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Power inverter.

Posted by poohbear2767 (My Page) on
Fri, Apr 7, 06 at 5:43

For Christmas I got a 700 watt (1400 watt surge) power inverter.
I have wanted one of these for a long time.

Hoping you can answer these questions.
I know I could probably get the current draw off of each of these.
and multiply it by the voltage to get the watts needed.
700 watts means about 5.8 amps max I think.
But's it late and I felt like posting this info instead.

Can I run:
My weed eater (cheapo $49 model from Lowes)
14 inch hedge trimmer
3/8 drill.
jigsaw
angle grinder
sawz-all
My computer, monitor, network hub, modem/router all at the same time.

I wanted it mostly for my computer. I have a battery charger.
Add a deep cycle battery and I would have a great battery backup.
We have frequent power outages.
Usually just blips or maybe a minute or two.
I once counted 17 blips in two hours.
After that I got a small battery backup.
I get about 5 minutes out of it to shut down.
I always have my computer doing something. 24/7.
I do a lot of video work. Takes lots of time to do anything.
I'm either downloading or uploading or just processing.
Having the computer shut down sets me back quite a bit.
I get thru the blips fairly easy. A minute or two is no problem.
but longer than two minutes and I have to start the shut down procedure.
Be nice to have longer to go, I could go several hours with this setup.
And all I would have to do is reach over and unplug my current
battery backup from the wall and plug it into the inverter.
If this inverter is not big enough for this can I run two
inverters off of one battery. Run the tower and modem/router
off one inverter and the monitor and network hub off the other.
It would drain the battery twice as fast I suppose
I already have a deep cycle battery and a charger for it.
It's a big battery for use with a big trolling motor.

Another question.
I read something in the owner manual saying something about
certain motors may not run off the inverter unless a small
light bulb was put in series with the motor.
I can't seem to wrap my mind around this concept.
Could anyone shed some light on this.

Thanks.

Pooh Bear


Follow-Up Postings:

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RE: Power inverter.

I checked my weedeater today 4+ amps.
Jigsaw was 3+ amps
Hedge trimmer was also about 3 amps.
Angle grinder was 5.5 amps.
My brother told me I shouldn't go over 5 amps.
So I don't know about the angle grinder.
Didn't get to check anything else today.

Pooh Bear


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RE: Power inverter.

It's only four amps of AC to run that weedeater, but it must pull the equivalent from the 12 volt battery, which would be about 40 amps. Wouldn't get much use and things would run warm.

It should run the confuser and monitor and such, unless you got some big honkin' system with 20 inch monitor.

Maybe just increase the battery size of your UPS?

I was given a used UPS with a 7 amp battery. I could run my Imac and also a lamp beside it, plus a satellite receiver and 17" TV for 10 minutes or more. We usually see some power failures here nearly every thunderstorm and we got a lot of use from it, till the battery finally died.

Just for fun, I'll try hooking a car battery to it to see how it works.

A small 300 watt inverter I have will run the dish, a small 10" color TV plus one small lamp for about 4 hours off a "standard" car battery. It came in very handy for entertainment when we lost power for 5 days a few winters back. If you exceeded what it could do, it shut down and you had to power it off, reduce the load and try again.

-Ed


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RE: Power inverter.

Pulling 40 amps from a battery I wouldn't get much use for long.
But the battery would be in a tractor sitting nearby with the engine running.
Not that it will be an option now with fuel at $3/gallon for the tractor.

I have been using a 250 foot roll of 12-2 romex and two 100 foot extension cords.
May have to just keep doing that for remote parts of the property.

That would leave the inverter for the computer.
I really miss my computer when the power goes out during a storm.

Pooh Bear


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RE: Power inverter.

Hmm, maybe look for a 12-volt rechargeable whacker, clipper, etc. Harbor Freight has some good deals.

You could always try it once and see how long the inverter would run it. Or try it 10/20 minutes then feel for how warm it and the 12 volt cables are getting.

If you have a multimeter, you can check the 12 volt level and the AC side too and see how much they drop under load.

On your other question, some inverters may need to see a little resistive load, not just purely inductive. Transformers and brushless motors like a window fan are inductive, while lights and brush-type motors are resistive loads. My little 300 never cared what was plugged into it, just so long as it wasn't too much of a load.

I just tried my old pickup battery on my UPS and it seems to work fine in place of the sealed 7 amp battery it came with. Of course, it's no longer a cute little all-in-one package, as now it has this big, dirty truck battery on the floor beside it, but it does work!

-Ed


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RE: Power inverter.

some inverters may need to see a little resistive load

Hmmm.... I wonder why.
Inductive loads have a certain resistance to them already.

Good to hear it will run a computer with no problems.
That's what I wanted it for more than anything.
Thinking of making my own little generator using a lawnmower
motor and a high output alternator. Let that keep the battery
charged when power is out for long periods of time.

Pooh Bear


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RE: Power inverter.

Yeah, I don't know about that resistive load thing, either. Nor why they ask for it in series. That would tend to divide the voltage between the motor and the light, sort of like an old-fashioned TV repairman's "Dimbulb" tester.

My big desktop Mac with hefty power supply pulls 3 amps (360 watts) according to the info on the rear panel. A monitor probably doesn't use much, maybe running the brightness lower or shutting it off while doing a long task would extend the time you could be "off the grid." If you have an LCD monitor, that probably would use next to nothing. Same for the hubs and other powered accessories. A wallwart could probably run them.

Inverters used to be known for having a "rough" AC waveform, maybe they are still that way. Thus, they're kinda noisy and the voltage is not held as true to 120v as one might like. With a large load, the AC output voltage will drop lower. Most computer supplies could probably handle a drop to near 100 volts, but I'd want to give the inverter a few brief tests before launching that overnight task.

I kinda like the idea you had of running the UPS off the inverter. That way, it will filter the inverter's AC waveform and help make up the difference if the inverter's voltage drops or is too rough-edged. When an inverter quits, there's not much warning, so you also get that added little safety buffer provided by the UPS.

We had a late spring storm a couple weeks ago. We got 18 inches, but the lines held in our area. Just a few miles up the road quite a bit more snow fell, my sister lost power for a few days and some folks up north of here are still without power, as over 800 poles went down.

No way are we gonna run our household for two weeks off one of these gadgets, but with a little power management you could get a few hours a day of internet, plus some minimal lighting and other uses.

My dad built a motor driven car alternator gadget that he used to charge batteries. It wasn't the best arrangement, but it did work!

Speaking of this low-buck "off the grid" stuff, I've read about people who ran strings of LED lights using the voltage available on their phone lines and got "free" electricity for their home lighting!

-Ed


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RE: Power inverter.

Our power goes off very often, but it is usually for under a minute.
A number of times it has been over 30 minutes.
A few times it has been over an hour or so.
Only been off 2+ hours 3 to 5 times in the 5 years I have lived here.

Yeah, I figured running the UPS off the inverter also "conditions" the power.
So any rough spots get evened out.

Running low voltage lights off phone lines is an old trick. Real old.
I think line voltage is 42 volts or something like that.
The ring voltage jumps up to something like 90 volts.
But the current is real low. So can't run nothing major.

Pooh Bear


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RE: Power inverter.

Brief outages may just be from tree branches hitting the lines in the wind.

The system is designed to kick out and reset automatically two or three times, but if the fault keeps occuring, after that, they stay tripped much longer or till manually reset.

Might not hurt to take a little look around your place and the neighbors', ask if anyone else is seeing the brief outages, etc. If you can spot some close-by trees, call the power co, and they will send out a crew to do some limbing or tree falling to clear the lines. That's what I did here, and it apparently helped trigger some needed maintenance over a much wider area than just at my place.

-Ed


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RE: Power inverter.

They just finished about 2 months ago the tree trimming around here.
I got several truckloads of free mulch from them.
And the problem has been better.

When I was a little kid I learned we could count the number of times the power went off to know if it was gonna stay off or come back on. During storms it would go off for about 10 seconds, then come back on. If it did this 3 times in an hour then the power was gonna be off for a long time. I finally learned why that was that way and about arc-fault breakers.

Pooh Bear


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RE: Power inverter.

If you run the inverter straight off a batery without a constant alternate charge it will ruin the battery internaly and shorten it's life . Running just on battery may also burn up the inverter if it's fuses fail . The inverter is good for powering garden tools and small shop tools but the 50hz wave form is not recomended for household ( especially) electronic items . Bigger battery backup for your PC or maybe invest in a small generator .


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RE: Power inverter.

A 700-watt inverter will not run a computer for any appreciable length of time UNLESS you don't mind a monitor without "full" power. You may start to lose resolution and/or color quality.

Since you would be running the inverter off tractor battery, you're better off using a generator to power a UPS (I hope you run your computer off UPS and not directly off utility power!).

I have a 2000-watt inverter, which I run off a separate car battery, then move to jump-starter/battery source.

Unless you are RUNNING your vehicle and using a 1500-watt+ inverter, things with "motors" are not liked much by inverters. Electric grills, refrigerators, etc., even toasters, can cause shut-down.

An alternative would be marine/deep-cycle batteries for your inverter. I believe they can be charged by the inverter, if "wired" correctly, when utility power is running.


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RE: Power inverter.

Inductive loads and sources play havoc with inverters.
To long a feed line from the battery, motors and transformers on the load side, even long load wires.
The regulator circuits can only sense what is happening at the terminals of teh inverter and become unstable if the load (or source) is inductive.
On the DC side you can add capacitors to swamp the wiring easily. It is a little harder on the load side since you need small enough caps to not dissipate to much power, but large enough to swamp the load. The capacitor size on the load side also vaires with the load.


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RE: Power inverter.

I have used the inverter several times over this past summer.
I ran it off the tractor battery each time.
First time I ran the weed-eater thru a 50 foot extension cord.
Had to set the tractor throttle up a bit or I kept getting a low voltage beep.
Then I rode around the yard on the tractor and used an electric
hedge trimmer to cut all the low branches that keep hitting
me when am I mowing. It worked great for that.
I ran a 350 watt water pump off of it thru a 50 foot extension cord.
Had to run the tractor at full throttle for that
or I kept getting that low voltage beep.
Ran a work light off of it one night.

And I did finally run a computer off of it.
I wanted to test a computer and there were no electrical outlets near it.
So I got one of those jump start battery packs and hooked
the inverter to it and plugged the computer and monitor
into the inverter. Started right up and ran no problem.

My only complaint with running off the tractor is I have to
keep the throttle up to keep the voltage up.
So I'm working on a setup to run an alternator and battery
off the PTO that will let the tractor sit there at idle
and let the PTO spin the alternator hooked up to its own battery.
Then I can hook the inverter to that and not waste so much gas.
I would rather have a regular PTO generator but that's just not in the budget.
But my setup should handle my needs just fine.

Thanks.

Pooh Bear


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