Water Maker AC Or DC

[Jsta_Rebel]

Originally Posted by SV THIRD DAY

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.

Do your systems offer a post fresh water flush option and choice of membrane manufacturer? I ask because the price you quoted is pretty good.

Thanks,

TSG Water Resources.

[SV THIRD DAY]

Originally Posted by Jsta_Rebel

Do your systems offer a post fresh water flush option and choice of membrane manufacturer? I ask because the price you quoted is pretty good.

Regarding the Membranes:
As a liveaboard cruiser myself there is nothing I detest more than the proprietary parts game, which translated to Cruiser Speak means "screw you". So we use the off the shelf Dow Filmtec SW30-2540 RO Membrane and sell them for $197ea. Some manufactures have special size membranes built out of the same membrane film so now they cost $1200...that is nuts! Other manufacturers use the standard Dow SW30-2540 membrane, but change the label or won't tell you the type and hit you for $500. Now they will tell your their membrane performs better to justify it, but that is just sales and marketing hype. I even heard once that Dow sells the top performing membranes to them and the lower performing to us, which is why we sell them so cheaply. That is total BS.

Regarding the Fresh water flush:
The water maker comes standard with a manual fresh water flush, you turn on the boost pump and turn a 3-way valve for 4-5 minutes.
Or for $595 you can add on the Automatic Fresh water flush and just turn the panel switch to "Auto" and the water maker will automatically fresh water flush at your set interval (we recommend every 4-5 days for 4-5 minutes in duration).

[fallingeggs]

Originally Posted by SV THIRD DAY

It's fools gold...

...basically forget about powering that from your batter bank.

That depends on how much "free" energy you think you have. By that I mean, how many amp hours are you not capturing from solar or your alt because the LiFePO4 bank is full? With a decent size solar rig and high output alt (along with normal motoring around), and fairly low electrical demands elsewhere, it might be a sizable chunk that could be diverted to running the 80 amp motor.

Just thinking out loud here. Need to figure out how much "free" energy I might have first. I do give you that 80 is a large number to have to replace every few days.

(PS, if 80 amps is for a full 1hp and you're running the 1.6 gpm pump at lower than its max psi, I wonder how many amps are really used?)

[SV THIRD DAY]

Originally Posted by fallingeggs

(PS, if 80 amps is for a full 1hp and you're running the 1.6 gpm pump at lower than its max psi, I wonder how many amps are really used?)

1.0Hp 12v DC motor coupled to a 1.6GPM pump...80A at 800PSI.

[Jsta_Rebel]

Originally Posted by SV THIRD DAY

Regarding the Membranes:
As a liveaboard cruiser myself there is nothing I detest more than the proprietary parts game, which translated to Cruiser Speak means "screw you". So we use the off the shelf Dow Filmtec SW30-2540 RO Membrane and sell them for $197ea. Some manufactures have special size membranes built out of the same membrane film so now they cost $1200...that is nuts! Other manufacturers use the standard Dow SW30-2540 membrane, but change the label or won't tell you the type and hit you for $500. Now they will tell your their membrane performs better to justify it, but that is just sales and marketing hype. I even heard once that Dow sells the top performing membranes to them and the lower performing to us, which is why we sell them so cheaply. That is total BS.

Regarding the Fresh water flush:
The water maker comes standard with a manual fresh water flush, you turn on the boost pump and turn a 3-way valve for 4-5 minutes.
Or for $595 you can add on the Automatic Fresh water flush and just turn the panel switch to "Auto" and the water maker will automatically fresh water flush at your set interval (we recommend every 4-5 days for 4-5 minutes in duration).

It pleases me that your using good quality membranes. My question wasn't mentioned to imply proprietary where I share your opinions. I'd like to see some drawings and cut sheets on your systems. FYI, We do industrial systems ONLY. Nothing less than 50,000 gpd in a containerized plant. My personal water maker I have aboard runs a cat pump off or the main engine producing 1.2 GPM. I'm a big believer in freshwater membrane flush as I have seen personally through membrane autopsy the amount of degradation that occurs within the membrane when it is not done. Thanks for your response.

[Tellie]

Spectra tends to be typecasted as the low out put low voltage systems. But we make extremely energy efficient AC systems as well. Though these are usually for higher end boats whose water needs are larger than the smaller cruising boat, these systems are engineered for light weight, small foot print, and low power requirements. I have units that will make 130 gallons per hour using only 1200 Watts. Hey, you could literally use your Honda EU2000 to fill your tanks and three neighbors tanks while still charging your batteries.


Halden Marine Services – Marine Watermakers, Solar Panels, Wind Generators

[Emerald Sea]

Considering your size of genset and with excess DC energy available, your philosophy of purchasing a combined DC/AC watermaker is the right one. Why wouldn't it be? We have an AC/DC unit and use it in this same manner. It also offers redundancy should one of the two motors should breakdown. Ours is a Dessalator DUO100 which has been 100% reliable since new, over two years of liveaboard constant usage. Cheap and readily available 5micron filters also.

[sailjumanji]

It's not what the cat owner is looking for, but just wanted to say we installed a spectra 150d for our cruise thru Florida and Bahamas. Been cruising over two months. Still here in Berry's at the moment. Ran the watermaker off of solar panels. We use about ten gallons per day and the spectra made between 7 and 7.3 gal per hour at probably around 8 amps. The panels ran a bit above 13 volts in the bright sun, which I understand is the reason it performed above published specs. Ran the watermaker about every second or third day. No issues at all. No skimping on water, no hauling jugs, no running a generator. And whoever said the spectra is noisy, well, not mine. It's a bit of a low hum. We heard some noisy water makers on other boats, and those guys couldn't believe how quiet mine was. My wife initially had concerns about spending the money, but a month into the trip was very happy. Fresh showers and dish washing, and rinse off after swimming. I even rinsed off some deck hardware and windows. And the water tastes great.

Thanks JT (Tellie) for the help in comissionIng. It has worked flawlessly. Will give you a call when it is time to pickle. Mike, with the catamaran, from Texas. You may or may not remember me.

[Jsta_Rebel]

Originally Posted by Tellie

Spectra tends to be typecasted as the low out put low voltage systems. But we make extremely energy efficient AC systems as well. Though these are usually for higher end boats whose water needs are larger than the smaller cruising boat, these systems are engineered for light weight, small foot print, and low power requirements. I have units that will make 130 gallons per hour using only 1200 Watts. Hey, you could literally use your Honda EU2000 to fill your tanks and three neighbors tanks while still charging your batteries.


Halden Marine Services – Marine Watermakers, Solar Panels, Wind Generators

You mention low power costs but failed to add documentation with reference to power costs in kw/gallons of production. Also, does spectra have any sort of guarantee with power usage per 1000 gallons produced?. if you have any power documentation, would you please post it??

Thanks in advance.

[Jsta_Rebel]

All SWRO manufacturers have documentation regarding power usage per 1,000 gallons of permeate (product water) produced. Knowing how much power you are going to use to manufacture your water is an important factor when deciding on a system. Membrane flux rates as well as recovery rates ( percentage of feed water recovered as permeate) are important factors used in this calculation as well as is the brand and type of motors used to drive the HP pump and the LP seawater feed pump. These power costs vary greatly between manufacturers. Unfortunately, with exception of Matrix which manufactures larger systems for larger ships, I have not seen these factors readily available to the public which is why I asked the gentleman for his. Also ask about whose membranes are being used in the system. The one gentleman I asked politely answered Filmtec membranes which are top shelf membranes. The system membrane and pump system is the heart and soul of the water maker which is why it is important to ask these questions when purchasing one. With a water maker, you get what you pay for so unless you are building one yourself which many boaties do, make sure you thoroughly check out what the components that make up your water maker are. Questions include; is the pump liquid end made of duplex stainless, bronze or plastic. No way I'd buy a system with a plastic HP fluid end. Waste of money. Bronze ends are ok, but this needs to be taken into consideration when comparing systems. The type of pump is also important. Is it a plunger style pump? Does it come with spare packing sets or valve sets? Are they available for purchase, and how long will they typically last?? also ask what components are included in the warranty and what are not. Typically, you will find that your water makers pump warranty is whatever the pump manufacturer has listed and sometimes is not included in the overall warranty of the water maker. These systems are not cheap by any means, so do yourselves a favor when purchasing, and check things out thoroughly so you don't get surprised after it's installed. I'm also a fan of freshwater flushing of the membranes as this will increase the membranes life and insure quality permeate water with minimal permeate wash down (the amount of poor quality water that enters your storage tank as the membranes wash down to quality after start up).

[downunder]

Originally Posted by SV THIRD DAY

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.

There is a chap in Cairns who built himself a small powercat running outboards and solar panels who is running both his watermaker and scuba compressor off inverter AC by using variable speed drives (similar to inverter air conditioners - he is a air con/electrian). Indicates some interesting possibilities for a cat with over 1kw of solar panels.

Very interesting

"Groper watermaker

I dont think its a s simple as that Alan... the permeate flow rates given by DOW on their membrane is onlt a data point at a specific test condition ie water temp, pressure, total flow rate, recovery rate = 8% etc... its not an indication of what you always get.

Looking at the specs of the efficient marine watermakers, without energy recovery devices, they seem to share one thing in common. They reduce the speed of the pump so the total high pressure flow rate is small, whilst keeping the membrane suface area the same (2540 size). This results in a higher recovery rate of somewhere near 20% - not the 8% data point quoted by dow in their specifications. The problem with doing this in a simple DIY setup is that its very difficult to direct couple the pump to a motor which only turns at circa 500rpm. all of the single phase induction motors and most of the DC motors ive looked at spin at a minimum of 1400rpm and thus move alot more water than is required in order to get the 20% recovery rate. Echotec uses a gear reduction pulley system on theirs, but i dont want that extra complexity. I think where its heading for me, will be a 940rpm motor which is driven via a variable frequency drive so i can slow it down to circa 500rpm. The drive adds an extra $300 to the cost, but it also allows flexibility in terms of flow rates and power consumption... An 240VAC induction motor plus variable speed drive ($600) still costs less than a 375w 12vdc motor on its own...

Once i get this all up and running, the efficiency should not be too far different to the commercial units, the only difference being a slightly lower motor efficiency of im guessing around 10% compared to a brushed DC motor...

No plans mate - we are designing the system and building them ourselves...

All the parts are available in australia - however we have chosen to source some of the more expensive bits from the USA as saves quite a bit of money compared to local prices...

The system consists of a saltwater lift pump - im using my jabsco deck wash pressure pump, - tee off a low pressure line to the desal system;
A couple of prefilters - the washable type - 20micron and a 5 micron in the plastic housings etc and a low pressure guage - to detect blocked filters etc;
the high pressure pump - Stainless steel CAT pump 2sf15seel - driven by a 750w rated single phase 4 pole 240vac induction motor - sourced and modified locally to fit the imperial pump mounting flange to a metric frame electric motor;
high pressure housing and membrane 2540 size, high pressure guage, and Stainless needle valve to control brine pressure;
A few lines and Y valves etc for diverting water to tanks, buckets for testing, and freshwater flushing etc;
Manual TDS meter to test product water before collecting.

Its all pretty simple, designed to be reliable, and low cost. the high pressure pump motor runs off the 240v inverter - which is probably the weakest link in the systems reliability - im contemplating keeping a second inverter on board in case it fails - they are cheap enough at $200 for a 2kW pure sine these days...

projected power input is about ~45amps inc the 10% inverter loss, and the water output should be around 48L per hour... total cost is under $3500...


Good news - my variable speed drive arrived on friday and i connected it all to the dive compressor... it ran fine on plugged into the mains but kept tripping the inverter when i tried to run it from the boat... good news is i added an inductor to the line as a line filter and everything is now ok - the variable speed drive generates quite a bit of noise and harmonics on the incoming power supply which the inverter doesnt seem to like much - it wasnt a current problem - the unit only draws 9amps at 240V and that is happening once the compressor is upto full pressure...

And one more thing about big motors...

Induction motors typically use between 5 and 8 times their full load current on startup - its called inrush current, and its so large because the rotor is not turning and their is no inductive reactance to provide any other impedance to current flow. Only the resistance of the stator coil is there until the rotor gets moving, and typically a small induction motor like this will have a stator winding resistance of a few ohms - like 2-4ohms or similar. If you apply DC theory to that youll know that current I, = v/R. If you assume a winding resistance of 3 ohms (about typical) then you should see 240v/3ohms = 80amps @ 240VAC - woah! But yes its true if only for a split second... So why does the running current of the motor look more like 4 amps? As the rotor builds speed, it interacts with the magnetic field of the stator and you have a conductor moving in a magnetic field - so the rotor generates a back EMF which opposes the current flow - so even tho the winding resistance is still 3 ohms - the inductive reactance is also at play and adds to the resistance to give a total impedance. Impedance refers to circuits which are generally AC in nature and can be not just in the form of copper resistance like in DC theory, but also inductive reactance, and capacitive reactance which occur in AC circuits but have the same effect - more impedance mean less current flows...

The problem with motors runn from inverters is tripping the overload protection of the inverter. If you try to start an electric motor and it pulls in excess of the burst current rating of the inverter - it will trip out and you loose all power until it resets and repeats. Net result is you cant get your motor moving and your SOL... So you need a big rating on the inverter so the inrush current wont trip it before it gets moving. Once the motor is turning, your all good provided the motors electrical power input (remember you also need to account for power factor on an AC motor - typically 0.8) doesnt exceed the maximum continous current rating of the inverter. So my 3000w -6000w burst inverter will have an instant trip at 25amps (6000/240) and it will be able to sustain a current of 12.5amps - which is only 3000w at power factor = 1. Its less than 3000W as the power factor drops - which it will do with induction motors running off it - 2400W if you assume PF = 0.8 as the current is still 12.5A...

This gives you the idea as to why generators are rated in KVA and not KW - they dont know what the power factor will be as it depends on the loads the consumer connects to it!


So now i have a 2.2kW scuba tank filling compressor running from my 3kW inverter - powered by solar (and engine alts if need be)

The compressor isnt as nearly as noisy as the petrol engine powered versions - obviously there isnt a combustion engine running it. But its still noisy, just the pistons of the compressor do make a bit of noise - at full speed its the same as any other small size electric motor and belt driven air compressor you would run for air tools and spray painting etc

The good thing is now i have full control of the RPM so i can slow it down a bit if i want to and the more i slow it down the more quietly it runs and the less power it uses - at 30hz it runs very quietly and uses nearly half the power... 35hz seems to be a good compromise on speed to fill a tank and noise levels are tolerable.

At full speed it fills a medium size tank in 20mins from empty, 15 mins if there is 50BAR already in it. Its output at full speed is 100L/min. So a 10L tank (85cu ft imperial) is 20 mins to input 200BAR.

Thanks for the tips on the watermaker - no doubt they will come in handy. I was going to add a rotometer for the product water flow but thought i wouldnt need it as i will be running it into a bucket for testing before diverting. I figured i would guage the flow from that as i collect a test batch before diverting it to tank... The maximum flow for these membranes is 115L /hour - youve seen it this high in real world use in estuaries?"

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efficient 10m displacement powercat (build thread) - Page 33 - Boat Design Forums

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[Wight Mistress]

Hi Folks,
Sorry if I am doing this wrong, I am a bit new to forums etc.
I have a Fisher 34 wheelhouse ketch and a friend has fitted a new watermaker to his 50ft(ish) Beneteau, giving us the old one, complete. It is a Balmar Aquapac Voyager and the CAT pump is on a belt wheel with a solenoid clutch. I have an extra take off belt wheel on my engine and for the next few years only intend to cruise around European waters. I do not have a generator and the solar I have fitted runs my fridge all on its own. Does anyone out there have any information, drawings, instructions etc that they could scan and send to me please? I wrote to Balmar and this morning received a nice reply. They haven't made that model 'over 15 years ago' and since moving buildings and having a clear out, they only have a 1990's vintage price list. Working on these systems being made of discrete modules, I want to rebuild it. (I did a chunk of work on a big watermaker on a boat in Oahu back in 06) so if anyone has any info please, muchly appreciated.

Regards

Steve White
SV Wight Mistress
Island Harbour Marina
Isle of Wight
England

[Kenomac]

And then there are cruisers like us, with a 7.5 kW generator using two spectra 380c units producing 34gallons per hour. Hopefully adding 400-500w of solar over the next few weeks. We buy parts from Tellie and Rich, both great guys with excellent service.

Boy, we're right in the middle..... We're like biaqua.

[SV THIRD DAY]

Originally Posted by Wight Mistress

I want to rebuild it. (I did a chunk of work on a big watermaker on a boat in Oahu back in 06) so if anyone has any

Hey Steve
We do that type of older system rebuild all the time. So the starting point is snapping some photos of the components you have and email those to me at Rich@cruiserowater.com We can then bounce back and forth with what you will need to get the system up and running based on the working parts you have.

As a cruiser myself, there is no obligation to buy anything from me, I'm just happy to help out another cruiser.

Cheers

[Wight Mistress]

Hi Rich, many thanks for your prompt response. I will email you some pics.
Currently I have another water system in bits (my bathroom in our house - 75 paces away from our boat) so it will be a week or so before I can get back to you. Emailing you now as well.
A huge thank you for your response, we really appreciate it.
Regards
Steve and Barbara