How long will this battery last using inverter?

Lots of great comments thank you. Certainly less than I remembered. Someone said something about fans and TVs not drawing much. That’s true, I am probably over stating what I will be drawing but I certainly didn’t want to over estimate my run time so this exercise was helpful to me. I suspect my real draw will be closer to 140-150 so that will boost my run time by 25 percent, but still less run time than I was hoping for.

Is the best way to determine watts used is by looking at back of the tv and if it says 50 watts and I’m running 2 TVs, then burn is only 100, then adjust for the 90 percent efficiency so maybe I’m at 110-115?

100ah @ 5A ~ 85ah@18A, 85ah/18a - 4.7h /2 - 2.3hrs
100ah @ 5A ~ 75ah@25A (RC180)

my box fan does not like cheap inverter.

allen8106 wrote:
Batteries are considered discharged at 11.6 volts. If you are taking them down to 10 you are damaging them.

I believe that is resting. BCI reserve capacity (RC) is 25 amp draw to 10.5 volts and I believe this is the common voltage under load to designate 100% discharged.

Mostly semantics. Ether 11.6 or 10.5 is too low to get decent life out of a battery.

Now that I think about RC rating in minutes.... OP could probably use that as a guide as the draw is similar. Just cut the RC minutes in half to get to 50%. Trojan group 27 has 175 minutes so 1.5 hours could be real close.

pianotuna wrote:
Hi,

About 1.34 hours to 50%. Discharge is not linear.

tealboy wrote:
connected to a 100 amp hour deep cycle battery with a 200 watt continuous load.


Is the math 200/10=20 amps which means 2.5 hours run time before reaching 50 percent and shutting down or can I get a decent amount more run time!

The SG and voltage per SOC during discharging is fairly linear especially for the top 50%. Recharging is different with SG lag and the voltage jump past 80%

OTOH, when the draw is by inverter, a steady inverter load will have the amps draw rising as voltage goes down to try to maintain the watts. So in that case it would not be so linear.

Batteries are considered discharged at 11.6 volts. If you are taking them down to 10 you are damaging them.

Ed_Gee wrote:
Rule of thumb: for 100W AC , the 12VDC current out of your battery would be ~ 10 Amps, so your 200W load would be drawing about 20 Amps from the battery. That gives you about 2 1/2 hours to reach the battery capacity half point where you should stop. If you run your battery down to 10.5 VDC more than once or twice you most certainly kill your battery.

pianotuna wrote:
About 1.34 hours to 50%. Discharge is not linear.

So 1.5 - 2.5 hours is a reasonable range.

I would go for the low number.

100 amp hours. IF Deep cycle you can use 50 If not 25
200 amp load at 90% conversion effiency means roughly 220 watts
Divide by 12 .. Well normallyu I'd just divide 200 by 10 to give 20 amps at 12volts. Add in the Purkett (Spelling) effect.. about 20 minutes.

Hi,

About 1.34 hours to 50%. Discharge is not linear.

tealboy wrote:
connected to a 100 amp hour deep cycle battery with a 200 watt continuous load.


Is the math 200/10=20 amps which means 2.5 hours run time before reaching 50 percent and shutting down or can I get a decent amount more run time!

Rule of thumb: for 100W AC , the 12VDC current out of your battery would be ~ 10 Amps, so your 200W load would be drawing about 20 Amps from the battery. That gives you about 2 1/2 hours to reach the battery capacity half point where you should stop. If you run your battery down to 10.5 VDC more than once or twice you most certainly kill your battery.

assuming this battery is 100AmHr at the 20Hr rate of 5amps
using 17-18 amps, 6hrs to total dead if inverter has extreme low voltage shut down, maybe 3.5 hrs to 11.x volts

TV won't use that much, neither will a fan
seems like you might be trying to use a small electric heater

now you have to recharge a dead battery, all day generator or engine run

NOT the best of ideas

good thing to ask questions first
you could try it one time 'at home' in driveway and find out for real then charge battery to full could take 2 days reach full charge zero amps

keeps us posted