Power Inverters

[PBMAX]

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]

</font><font color="blue" class="small">( Depending on design and cost.. you can get everything from square wav, modified square wave ( stepped ) modified sine, or true sine wave output.)</font>

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.

</font><font color="blue" class="small">( 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..)</font>

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]

/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]

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]

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]

<font color="blue">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?</font>

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]

</font><font color="blue" class="small">( 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. )</font>

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]

</font><font color="blue" class="small">(
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.)</font>

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]

</font><font color="blue" class="small">( My pick for an inverter will be a new Coleman Powermate 2000/4000 watt unit off ebay.)</font>

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.

 

[LAGEORGE]

60 Hertz always

George

 

[JRP]

Why 2000 watt?

Inrush and capacity.
A 15 amp skill saw draws 15 Amp x 120 volt = 1800 watts.
This is before inrush is considered.

With a wall outlet the wiring and breaker can handle short periods above 15 amps without fire or trip. With an inverter you have very little extra. Only perhaps a second or less at "peak" ated power.

When you are mowing you might draw 10 hp from your tractor. Should you get a 10 hp tractor? No.

As far as the starter buring up the alternator my point is that you can power inverter loads from the battery only without risk to the alternator, just like starting a motor with your starter.

Ebay has lots of new Coleman 2000 watt for $170. I plan to order one this week. We will update this post after it has arrived.


I'm more likely to power a skill saw than a cumputer while working around my tractor.

 

[Soundguy]

This reminds me of the post about tractor lights, alternator ratings, and loads.

Someone was asking about installing lighting to their tractor, that. if all lights were on.. it would exceed the rating of there alternator. Some told them they couldn't do it.

I pointed out that they could but, the storage battery would be in a state of discharge carrying the load above the capacity of the alternator for the lights. As a temporary condidtion this is no big deal.. only till it runs the battery past ignition power 9 gas jobs ) or starting power ( or fuel cutoff solenoids... etc..diesels ) would it be an issue.

Soundguy

 

[Charlie_in_TX]

Your circular saw is a DC type motor with brushes. It is not like the induction motor in an air compressor. The starting current for your circular saw will pull no were near 15amps at startup. I have started mine from my 200watt inverter. Starting it is easy, it had a hard time cutting a twig.

You have made many comments along the lines of it is no different than installing a low battery in your auto to charge it. Been there done that to the price of a $500 120amp alt in my wifes car. Have you ever heard of surge rating? The surge rating of the diodes used in alts are 10 time there continuos rating. And that is only when properly heatsinked. In an alt they are not well heatsinked. If you want to take out the rather expencive alt in your tractor, thats fine. Recomending it to others is somewhat reckless.

The next consumer grade inverter to get anywhere near 95% effecent will be the first I have ever heard of. Do you think there is a reason they put fans on 400 watt inverters? I assure you it is not because the are disipating 20 watts of power.

You have stated you can prove me wrong. I await your proof.

 

[TBAR]

I had this one mounted to my tractor for a while. Heavy duty industrial type.

http://community.webshots.com/photo/111851761/111852069CrJecN

http://www.campsitevideos.com/rediline.html


TBAR

 

[JRP]

I think you are right. Many of my tools have universal motors so it should not be a problem.

At work we calculate available fault current for switchgear. It is amazing how much amperage a 2000 KVA transformer can generate during a fault, and how much amperage a 20 amp breaker will source for the short duration of starting an induction motor.

An inverter just can't compare. Another reason to get a larger inverter.

 

[texastomtom]

Use a True RMS meter,,,

it should show 110


The battery backup systems designed specifically for computers have a 12v lead acid batter and an inverter.

If you measure the output with a 'common' meter it will show 80-90 volts. Use the proper test equipment and you will see 110-120.

Perfectly normal and should be fine for your notebook.

I use an inverted in vehicle for laptop regularly...