12V battery + inverter for emergency use?

[MushCreek]

Having just come off of a long power outage, I had a question for the electrical gurus out there. Suppose I had a 100 AH deep cycle battery, and an inverter to convert it to 120 VAC. Pretty common stuff. How long could that battery provide usable power in an emergency? Lets say the draw is 1200 watts, or 10 amps at 120V. How long could that battery feed that draw before the voltage got too low? One hour? (100 amps @ 12V?) Not that I would use it that hard; just curious. I figure modern TV's use very little power, so a rig like this would at least enable one to watch the news, charge phones, and maybe make a pot of coffee.

 

[bczygan]

You need a magic battery.

 

[dogdog]

That calculation is assuming that you have 100% conversion and efficiency... mostly not the case... in real life, probably 20 to 30 minutes if you are lucky... pretty sure if you have those cheap modified sine wave inverters, it'll destroy your electronics before the juice of that battery runs out.

 

[ddawg16]

If you want to watch TV, you would be better off getting a DC powered TV. They do make portable radios for the news.

And if you want to watch TV....I hope it's over an antenna.....if the power goes out, you may not have cable.....depending on your setup.

If you are worried about it, you would be better off with a UPS. Not only will it run some electronics for an hour or two, it will do a great job of protecting your electronics.

 

[Road Wrench]

Deep cycle battery capacity by amp hours is measured at a 20 hours to discharged, and 100 hours to discharged which is the capacity usually on the battery label meaning it supplied 1 amp for 100 hours before it was considered fully discharged. The total amp hours is reduced as the draw rate is increased over that 1 amp rating. No load resting voltage of a lead acid battery is 11.8 fully discharged and 12.7 fully charged. Inverters have an operating range typically between 12.0 and 14.5 volts. Below the min voltage will trigger the low voltage protection and cease operation. To supply the enough current to an inverter at a voltage within the operating range of the inverter to power 1200 watts will take multiple batteries configured in a bank, so that under the draw of roughly 100-110 amps the voltage drop does not fall below the operating range. Deep cycle batteries should not be cycled below 50% capacity repeatedly, as it shortens lifespan considerably. True deep cycle batteries which you wont find at sams or costco can be cycled a bit deeper. A bank of four group 29 batteries rated 110 amp hours a piece wired in parallel for 440 amp hours could supply 220 amp hours at 50% cycle. No load voltage of the bank at 50% is 12.2 volts. A large current draw will have the voltage sagging below that, which would trigger low voltage shutdown in the inverter if your pulling heavy with it. So at 1200 watt load you could expect to hit the low voltage protection before reaching 50% of discharge. So you likely would get 1 to 1.5 hours runtime on those 4 batteries running an inverter powering 1200 watts load. On just one battery, its a matter of minutes before it trips.

 

[Ole Slewfoot]

I have a 3K inverter and a diesel truck. It will run pretty much anything for a little while without starting the truck.
My kitchen is all gas, so really with a coffee grinder, a string of s lights and a book, I'm fine till the fridge gets warm.

 

[ForceFed70]

Having just come off of a long power outage, I had a question for the electrical gurus out there. Suppose I had a 100 AH deep cycle battery, and an inverter to convert it to 120 VAC. Pretty common stuff. How long could that battery provide usable power in an emergency? Lets say the draw is 1200 watts, or 10 amps at 120V. How long could that battery feed that draw before the voltage got too low? One hour? (100 amps @ 12V?) Not that I would use it that hard; just curious. I figure modern TV's use very little power, so a rig like this would at least enable one to watch the news, charge phones, and maybe make a pot of coffee.

Technically 100Amp Hour = 100amps for an hour. But as others have mentioned there's more to it. Efficiency of conversion, actual capacity vs advertised capacity, battery condition, and the fact that you never want to draw the battery down below 25% are all good examples of influencing factors.

From my own experience I can say that a single 12V deep cycle battery will not be able to power a 1200W load for long. 15-20 minutes at best assuming a good healthy battery.

 

[DFB]

You need to GET a small genny for your needs it sounds

Cripes many Milwaukee battery tools like lights and radio will get you the news just fine and charge your phone when the power is out

Oh and a small power invertor running of a motor vehicle can keep your batteries fully charged too

 

[HOTFR8]

A decent jump pack and small inverter would cover the very basic.

 

[MushCreek]

Sounds like I can use one for small loads, such as electronics, but the heavy loads would require running it off of a vehicle. Ironically, I HAVE a generator, a good one, but due to lack of use the carb is gummed up. I was lazy about draining the gas out of it one time, and the next time I needed it, it was a no-go. The question about the inverter was more out of curiosity. I really need to get my genny fixed up, and invest in a transfer switch.

 

[u3b3rg33k]

I have 2x 12v AGM (90Ah IIRC) hooked up to an APC 1250RM. i get 45-60 min runtime at about 60% load.

I used to have a 1500W inverter mounted in my trunk (trunk mounted battery). that was way easier to deal with than starting up a generator for 99% of things. I could even run a circular saw off it if I didn't feed too fast.

 

[Captain Spaulding]

Sounds like I can use one for small loads, such as electronics, but the heavy loads would require running it off of a vehicle. Ironically, I HAVE a generator, a good one, but due to lack of use the carb is gummed up. I was lazy about draining the gas out of it one time, and the next time I needed it, it was a no-go. The question about the inverter was more out of curiosity. I really need to get my genny fixed up, and invest in a transfer switch.

Carbs are cheap. I keep both a rebuild kit and a complete extra carb for my generator on hand. Cost $35 IIRC.

 

[b-boy]

If you want a practical test of this, I had a power outage a few years ago. I used my boat battery and a radio shack invertor to power 1 light and a radio. It didn't last long. I only got a few hours out of it.

 

[slow]

General rules for an offgrid power solution like this (these are very conservative, but gives a ballpark of capacity) 10% of the amp hour of the pack should be the draw rate, so a 100 amp hour battery, should be able to provide 10 amps continuous. The depth of discharge, at 50%, would mean your 100 amp hour pack can provide this 10 amps for 5 hours.

Assume 90% inverter efficiency, you can power a 100 watt appliance for 5 hours.

To be fair, I have a similar setup as one of my emergency power solutions, but it is intended to power small electronics and a fan at night, I also have a 100 watt solar panel to charge it during the day, as well as ways to charge it off the generator or vehicle.

 

[bczygan]

Having just come off of a long power outage, I had a question for the electrical gurus out there. Suppose I had a 100 AH deep cycle battery, and an inverter to convert it to 120 VAC. Pretty common stuff. How long could that battery provide usable power in an emergency? Lets say the draw is 1200 watts, or 10 amps at 120V. How long could that battery feed that draw before the voltage got too low? One hour? (100 amps @ 12V?) Not that I would use it that hard; just curious. I figure modern TV's use very little power, so a rig like this would at least enable one to watch the news, charge phones, and maybe make a pot of coffee.

Natural gas powered emergency generator?

Bill

 

[Citation]

Technically 100Amp Hour = 100amps for an hour. But as others have mentioned there's more to it. Efficiency of conversion, actual capacity vs advertised capacity, battery condition, and the fact that you never want to draw the battery down below 25% are all good examples of influencing factors.

From my own experience I can say that a single 12V deep cycle battery will not be able to power a 1200W load for long. 15-20 minutes at best assuming a good healthy battery.

I used to work in energy storage. It isn't correct to assume 100Amp Hour = 100A for 1 hour (a 1C discharge rate). When buying cells we always specified discharge rate associated with a stated capacity.

 

[Falcon67]

Honda EU2200 is a better idea than any battery and inverter for a 1200w-ish draw over any period of time.

 

[kelpaso1]

Even a Honda EU 1000 gen will run a lot. When the power goes out I use it to power 2 36 inch tv's, 2 tv boxes, router, cordless phones, 2 laptops, 2 fans for my wood stove, 4-5 LED lamps. And if the power is out long enough it will also run everything mentioned PLUS my fridge. And the little honda gen will run for at least 6 hours using only a half gallon of gas if I don't plug in the fridge. About 4 hours if I have the fridge plugged in.

 

[DFB]

You know talking about cheap little gennys and related to the original inquiry a guy I worked with was into building his own house on a piece of rural land. So he purchased one of those $89 HF 800W units, I said "What good is that? You can't run a table saw or air compressor with it!" And says "No, but I can run my TV with it"

 

[MushCreek]

I have a 6500 watt Honda generator. A real Honda genny, not just the motor. Street price is like $2500. But I do need to get a carb for it, and then I have to take proper care of it. One of the problems is storing gas for the possibility of an outage. No natural gas available here. The good news is that it could run most of my house. The mini-splits only draw 10 amps max @ 240V., so the genny would run them for heat. Our house is so well insulated (ICF) that it only dropped 3 degrees in 36 hours. My only real concern was the food in the freezer, but even that was fine for the duration.

I think I'll pick up a cheap inverter to run the TV and charge the phones. Without smart phones, we had no TV or internet. I didn't know my job was opening late on Monday until someone texted me.

 

[ForceFed70]

I used to work in energy storage. It isn't correct to assume 100Amp Hour = 100A for 1 hour (a 1C discharge rate). When buying cells we always specified discharge rate associated with a stated capacity.

Yes, I know that. But regardless - 100amp Hour literally means 100amps for 1 hour. Or 10 amps for 10hours, or 1amp for 100hours.

I agree - Amp Hour is not a good way for measuring battery capacity/ability. You'll notice I estimated 15-20 minutes for a 100A load and I think that was being generous.

 

[Backwodsurvivor]

I had a 1200 watt inverter that recently went out. I replaced it with a 200 watt cheapo. Realistically I only run a router and maybe a light bulb or 2. Router pulls 50ish watts and 2 LED bulbs are 15 watts maybe. Plus charging the phone will last all night.

 

[HenryAZ]

If you want to watch TV, you would be better off getting a DC powered TV. They do make portable radios for the news.

This, and some 12v lights. This would increase your battery life a lot. Check RV places for 12v accessories.

 

[dogdog]

Skip the battery setups..

I think I saw an solution on youtube.... an Electric motor powered Alternator that can power the driving motor AND you'll have Infinite P O W E R R A....

 

[Captain Spaulding]

Skip the battery setups..

I think I saw an solution on youtube.... an Electric motor powered Alternator that can power the driving motor AND you'll have Infinite P O W E R R A....

I spent several pages of typing to convince a person on another forum that he couldn't hook an inverter to a battery, plug a charger into the inverter and be set with all the power he needed. I'm not convinced he ever believed me.

 

[MushCreek]

We have LED camping lights that last a LONG time on batteries. I have a portable radio, and spent a long time trying to find a news station, but they don't really seem to exist around here. Our 32" TV only draws 45 watts- hardly an energy hog.

 

[TractorJeff]

Skip the battery setups..

I think I saw an solution on youtube.... an Electric motor powered Alternator that can power the driving motor AND you'll have Infinite P O W E R R A....

I had an Electrician explain this to me when I was about 7 years old!
Sad part is I understood the whole speed drooping under load and it would go slower and slower till it stopped!

 

[theoldwizard1]

Skip the battery setups..

I think I saw an solution on youtube.... an Electric motor powered Alternator that can power the driving motor AND you'll have Infinite P O W E R R A....

Believe it or not, in the 1960, early computers used a large 3 phase AC motor to drive a low voltage DC generator to supply the necessary current. The worked very well providing very steady current, but did require regular maintenance, like lubing the bearing (couple drops of light oil in the feed cup), cleaning the carbon from the brush wear and replacing the brushes.

Yes, they had computers back then !

 

[dogdog]

We have LED camping lights that last a LONG time on batteries. I have a portable radio, and spent a long time trying to find a news station, but they don't really seem to exist around here. Our 32" TV only draws 45 watts- hardly an energy hog.

It's fine when you are using dc to dc appliances even with buck boost or buck converters they are still only 90-ish% efficiency... but when you are talking about taking the inverter to AC then change it back to DC to run electronics... well I think those efficiencies goes down very fast... especially if you ever look at the Modified sine wave forms .. There are plenty of youtube videos on this... even your favorite AvE have one. Some of those Modified Sine wave inverters are very damaging to electronics that also uses inverter technology to converts AC to DC TV operating voltages...basically you are doing two or three conversions... From DC to emulated AC then from AC back to DC... It gets pretty bad...

I remember I tried a cheap 300Watt inverter to power a 75Watt Laptop adapter... that thing almost fry it self after a 2 hour trip and the battery go drained on the laptop...

 

[dogdog]

I had an Electrician explain this to me when I was about 7 years old!
Sad part is I understood the whole speed drooping under load and it would go slower and slower till it stopped!

LOL that is because your set up is not 110% efficient.... you got to use those super lubes... that is the secret sources I believe.

Believe it or not, in the 1960, early computers used a large 3 phase AC motor to drive a low voltage DC generator to supply the necessary current. The worked very well providing very steady current, but did require regular maintenance, like lubing the bearing (couple drops of light oil in the feed cup), cleaning the carbon from the brush wear and replacing the brushes.

Yes, they had computers back then !