[HELP] Trying to build very specific portable battery!

111W for 3 hrs = 333Wh. A 100% efficient inverter powered from 12VDC would therefore need a capacity of 333/12 = 27.75Ah. Allowing for inefficiencies you'd need around 40Ah @12V (or 80Ah @ 6V). Hence the car battery, or equivalent.

 

It has wheels, so is portable. Box it all up and you're good to go



Martin

 

An example here

 

For your calculations, Alec_T did say you must also look at the inefficiency.
Efficiency( approx 67%) and select a power source capacity from that.
So your calculation of 10Ah needs to be much higher.

Having a run time from 30 minutes to 1 hour means you will have to calculate at 1 hour as it is double the requirements.

If you want specifics, you have to be specific.

 

Why don't you buy an AC inverter and try it out? You are gonna need an inverter no matter what "battery" you come up with to power it, so you might as well get that out of the way now.

I do think you will be disappointed in the "run time" you get from a pair of 6V lantern batteries. Even the 12 V 22 AH sealed lead-acid will only provide 100 watts a power for about an hour before you have to stop and re-charge it. Deep discharge of lead-acid batteries is not recommended, even for the ones labeled as such, or labeled as suitable for marine duty. Other battery chemistries are not as sensitive, but always follow the battery manufacturer's recommendations concerning discharge and re-charge parameters. Oh, and why does the battery have to be a flat cylindrical shape?

A few years ago I bought an inverter for the sole purpose of powering up my HP laptop while on long road trips. I probably could have found some sort of "adapter" that would plug into the cigarette lighter socket, or into the auxiliary power socket, to provide the right voltage to my laptop, but since I already have a line-operated thingy to recharge the laptop battery, I figured why not plug that into an inverter and power the inverter from the cigarette lighter socket? Plus, I would then have 115 VAC power available for other purposes while "on the road".

Usually the laptop goes into the hotel room for the night and I connect it to an HDTV in the room with an HDMI cable, powering up the laptop from a convenience outlet. Using the hotel wireless WiFi, I call up Netfilx or Amazon Video on the laptop and stream movies from the laptop to the big-screen TV provided by the hotel. I have never had a bandwidth problem doing this, but your mileage (or kilometers) may be different. On the road, I don't use the laptop much, especially if I am driving. My wife insists on it. So, it turned out not to be a very useful purchase after all since I gave up on my Sprint "hockey puck" hot spot because it was seldom used and very expensive on a month-to-month basis.

It might help if you told us what you actually want to do with your rig. That is, describe the problem instead of what you think might be a good solution. For example (theoretical only): "I have diabetes and during long road trips my feet become swollen and I need to plug in a foot-warmer with built-in massage magic fingers. The Diabetes-R-Us store had a really spiffy model on sale which I purchased, but unfortunately it requires 110 - 120 VAC, 50/60 Hz, 120 watts and I need to power it for portable operation.... I am a long-haul truck driver with in-cab 12 VDC electricity available to power this puppy.... yada, yada, yada."

Hop

 

To answer your question. A 120W appliance operated for 1 hour need 120 Watt Hours.

From a 12V battery this is equivalent to 10 Amp Hours.

But,

1. Efficiency will likely be about 80%, so 10 / 0.8 = 12.5AH.

2. Batteries of this size are rated when discharged over 20 hours. At higher discharge rates they do not have as much capacity. At a discharge rate of 1 hour, the capacity is likely 1/2 the rated capacity. So 25 Amp Hours.

So, to run your device for 1 hour off a 12V battery, I would expect it to take a battery rated at about 25AH.

Bob