power inverter gives 120V exact or not?

[Orc General]

I just bought a power inverter from a friend of mine as he doesn't need it
anymore. Its for use in the car, ie. those thing that gives you 120V from
the cigaret lighter plug. Anyway the model is rated at 400Watts puting out
2.6Amps on the label.

I plug it in and having a hand held power drill I immediately plugged it in
to test. I get power of of it and the drill rev up etc. However I notice
as I release the drill trigger, the fault light on the inverter goes on red.
It detected a fault when I disconnect power to the drill. Is this a normal
behaviour?

Another thing, I pulled out my handheld multimeter and tried to read the
voltage from the inverter and was quite surprise to read 400Volts or more.
Which is totally weird.
I don't think this is that high, cause my drill would have burnted out. Can
someone please explain what's going on?

 

[Al Bundy]

I just bought a power inverter from a friend of mine as he doesn't need it
anymore. Its for use in the car, ie. those thing that gives you 120V from
the cigaret lighter plug. Anyway the model is rated at 400Watts puting out
2.6Amps on the label.

I plug it in and having a hand held power drill I immediately plugged it in
to test. I get power of of it and the drill rev up etc. However I notice
as I release the drill trigger, the fault light on the inverter goes on red.
It detected a fault when I disconnect power to the drill. Is this a normal
behaviour?

Another thing, I pulled out my handheld multimeter and tried to read the
voltage from the inverter and was quite surprise to read 400Volts or more.
Which is totally weird.
I don't think this is that high, cause my drill would have burnted out. Can
someone please explain what's going on?

Even a tiny power drill is at the limit of yout tiny inverter. And you
better be clipping it direct to the battery because you won't be
pulling 400W out of the lighter receptacle.
The no load voltage is not what counts so the 400V means little.
The momentary fault light can be ignored.
Have some fuses handy and try to drill a hole using the cigarette
lighter plug.

 

[« Paul »]

I just bought a power inverter from a friend of mine as he doesn't need it
anymore. Its for use in the car, ie. those thing that gives you 120V from
the cigaret lighter plug. Anyway the model is rated at 400Watts puting out
2.6Amps on the label.

I plug it in and having a hand held power drill I immediately plugged it in
to test. I get power of of it and the drill rev up etc. However I notice
as I release the drill trigger, the fault light on the inverter goes on red.
It detected a fault when I disconnect power to the drill. Is this a normal
behaviour?

Another thing, I pulled out my handheld multimeter and tried to read the
voltage from the inverter and was quite surprise to read 400Volts or more.
Which is totally weird.
I don't think this is that high, cause my drill would have burnted out. Can
someone please explain what's going on?

You might want to review Ohm's Law. I = E/R
Either the unit is somewhat less than 400W or slightly greater than 2.6A.
2.6A at 120v is 26A at 12v plus the draw of the unit itself.
You are probably pulling close to 30A from the cig lighter with the drill.
It's a wonder your car did not burn up.
Anyhow... The fault light... You did not say what kind of drill...
VSR, standard??? A motor generates all sort of hysteresis currents
when spinning down. They could severely damage your inverter.
Voltages above desired is normal for circuits without good regulators
when running no load. Its nothing to worry about. Put a load on it
and it will be at spec. Your inverter really should be used for
light bulbs and not much else.

 

[Mac]

I just bought a power inverter from a friend of mine as he doesn't need it
anymore. Its for use in the car, ie. those thing that gives you 120V from
the cigaret lighter plug. Anyway the model is rated at 400Watts puting out
2.6Amps on the label.

[snip]

Another thing, I pulled out my handheld multimeter and tried to read the
voltage from the inverter and was quite surprise to read 400Volts or more.
Which is totally weird.
I don't think this is that high, cause my drill would have burnted out. Can
someone please explain what's going on?

You have (at least) two problems. The first one is that cheap inverters
don't even come close to putting out a sine wave. They call it a modified
sine wave, but it is more like a modified square wave.

The second is that cheap Volt meters don't read RMS voltage. They assume
when they are in AC mode that they are getting a sine wave, and so they
don't give correct readings when the waveform is NOT a sine wave.

Most cheap inverters are very optimistically rated. Your 400 Watt inverter
might only be able to put out 400 Watts for a minute or less before
over-heating. And of course, it is difficult for the cigarette lighter
outlet to deliver 400 Watts, as another poster said. After all, 400 / 12 =
33 Amps! And thats neglecting the inevitable losses in the inverter itself.

In general, ignore the power rating for the inverter. If you want to use
it to power something, give it a try, and if it works, great. If not, then
lesson learned. Of course, don't bother trying to power things which you
know consume more than 400 Watts.

And as the other poster said, be sure to buy a bunch of fuses for the
cigarette lighter circuit if you plan to use the inverter much.

--Mac

 

[Bill]

I can't argue with what has been said. Since this is the first question I have
noticed on this subject I have a related question.

Is it safe to run computers and other electronic equipment with the square wave
inverters. My one experience running a lap top computer seemed to work fine until
I noticed the next day that the battery on the computer was 'bad'. I subsequently
determined that the small circuit board in the computer's battery had gone bad. I
wonder if that was due to the inverter?

I just bought a power inverter from a friend of mine as he doesn't need it
anymore. Its for use in the car, ie. those thing that gives you 120V from
the cigaret lighter plug. Anyway the model is rated at 400Watts puting out
2.6Amps on the label.

[snip]

Another thing, I pulled out my handheld multimeter and tried to read the
voltage from the inverter and was quite surprise to read 400Volts or more.
Which is totally weird.
I don't think this is that high, cause my drill would have burnted out. Can
someone please explain what's going on?

You have (at least) two problems. The first one is that cheap inverters
don't even come close to putting out a sine wave. They call it a modified
sine wave, but it is more like a modified square wave.

The second is that cheap Volt meters don't read RMS voltage. They assume
when they are in AC mode that they are getting a sine wave, and so they
don't give correct readings when the waveform is NOT a sine wave.

Most cheap inverters are very optimistically rated. Your 400 Watt inverter
might only be able to put out 400 Watts for a minute or less before
over-heating. And of course, it is difficult for the cigarette lighter
outlet to deliver 400 Watts, as another poster said. After all, 400 / 12 =
33 Amps! And thats neglecting the inevitable losses in the inverter itself.

In general, ignore the power rating for the inverter. If you want to use
it to power something, give it a try, and if it works, great. If not, then
lesson learned. Of course, don't bother trying to power things which you
know consume more than 400 Watts.

And as the other poster said, be sure to buy a bunch of fuses for the
cigarette lighter circuit if you plan to use the inverter much.

--Mac

 

[Mac]

I just bought a power inverter from a friend of mine as he doesn't need it
anymore. Its for use in the car, ie. those thing that gives you 120V from
the cigaret lighter plug. Anyway the model is rated at 400Watts puting out
2.6Amps on the label.

[snip]

Another thing, I pulled out my handheld multimeter and tried to read the
voltage from the inverter and was quite surprise to read 400Volts or more.
Which is totally weird.
I don't think this is that high, cause my drill would have burnted out. Can
someone please explain what's going on?

You have (at least) two problems. The first one is that cheap inverters
don't even come close to putting out a sine wave. They call it a modified
sine wave, but it is more like a modified square wave.

The second is that cheap Volt meters don't read RMS voltage. They assume
when they are in AC mode that they are getting a sine wave, and so they
don't give correct readings when the waveform is NOT a sine wave.

Most cheap inverters are very optimistically rated. Your 400 Watt inverter
might only be able to put out 400 Watts for a minute or less before
over-heating. And of course, it is difficult for the cigarette lighter
outlet to deliver 400 Watts, as another poster said. After all, 400 / 12 =
33 Amps! And thats neglecting the inevitable losses in the inverter itself.

In general, ignore the power rating for the inverter. If you want to use
it to power something, give it a try, and if it works, great. If not, then
lesson learned. Of course, don't bother trying to power things which you
know consume more than 400 Watts.

And as the other poster said, be sure to buy a bunch of fuses for the
cigarette lighter circuit if you plan to use the inverter much.

--Mac

I can't argue with what has been said. Since this is the first question I have
noticed on this subject I have a related question.

Is it safe to run computers and other electronic equipment with the square wave
inverters. My one experience running a lap top computer seemed to work fine until
I noticed the next day that the battery on the computer was 'bad'. I subsequently
determined that the small circuit board in the computer's battery had gone bad. I
wonder if that was due to the inverter?
[/QUOTE]

Could be. I'm not really sure about this, but I would probably use a sine
wave inverter just to avoid problems.

Hopefully someone who knows more about it will chime in.

If not, maybe you can start a new thread in sci.electronics.design asking
whether it is safe to run electronics from a modified square wave inverter.

--Mac

 

[Tom Ivar Helbekkmo]

Is it safe to run computers and other electronic equipment with the
square wave inverters.

No. Modern computer equipment uses switched power supplies, and they
do not like square wave input. Pay a bit more, and get a sine wave
inverter, and your computer will thank you.

-tih

 

[Pooh Bear]

Why would a switching power supply object to a square wave? It rectifies
and chops the incoming AC before running it through a transformer. It
doesn't know the waveform.

Electric motors are more likely to object to square waves.

I suppose one problem with a switching power supply is that the input
voltage (at the first stage of rectification) might be wrong if the waveform
is not a sine wave. Has anyone ever experienced a real problem?

A square wave ands sine wave with the same rms voltage have different peak
voltages ( which is what the input reservoir cap will charge to ) for one
thing.

Graham

 

[John Woodgate]

I read in sci.electronics.design that Pooh Bear

A square wave ands sine wave with the same rms voltage have different peak
voltages ( which is what the input reservoir cap will charge to ) for one
thing.

This is why the 'modified sine-wave' inverter was invented. The waveform
is far from sinusoidal, but the peak-to-RMS ratio is similar. Thus it
gives an acceptable DC voltage on the filter capacitor (which is related
to, but a little less than, the peak voltage of the supply waveform).