How long lifepo4 battery power tv

[mrel]

Have lifepo4 battery 100 ampere hour, 12 volts.
Questions
(1)Using power inverter 400 watts ,not pure sine wave inverter, connect inverter to battery plus and minus terminal.
(2) Television draw 120 volts ac using 25.75 watts, how long can use battery and the inverter before battery drain out?
mrel

 

[bertus]

Hello,

What is the efficiency of the used power inverter?
Assuming an efficiency of about 80 %, the consumed power is about 32 Watts.
At 12 Volts that is 2.7 Amp.
100 Amphour / 2.7 Amp = 37 hours.

Bertus

 

[dave9]

If you mean that you have one of those (consumer rather than industrial grade) battery power packs sold as an already integrated unit and its rating is 100Ah and 12V, then it is most likely that it is not 100Ah AT 12V but rather, 100Ah at 3.7V. Mathematical shenanigans.

 

[Harald Kapp]

+1 for @dave9 's assumption.

That would make 100 Ah at 3.7 V equivalent to 100 Ah/12 × 3.7 = 30.8 Ah @ 12 V assuming an ideal step-up converter. Since such a thing doesn't exist assuming 80 % efficiency (as @bertus did) leaves you with 30.8 Ah × 0.8 = 24.6 Ah useable capacity.
Stepping this up to 120 V again with 80 % efficiency leaves you with 24.6 Ah × 12 / 120 × 0.8 ~ 2 Ah.

Your TV requires 25.75 W / 120 V = 0.215 A. Your battery should last for 2 Ah / 0.215 A ~ 9 hours.

 

[dave9]

OOPS! I'm wrong. LiFePO4 nominal is 3.3V not 3.7V... so take Harald's calculation and * 3.3/3.7 = ~8hrs runtime, although with 3.3V cells, I wonder of they just put them in parallel series of 4 cells for 13.2V and called it 12V to save on the BOM by omitting a boost converter, then it gets 20% better efficiency by not having one.

Can you link to this product if it is an all in one rather than self-built battery?

 

[mrel]

Have lifepo4 battery 100 ampere hour, 12 volts.
(1)Using power inverter 400 watts ,not pure sine wave inverter, connect inverter to battery plus and minus terminal.
(2) Television draw 120 volts ac using 25.75 watts, how long can use battery and the inverter before battery drain out?
I am one that post this questions ,I did test ,using setup as i posted the battery power television for 32 Hours before Bms turn the television off.
mrel

 

[Harald Kapp]

32 h × 25.75 W / 120 V = 6.87 Ah on the 120 V side.
Equal to 120 V / 12 V /0.8 × 6,87 Ah = 85 Ah on the 12 V side. The difference to the 100 Ah rated are possibly due to a lower than assumed efficiency of the inverter, a not fully charged battery and/or a bit less than 100 Ah capacity of the battery.
The ratings of your battery are obviously and truly 100 Ah @ 12 V, not at 3.x V as we assumed.

 

[dave9]

We need to know exactly what this "battery" is. It cannot be just a battery and be 12V, the sum of a series of LiFePO4 will not equal 12V nominal. Further, how was the TV average wattage determined?

We are left assuming things that I am not comfortable assuming, if you needed assistance doing a basic power conversion equation.

If you have this assembled and working to test, why even ask us rather than just do the test and there is your answer?

The bigger question in my mind is why devote all the expense of a 100Ah LiFePO4 battery to power a TV? I could appreciate it if living off the grid but then, I'd want far more than only a 400W inverter, since that can't power more important things like a stove, HVAC, decent sized refrigerator, coffee maker, etc. unless a low power variant more often designed for mobile 12V use and then you don't need the inverter at all.