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Old 26-01-2018, 07:49   #136
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Re: Water maker comps

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Originally Posted by john61ct View Post
These discussions help clarify the various factors for those that are interested, especially noobs like me.
sorry but after 4 pages of the same item I question the topic effectiveness
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Old 26-01-2018, 07:56   #137
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Re: Water maker comps

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Originally Posted by john61ct View Post
And BTW my use case, high-output DC only power sources

fits neither of your examples.

Which is why I'm looking for DC with high gph output, to be run only while high-amp sources are charging.

Or maybe adding an inverter if the right unit, at the right price, comes only in AC.
No you only having high output DC makes you a DC WM customer so you can run it off the batteries. See that wasn't hard at all.

The inverter is another question and if you get an inverter and decided it is now better/cheaper to run an AC WM off it while powering the inverter with your engine and that DC charging source that's a different decision.

BTW - it probably is less cost to get an AC WM and run it off an inverter/alternator than to buy a DC WM, but it's close. The big plus is than now you have an inverter.
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Old 26-01-2018, 08:08   #138
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Re: Water maker comps

Personally I'd either go Spectra 12 volt or any number of 110 volt units run by Honda or other genset. I really can't understand why one would want a 12 volt system that required a huge drain on the batteries or charging system to run. There are 12 volt systems other than Spectra that can run on solar if you have a decent sized solar system but they dont really have high output. Your desires sort of confuse me, mind you these days it's getting easier.
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Old 26-01-2018, 10:00   #139
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Re: Water maker comps

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Dessalator says between 2.5 to 5% less output per degree below 25°C. I checked echotech, they say 2% per degree. Dessalor is rated at 25°C, echotech at 26°C.

So if using average value from Dessalator, that is 3.75% per °C, then at 17.5° I should get 100l/h x (1 - 3.75*(25-17.5)/100) = 72 l/h !!!
I have always been curious about the temperature dependency. It would appear to make sense to install a heat exchanger driven by cooling water">engine cooling water on the watermaker input. We need to make some calculations to make sure we do not exceed the membrane max temperature (46C/112F), also account for the fact that the high pressure pump raises the temperature as well. Yet, if we increase the inlet water temp by 15C, we may be able to boost the capacity by 50% (with engine running which is a safe assumption for a high power DC driven watermaker. Sounds like a good project.

Curious what Rich thinks about this.

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Old 26-01-2018, 10:12   #140
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Re: Water maker comps

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I did some measurements yesterday of my Dessalator DC100, I'm sure some cruisers here will be interested in such real life numbers, it would be nice to have reports for other brands.

Power consumption: 49A @ 12.76V steady, that is about 625W
Water production (average on two measures that were almost identical): 72l/h
Water temp (~1m below WL, at WM input): 17.5°C

Dessalator says between 2.5 to 5% less output per degree below 25°C. I checked echotech, they say 2% per degree. Dessalor is rated at 25°C, echotech at 26°C.

So if using average value from Dessalator, that is 3.75% per °C, then at 17.5° I should get 100l/h x (1 - 3.75*(25-17.5)/100) = 72 l/h !!!

if Echotech is right with 2% per °C, then I should be getting 85l/h

I will need to wait a few months before I can make a measure in 25°C to know if I really have a 100l/h WM... The ouput meter of my WM is wrong anyway as it has always shown values above 100l/h. I sent an email to Dessalator.

@Kenbo: Though a bit disappointing to me, those numbers are above your expectations dictated by the "physics of WM". I'd like to know what you think about that.
It's hard for me comment knowingly because I really don't know the design of your WM, i.e. the actually hp of your pump's motor, how many pressure vessels are in the system, what pressure you operate at, what percentage of your amperage draw is powering the high pressure pump, etc.

But assuming you have a 1/2hp (40A of the 49A total) pump and your running at 800psi then your feed water flow rate should be, 0.91 gpm or 54.75 gph. So your 72l/h (19g/h) permeate equates to a recovery rate of 34.5%. That's absolutely spectacular and beyond what I've ever seen on a small system using a Dow Filmtec membrane.

So maybe you have a metric motor that is not 1/2hp or 3/4hp but somewhere in between. Let's run the numbers for a 3/4hp pump (58A of the 49A total???), new feed water flow rate is 1.37 g/m or 82 g/h. the new recovery rate is 19/82= 23%. Not quite as spectacular but still on the very high side of what is typically seen as around 18-20%.

So maybe you have a different type of membrane than a Dow Filmtec or you're running at a different pressure than 800psi or your running multiple membranes in series. It's hard for me to say not knowing your unit at all.

More likely, the answer is just like your rotameter was giving you very inaccurate data, I suspect that your other data inputs may be inaccurate. Sorry, I am very distrustful of yacht instrumentation coming from the pharmaceutical industry where we had to calibrate our instruments periodically and prove it or the product never left the plant.
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Old 26-01-2018, 12:26   #141
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Re: Water maker comps

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Originally Posted by Pizzazz View Post
I have always been curious about the temperature dependency. It would appear to make sense to install a heat exchanger driven by engine cooling water on the watermaker input. We need to make some calculations to make sure we do not exceed the membrane max temperature (46C/112F), also account for the fact that the high pressure pump raises the temperature as well. Yet, if we increase the inlet water temp by 15C, we may be able to boost the capacity by 50% (with engine running which is a safe assumption for a high power DC driven watermaker. Sounds like a good project.

Curious what Rich thinks about this.

Pizzazz
Dessalator actually talks about that on their website, for those using WM at higher latitudes and very low water temp.

For those like me who are running their WM without a genset or engine it would not be so complicated to have an additional hose, like quite long, that would run through some warmer places on the boat, or possibly outside in full sun. As to not exceed max temp, a 50EUR thermostatic valve at the input of the WM could do the trick (connected to directly to the thruhull for "cold" and to that special hose for "hot"). Interesting project indeed ...

@kenbo; I was expecting a little more from you maybe I will have a look at the physics of WM if you have a good link to share. So much spare time these days and so many unanswered questions !
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Old 26-01-2018, 19:02   #142
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Re: Water maker comps

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No you only having high output DC makes you a DC WM customer so you can run it off the batteries.
I've tried to make clear, the WM will never run off the batteries.

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Originally Posted by robert sailor View Post
I really can't understand why one would want a 12 volt system that required a huge drain on the batteries or charging system to run.
With far more power output from the DC genset than a Honda will ever produce, maybe only 20-30% of the output is goung to even the largest watermaker. Certainly there is zero drain on the bank, in fact they are getting charged with the rest of the output.

So far no need for any inverter, for sure no electricity is used for washing clothes.
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Old 27-01-2018, 04:57   #143
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Re: Water maker comps

you need to design your own system and make it complicated and unpractical because that's what I believe you want
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Old 27-01-2018, 05:00   #144
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Re: Water maker comps

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Originally Posted by john61ct View Post
I've tried to make clear, the WM will never run off the batteries.

With far more power output from the DC genset than a Honda will ever produce, maybe only 20-30% of the output is goung to even the largest watermaker. Certainly there is zero drain on the bank, in fact they are getting charged with the rest of the output.

So far no need for any inverter, for sure no electricity is used for washing clothes.


But a cruise ro system with a 1 hp 12volt dc motor....done.
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Old 27-01-2018, 06:39   #145
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Re: Water maker comps

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Originally Posted by john61ct View Post
I've tried to make clear, the WM will never run off the batteries.

With far more power output from the DC genset than a Honda will ever produce, maybe only 20-30% of the output is goung to even the largest watermaker. Certainly there is zero drain on the bank, in fact they are getting charged with the rest of the output.

So far no need for any inverter, for sure no electricity is used for washing clothes.
Ok, so, it never runs off of batteries. What is the problem with the 24V system, or similar, as already recommended?
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Old 27-01-2018, 06:44   #146
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Water maker comps

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you need to design your own system and make it complicated and unpractical because that's what I believe you want


No, he is where I was a couple of years ago.
That is convinced that AC power is simply inefficient, that the most efficient use of power on a cruising boat is DC.
Then I bumped into the reality that you need a monsterous bank, or a big LifePo bank $$$ to really realize the increased efficiency.
Then I found there is no off the shelf solution for a DC generator, or if there is, I didn’t find it.
Rolling your own can of course be done, but then who do you call for parts, and will there be any bugs in it to work out, and can you afford both the time and money to build your own, or had you rather be out cruising?
I figure the conversion losses are way less than 10% and the most commonly available appliances are AC anyway, washing machines, blenders, toasters, coffee makers, vacuums, counter top ice makers etc. so your in the end either going to be changing DC to AC or AC to DC anyway, so why bother?
It’s sort of like building your down Watermaker. Of course you can, but why? Unless you have excess time on your hands and are looking for a project, maybe your better off buying something that has all been figured out, and has no bugs and has a good supply network in place.
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Old 27-01-2018, 08:24   #147
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Re: Water maker comps

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Originally Posted by belizesailor View Post
Ok, so, it never runs off of batteries. What is the problem with the 24V system, or similar, as already recommended?
Quote:
Originally Posted by Sailmonkey View Post
Buy a cruise ro system with a 1 hp 12volt dc motor....done.
Nothing, when the time comes looks like that would be ideal. Just clarifying what I'm looking for, for those who keep misunderstanding the scenario.


So, yes it seems the way to go wrt the WM is asking Rich to recommend / source a 24VDC motor to replace the AC one in one of his higher-output systems, or base off his engine-driven one.

I don't see how it would be that complicated.

But choices would good, if anyone can recommend an alternative, that would be welcome.
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Old 27-01-2018, 08:37   #148
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Re: Water maker comps

As I said yes the bank is LFP. Is 800AH 'huge'? Big enough for me I think.

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washing machines, blenders, toasters, coffee makers, vacuums, counter top ice makers etc.
None of these are important to me, even on land, or easily accomplished without AC.

And DC genny is just an alt, not necessarily high tech, and higher amps output means far shorter runtimes.

There are plenty of OTS DC gensets but not worth the expense IMO.

In any case all off topic for the thread, we can get into those details another time.
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Old 12-02-2018, 05:04   #149
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Re: Water maker comps

Very informative thread, indeed. Thank you fellows. Do someone have experience about belt driven WM:s?
That sounds good option to us because we do have free space in the engine room, and large diesel tanks. High output WM would make sense... to get 100 litres fresh water while loading batteres and/or motor-sailing one and half hours. And that would be enough water for two on board for several days.
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Old 12-02-2018, 10:01   #150
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Re: Water maker comps

Cruise RO do sell them, but Rich says less than 1% of their unit sales, complicated drive trains can cause more frequent maintenance issues than the electric ones.

So, of you are already setup to generate significant electricity, AC or DC, might be better to just size as high a gph unit as possible to suit that output.

But if you do go engine-powered, I'm sure with Rich's support it'll work fine.
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