Best Inverter for the Buck

[prroots]

Originally Posted by goboatingnow

It could be but I think we're up to 4 poles now,

I don't understand, can you explain. I calculate that two poles will do it.
Pete

[CarinaPDX]

I feel like I should apologize for ever bringing up the 3-gang switch, as it has confused things. It solves a problem, but isolation is a better solution to that problem. What I was reacting to was the need to avoid the connection to the local ground, which should be avoided. The connection is called for in the ABYC standard, and is widely disputed.

What is agreed to by all is that some form of isolation is recommended. A galvanic isolator protects against galvanic (and stray current) corrosion caused by less than 1.2V (approx) on the shore ground while allowing the shore ground to conduct with higher voltages. It is a compromise: it will deal with most situations of galvanic (i.e. dissimilar metals) corrosion while maintaining the safety of the ground connection. It is smaller, lighter, and less expensive than an isolation transformer. I think it is a false economy for a cruising boat. Apparently Hunter agrees: all of their boats 33ft and above are now equipped with isolation transformers. Isolation transformers prevent electrolysis caused by shore ground regardless of the voltage, and isolate from reverse polarity issues in the marina, while assuring that both the AC neutral and ground on the boat are at the same potential as the water around the boat for maximum safety. And it can be used to adapt foreign voltages.

Perhaps this doesn't belong in a discussion on inverters; if so, another apology. I tend to think it should be noted in most AC wiring discussions.

[goboatingnow]

Originally Posted by prroots

I don't understand, can you explain. I calculate that two poles will do it.
Pete

Live, neutral, shore earth disconnect , on board earth neutral connect.

Dave

[goboatingnow]

Originally Posted by CarinaPDX

I feel like I should apologize for ever bringing up the 3-gang switch, as it has confused things. It solves a problem, but isolation is a better solution to that problem. What I was reacting to was the need to avoid the connection to the local ground, which should be avoided. The connection is called for in the ABYC standard, and is widely disputed.

What is agreed to by all is that some form of isolation is recommended. A galvanic isolator protects against galvanic (and stray current) corrosion caused by less than 1.2V (approx) on the shore ground while allowing the shore ground to conduct with higher voltages. It is a compromise: it will deal with most situations of galvanic (i.e. dissimilar metals) corrosion while maintaining the safety of the ground connection. It is smaller, lighter, and less expensive than an isolation transformer. I think it is a false economy for a cruising boat. Apparently Hunter agrees: all of their boats 33ft and above are now equipped with isolation transformers. Isolation transformers prevent electrolysis caused by shore ground regardless of the voltage, and isolate from reverse polarity issues in the marina, while assuring that both the AC neutral and ground on the boat are at the same potential as the water around the boat for maximum safety. And it can be used to adapt foreign voltages.

Perhaps this doesn't belong in a discussion on inverters; if so, another apology. I tend to think it should be noted in most AC wiring discussions.

I don't understand , isolation is a different discussion, whether you have and isolating transformer you still. Need to switch the AC systems from shore to inverter

Ps how is "while assuring that both the AC neutral and ground on the boat are at the same potential as the water around the boat for maximum safety. And it can be used to adapt foreign voltages." the case with isolating transformers. It doesn't matter that the AC isnt at water potential, there's no circuit.

[mitiempo]

Originally Posted by goboatingnow

Live, neutral, shore earth disconnect , on board earth neutral connect.

Dave

The on board neutral/earth connect is internal to the inverter, not elsewhere.

[goboatingnow]

Originally Posted by mitiempo

The on board neutral/earth connect is internal to the inverter, not elsewhere.

No it isn't. Very few inverters have earth neutral relays. You must have some sort of earth disconnect if you use your ships AC earth with an inverter install. You need to break the link when shore power reappears. I've noticed that many people ignore the issue , leaving the boats AC protective earth doing nothing, when the inverter is powered up. That's ok for one or two devices , but for whole or nearly boat inverter connection you need a transfer relay or switch

The alternative is cheapo ones that have them permanently connected , that's ok for the versions with a socket on them designed to drive one AC device. It's not acceptable for whole boat systems.
Dave

[mitiempo]

Yes the connect of earth/neutral is in the inverter. It is a disconnect that is needed, but only if the inverter will be run while on shorepower, as Pete thinks it may be. It will be connected in any inverter without a transfer switch. But he still only needs a 3 pole switch, not 4 pole as you have posted. With only 3 wires what could the 4th pole be?

With the type of inverter Pete is looking at buying the best solution is either the AC outlets on the inverter itself or a dedicated outlet that is inverter only. I understand he is trying to save money but I don't believe this is a good place to do this. If an inverter is to be integrated into an existing AC system I think it should be one with an auto transfer switch, found on many marine quality inverters. The less expensive ones are best suited to RV's where there are no corrosion issues to deal with.

My preference is a sub-panel (or a segregated part of the main panel) that is powered by shorepower when plugged in to shore and the inverter when not.

Also, with what Pete is planning I would still want a breaker between the inverter and the outlets, which he has not addressed. The Aims also does not have GFCI outlets so the first in line should have one if not there already.

[prroots]

Originally Posted by CarinaPDX

I feel like I should apologize for ever bringing up the 3-gang switch, as it has confused things. It solves a problem, but isolation is a better solution to that problem. What I was reacting to was the need to avoid the connection to the local ground, which should be avoided. The connection is called for in the ABYC standard, and is widely disputed.

Thanks for your honesty. No apology is necessary. In my mind, the free flow of honest opinions is how these forums are best served. It's clear to me that you think outside of the box rather than merely accepting conventional wisdom. This is very refreshing. I'm glad to hear that you agree that isolation of the shore ground (whether by isolation transformer or galvanic isolator) can be an alternative to the 3rd pole. This is a point I wanted to clarify.

There are a number of requirements that I would like to satisfy as part of the inverter install as follows:

1. Prevent electrolysis
2. Ensure ground and neutral tried together at one point only
3. Ensure AC safety
4. Prevent inverter from inadvertently feeding water heater or battery charger
5. Ensure that inverter can never drain batteries flat due to automatic transfer switch
6. Provide pure sine wave output from inverter to eliminate potential for poor equipment operation or damage.

The concept that I presently favor uses a 2 pole rotary switch that switches hot and neutral (but not ground). The switch is installed downstream of the 15A breaker feeding my AC outlets. The center tap of switch feeds the AC outlets while the other two taps (eg, 1 and 2) are connected to the shore power and inverter, respectively. The inverter is of the standalone pure sine wave variety. A galvanic isolator is installed in the ground line from shore. Hot and neutral are tied together at inverter (whether by design or jumper). The onboard AC safety ground is connected to shore ground (via galvanic isolator) and to inverter ground. The AC safety ground is tied to the DC ground terminal which in turn is connected to engine block.

Let's see if this concept satisfies the 4 criteria listed above. First, electrolysis is prevented by the galvanic isolator since the DC path from ship to shore has been isolated. Second, the 2 pole switch breaks the neutral line in such a way that only one connection point is made from neutral to ground whether in the shore or inverter switch position. Third, AC safety ground is tied to shore ground (via galvanic isolator), inverter ground, and DC ground to ensure safety. Finally, the switch is installed downstream of breaker servicing AC outlets so there is no path from inverter to either water heater or battery charger.

Is the above correct? If not, please point me to the errors
Pete

[mbianka]

Originally Posted by prroots

Thanks; that's a good point. I run my laptop off a DC-to-DC converter from house batteries. On the other hand, we have been charging iPhone via a cheap power adapter from the AC. We also have a 12VDC cigarette lighter iPhone adapter so this could be used if necessary. Really, the boat is designed to run everything including lights off 12 VDC so mostly it's kitchen appliances and power tools that would be using 110 VAC. I think the final decision will be based on the cost difference. If it's not too great, the true sine version would be nice otherwise it seems I can easily make do with the modified sine version.
Pete

Pete:

I've been using the same small Powerstar inverter since the 1980's:
THE BIANKA LOG BLOG: WHAT WORKS ON BOARD: Powerstar DC Converter
It's a cheap square wave inverter that works fine powering my 120 volt Dremel Tool and my Braun hand blender in the gallery. It's portable so I can move it around the boat to where I need it. It's power is too dirty for a switching laptop supply but, it is handy when I'm working on projects in the cockpit. Another alternative you might want to consider before buying a pure sine wave inverter is to instead put the money toward a reliable Honda 2000i generator. For around the same price as a whole boat sine wave inverter you will have an additional backup power source on board. You could:

1) Use it to power a microwave. Seems a waste to spend the money for a sine wave inverter with enough power for a microwave when you will only be using it a few minutes each day.

2) Will provide an additional backup charging source for your batteries so you don't have to fire up the diesel engine for battery charging at anchor. An inverter will only draw power from your bank not put power into it.

3) You could also use it for other heavy duty power needs on board. I have an electric hookah dive setup. I use the Honda 2000 to power it. I don't need to worry about getting Scuba tanks refilled when I want to clean the bottom no matter where I am. Also use it with a heat gun for stripping varnish etc...

Anyway just something to think about.

[goboatingnow]

Originally Posted by prroots

Thanks for your honesty. No apology is necessary. In my mind, the free flow of honest opinions is how these forums are best served. It's clear to me that you think outside of the box rather than merely accepting conventional wisdom. This is very refreshing. I'm glad to hear that you agree that isolation of the shore ground (whether by isolation transformer or galvanic isolator) can be an alternative to the 3rd pole. This is a point I wanted to clarify.

There are a number of requirements that I would like to satisfy as part of the inverter install as follows:

[*]Prevent electrolysis[*]Ensure ground and neutral tried together at one point only[*]Ensure AC safety[*]Prevent inverter from inadvertently feeding water heater or battery charger[*]Ensure that inverter can never drain batteries flat due to automatic transfer switch[*]Provide pure sine wave output from inverter to eliminate potential for poor equipment operation or damage.

The concept that I presently favor uses a 2 pole rotary switch that switches hot and neutral (but not ground). The switch is installed downstream of the 15A breaker feeding my AC outlets. The center tap of switch feeds the AC outlets while the other two taps (eg, 1 and 2) are connected to the shore power and inverter, respectively. The inverter is of the standalone pure sine wave variety. A galvanic isolator is installed in the ground line from shore. Hot and neutral are tied together at inverter (whether by design or jumper). The onboard AC safety ground is connected to shore ground (via galvanic isolator) and to inverter ground. The AC safety ground is tied to the DC ground terminal which in turn is connected to engine block.

Let's see if this concept satisfies the 4 criteria listed above. First, electrolysis is prevented by the galvanic isolator since the DC path from ship to shore has been isolated. Second, the 2 pole switch breaks the neutral line in such a way that only one connection point is made from neutral to ground whether in the shore or inverter switch position. Third, AC safety ground is tied to shore ground (via galvanic isolator), inverter ground, and DC ground to ensure safety. Finally, the switch is installed downstream of breaker servicing AC outlets so there is no path from inverter to either water heater or battery charger.

Is the above correct? If not, please point me to the errors
Pete

The only error is you need to disconnect the invertor earth neutral connection when on shore power a simple contactor or a/c relay is all that's required. Of to put it another way you need to connect earth and neutral at the inverter when the shore power in off and the inverter is on.

If your not switching shorepower ground ( ands that's a bad idea anyway) I suggest using a 3pole rotary switch to connect the inverter earth to its neutral on inverter switch over. Also ensure the switch is break before make.
Dave

[prroots]

Originally Posted by mitiempo

Yes the connect of earth/neutral is in the inverter. It is a disconnect that is needed, but only if the inverter will be run while on shorepower, as Pete thinks it may be. It will be connected in any inverter without a transfer switch. But he still only needs a 3 pole switch, not 4 pole as you have posted. With only 3 wires what could the 4th pole be?

With the type of inverter Pete is looking at buying the best solution is either the AC outlets on the inverter itself or a dedicated outlet that is inverter only. I understand he is trying to save money but I don't believe this is a good place to do this. If an inverter is to be integrated into an existing AC system I think it should be one with an auto transfer switch, found on many marine quality inverters. The less expensive ones are best suited to RV's where there are no corrosion issues to deal with.

My preference is a sub-panel (or a segregated part of the main panel) that is powered by shorepower when plugged in to shore and the inverter when not.

Also, with what Pete is planning I would still want a breaker between the inverter and the outlets, which he has not addressed. The Aims also does not have GFCI outlets so the first in line should have one if not there already.

Thanks. I'm thinking I only need a 2 pole switch to switch hot and neutral. When in shore position, there should be no path from neutral to ground at the inverter since it's neutral has been interrupted. Likewise, when in inverter position, there should be no path from neutral to ground at shore since it's neutral has been interrupted. Is this not correct?

I don't understand why dedicated outlets are required (or recommended). It seems that the 2 pole rotary switch should do the job it was designed to do. In my case, it is impractical to use dedicated outlets although I understand that on smaller boats this may be practical. In this instance, the issue is not about saving money; it's about providing the needed functionality in a practical manner.

The transfer switch is a very bad idea in my application. It raises the possibility of draining my batteries flat. It seems that transfer switches are designed to provide critical backup, but that certainly doesn't apply in my case. Also, one must keep in mind that this is a non-critical application mostly used to run a few galley appliances such as our microwave. The cost associated with a marine grade inverter with transfer switch is just not justified. I do understand that integrating a standalone inverter into an existing AC system is more difficult to ensure that all requirements are satisfied; it's not a job for the light of heart

You are right, I have not addressed the issue of a breaker on the inverter side. The Samlex SSW-1500-12A inverter I'm favoring does have overload shutdown protection. I was hoping that would be sufficient.

With respect to the neutral to ground connection issue here is a quote from the Samlex manual:

For SSW-350-12A & SSW-600-12A, the “Neutral” terminals remain powered with respect to
the “Ground” terminals.

The manual covers all ratings of the SSW series inverters. Since the above quote does not mention the 1500, it is clear that this model does internally connect neutral to ground. It also makes it clear that one cannot generalize as to whether inverters internally connect neutral to ground.

With respect to GFCI here is a quote from the Samlex manual:

EARTH FAULT PROTECTION
This inverter complies with the standard current leakage allowance. When large current leakage to earth
terminal occurs, the protection circuit activates and shuts down the inverter, which prevents electric shock to
humans. Turn OFF the inverter, unplug the fault AC appliance and then turn ON is the only way to restart it.
The 1000, 1500 and 2000 W models are provided with a GFCI that will trip in case of any leakage on the load
side. The GFCI will be required to be reset

so I'm thinking that issue is satisfied. Thanks again for your post.
Pete

[prroots]

Originally Posted by goboatingnow

The only error is you need to disconnect the invertor earth neutral connection when on shore power a simple contactor or a/c relay is all that's required. Of to put it another way you need to connect earth and neutral at the inverter when the shore power in off and the inverter is on.

If your not switching shorepower ground ( ands that's a bad idea anyway) I suggest using a 3pole rotary switch to connect the inverter earth to its neutral on inverter switch over. Also ensure the switch is break before make.
Dave

Thanks Dave. It's obvious we've been posting at the same time. I still don't understand why a two pole switch doesn't break the neutral to ground connection at inverter when in the shore position. The neutral from the inverter is totally disconnected by the switch so where is the path to ground? Also, as mentioned in my recent post, the neutral to ground connection is internal to the Samlex inverter that I'm favoring (see the quote from manual). Maybe someone else can jump in because somehow I'm missing something here. I've made a crude back of the envelope schematic and I see no path from neutral to ground at inverter when switch is in shore position.
Pete

[goboatingnow]

Originally Posted by prroots

Thanks Dave. It's obvious we've been posting at the same time. I still don't understand why a two pole switch doesn't break the neutral to ground connection at inverter when in the shore position. The neutral from the inverter is totally disconnected by the switch so where is the path to ground? Also, as mentioned in my recent post, the neutral to ground connection is internal to the Samlex inverter that I'm favoring (see the quote from manual). Maybe someone else can jump in because somehow I'm missing something here. I've made a crude back of the envelope schematic and I see no path from neutral to ground at inverter when switch is in shore position.
Pete

sorry yes in a system where the AC ground is connected internally in the inverter and you isolate the inverter neutral ( and live) when on shorepower, theres no issue. ( I wrote too much english actually !). I was dealing with the situation where the inverter does not connect them internally, as in the case of some big system inverters.


PS an automatic transfer switch isnt a problem as long as the battery charger and other high current AC devices are on a seperate bus. Its avoids another switch to install. Modern inverters have low batt protection anyway
dave

[prroots]

Originally Posted by goboatingnow

sorry yes in a system where the AC ground is connected internally in the inverter and you isolate the inverter neutral ( and live) when on shorepower, theres no issue. ( I wrote too much english actually !). I was dealing with the situation where the inverter does not connect them internally, as in the case of some big system inverters.


PS an automatic transfer switch isnt a problem as long as the battery charger and other high current AC devices are on a seperate bus. Its avoids another switch to install. Modern inverters have low batt protection anyway
dave

Great and thanks again

In my case, I don't allow the batteries to discharge below 50% SOC and the inverter isn't setup to prevent that. This is why a transfer switch is inappropriate in my application.
Pete

[goboatingnow]

Originally Posted by prroots

Great and thanks again

In my case, I don't allow the batteries to discharge below 50% SOC and the inverter isn't setup to prevent that. This is why a transfer switch is inappropriate in my application.
Pete

My systems using a homebuilt transfer switch was useful , because you still had the manual decision to switch on and off the inverter using its remote panel, There was never the case that the inverter came on automatically on disconnecting the shorepower.

but I had and used both in my current boat I use a automatic switch in my previous it was manual. But in my current boat I just use the automatic switch to switch two sockets ( outlets) one in my Galley and another in the saloon, so that I can keep track of whats using the inverter AC

Dave