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Old 28-02-2010, 14:54   #1
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Help in Wiring Up Watermaker, Please

I recently purchased plans on ebay and am in the process of building a 12v Watermaker. During my research I came across other self builders on this forum which encouraged me to proceed with this project. Whislt the plans give details of the plumbing there is no guidance on the wiring front. I am using a 1/2 hp 12v dc motor driving a small Wanner high pressure pump, but I am unsure on whether to add an additional breaker to my distribution panel or wire back to the main service breaker as per my windlass, and what size of circuit breaker to use. Can anyone please point me in the right direction on where I may be able to get this information to ensure I have a safe setup.
Many thanks
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Old 28-02-2010, 15:18   #2
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Greetings and welcome aboard the CF, mpo1991.

A 40 A breaker might be appropriate for a 1/2HP @ 12V motor.
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Old 28-02-2010, 15:51   #3
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1/2 hp is 373 Watts...at 12 V = 31Amps...when its running

DC Motor startup current can be twice running current.

I'd go for an 80 Amp breaker...
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Old 28-02-2010, 16:56   #4
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I've resisted for a long time responding to the build your own water maker super duper cheap threads for a long time. "Might be's" "Could be's" and "This is what you need" forum advice will get the uninitiated into trouble faster than you can say "Uh Oh!" There is no one right answer without the right information which you have not given. While these online plans seem wonderful at first sight, and who can resist a gadzillion GPH water maker at less than a 2K build out? Well they tend to fall very short in applicable real world info. One of the many pitfalls in the DIY water maker is the area of 12 volt wiring. It is not as simple as throwing in an oversized breaker and any wire laying about. Amperage, voltage drop, wire run, current draw/both start up and running, have to be considered before sizing either the wire or the breaker. One day I'm going to write more than a two or three page "How to build it cheap" and more like "Are you sure you know what your getting into?" and sell it on E-bay and reveal the real costs and the plethora of commonly made mistakes of undertaking this particular DIY project. For $15 a copy I can save most people a 2K-3K mistake. OK mini rant over and off to write a very long book.
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Old 28-02-2010, 20:08   #5
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Old 28-02-2010, 20:31   #6
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Tellie your post is hor£&s@it. Watermakers are very simple basic pieces of kit. Also any decent high pressure pump can be made to work. The fact is the tech is in the RO element and that's not a diy item. The fact is that marine watermakers are like are other "marine" gear, vastly overpriced for what they are this is true of most marine items the markups in the industry are huge, way beyond industrial kit in fact if you build your diy watermaker out of good branded industrial kit it will be better then the marine grade junk. I have looked over the years many of the marine watermakers and most are poor diy lashups anyway

Well done OP. Use a 40 amp breaker and decent cable and it will be fine. Don't
be put off by bogeyan stories.
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Old 28-02-2010, 21:45   #7
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Goboating; everyone is entitled to an opinion, but I think it in better taste to leave the biodegradable matter over in the compostable head thread. ok?
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Old 28-02-2010, 21:58   #8
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Anybody who claims to know how to size the breaker for this if full of it. Nameplate rating determines current draw and thus, wire and protection size.

Throw the 750 watts per horse formula out the window, it does not apply to fractional hp motors, as they are very inefficient.

I personally won’t use a breaker for over current protection. The NEC says quite a bit about this. Look at the interrupting rating on a breaker, it is more a guess than science. Use a breaker as a circuit disconnect and fuse a motor circuit to protect the motor.

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Old 01-03-2010, 01:24   #9
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Many thanks for your comments

Many thanks for your comments, various suggestions that I will explore further. I would agree that buying cheap plans off ebay is not the solution to DIY build but they are a reasonable starting point. A lot of RO equipment is US built and even sourcing NPT pipe fittings outside of the States can be challenging, so just getting some initial supplier info repays the small cost of the plans. 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 have and historically only run my engine for less than 100hrs a year ( it is a sailboat afterall ) and never just to charge the batteries, so as I don't have a generator or facility for an engine driven pump ( twin alternators fitted ) 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. As you are probably aware I am presently not confident in my electrical expertise, but am gaining experience with each project, thanks to knowledgable folk like yourselves.
Many thanks again for your guidance so far, but any additional ifo is always welcome.
Mark
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Old 01-03-2010, 14:49   #10
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sarafina, appologies, must remove keyboard from mouth. all the rest still stands though


As to circuit breakers, Firstly there can be a bit of trial and error selecting a correct breaker. However rember that most circuit breakers are quite "slow blo", they will gernally take starting surges. In my view fuses have no place on a boat unless they are all simply placed in a visable and readily accessible location. I shudder to think of the forgotten fuses in most boats.
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Old 01-03-2010, 17:12   #11
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GBN,
There is NO place for trial and error in selecting circuit breakers. It’s called either the laws of physic or the electric code, be it the NEC or the ABYC.

Circuit breakers are not allowed as over-current devices for motor control circuits as per the NEC. Why? Because they don’t protect! The typical DC breaker is time delay but really only good for ground fault detection not for motor over current protection. Do you understand the difference?

Expensive motor should have the over current protection sized as closely as possible if using fuses and for real protection a motor controller using either current transformers or old fashioned heaters to set the FLA (Full load amps) limit.

On something such as the homemade water maker, the motor current is indicative of the operation and should be closely monitored.

As to this watermaker: If this makes a gallon and a half an hour and draws 30 to 40 amps, why would you want it? My Katadyn 40, which nobody but me seems to like, draws 4 amps and makes a gallon and a half an hour. I couldn’t see coming up with that kind of power to make so little water.

As to your comment on hidden fuses, yes, I agree but we didn’t say hide the fuse, did we? I will use fuses when appropriate and breakers when appropriate, knowing that my equipment is properly protected. You may continue with trial and error.

Um Saudade
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Old 01-03-2010, 17:23   #12
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Agree with this high current low production comment !

I have a Schenker that produces 35 litres/ hour for 8 Amps draw...sure it cost more money than a 2 gal/hr 40 Amp DIY...but its efficient and reliable.

regarding breakers and fuses...they don't protect the device in the fused circuit, they protect against high currents (like short circuits) that could damage your power supply and wiring and potentially set fire to your boat. They need to be sized appropriately to take account of ALL normal load on the circuit eg motor startup current so as not to trip under normal circumstances.
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Old 01-03-2010, 17:24   #13
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Goboating; everyone is entitled to an opinion, but I think it in better taste to leave the biodegradable matter over in the compostable head thread. ok?
Thanks Sarafina. That was a very tactful way to handle the outbursts. Much better than the heavy handed techniques.
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Old 01-03-2010, 18:47   #14
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Originally Posted by mpo1991 View Post
Many thanks for your comments, various suggestions that I will explore further. I would agree that buying cheap plans off ebay is not the solution to DIY build but they are a reasonable starting point. A lot of RO equipment is US built and even sourcing NPT pipe fittings outside of the States can be challenging, so just getting some initial supplier info repays the small cost of the plans. 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 have and historically only run my engine for less than 100hrs a year ( it is a sailboat afterall ) and never just to charge the batteries, so as I don't have a generator or facility for an engine driven pump ( twin alternators fitted ) 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. As you are probably aware I am presently not confident in my electrical expertise, but am gaining experience with each project, thanks to knowledgable folk like yourselves.
Many thanks again for your guidance so far, but any additional ifo is always welcome.
Mark
not trying to bust your bubble but your 2 GPH for a couple hours a day wont cut it.. The worst destroyer of a membrane are those little critters that grow within.. when you've finished using the unit, you need to flush it with fresh water to clean out the little critters and the growth you dont want inside.. A minamum flush will cost you 4 to 6 gallons for a 24 inch membrane.., so not only do you need to produce the water needed, you also need to produce the water needed to flush the unit..
so if your unit produces 2 GPH, the first 2 to 3 hours are lost to fresh water used to clean the membrane.. hope you build the unit with a flush system as part of it...If you dont, count on it going to crap in a very short time..
Randy..
(my info comes from a good number of years servicing and selling watermakers as we've been cruising)
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Old 01-03-2010, 21:06   #15
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Just for the record, I was not offended.
UmSaudade is correct. Guessing and experimenting with electrical loads and their protection is exactly one of those "Uh Ohs" DIYers I spoke about originally find out about. If they're lucky, not too late. 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.
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