Power Inverters

PBMAX · Mar 18, 2004

The thing that hurts your drill is lick of continuos Current.... I'd imagin the drill pulls 6/7 amps under load... if not more. My lap top pulls max 1.5 amps and runs fine on a 75 watt cheapy inverter. Just don't ask it to do more...

when I worked for nextel I had a 300W unit from Rshak and ran my AC cell phone charger and laptop no problem..and even printer once....

BTW if you travel a lot in your car and would like a nice (but not cheap desk) look up Jotto Desk... It's what I used back then....in my company F150...and explorers.

uhmgawa · Mar 18, 2004

( Depending on design and cost.. you can get everything from square wav, modified square wave ( stepped ) modified sine, or true sine wave output.)

Most conventional inverters output a square wave of less that 100%
collective duty cycle. That is the positive and negative cycles have
an intervening blank time. This is done to tone down both the
high frequency components as well as approximate the energy in
an equivalent sine wave.

( Depending on what type of power supply your laptop uses, there may be no ill effects. Say for instance.. the laptop used a regular ac transformer and drifge/filter .. just about any output would be fine... that square wave ill be worked over by coil inductance and smooth it quite a bit.. won't matter by the time the wavefrom gets flopped and filtered..)

Switchers fair better than 60Hz transformers in this scenario as the
input is rectified to DC before being bucked to the desired output
voltage. I've routinely run switchers directly from the 150~160
volt DC internal to an inverter rather than the chopped 60Hz
square wave output to avoid the associated high frequency noise.

Incidentally these high frequency components of a square wave
do get 'rounded' by a transformer designed for 60Hz but this is
due to losses in the core material and winding parasitic capacitance.

That said, I don't think I've ever seen a linear power supply for
a laptop in the last near decade. So operating from a square
wave inverter shouldn't be an issue. Also 300W is way overkill
for powering a laptop switcher. Likely 75W is more than
sufficient.

Soundguy · Mar 19, 2004

/forums/images/graemlins/tongue.gif

Yer preaching to the choir. /forums/images/graemlins/laugh.gif

As for the square wave and the ac transformer. Inductance of the coil has alot to do with it as well.. that lagging current when voltage is present adds a time factor.. and kind of averages the ontime of the wave. I used to have fun making charge pumps out of quick and dirty pulsed dc power supplies. You can make some decent high voltage using a few ceramic disc caps, and a v-quadrupler circuit .. Not practical for anything but 'play'.. but neat in and of itself..

I Like I said.. switchers are way forgiving... lighter too.. not so much copper to tote around.

Soundguy

JRP · Mar 19, 2004

My tractor starter motor draws way more amps than my alternator can supply and therefore I should not start my tractor engine? Will I burn up my alternator?

I install and repair very big UPS systems for a chemical plant. Imagine an entire romm with only a charger, inverter, and batteries. I'll argue against some of the above posts all day long and prove they are wrong.

The case for an inverter is not for steady state heavy loads like a home electric furnace, clothes dryer, or water heater. Most field uses of power are for power tools. Like your starter motor that draws hundreds of amps, your table saw or electric chain saw will be used for perhaps 15 seconds every few minutes. It is the battery capacity in amp-hours that is most important, not the alternator capacity. You probably could run very heavy loads for short times with the tractor OFF, then start the tractor and let the battery charge. No more risk than putting a somewhat low battery in the tractor and starting the tractor to charge it. The trick is knowing how low is too low before a diesel will not start. If your load is not high and constant then you probably will not burn up an alternator.

My pick for an inverter will be a new Coleman Powermate 2000/4000 watt unit off ebay. New cost is about $170 + ship. The larger capacity is needed for the inrush or starting current for electric motors, as discussed in above posts. This unit should easily operate hand electric tools and may start my table or radial saw OK. It will not start a 2 hp air compressor because an air compressor starts under full torque load, difficult for an electric motor.

If you have a good battery you will not have a problem. My plan is to make an esay carry package of inverter attached to a battery, with a clips or cig. lighter adapter to let it charge.

An 80 amp-hour 12v battery should provide 960 watt-hours of power. Derate this by 5% to 912 watt-hour due to inverter ineffency. This means a 15 amp (1800 watt) circular saw should opeerate under full load for 36 minutes. A 60 watt drop light would operate 15 hours. This is battery only, no alternator.

Modern inverters have good controls that meassure input and output voltage and shut off when battry voltage gets low, protecting the tool (computer) from undervoltage. Inverters also need some load before they ramp up to rated output voltage. To test output voltage plug in a drop light or other light bulb type lamp, then measure output while the lamp puts some load on the inverter.

I'd be glad to help with questions. jrpoux@wcnet.net

Lazy · Mar 19, 2004

Hi
Has anyone ever checked the frequency on an Inverter and if so how close to 60 hz was it and how stable was it?

charlie.

PBMAX · Mar 19, 2004

My tractor starter motor draws way more amps than my alternator can supply and therefore I should not start my tractor engine? Will I burn up my alternator?

Hmmm good question? but your starter pulls from the battery. as you seem to be aware /forums/images/graemlins/grin.gif of good catch to I should have pointed it out.... I was talking about the inrush as you mentioned but how many know that term? current draw is some thing most out here are familiar with if not exactly accurate...Just trying to keep it simple /forums/images/graemlins/grin.gif

What the heck are you going to use a 2000watt unit for /forums/images/graemlins/cool.gif You strapping a Refer and microwave on the tractor so you don't lose any seat time stopping for lunch.. /forums/images/graemlins/grin.gif

I gave up on explaining inrush when My wife wanted to know why the pool pump at our old house would not start up and run on the 14awg extension cords she had run 150+ feet from the house to the pump.

13amp start and 7 amp continous load... /forums/images/graemlins/grin.gif
Really blew her mine when I walked over and kicked the moter and it started pumping.... /forums/images/graemlins/blush.gif

As mentioned, I use a 75watt inverter when I travel in rental cars for my laptop works fine... But will not power anything else at the same time...at least not for long...as I said Cheapy, Hey it was free.... some of the other brands may do better...

uhmgawa · Mar 19, 2004

( Hi
Has anyone ever checked the frequency on an Inverter and if so how close to 60 hz was it and how stable was it?

charlie. )

You can expect +/-5% at best. The consumer grade inverters
use simple R/C oscillators which drift with age, temperature,
etc.. It isn't difficult to improve on this design, rather it is
an issue of cost. Typically this is a non-issue as most things
you are going to plug into such an inverter are largely
insensitive to the modest frequency variation.

uhmgawa · Mar 19, 2004

(
As for the square wave and the ac transformer. Inductance of the coil has alot to do with it as well.. that lagging current when voltage is present adds a time factor.. and kind of averages the ontime of the wave.)

The only inductance you should see in a properly designed 60Hz
transformer is leakage inductance which should be small. You can
measure it by shorting the primary winding and measuring the
inductance of the secondary. Thus the transformer doesn't
store energy as an inductor is intended to do.

The steel used in the core of 60Hz transformers becomes
more lossy with increase in frequency. Nailing it with a
sharp pulse (square wave) results in distortion due to
loss. The DC content of the square wave also causes
more rapid saturation of the core material compared to
a sine wave which also contributes to distortion.

uhmgawa · Mar 19, 2004

( My pick for an inverter will be a new Coleman Powermate 2000/4000 watt unit off ebay.)

If you are relying on it, I'd be careful to get the full test
conditions of the 4000W surge rating. Unless the inverter
can produce a few seconds of energy at this rating it will
likely not be able to start surge motor loads over 2KW.