Learn me power inverters

I occasionally wish I could work on something with power tools when I am nowhere near an outlet. I see power inverters advertised for cheap and was wondering what the minimum.output would be to run a grinder or 110 volt welder off of it? And would I have to get another battery or alternator to do this even if I left the host vehicle running during use? Just curious how realistic this option is.

I have a 5000 watt that I carry that does a good job. I don't know about a welder, but it will run a 12" chop saw so a grinder won't be a problem. For short jobs as in 10 minutes or less, the battery shouldn't be an issue. For long jobs lasting hours, get a generator.

A 5Kw inverter is going to draw better than 400 amps at full load. It will take a lot of battery to run it long. I run mine off of a deep cycle marine battery. From a full charge, running small stuff, battery chargers, a hammer drill and a fan in the summer, the low voltage alarm goes off after a couple of hours. With a heavy load it will go off in minutes. I've started carrying a generator to the all day jobs and the inverter gets used on service work where I only need power for a short period of time.

Edited for clarity and because I can't spell worth a damn.

Welder would require a MASSIVE inverter. W = V x A. So, to make 20 amps of 120v would require 200 amps of 12v. Then take into consideration that there is a rather large potential for inefficiency in the conversion and you might need 300 amps to drive the inverter.

The inverter would need to be very large... on the order of 5000 watts. They typically cost in the $600 range and weigh about 50 lbs. Your battery would last about 3-4 minutes They're designed for large yachts which sometimes have the equivalent of 50-60 batteries.

Most welders are on the order of 24v output. Many of the offroad guys carry a set of jumper cables and some welder sticks. They put two batteries in series and use the jumper cables as a stick welder. No need to step up voltage just to step it down again.

Just remember watts equals volts times amps. Or, the easy way to convert (since 120v is ten times 12v), just take the amperage of the appliance and multiply by 10. If you want to run a 10-amp grinder, it will draw 100 amps or more at the battery.

Thanks for the insight! Very helpful!