Using Inverters with Auto Batteries

[stanchion]

Despite the fact that I've been involved in
electronics all my life, I only know two things
about lead-acid auto batteries. CCA (cold
cranking amps) is the rating you use to
select the battery that meets the starting
requirements of your vehicle, and auto
batteries should never be deep cycled.
That's all I really know about these fifty
pound black boxes!<p>I've got a small hand-truck and I'd like to make a
cart that would hold an auto battery and inverter.
I want to run electric (the corded kind) lawn
mowers, chains saws, drills, etc.<p>These days you can buy 2000 watt continuous
modified sine wave inverters for under $200.00.<p>Typically, electric mowers or chain saws are in
the 12-to-13 amp range. Not a whole lot of
current at 120 vac, but ohms law really kicks
you in the butt when you drop down to 12 vdc!<p>The inverter would need a battery that could
supply at least 120-to-130 amps. The battery
must not overheat, and it should provide at least
60-to-90 minutes of intermittent power before
needing a recharge.<p>Is there such a beast available at my local auto
store? If I had to gang together three or four
of these lead and plastic blocks my cart would
be so heavy I don't think I would want to drag
around anything like that. Plus, charging and
storing all those batteries would be something
of a nightmare.<p>stanchion

[wolfcreek]

Don't use car batteries. They are not meant for deep cycle use. Get a couple of 100+ amp hour rated marine/deep cyle batterries from Wal-mart. You should be able to get them for 60-70 a piece.

[Chris Smith]

I second the motion. <p>Marine Batteries are what you need, deep cycle and use more than what you need by at least 25%. [min]

[jwax]

stanchion- Since this is a hobbyist forum, you ought to add as many batteries as you can afford to your pack, then add one more thing- A MOTOR!
Let your "Porta-Power-Pack" be self-driven!

[stanchion]

I used to visit marine supply shops all the
time. I clearly remember those big, bold, words
printed on every marine battery. "DEEP CYCLE,"
they all said. The funny thing is, my Dad and I
loved everything about the water. If we had to
spend more than a couple of hours on a boat we
would always get incredibly seasick!<p>I guess I thought I might be able to save some
bucks if I used an auto battery. You guys are
right. One or two deep cycle marine batteries is
only thing that will do the job at a reasonable
price.<p>stanchion<p>[ April 15, 2005: Message edited by: stanchion ]<p>[ April 15, 2005: Message edited by: stanchion ]</p>

[terri]

Get practical and buy a small gas generator and cart that around. Lead-acid batteries are not suitable for that kind of load/application and are a royal pain both in weight and maintenance, etc., etc., etc., etc., etc., etc. <p>Make sure the cart has large-ish diameter and large-ish tread wheels if you're going to push it around in the woods or any kind of rough ground.<p>Experience speaks.<p>If you are really, really, really married/dedicated to the idea of using batteries, you'd probably be better off to series-connect 8 or 10 small (maybe motorcycle-sized) batteries in series and run the equipment off the resulting 90 to 120 volts DC directly, since most of these motors are of the universal brush-type.<p>Oh. And go down to the drugstore and buy a truss. <p>You'll need it.<p>[ April 16, 2005: Message edited by: terri ]</p>

[k7elp60]

Some times people get confused about the term deep cycle in regards to lead-acid batteries. What it really means is that the deep cycle form of the battery is designed to supply a small amount of current for a long time. Typical is 20 hours. If one is to take a 70 amp/hour battery and have a continious load that draws 70 amps, the battery with typically last only 30 minutes.<p>Watts are watts. 1200 watts at 120 volts is 10amps. At 12 volts it is 100 amps.<p>As a side note I have a battery powered lawn mower, it uses a 24V 7Ah battery. I have a medium sized yard and can get two full cuttings on one charge. I was a little hessitant to buy it, but I don't have buy gas, change the oil or put up with the loud noise.

[Chris Smith]

Deep cycle refers to being able to use the full extent of the battery, from high to fully low, with out the battery suffering. <p>Yes, you may need more than one to do the job, but you can use the full gas tank worth of amps with out killing the battery.

[ampedtech]

get the generator

[terri]

Thanks, ampedtech.<p>I sometimes get a big laugh when I follow some of the impracticalites expressed on this board. One of my favorites was someone who was designing a super-high-tech circuit, including a PIC, to do something that could have been done with a DPDT relay.<p>I guess people get brainlocked sometimes. I held back on posting on that one, and sure enough some party --after something like ten posts --suggested the relay.<p>In this topic, I was amazed that nobody mentioned watt-hours per pound. Lotsa pounds are ok if you're hauling the darned battery around in your SUV or the batteries are in stationary service.<p>And I didn't mention it in my previous post 'cause my posts tend to be longish, but maybe someone ought to sit down with a four-banger calculator and a couple of catalogs and figure out the relative costs involved.<p>A very fine engineer once taught me: "Design from the function, not from the hardware."<p>I've said that before on this board, but it needs another iteration.<p>Again, 10 e 6 TNX.<p>Now let's watch the fur fly.<p>[ April 17, 2005: Message edited by: terri ]</p>

[Chris Smith]

Terri<p>Trying to pass on a education or wisdom with simple words rarely ever works. <p>There is very little learning in that process. <p>Making mistakes is better than ten thousand words in any book or type. <p>Doing things the hard way, like the best of us have already done, is what makes great a persons knowledge.<p>Not simply being told. <p>Frying something is the best way to push the limits and learn things that no book will ever teach you. <p>Experience is far better than any possible words written down.<p>I encourage mistakes, as long as it only hurts your pocket book and time schedule.

I know things you will never be able to read out of any book, because I tried it and failed, and then figured out how to win. <p>Tomorrow’s inventor doesn’t need to be told, they cant do it that way. <p>Think outside of the box. <p>The only Cardinal sin is reinventing the wheel using more parts than the original.

[terri]

Much of what you say is unarguable, in an academic or hobby setting, and indeed I've smoked enough things in my lifetime to know the benefit of boo-boo-ing.<p>But for the most part, these goofups taught me more than just "don't do that again," they taught me that a methodical plan of thinking about the problem beforehand would have avoided most of these problems. That was the biggest lesson in these foulups --not simply "well, I won't do that again."<p>Yeah, I know that you can't predict stuff in an exploratory, experimental setting, but at the very least you can apply some forethought to the problem. After all, who'da thunk a stupid seal would blow out or a tile would fall off on a space mission? <p>In fact, applying hard, firm, thinking to problems in advance is precisely what generates the creative thought and novel solutions that everyone calls "thinking out of the box," and is so admired by one and all.<p>Encouraging mistakes is one thing, and, as I said, admirable in an academic setting, or for when you have a new Tech on staff. But I believe it is more valuable to teach them to think about the problem, to, in other words, do the doggoned homework/noodlework first --before they burn out the milliammeter by hooking it across Vs.<p>And that's how Tech Is get to be Tech IVs!<p>Or even Instrument Maker I.<p>[ April 18, 2005: Message edited by: terri ]</p>

[Chris Smith]

But the main point here is “there are no short cuts in life or learning”.

Looking back with hind sight, we always protect our butts and say, “I would have done it differently”. <p>But then that would take the future knowledge that hasn’t happened yet to accomplish, and That’s a catch 22 and the whole point of hands on learning.

[terri]

SMOKE HAPPENS<p>We have legitimate points of view. To me, I'd rather they be trained in thinking about how not to generate the smoke in the first place, rather than just recalling that the last time they did this-or-that, smoke happened.<p>As I said in response to the "Interview" question a couple of weeks ago, "Personally, I'd rather have a not-so-educated assistant who would bash and slash and mash away at a problem until he understood it and solved it, than one who could simply reiterate what he'd learned, but could not or would not really analyze the problem in depth."<p>Nevertheless, of course,<p>SMOKE HAPPENS<p>Hm. Maybe I'll post that over my workbench.<p>Or stove.

[sofaspud]

"Fools you are... to say you learn by your experience .... I prefer to profit by other's mistakes and avoid the price of my own." - Otto von Bismarck, 19th Century Prussian Chancellor.