12v dv vs 240v ac watermakers

davethedog

davethedog

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Morning,

Possibly looking at buying a watermaker for our trip next year and am looking at options for what type (12v or 240v). We have a 4kw generator already built in to the boat so can go for either type.

I know the 240V will produce more water/hr but it also depends upon the generator working all the time, with the associated maintenance issues etc. Although am I right in assuming that it could be run through an inverter in extremis?

But, am thinking that a 12v system would remove one "link" from the chain (the generator).

Thoughts please?

DTD
 
I build my own water maker , you find info here some where it wasn't not long I started a thread with some good info from others who also build their water maker , mine is 240v it works great given me around 80/90 LPH , I couldn't justify buying a new one , but if I was I would go for a 12v , yes they use a lot of power and don't give so much , but it just mean everytime your engine on is running it , replacing the power you use .
Although there a big advantage in building your own , your not tied down to one manufacturer parts and their prices.
I can get any part I need off the self .
 
Dave, you are doing the right thing, considering how the watermaker will be powered. This is the most important aspect when choosing the best model.

However, rather than a distinction between 12v and 240v the most important difference is between the energy recovery models (such as Spectra) and the non energy recovery models. There are 12v non energy recovery watermakers and even some 240v energy recovery watermakers.

The energy recovery process significantly reduces the power consumption and makes it practical to run the watermaker from solar, wind, or the engine alternator. The non energy recovery models can be 12v but the power draw makes it generally impractical to run these models for any significant time without a generator running, or at least a very large alternator.

Basically, if most of your power comes from a generator you are best choosing a non energy recovery (because they cheaper) watermaker. Make it as large as possible so you can make all the water needed in a short generator run time. If most of your power comes from alternative sources (solar, wind) you are better with an energy recovery watermaker. It can be reasonably small because there is no necessity to keep the run time short.

The above is a simplification, but it is a starting point.
 
From my experience, those that get the best from 12v energy recovery watermakers have a large solar array. They work best on catamarans where 1000w or more is not a problem. On monohull with typically less than 600w of solar a 12v watermaker works great when there is plenty of sun but when charging batteries from the nightly discharge and making water there is a conflict. It will obviously take longer to charge the batteries. If there is no sun for a few days then you are likely to need the engine on to make water. It is surprising how often our friends with 12v watermakers run their engine.
If you have a generator already then you are set up for high output watermarking. 250 l/hr is achievable with three 40" membranes. Generator run time is tiny and a low frenquency 3kw inverter as a back up in case of generator failure will still allow you to make water with the engine running for alternator output although the alternator won't keep up with the power demand. This is the set up we opted for. It works well for us and we wouldn't swap to 12v as the watermakers run times are too great and the energy recovery watermakers are expensive and complex. They work fine until they go wrong and parts of very expensive. I built my 220v watermaker from parts. Very happy with it
 
I have a Spectra one running from 12V and find that its energy consumption is pretty irrelevant compared to the 'fridge and, if underway, the autopilot. It only takes around 9A at 12V and I only have to run it for a couple of hours every couple of days. Hardly a problem for the 600AHr battery bank.

Choosing the best size - by which I mean litres made per hour - is another factor which I think merits thought.

One view is that you should get the biggest you can afford / fit because that way you can take advantage of spare electric power, eg when the engine is on, and do not need to make water for several days in between.

Another view, which I share, is that the real pita of watermakers is keeping them clean and hygienic between uses. Like diesel engines they thrive on use, and if being left you have to do some fiddling, as follows:
- leaving <48 hrs: Just turn off, an then when restarting discard the first few (3-ish) litres. And actually we use this gash water to rinse rigging and other stainless bits.
- leaving < 1 week: flush the seawater out with fresh water before turning off. Easy enough to do, but note that this consumes the amount of fresh water that you can make in about 30 minutes running.
Longer and you have to pickle them. So I find that it's best to run the watermaker every other day. How long for? Perhaps an hour. So imho there's little point in having one bigger than one which makes in an hour more than you consume in a day or two.
 
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jdc said:
I have a Spectra one running from 12V and find that its energy consumption is pretty irrelevant compared to the 'fridge and, if underway, the autopilot. It only takes around 9A at 12V and I only have to run it for a couple of hours every couple of days. Hardly a problem for the 600AHr battery bank.

Choosing the best size - by which I mean litres made per hour - is another factor which I think merits thought.

One view is that you should get the biggest you can afford / fit because that way you can take advantage of spare electric power, eg when the engine is on, and do not need to make water for several days in between.

Another view, which I share, is that the real pita of watermakers is keeping them clean and hygienic between uses. Like diesel engines they thrive on use, and if being left you have to do some fiddling, as follows:
- leaving <48 hrs: Just turn off, an then when restarting discard the first few (3-ish) litres. And actually we use this gash water to rinse rigging and other stainless bits.
- leaving < 1 week: flush the seawater out with fresh water before turning off. Easy enough to do, but note that this consumes the amount of fresh water that you can make in about 30 minutes running.
Longer and you have to pickle them. So I find that it's best to run the watermaker every other day. How long for? Perhaps an hour. So imho there's little point in having one bigger than one which makes in an hour more than you consume in a day or two.
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Or you run a bigger one for 1/2 hr every three days. Rinsing with product water is a none issue in terms of used water as you have an abundance of water so leaving it for a few extra days is not a problem. We found big is best but it depends on how you cruise and where you are. If you are in a dirty harbour and you don't trust the local tap water you can nip out of the harbour for an hour or two and make 1/2 ton of water. If you have guests on board then water consumption doubles or triples. No problem. You can make lots. The big charter cats over here in Curacao makes 500 litres per hour on their watermaker for good reason.
Watermakers can be very simple devices if you opt for none energy recovery. They are very reliable if you keep them simple.
if I hadn't built my own we would probably have installed an Echotec unit made in Trinidad. They are cost effective. £5600 gets you 260 l/hr on 220v. We make 210 l/hr but mine cost me £2.5k to build
 
geem said:
Or you run a bigger one for 1/2 hr every three days. ...
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As I said, it's worth thinking about; I wasn't being too didactic I hope and I tried to represent the two views fairly.

But it strikes me that running the watermaker for 30 mins to make water, and then another 30 mins just to make flush water, seems somehow inefficient. Maybe a bigger watermaker than mine (Spectra Ventura 150) would use less than 30 mins worth of fresh to flush (the volume of the filters probably doesn't scale up with capacity, although the volume of the membrane housing does) and that would tip the balance. But worth checking in the manual imho.
 
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geem said:
This is the set up we opted for. It works well for us and we wouldn't swap to 12v as the watermakers run times are too great and the energy recovery watermakers are expensive and complex. They work fine until they go wrong and parts of very expensive.
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You will find the energy recovery high pressure pumps are very simple. One of their advantages is that they are much simpler than a conventional high pressure pump. The high pressure pump does not even need an electrical supply!

Anyway, Spectra offer a lifetime warranty on the high pressure pump (for the original owner).

In any watermaker discussion you will find two camps divided between favouring a relatively low volume, energy recovery water maker and a high volume, non energy recovery watermaker. Often one side cannot possibly understand why anyone does not want the solution that works well for their situation. In truth, both solutions can be best depending primarily on how the watermaker is powered.
 
noelex said:
You will find the energy recovery high pressure pumps are very simple. One of their advantages is that they are much simpler than a conventional high pressure pump. The high pressure pump does not even need an electrical supply!

Anyway, Spectra offer a lifetime warranty on the high pressure pump (for the original owner).

In any watermaker discussion you will find two camps divided between favouring a relatively low volume, energy recovery water maker and a high volume, non energy recovery watermaker. Often one side cannot possibly understand why anyone does not want the solution that works well for their situation. In truth, both solutions can be best depending primarily on how the watermaker is powered.
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I think that is what I was trying to say, but maybe badly. If you have a large cat with 1000-1500w you don't need a generator. Energy recovery watermakers are ideal for this scenario. We know several people who have this set up and it works for them.
It becomes less ideal when your solar panel space is limited. If you already have a generator then 220v is a very viable option, especially if space for lots of solar is limited.
 
jdc said:
As I said, it's worth thinking about; I wasn't being too didactic I hope and I tried to represent the two views fairly.

But it strikes me that running the watermaker for 30 mins to make water, and then another 30 mins just to make flush water, seems somehow inefficient. Maybe a bigger watermaker than mine (Spectra Ventura 150) would use less than 30 mins worth of fresh to flush (the volume of the filters probably doesn't scale up with capacity, although the volume of the membrane housing does) and that would tip the balance. But worth checking in the manual imho.
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If you run the watermaker for 1/2 an hour every three days you don't need to flush it. Flushing it uses a tiny amount of water. We make over a 100 litres in half an hour so maybe 10 litres to flush if you are leaving it unused for a few days
 
geem said:
I think that is what I was trying to say, but maybe badly. If you have a large cat with 1000-1500w you don't need a generator. Energy recovery watermakers are ideal for this scenario. We know several people who have this set up and it works for them.
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I think we are agreed that if the primary power is:

Solar = Energy efficient watermaker
Generator = High capacity non energy efficient watermaker.

(The above is a guideline, not an absolute rule)

However, I would suggest that 1000 -1500w of solar is not needed. The energy efficient watermakers are perhaps not surprisingly energy efficient :).

Our previous boat had 340w of solar. 95% of our energy was solar. An energy efficient watermaker produced nearly all our water. We collected some rainwater in winter, but otherwise an estimated 70,000 L was all watermaker water.

This is not the ideal for everyone. If you use a generator, an energy efficient watermaker is generally a waste, but if you want to run a watermaker from solar, energy efficiency is the only realistic option. The good news is power draw becomes low enough that even a medium sized solar array can run a watermaker.
 
noelex said:
I think we are agreed that if the primary power is:

Solar = Energy efficient watermaker
Generator = High capacity non energy efficient watermaker.

(The above is a guideline, not an absolute rule)

However, I would suggest that 1000 -1500w of solar is not needed. The energy efficient watermakers are perhaps not surprisingly energy efficient :).

Our previous boat had 340w of solar. 95% of our energy was solar. An energy efficient watermaker produced nearly all our water. We collected some rainwater in winter, but otherwise an estimated 70,000 L was all watermaker water.

This is not the ideal for everyone. If you use a generator, an energy efficient watermaker is generally a waste, but if you want to run a watermaker from solar, energy efficiency is the only realistic option. The good news is power draw becomes low enough that even a medium sized solar array can run a watermaker.
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I don't disagree but to add a third option, engine driven. Again it makes sense to run the engine for as short a time as possible so maximum output with three 40" membranes circa 250 l/hr is possible. We have friends that are very happy with this system. They run it entering or leaving a harbour to fill there tanks. The additional hours on their engine are negligible.
One question, do you routinely leave your watermaker running whilst you go ashore? I always found with my old 12v system that I would rather be onboard when we were making water. For a low output machine this was a pain as you were stuck aboard. I am still stuck aboard now we use the 220v system but never for more than an hour. Maybe I was just being too nervous that something would go wrong
 
geem said:
I don't disagree but to add a third option, engine driven. Again it makes sense to run the engine for as short a time as possible so maximum output with three 40" membranes circa 250 l/hr is possible.
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This can work well. We had an engine driven watermaker on a previous boat, but the high pressure pump was belt driven from a seperate 12v generator (a 15hp diesel) rather than the main engine. For the main boat engine, installing a couple of large alternators rather than an engine driven watermaker is another option. The alternators are easier to mount and more versatile because they can be used to make water (indirectly) or electricity as required.

geem said:
One question, do you routinely leave your watermaker running whilst you go ashore? I always found with my old 12v system that I would rather be onboard when we were making water. For a low output machine this was a pain as you were stuck aboard. I am still stuck aboard now we use the 220v system but never for more than an hour. Maybe I was just being too nervous that something would go wrong
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On out new boat we have not installed the watermaker yet. The deck rain collection system is working so well that I am in no rush. We can collect more water than we could possibly use. At the moment it only drizzling, but we are collecting about 75-100L an hour using no electricity and with no noise. It is even better than solar :).

I share your concerns and don’t like leaving machinery running when away from the boat as a rule, although I have often gone for a swim etc with the watermaker running. Our system is not automated so it requires manually shutting off.

With our previous boat we made water every second or third day for two to three hours so it no great hassle to arrange this at a suitable time. The low power draw means it can be run at any time. The only real restriction is, if not run for five days it needs another rinse, but this only takes 5 mins. Even a relatively small boat water tank provides a large reserve, so watermaker runs can be at convenient times.

If plans change and you want to go ashore, just turn off the watermaker and start it again (or not) when you return. Even with a completely manual system such as ours starting and stopping only requires a few valves to be changed and the circuit breaker flipped. There is no generator or main engine to start/stop, as the watermaker is running from battery power/solar.
 
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