portable power carving

madmangil · #1 02-20-2005, 12:38 AM

Here's my idea and questions...

Get the following:
die grinder (2 amp at 120vac) (already ordered)
inverter (400 watt at 120vac) (have it)
rheostat (15 amp 120vac) (have it)
deep cycle marine battery (need it)

The above list should give me portable power to power carve away from home. Any suggestions?

I am wondering about the battery. Should I go small or as big as possible? Does anyone know how to convert 120vac amps/watts to 12vdc amps/watts? An 80 amp hour battery should run a 2 amp load for about 40 hours. ...that is if amps convert equally from 120vac to 12vdc. The inverter will probably cost some small amount of power. Knowing how long the tool will last on a battery would help me to decide what size battery to buy. Or the other way to go is if someone has already done this then they could tell me how long a tool lasts on a battery and inverter.

thank you in advance

gil
madmangil@hotmail.com

Ky_Whittler · #2 02-21-2005, 02:01 PM

Not sure how hte hours convert but from experience with my trolling motor I would get the largest I could find. Check into some of the charging units that are available through marine dealers. This could prolong the life of the battery as well as useful time. Whittler

Plain_Ol_Ed · #3 02-21-2005, 03:01 PM

2 amps at 120 v is 240 watts ( Power in watts = current in amps times voltage in volts). At 12 volts the battery will have to deliver 20 amps to provide 240 watts. As the battery runs down, or loses voltage, it will need to supply greater amounts of current to keep the power at the same level. As you correctly assumed, your going to have loss in the inverter. How much. Can't say. Will depend on the inverter, but efficiency should be somewhere between 80 and 95 percent. Not only that, but many inverters do not put out pure sine waves, but triangular shaped waves or square waves with various and assorted number and magnitude of spikes. How yours is, can't say. You might be lucky and have one that gives a pure or nearly pure sine wave. A quick look with an ocilloscope would tell or it may even say on the label or should be in the manual if you still have it. Keep the wires from the battery to the inverter as short as possible and as big as you can stand, 6 ga. should be fine. Anyway as the Whittler says get the biggest baddest battery you can find. Ain't nothin' worse than a dead or dying trolling motor battery on a real windy day. Whatever your going to use the rheostat for, it's going to eat power too. When you use it, it gets warm/hot, all that heat is going to be wasted battery power.

It might be simpler to just buy a small generator that could also be used for other things. Having a good supply of 120v available is not always a bad thing.

AlArchie · #4 02-21-2005, 03:32 PM

I have a 400 watt inverter and ran my Dremel from it with no problems. Used the cig lighter outlet in the truck and ran for a couple hours with no appreciable drain on the battery. Course I had a dual battery diesel so there was ample amps????? Used that setup for several months while travelling Alaska in 97.

Al

madmangil · #5 02-21-2005, 04:23 PM

Plain_ol_ed,
What I think that you are saying is that watts can be considered the constant, meaning that a particular electrical device will burn the same wattage regardless of the voltage or type of current (ac or dc). Also, given a particular electrical device, the amperage that it runs is inversely proportional to the voltage (amperage ALWAYS goes up/down as voltage goes down/up).
Am I making sense?
If I am understanding you then this is exactly what I need to know to decide on what size battery to buy.
gil

Hi_Ho_Sliver · #6 02-21-2005, 05:54 PM

why not just put an inverter on your vehicle? and you can always mount an extra battery under the hood and

electricbill · #7 02-21-2005, 06:32 PM

first ...dragging a 50 lb. battery around isn't really "portable"!!
as far as the inverter...Plain_Ol_Ed is right about it putting out a square wave instead of your normal household sine-wave...this matters more for electronic stuff...i.e. computers.
check the inverter specs. for its ability to run a motor...when a motor starts it has an inrush current many times higher than its running amps which that 400w inverter might not handle...
bill

dutchmanmk3 · #8 04-07-2006, 05:13 PM

Personally I would probably go with a 1/4" flex shaft (Wecheer makes one), and a good 18-24 volt cordless drill. But I have hooked up inverters in my van, and often use my Lincoln cordless Weld Pack as a power supply in the field.

An inverter with a a good 12V micro motor system (Proxxon) would probably be the most efficient. But waffling back and forth on voltage seems redundant ? Still, It Works !

The arrangement with the Cordless drill turned out to be the easiest for short term work, and the latter low voltage system ran the longest, but didn't offer a great deal of torque.