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I was looking through the schematics for the Quattro 240V (mine is a 48/15000) and I'm not sure I saw one that applies to my situation. We want the Quattro to output single phase 240V (our cable has an L, and N, and G wires) to an AutoTransformer that will split it into two legs of 120V.
The reason we want to do this is the cable is 700 feet long so we want to keep the voltage high. Is there a schematic for this? Many thanks for any help.
Hi,
I found this thread that might be useful, sounds like they had a similar setup to yourselves. @Mike Dorsett explains it well here:
As I (and others) mention in the other thread, you need an isolation transformer in order to create a 120-0-120 split phase output from a 240-0 input.
With 700 feet of cable, in order to keep voltage drop within 3% you are looking at 600 KCMIL copper wire. That's for split phase which works out to 62.5 amps per leg. That's 1 inch in diameter per conductor.
I think for that run, you will need to step up to a much higher voltage at the source and step back down again at the other end. Stepping up to 480 volts would reduce the wire size to 1 AWG.
Hmm, my calculations for 240v, 427m round trip (700 feet x2), result in a minimum cable size of 90mm^2 for 3% drop. This cable size should be readily available. Moving to a 3phase 5kw per leg system would help reduce losses. this could be done with 4 x 16mm^2. ( In copper) in aluminium, sizes would be 25mm^2 for the three phase solution, and ~120mm^2 for single phase.
you would need to disable the grounding relay in the inverter, and then you can permaently ground the centre of the auto transformer. This leaves the inverter output floating.
This manual seems to show the potential use cases for a single auto-transformer (whereas it seems like you'd need two for your use case):
https://www.victronenergy.com/autotransformers/autotransformers#manuals
We are running single phase 230V through the cable, so our math shows that a triplex 250-250-3/0 wire should suffice.
In other respects the autotransformer will be fine for what you want to do provided you do not connect the centre tap of the generator to the ground or anything else.
Particularly do not connect it to the centre tap of the autotransformer as any small imbalance in the windings of either can then result in large circulating currents.
a. Power 120V appliances with a maximum of 28-32A of unbalanced load
b. Power 120V appliances with a max of 100A of balanced loads (minus any unbalanced loads)
c. Power 230V appliances up to 100A of load (minus any 120V loads)
If this is the Honda EU7000is generator, it is split phase. Max continuous power is 5500 watts (7000 for 30 minutes). 5500 watts is 23 amps at 240 volts. This generator's output is 120-0-120 but the neutral is NOT connected to safety ground. Normally, that neutral to safety ground connection is made in the switch gear. In your case, you can probably leave it open unless local codes dictate the generator's neutral needs to be connected to safety ground. The Quattro's internal ground relay MUST BE DISABLED! The L-N output of the Quattro can connect between the two line inputs of the auto transformer. The autotransformer will create 120-0-120. How you set up the autotransformer's ground relay will depend on if you connect the generator's neutral to safety ground. I the generator neutral is connected to safety ground, the autotransformer's ground relay must be controlled by the Quattro. If the generator's neutral is not connected to safety ground, then the autotransformer must make a permanent neutral to safety ground connection.
In this case, the Quattro neutral is NOT at ground potential. Rather it is at 120 volts relative to safety ground. The Quattro is rated for this and is in fact shown in one or more of the Victron system drawings.
Quattro 15000 at 25 C max continuous power is 12000 watts or 50 amps at 240 volts. With generator plus assist that's 73 amps at 240 volts. Won't make 100 amps!
Perfectly balanced you could get 73 amps out of each 120 volt leg. The autotransformer will tolerate 28 amps of imbalance.
If any of this confuses you, please seek out an electrician or Victron installer to sort out any details. Failure to understand the system and installing it properly can create a electrocution risk or equipment damage probably not covered under warranty.
Yes, the 100A assumed we added more power.
You had stated above that "As I (and others) mention in the other thread, you need an isolation transformer in order to create a 120-0-120 split phase output from a 240-0 input."
Later, you wrote that "There are many valid applications for an autotransformer. Yours is probably not one of them."
In this latest post, after some discussion, you stated:
"The L-N output of the Quattro can connect between the two line inputs of the auto transformer. The autotransformer will create 120-0-120."
So it seems we're now on the same page which is that we can use the Quattro 48/15000 to supply power over our triplex wire to our single Autotransformer to supply 120V and 230V loads at our cabin without using an isolation transformer.
We will most definitely be having an engineer install this, but we need to know what to buy before then, which is why we are trying to understand how this stuff works.
Thank you for your opinion. We live in Alaska way off grid. We have relied on the well trained Victron dealers to select the equipment we would need. While that hasn't been perfect, and given that we now agree that the Autotransformer can provide what we were told it would provide, it appears to at least be working for us in the case of the Autotransformer.
This is an interesting blog post as we have a very similar setup that works just fine. We have a Quattro 48v/10kVA at 240v single phase that outputs to an autotransformer yielding 120-N-120, with the two 120 AT legs yielding split phase 240v. For legacy devices that require single phase 240v, we pull directly from the Quattro output. It has been working flawlessly. Maybe I am missing some nuance in prior posts or not understanding?
