The New Pump In Action? Well, Not Really.
Once on the water I started the very appreciated, very professional, very expensive, very good-looking Danfoss APP by slowly turning the knob on the very appreciated, very professional, very expensive, very good-looking Hitachi VFD. And the water poured out of the brine through-hull: very appreciated, very powerful. I was overwhelmed.
So, I started to close the needle valve to increase pressure. At 20 bar / 290 psi the very professional 3-phase VFD-controlled AC-motor stopped. It was clear that it did not have enough power to run the Danfoss pump under pressure conditions. After several tries I gave up and connected the Karcher again. Everything went fine. Water without ending, even enough for our little washing machine that we have aboard since this summer. But I was sad. It was still the Karcher, not the very appreciated, very professional, very expensive, very good-looking Danfoss APP.
When we returned from our holidays I tried to find out what went wrong. I disassembled the whole watermaker to test it. And I knew I would not give up until I’d find the solution. But whatever I changed and tried, the result remained the same: The motor seemed to be too weak to run the watermaker. How could this be? A couple of days I made any test that came to my mind. Still no improvement.
One day, at about 10 p.m., I wrote my problem to an electric engineering forum. At 10 past 10 p.m. there was an answer: “Instead of a star-connection use a delta-connection.” (or was it the other way round?). After another hour or so I had learned from Wikipedia that AC asynchronous motors are usually run from 3-phase-electricity, which is (here in Europe) 400 V, compared to the 230 V “household” power line electricity.
When you use a VFD to convert the “normal” 230 V single-phase household electricity into a 3-phase-electricity you won’t get 400V. Therefore, you have to connect the motor in a different way, so that it works also with 3-phases at 230V. Otherwise it lacks power. Um …
The other morning, must have been 6 a.m., I went into the garden to the watermaker. Changing from star- to delta-connection (or was it the other way round?) was 3 screws and done within five minutes.
I turned everything on. I started to close the needle valve. The pressure went up slowly. It reached 20 bar / 290 psi. I went further and – it worked!
Now it works at incredible rates. With the Karcher I used 3/8”-hoses both for brine and permeate. I had to change to ½“-hoses for the brine, because it is really too much now! The production rate (with selfmade test seawater from the tank) has almost doubled! At those rates the power consumption is +20 per cent compared to the Karcher. If I stay at the same power consumption as with the Karcher the permeat flow is still 70 percent more than with the Karcher.
Another – probably even more important – effect has to be mentioned: The Karcher is at the lower end of the minimum flow rate that is demanded by FilmTec, which might lead to premature clogging of the membrane, in the long run. Now, with the Danfoss APP, the brine flow rate is high enough to flush the membrane when in use. So, this might extend the membrane’s life.
So far, we have no practical operating experience, as this all happened only after our summer vacation. But I shall update this section after our spring trip 2012!
Conclusion
Do you need the Danfoss APP plus the additional hurdles instead of the Karcher, or any other high-end pump from CAT, Wanner or so? Frankly speaking: No, not at all. The Kärcher-concept, which makes the whole thing so attractive, is a fantastic, reasonable way to start with watermaking. You learn how it works, the system does what is expected, at affordable costs. Even if you cross an ocean it might be cheaper and still reliable if you put 2 or 3 Karchers as spare parts somewhere on the boat. And should you once find that you want to up-grade, you still have this option. We do not need the Danfoss pump, we still could go on with the Karcher. But it is fun to play and try and tinker, isn’t it?