Inverters: pure- V quasi- sine

[tobble]

As I understand it, other than being a bit cheaper per Watt, quasi-sinewave inverters are a little less efficient (albeit not a lot), but also have a tendency to upset electronic equipment. I have charged my phone via a cheapy Lidl inverter with no ill effects, and so wonder if this is more marketing myth than reality, especially give no electronic stuff runs directly off 230V AC, there's always a transformer, rectifier and whatever other gubbins first.

Does anyone have any experience of quasi-sine inverters causing problems with electronic stuff?

 

[pampas]

No

 

[rogerthebodger]

We are currently having lots of power outages at home and I run my TV, Video recorder, DVD player, DVD recorder, Hard drive video recorder, Audio tape recorder and HiFi audio system and my home PC computer network from a quasi-sinewave inverter with no ill effects

 

[tobble]

hmm, thanks for that guys! another case of the technical wool being pulled over the consumer's eys? or just manufacturers watching thier backs? Unfortuneatly I was suckered a while ago, but have been wondering about it and a friend is about to purchase an inverter.

 

[ccscott49]

In the long term you will have trouble running electronic gear/electronic controlled gear from a quasi sine wave inverter, so it's not guff, I can vouch for that from personal expensive experience. But you can of course believe what you want. All emergency computer battery supplies are pure sine wave, so that may tell you something.

 

[andyball]

have a non-sine wave one - 1500W & about 700AH bank & suitably large cables, so noprobs with input voltage.

Microwave is noticeably less powerful & a bit noisier, or maybe a different sound.

Kettle noticeably slower to boil.

Mobile phone/ laptop charger - no probs.

lcd tv, works fine, but a buzz from the psu that isn't there on mains supply & a bit annoying if it's quiet otherwise.

vacuum cleaner - again, noisier/less pokey.

700W mini oven seems fine, tho' a bit less powerful at full chat too.



All useable, but would prob plump for a sine-wave one if buying new.

 

[sarabande]

a "clipped" sine wave out put will not provide the same regular source of power into whatever it's driving as will a pure/regular wave ouput. Think about the top of a mountain being sliced off, and having a flat peak at, say, 240v for a fraction of cycle, when what the motors or electronics need is a "peak" which reaches the aforesaid 240v then immediately starts to descend.


Yes, though, the majority of crude devices will accept a clipped sine wave output, but some more sophisticated / sensitive devices will not.

Borrow a scope or use one of the internet oscilloscope simulator sites:
up and down waves

more wave forms

 

[Marmalade]

macbook won't run on a quasi

Simon

 

[tobble]

Englander, please could you expand on the issues you've had?

 

[andyball]

may depend on the err quality of the quasi I spose - my mbookpro is fine.

 

[Avocet]

Our old IBM Thinkpad is fine on a modified sinewave inverter. We've been running it in the car for a couple of years now and it seems happy enough although that probably only amounts to ablut 50 hurs or so.

 

[lw395]

If your kettle is slower to boil, that indicates a lower RMS voltage being fed to it. This is a separate issue from the waveform. Likewise you are hearing the switchmode psu for your telly working harder because it has less volts.
Most modern psu's just rectify the input and then use a switcher or inverter to generate AC at tens or hundreds of kHz, which is then stepped down to whatever DC level(s).
This allows much smaller transformers/inductors to be used, keeping cost and weight down. If a 400W computer psu had a simple transformer at 50Hz, it would be a lot heavier!
Probably the best answer is where possible to use a dc-dc converter to power Pc's etc straight from 12 or 24V.
I have seen some quite nasty 'quasi sinewaves' on a scope, with inverters run either lightly or heavily loaded, sometimes half a sine is virtually missing. This doesn't mean that every quasi-inverter is a bad idea though!
The voltage out of 'true' sinewave inverters will tend to vary with the load, and some loads, particularly switch-mode psu's, will distort the waveform for any other equipment.
It seems quite conceivable that stuff powered from any inverter could have a shorter life. Perhaps its best to look for equipment that accepts 100-250V AC without any adjustment, but I don't think that will be available in a domestic microwave?
Luckily I don't want a telly on my boat!
Cheers,
Chris

 

[Gumpy]

my2p worth:

Modified sine wave are more efficient than pure sine wave
They also tend to have a lower standby current so consume less from the battery overall.

MSW inverters will not generally run anything with an electronic timer. Washing machines, microwaves with digital timers etc.

Some audio power amplifiers (yes I have a silly stereo on the barge) do not like MSW inverters and it can cause the transformer to buz.

Some televisions get wavy lines across the screen on an MSW inverter.

Some motors ( aircon, fridges etc can suffer long term damage from being used on a MSW inverter.

A pure sine wave inverter consumes slightly more power but will run just about anything.

Julian

 

[fuss]

In my experience....
Modified sine wave inverters will damage some electrical equipment. Sometimes they will be damaged quite quickly eg a tube work light. Sometimes more slowly eg an electric toothbrush charger, which takes about a week before it stops working.
I assume that other equipment that make buzzing sounds when on an inverter may also be damaged in the longer term.

 

[ccscott49]

Destroyed a DVD player, went all funny!! Destroyed a LCD TV, also wavy lines then screen deteriorated, crew hair straignteners??? wouldnt work atall, (electronic control) Destroyed freezer compressor, funny buzzing coming out of it all the time on inverter, then packed up, no noise on mains. I dont want to risk anymore stuff thanks, have fitted 24volt x 3kw pure sine wave inverter, to run things I need to run on board. Shouldnt have problems with laptop chargers, computer should be immune to that, but it will screw phone chargers, done two of mine in. Pure sin wave for me!

 

[Beadle]

A square wave will contain more power than a sine wave of the same peak voltage.

I suspect the problem with quasi-sine waves is more connected with high frequency harmonics which could get into the clocking bits of electronic and computery kit.

I use a QS inverter to power a laptop and one or two other bits without any problems.

If the power supply of the kit uses a switch mode circuit there will probably be adequate filtering in it to reduce any hf harmonics to an acceptable level.

I appreciate that professional computer installations will specify sinewave inverters, but as you know that is a question of balancing possible consequences against actual costs.

For most "amateur" applications it is unlikely that the same balance would justify the expense.

 

[Niander]

Was happy to watch sky news the other day [during power cut]

using 700w cheap silverline inverter

so tv and sky box worked fine..

dont think it the pure type...

 

[Anonymous]

fuss - that's exactly my experience also. I have had problems with other kit, psus blowing up by getting too hot (presumably due to the filter on the input absorbing too much energy).

Basically it's up to the user. It might work fine forever, it might blow up straight away, it might just not work or it might take a week or so before blowing up. If you get a pure sine inverter it WILL work fine.

 

[sarabande]

I t h i n k I understand what you mean by "more power" in that it seems that 240v is delivered for a longer period of time, but where kit relies on motors which need to be turned at a regular rate, then clipped sine will not do the job properly. Intuitively, it would seem to be tiny, low mass motors which would cope less well with uneven drive from the emf of an irregular sine.. (?)

There's loads of reference material if you search for "clipped sine" and "problem", but most of it is techy radio stuff.


It's ages since I did any work on this with AC motors, and much seems to have changed ! I'll read around a bit more.

 

[Beadle]

Perhaps depends on how you look at it.

Any waveform can be described as a number of sine waves.

A square wave for example is a sine wave with an infinite number of odd harmonics. Try drawing it and see!

My statement that it was the high frequency harmonics that caused the problems was based on this principle. What those harmonics are I cannot say. That will depend on how the inverter "chops" the DC voltage and the filtering - or lack of it.

It really is a question of filtering.

If you start with a square wave and pass it through a low pass filter you will get a sine wave. You eliminate all the odd harmonics.

So the question of whether any particular piece of kit will work with a QS inverter is in part dependent upon the filtering in its own PSU and in part dependent upon the inverter itself.

Most AC motors depend upon a capacitor to shift the phase of the current fed to the field coils. If there is a substantial amount of high, or perhaps higher frequency than the 50 Hz then this phase shift will be affected, which in turn could cause some of the odd effects described in other posts.