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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 have a single phase of 240V coming out of the inverter. We were told, the autotransformer would take that and split it into two legs of 120V and balance those legs.
This is very strange to find out that for some reason we need something different.
Our dealer recommended it precisely for this use. And I can't imagine what other use it would be for. Everything I've read says this is how it's used.
Why do we need an isolation transformer, and what exactly is the purpose of the AutoTransformer if you say it doesn't do as we were told it does?
Here is a blog post that seems to describe it doing what we need it to do.
From the blog post:
"The Victron Energy Autotransformer is the one item we sell that causes the most confusion... In this case we are using the Autotransformer in its capacity to make two split phases of 120 volts from a 240 volt input, and to balance the loads between the two legs."
https://shop.pkys.com/autotransformer.html
Which sounds like they're doing what you're doing and it sounded like they needed 2 aufomatrnformers to get 2 legs of 120v from single phase 240v rather than just just 1 leg of 120v
They seem to have output 240-120-0 rather than 120-0-120. However Ive never tested this myself sorry, just passing on what I've read
Thanks, I appreciate you passing on that thread, it's helpful.
Maybe @Kevin Windrem will weigh in since he seems to have a different understanding than the person who wrote the blog post.
As the blog post notes, the Autotransformer remains the most confusing item Victron sells.
I'm not 100% on this (I'm DIYer) but I think the issue is the N is referenced to Earth on the single phase 240v input.
So L2 will be 0v to earth as its not an isolated transformer. So I think theoretically it works fine until you reference the new neutral (on spit phase side) to ground/earth which Im pretty sure is needed for safety. Maybe the article linked is more suited for setups without referencing neutral to ground?
Someone please correct my broken logic if any above
Do you need 2 phases of 120 or could you get away with just 1 as that is supported
Did you take a look at the Ground Relay that is included with the Autotransformer? It allows for grounding the AT or not grounding it based on the software setting in the inverter I believe.
"There is a single ground connection and there is also the ground relay connection which connects to the ground relay terminal of the MultiPlus. Below is the corresponding terminal area on the Multiplus where the ground relay connection is in the middle of the block."
But your multiplus earth and At are the same regardless of the relay though aren't they? I imagine you're using an earth rod in the ground. So relay open or close L2 is still 0v to ground.
I'm out of my depth now, borderline guessing I'll let someone in the know respond.
Does that maybe mean if multiplus isn't earthed or have grid connection that it might work?
What's feeding the INPUT of the inverter? If that is split phase also you'd be OK with the autotransformer on the output.
If your input is 240-0 where the 0 is connected to the system neutral and the safety ground, then the issue is connecting the 0 from the 120-0-120 of the autotransformer to the 0 of the input. In that case you short out the 0-120 half of the transformer.
Isolation transformers have separate input and output windings so you can create a new neutral at the center tap of the output winding.
There are many valid applications for an autotransformer. Yours is probably not one of them. Autotransformers exist because they are less expensive than isolation transformers because there's only one winding.
Maybe this illustrates the issues:
What will be feeding the input of the inverter will be DC power inverted from a battery bank or from the solar panels.
The Quattro will also have a Honda 7000 generator hooked up to it supplying 240V (two hots, a neutral, and a ground).
It would appear to me that my application would be a valid one for the Autotransformer (taking single phase 230V and splitting it into two legs of 120V) since that is what the dealer said it would do and what I would think 99% of people would use it for. And it's what this blog post says it can do.
"The Victron Energy Autotransformer is the one item we sell that causes the most confusion. It can be used in a number of different applications but this article is about using it with a US 120/240 volt shore power system and with a 240 volt inverter charger or generator. In this case we are using the Autotransformer in its capacity to make two split phases of 120 volts from a 240 volt input, and to balance the loads between the two legs."
Still we could be wrong. How confident are you that it won't work in our case? Are you suggesting that it won't:
- take 230V and split it into two 120V balanced legs
- allow us to use 230V appliances
or both?
What application do you see the Autotranformer being most used for if not to take single phase 230V and split it into two legs of 120V and balancing them?
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?
