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Old 27-01-2012, 12:50   #1
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A/C or DC ?

Hi Everyone, I'm building a water maker and need a 2hp electric motor to run it. My question is two fold. 1. What would be the best way to go, 12vlt or 110vlt and run it through an inverter ? If so what size inverter would be needed. 2. What would be the total Amp draw on the batteries ? I'm just as concerned about reliability as I am cost. I realize that there's the added cost of the inverter but I will be buying one anyways so its just a matter of how much more for the bigger one. I have 4 T-105's(250amh@50%) for my batt bank and 2 solar panels @ 85w each.

Thank You
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Old 27-01-2012, 13:18   #2
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Re: A/C or DC ?

It will need to be 120 vac. It is impractical to run it on 12v batteries because the current draw would be on the order of 200 amps to feed an inverter to support a 2 hp motor. Your best option is to run it from a generator.
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Old 27-01-2012, 22:27   #3
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Hello Billypage,

You may want to reconsider the amount of water you need to make. Your 2HP motor requirement suggests either you are trying to make a lot of water or your water maker is very inefficient. You can get water makers that use only 12V motors. Usually there are 2 pumps. One for feed water and another high pressure pump to drive the membrane. In most cruising boats neither of these motors are nowhere near 2HP.

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Old 27-01-2012, 23:45   #4
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Re: A/C or DC ?

G'day, mate. Yup, Transmitterdan's advice to start with how much water you want to make is a good one, even if you have to buy a different pump and motor. Having said that, you also want to consider how long you want the watermaker running. They do make a bit of noise.

We use about 10 gallons of fresh water a day. Our 110 VAC watermaker will make that in about 1/2 hour (depending upon the conditions). I had a mate with a much smaller 12 VDC watermaker (he even had a 15KVA genset ) on a 75 footer and it ran most of the day creating the most annoying noise.

In the end, if you are going to have a genset (you can almost get a Honda 2000i for the cost of a large inverter, but of coarse you have to carry gas then) on board as St. Elsewhere suggested, my advice would be go the AC route. If you are going to go the solar panel route, go the DC route and downsize the watermaker and live with the noise. All the best, Cheers
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Old 28-01-2012, 00:05   #5
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Re: A/C or DC ?

If you have the option the better drive would be off the engine or as a friend of mine has a hydraulic run unit, with his engine having a hydraulic pump built on as an extension off the top end of his drop shaft transmission. Mine is 120vac but I have to run it off my generator. It can produce 400gal/day or 16gph with a 1.5hp.motor while drawing approxiametly 12amps (would be 120 amps @12 volts) when this pump fails I will opt for one run off the engine using a magnetic clutch to engage the pump.
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Old 28-01-2012, 02:24   #6
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Re: A/C or DC ?

I don't think 2hp makes sense for a watermaker unless you need to supply about 30 people or more. In any case, you _can_ run 2hp on 12 with a lot of current, or even at AC with a large enough inverter (like 2000watts which they do make) but if you did, it would make more sense to have a 24 or 48 volt system and run from that or invert from that.

In any case, I would be looking at a lower power motor, in the 1/4-1/2hp range. It might run longer but so what, it isn't going to be continuous anyway.

Alternately, you can do like me and just use rainfall and a solar still, and fill up at docks of course, then get a cheap $100 dehumidifier if you feel you must make water from electricity in an emergency, but I haven't needed mine.
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Old 28-01-2012, 06:13   #7
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Re: A/C or DC ?

I agree with Lancer, if possible, a good source for power is to run from engine. Another problem besides amp draw, is over heating of motor. I know people who required a small fan to control heat build up of motor. Basically run the WM while motor sailing or just for an hour, to make some electric and water at the same time. It works well for us and saved buying a motor and wiring for same. Cat pump's web site has a chart for sizing pump/motor HP for various flow rates
http://www.catpumps.com/products/pdfs/231.pdf
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Old 28-01-2012, 07:18   #8
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Re: A/C or DC ?

Greetings and welcome aboard the CF, Billypage.
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Old 28-01-2012, 08:28   #9
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Re: A/C or DC ?

WOW ! Thanks for all the advise and tips. Now I really have to put my thinkin cap back on. I have considered engine driven. I have a 27hp Yanmar and have the room to mount it. But talk about noise. I figure @ 20glh I will run it 1-wk for 3-4hrs. That will include the start up and back flush at the end. I cant afford a new system off the shelf, so this is my only way to do it. If anybody has a way to do this cheaper and be reliable, I'm all ears. If I go engine driven, I can do a 20glh system (very basic) for less than $1500.00, all parts are new.
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Old 28-01-2012, 09:15   #10
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Re: A/C or DC ?

that is exactly what I built, 20 gph, and we run it about 3 hrs per week. But like I said we are generally motor saing or just plain motoring about that much per week anyway . I got my pulley/PTO from "Seafrost". Their engine driven refridge uses the same size as I required, and it only cost about fifty bucks
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Old 28-01-2012, 09:21   #11
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Re: A/C or DC ?

My Village Marine watermaker uses 110v. and makes 30g/hr. At anchor, I run the genset every morning to recharge the battery bank. I easily re-fill the water tank at the same time so the water is "free".
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Old 28-01-2012, 09:41   #12
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Re: A/C or DC ?

There are many who will opt for a high output watermaker, one that requires a 2 HP motor. I am one of them. We use a lot of water.

But I suggest that you read the numerous threads here in the Forums (try the Plumbing Forum) about watermakers. Each approach has its own features along with liabilities. I also recommend that you do your design on paper before purchasing any hardware. There is a book somewhere that suggests that one can build a high output watermaker for less than $800! Yeah, and Detroit can build a 6 passenger car that can get over 100 miles/gal! Don't be sucked in by unrealistic hype.

Building a watermaker can be a lot of fun. I have been working on mine since last year, hope to have it installed this coming season. My advice is if one is building a watermaker just to save money, just maybe he is building it for the wrong reason.

Good luck, I wish you the best with your project.

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Old 02-02-2012, 11:39   #13
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Ok, I have done a lot more thinking, looking and listening and have found and purchased a Survivor 80 used. Got it very cheap ! Everthing works. Just need new membranes. My question now to all who might know, is there a replacement membrane other than Katadyn ? There $340 each ! I need 2. I've heard there is another pressure vessel and membrane combo that works with this unit that together is cheaper than just the membrane.
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Old 02-02-2012, 11:51   #14
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Re: A/C or DC ?

Quote:
Originally Posted by Billypage View Post
WOW ! Thanks for all the advise and tips. Now I really have to put my thinkin cap back on. I have considered engine driven. I have a 27hp Yanmar and have the room to mount it. But talk about noise. I figure @ 20glh I will run it 1-wk for 3-4hrs. That will include the start up and back flush at the end. I cant afford a new system off the shelf, so this is my only way to do it. If anybody has a way to do this cheaper and be reliable, I'm all ears. If I go engine driven, I can do a 20glh system (very basic) for less than $1500.00, all parts are new.
This worked well for me. How much water storage do you have? A couple advantages: when motoring for a few hours it's easy to fill the tanks. If you need to charge off the engine at all it's like free. If you are going full solar/wind type of thing, and wil be stayinlg in the same spot for a long time, then probably a little (noisy?) 12v unit is best.
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