back to article Are you broke? Good with electronics? Build a better AC/DC box, get back in black with $1m

There's a million dollars in prizes up for grabs from Google and the Institute of Electrical and Electronics Engineers (IEEE) for the clever clogs who can build a direct current (DC) to alternating current (AC) converter that's the size of a laptop. The Little Box Challenge aims to solve one of the dilemmas in modern-day power …

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All of this??

So you can convert it back to something around 12-18 volts to power the computer that is the size of a laptop.

Yes, many things run from low(er) voltage DC in these days of solid state devices. Just look around your desk and see. There are lots of "wall warts" of varying sizes needed to power everything. Now this doesn't include charging your Nissan Leaf, or Tesla roadster, but many things just use the 120/240 volts mains to get from point A to point B. The actual use is another matter.

OK, there are some exceptions, like the refrigerator and the clothes washer (they have motors!) but not much else.

The big problem with lower voltages for power distribution is that a voltage drop of 1 volt is significant (it is not at the higher voltages). With more current these add up to a bunch of heat (and melted insulation if you aren't careful).

Oh, don't forget: 400+ volts of DC is not very "user friendly".

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ql
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Re: All of this??

"So you can convert it back to something around 12-18 volts to power the computer that is the size of a laptop."

Well, I do exactly this.actually, and the reality is that some form of conversion is required anyway. We're off grid, but in front of me is my laptop, to the right of my desk, a small mini-ITX-based debian server which is on 24 hours a day, to my left an ADSL router and access point. My laptop comes with a AC->whatever-the-laptop-wants block, which in this case is 20V. The server, router and AP want 12v. As it's summer, my solar panels feed a 24v battery bank (I wish I;d gone for 48v, but you live and learn....) and later in the year, my small wind turbine will provide more power than the solar panels. Both the panels and the turbine put out around 50v open circuit, but the size of the battery bank makes this no big deal. The 24v battery bank gets up to 29.5v during equalisation charging, though I never let it go below 24v (50% state-of-charge with my type of batteries) but quite a range.

The battery bank feeds a small sine-wave inverter of 350w. This provides power for lights, the above-mentioned stuff, my wife's laptop, tablet charging, printer, weather station, telly,. radio, mini-hifi and so on. A bigger 1.2kW inverter provides power for the fridge, occasional vacuum cleaner, washing machine and so on - note anything with a motor, which takes a thump to get it started.

Sticking with an all-DC option would mean I need to stabilise the range of voltages coming off the battery bank as it is charged and discharged. Using power directly from the sources means even more stabilisation as the open circuit voltages fluctuate wildly. We now use mostly LED lights, which I think are minuscule voltages internally but for convenience ar simple 230v devices. The tablets want 5v. The weather station wants 6v. The telly wants 230v and so on and so on. "Mains" style voltage and AC turns out ot be a convenient standard.

I do, though, run the server, router and AP off a single 12v block. That choice very nearly halved the power draw at the battery bank for those three devices in comparison with running three transformers, so the idea of reducing the number of transformers absolutely is one that would be helpful in reducing consumption.

Not that I think Google have our situation in mind ;-)

S

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Re: All of this??

Sounds like you need to be looking at the "marine" side of things - can't recall whether that is a 24v or 48v standard, but it is plain DC, all the way.

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ql
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Re: All of this??

"Sounds like you need to be looking at the "marine" side of things"

Too expensive and too much hassle. This stuff is becoming off-the-shelf these days, rather than needing specialist suppliers. But yes, early learning was indeed on boats, and I have those ideas in mind when I set things up.

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User friendliness of 450v DC

What would you prefer, that solar panels output at 24v or 48v and lose a lot more power or use much heavier gauge wire at greater expense to avoid wasting energy?

If the device can be made this small it could be located on the roof itself so 240 VAC power would enter the house, if that makes you feel any better...

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Single phase 240V AC @ 60 HZ?

I guess output amperage isn't important? Most peculiar specs with the killer going to be the temperature maximum and the efficiency. I'm wondering if they're looking for a low-budget, semi-in-house method of powering their data centers from solar?

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Re: Single phase 240V AC @ 60 HZ?

"I guess output amperage isn't important?"

Guess again. The article stated that the inverter has to be able to handle loads of 2kVA. Anyone with sufficient electronics savvy to go in for this should be able to work out the A given the V.

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Re: Single phase 240V AC @ 60 HZ?

Have a thumbs up from me... I missed that bit. Gotta' get new glasses I guess.

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Bundy bear?

What is a picnic cooler... an esky?

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Re: Bundy bear?

Yes.

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Re: Bundy bear?

Ut's a chully bun, broo.

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No they don't

The reason we use AC rather than DC is because it's more efficient to transport over long distance, lossy power lines, and more efficient to step up and down in voltage. The vast majority of home equipment actually wants DC power input - much of the power supplies inside the equipment, everything from fridges to laptops need DC at the correct voltage and current.

The solution is not to go from DC (cells/solar) to AC (inverter) back to to DC (internal transformer, rectifier, smoothing capacitor, DC regulator)

What we should be building is a generation of devices for the home with a standard voltage DC connection (as well as an AC connection) so that home solar, microgen wind etc can be fed straight of the devices or the cells used to store charge from them during excess, bypassing the loss associated with conversion between the two.

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Re: No they don't

I already do Richard :-D

I stick the 12v output from my little panels across a pair of 6v SLA batteries.

6v (often closer to 7v when charged) is a useful voltage... It gives me some voltage in hand for my cable run to the USB sockets by the bed and in the living room (and an LDO regulator behind the wall plate to put a final limit on it). One battery does each room. By complete fluke, they generally stay pretty well balanced.

Free charging for the tablets, phones, Satnav and all those other things with a USB power requirement.

Yes, Raspberry Pi runs fine too :-D

80% of the available energy delivered to the devices... Not bad for a DIY lash-up with bits I had laying about :-)

Okay, I know you were probably trying to save a little bit more energy on bigger devices.

You could always buy a TV, fridge and stereo designed for a caravan.

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Re: No they don't

I agree 100%! Things should come compatible with AC or DC where that's feasible. There would be cost issues on the manufacturer side, but those costs would be less than manufactures incur from the specialty lines they all operate to produce specialty products.

That last bit is important, because the low volumes of specialty equipment make that equipment a financial loser for all but the most expensive and esoteric products. Most manufacturers would rather not bother with the multiple input products they make, but not making them risks customers leaving for a competitor that does offer those things. Apple sure as hell didn't invent the 'ecosystem' concept.

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Re: No they don't

The reason we use AC is that voltage transformation is easier, so the changes needed to get from power stations to homes is easier. For long distance efficient transport of power we use DC in the form of HVDC. This is 80kV or more (800kV in china). These converters are expensive, so only used when the power transfer justifies it or where AC just doesn't work (e.g. underground cables more than 100km long).

AC is good for spinny things too. Not everyone has nice variable reluctance motors in their appliances (thanks F&P), so single phase induction motors are going to be around for some time.

A standard home DC bus of 48V or so would be nice. ELV, so no licence required for DIY work here in Australia at least.

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Re: No they don't

Many if not most switch mode power supplies SMPS convert the incoming 50Hz AC to DC then drive a small/tiny transformer with 10kHz to 1MHz AC signal.

Most PCs and laptops and 5V USB chargers could probably take AC or DC,

It should be noted the peak voltage of the 240V mains is 41% higher (339V) than the RMS.

I heard France had a DC grid, in the old days you had a DC motor drive an AC alternator.

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Re: No they don't

>A standard home DC bus of 48V or so would be nice. ELV, so no licence required for DIY work

Ever tried to switch off 100A of 48VDC?

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Re: No they don't

The little town in Denmark that I lived in when I was a kid had a DC grid despite AC being already common in most of the rest of the country. My dad had DC motors in his furniture factory and they were pretty big compared to modern three phase units. Anyway, the town switched over to AC in '57 or so.

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Re: No they don't

Let's not forget we're only talking 2kVA so it's not a whole lot of amps at either 450 VDC or 230 VAC. I don't know how easy it will be getting it all to fit in a box that's 40 cu. in. which is about half the size of a Mac Mini.

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Re: No they don't

"only talking 2kVA"

That is quite a lot of power - the average UK 230V 13A plug will get warm running that for more than a few minutes. Even if the finished unit gets down to only 5% losses (quite a challenge), thats 100W heater sitting on your lap.

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Re: No they don't

"The reason we use AC rather than DC is because it's more efficient to transport over long distance, lossy power lines, and more efficient to step up and down in voltage"

ITYM: It's more efficient to use High Voltage to transport over long distance.

HV AC lines have non-insignificant losses when transported over long distances.

DC is better - the higher the frequency, the higher the losses, but the less iron needed in transformers - which is why aircraft systems are 400Hz and older HV electric train systems used 16Hz (AC has one major advantage over DC - any arcs which might be generated self-extinguish every half cycle)

What is true is that it USED to be more efficient to step up/down using AC, but that hasn't been true for over a decade, and that's been leading to quiet changes in power distribution infrastructure worldwide.

+1 for standardised DC supply voltages, but it has to be borne in mind that DC distribution setups have to be built to deal with and control arcs (this is why switches are usually rated for 20% of the DC current vs their AC rating.).

240V DC distribution used to be common in many industrial areas. It was discontinued because it's unsafe - one anecdote I've heard related was that a blown bulb arced internally, and the arc then ate its way through the bulb base, socket, suspending wire and into the ceiling rose before someone managed to shut the power off.

Personal experience from cutting through a live 48V feed (4mm2 wiring) is that the amount of current which flows is scary (the wiring got hot before the fuse at the other end blew and the arc completely destroyed the wirecutters I was using - the feed was supposed to be dead.). On another occasion I watched a 22mm spanner accidentally dropped between 48V busbars get completely destroyed and the resulting arc almost became self-sustaining.

Lower voltages may be less inclined to arc, but they need higher currents, which in turn means heavier cabling. It's all roundabouts and swings.

+1 also for 48V battery, but higher voltages are better in your storage bank because that translates to lower charge/discharge current (longer life, less droop) and thinner wiring (less voltage drop, lower cost). Electric cars often use 600V - 48V is used in telcos because that's about the highest voltage which is "safe" for dry skin to come in contact with. and using heavier wiring isn't a major problem. Higher voltages are regarded as "mains" for all intents and purposes and usually require electrical qualifications to work on and sign off on.)

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Re: No they don't

"The average UK 230V 13A plug will get warm running that for more than a few minutes."

Only if badly wired.

UK 13A sockets are rated to pass 3.2kVA (not kW) and under normal circumstances they won't change temperature if that kind of current is passed through them.

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Re: No they don't

@Alan Brown

"won't change temperature"

I beg to differ - but maybe not a lot at 8 to 10A.

The plug certainly will change temperature, mainly due to the fuselink and I^2R. The socket will depend more on the wiring size perhaps.

I have run 13A plugs at 16A on test and they get HOT. Much more and they fail of course.

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Trollface

But Who gets the patent.

I can see this being worth a lot of money. Much more than the prize. So who owns the patent?

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Re: But Who gets the patent.

For the hard of reading the answer is in the penultimate paragraph:

"All intellectual property for the winning designs will remain with the inventors."

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This isn't what you think it is.

This is a specific device for a specific job. There are are a bunch of people who would be ripe for the picking in designing the project. It is very much attainable with today's tech, it is within the "perceived limits of engineering", even if the the environmental specifications are a bit vague.

But what if you're not willing to pay what it would normally cost to get the project done? You hold a competition of course!

Why aren't any of those existing engineers entering? Because they're not stupid. Why are none of the established design firms (engineers, project managers, admin staff etc) entering? Because, again, they're not stupid. If they were commissioned through regular means to do the job, they'd be earning a whole lot more than whatever the "up to one million" means.

The fact is, Google is hoping to do it on the cheap, and is too cheap to say.

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Re: This isn't what you think it is.

They may get something from a University or such that is not paying "project managers, admin staff etc" who will be quite happy with a million.

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Re: This isn't what you think it is.

I've got to disagree with you John. The point of this exercise isn't to do what we know can be done, as you correctly pointed out, it's to find a different way to do what can already be done. The result isn't the challenge here. The challenge is how the result is arrived at.

There isn't a big field of contestants, yet, because with the constraints imposed by the Challenge requirements there aren't exactly a lot of, proven, alternative ways to get there. Google could go to Thales, URS, Lockheed, my company, any best of field engineering company and they would get pretty much the same answer solution from everyone. I would wager $10k that the cost estimates from every engineering firm in that class would be within 8-10% of each other.

The idea here is for some bright spark to come up with a different approach. Maybe some junior Engineer that read something in one of the way out there micro journals a while back. Perhaps someone from a skunkworks division at an advanced engineering company, like our Global Domination Division, has already done this but tossed it in the closet after it failed to open a stable wormhole or it burnt their popcorn or something. It could be an undereducated Romanian foundling who taught himself to read by stealing other kids homework (I know that happens, a lot. Bastard stole my homework for ages).

Point is, the money is supposed to start wheels turning in places and in ways 'outside the box' (please forgive me for using that stupid phrase, my brain is tired). You're 100% correct that big name firms aren't going to get into this as 'branded entities'. It simply isn't worth it, you're spot on. But firms like mine or Thales or URS aren't who this is aimed at. This is aimed at those with the PARC and (old) Xerox mentality where financial viability took a backseat to 'fuck it, see what happens'.

In closing I'll add this. Making something work is only about 20% of having a product. The ultimate winner in this Challenge will need tremendous resources they probably aren't going to have access to. That's where Google will start playing their 'gotcha' cards. The winner likely won't get as much money as they could have, but I guarantee it'll be several million fucktons than they would have made spending their career at a test bench and being ignored by management.

Yes, Google certainly hopes to benefit from this, absolutely. But it's incorrect to say they're doing it solely to save a few bucks. A prize of this size is big enough to get clever people involved, people who will have new ideas. But the prize is too small to have heavyweight companies come in and 'win' by way of standard heavyweight shenanigans. This is all a good thing.

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Re: This isn't what you think it is.

"I've got to disagree with you John. The point of this exercise isn't to do what we know can be done, as you correctly pointed out, it's to find a different way to do what can already be done."

I respectfully disagree with your disagreement. :-)

In regard to your "different way to do it", the quality of design usually only comes up to the curious few who take the apart the "black box" so see what's inside. So bascially, few people care about that - even though it may have consequenses on performance or service life, or safety...

It is said: "an engineer can do with 50cents, what a backyard hack can do with a dollar". I'm paraphrasing so it may have lost a bit of meaning, but it means that an engineer may cost more as a one-off, up-front development cost, but the per-unit cost will come down. A backyard hack will cost less initially, but their unit cost will be higher.

There's nothing specifically wrong with this philosophy, it's just a question of economics and quality of product (if you care about that).

And in regard to the economics, what I said from the start: Google is taking the cheap way out.

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Re: This isn't what you think it is.

Google like to build their own hardware, don't they?

It's not that the mighty Google is "looking to do it on the cheap", it's that their Data Center design team is hiring ...

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Anonymous Coward

Seems wasteful

DC->AC->DC seems really stupid. Most servers run off of 3.3V/5V/12V internally, and a lot of commercial servers already have an option for a DC-DC converter (voltage regulator) to take -48VDC for telco COs. (Ah, ye good olde days).

Why not just stick with -48VDC? Yes, you still need to drop it down to 12VDC on each server, but it cuts your amperage on your busbar to a quarter.

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Title fail?

AC/DC != DC/AC

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Hmmmm I'm guessing the 450vDC in is from PV panels

as that's what a lot of the seem to generate.

As for the AC out - well that’s standard. 60hz is OK for the 3rd world I guess but easy enough to make a 50p pic controller make 50 or 60 hz pulse width source at the drop of a resistor.

So just need some amping and some drive trannies...

There must be more to this than you've printed in the article...

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Re: Hmmmm I'm guessing the 450vDC in is from PV panels

As usual - this is the reason why good engineers get paid quite handsomely.

The problem is in the details - size and efficiency. In order to get size down, you'll need to get switching frequency up (smaller capacitors, smaller inductors). But that goes exactly against getting efficiency up (every state change induces losses).

While you can apparently without too much trouble switch 5 V at 1 Amp at around 1...2 MHz (and, at this level, the difference between 85% and 95% efficiency is negligible), doing the same with 450 Volts and 5 Amps (or 240 V and 10 Amps) tends to be a bit more difficult.

I got a couple of 5 kW boxes at home - picnic cooler is a bit exaggerated, though. Squeezing half that power into the size of a laptop - well, it'll depend on the laptop, but it looks feasible.

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Coat

Actually it's the *combination* of factors that's challenging

You've got X Kw (I can't find the FAQ so I've not seen an actual number) Volume and temperature.

And of course the cost

Big items (and big ticket items) have been things like transformers, smoothing capacitors and switching transistors.

Do you need a transformer? Possibly not. Capacitor tech has gotten a lot better (electrolytics are no longer the only choice here) and there are those wide band gap semiconductors.

Personally I'm not convinced the performance improvement they can deliver is worth the cost over a good Silicon power transistor.

The big joker is that temperature limit without liquid cooling. Does that mean no heat pipes to spread the heat? Clever heat sink designs to generate turbulent flow? Hanging curtains of pyrolytic carbon fiber (150W longways)? Forced air? PZ fans?

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Joke

Re: Actually it's the *combination* of factors that's challenging

Naaah, you just make it 99.9% efficient off the bat, and who needs cooling for that...

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Title win!

So... many... puns...

Pun... overflow...

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Anonymous Coward

Free market approach

Sell your DC to someone who wants it, use the money to buy AC.

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Mushroom

Ripple

"Must have an input ripple current of < 20%"

"Must have an input ripple voltage of < 3%"

That's tough when producing 2 kVA at 60Hz. It would probably require a second power conversion system to pump power in and out of a capacitor bank. You can create a virtually large capacitor for small voltage ranges using PWM and an inductor to maintain a ratio of voltages. For example, 437-450V on the input mapped to 50-450V on the capacitor bank. The catch is that capacitors fancy enough to be small and not explode with so much stress are EXPENSIVE.

Semiconductors that can switch 450V at high frequencies without going 'POP' are expensive too.

The design sounds very straightforward and doable but there's only one winner. Everyone else loses a lot of $$$$$ on component costs.

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Paris Hilton

Doomed from the start

Input is 450V through a 10 ohm resistor for an output power of 2kVA.

Doing a rough equivalence of 2kVA = 2kW (yes, I know this is not necessarily true)

We have an input side current of 4.4444... amps.

Power dissipated by resistor = 197W.

This is already close to 10% of the 2kW.

Hence, the project cannot achieve its stated efficiency of >95%

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Re: Doomed from the start

I suspect the 450V and 10 Ohms are to represent a real life power source of 450V with an internal impedance of 10 Ohms so the 197W dissipated by the resistance will be internal to the power source and cannot be changed. There will also be unspecified losses delivering the AC to the load. The >95% refers to the DC/AC converter alone.

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Re: Doomed from the start

I think that's key, we're talking about just the DC/AC converter. Given the constraints it makes sense that it is the only thing being considered, wire in @ 2kVA - DC/AC converter - wire out @ 2kVA * .95+, that's it. They aren't interested in loads, breakers, switches etc. and it's likely they want to put it in something to make a complete package which may explain why liquid cooling is out. At least that's the way I read it since we're talking about a 1" thick box that's 6 5/16" square.

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Paris Hilton

Re: Doomed from the start

Which is why Paris for being a little flip. Nevertheless ...

From the official requirements doc:

"The inverter will be tested using a near ideal voltage supply set at 450 V. This power supply will

be floating. Its positive terminal will be connected to a 10 Ω wire wound resistor which will in turn

be connected to the positive DC input terminal of the inverter. The voltage source will be very

close to ripple free."

Efficiency is computed as:

"The inverter must demonstrate an efficiency of > 95 %. The efficiency is defined as:

Efficiency = DC Power Input / AC Power Output

and will be determined by measuring the input voltage and current and output voltage and

current, using the real component of the power at the fundamental frequency."

I argue that they do not specify on which side of the resister the are measuring the DC Power Input.

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why not

A smart power network in the home.

You plug in said device, it queries the socket and asks for a specific voltage.

Problem solved.

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Re: why not

And if the conversion steps go bad?

Whatever happened to Keep It Simple, Stupid?

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Re: why not

the plug detects the incorrect voltage and trips. -I'm not advocating a total lack of safety features.

I agree with Keep it simple stupid. Nothing wrong with that at all. But what is wrong with a bit of progression.

Keep it too stupid and we all get a scenic star scene for bed time.

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A decent sinewave and no RFI makes it hard.

It's trivial to do for sort of rubbish pseudo near square wave converters typically sold.

Good design and quite old power MosFETs can do this easily for pseudo near square wave converters. I'm baffled as to why it's a competition though.

Perhaps the real purpose is Google publicity.

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TRT
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Why does it have to be solid state?

I know they generally stopped using M-G sets donkey's years ago (when donkey's were used as generators), but could a modern design meet the efficiency requirement?

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Re: Why does it have to be solid state?

Mmm - a 2KVA M/G set the size of a laptop - now there's a REAL challenge...

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disconnect?

even if you can get the inverter packed into 40in³ or so, the disconnect switch (AC and DC simultaneously) is going to take up *at least* 400in³ if you want to meet most electrical codes and i wouldn't recommend running it without. maybe a custom designed switch could be smaller but *very* expensive. don't even think of plug connectors - you don't disconnect 450VDC under load using a plug unless you really hate your present eyebrow configuration.

then there's the problem of conduit entry/between/exit and connections to the switch and inverter that are going to run into trouble with minimum bending radius problems for the wire itself if you get too tight . . . and you might want to leave enough room in the switch box to get your fingers in there to actually make the hookup.

an off-the-shelf 2kW unit is about 30x12x4in and fully a third of that is the switch so this seems like an exercise in miniaturization to save a little more than half the total volume out here in the real world.

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