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I want / need to take a 3kW, nominally 240vdc say again DC and obtain "3-phase, high-leg delta (aka wild-leg delta) from it.

(I won't answer questions on why, but if I feel the need later, I'll make a new question).

I'm not satisfied by the market solutions I see - they all seem to want low voltage inputs, necessitating a pointless stepdown to 24 or 48 volts DC. That seems dumb. Will I need to design/build this?

I'm also concerned that inverters based on "chopper" technology won't provide a smooth and reasonably pure sine wave (of course, I'm no inverter expert).

I'm perfectly competent, I'm just having a heck of a time finding any suitable products in the marketplace. I realize StackExchange isn't a shopping assistance site, but help me out - am I searching in vain for something that simply doesn't exist?

LOL I'm half tempted to consider an M-G set, but I need "high leg delta" and I don't think they can do that.

enter image description here

240V on a side... 120V L1-N.... 120V L2-N... 208V L3-N.

Harper - Reinstate Monica
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Richard T
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    You haven't actually proposed anything meaningful, so we'll just have to go with "yes, you're quite wrong". Anything that does what you're asking for is an inverter, by definition. They can be quite efficient. You don't have to go down to 12V (48 is plenty common, and 240VDC ones can be found) but even if you did drop down to 12 you'd *still* be coming out well ahead of a motor-generator set efficiency-wise. – hobbs Mar 04 '23 at 01:47
  • @hobbs Uh, OK... ...Your comment is helpful in quite a few ways and in a way you might not have expected: It basically reframes (and shortens it), and IDK why you don't just make it an actual answer, minus the derogatory parts. (IDK why you think a question has to "propose anything meaningful", especially given the content! What, we all have to be experts here?!) Anyway, I do appreciate the input. AND I'm glad to learn about the opportunity for maybe finding a 240 one to do this! So far, what I found expected you to go to batteries, as in solar storage... Can you suggest a vendor? – Richard T Mar 04 '23 at 01:54
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    Because you're asking for validation for an idea, but didn't say what the idea is besides "not an inverter". We don't do that. – hobbs Mar 04 '23 at 01:59
  • @hobbs NO, I didn't ask for validation of an idea, I only said this other stuff seemed like overkill, suggested a not necessarily valid alternative, and openly admitted many times, in several ways, "I may be wrong". ... And I have no idea WHY you think I didn't say what the idea is since you yourself answered a good part of it... However, do these inverters address the stinger problem? – Richard T Mar 04 '23 at 02:01
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    (Turning a "bus voltage" into three-phase AC is close to what (3phase) VFDs do, too. You just don't need the tolerance of AC input, the variability of output frequency&voltage. You may need something closer to a clean sine than the PWM that may be unfiltered at the VFD output, expecting to feed a seriously inductive motor.) – greybeard Mar 04 '23 at 07:04
  • I have a slight problem to imagine how to provide a neutral with a standard (?) three half-bridge inverter. How much apparent power do you need @120 V? How much at 240 delta? Do you need power at 208 V (#phases?), any potentials involved shared or isolated, any phase relation between the 120 V voltage (&possibly the 208 V one) and the 3phase system? `input is substantially higher than every leg` not really - 208 V RMS sine is 294 V peak. *How do the utilities do it* they use (base frequency) transformers. – greybeard Mar 04 '23 at 07:34
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    `WHY I want to do this I see as a distraction` ... I don't mean to sound rude, but 90% of your post is a distraction – jsotola Mar 04 '23 at 18:39
  • @greybeard Thanks, Greybeard, - my beard's also grey at this point!... Yes, I have at least one notable single-phase load. It's an induction motor that presumably has a high (relative to the stead-running-state) (and unknown to me) startup current, but after starting, the running load is pretty modest ... Unfortunately, the data tag on the unit is damaged, so specific specs are unknown, but it's on a 20A circuit and uses nothing like that in power. There's a rare use case for one other such load. Otherwise, I expect the full 3kW to be "used up", but it will NEVER get over about 3.75 kW. – Richard T Mar 04 '23 at 23:19
  • There are other forums where people like being conversational and supportive and enjoy miles of idle chit-chat, of course, they also kinda suck for that same reason. StackExchange's brand is concision and high signal/noise ratio. We're happy to help but respect us here with ***BREVITY***. Edited. – Harper - Reinstate Monica Mar 05 '23 at 07:41

1 Answers1

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Lower capacity systems, that may meet your requirement, are available.

Here's one.

enter image description here

vu2nan
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  • It took me HOURS of web searching to find that, but, indeed, I found it eventually. ... I wish you'd have said "Nova" somewhere, or given a link instead of an image, but THANKS! One of their units looks like just what I need! .. But, as it's a weekend, I don't know the pricing yet! ;-) – Richard T Mar 05 '23 at 02:07
  • Hi Richard, I'm glad you could find it and do hope that it suits your budget. – vu2nan Mar 05 '23 at 03:25