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Old 18-05-2016, 07:48   #1
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Water Maker AC Or DC

I have a 12 KW generator on my 42 foot cat and I want to add solar panels and a water maker.

I have been told that since I have a relatively large generator I should get a larger AC water maker that would minimize the generator run time to make water.

I have also been thinking that perhaps one that runs both AC and DC would be better as I could run that off the solar when I have excess solar.

I am interested in your thoughts and if you have a brand or size recommendation.
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Old 18-05-2016, 08:03   #2
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Re: Water Maker AC Or DC

I agree with a larger output unit ran off a/c power. Figure your total storage, and size a system that can fill your tanks in a couple of hours or less.. Funny thing about Desalination systems. Up sizing isn't that much more expensive than a small unit, and you will have less maintenance than using a 12 volt system. Oh, I suggest that you look for a basic unit without all of the bells and whistles that includes a fresh water flush of the membranes upon shut down so stagnant saltwater doesn't sit in the membranes.
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Old 18-05-2016, 08:25   #3
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Re: Water Maker AC Or DC

I bought a Rainman about 60 days ago and am super happy. It has been putting out its rated capacity here in the Bahamas. We run the maker about 3.5 hours every 4-5 days.

I looked at a Spectra before picking the Rainman and was surprised how loud they were. I'm glad i went with a faster maker for shorter run times and less overall noise.
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Old 18-05-2016, 08:58   #4
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Re: Water Maker AC Or DC

The original statement to use your (large) generator for an AC powered water is a decent proposal, however it does suffer from the downside that without a generator, you may not have enough ac capability, and if not, no water.

I would most certainly be looking for an ac/dc or a dc system, after all you will have 3 ways to provide dc (gen, solar, engine) and only 1, or possibly 2 ways to provide ac.
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Old 18-05-2016, 09:02   #5
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Re: Water Maker AC Or DC

Drive the high pressure pump right off the generator . Only one thing in the chain to fail and make more water at a time .

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Old 18-05-2016, 09:10   #6
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Re: Water Maker AC Or DC

An important thing to remember about the AC vs DC water maker question is that the only difference is how do you get sea water up to 800psi to drive a portion of it through the RO Membrane. I know that seems basic and almost obvious to say, but starting with that understanding can help with the decision. Sure different brands of water makers have varying levels of automation, control and features but at the end of the day that fact drives Cost, Fresh Water Production Rate, Power Usage, Maintenance, everything.

The focus of the DC approach is energy efficiency and giving the client the ability to run the system from their battery bank, so good DC systems use an energy recovery pump to get sea water up to 800PSI. But this focus on low energy usage also makes you will live with low production and need to run the unit for longer periods. The energy recovery pumps also add in cost, so expect to pay more for a lower output DC system.

The focus of the AC approach is High fresh water production, the AC approach says we have power available while running the generator, so lets make as much water as possible and use a energy hog off the shelf piston pump. This approach can give you a 30GPH water maker for almost 1/3 the cost of a 20GPH DC energy recovery system, so if the goal is having larger amounts of fresh water and you have a generator available then the AC system usually wins out. But if the goal is running off solar and your batteries, then you have to go with a lower output DC unit.

A common worry going the AC approach is what if my generator goes down...do I then lose my ability to make water? No, not if you have a 2000W inverter, you can make water through your inverter. Our approach is to use our generator to make water while at anchor and then when underway with the alternator running, once the batteries become topped up, we turn on the water maker through the inverter being powered by the alternator. So that way you have a back-up approach for if something happens to your generator. Now unless you have LiFePO4 batteries, it is unrealistic to think that you will run a high output AC water maker off of your battery bank using just wind and solar...but it can easily be done while running your alternator.

There is no "wrong answer" in the AC/DC decision, as long as you know the pluses and minuses to each approach and line that up with your cruising plans and expectations. Speaking in generalizations (which is always risky) the owner and crew of a 42ft Cat tends to have different expectations than a smaller mono hull cruiser in terms of comfort, showers, deck and gear rinse-downs, and general water use. It is much easier to meet those expectations with a higher output AC water maker than a lower output DC system.

Here is a link to download a copy of our SM30 (33GPH water maker for $5250)
www.cruiserowaterandpower.com/uploads/sm30.pdf

Of course I am a predisposed to like the AC approach not just because I build and sell them, but because our family of 4 would not be on year 9 of cruising and living aboard if I had to tell my wife and daughter to constantly be watching their water use. Part of meeting our expectations for comfortable cruising and living aboard was having unlimited showers and a washing machine, so the AC high output water maker was the best way to meet our expectations.
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Old 18-05-2016, 09:13   #7
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Re: Water Maker AC Or DC

We've got a 12v 8-9gph village marine, but if I could do it over again I'd put in a 20gph cruiserRO that's AC.

Whatever system you put in you should be able to run it frequently, that's the key to keeping a watermaker happy.
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Old 18-05-2016, 10:11   #8
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Re: Water Maker AC Or DC

I don't yet have one yet, that's next years purchase, but I'll have a high output AC. question is 30 or 40 GPH?
If my generator breaks, as everything eventually does, then I'll use my engine with it's 125 amp alternator and Magnum inverter. Having enough Solar to run a high output AC watermaker would be tough.
In my opinion once you decide on having a generator, you get into where a high output, inefficient AC watermaker makes sense.
No generator? Then is there another choice other than a Spectra?
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Old 18-05-2016, 10:22   #9
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Re: Water Maker AC Or DC

Quote:
Originally Posted by a64pilot View Post
I don't yet have one yet, that's next years purchase, but I'll have a high output AC. question is 30 or 40 GPH?
Ah...
Here is my thinking. The 1.0Hp motor on the SM30 can be ran with a 2000W inverter, but the 12v DC amp usage to power that inverter is pretty big (like 90A DC). So while you can run that through a 2000W inverter, it is also something that I think you need to have your alternator running to handle of you can crush your battery bank. Now if you go up to the SM40, that uses a 1.5Hp motor and the 12v DC amp usage to power the inverter would be huge...like 140A..so is that a realistic load to run through an inverter even with the alternator running? I don't think so. Therefore, for cruisers wanting a power source back to their generator, I recommend that they stay with the SM30 over the SM40.

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Originally Posted by a64pilot View Post
No generator? Then is there another choice other than a Spectra?
In my mind, No!
Spectra is the undisputed king of the DC water hill and all the time I walk folks down to the Spectra booth when people tell me at boat shows that they don't have or want a diesel or Honda 2000 gen aboard.

The issue to me is that once you go the DC route, what matters to you most is efficiency. You want to make the most gallons of water for the least amount of Amps. There is simply no other DC water maker on the market that comes close to Spectra. They are also a great company, with a fabulous reputation for service, support and performance.
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Old 18-05-2016, 10:37   #10
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Re: Water Maker AC Or DC

OK, got it, I have installed a shunt to monitor the actual output of my alternator and it seems my 125 amp alternator can actually be counted on to produce about 85 amps continuously (heat build up).
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Old 18-05-2016, 12:40   #11
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Re: Water Maker AC Or DC

[QUOTE=1tviere;2123377

I am interested in your thoughts and if you have a brand or size recommendation.[/QUOTE]

Far as I'm concerned if you have a generator it doesn't make $ sense to get a DC water maker! For my boat getting an AC watermaker, that was higher capacity than the DC units, the price difference paid for half the cost of my installing my 4KW generator.
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Old 18-05-2016, 13:14   #12
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Re: Water Maker AC Or DC

When I was searching for a watermaker for cruising I had several criteria...
  1. 12v - So I had mulitple ways to run the Machine (Batteries, Alternator, GenSet and Solar)
  2. High Output
  3. Easy to Use

I purchased the Spectra Newport 400 II with the Z-Brane unit.

It makes between 16 and 18 gallons per hour, depending if I am running off batteries or a charging source (Alternator or GenSet).

Spectra Machine like lots of voltage and so having a charger on the batteries will increase the output by as much as 1.5 gallons per hour.

With the Z-Brane and Automatic Back Flush there is No Pickling! As long as there is fresh water in the tanks to back flush the machine just keeps running.

Spectra has great support and I would definitely purchase another!
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Old 18-05-2016, 13:42   #13
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Re: Water Maker AC Or DC

Most water makers these days (DC or AC) have a automatic fresh water flush option, which eliminates the need to pickle your water maker when not in use (as long as there is fresh water in your tank). But since pickling doesn't hurt your membrane (contrary to popular myth) most people still pickle the water maker if they are leaving the boat in storage for the season. Where the automatic fresh water flushing comes in handy is when you do extended stays in a marina...it makes one less thing to worry about every 5 days if you are not making water.

Pickling sounds like something exotic, but it just evolves turning a valve and pulling in a food grade sterilizing agent into the system to keep the animals from growing and taking over the system. I made a YouTube Video about water maker maintenance if you want to take a look:
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Old 18-05-2016, 15:08   #14
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Re: Water Maker AC Or DC

You can have a 20 gph output via DC, you just need to be prepared. My research tells me that a 1 hp 12v DC motor can get you the 20 gph, just at a cost of 80 amps.

One would need a very large lead acid bank to support this and folks with this size probably have a generator needed the easier AC motor.

Or it takes LiFePO4. A reasonably sized 400 amp hour LiFePO4 bank can handle the 0.2C discharge for 3 hours/60 gallons with no problem. Of course you'd have a nice solar rig or a massive alternator so as to not have to run your engine for hours to recharge!
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Old 18-05-2016, 15:22   #15
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Re: Water Maker AC Or DC

Quote:
Originally Posted by fallingeggs View Post
You can have a 20 gph output via DC, you just need to be prepared. My research tells me that a 1.5 hp 12v DC motor can get you the 20 gph, just at a cost of 80 amps.
There could be a little confusion in terms of energy recovery vs non-energy recovery pumps, but both running on DC 12v.

The Spectra DC energy recovery water maker can make 16-18GPM on 12v DC for about 18A DC 12v.

Now do away with the energy recovery pump and use a 1.6GPM energy hog piston pump and a 1.0Hp motor. That set-up will make 20GPH but will use 80A at 12v DC.

So the energy recovery Spectra will basically make water for 1Amp per gallon. While the non-energy recovery piston pump will make water at 4Amps per gallon.

It's why I think that if your water maker criteria is to run it completely off Solar, then you just have to bite the bullet and pay the extra money for the Spectra water maker with an energy recovery pump. A non-energy recovery pump trying to run on 12v is one of those things can work on paper, but then out in the real world of cruising is a disaster. Even if you cut the pump/motor in half and accept 10GPH rather than 20GPH, you are still looking at 40A. It's fools gold.


[[Just a techy note from the quote: A 1.5Hp motor will not use 80A, as indicated, but closer to 120A...basically forget about powering that from your batter bank. But you don't need a 1.5Hp motor to make 20GPH, a 1.0Hp/1.6GPM pump will do it fine.]]
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