Question on 3K inverter

Not sure at the current time.  A 3k inverter definitely won't need 70A and 120A output relays, that's for sure.  But it's a lot easier to use the same design for everything, than have a lot of diff. variants.

A 3kw would have a smaller transformer AND a smaller mainboard.  Syslocked to 3kw of course unless you voided the software warranty--but then you'd probably find that it overheats at 4kw or thereabouts anyway.

You can use the same design just with smaller output relays. I would not bother with the 1.5k model not much you can do with that. 3k 6k and 12k are fine.  I guess the 3k would have only 3 or 4 mosfets in parallel vs 6 for the 6k and 11 for the 12k.

Are you planning to have a prototype out before the end of 2021 ?

Is there a particular need for 3k inverters?  As of right now, the effort is to get the Rev. C board order placed, then the 12kw...but if there's a commercial need for a 3kw, we can try to work on that as well.

I would say for 24v systems 3k there is a need as not everyone needs a 6k or 12k inverter. As for 1.5k I don’t really see a need but it’s good for 12v systems and can power up some low powered devices.

6k and 12k are best for for 48v and 60v systems

3k best for 24v systems

1.5k best for 12v system

Well at least that’s my thoughts on the subject. Basically you don’t want to pass 200 amps continuous on your primary windings on the transformer.

So I would agree that a 3k inverter would be a nice addition to the lineup. You can design a new mainboard and power board for the 1.5k and 3k lineup

Let's see if I can find some latching 2-pole relays in a smaller size.......

...though it is worth noting that we are seriously considering offering the 12kw inverter as low as 24v.  Yes, that's 600A.  Note that I said considering...we may not be able to guarantee full operation at 24v, though from a mathematical technical standpoint, it should be possible. 

I'm aware of 1 GS customer @ 12v (6kw inverter), and while we definitely can't recommend that, I've heard that they've had it up to 5kw.  Lots of amps, for sure.

600 amps at 24v that’s insane...I would not sell that option. 

For the 12k you need at least 48v that’s 400 amps already. 60v is a bit better. 
 

Most people with 12v are either in small cabins, rv or small boat. So 1.5k is more that enough. Most users are either 24v or 48v battery systems. So most inverter sales are going to be 3k and 6k. For the people who want 12k is because they want a large surge capacity or just want to run whole house on one inverter.

12kw @ 48v is 400 amps????

12000 / 48 = 250A...that's obviously assuming 100% efficiency.

If assuming a nominal 53v battery voltage and a worst-case 80% efficiency, that's (12000*1.2)/53 = 272A.

24v is just double that, or 543A.

Transformer can definitely handle it (by design if it can handle 48v, 24v is exactly the same).  Whether the PCB can handle it is a different story, but that remains to be tested.

12kw universal transformer can support 24, 36, 48 and 60v options, though the 60v is limited by the absolute max 80v of the power supply chips on the control board and WiFi board.

You are correct in your calculations as always. I am using estimated values. Basically you don’t want to push more that 200-250  amps on the primary.  Then it starts getting insane in amps. Again you are correct running 12k inverter on 24v power bank is possible however I would not do it. For 12k you need at least 48 power bank. That is my thoughts on that. Looking forward to your new 3k design that would be good for a 24v power bank. Good for vans, rv’s , small cabins and small boats. It should sell very well.

Would have to ask, "why not push more than 200-250 amps on the primary"?  With the GS universal transformer design, running 500A @ 24v is completely identical from the transformer's point of view to 250A @ 48v.  The only part of the inverter noticing the doubled amperage would be the FETs / wiring--the former causing a reduced surge capability.

I do agree that 48v makes high wattage super easy.  The main issue with the 3kw GS design is that the base costs are very similar to that of the 6kw--meaning that per KW, the 3kw price is a good bit higher than for the 6kw.  Anyone looking at the dollar will figure out that they get a lot more bang for the buck with a 6kw...at least that's what happened in the preorders.

Perhaps with a redesign (i.e. smaller mainboard, smaller chassis) the cost could be reduced slightly--but international shipping is by volume, not weight.

The engineers I have spoken to say 200-250 amps is the most you can push on the primary windings. They suggest that if you need more power you can just put the transformers in parallel. That’s what Victron does. As for costs your right the 6k would be best value as the 3k model would not be much cheaper to make vs the 6k model.  Your manual does mention the 3k inverter I just thought you already were designing a new mainboard. I would just stick to 6k and 12k if there is demand for 3k you can always work that out.

That would be correct based on their transformers and/or not understanding how the GS universal transformer works.

Seriously now, if I have a 48v winding rated for 250A...I can run 250A through it all day all night, right?  Well, let's cut that winding in half (lengthwise, not in strand width).  And then put both halves in parallel.  Now we have a 24v winding rated for 500A.  To the transformer, the turns/volt, tesla and magnetic requirements are completely identical to the 48v configuration--same wattage, same turns/volt...NOTHING has changed except the required input voltage.

If the transformer can do the wattage at 48v, it technically from a mathematical standpoint can do it at 12v...if the primary winding thickness is quadrupled at the same time the wire length is quartered (i.e. keeping the same total amount of wire at work).

Now as far as the FETs are concerned, there's quite a big difference in amperage.  But that's what the battery current limit is for.

Again you are correct. Your universal transformer is unique and I was talking about a single wound transformer for single phase no center taps. Like how Victron does it. That is why they parallel their transformers. Your universal transformer is a different animal altogether.

OK, just wasn't sure.  Have all sorts of weird ideas thrown at me from time to time 😉...it can get hard to separate "wild idea" from just "misunderstanding".