Simple , cheap , portable inverter is poor?

[Faringdon]

Hi,
The attached, LTspice and PNG, shows a very simple low power portable inverter schem. Not pure sine, but
most loads are a bridge rect followed by a smoothing cap, then an SMPS, ..so that doesnt need a 50Hz sine anyway.
The AC "thing" is  necessary, but only so that one half of the bridge rect doesnt possibly burn out.
Probably a waste of time though, a simple cascaded booster from 12V to 350V  would suffice, but there you go.

Anyway, the ground of the 350VDC supply would be the same ground as the 12V battery, which is likely to be earth
ground. So the connections to the external SMPS are going to be pinging up and down like mad by 350V.

As such, i am sure you would agree this setup is not good?

[Jeroen3]

Anyway, the ground of the 350VDC supply would be the same ground as the 12V battery

No. That should not be the case. The 350V should be from an isolated DC-DC converter stage.

_{*op identity notice*}

[jpanhalt]

Is there a purpose in analyzing poor designs that so far as we know do not exist commerce?  And even if they did, then what?

[Faringdon]

The 350V should be from an isolated DC-DC converter stage.

In this case, the input is likely to be from a battery...since its a portable inverter...so as such the battery is already isolated.
However, in many systems, someone  may earth the battery ground.

Also, the use of an inverter in this bridge form, is poor, since the attached shows that the outputs of this inverter are banging hellishly up and down with respect to the battery (input) ground.

[jonpaul]

FTSS TROLL...IGNORE GARBAGE

j

[Faringdon]

The thing is ....there is massive dv/dt.
There are different ways of providing +350V, -350V, +350V......, so why dont people use those instead.
The load need not be in the "bridge" of a 4 FET arrangement.
As you know , there are other ways, specially here where it only needs to be +350V for 20ms or so, then -350V for the next 20ms or so...etc etc.

[Andy Chee]

so why dont people use those instead.

do you actually want to know why, or are you just asking rhetorically? (and ignore any answers given)

[Faringdon]

Thanks , yes.
Its a real situation.
Say some People have no access to mains electricity, but they have a device with a mains plug....all they have is a 12V battery, and they need to power the device.

The device is <75W and has a big cap after the mains rectifier...all it needs is a 300VDC PSU to power it.
This seems incredibly obvious.
But i dont see it happening.

This could be a product idea for us to go into the market and make a fortune.

Please may i enquire...do such products exist already?

If the "high voltage DC" aspect makes it a H&S hazard...then we can just make the 300VDC go 300V,-300,+300, etc etc...with period of say 20ms or so...and solve that problem  like that.

Theres also the question of whether to provide the +300v..-300v...+300v via a bridge, or via a simple switchover setup...which has far less dv/dt with respect to cct ground than the bridge method.

[Andy Chee]

Thanks , yes.
Its a real situation.
Say some People have no access to mains electricity, but they have a device with a mains plug....all they have is a 12V battery, and they need to power the device.

These people can buy an existing 150W inverter in the marketplace today.

Your design for a 75W inverter seems to have no market.

I could continue and do a technical analysis of the electronic design, but the marketing analysis should be enough to put a halt on product development.

Bottom line, how much do you expect to sell these 75W inverters?  What’s your estimated consumer RRP?

[jpanhalt]

Its [sic] a real situation.

@Andy: That's a clue. 

[jc101]

75W   https://www.amazon.co.uk/BESTEK-Charger-Inverter-Converter-Transformer/dp/B00HZE2BFG

150W (Cheaper). https://www.amazon.co.uk/Bapdas-Power-Inverter-Converter-Adapter-Red/dp/B0B1TXJPN6/ref=pd_ci_mcx_pspc_dp_d_2_t_3?pd_rd_w=B1HYp&content-id=amzn1.sym.8db49f41-2d78-4c1c-bc3b-fb9e44b9efb4&pf_rd_p=8db49f41-2d78-4c1c-bc3b-fb9e44b9efb4&pf_rd_r=QSC29BX4027CGPAA50DJ&pd_rd_wg=kJtZa&pd_rd_r=bb00ae9c-e333-4d45-9753-d35208fafc48&pd_rd_i=B0B1TXJPN6

[Faringdon]

These people can buy an existing 150W inverter in the marketplace today.

Thanks yes they can...but it can be done cheaper than that...it doesnt need to be an inverter...it can just be an SMPS which boosts 12V to 300V.
Or if you want it bipolar so both sides of the mains diode bridge gets used, then two SMPS's which alternately chuck out +300v, -300v...etc etc.
Thats a lot cheaper than an inverter, which is a 4 FET bridge and has the above shown EMC problems to add in.

[jc101]

It's time to make a quick buck, then!
Get it designed, built, tested to appropriate standards, and distributed for less than £5 delivered, and you're golden.

https://www.aliexpress.com/item/1005006661132764.html?spm=a2g0o.productlist.main.3.5e3dbFOJbFOJV9&algo_pvid=3e6c792c-ba0c-40fd-9c37-10e3df09ca3a&algo_exp_id=3e6c792c-ba0c-40fd-9c37-10e3df09ca3a-1&pdp_npi=4%40dis%21GBP%2115.82%214.06%21%21%21140.71%2136.07%21%40211b81a317118959446527033e25f1%2112000037952232390%21sea%21UK%210%21AB&curPageLogUid=Hz2AIQFx50Sh&utparam-url=scene%3Asearch%7Cquery_from%3A

Once the product is shipping, drop a link on the thread.  Until then, no further discussion is required.

[Faringdon]

....Thanks for that jc101,  the product from your kindly supplied #12 post says its "50Hz". So i believe i could do it cheaper, as there is no need for such a device to be "50Hz".
All it needs to do is output +300Vdc.
Or if we want to be snazzy, then we can get it to go +300V, -300V, +300V...etc...but of course, this certainly neednt be at "50Hz"....could be say 5 Hz, or whatever.
But yes, £4.05 is very cheap....the postage would of course be more than that, and that would have to be payed. There is also the
point that it wont be on the market till eternity at £4.05, since they are obviously not making a profit at that pricing.
That pricing is done to suck in greedy Western middle men and gazump all other competitors out of the market and make them go bust....which is a bona fide marketing strategy...but not something
that can be done forever.

Bottom line, how much do you expect to sell these 75W inverters?  What’s your estimated consumer RRP?

...I believe we can make a profit as ours is simply boosting up to +300VDC, and not messing with 50Hz.
Even if we dont sell it for much less than current offerings, it doesnt matter, since all you need to do in UK
is "get into the market with a known and registered prescence as an electronics designer and manufacturer"......once you have achieved that,
you can then make massive money by importing electronics in for people from China (middle-manning)...because your status as an electronics
company makes people think you are knowledgeable enough to buy in their electronics from China for them, and you then take your mega-riches, middle man cut.

[jc101]

The £4.05 includes free shipping to the UK. The regular price is £15, including shipping to the UK, but it is undoubtedly much cheaper in bulk. There are 100's available to choose from around the £15 mark, delivered to the UK. 

If you are trying to make a 240v inverter, then what you plug into will probably expect 50Hz/60Hz. But you don't say what the end user will plug into this new, super cheap inverter.

Still, when you've got your product to market, drop a link to where it is available.  You should have it done and dusted in a couple of months tops, I'll check back then.

[Faringdon]

if you are trying to make a 240v inverter, then what you plug into will probably expect 50Hz/60Hz. But you don't say what the end user will plug into this new, super cheap inverter.

Thanks, as you know, only certain types of fans and drills need 50Hz sine. The vast majority of loads will not need 50Hz either sine or quasi sine...they simply have a big capacitor after a rectifier bridge...absolutely no need for any 50Hz. As you know 50Hz is what we have to work with because of the physics of the electrical distribution grid. When there is no grid, (eg youre camping etc) and all you have is a 12v battery, the situation of the grid becomes irrelevant.

[Gyro]

....Thanks for that jc101,  the product from your kindly supplied #12 post says its "50Hz". So i believe i could do it cheaper, as there is no need for such a device to be "50Hz".
All it needs to do is output +300Vdc.
Or if we want to be snazzy, then we can get it to go +300V, -300V, +300V...etc...but of course, this certainly neednt be at "50Hz"....could be say 5 Hz, or whatever.
But yes, £4.05 is very cheap....the postage would of course be more than that, and that would have to be payed. There is also the
point that it wont be on the market till eternity at £4.05, since they are obviously not making a profit at that pricing.
That pricing is done to suck in greedy Western middle men and gazump all other competitors out of the market and make them go bust....which is a bona fide marketing strategy...but not something
that can be done forever.

Bottom line, how much do you expect to sell these 75W inverters?  What’s your estimated consumer RRP?

...I believe we can make a profit as ours is simply boosting up to +300VDC, and not messing with 50Hz.
Even if we dont sell it for much less than current offerings, it doesnt matter, since all you need to do in UK
is "get into the market with a known and registered prescence as an electronics designer and manufacturer"......once you have achieved that,
you can then make massive money by importing electronics in for people from China (middle-manning)...because your status as an electronics
company makes people think you are knowledgeable enough to buy in their electronics from China for them, and you then take your mega-riches, middle man cut.

Happy Easter everyone!


P.S: You're proposing to put 300V DC on a standard UK mains socket? 

[tggzzz]

...

P.S: You're proposing to put 300V DC on a standard UK mains socket? 

You sound as if you are surprised!

Don't forget the old aphorism about a certain class of people being "so damned ingenious".

[ejeffrey]

if you are trying to make a 240v inverter, then what you plug into will probably expect 50Hz/60Hz. But you don't say what the end user will plug into this new, super cheap inverter.

Thanks, as you know, only certain types of fans and drills need 50Hz sine. The vast majority of loads will not need 50Hz either sine or quasi sine...they simply have a big capacitor after a rectifier bridge...absolutely no need for any 50Hz.

Also anything with a capacitor dropper power supply won't work.  Plus with DC the interrupt rating of power switches, fuses, and circuit  breakers will be violated so as you say you need to chop the waveform.  Doesn't really have to be 50 Hz but why not?  It's not like its cheaper to chop at 55 Hz.  A 300 V square wave will work for some things but anything with resistive heaters or universal motors run directly from the line will potentially overload due to the high RMS voltage, so you will want to add some dead time to avoid overloading those devices and have a correct RMS voltage.  Now you have a bog standard modified sine inverter.

[jpanhalt]

The £4.05 includes free shipping to the UK. The regular price is £15, including shipping to the UK, but it is undoubtedly much cheaper in bulk. There are 100's available to choose from around the £15 mark, delivered to the UK. 

Now, you are being too serious for the occasion.  Vapor hardware, like vapor software, costs nothing to ship.

[Zero999]

A good number of devices, designed for 230VAC will work fine from 250VDC. No need for an inverter. The switch not being rated for DC is seldom a problem because the same switch will be designed to withstand the large surge taken to charge the filter capacitor, which already requires considerable over-rating. Light switches are also a non-issue, since they were originally designed for >100W light bulbs and the associated turn on surge, so will be able to handle tens of watts at DC.

A modified sine wave is a little better than DC because it will power most old linear power supplies, but will damage capacitive dropper circuits which will pass huge surges. It should be easy to put together an inverter with a battery and H-bridge, driven with a modified sine wave. The MOSFETs, or indeed BJTs, could be driven via small transformers. A cheap, off the shelf switched mode power supply could power the driver circuitry.

[Gyro]

A good number of devices, designed for 230VAC will work fine from 250VDC. No need for an inverter. The switch not being rated for DC is seldom a problem because the same switch will be designed to withstand the large surge taken to charge the filter capacitor, which already requires considerable over-rating. Light switches are also a non-issue, since they were originally designed for >100W light bulbs and the associated turn on surge, so will be able to handle tens of watts at DC.
...

The issue with AC switches isn't anything to do with the turn-on surges, it's the turn-off... breaking a DC arc, without zero cross interruptions.

[Zero999]

A good number of devices, designed for 230VAC will work fine from 250VDC. No need for an inverter. The switch not being rated for DC is seldom a problem because the same switch will be designed to withstand the large surge taken to charge the filter capacitor, which already requires considerable over-rating. Light switches are also a non-issue, since they were originally designed for >100W light bulbs and the associated turn on surge, so will be able to handle tens of watts at DC.
...

The issue with AC switches isn't the turn-on, it's the turn-off... breaking a DC arc, without zero cross interruptions.

I know, but that doesn't matter. If the switch is selected to withstand more than an order of magnitude times the steady operating current, then using it to break DC won't be a problem. In other words charging tens of µF of capacitance when the mains is at the peak voltage, is going to be far harder on a switch, than breaking a much, much smaller DC load.

[Gyro]

Sorry, I disagree. It does matter  Just because a switch has the standard 3mm open contact gap for AC mains doesn't mean that it is sufficient to break a 250V DC arc (at whatever current).

[jc101]

You are assuming the OP with go to the expense of a switch on their new inverter. Surly too it can be omitted as a needless expense?