Victron

Michael,

How about an inverter such as those used by narrowboat owners? They seem to be able to run most appliances from them – OK, maybe not an oven, but I suppose it depends what you want to run off it.

John

– I’m back after a swift Google for marine inverters.  Pure sine wave ones are very expensive.  The first one that I found (admittedly on marine chandler’s site), was a shade over £720! That gives an output up to 2000W continuously and 4000W peak that was advertised as suitable yo power a laptop or LCD tv, etc.

A pure sine wave inverter will intrinsically be hard to make with high efficiency.  Think of it like an audio amplifier with high voltage output but low distortion.  If you made it class B its maximum efficiency would only be 78.5%, and either it would need a high supply voltage or a beefy output step-up transformer.  A practical inverter will have to be switched-mode and probably have quite a complex output filter.  Look at prices for high power low distortion high efficiency amplifiers.

The one Michael linked to is 500W12v input, so I has a look around very briefly from non-eBay sources
This one from a solar supplier claims pure sine wave; the spec sheet says 3%THD, (total Harmonic Distortion) though it doesn’t show a scope trace.
I would hope they know and can supply their market.
https://www.sunshinesolar.co.uk/Item/C60012
The other alternative might be a more mainstream supplier, such as RS, who offer both modified and “pure” sine wave converters, though disappointingly this one doesn’t give a trace example or a THD on the separate spec sheet pdf.
https://uk.rs-online.com/web/p/power-inverters/1793327?gb=s

Interesting debate here on whether the jagged sine wave is the inverter or the cheap scope.

https://www.motorhomefun.co.uk/forum/threads/checking-my-inverter-with-an-oscilloscope.232808/

Bill

On 7 September 2024 at 18:56 Michael Gilligan Said:

On 7 September 2024 at 16:57 peak4 Said:

I pressed submit by accident before adding this one.
It again uses a cheap sine inverter, and a budget digital scope, which needed a step down transformer to lower the input voltage; I’m not sure how much smoothing that might add.
I only have conventional analogue scopes myself, so wouldn’t be able to compare.

Bill

Sorry, Bill … can’t see the embedded video … could you post the link, please

MichaelG.

That’s interesting, neither can I, it seems the post has been deleted.
I didn’t check the source of the inverter the guy was testing, so maybe it came from AliExpress or somewhere, but the reason I posted it at all, had nothing to do with a suggestion to buy the inverter itself, but was to show the form of the display on a cheap digital scope.
As an aside, I’ve just been up to the bedroom workshop to check the waveform output of a little inverter I carry in the car; I couldn’t see that either as my Phillips analogue CRT scope’s died. 😪

Bill

On 7 September 2024 at 16:57 peak4 Said:

…
It again uses a cheap sine inverter, and a budget digital scope, which needed a step down transformer to lower the input voltage; I’m not sure how much smoothing that might add.
…

Bill

The transformer is likely to make the waveform look much smoother because sharp switching transients are choked by the core, whilst energy stored in it’s windings tend to smooth out the bumps.   Loading the transformer reduces the energy available for smoothing, so the waveform at full power as viewed by the scope might be jagged again.   Also have to be careful about digital scopes introducing display artifacts:  more expensive scopes reduce the problem by sampling faster.

Fitting a tuned filter is the obvious way of making sure the output is a pure sine-wave, or at least close enough for all practical purposes.  Problem is filters at 50 or 60Hz need a hefty inductor – lots of copper and steel – and likely to be as expensive as the total cost of all the other components.  Good filters are more expensive than simple ones.

An alternative is to convert to AC electronically and amplify the signal, which can be near perfect.  Efficiency is low though: bad news on a battery powered system, and the converter comes with a hefty heat-sink.

Worst of all is a dynamotor – these are expensive, poorly regulated, heavy, inefficient, hot, and noisy!

Dave

Andy,

You have a PM.

It shows up for me.

(Firefox/Win 10/logged in)

On 7 September 2024 at 23:20 Michael Gilligan Said:

Thanks for that, Andy … a ‘scope trace from an actual product of interest [rather than some random YouTube offering] would be very helpful indeed.

MichaelG.

Didn’t get a chance today, sorry (and it was pee-ing down), but hopefully tomorrow.