surge currents via power tools

[birdhouse]

hello-  

i've started to shop around for inverters and have read many posts about them.  i think i've decided on a mod sine wave.  no computers being used.  thinking 2-3k watts.  so i understand that induction motors have some pretty intense surge upon start up.  my favorite framing saw is a bosch worm drive 7.25" blade on left circular saw, and i have a cabin to build.  i have tripped 15 amp breakers with this saw.  

actual question:    do you think a 2300 watt cont. 4600 surge inverter would run this saw?  

i've been looking at smaller amperage tools specifically for the ranch, but don't really have the funds for them as of current.  

oh- i've been looking at those el-cheapo power bright inverters.

thanks for any help!

adam

[TomW]

adam;

AC motors like your saw can draw up to 8X the nameplate rating on startup no telling how much if you pinch it or jam it during a cut.

Here is a thought:

You buy a cheap inverrter that just covers your needs and discover your tools will not operate on it reliably.

Usually this is after you have it and are stuck with it.

Now you need either another inverter and / or new tools.

This is a trap that is easy to fall into.

I started this way. I also started at 12 volts. Both were BIG MISTAKES that cost more to make right than it would have to do it right, of course.The cheap inverter did not last and running anything powerful from 12 volts is impractical with huge cables to handle the 200+ amps a 2500 watt or bigger inverter will draw.

"7.5 inch worm drive" tells us absolutely nothing of the saws power needs. If it can blow 15 amp breakers it can draw 1800+ watts. This leaves very little head room for surges above the motor draw capacity on a 2500 watt inverter. On start up you may see several times that power draw. While a cheap inverter may handle this awhile it will not last. Cponstruction saws get cycled a lot so that abuse will be cumulative and hard on the inverter.

Best advice I can give is bite the bullet now and buy a quality inverter. Or go cheap now and do it all over again.

By going with good gear to start there will be no surprises later.

My Outback FX 2524 inverter handles my one horse table saw or my ginormous SkilSaw worm drive saw no problems I can even weld with it with my 120 AC wirefeed fixit welder but I only did that as a test as welders seem to be extra hard on inverters.

There you have it.

Bottom line is. Do it cheap and probably have to do it again or do it with quality and be done with it.

Probably not what you wanted to hear but the voice of experience speaks loudly.

My advice is to start with at least 24 volts, 48 be better. Buy a quality inverter just once

Good Luck with it!

Tom

[Volvo farmer]

I have a Xantrex Xpower 1500/ 3K surge out in the garage at 12V. It does not like to start my circular saw at all, but mine is Craftsman, non-worm drive.

There is some sort of soft start technology built into this inverter where it will pulse on and off, trying to start the saw. It seems that if the pulses go just right, the blade gets up to speed and then thew saw will run and I can make my cut. I can usually coax it into starting, sometimes by shaking the saw or tickling the trigger. This all works just fine for the occasional project, but it would be a real pain to build a cabin with it.

[DanB]

I'm no expert here at all but my take on this is...

the surge rating of your inverter is important, but also the period of time during which it can handle that surge.

Inverters that deal well with big surges for a period of time (like that required to start a motor) tend to be expensive and heavy... they have big transformers in them that take a little while before things get too hot.

If you're on a real budget and needing a good modified sine wave inverter that handles surges nicely, maybe watch ebay and pick up an old Trace U series.  Most are around 2500 Watts, some have nice chargers built in, they handle big surges and they seem to go for $200-$400.

[ghurd]

I would say if you want to go cheap to get started, get a better quality used inverter.

Something heavy.  Heavy because they have big transformers in them.

I am partial to the Tripp Lite PV-xxxx-FC series.  

Their overload ratings are great, rated in minutes instead of seconds or milliseconds.  There are two 2000W on ebay now for $200, and a 1200W for $145, all 'buy now'. Sometimes can get them considerably cheaper.  Shipping is always steep because they are Heavy.  My 1100W 12V starts everything we ever plugged into it, as long as the battery and cables can handle it.

The 2300/4600 is 24V?  Not sure that's the greatest idea as a temporary solution.

What will be done with it later? Unless it is a spare.  'Building' a cabin sounds like nothing is there yet, so will need a way to charge the 24V bank.  A 12V can be charged with a old car alternator and 3.5HP B&S mower engine.

A 12V could be handy on a ranch later.

G-

[Ronnn]

I would like to second what Tom has said here. Living off grid continually since 83 I've made all the mistakes you are considering. I would emphasize the 24 volt change. It makes a very large difference down the road on many levels. The more you invest in a 12 volt system the more money down the drain when you realise you have to move to a larger system. The physical size of your cabin asside, with a decent 24 volt sine wave inverter you can buy mass produced electric divices that run on plain old 120 vac. People who buy good tools, like your worm drive saw, [ I always wanted one of those ] or electronic equipment never, ever, regret buying better grade equipment. But the cheap stuff always gets in your face with poor service or inadequate power or some short comming. No matter how simply you start out your system is going to grow. 12 volts is kind of a dead end system. Try  to stay away froms RV stuff. Lights, electronics or whatever. I don't know how it is now but it used to be this stuff is not rated for long term continuous use.

The Outback inverter company Tom mentioned makes very good quality equipment. Mine's been going round the clock for around 5 years with never a hiccup. I really like their charge controlers too, but my next one will probably the Midnight model in development now. It will supposedly deal with a wind charger. There are not any MPPT controlers that I know of that will do this now.

Ron

[Opera House]

Get a generator.  I just built a garage with a 2250W generator.  Ran saws and compressor without much problem.  I can't even imagine doing this with an inverter.  MSW inverters get a bad rap.  I do suggest a RC surge absorber on the output.  Many inverters use the output fets to absorb transients with their internal diodes.  This just heats up the fets causing then to fail.

I must admit I ill have a longing to pick up a large sine wave inverter, but from a technical standpoint the idea is absurd. Nothing out there needs one.  About as necessary as all those voltage stabilizers they sold for computers!

[birdhouse]

hey all-
thanks for the replies.  i totally forgot i even posted this thread!  thus the delayed response.  very sorry. 

still have yet to buy an inverter.  still looking.  yes, i'm going 24 volts.  the turbine i've been working on will hit 26 volts at around 250rpms.  it's an 8.5 foot dia.  just got a coat of fibre glass on the fir blades two nights ago.  using a 50 lbs. fanuc servo motor.  i'll get some pics up once i get it together a little more.  still need to paint the blades, get a chunk of nice ply for the tail, and some other stuff.  then there's the tower, been pricing pipe ect. 

i've been pretty slugish until recently on getting my system up and going.  lately i've been getting after it though.  picked up (2) 200 watt panels.  plan on using (4) sams club golf cart batteries wires series for 24 volt.  morningstar ts-60 for charge controller. 

actually working on my dump load this afternoon. 

i hear you guys on getting a quality inverter.  the more i think about it i don't think my system will keep up with my usage.  did find a new saw that i may buy that only pulls 9 amps and still has the blade on left (yes i'm a west coast framer).    it gets rave reviews too. 

http://www.deltaportercable.com/Products/ProductDetail.aspx?ProductID=11003

i do have a 5500 watt coleman generator, but i hate the thing.  well, it's pretty nice, starts first pull EVERY time, but its loud and pretty heavy to move around.  i hate the noise so much i built a 4-sided box for it and it help quite a bit. 

been drawing 24 x 30 foot for the footprint of the cabin.  being a contractor, i managed to get three used windows out of a commercial store front for $200.00  they're double paned with aluminum frames 6 foot wide by 13.5 foot tall.  so i think i may go for an even 16 foot stud wall. 

really the inverter i would need would have to run the air compressor and circular saw maybe not at the same time, but i think i'd drain my proposed (and all i can afford) 210 a/hr  24 volt bank pretty quick.

it would be nice though at the end of the day to do more pidly, less power usage tasks for maybe the last hour or so without having the generator running.  and from what i'm hearing i'm gonna want a pretty quality used inverter. 

thanks for the wealth of information here.  i have spent countless hours learning!

birdhouse

[Sr WiNdTeCh]

I must admit I ill have a longing to pick up a large sine wave inverter, but from a technical standpoint the idea is absurd. Nothing out there needs one.  About as necessary as all those voltage stabilizers they sold for computers!

Things may not 'need' a pure sine wave... but for longevity of whatever your powering, I'm sure if it could talk, it would thank you.... I'm trying to figure out a way to turn a Mod sine wave to a pure or close to pure sine wave.... Not sure if it can be done easily...