2 inverters?

Kevin.Hutch

2011 Mercedes 313 906
All of these complications are moot

if you do not wire mains power circuits and outlets.

I like to keep things simple:

99.9% of consumption is direct DC, no inverters

any AC load devices plug directly into their inverter

if there were an AC outlet, it would be impossible for it to be fed by more than one inverter

the only thing fed directly from shore power or the genset is the charger, and that just physically plugs in

if I had electric aircon, it would also plug in like the charger, but likely to a separate AC circuit or genset from the charger
100% correct, if the charger is the more common transformer type the isolation is guaranteed if one device is connected to one power source at a time, be it generator or inverter there is no problem.

The complication is when multiple devices are powered at once and a ground connection is introduced, the interconnection issues begin via the common connection.

Most generators or inverters do not have an internal connection between one of their live wires and the frame/ground/earth and often these three are at not the same voltage, so by definition, there is no return path for a GFCI detection to activate ie no protection.

The only way I know to detect a Ground Fault in this situation is to measure the voltage between the live wires and earth and if either exceeds 40volts it can be potentially lethal.
 

Kevin.Hutch

2011 Mercedes 313 906
40 years in the electrical industry and I can't figure out what you guys are talking about.

My inverter feeds a small 120 volt breaker box. The neutral is connected to the enclosure at this location only. This is called the bonding of the neutral. All metallic parts of the van are also bonded to this location via bond wires in the cables. That's it. No connection to earth/ground is required as the electricity is separately derived in the van. This way, the breakers will trip when a hot wire makes contact with any of the metalic parts of the van. Yes, the GFCI receptacles will also work with this set up. The ground connection is only to provide a path for lightning or static electricity anyways. Use a piece of rubber dragging on the ground to dissipate that if it's a problem. Shore power connection to the van is what complicates things as the shore power should be bonded back at it's source. I prefer to use the shore power to only feed my battery charger thus avoiding any multiple path issues. In other words, never connect the van 120v panel to shore power, keep it isolated. I always use the batteries/inverter/battery charger when on shore power.
Clearly done by an experienced household and/or industrial electrician and 100% correct and the transformer of most battery chargers gives perfect isolation.

The gotcha as you say is if you wanted to alternate shore power to devices in the van (maybe a future owner) the neutral bond would trip a shore power GFCI necessitating the neutral bond be switched out. Readily done with a 'break before make changeover' but the earth GCFI required neutral bond would be lost when the shore power is unplugged without switching.
 
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Kevin.Hutch

2011 Mercedes 313 906
Just like water, electrons circle or flow in the opposite direction in Auz, or south of the equator....
No unlike popular belief we are held down by the same gravitational pull too, the only difference is that our phase to neutral voltage is 230 (We use to be 240 until recently) and our convention is to have the active or hot pin clockwise from the earth when looking at a socket, also our active/neutral pins are 45% to the earth not horizontal like the US.

We commonly have red active/Hot and black neutral instead of Black active/hot and white neutral although we have adopted the international Brown active/hot, blue neutral convention but not retrospectively and many boats here are imported from the USA.

20 years working for an American computer company designing and installing computer rooms plus standby power systems, followed by many years in boats taught me a lot about the differences in US and Aus power and a healthy respect for earth leakage as well as ways to detect and protect.
 
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AirJoseph

Member
The gotcha as you say is if you wanted to alternate shore power to devices in the van (maybe a future owner) the neutral bond would trip a shore power GFCI necessitating the neutral bond be switched out. Readily done with a 'break before make changeover' but the earth GCFI required neutral bond would be lost when the shore power is unplugged without switching.

Unless you are willing to test that the shore power supply has it's polarity and bonding correct, then disconnect your power panel neutral bond each time you arrive at a camp ground, it's not safe using shore power directly. Even if you have everything wired correctly, your neighbor camper may not and could heat up your bond etc... It's just better to isolate.

Remember, electricity seeks all paths back to it's source. You don't want to be one of the paths....

I used to be responsible for two Marina's in the city and witnessed all kinds of electrical horror shows from boaters who 'diy wired their boats' including burning their boats down to the water line.
 
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AirJoseph

Member
No unlike popular belief we are held down by the same gravitational pull too, the only difference is that our phase to neutral voltage is 230 (We use to be 240 until recently) and our convention is to have the active or hot pin clockwise from the earth when looking at a socket, also our active/neutral pins are 45% to the earth not horizontal like the US.

We commonly have red active/Hot and black neutral instead of Black active/hot and white neutral although we have adopted the international Brown active/hot, blue neutral convention but not retrospectively and many boats here are imported from the USA.

20 years working for an American computer company designing and installing computer rooms plus standby power systems, followed by many years in boats taught me a lot about the differences in US and Aus power and a healthy respect for earth leakage as well as ways to detect and protect.
Just out of curiosity, what's your standard three phase voltage phase to phase? 50 or 60hz?

Thanks

Joe
 

Kevin.Hutch

2011 Mercedes 313 906
The gotcha as you say is if you wanted to alternate shore power to devices in the van (maybe a future owner) the neutral bond would trip a shore power GFCI necessitating the neutral bond be switched out. Readily done with a 'break before make changeover' but the earth GCFI required neutral bond would be lost when the shore power is unplugged without switching.

Unless you are willing to test that the shore power supply has it's polarity and bonding correct, then disconnect your power panel neutral bond each time you arrive at a camp ground, it's not safe using shore power directly. Even if you have everything wired correctly, your neighbor camper may not and could heat up your bond etc... It's just better to isolate.

Remember, electricity seeks all paths back to it's source. You don't want to be one of the paths....

I used to be responsible for two Marina's in the city and witnessed all kinds of electrical horror shows from boaters who 'diy wired their boats' including burning their boats down to the water line.
We are clearly on the same page, I fully agree isolation from other's power issues is the best option when sharing a power source having the only shore powered device the battery charger is an excellent compromise.

Isolation transformers of adequate capacity to run aircon and fridges are bulky, heavy and expensive so rarely used, but still the best option.

Here in Aus we have had double pole RCD plus double pole switches mandatory in all mains powered mobile accommodation (boats, caravans, campers, motorhomes and portable buildings) plus marina and trailer park outlets for many years so isolation is a lesser safety issue here.

Now we are seeing isolated power gensets and inverters commonplace as portable power sources and the mandate of a neutral ground connection before the RCD, is ignored.

I have replaced the RCD in my motorhome with a Residual Voltage Device that detects either the earth neutral presence or a voltage less than 40v live to ground, isolating the circuit within milliseconds.

This video shows the advantages of this approach; https://youtu.be/-Z6x5yZTXcc
 

Kevin.Hutch

2011 Mercedes 313 906
Just out of curiosity, what's your standard three phase voltage phase to phase? 50 or 60hz?

Thanks

Joe
Our phase to phase is 415v and all our AC is 50hz
 

rollerbearing

Well-known member
Man....this is complicated

It is and it isn't. You will not have any problems if you properly install a transfer switch so that power can only come from a single source (big inverter, small inverter, shore power) at a time.

Proper installation includes consideration of the neutral/ground bonding issues of the sources and that is not that difficult when dealing with single (at a time) sources.
 

john61ct

New member
Man....this is complicated
I feel ya Bob.

It really isn't, if my high-efficiency KISS design principles outlined above apply to your use case, just copy and paste from my posts, maybe starting with the latest one first.

If you actually want the more mostly-AC, auto-switched inputs to wired outlets approach where all the complexity is required for safety, and different approaches for different code jursdictions

my advice is, hire a well recommended professional.
 

Kevin.Hutch

2011 Mercedes 313 906
Man....this is complicated
You are right when discussing AC distribution on a worldwide forum a mix and changing understanding can become very complicated. Simplistically there are two systems North American 60hz and the 50HZ for most metric counties and 60hz for others.

Then there are multiple interpretations, resulting in phase to neutral of 120 or 240 and phase to phase of 240 - 420 now most common, but there are others and some countries have changed. There are delta and Y configurations with ground-referenced and isolated systems and often variations within countries with historic colour code variations to identify phases neutral and ground conductors with a plethora of plug types.

Things like boats that can show up anywhere in the world from any origin with any standard of power to raise the confusion bar, so the safety and compliance issues become very complicated with many workarounds, making isolated systems the ultimate.

In Aus it is legally mandated that any connections above 50v AC wiring be signed off by an electrically qualified professional with RCD protection for high-risk circuits and we still get it wrong.

Thankfully the RV world is much more confined in travel, so it is safer to consult a local electrical professional than rely on open international forum interpretations. Imported RV's are a nightmare just like boats.

International DC implementations are thankfully less complex and fewer variations when isolated by a transformer type battery charger.
 

john61ct

New member
Could you link to commonly used high amp battery chargers that do not fall within that category?

What about DCDC and solar chargers (controllers), are they included?

Just wondering why that qualifier is included, as I do not see the DC charge sources as having anything to do with the consumer-device / inverter output circuits.
 

Kevin.Hutch

2011 Mercedes 313 906
Could you link to commonly used high amp battery chargers that do not fall within that category?

What about DCDC and solar chargers (controllers), are they included?

Just wondering why that qualifier is included, as I do not see the DC charge sources as having anything to do with the consumer-device / inverter output circuits.
1. No, I can not provide a link for a high current battery charge,r but with technology in switched-mode chargers moving so fast I would expect there would be chargers without complete isolation soon if not now.

2 DCDC and solar chargers are unlikely to be mains connected, although the panels that now have micro-inverters do make it a little more confusing.

3. The DC charge source is relevant if it provides primary to secondary direct connection and hense not isolated, such as an autotransformer.
 

john61ct

New member
I was asking about that "transformer type" qualification for battery chargers. Is that difference from "switched-mode" in any way that is relevant to the topics we are discussing?

And I just mentioned high amp output as mainstream available units, as opposed to irrelevant examples.

What is the point of "complete isolation"?

I don't think that is very common outside specialist industrial / ICT contexts.

Do you mean no "grounding" in common between input or output?

And finally, what is an "autotransformer" in this context, do you mean like 120Vac to 240Vac?

Just trying to get a handle on, if any of these topics actual pertain from a **practical** POV, within the context of my "high-efficiency KISS design" principles above.

If they are only relevant to the context of

> the more mostly-AC, auto-switched inputs to wired outlets approach where all the complexity is required for safety, and different approaches for different code jursdictions

then I will happily remain ignorant of their finer points.
 

Kevin.Hutch

2011 Mercedes 313 906
I am not sure where this is going but;

>I was asking about that "transformer type" qualification for battery chargers. Is that difference from "switched-mode" in any way that is relevant to the topics we are discussing?

>And I just mentioned high amp output as mainstream available units, as opposed to irrelevant examples.
I felt a qualification was necessary to exclude battery chargers that have an electrical connection primary to secondary. Switch mode chargers are becoming commonplace even the majority of mobile phone and laptop computers now have switch mode chargers so why would there not be high current ones.

>What is the point of "complete isolation"?
Compete isolation of power sources is paramount to prevent single fault interaction.

>I don't think that is very common outside specialist industrial / ICT contexts.
Isolated power sources in the marine environment is very common to reduce the problems of Galvanic corrosion.

>Do you mean no "grounding" in common between input or output?
Grounding is a grossly misused term to imply a common connection to a frame and sometimes a connection to the earth. For safety reasons, this must be a low impedance connection

>And finally, what is an "autotransformer" in this context, do you mean like 120Vac to 240Vac?
An autotransformer is one with a connection between the input and output on one side of the primary and secondary. By definition, therefore, it does not provide isolation.

> Just trying to get a handle on, if any of these topics actual pertain from a **practical** POV, within the context of my "high-efficiency KISS design" principles above.
I wholeheartedly endorse your "high-efficiency KISS design" as it provides complete electrical isolation from shore power unless a non-isolating battery charger is used.

>If they are only relevant to the context of

> the more mostly-AC, auto-switched inputs to wired outlets approach where all the complexity is required for safety, and different approaches for different code jursdictions

>then I will happily remain ignorant of their finer points.

>The relevance to the OP question "about running 2 inverters" is when handling multiple AC power sources isolation is paramount no matter how it is achieved.
 
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Kevin.Hutch

2011 Mercedes 313 906
Just going in circles, I give up
Sorry to hear that, I hope we didn't confuse other readers about the need to keep ac power sources isolated, especially as out of phase power can be catastrophic.
 

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