View Full Version : Inverter powered watermaker

09-11-05, 20:38
Anybody out there using a watermaker powered by their 12v batteries through an inverter. If so, what capacity watermaker and what size inverter? Spectra (USA) have just advised me that they can get 190 litres per hour from 750 watts!! Seafresh tell me they need a 6 kw generator for a 60 litres per hour watermaker - totally confusing to me!!!!

Many thanks.

10-11-05, 08:37
I have a village marine water maker 12v high pressure pump no inverter the book says 60 litres an hour probably more like 40 .
ps. does anyone know a source of cheap membranes ?

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11-11-05, 08:00
It is a bad idea to power a watermaker from an inverter, there are two sorts of watermaker, low voltage DC driven ones and mains driven, they are quite different beasts. As you know they work by producing a very high pressure and forcing sea water through a spm, some water comes out virus/bacteria/salt free, most of it goes back to the sea. Mains driven ones produce a high flow rate for short period of times, because of the type of motor they use a modern sine wave invertor will not work efficiently, you will notice the motor will run warmer than if you used the shore mains. A DC driven watermaker produces a lot less water per hour but power per drop is much better, this is because the design is different and the pump is lot more complex, quite often the high pressure discharge side is also pumped meaning that the pump is double acting with high pressure on both sides of a reciprocating unit which makes the installation way more efficient. They still consume a fair bit of power but power per drop is a lot less. (Obviously mains driven ones are not designed to be efficient, the emphasis is on max water flow in a given time to minimise generator run time).

If you install one of these, fit an extra isolator next to the watermaker so that when the unit is in 'storage mode' it remains off even if somebody accidently turns on the CB, also you will find it so much easier if you install a nrv between the brine diverter and the hp waste and fit a few extra ball valves so the unit can be stored, cleaned and tested. That way you can run the water maker and divert the output into a glass jar which you can sample and see what it tastes like before adding it to your tanks.

On the subject of cheap spm, of course what they are made from means that they wont be cheap! A knacked spm probably isnt really knacked just clagged up, if soaked in the the proper acid and kept warm overnight (ie next to a fan heater), then flushed through for a day with clean fresh water (ie ask the watermaker to make water from fresh water but discharge the results) then soaked in the alkaline solution the following night (and kept warm), then once again making fresh water from fresh water for a day, it might well recover. If this still doesnt work there are kill or cure techniques available!

11-11-05, 12:05
Many thanks Paul. I thought that there must be a catch -otherwise we would all be running them off inverters. I shall advise my Swedish friends.

11-11-05, 14:04
Paul you are obviously the man to talk to ! my water maker has been pickled in metabisulphate for the last 10 months and 4 days ago I decided I'd ought to try it so after changing all the filters and bleeding the sytem it eventualy after some time rose to 800 psi and started to produce water from the sample pipe - however even having run it for a couple of hours or so every day since it still tastes a bit salty!
any advice you can give me would be great. eg what type of acid / alkaline etc to clean the membranes
thanks Pete

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