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Old 01-03-2010, 21:35   #16
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Old 01-03-2010, 21:38   #17
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pieces of kit.....that term always seemed so quaint.

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Old 01-03-2010, 21:49   #18
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Obviously some posters didn't read enough of Tellie's posts because he is right as usual.

However, I will give you the right way to determine breaker size here. The breaker to use should be up to the maximum current value of the wiring used, taking into account the factors for bundling wires or running them through hot places like engine rooms. That is the only right answer because the breaker protects the wiring.

Now I can guess the next question: which size wire should be used? Well, Tellie mentioned voltage drop and that hint should be enough to determine that. If it isn't, you better have someone with you who can calculate it for you.... or, if you didn't put more than the costs for the plan into it, give Tellie a call and buy one that's ready to run ;-)

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Old 01-03-2010, 22:49   #19
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Simplify and get it wrong! This is wrong! We call all the other stuff de-rating wire. For example a 20 amp circuit that gets run with 30-amp wire because of de-rating for length, conduit fill, ambient, etc. We would not fuse this circuit at 30 amps but at 20 amps even though the wire is 30-amp wire. If we allowed a de-rated circuit to be fused to the wire ampacity without de-rating we would have a fire hazard.
 
The breaker to use should be up to the maximum current value of the wiring used…

This misleads! It is not the whole calculation.

I could have a long run of #2 wire fused for 20 amps when the voltage drop is calculated. # 2 could be 100-amp wire.

And, which wire? While wire size is wire size, insulation is the big determining factor in de-rating. Some #12 wire is rated at 30 amps for de-rating purposes. This does not mean it is 30 amp wire it means it can be de-rated from 30 amps as long as the final circuit over-current protection is not over 20 amps.

This is not rocket science but it is not for the do-it yourselfer. At least let someone with the knowledge do the calcs.

The fuse or breaker has two three functions: One—circuit disconnect. Two—over current protection, three--- ground fault protection.

There is a big difference between Ground Fault protection and over current protection. Any breaker or fuse will give GFI protection because the fault current is maximum and the breaker trips. Over current protection is much more complicated.

When installing a motor circuit you have to consider more than protection of the wire, you must protect the motor, especial if it does not have an internal overload. Wire sized to the breaker can cheerfully fry a motor running under excess load. It all must be considered and more so when a motor circuit is in constant use rather than intermittent, say such as the macerator on the holding tank. It is not going to run for more than a few minutes, if that, much different than a motor that runs for hours at a time.

Nick, you gotta quit cutting and pasting and start reading for comprehension. I think you mean well….

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Old 02-03-2010, 07:03   #20
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Quote:
Originally Posted by Tellie View Post
I would suspect that there are plenty of board members here that have bought used boats who can relate some very interesting tales on how their boat was wired by POs and thier freinds that thought "How hard can this electrical stuff be?" People that don't know the difference between Anchor and Ancor.
Yeah, tell me about it.
When we bought Enchantress I expected that since it was an older boat the wiring would not be up to ABYC standards. But what I found was something else entirely. It had a fuse board that seemed to be put together from parts that didn't like each other, non-standard wiring in colors I didn't know existed and... well I could go on forever. However it did make it mandatory to rewire the entire boat from bow to stern and masthead to keel.
When I did the wiring, I started with two basic ideas. First to protect the circuit (wiring) the second to protect the device. As has been pointed out very well by Tellie and umsaudade, these are two different animals. Basically I use breakers to protect the circuit and fuses to protect the devices. for the breakers you need to calculate de-rating factors and size your breakers accordingly. You should be able to get your fuse size from the specs of the device -- in this case the 1/2 hp motor.
Completely separate, it's a good idea to have a complete wiring diagram of your boat to tell what devices are controlled by what breakers and making any in-line fuses the may exist. Will save you lots of searching in the future.
I would also sugegst getting a good book on marine electrical systems which should include explanations of how to do the math to figure wire, breaker and/or fuse size.
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Old 02-03-2010, 07:41   #21
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Originally Posted by um saudade View Post
Simplify and get it wrong! This is wrong!
So, I write a sentence in bold-face; for some reason you decide to quote only the first part of it and then tell us that it is simplified and wrong and then continue with reasoning that is exactly the second part of my sentence that you left out??!! You must be a journalist! ;-))

When you use a 20A breaker on a 100A max current wire, that conforms to my statement 100%, so how wrong is my statement?

If you use larger wire to reduce voltage drop... you have to calculate that, but it is not de-rating the wire. De-rating is exactly what I wrote: bundling or hot spaces, nothing more, nothing less. In other words: length of the wire has no influence on it's current carrying capacity.

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Old 02-03-2010, 08:40   #22
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Originally Posted by um saudade View Post

There is a big difference between Ground Fault protection and over current protection. Any breaker or fuse will give GFI protection because the fault current is maximum and the breaker trips. Over current protection is much more complicated.
Oh my....

GFI has nothing, nothing to do with DC circuits and no regular breaker provides ground fault protection.

In AC circuits you need ground fault protection to increase safety only. It isn't needed to run something. There are two ways to create that safety: 1) a third wire called the ground wire, connected to the metal parts of the electric device. Now, in the even that a short between the phase and the metal part occurs, the ground wire will carry the current to ground and the regular breaker will flip. It is the ground wire that provides the protection, not the breaker.
2) a ground-fault protection device. There is no need for a ground wire for this device to work. What this device does is simply compare the current through the phase with the return-current through the neutral. When the difference exceeds the mA value of the protection device, it assumes that some of the current has found another path back (like through your body->hull->ground) and it interrupts the circuit.
You can use both mechanisms for even more safety.

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Old 02-03-2010, 09:04   #23
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[QUOTE
GFI has nothing, nothing to do with DC circuits and no regular breaker provides ground fault protection.

Nick.[/QUOTE]

Being Dutch I may make mistakes when translating stuff but I tend to agree with GFI having nothing to do with 12 or 24 Volt boat installations. It is device looking at current in and out of a (AC 110 or 220V) circuit and breaking it when more than 30 mA are lost (thats right milli Amps). If you do get a full short from the life wire to 'ground' (e.g. to bus bar or engine) to the breaker this looks no different than drawing too much amps. The better breaker types work together with thermal input (used to be PT 100's) which you will not find on the normal motors. A simple 0,5 Hp engine will draw more (when fully loaded) than the theoretical amperage due to efficiency losses (divide by a number smaller than 1 makes it bigger); what it will really use depends on the load put on it. If the pump just need 100 watts to turn the amperage will be lower. If you still fuse it at 40 amps; the pump may self destruct without the breaker knowing it.
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Old 02-03-2010, 16:43   #24
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!@ volt DIY Watermaker.....read more, BEFORE you spend more $$$

Mark,
My typical first comment is to recommend choosing / sizing your watermaker based on your needs and your application...AND making your decision along with your energy decisions......(meaning that your energy budget, and charging capabilities have as much to do with your watermaker decisions as how much fresh water you require...)
And, secondly, to make sure you actually need a watermaker.....

But, rather than ramble on about those things...how about an answer or two for you....


1) Others have posted in detail the reason that we need more info before giving you an exact answer.....
But perhaps I could give you a quick way of figuring this out????

Most 12vdc, 1/2 hp, motors will draw about 39 - 40 amps, under full load....
(That's a BIG load to supply for a considerable of time!!!)
So, you will of course need to size your wiring (and breaker) accordingly (based on length and type of wire).....
But, my guess that you'll use a 40 - 50 amp breaker......


2) BUT, the real reason I'm posting here is because of this....
Quote:
Originally Posted by mpo1991 View Post
I am only expecting to build a unit that produces approx 2 GPH for a couple of hours a day. I recharge mainly through the large array of solar panels.....
I need to acheive a 12v solution. I need a system that I fully understand and can repair myself which is as simple as possible.
Most DIY watermaker projects are either lower power consumption (and lower capacity) 12vdc units.....or higher capacity diesel motor-driven units......
Your numbers just don't make sense....

As another wrote, you will want to use some of your fresh water to "flush" the membrane and filters after each use.....so that WILL take some of the newly-made water.....
But, unless what you wrote is a typo ("2 GPH for a couple of hours a day"), you're going to find that your "design" is simply NOT going to work for you.....
Sorry to burst your bubble, and I DO encourage DIY projects, but how are you going to generate enough energy to run this beast on 12vdc for a few hours each day for your water consumption needs, AND a few hours a day to make enough water to flush it after use?????
Solar panels are GREAT, and I have a 520 watt array, but you'd need almost that much, to run just your watermaker......say 3 hours to make 6 gallons to use, and another 2 hours to make 4 gallons to flush with......that's 200 A/H per day just to get yourself 6 gallons of fresh water????

Mark, I'm truly NOT trying to dissuade you from building your own watermaker, rather just trying to make sure that you don't spend over a $1000 (and LOTS of time / hard work) and THEN find out that you've got no way to make it work...

Current state-of-the-art 12vdc watermakers typically use about 1.1 amps per gallon of fresh water produced, but they are very expensive....
Less expensive and less efficient 12vdc units, typically use about 2 - 2.5 amps per gallon of water produced.....(with a few older units using a bit more power per gallon...)
So, using the numbers your provided, you're looking at using 20 amps per gallon of water!!!


3) There are many who've sailed around the world and/or cruised in remote areas without a watermaker, and many still do.....
So, there's no "need" for one, rather they are a luxury.....

If you have determined that you do want/need a watermaker, then please read over a lot more discussions before you spend more $$$....

Do a search here and at the SSCA disc boards...
By happenstance there is a current discussion on "12VDC watermakers" going on right now on the SSCA disc board....
Have a look here....
SSCA Discussion Board • View topic - 12VDC watermakers


IF you want to undertand others choices, and their energy budgets/generation/etc. there's a lot of this info out there as well....
Here's mine....
Watermaker
Solar Panels
And, here's another cruiser's....
Whoosh - Watermaker



I hope this helps you somewhat....

John
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Old 02-03-2010, 20:34   #25
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That 2 gph must be a typo... 20 gph sounds more logical with a 1/2 hp motor.

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Old 03-03-2010, 06:34   #26
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Um_saudade, firstly, I have over 25 years in industrial electronic design , including ac motors drives, high frequency invertor drives, dc stepper drives ( upto 50 horse power). etc etc , I have protected more motors then you have had hot dinners.

Firslty let me quote a piece from one of the worlds largest manufacturers of DC circuit breaker ETA ( we are talking about DC motors, simple PM motors at that)

"With simple operation through the heating effect of current, thermal circuit breakers offer one of the most reliable and cost effective forms of protection device available. As a result they are ideally suited to the protection of a broad range of components and systems - from motors and transformer windings, through printed circuit boards, to the low voltage power distribution circuits of road vehicles, boats and battery powered machines.

Such applications all require the ability to discriminate between safe switch-on surges or transients on the one hand, and harmful sustained overloads on the other. Thermal circuit breakers can withstand high level surges, which arise from lamp loads or motor starting, for example. At the same time they afford protection against the effects of genuine failure such as motor locked rotors.With simple operation through the heating effect of current, thermal circuit breakers offer one of the most reliable and cost effective forms of protection device available. As a result they are ideally suited to the protection of a broad range of components and systems - from motors and transformer windings, through printed circuit boards, to the low voltage power distribution circuits of road vehicles, boats and battery powered machines.

Such applications all require the ability to discriminate between safe switch-on surges or transients on the one hand, and harmful sustained overloads on the other. Thermal circuit breakers can withstand high level surges, which arise from lamp loads or motor starting, for example. At the same time they afford protection against the effects of genuine failure such as motor locked rotors.


All this from the simplest form of thermal circuit breaker. PLEASE dont quote nonsense at me.

Fuses do virtually nothing in protecting circuits, ( even less then breakers) . In the case of elctronics, puting fuses into power feeds in electronics is laughable. The elctronics acts as a fuse for the fuse!.

Secondly circuit breakers ARE ( as show above) more then suitable). Secondly the reason I said that there is a bit of trial and error , is that the calculated motor current and the actual motor current can be somehwat different. When designing protection into designs all electronic enginners characterise their motors ( a nice way of saying trial and error) so that the know the real world operating parameters of the drive electrics

Lets put this issue to bed once and for all, circuit breakers are not JUST there to protect the wiring, that is merely ONE use of circuit breakers.

IN the case of the aforementioned watermaker. I would run a dedicated DC feed with wiring sized at least 25% above the normall running current ( worse case, not starting current). I would size my breaker to protect the motor, which would also protect the wiring. Then I wouldnt have to hunt around for stupid fuses, while in a F9.

Listen up UM and smell the coffee.


Quote:
When I did the wiring, I started with two basic ideas. First to protect the circuit (wiring) the second to protect the device. As has been pointed out very well by Tellie and umsaudade, these are two different animals. Basically I use breakers to protect the circuit and fuses to protect the devices. for the breakers
no it isnt, it can be ( ie where you are feeding many devices off one feed circuit) but it doesnt have to be and for high current sinks it shouldnt be.
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Old 03-03-2010, 07:12   #27
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by the way OP, using a Wanner pump puts your design up beyond most "professional" units straight away, far better then the nasty piston pumps.

Dont listen to the knockers, with a bit of intelligence you can build a watermaker that will outperform most on the market , except thoses with hydraulic intensifiers of course.
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Old 03-03-2010, 07:20   #28
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People that don't know the difference between Anchor and Ancor.
Anchor = device for holding you in oneplace

Ancor = vastly overpriced products that come in the fist place from the industrial supply chain, have the word marine added on, and then people who dont know any better buy them and are convinced they are superior, ( without knowing anything about the theory).
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Old 03-03-2010, 08:36   #29
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Interesting how threads develop. GBN, I believe your longer post above though very through tends to prove my original point. You have 25 years in design. I have more than that in commercial electric work and have had many, many, a cold dinner in some very interesting places while installing and servicing motors. What may seem simple and what comes as second nature to people with your experience does not, as I said before, to the "uninitiated" To believe that most people who undertake a DIY watermaker will understand what you posted above is not realistic. True, RO itself is a simple concept, a membrane and a pump to create enough pressure and there ya go. I have never said that people should not undertake building their own watermaker. It can be done and has been done. There are a half dozen examples on the net. But I still stand by my comment that many get into trouble when they undertake this particular project and find their costs take off over a few mistakes everyone tends to make on any new venture they try for the first time. I know this well because they tend to call me for bail out advice. I'm a sailor and so I like to pick on them a bit more. This forum has thousands of posts on how to cut corners and cut costs on hundreds of different boat systems. Some of that advice is good and as you know some is not. Being able to discern what is good and what is bad based on what it will cost is where some get into trouble. Sailors as a whole are cheap (gonna get it for that one I'm sure) and there are many with little or no experience and they will often opt for the cheapest way of doing things not because they are stupid but, however well intentioned, they just don't know better. Experience can be a hard teacher. It would be a shame for that teacher to show them what can happen on what for most people is their most expensive toy or their home on the water. I have a personal rule to not give out electrical advice on forums. There are too many unknown and unseen physical parameters that can not be properly verified on just electrical theory alone. Also most people whether they want to build their own or buy one ready made need to be aware of many, many, things before deciding on which watermaker to go with. Their is a lot of disinformation out there on the net telling people about what watermaker is the best or will best suit their needs. Most of it from people whose only experience is from the watermaker they have had for awhile and from what their boat buddies have to say. Much of it just doesn't apply to everybody. Every boat is diffrent, every cruisers needs are differnent. My profile tells everyone what I do. I don't hide it and I don't promote it. But be assured it has been a long road to get there with all kinds of watermakers under my belt from ones I've built myself to the hundreds (probably in the thousand range by now) I've serviced and sold over the years. I've heard all the comments probably more times than yours or mines dinners together add up to. It's not rocket science, it's easy to do, they all fail, they cost too much, my 30 gallon tanks are big enough to cross oceans, they're a luxury, etc. etc. etc.... Like I said I could write a book. If I did, I would include building your own watermaker. Not necessarily how to build one but a guide on what to be wary of and careful with to help avoid the pitfalls I see several times a year on DIY watermakers and store bought ones. This of course is just my opinion and we all know about those.
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Old 10-03-2010, 21:51   #30
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Sorry to be a little late on this reply but I’ve been out sailing.

GFI: ground fault interruption. Short circuit protection, ground fault protection. Used by most professionals to mean the same thing but they don’t, as a ground fault is a hot to ground and a short is an inadvertent ground to return connection. The point is that either one is a maximum inrush current and a tripping of the breaker. All breakers have a maximum current interrupting rating and if the source can provide more current the interrupting rating the breaker will fuse and burn.

Now this is not to be confused with a GFCI, which is a special breaker type, used on AC that looks for imbalance in the two conductors. That analysis was correct as to the physics. I did not refer to a GFCI. I said a ground fault.

We do have a grounded conductor on boat DC circuits so we can have a ground fault condition on a boat. Drag a 12-volt hot wire across the engine block and you will see what I mean. Ground Fault!

I looked at a couple of stocks today and the companies in question had glowing reports as to their wonderful potential. I feel the same about a breaker company harping their wares. If I sold breakers, I too would think they were the cure for all over-current conditions. But the codes say other wise and for good reason.

There are adjustable breakers available for some AC applications. These do offer motor circuit protection, as the trip current can be fine-tuned. They are also to be kept under lock and key by professional personnel. I have never seen an adjustable DC breaker.

As to electronic circuits protecting the fuse (I think that’s what I read) I simply don’t agree. Fuses protect delicate circuits all the time, they minimize fire hazard and minimize damage to the circuit if something fails and the load current goes too high. I have replaced blown fuses after finding the cause of the over current and I have replaced major components or systems because there was not enough left to troubleshoot after the breaker popped. Not always? No, not always, but how many big bills do you wish to throw away?

I know a little bit about design of circuits, especially motor controls and there are several salient points that must be considered AC or DC.

The only variable is the operating current of the motor in actual operation. A motor may not be operated at FLA (full load amps) but the circuit should be designed so the motor is running very close to FLA, especially if the duty cycle is much over very intermittent use. When the motor draws more than the FLA for any reason other than inrush, then the over current protection (not the service disconnect or the circuit breaker will protect the motor winding if the motor is being over torqued, long before the motor is damaged. Time delay breakers do get closer to adequate protection but not good enough.

Since DC breakers come in 5 amp increments (or ten) and are notorious for not tripping at the rated set point I will not use the breaker for over current protection. The time delay fuse gets closer to good motor over current protection, the use of overload heaters in a magnetic starter is better and the ultimate protection is a solid state current monitor (current transformers work great on AC) that shuts down the contactor if the FLA is surpassed.

Again, I will remind you all that we are talking about a 100% duty cycle circuit. This is far more critical than something such as a macerator or an anchor winch. There is also many more failure potentials internal to any DC motor than a comparable AC motor.

Other than this final step, the circuit calcs are all in the book and there is no guessing. Wire size, temp rating, conduit fill, length of run, etc are all in the book.

I am not sure I would be worried about running the water maker in an F9, but we all have our priorities!

Now there are circuits that should not have over current protection and they include fire pumps and the like, but that is another lesson in codes and physics.

I tend to agree on Ancor products being badly over-priced but they are designed for the DIY who does not have the experience to know what can and can not be used in regards to safety and longevity.

I have even been seen using non-tinned wire on a boat! Some of that was 30 years ago and the circuits are still in daily service. I guess my methods work more often than not. Experience, I guess.

Um Saudade
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