A pure sine wave inverter should be the ideal choice for electrical appliances. Are you sure you don't have a "modified sine wave" type?

https://www.edecoa.com/products

It might help to see the damage on the PCBs. That might give us a clue as to what happened.

When a Victron Phoenix Inverter 12/3000 costs $1700 to $1900 something has to give when one costs less than $300

Agreed. You won't buy a 5kW sine wave for $290.

In another post you mentioned being an electronics technician so I suggest you measure its 240V output with your DMM set to AC. If it's sine wave it should read 240V give or take, if it's square wave it'll read something quite different, guessing, maybe 150V. As always, don't stick your pinkies in bad places.

Thanks again guys. Yeah I did measure the 240v going into the slow cooker PCB. I'd need an oscilloscope to have a look at the inverter output. Also, there's no visible signs of damage to the slow cooker PCB so suspect something from silicon Valley has buggered up.

It doesn't actually solve the problem but at least you will not destroy another toothbrush.

 

https://thegreynomads.activeboard.com/t65253740/oral-b-2-x-aa-battery-toothbrush/

I don't understand how a sub $300 inverter 2500 watts can also have a surge of 5000 watts.

 

As compared to a professional UPS 3.0kVA 2700 watts & no mention of a surge capacity.

 

https://www.techbuy.com.au/p/169038/UPS_RACKMOUNT/EATON/5PX3000IRT3UAU.asp

 

I have an old version of this UPS plus additional battery units. Ok I am comparing a UPS to an inverter without its only battery. But really 2700 watts of quality power costs a "touch" more the $300

I would think that most inverters would have a surge rating to allow them to accommodate inductive loads such as electric motors. These draw substantial currents during starting.

As for the weights of the Victron inverters, my question would be, what is inside an expensive inverter?

 

I can see that this 2400W / 20kg unit has a large toroidal transformer:

http://www.scpowsolar.com/h-pd-41.html#_pp=0_336_8_-1

http://7498591.s21i.faiusr.com/2/ABUIABACGAAgn5DfsgUo0uuiogMw2AQ41wQ.jpg (inside view)

 

Here is a datasheet for a 3kVA / 25kg toroidal transformer:

https://www.farnell.com/datasheets/2279510.pdf

 

I suspect that the cheaper inverters may step up the battery voltage via a high frequency ferrite transformer, and then produce a pseudo-sinusoidal output by pulse-width-modulating the output voltage via MOSFET choppers and a couple of series connected inductors.

Something like a Class D audio amplifier ...

https://en.wikipedia.org/wiki/Class-D_amplifier

 

-- Edited by dorian on Friday 15th of July 2022 06:02:55 AM

Here are several high power car subwoofer audio amps, some as high as 4000W:

https://www.forbes.com/wheels/accessories/best-car-subwoofer-amplifiers/

They most probably all use Class D topologies. That's probably how the cheaper inverters work.

FreecamperTas wrote:

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Did you measure it on your DMM set to AC? If so what was the reading?

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 Yep. 240v ac.

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Interesting, Maybe under no load it is a square wave and fools the meter? These inverters are usually triangular waves.

As for oscilloscopes; I always remove the earth from oscilloscopes at the mains plug although nowadays most scopes are digital and powered from a plug pack so the issue doesn't arise however what I really meant is that the input spec of most scopes is not adequate for the 340V mains peak.

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Dorian: I believe you are correct in your description of inverters.

My Victron 500W synthesizes a sine wave at low voltage and subsequently transforms it to 240V whereas the cheaper units use a high frequency chopper and wave shape afterwards.

The Victron approach is much better as it keeps semiconductors away from the higher voltage and ensures they are not subject to such things as mains level inductive spikes but it does make the inverter much more expensive and heaver but I suspect the cheaper approach will have a hard time meeting EMC emissions requirements which is why most of the cheap Chinese simply don't bother to even try.

There are several inverter circuits here:

https://elektrotanya.com/showresult?what=inverter&kategoria=All&kat2=All

You'll need to refine your search to exclude the inverter circuits in monitors, for example.

Here are 3 high power inverters and one 200VA.

https://elektrotanya.com/e-ast_12v_2000w_pure_sine_inverter_sch.pdf/download.html (E-AST 12V 2000W PURE SINE INVERTER)

https://elektrotanya.com/novopal_puresine_ps3000_-_48v-230v_3000w_inverter_schema.pdf/download.html (NOVOPAL PURESINE PS3000 - 48V-230V 3000W INVERTER SCHEMA)

https://elektrotanya.com/3000va_power_inverter_12vdc-230vac_modified_sinus.zip/download.html  (3000VA POWER INVERTER 12VDC-230VAC MODIFIED SINUS)

https://elektrotanya.com/200va_power_inverter_for_cars.pdf/download.html  (200VA POWER INVERTER FOR CARS)

kgarnett wrote:

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I have also removed the earth at the mains plug on my Tektronix scopes and also the try to remember that the scope frame is floating.

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If you are doing general electronics development it's a sensible thing to do although occasionally, for noise purposes, I have reconnected it. On one scope I split the earth lead at the mains plug and affixed a male/female spade connector so I could easily earth it or not.

And yes, it's easy to forget the scope is floating and if your mind is on other things and to attach the line side to said scope with embarrassing results for your fingers or, perhaps, signal generators et al :)

I did quite a lot of work on HV testing systems and a qualified rubber mat brought some peace of mind nevertheless I have never forgotten what my tutor of 45 years past told me; "A competent electrical/electronics/HV engineer always works with one hand in his pocket... you never quite know what he's doing with it though...." :)

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Dorian: Thanks for the info, I'll take a look.