 10S bird. Logo 600. I charge a pair of 5S 4500's at 2-3C using 26A max and it's done in 15 minutes. I can't fly fast enough to outfly the charger. I need more rest.
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03-24-2015 11:40 PM  4 years ago
Aaron29

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USA

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Short answer to your OP is 1260W.

2 x 25.2 x 25=1260W
2 batteries, 25.2V end charge, 25A

I wouldn't try it. Because that's 1260W going into the battery. The charger will need a bit more than that from the power supply to account for losses. So, a 1200W PS will be overtasked.
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03-24-2015 11:47 PM  4 years ago
McKrackin

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Lucasville,Ohio

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My supply wouldn't be over worked. It would just limit the charger.

I'll just have to try and see what it does with two packs at 25 amps.
I wouldn't be too disappointed with a 33 amp charge I guess.
I usually charge the evening before anyway.

Typical day would be two flights with the 700 and a dozen or so with a micro.
I might sometimes fly a bit more with the 700 if I'm feeling it but not that often.
I literally never use the word literally right.
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03-25-2015 01:17 PM  4 years ago
ssmith512

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Indianapolis, IN USA

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Short answer to your OP is 1260W.
2 x 25.2 x 25=1260W
2 batteries, 25.2V end charge, 25A
That's not correct (unless the OP is talking about charging EACH pack at 25amps.)

You dont combine the voltage of multiple packs in parallel charging. If the charger is outputting a total of 25A to 2ea 6S packs in parallel, then the charger is outputting 25*(4.2*6) = 630W. Each pack is seeing 25/2 = 12.5A.

I was under the impression the OP was talking about total charge rate and not individual pack charge rate. My apologies if I am incorrect.
Steve
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03-25-2015 01:51 PM  4 years ago
ICUR1-2

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Ottawa, Ontario

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In most cases if your charger tries to draw to much from the power supply the charger will go into error mode "most times"

If you continually max out the power supply it will have a short life expectancy. Try to get a supply of 20% more that what you need.

Another to keep in mind is the wattage needed decreases as the battery charges up.
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03-25-2015 02:00 PM  4 years ago
ICUR1-2

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Ottawa, Ontario

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To determine how long it takes to charge a battery the formula is
60 minutes divided by the C rate

60/1=60, 60/2=30, 60/3=20, 60/4=15, 60/5=12

As you can see you get diminishing returns after 4C

since we only take out 80% of the battery, you use 80% of the batteries MAH rating so a 5000mah is actually 4000mah X the C charge rate to get the amps required to charge
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03-25-2015 03:11 PM  4 years ago
ssmith512

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Indianapolis, IN USA

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Also, just as a point of reference; if you aint chargin' at 1.21 gigawatts, then you aint chargin'.Steve
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03-25-2015 03:35 PM  4 years ago
Aaron29

rrProfessor

USA

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Ssmith, If he means 25a split between any number of batteries I would think stating the number of batteries would be pointless from a PS consumption perspective. I just assumed he stated two because the information was pertinent. There are duos that will do over 25a per side so it isn't a stretch to assume 25a per 6s.

Plus McK never used the word parallel. Looks like folks have different ideas what he's trying to do.

Maybe he can enlighten us?

Edit.nm. He stated he wants to hook up two chargers to one power supply. I stand by my math.
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