Honda EU2000 Transformer Problem

[bcroe]

Auto transformers do not have to use larger wire than isolation transformers
in general, and with 1:1 ratios in particular.

With all this fun, I'll just throw in a couple things. Likely the def of an auto transformer isn't that
important. A regular trans converts ALL the electrical energy to magnetic, then back to electrical
energy again. I define an auto trans as one where only only SOME of the energy going in is
converted to magnetic and then back; the rest flows directly through to the output. The ability to
flow through eliminates any possible input-output isolation.

Things like welders may use more complex magnetic circuits than a simple trans. The usual
intent is to provide current limiting without any overload or overheating. Ferro resonant is
popular at my house, except I don't really understand them. Bruce Roe

[inetdog]

What is it that you do not agree with? Autotransformers have to use larger wire than isolation transformers, thus look like a dead short on start up. I think we might be on the same page but looking at it differently.

Auto transformers do not have to use larger wire than isolation transformers in general, and with 1:1 ratios in particular.

An autotransformer designed for small ratio buck or boost will have to have a larger winding, or else have the wire size vary between the two sections of the winding. But for the 1:1 ratio we are looking at here, the wire size will be exactly the same as for a comparable isolation transformer.

Look at the design equations based on winding current.

Now an autotransformer designed for 240 volt single ended in and 120 volt single ended out volt out would indeed appear to require a larger wire size if wound with a uniform wire size. But that is NOT actually the case.
An isolation transformer for 240/120 use would require twice the wire gauge on the secondary. An autotransformer does not.

[ChrisOlson]

What kind of a transformer does my MIG welder have in it? That's another one that has high inrush. Sometimes when I throw the switch on it, it used to fault the SW Plus inverter on overload and the inverter would shut down. By putting a 100 foot cord on the welder, then it didn't do that. For whatever reason it doesn't bother the XW inverter at all without the long cord on it.

[Sunking]

I have to disagree with you there. The fact that there is a single chunk of wire instead of two chunks wound around the core does not have any effect at all on the inrush current.
I will, however, grant that the common applications for autotransformers tend to lead to design decisions that in turn mean higher inrush.

What is it that you do not agree with? Autotransformers have to use larger wire than isolation transformers, thus look like a dead short on start up. I think we might be on the same page but looking at it differently.

[inetdog]

OK lesson one. An Autotransfomer is not isolated from primary to secondary, thus the huge magnetic current to get them started.

I have to disagree with you there. The fact that there is a single chunk of wire instead of two chunks wound around the core does not have any effect at all on the inrush current.
I will, however, grant that the common applications for autotransformers tend to lead to design decisions that in turn mean higher inrush.

Case in point: As seen from his measurements, Chris' "autotransformer" is actually an isolation transformer with two wires connected to the same terminal block at the factory. And it has high inrush comparable to what a "real" autotransformer would have when designed for the same application.

[ChrisOlson]

Ah, OK I see now studying those pictures from Sunking how that works. And inetdog, you're probably right on how they market the thing. It comes all factory pre-wired and all you have to do is connect your wires to the breaker and the neutral bus, and ground the chassis. I never seen anything in the instructions about taking those white wires off the neutral bus - they just give like three different wiring diagrams for it, depending on what application you're using it for. It just so happens that the step-up and balancing are the same if you remove the L2 wire from the picture for step-up. So the transformer can be used with either a 240V gen for balancing, or a 120V gen for step-up without changing any wires around in the transformer - all you have to do is feed either L1 or L2 with the 120V gen and make sure the other end of the wire going to the other generator is isolated with the use of a contactor.

Regardless, those Outback transformers are pretty dang efficient. It does wonders for a split-phase generator. The inverter can handle really big leg imbalances with no problem, but the generator can't. With the transformer on the generator, the generator can be used at full rated capacity. Without the transformer, the generator is limited to the highest loaded leg and if the other leg is a lot lower load on it, you can't get full power from the generator.

[ChrisOlson]

You should notice that sometimes the thump is louder that others, depending on where the voltage is in its cycle when you close the switch.

Yeah, I've noticed that with our transformer. The sequence of events on an auto-start is such that the AGS starts the generator and allows it to come up to speed. Then the AGS closes a contactor in the generator room that connects the genset to the inverter. Sometimes that seems to be pretty smooth and sometimes the transformer goes "THUD" and the cups rattle and me and Kristin look at the wall and she says "what the hell?"

I should've put that transformer in a different place. But we used to use it with our SW Plus 5548 inverter because that inverter was only 120V output and we needed the transformer for split-phase power. When we put in the XW I just left the transformer mounted right where it was. It was powered up all the time with the SW Plus so it never did that.

[Sunking]

OK lesson one. An Autotransfomer is not isolated from primary to secondary, thus the huge magnetic current to get them started.



Isolation Dry Transformer has isolated primary and secondary and thus do not take much current to saturate the core to get it going. Isolation transformers serve a number of purposes like isolation, balance current, step up or down voltages. derive 2, 3 or 6 pahses from a sinble phase, or derive multiple phases from a single phase. Only thing an Autotransformer can do is step up or down voltages, or derive phases from a single phase with no isolation.

[inetdog]

So, this is not a "real" or true autotransformer? I sure wish I was an electrificution engineer because I'm confused now

This is what it says on the front of it (hope you can read it OK)

Yup, I can read that just fine.
Two speculations:

1. Since they want to limit the applications to ones that they have tested and not assume responsibility for your mistakes they tie the two white wires (two wires brought out from the two halves of the "single winding" where they meet at the midpoint) together and call it a day.
2. That factory connection relieves them of all sorts of UL requirements for the voltage isolation between the two windings (since it is officially just one winding) and makes it easier to get the unit UL listed.

And since it is labelled as an autotransformer, you would be violating the listing instructions by separating the two white wires and doing something else with it.
So keep your hands off!

[ChrisOlson]

So, this is not a "real" or true autotransformer? I sure wish I was an electrificution engineer because I'm confused now

This is what it says on the front of it (hope you can read it OK)

[bcroe]

You should notice that sometimes the thump is louder that others, depending on
where the voltage is in its cycle when you close the switch.

Yea, and the state of magnetism last time it was turned off.

[inetdog]

OK, well, being I got a bunch of electrificution engineers right handy here, and these electrificution engineers are willing to teach me, I need to learn these things......

So an autotransformer is just a big electrical steel core with a big coil of copper around it that's center tapped? Here's a photo of the inside of our transformer - this is the same unit the neighbor just got:

We had a problem with the breaker on ours once and I was checking it out with the ohm meter because I thought it had a burnt out winding. It has four wires coming out of it - a red and a black and two whites. IIRC I had no continuity between the red and black. But I had continuity from the red to one white and from the black to the other white. If I hooked the whites together (where they normally are on the neutral bus in the thing) then I had continuity from the red to the black.

So how come there's four wires coming out of the confounded thing?

<lecture mode>

Yes, it is essentially one long winding with a center tap. In some cases, such as a buck or boost autotransformer with a small voltage difference that one winding will actually change wire size at the center tap. But you can ignore that for a 1:1 ratio.

You have four wires because it is NOT an autotransformer. It is a isolation transformer with two separate windings. But if you wan to use it that way you have to put a red marking on the white that shows DC continuity to the red and a black marking on the white that shows DC continuity to the black.

It is apparently marketed as an autotransformer based on the fact that it is shipped to you with the whites connected together. And the rest of the design may have been optimized for that configuration. But it is actually an isolation transformer.

PS: The DC resistance is close to zero but the impedance at 60Hz is quite high (and mostly inductive). That is what limits the no-load current flow once the transient issue of core magnetization has been dealt with.
PPS: And if it were not for magnetic hysteresis, the inrush current would not be nearly as bad. You should notice that sometimes the thump is louder that others, depending on where the voltage is in its cycle when you close the switch.



</lecture mode>

[bcroe]

OK, well, being I got a bunch of electrificution engineers right handy here, and these electrificution engineers are willing to teach me, I need to learn these things......

So an autotransformer is just a big electrical steel core with a big coil of copper around it that's center tapped? Here's a photo of the inside of our transformer - this is the same unit the neighbor just got:



We had a problem with the breaker on ours once and I was checking it out with the ohm meter because I thought it had a burnt out winding. It has four wires coming out of it - a red and a black and two whites. IIRC I had no continuity between the red and black. But I had continuity from the red to one white and from the black to the other white. If I hooked the whites together (where they normally are on the neutral bus in the thing) then I had continuity from the red to the black.

So how come there's four wires coming out of the confounded thing?

What you have is a 2 winding 120 VAC to 120 VAC transformer, used to create an out of phase power
leg. It only needs to be large enough to carry 120 V loads on the added leg, perhaps 1000 VA (half).
If a 240 V load were placed across both legs, the same could support 2000 VA (working as an auto
trans). Bruce Roe

[ChrisOlson]

OK, well, being I got a bunch of electrificution engineers right handy here, and these electrificution engineers are willing to teach me, I need to learn these things......

So an autotransformer is just a big electrical steel core with a big coil of copper around it that's center tapped? Here's a photo of the inside of our transformer - this is the same unit the neighbor just got:



We had a problem with the breaker on ours once and I was checking it out with the ohm meter because I thought it had a burnt out winding. It has four wires coming out of it - a red and a black and two whites. IIRC I had no continuity between the red and black. But I had continuity from the red to one white and from the black to the other white. If I hooked the whites together (where they normally are on the neutral bus in the thing) then I had continuity from the red to the black.

So how come there's four wires coming out of the confounded thing?

[inetdog]

Yeah, the only thing is that he wanted to be able to use the transformer to leg balance his Perkins diesel generator too. Without the transformer he has to set a conservative gen support level on the Perkins or it will trip the breaker on it and he can't use it for battery charging.

So the transformer is doing two things - leg balancing one generator and producing L2 for the other one - and I don't know if you could do that with a regular transformer.

I know the core saturation on the autotransformer is really big. Our power room is on the other side of the north kitchen wall and our autotransformer is hanging on that wall. When our big Honda generator auto-starts we know when it starts because that transformer makes a horrible "thud" that rattles the cups in the cupboard

You can do anything with an isolation transformer that you can with an autotransformer, just be wiring it up the right way.
What the autotransformer theoretically provides is a little less copper usage and a smaller overall package since you do not need to separate the windings.
When you go to a 1:1 ratio of primary to secondary (or partial winding to full winding) many of the advantages of an autotransformer go away.