3S LiPo (12.6v) AND Inverter (Power usage & Battery Drain)

Thread Starter

Guest3123

Joined Oct 28, 2014
404
So if your devices use 120VAC line voltage, and they draw 150 Watts of power, how much current will that draw from the batteries if you wanted to use LiPo batteries to power an inverter?

Well, ohm's law states that Power (Watts) divided by Voltage (VAC or VDC) equals current (I).
150 Watts / 120VAC = 1.25 Amps.

So what about batteries? The 3S LiPo battery has a maximum fully charged voltage of 12.6VDC.

150 Watts / 12.6VDC = 11.904Amps, or 11.904 Amps for 1 hour is equal to 11,904 mAh.

So if I had a battery, 3S 12.6vdc, 5,000mAh (5Ah), rated for 25C. 25 x 5Ah = 125 Amps.

5 Ah battery / 11,904 mAh = 0.4200268 Hours.

0.4200268 hours x 60 minutes = 25.201 Minutes.
0.201 x 60 seconds = 12.096 seconds. (25 Minutes : 12 Seconds), 100% Efficiency.



Does this look correct?
 

#12

Joined Nov 30, 2010
18,224
ohm's law states that Power (Watts) divided by Voltage (VAC or VDC) equals current (I).
Actually, that's Watts Law.
Yep. You seem to be running the math just fine.
Except it's a bit too perfect. Batteries age by losing some of their capacity and there's no such thing as a 100% efficient converter.
You can run the math to 3, 4, 5 digits, but those digits don't mean squat in the real world.
The tighter you math, the more certain the circuit won't turn out exactly that way.
 

Thread Starter

Guest3123

Joined Oct 28, 2014
404
Actually, that's Watts Law.
Yep. You seem to be running the math just fine.
Except it's a bit too perfect. Batteries age by losing some of their capacity and there's no such thing as a 100% efficient converter.
You can run the math to 3, 4, 5 digits, but those digits don't mean squat in the real world.
The tighter you math, the more certain the circuit won't turn out exactly that way.
Watt's Law... I honestly didn't know what it was called.
Now I know when I convert down to a lower voltage, I know what it's called.

I kinda figured it wasn't going to be exactly 100%, but, it's still good practice to take a look at roughly how long it might last.
 

#12

Joined Nov 30, 2010
18,224
it's still good practice to take a look at roughly how long it might last.
Certainly. It's just that, "roughly" can be done in your head with about 2 or 3 digits.
For instance, what I actually did was, "12.6 volts times 11.9 amps = a fat 12 squared."
That's 144 fat and you said 150 watts. Roughly close enough.;)
 
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