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Old 22-05-2010, 15:32   #16
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Very Good thought Nauticatarcher and it was one of my first ideas after I upgraded my DC capacity along with a new Victron multi 3000w/70amp Inverter/24v Charger.

But I was told by the local electrical tech that the start-up load on my System 9 pump motor which is 220/240 AC 50/60Hz is too much for the inverter, so I never tried.

Perhaps some electrical gurus can confirm this for me the size of inverter needed as the specs say pump motor is rated at 1.6hp and consumes 2Kw under load, but does not indicate start-up load as the plate is worn out.

I wonder if it would be practical to find a dedicated inverter for this load, so that I could keep the pump AC for Gen use but switch to inverted power when sailing.

No idea how big a beast that inverter would be… does anyone have an idea?

Edit: Just read yours Paul... you guys have me excited about that option

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Old 22-05-2010, 16:32   #17
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That is a very nice inverter you have. Two options: The spec sheet says it can handle a peak load of 6 kW, so it may be able to handle the start-up. According to this page ( ), the start-up load should be just under 6 kW If it were me, I would try it and see what happens. Of course, make sure all other loads are off.

Also, those units can operate in a UPS function and switch on in 20 milliseconds. You can always just start the motor on the genset for 30 seconds and then switch off the genset and let the inverter take over.


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Old 22-05-2010, 17:19   #18
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When we tested we found the Victron specs a bit optimistic and did not take into account any line loss which we calculated at about 15% for my installation.

That is a nice link for calculating loads (although I feel a headache coming on)

Lacking a code plate I used Chart B to estimate code K for my 1.6 Hp motor

Then following example to calculate LRA (for single phase) I got:

1.6 x 8.99 x (1000/240) = 14.92 x 4.167 = 62.17 amps (LRA)

So if my math and understanding is correct the inverter must produce 62.17 amps at 240 to start the pump motor so that is 62.17amps x 240volts = 14,921 watts of inverter power would be needed.

Did I do this wrong?
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Old 23-05-2010, 05:34   #19
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Originally Posted by Paul Lefebvre View Post
... According to this page ( SIZING A GENERATOR FOR ELECTRIC MOTOR LOADS ), the start-up load should be just ...
About NEMA Design Letters & Locked Rotor Code Letters
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Old 23-05-2010, 10:33   #20
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Devices are available to reduce the start up spike. Here is one sold for a marine air conditioner:
products - Dometic

Don't know if it would work for your watermaker but if not something similar probably is available.
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Old 23-05-2010, 12:54   #21
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There have been some advances in RO technology, primarily in efficiency, in the last couple of years. The engineers have manages to help the high pressure pump do a bit less work thereby saving some power. You might consider looking at that technology.

I'm giving serious consideration to an RO on my personal sailboat, even at the expense of not having radar. I don't want a big one and would be happy with 80gpd so the choices are fewer for me. This'll probably mean a DC version as I'm not sure I want to carry a genset. I also like the ability to quickly move the basic RO to the abandon ship bag, and make water while waiting for rescue.

While these big units draw a LOT of current at startup, there are "soft-start" devices that can make the initial load lower, thereby reducing the size of the genset and prolonging the life of the motor. We've got 2 on board and they've dropped the initial inrush current by about 40%. They're another thing that can go bad (but can be easily bypassed) but they do work.

Another idea is to look at how the RO configures itself on startup. We've got manual units that require the user to dial in the pressure and therefore the load at start is the smallest possible. When the high pressure motor's running well, we crank the pressure to around 800psi (depending on the inlet water temp). The RO brains know when the water's pure and switch over to filling the tanks. I offer this as I've seen some units that seem to start at high pressure in order to minimize the start to product time, but as dangerous as manual control is, I've always though the low load start was a good idea.

RO's aren't cheap to purchase, install, or operate. They can mitigate the water jug schlep, questionable water source, and no water problems, however.

For me, it's based on experience. I've been pleased with the radar far fewer times than I'd have been with an RO. It may be me, but I seem to run out of water far sooner than diesel (or even gas). For short distances, and population centers, RO may not be economically feasible. However, when the next safe harbor is 1000+ miles/10+ days away, having an RO can not only make the passage more pleasant, but give you much longer in that dreamed about anchorage.
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Old 23-05-2010, 19:30   #22
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Thanks Douglas, my long term experience is also on Super Yachts where the engineers ran large units daily making up to 8-10 tons of water if needed. I usually specified the larger HEM units.

The old (1990) HRO System 9 -500 I have on my own sailboat is like the one you explain, where it starts up… then you slowly turn a valve until about 800 psi then (if the salinity probe is working.. which it is now not) safe water light comes on and you manually divert product water when happy with the product.

I liked it, simple and hands on, but after being shut down for 2 years, while doing refits, I want to either rebuild this one to give me a DC option or look at buying a new one.

Since the motor plate is heavily painted over, still trying to calculate size of inverter I would need for this old 1.6hp motor. My calculations of wattage needed seems wrong as my 10kw Gen starts it easily, so I have screwed up somewhere?

The soft start up device that you and Gosstyla mention is a possibility, but I need to get my numbers confirmed first
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Old 07-06-2010, 19:00   #23
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Thanks Jay,,,,I wonder if Tellie is around to be able to confirm that I can get a no frills 700.

I will try and PM him.

Still would be interested to know more about the Schencker

Hi Pelagic,

Unfortunatly Spectra does not make a 700 no frills Their New Port 700 MKII comes standard with the MPC5000 electronic controls. The only manual units to be had from Spectra are the Ventura 150 and the Cape Horn Extreme 330.
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Old 07-06-2010, 20:02   #24
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I have an AC unit and wish I had gone with the DC unit. Making water at anchor with the genset running is fine most times but the real problem is dirty harbors. There are fewer and fewer "clean" harbors these days. So making water while underway out away from land and the local pollution sounds real attractive. And the DC units are the way to go as you can use wind gen's, solar, or even the engine alternator to power the DC R.O. watermaker - while your are underway to the next harbor. Go with the DC units!

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