Watermaker - Best Power Supply

[Wandering Star]

I've just purchased a 230 volt watermaker on eBay. Problem is it's a big capacity watermaker (25 galls an hour) for my small boat! I only bought it because it was a bargain, a small 12 volt jobby would have been far wiser.

But having bought it I now need to consider what my options are for powering it. It needs a max 3.5Kw at startup reducing to 1.5Kw continuous draw in use. I don't want the expense of plumbing in a marine generator.

I've got 450 amps of house batteries, would an inverter solution work? How do I calculate the draw from my batteries. Would running the engine (90 amp alternator with Sterling smart regulator) replace the amps immediately? Does anyone else do this?

Otherwise how about a cheap Chinese diesel generator on deck but kept under cover? Another thread dealing with the shoddy Kipor fuel tap doesn't inspire me with confidence that a cheap generator will last the distance at sea though at only £600 for a 5 Kw model, if it lasted 2 years I 'd be quite happy and would treat it as a disposable!

Any other thoughts or ideas? I wonder if an engine driven pump could be used instead of the 230 volt pump? What type should I use? Are they expensive, can they be retro fitted?

Look forward to reading any comments.

Cheers, Brian.

 

[markdj]

If you have a 12 volt system then 1.5kW using an inverter would take about 140 Amps out of your batteries - like running a starter motor continuously but if you have a 24volt system it will be half that value, 70Amps approximately.

With a battery bank of 450Ah, usable approx. 220Ah you could run the water maker for about 3 hours for 24v, 1.5 hrs for 12v if your batteries are in peak condition.

You could run the watermaker while under way which will be a heavy load on your alternator or using a generator would be the best option.

Mark
www.boatdoctorni.com

 

[seamaster30]

With a battery bank of 450Ah, usable approx. 220Ah you could run the water maker for about 3 hours for 24v, 1.5 hrs for 12v if your batteries are in peak condition.

www.boatdoctorni.com

If you had a 450AH bank of 12v batteries wired to give 24v it would only yield 225ah at 24v - you would only get 450AH at 12v - so the power you can draw is the same - you can just get away with smaller cables on 24v (although I think the batteries would survive better in the 24v scenario due to the high load)

 

[William_H]

Powering your watermaker

I would suggest you consider fitting a 250V AC generator (alternator) to your engine driven by an added belt off the front of the engine. I think you will get into trouble and have huge inefficiencies trying to run it off 12v via an inverter. You will have to choose a drive pulley ratio to give the correct speed for the alternator to give 50 hertz (3000RPM or 1500RPM) and always run the engine at that speed when making water or using the 250V AC.
You may find the watermaker uses an induction motor (like a fridge) which really needs pure sine wave AC
hence you would need a sine wave inverter (more expensive) or a generator with pure sine wave o/p (often indicated by an engine that runs at constant speed ie 3000 or 1500 RPM)
good luck olewill

 

[nimbusgb]

An inverter rated at 3.5kw is going to set you back the price of a small boat! When your watermaker starts up is will draw 300 amps ( and some ) out of a 12v bank. Just the pieces of cable to the inverter will cost £50 or so.

( beginning to see why this was a cheap unit )

Is there any way to derate the unit? Perhaps fitting a much smaller drive motor geared down will solve two problems at once. It will reduce the amount of water you get out and reduce the power you need to put in.

> It strikes me you might just have purchased a domestic unit that will be fitted with membranes unsuited to saltwater useage. <

 

[PaulJS]

Ebay bargain?

It might feasibly be worthwhile contacting the manufacturer to see if they do a 12v or 24v dc version and if they could supply, or very optimistically part exchange your 230v ac pump/motor.
Failing that fit a smaller 12/24v dc driven pump that will have lower power requirements and will reduce the permeate quantity supplied. Also if it is fitted with more than one permeator pressure vessel and you can obtain a smaller capacity HP pump you can simply reduce the output by reducing the number of them and changing the pipework to suit.
You should be able to adapt the control circuit so that the main pump is fed from your dc supply and use a small inverter to supply the control circuitry.
I'm guessing that it will be fitted with standard 2 1/2 inch diameter membranes, if so you can probably buy suitable sea water membranes off the internet.
However if it was not designed for sea water use please ensure that the permeator pressure vessels are capable of withstanding the higher pressures required, they will probably need to be rated at 1000psi
Good luck!
Failing the above, I would suggest putting it back on ebay!!

 

[markdj]

If you had a 450AH bank of 12v batteries wired to give 24v it would only yield 225ah at 24v - you would only get 450AH at 12v - so the power you can draw is the same - you can just get away with smaller cables on 24v (although I think the batteries would survive better in the 24v scenario due to the high load)

He didn't specify whether he had 12 or 24 volt system so I was covering both scenarios - he could have 4x110Ah for a 12v system or 8x110Ah for a 24v system; both systems having a 450Ah capacity.

An AC alternator isn't a good solution as you will never get the correct frequency to run at 50Hz unless you use a digital RPM meter on the pulley so that is, in my opinion, unworkable.

Nimbusgb has a very good point - your filters may not be suitable.

I think either use a generator or up on ebay and get a Spectra watermaker which will work off 12volt - I think Furneaux Riddall do them.

 

[Wandering Star]

Thanks for all the advice, very useful opinions. As a result I've decided against an inverter, I've also decided against a diesel driven generator as they seem massively heavy and will take up deck space. I did actually consider the AC dynamo solution but after reading the comments here have decided against that too.

So I'm left with a mechanical pump solution run off the engine or to ask fNimbusGB for more information/explanation about what he means re reducing the output etc - how do I achieve that?

Actually, I think the problem may be practically unsolveable and I'm sort of kicking myself now for being so impulsive, I'm just such a sucker for a bargain! I was looking for a 12 volt low output system when I spotted that beauty! So I've posted on the Liveaboard forum to see if there's anyone there with a smaller 12 volt system who would like to swap for my laarger 220 volt system. A bit of an unorthodox solution!

By the way my boat is plumbed for 12 volts throughout.

Thanks again for your comments and advice.

Cheers, Brian.

 

[nimbusgb]

PaulJS had the right approach. Could you downrate by going to some sort of 12v DC geared motor to drive the existing gubbins.

Before going any further i'd try to sort out the question about the membranes first. They are the expensive bits.

 

[Wandering Star]

It might feasibly be worthwhile contacting the manufacturer to see if they do a 12v or 24v dc version and if they could supply, or very optimistically part exchange your 230v ac pump/motor.
Failing that fit a smaller 12/24v dc driven pump that will have lower power requirements and will reduce the permeate quantity supplied. Also if it is fitted with more than one permeator pressure vessel and you can obtain a smaller capacity HP pump you can simply reduce the output by reducing the number of them and changing the pipework to suit.
You should be able to adapt the control circuit so that the main pump is fed from your dc supply and use a small inverter to supply the control circuitry.
I'm guessing that it will be fitted with standard 2 1/2 inch diameter membranes, if so you can probably buy suitable sea water membranes off the internet.
However if it was not designed for sea water use please ensure that the permeator pressure vessels are capable of withstanding the higher pressures required, they will probably need to be rated at 1000psi
Good luck!
Failing the above, I would suggest putting it back on ebay!!

Thanks very much for your useful input.

The watermaker is definitely designed for seawater use, I know someone who has a Sea Recovery watermaker and it's fantastic and very reliable, one of the best. The specifications can be seen at http://www.beardmarine.com/uwm.html

I had already approached the main distributors of this watermaker and they reported the manufacturers recently dropped a 12 volt option for the model I have which is the Ultra Whisper Modular 600. However if you look towards the bottom of the specifications sheet, they do list a 12 vdc model for the 400 model which draws 22amps.

I don't really know much about watermakers except that I'd like one! Can I take my 600 spec down to 400 spec using simple DIY? If that's possible, all I need is to purchase the 400 model 12 vdc motor. Any reduction in water making output by making the change would be considered a positive rather than a negative! If that's not feasible, perhaps you could advise me what exactly I'm looking for in terms of sourcing a suitable 12 vdc motor able to handle the high pressures?

Cheers, Brian.

 

[PaulJS]

Hi Brian, I was a bit confused by the description of the "energy conversion device" so I did a bit of googling. It's quite an ingenious device which appears to use differential pressures to generate the high pressures required.
I had assumed that your system had a low pressure feed and a high pressure pump which was the real power hungry item. It looks as though it might be feasible to simply replace the system pump for either a dc motor or engine driven one of similar flow and pressure capacities, or even arrange an alternative drive to the present pump. It would appear that the controls are dc supplied anyway, the circuit diagram if any, will have a step down transformer for ac use - you might be able to connect your boats dc supply directly if it's in the same range, although marine control circuits are more often than not 24 volts dc.
If you do manage to either use the present pump with an alternative drive or fit a similar capacity pump it will be more simple to retain the present output capacity and simply run the watermaker for only as long as required on a regular basis.
RO systems will quite happily stand idle for 24 hours so it would be easy to run the plant for an hour or two per day just to keep tanks topped up, but for longer periods of idleness follow the instructions about chemical treatments.
While googling I found one very dissatisfied customer (http://www.cruising-newcaledonia.com/water-makers-desalinators-comparisons.html), but he raised some very good points about the quality of components, it might be worthwhile replacing any chromed brass with good quality stainless, and apparently all of the fittings are US standards so it would be worthwhile finding a reliable and knowledgable source.
I've been a marine engineer since sails were still fitted and I still can't figure out the American threads!
Anyway, good luck! Keep us up to date on the saga...