buck-boost for inverter

2kW says custom magnetics to me -- you looking at an off the shelf part? If you've been designing inverters for a living, you probably have at least as much switching-power chops as the rest of us (unless they've all been square wave converters at 60Hz).

"More money than time" says "go buy one that comes in a metal box" to me. Surely 48V is a common power rail for off-grid applications!

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You can probably pick up a 48-120VAC 2kW inverter on the Internets for well under a grand if one is okay ordering it from CHINA

Well, my first comment is, if this is to be a permanent setup, you ought to think hard about setting up as much as you can to run off 48V directly. (Hmmm, why did you go with 48V, why not, say, 96 or 120 (nominal) V instead? That would make inverters easier to do.)

Anyway, why not make all lighting LED, running off LED power supplies that run directly off your DC bus? I've been making my own LED light retrofits and have been very happy with them. I can share details if you are interested.

If you had a 120 V bus, you could run heating appliances directly off DC (stoves, toasters and such.) Run the well pump off a VFD with a boost converter that only is powered up when the well pump is running.

And, then, finally, there would be some appliances that really need AC such as refrigerators. But, this would allow you to greatly downsize the inverter, which might need to run all the time.

Just some thoughts, although you might be pretty far down this road already.

Jon

buck-boost transformer: as I understand it that's the auto-transformer used in AC Voltage Regulators.

A "2KW" part ( sized for regulating the voltage to a 2000KVA load ) can only transform a few hundered watts of real power which provides the voltage to be added to or subtracted from the input voltage.

You could use one of them, but you've need a 2KVA one to provide a 2KW output. so primary 32VAC @ 64A or similar

As I understand it many inverters run a high frequency transformer at several kilohertz to step the voltage up and then rectify the output and switch its polarity to produce AC.

Doing this allows the use of a smaller transformer, this saves on copper, iron, and shipping costs. I have a 1500W inverter that weighs maybe 2kg.

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I haven't done a square wave inverter since early 80s.

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Thank you all for the input. It was a few years back that we conceived of the home and that's when I decided on a 48v bus. Since then I've accumulate d quite a bit of hardware and in particular, a 12kVA 240v:480v tape wound 6

0Hz transformer. I can put together an inverter over the next few weeks th at will put out gobs of power and use xfmr for well pump. I think the right decision, as Don brought up, would be to stack the batteries in series and invert that. 200v inverters in the tens of KW can be done with TO-247 mos fets very easily. I have a 2KW inverter now and will limp along with that. We have 8 panels now and will have 16 on trackers before long. On a hilltop facing south wi th a stream running through the property so all kind of RE possibilities.

thanks again Bob N9NEO

rid, but I have a 500 gallon propane tank to run generator. We will be in b efore thanksgiving. The power company wanted $17k to wire service, so I sa d no thank you.

y 16 die-hard deep cycle wet cell batteries. (I was surprised that inverte r was able to start the well pump.) I have an 11kW generator that I use to charge batteries in the morning through a 2.5kW charger. I will add more ch arge capability down the road.

r would have 60Hz transformer to get to the 120v. I would run a pair of th ese off of the same pwm generator to get to 240v. I have programmed a pic to do the pwm and have the control board and power boards laid out. My bac kground is developing large inverters so this is an easy task for me.

ed

Hi Jasen. I think the buck-boost units have an isolated secondary. I had a 1kva unit a few years back and the low voltage winding was fairly large d iameter stuff. I'm fairly certain a 2kva buck-boost will get you 2kW out.

Yes, many inverters use a full bridge to get the 48v up to about 200v. Usu ally running at frequencies in the hundreds of KHz. Others are of the 60Hz variety. The transformer goes after the inverter to step it up to 120v. The transformer is also used to charge batteries when the line voltage is t here. I have bought 4 of the 48v/25A units. My generator is 11kW I want t o keep it loaded up and only run for an hour or so per day. As I said I ha ve an AIMS 2kw inverter now. It can run all the gear I have, but not everyt hing at once.

My 2kw probably weighs about 20kg. Who makes the inverter you have? Must b e HF inverter with that light weight.

regards, Bob N9NEO

Some dude in China, yes HF.

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