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Old 12-02-2016, 03:18   #31
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Re: How do I connect my new inverter

Quote:
Originally Posted by ramblinrod View Post
Well, I thought I covered it with considerable detail but, here goes...

1. Your post, "If you want it permanently installed, AND assuming you have a free breaker on your DC panel, then just connect it to that..."

Ummm, I don't think so. As stated in my response, if the DC panel has a spare breaker, it is most likely 15 A, which will be totally inadequate for a 350W inverter.

2. Your post, "That is because DC at low voltage is less efficient than AC."

Ummm, I don't think so. As stated in my response, electricity is a form of energy. Whether it be AC or DC it is 100% efficient. The transmission line and load may have an efficiency factor, the electricity itself does not.

3. Your post, "Then install an AC socket somewhere, and run three-conductor, sheathed cabling from the inverter to there."

Ummm, I don't think so.

a) The inverter in question is not likely designed to be connected to external AC wiring.

b) If it is, and the outlet is in a galley, head area, engine compartment, or anywhere it could get splashed, it must be a GFCI.


4. Your post, "Follow ABYC standards: American Boat & Yacht Council Standards for Boats E-11 | Ancor (link)"

Ummm, I don't think so. That excerpt only covers cabling. To install an inverter to ABYC standards, one must consider E10 - Storage Batteries (8 pages), E11 - AC and DC Electrical Systems on Boats (96 pages) and A31 - Inverters and Chargers (15 pages). The little excerpt on the Ancor site is outdated and a very small portion of the applicable relevant standards.

5. Your new post, "Hiring professionals can be a good idea in many situations, but you had better know enough about all of your systems, and the principles upon which they work, to recognize whether you are getting good work or not."

Ummm, I don't think so. It is not a requirement to be as knowledgable or nearly as knowledgable as a professional of any trade or profession, it isn't even practical. And if you were, then why hire a professional?

6. Your new post,"In my experience, the average skill level of professional marine electricians is particularly poor."

I'm sorry you have had a bad experience. Are you sure these were really certified professionals? If they were, you should have contacted the certifying agency, filed a complaint, and they would have been called up. In all likelihood, they weren't certified professionals at all, rather just someone who agreed to take your money.

7. Your new post, "About half of them -- in my experience -- are not capable of doing the work as well as I can do it myself."

Again, I'm sorry your have had such a poor experience. While you could be an unusually capable DIYer, but I suspect you are referring to poorly educated and paid general labourers, and not certified marine professionals.

Notwithstanding, as there are literally millions of different products that have been installed on boats, it is not possible for any one marine professional to be knowledgeable of every single one. Whereas the boat owner, may have used a specific marine product daily, and poured over the manuals for hours on end, year after year, for 20 years. They will most certainly may be more knowledgable on that specific product than the average marine professional. However, the general knowledge of the marine professional, should enable them to solve the problem the highly knowledgable owner (of that specific product) can't.


I'll be the first to admit that I don't know everything about marine electrical systems, and some owners may know more about their specific systems than I, after all, they may have been intimately familiar with it for 20 years, whereas my expose to that specific model may be very limited. For


8. Your new post, "You have to look long and hard to find a really good one, and qualifications and other papers are not a reliable guide.

Any certified marine professional, has to have undergone fairly extensive training, and passed an extensive certification test, with a minimum grade (typically 80% or higher). This is not a fluffy test. Few pass it first attempt, after extensive practical experience and then specific training for the exam. Again, as I've said on this forum many times, when you hoire a marine professional, ask who they are certified by. It should be a well known agency or manufacturer. Before you let them on your boat, ask to see their certificate. If they aren't carrying it in their wallet 24/7, they most likely aren't certified at all, send them packing.
[/QUOTE]

You should not assume that boat owners without ABYC certificates are too stupid to check the amperage of breakers they connect to (and upgrade them if necessary), or to install a plug if their inverter is not designed to be hard wired, or to look at the whole text of the ABYC standards which were referred to, and not just some part (and which cover the requirement for GFCI's in some places).

For the sake, apparently, of trying to scare people off of doing their own electrical work, or even to talk about electricity, you willfully miss the point of correct advice like using sheathed cable (as opposed to lamp cord) for running cables through bulkheads etc., and to locate the inverter closer to the DC source, rather than to the consumer. It takes a lot less copper to transmit power at 110v than it does at 12v, with the same voltage and power loss -- that is the "efficiency" we are talking about, not some abstract idea about electrons at the quantum level.
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Old 12-02-2016, 03:37   #32
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Re: How do I connect my new inverter

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Originally Posted by StuM View Post
On the 12V DC side where those cables will be 300W =~ 25A. And with a peak output of 600W, that is 50A.
Oh yeah, makes sense now

It would be much better if we lived in a world where we could get power from nothing
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Old 12-02-2016, 10:05   #33
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Re: How do I connect my new inverter

You should not assume that boat owners without ABYC certificates are too stupid to check the amperage of breakers they connect to (and upgrade them if necessary), or to install a plug if their inverter is not designed to be hard wired, or to look at the whole text of the ABYC standards which were referred to, and not just some part (and which cover the requirement for GFCI's in some places).

I made no such assumption. If the boat owner needs to be told to ensure they follow electrical standards, then it is reasonable to believe they know very little. Your advice was to connect a 350W inverter directly to a spare breaker in a DC panel. IMHO, this is very bad advice for the reasons stated. Sorry if you disagree, or it upsets you, but that is still my position.

For the sake, apparently, of trying to scare people off of doing their own electrical work, or even to talk about electricity, you willfully miss the point of correct advice like using sheathed cable (as opposed to lamp cord) for running cables through bulkheads etc., and to locate the inverter closer to the DC source, rather than to the consumer.

I am not trying to scare anyone off anything. I am stressing the importance of handling electrical installation with care ALWAYS. I've seen too many boat fires first hand, and in photos, to do otherwise.

It takes a lot less copper to transmit power at 110v than it does at 12v, with the same voltage and power loss -- that is the "efficiency" we are talking about, not some abstract idea about electrons at the quantum level.

With the same "voltage". Clearly 110Vac and 12Vdc are not the same voltage. I am sorry, but you are using an incorrect term. If one knows about electrical properties they know E=IxR and P=ExI. AC is not more efficient than DC. For either AC or DC, the higher the voltage (E) the lower the current (I) for the same power (P). This is not an "efficiency" issue.

In the case of an inverter, it is wise to keep the DC cable run as short as practical, as the voltage is lower, and therefore current is higher, for the same power. So I now understand you had the right idea, but were just using the wrong term (efficiency).

Sorry if I offended you; it wasn't the intent. Many parts of your post appeared incorrect, and I offered an alternate opinion, for the benefit of the OP.

[/QUOTE]

Disclosure: Sheen Marine is a marine service provider. Part of our service is to sell, install, warrant, and service marine electrical systems including DC/AC inverters. This post is intended as free advice and not to solicit business.

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Old 12-02-2016, 10:26   #34
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Re: How do I connect my new inverter

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Originally Posted by ramblinrod View Post
I stand corrected, there is such a thing as called "170 Amp" cable in the UK, with which this Canuck was not previously familiar.

Sorry for the incorrect error accusation, and thanks for the lesson.

But 25mm^2 cable for a 300W inverter? Seriously?
It actually makes sense to rate it by the amperage imho, because then it's easy to ensure that currents going through it are well below its rated capacity (so you don't have the copper heating up, going funny, increasing resistances, etc). In a way it's a bit of a warning to beginners, to look into what they are doing properly ("Why's that number there? What does it mean?").

It's very inexpensive futureproofing (if limited - I wouldn't really want to go over 750 watt inverter size for 1.5kw peak), given the short cable run you should have between the battery and inverter. It's nice and solid to mount with an isolation switch too.

Above that size, costs do rapidly go up a fair bit though.

No need to apologise, we all learn something new, especially when things are done differently elsewhere.

The stuff I am learning and relearning here every day, is quite staggering really.
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Old 12-02-2016, 10:55   #35
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Re: How do I connect my new inverter

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Originally Posted by rwidman View Post
The current capacity of a cable depends on it's gauge. Length has nothing to do with current capacity.
So if you run a 200 mile 4 ga cable to your starter, is it going to work?

How about if you shorten it to 4 ft?
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Old 12-02-2016, 10:57   #36
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Re: How do I connect my new inverter

I'm with Ribbit #34. In the interest of my learning and relearning, I'd like to ask RamblinRod to choose a colour other than red to set off his remarks. Red affords too little contrast for my tired old eye .-) DARK green might work, but why not stick with black and mebbe use a different font set in italics? That would be ever so kind to those of us who need Braille to navigate ,-)

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Old 12-02-2016, 11:17   #37
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Re: How do I connect my new inverter

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Originally Posted by Stufft View Post
170A cables seems a bit extreme for a 300W inverter. I always thought the '300W' stated was the output power, therefore if the inverter is a 110V system it would be 300W/110V=less than 3A

This is why people need to hire professionals.

Yes, 300w/110v is less than 3 amps.


What power source are you connecting the inverter to? A 12v battery bank? (Nod yes.) Well, then 300w/12v is more like 30 amps, when you factor in inverter losses.

Now how long is the power cable to the inverter from the batteries? Once you determine the length, double it (since you're using two wires) now you can look up the required cable size to conduct 30 amps of current with less than X % current loss (plug in your own number, 1%, 2%, etc.)

That's just the cable selection part. Now buy the correct tinned closed end lugs with the correct hole size, crimp it with a good crimper with hex dies, then use adhesive lined heat shrink to seal moisture out of the ends of the cable.


Now I'm having nightmares of someone using 12ga wire to hook up a 300w inverter because they thought it was capable of conducting 3 A of current. Poof! That burned up fast!
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Old 12-02-2016, 11:27   #38
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Re: How do I connect my new inverter

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Originally Posted by Ribbit View Post
It actually makes sense to rate it by the amperage imho, because then it's easy to ensure that currents going through it are well below its rated capacity (so you don't have the copper heating up, going funny, increasing resistances, etc). In a way it's a bit of a warning to beginners, to look into what they are doing properly ("Why's that number there? What does it mean?").

It's very inexpensive futureproofing (if limited - I wouldn't really want to go over 750 watt inverter size for 1.5kw peak), given the short cable run you should have between the battery and inverter. It's nice and solid to mount with an isolation switch too.

Above that size, costs do rapidly go up a fair bit though.

No need to apologise, we all learn something new, especially when things are done differently elsewhere.

The stuff I am learning and relearning here every day, is quite staggering really.


I'm sorry, but just because someone advertises a cable on Ebay as "170A cable" doesn't mean it's any sort of industry standard. If you read the actual ad, it goes on to discuss it as "110A cable."

Which is it? 170A or 110A? It's neither. How about just calling it 25mm2 cable and look up the current carrying capabilities in a chart, based on length.

BTW, nowhere in an ampacity chart is that sized cable (4 awg) rated for 170, or even 110 amps. It's rated at a MAXIMUM of 60 amps for power transmission.

Buyer beware, never make assumptions that what a seller advertises is true, much less electrically accurate.
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Old 12-02-2016, 14:04   #39
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Re: How do I connect my new inverter

Quote:
Originally Posted by Ribbit View Post
It actually makes sense to rate it by the amperage imho, because then it's easy to ensure that currents going through it are well below its rated capacity (so you don't have the copper heating up, going funny, increasing resistances, etc). In a way it's a bit of a warning to beginners, to look into what they are doing properly ("Why's that number there? What does it mean?").

It's very inexpensive futureproofing (if limited - I wouldn't really want to go over 750 watt inverter size for 1.5kw peak), given the short cable run you should have between the battery and inverter. It's nice and solid to mount with an isolation switch too.

Above that size, costs do rapidly go up a fair bit though.

No need to apologise, we all learn something new, especially when things are done differently elsewhere.

The stuff I am learning and relearning here every day, is quite staggering really.
FWIW, I really disagree with the max amperage being included in the cable name, and not just because I didn't previously know it was in the UK.

All cable has an absolute max current rating.

25 mm^2 cable (referenced here) is close to 4 AWG (actually a little under, but the original post is about a 350W inverter, so lets go with it).

Per ABYC 4 AWG has a maximum ampacity of 160A (for 105C temp rated, not bundled, not in engine compartment).

I quickly checked one source of 170 A Battery / Welding Cable and it had a max temp spec of 70C. Per ABYC, 4 AWG is derated to 125 A at 75C (outside engine spaces), or 94 A (inside engine spaces).

If you bundle 2 conductors up with 2 more, you are now derated to 78 A. (Even less by bundling more conductors.)

I absolutey cringe every time I see DIY wiring routed needlessly in big bundles through the engine compartment, because it's easier.

However, the maximum current the cable can be used for and not induce greater than 10% voltage drop, is based on length (round trip) and nominal DC voltage.

In the case of our 4 AWG cable, the maximum current it can carry for 60 ft round trip length (much longer than would normally be considered for an inverter install), in a 12Vdc nominal circuit, is 60 A.

For a safety related circuit (which an inverter isn't), a maximum of 3% voltage drop is permitted, which would derate this cable further to 20A max.

That's right; under these circumstances a 4AWG cable has a max current carrying capacity of 20A!

So as we can see, the max ampacity of the cable alone is of very limited value.

To me, using the max ampacity spec of the cable to identify it, could be very misleading to a newb (Joe Average boater, or even a thrice circumnavigating the globe trotter, for that matter).

(As evidenced by the look on experienced boater customer faces when I tell them how much the cable to run a new bow thruster off the house bank is gonna cost.)

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Old 12-02-2016, 14:18   #40
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Re: How do I connect my new inverter

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The current capacity of a cable depends on it's gauge. Length has nothing to do with current capacity.
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Originally Posted by Dockhead View Post
That's not exactly true..............
It is absolutely true and it was an accurate response to the post. Nothing was mentioned about voltage drop.

To be absolutely accurate, the current capacity of a cable does depend somewhat on where and how it is installed. Running a cable in an enclosed space or conduit and bundling it with other cables will reduce its capacity.


If you want the right answer, you have to ask the right question.
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Old 12-02-2016, 14:42   #41
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Re: How do I connect my new inverter

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............ Now I'm having nightmares of someone using 12ga wire to hook up a 300w inverter because they thought it was capable of conducting 3 A of current. Poof! That burned up fast!
If they followed the instructions, we would hope overcurrent protection was installed so that would take care of the situation.

The real issue is, someone bought an inverter and then went on a web forum to ask "How do I connect my new inverter?"

That's a bad sign and any advice more than "follow the instructions" or "hire a marine electrician" is more likely to lead to an unsafe situation or a fire. It's not that someone can't learn how to do this, it's that it's impossible to describe the entire process and know that the person asking the question understands the process.

Electricity is not one of the things you can "learn by doing", you need some instruction and need to understand how electricity works and the best practices of wiring. For some people, studying a good book on boat wiring might be enough. For others, it won't.
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Old 12-02-2016, 16:25   #42
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Re: How do I connect my new inverter

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Originally Posted by socaldmax View Post
So if you run a 200 mile 4 ga cable to your starter, is it going to work?

How about if you shorten it to 4 ft?
If it doesn't work is that because it can't safely carry that current?

Or is it because of voltage drop?

Two different issues?
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Old 12-02-2016, 16:29   #43
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Re: How do I connect my new inverter

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Originally Posted by socaldmax View Post

Now how long is the power cable to the inverter from the batteries? Once you determine the length, double it (since you're using two wires) now you can look up the required cable size to conduct 30 amps of current with less than X % current loss (plug in your own number, 1%, 2%, etc.)

!
No, VOLTAGE loss!!!

Totally different thing.
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Old 12-02-2016, 16:33   #44
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Re: How do I connect my new inverter

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Originally Posted by socaldmax View Post
Which is it? 170A or 110A? It's neither. How about just calling it 25mm2 cable and look up the current carrying capabilities in a chart, based on length.
You are repeatedly demonstrating a lack of understanding about the fundamentals of electrical wiring.

I suggest you refrain from posting further advise until you learn the difference between "resistance, heating and maximum safe current capacity" and "resistance and voltage drop over distance".
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Old 12-02-2016, 16:46   #45
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Re: How do I connect my new inverter

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Originally Posted by rwidman View Post
It is absolutely true and it was an accurate response to the post. Nothing was mentioned about voltage drop.

To be absolutely accurate, the current capacity of a cable does depend somewhat on where and how it is installed. Running a cable in an enclosed space or conduit and bundling it with other cables will reduce its capacity.


If you want the right answer, you have to ask the right question.
The sense in which it was true, was acknowledged. But this issue is completely irrelevant to the OP's question. What he cares about is sizing his cables correctly, and that's a question of voltage drop and power loss.

If you want to give the right answer, you have to answer the right question.
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