inverter questions

[wyrman]

Whatever you want to say Westie, I'm not going to get into an internet arguement but I stand by my statement.
Electricity will always go to ground through the path of least resistance, and it may just be a person.

 

[Westie]

Resistance only applies if you are talking about DC. Impedance applies for AC and is equal to the square root of the (resistance squared plus the reactance squared). There is really nothing to argue about.

 

[bajturner]

You are correct regarding the Honda generator; this unit is a generator / inverter whereas the inverter creates the AC power and does have a floating ground.
Now lets break down the boats system: When the boat is tied to the shore power it's hot leg is home run to the shore circuit breaker uniquely. The neutral leg is run uniquely to the shore panel board's neutral buss which is then bonded to the ground buss so at one point and only one point the neutrals and grounds are bonded together. If the boat has a transfer switch at no time are the neutrals and grounds tied together by the transfer switch. The transfer switch simply moves both the neutral and hot conductors either to the shore system or to the boats internal generator system but never are the two systems simultaneously tied.
The boat's ground system is also bonded through all of the metallic elements including engine blocks, generator chassis ( it it has a generator) and battery neg posts. The boat's ground system also should run through galvanic isolators then to the shore connection; this is to control galvanic corrosion yet still provide a path for fault current to ground. All onboard installed generators have the neutrals and grounds bonded internally so as to create that required single point bond when the transfer switch is positioned to the generator. The above configuration is a NEC and ABYC requirement. Should you loose your boat due to intentional faulty wiring (not compliant) the insurance coverage may be at risk and / or you may be exposed from a liability standpoint by the marina or others affected.

If the neutral is floating due to the design of the generator and the generator chassis is not tied to the boat's ground plane I would submit that any fault in the system has little chance to safely be vetted to ground and the configuration is much more hazardous than a compliant configuration. At all times if this generator is tied to the boat's power system any GFCI protection will not trip in a fault condition as there is no other path for fault current to pass to imbalance the equal current between the hot and neutral that the ground fault instrument is looking for. The safest configuration if one must go down such a path is to bond the neutral and ground at the plug that connects to the generator. This plug then must be dedicated to the generator and have no other purpose. From what I understand RV's deal with the same issues using these generator invertors.

It sounds like you are very knowledgeable, and you said a lot here, but you skirted the questionI posed. So here it is again: With an off-the-shelf EU2000 plugged into the shore power as described, and a hot to ground short, where is the current going? More directly, are the two little blond girls in my avatar going to possibly get electrocuted when they swim near that boat at an anchorage, or at least sufficiently disabled that they drown?

I'm going to switch gears a bit here with respect to tone (because I have been personally affected). If the answer to the question above is "not sure", "not likely", "depends", or "very likely", then bloody well don't do it. If I sound a little frustrated with the topic it's because I am. I see stupid stuff done on boats by people that are either ignorant or misinformed all the time and it irks me that I have to worry about such a thing when we are out just trying to have a safe, happy day.

These generators are not meant to be operated this way, plain and simple, because it isn't safe (for a number of reasons). This is the default position. Unless this can be refuted explicitly from a technical perspective (and no one has to date), don't surmise anything that may support the practice. Inconclusive statements and extraneous information raise uncertainty that can be used to justify the practice.

My rant for the day!

 

[bajturner]

Resistance only applies if you are talking about DC. Impedance applies for AC and is equal to the square root of the (resistance squared plus the reactance squared). There is really nothing to argue about.

The more important correction, I think, is that electricity will not singularly follow the path of least "resistance" (let's call resistance a lay term for electrical impedance, even in an AC circuit, to settle that one!), but rather all available paths, with the amount of current in each path inversely proportional to the amount of impedance.

 

[bajturner]

Yup, so a 2000 watt microwave will draw about 17 amps at 120VAC. With a typical inverter efficiency of 85% you will find a battery demand of close to 200 amps at 12 VDC. With this load running for 20 minutes between battery recharge is calculated at 208 AH then double that for reserve capacity so, lets say you need 400 AH of battery capability to ensure you never draw below 10.8 volts ( critical for battery life). A typical group 27 battery is about 100 AH so 4 Group 27 batteries will be required with a 2000 watt continuously rated inverter. Cabling between the inverter and batteries will need to be a minimum of 2/O and less than 4' long. Not a cheap venture.... But that's the story.

Don't forget you will have to de-rate the 100AH rating, which is likely a 100hr (1A) rating. At 2A you de-rate to around 80%, at 10A around 70%, and by the time you get to 50A from these batteries you will be way down the de-rating curve. You don't often see data for that kind of output current.

 

[ttmott]

I'm going to switch gears a bit here with respect to tone (because I have been personally affected). If the answer to the question above is "not sure", "not likely", "depends", or "very likely", then bloody well don't do it. If I sound a little frustrated with the topic it's because I am. I see stupid stuff done on boats by people that are either ignorant or misinformed all the time and it irks me that I have to worry about such a thing when we are out just trying to have a safe, and happy day

i would say that yes the risk is higher as some of the intrinsic and functional safety features are bypassed. If for one example the neutral is faulted to the boats ground system which may not be detectable and consequently has the potential to pass current through the water around the boat and the generator is running on a wet swim platform or someone touches the generator when coming out of the water then you probably would have a problem. Its all about where fault current is to be shunted or sent when a problem exists in a circuit. One may never know that a defect exists in a wiring system and consequently the reason for configuration and safety device standards. As you may have surmised I am very conservative when it comes to these things; wouldn't want to be in a position where I knew and then something went wrong.

 

[electricaldoctor]

It is really interesting about how the direction of this thread has drastically changed from inverters to generators. I think that all of this generator related banter really belongs in a different section all together. :huh:

 

[bajturner]

ok, i guess i should make this clearer. aside from finding a dedicated 12 volt blu ray player (which is impossible apparently) i would like mostly to be able to use the microwave already on the boat when away from shore power. the fridge is already 120v/12v. i am wondering if it is a nightmare to wire so it can be run by the inverter or shore power or would it be easier to find one that runs 120v/12v like the fridge?

Here's a 12V Blu-ray player...

http://www.audiovoxproducts.com/bluray/?sku=AVDBR1

No idea if it is any good.

 

[bajturner]

It is really interesting about how the direction of this thread has drastically changed from inverters to generators. I think that all of this generator related banter really belongs in a different section all together. :huh:

These inverter discussions are all quite similar and always end up about generators once it's understood how difficult it is to run something like a microwave from 12V batteries. The next phase of discussion is always about finding a simple, inexpensive, and at the same time safe and correct way add a generator capability.

Maybe there should be a dedicated topic under Maintenance/Other Stuff that can be referred to and read as a first step to anyone considering an inverter or generator. Here a few inverter-related threads I have participated in over the last year or so that are all pretty much the same, and there are dozens more.

http://clubsearay.com/showthread.php/49068-power-inverter?p=581070
http://clubsearay.com/showthread.php/27996-Power-Inverter?p=549514
http://clubsearay.com/showthread.php/48767-Inverter-install-questions?p=545558

All the same calculations, all the same conclusions.

 

[Danny Troy]

Referring back to my previous post about the microwave size.
Check the size of the microwave, if it is 1100, then consider buying a smaller one, 700W.
You can then downsize the invertor, and the battery capacity required.
Which will be cheaper in the long run.

Talking microwaves here.... I run my 600 watt Sylvania, which was what SeaRay put in the 280's, with my 2000w pure sine wave inverter. For whatever reason, whether it be overtaxing the inverter, or the storage battery not keeping up with the inverter amp draw, the m/w shuts down after about 2 to 3 minutes. Luckily, my inverter is smart enough to reset, and allows a restarting of the m/w to finish the job. What I do now to avoid this problem, when I need to use the m/w for more than 2 minutes, is start the Kohler genny and burn some gas. So, I would say stay away from the full size 1100 watt microwaves, when using a 2000w (or less) inverter.

 

[ttmott]

Talking microwaves here.... I run my 600 watt Sylvania, which was what SeaRay put in the 280's, with my 2000w pure sine wave inverter. For whatever reason, whether it be overtaxing the inverter, or the storage battery not keeping up with the inverter amp draw, the m/w shuts down after about 2 to 3 minutes. Luckily, my inverter is smart enough to reset, and allows a restarting of the m/w to finish the job. What I do now to avoid this problem, when I need to use the m/w for more than 2 minutes, is start the Kohler genny and burn some gas. So, I would say stay away from the full size 1100 watt microwaves, when using a 2000w (or less) inverter.

These may be symptomatic of lack of current to the inverter. Either the batteries cannot deliver the current or the 12V wires are too long or not correct gauge. My 1800 watt Xantrex has 2/0 cables that are only 18 inches long and three group 27's. It would power a 1100 watt microwave but not very long.... http://i1012.photobucket.com/albums/af244/bumpythecat/IMG_3691_zpsbff22421.jpg What happens is the inverter demands very high current and depresses the batteries voltage below the inverters threshold and the inverter shuts down to save the batteries. You need a lot of battery to support a full 1100 watt microwave for very long at all.

 

[Danny Troy]

These may be symptomatic of lack of current to the inverter. Either the batteries cannot deliver the current or the 12V wires are too long or not correct gauge. My 1800 watt Xantrex has 2/0 cables that are only 18 inches long and three group 27's. It would power a 1100 watt microwave but not very long.... http://i1012.photobucket.com/albums/af244/bumpythecat/IMG_3691_zpsbff22421.jpg What happens is the inverter demands very high current and depresses the batteries voltage below the inverters threshold and the inverter shuts down to save the batteries. You need a lot of battery to support a full 1100 watt microwave for very long at all.

Yes, the battery feeding the inverter is probably not able to keep up with the demand. I elected to connect to only one of my two batteries, since it kept the 2/0 cable length to a minimum. Connecting to both batteries after the battery switch, would have meant another few feet of cable run. Might have been the way to go, but I might as an experiment, I may try running the engine to see if the alternator will help the battery enough to keep the inverter from shutting down. Pretty much a moot point though, since I have the genny, but I do like using the inverter whenever I can, considering the price of gas on my lake!

 

[IanBat]

Considering you would need to run the engine at at least 1500rpm possibly higher for the alternator to have a chance of keeping up, .......the genny is cheaper to run


Sent from my iPad using Tapatalk HD

 

[bajturner]

About microwaves, don't forget the rated power is just the cooking power. It doesn't include the power for the lights, turntable motor, fans, electronics, etc. The actual power requirement can be a lot higher.

You need a lot of batteries to run one of these properly, otherwise you won't have a reliable, stable system with longevity. To get any kind of lifetime from a deep cycle battery, or bank of batteries, they need to be discharged relatively slowly (typically over 100 hours, but are also rated at faster rates like 20 hours), and never to a point below about halfway (ideally not below about 80%). If you do, they will start to fail after a set of recharge cycles numbering as low as the low 100s.

Here is a really useful chart:



Note the axes are logarithmic scales. These happen to be for Lifeline batteries, but similar batteries will provide similar capacities at the various discharge rates.

As an example, say a 600W microwave all-told draws around 70A from a single battery. In the case of the GPL-27 you would get about an hour in ideal conditions. If it's in a hot environment (above 85F), there may be a de-rating, depending on the battery. The most you want to discharge to is 50%, which gives you 30 minutes. Ideally you only discharge to about 80%, which gives you 12 minutes. And don't use it for anything else!

You may run into other problems already mentioned, like the inverter kicking-out due to voltage drop at such a high current draw.

 

[Tom Jones]

Can anyone tell me where to find my inverter. I have a 2004 Sundancer 300