Posted by lance_ryley (lance_ryley@…>)
Mdurki,
I use a cordless drill, but I thought I’d comment on it since it is an
interesting and useful exercise. First, you need to figure out what
kind of drill you’re going to use. I found a Craftsman Professional for
the purposes of this exercise with a draw of 6 amps at 120 volts.
6amps X 120Volts = 720 Watts, which is the minimum sized inverter
you’ll need IF the only thing you’re running is the drill AND the
drill’s “startup” draw isn’t much more than it’s running draw. Assume
that it draws 8 amps at startup (probably unrealistic for a drill, but
for edification’s sake) and you have a startup draw of 960 Watts, so
you’ll need at least a 1000 Watt inverter. If you’re only planning to
run power tools and lights, and microwaves, you can get away with a
modified sine wave (Prowatt 1000, about $250), but if you plan to run a
TV, Computer, Stereo, etc, then you’ll need to spend the extra money on
a pure sine wave inverter to avoid damage to the electronics (Prosine
1000, about $625).
Ok, so how long will your batteries run that power drill? Turn AC Watts
into DC amps with the following formula:
AC Watts/12 * 1.1 = DC Amps, so 720 Watts = 66 DC Amps
Doesn’t seem like much, right? Cool. How long can you run the drill?
Assume you’re inverter’s connected to an 8D battery, fully charged, 200
Amp Hours capacity. 200amphours/66amps = ~3 Hours! only… whoops… you
never want to discharge your batteries below 50% - very bad for their
longevity, so you really only have 100 amp hours to play with on that
battery, so you can run the drill for ~1.5 hours - again, assuming a
fully charged battery and no other loads - only, here we go again,
dagnabbed batteries! Higher amp draws deplete the battery at higher
rates, so you’ll really only get about 1.3 hours off that drill. A 100
amp hour battery gives you around 40 minutes before it’s time to run
the engine/generator/windpower/solar/shore charger.
Now that might be enough drilling for the day… if you were just going
to drill a few holes it’s probably not a bad deal, once you get over
the price of the Inverter. Personally, I don’t think I’d want to put
that much strain on a $550+ battery when I could buy a new 24v battery
pack for the drill for around $120.
Or you could spend around $700 for a honda 1000 generator… very quiet,
can run a battery charger, and should have ample power for your drill.
It’s also pure sinewave, so when you’re done drilling, you can plug in
the mini-fridge and the television and watch the game 
Hope this helps explain how you can figure out the loads and inverter
sizes you need for various applications.
lance
bright star
— In freedomyachts2003@yahoogroups.com, “mdurki” <vaughan@i…> wrote:
I’ll try again:
The battery packs of my 24 volt Craftsman cordless drill are beginning
to show wear, and I know that some of you use an AC drill with an
inverter. I would like to ask some questions about the arrangement.
-
Is it satisfactory?
-
Is the draw on the batteries significant?
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What size inverter to you need?
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My boat has an AC receptacle at the nav table; is that the one you
are using? and how do you have it hooked up?
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What drill are you using? How much torque?