Run AC Watermaker off Inverter?

[OldDan1943]

What kind of capacity WM do you have? I came across a Spectra product the other day that makes 8 gal/hr on 10 Amps and 12 V. It can run all day if it has to just on solar or from the main engine generator.

12 vt Spectra Newport 400 Mk2. Supposedly makes 400 gpd. To be honest, I have never found the need to run it. FW seems to always to be available.

I opted for the 12vt so I can run it underway or off the gen via the batteries.
I have 3x200 amp house batteries and 2x130 amp solar panels and a 150 amp engine generator.

Alas, I only have approx 150 gal water tank so if I want, I can flush the bilge with fresh water. Suuuuuure. LOL

 

[twistedtree]

I’ve had Spectra DC watermakers on our last two boats, and on the most recent it made probably 80% of the water we used over the course of our ownership. They work quite well

The benefits of a DC are easy operation while underway which is typically the best time to make water anyway.

A DC unit is typically assumed to also be very low capacity, but that doesn’t need to be the case. The first we had was a Ventura 200 gpd, or about 8 gph. The most recent was a Newport 1000 gpd, or about 45 gph. So they are readily available is sizes that will crank out water.

That said, I would not recommend anything bigger than the Newport 700. The 1000 operates at higher pressures to get the production rate, and appears to over stress the Clark pump and other components. I had to replace two cracked cylinders and deal with various other leaks that I think were all a consequence of stress cracking. The 1000 just seems to push that particular pump technology past its limit. And interestingly, Spectra’s larger units don’t use the Clark pump, and instead use a more conventional high pressure pump. So they seem to recognize the limit too.

Bottom line is that for anything 700 GPD or below, a Spectra DC watermakers would probably be my first choice.

 

[sdowney717]

http://www.trawlerforum.com/forums/s4/inrush-current-limiters-ac-compressors-39637.html

An inrush current limiter might work and its cheap to find out.
I need to get one of these too and play with it.

 

[ksanders]

This is interesting...

I’m thinking in all probability that the only problem the OP is experiencing is that his inverter is not capable of supplying the starting inrush currents his High Pressure pump is demanding.

I’ll be re-wiring my 40 GPH watermakers HP pump through a selector switch to choose either inverted power or raw AC power (from gen or shore whatever is online), this next week.

I’l let you know how it works out, but I’m betting that my Xantrex SW3000 will easily start the motor.

The reason for wanting to do this is simple... Redundancy. If my generator goes inop I would like the ability to desalinate.

Also if on a day long cruise there is really no other reason to run the generator but to desalinate as my inverter already handles most of the AC loads on the boat.

 

[DavidM]

Kevin:

This is a clip from Xantrex's specification page for the SW3000 inverter/charger:

Built-in transfer switch automatically transfers between inverter power and incoming AC power

So why are you installing a separate switch for the water maker? Won't the internal transfer switch do the same thing?

David

 

[ksanders]

Kevin:

This is a clip from Xantrex's specification page for the SW3000 inverter/charger:

Built-in transfer switch automatically transfers between inverter power and incoming AC power

So why are you installing a separate switch for the water maker? Won't the internal transfer switch do the same thing?

David

Suppose I am running the generator to recharge the batteries, and I want to desalinate at that time, which is the normal I operate the boat. When I run the generator I try to be cooking, recharging, clothes washing, etc...

Then the 10 running amps that the HP pump takes comes off of the 25 amps I have set for max draw on the inverter/charger limiting my battery charge capability.

then we have the issue of...

What if the inverter/charger fails.

Then I have zero way to desalinate.

I suppose, just brainstorming this a bit... I could connect the HP pump to my “inverter panel” which I can switch over to shore/generator power with two slide lockout breakers. That would give me everything I want, but... It would require me to switch back and forth every time I start and stop the generator.

Nope, I like the selector switch for the HP pump. I already have one abandoned in place in my panel anyway, so it’s easy peasy to integrate into the circuit.

The cool thing is that you made me think about it, that’s what I like about this place!

 

[eheffa]

Evan
Remember you and Jane (?) well. Nice boat, smart people and you live near Sidney as I recall. BC above Port McNeil is indeed fresh water short. Easy to see your wanting to get the water maker right. We’ll keep an eye out for you.

Hi Tom,

Thanks.

PM Sent.

-evan

 

[eheffa]

I know you already have your STW600 and had your heart set on running it from the inverter. I just went through a project reconfiguring an old boat with an old school electronics guy and he was very down on the use of inverters because of the inefficiencies in converting power and when you do the math, most boats do not have nearly enough batteries to do what we think we want to do. And stay over 50% charge to not kill the life of the batteries. So good choice to not run your WM from the inverter. One thought I had regarding the starting of the high pressure pump, would it work to just install a T in the pressure line with an extra ball valve that you could open for starting and then slowly close it to bring it up to pressure? Vent the leaked water wherever is handy.

My main thought for you is to use a smaller DC WM that only draws 10 amps at 12 Volts and is rated at 8 gal/hr. If you do your 8 hr cruise you could fill your 144 gal water tank from the main engine charging system and also have your battery bank charged at the end of the day. With that low of a draw you could make water daily from solar power and not run any engine. I found these Spectra WMs online and the Ventura 200T is the one the specs are for. List is $6,795. They have smaller ones too, about 4 g/hr for $4,000ish. Does anyone else have any experience with these DC units? Maybe OLD DAN will chime in!

Just a note on why your 1 1/2 HP single phase motor will not start easily is these single phase motors, specially on 120 volts, have a current in rush of at least 7-8 times full load running amps. Specs on a Baldor 1 1/2 HP 1800 rpm capacitor start motor are full load running amps 6.2 amps at 230 V, 12.4 amps at 115V which is what you had from the inverter, and 7.7 times full load amps at start. So now you have 12.4 A x 7.7 = 95 amps trying to supply power down a #10 or #8 wire so your voltage drop is very bad. Take into account the hundreds of feet of wire in the marina supply system that is rated for a 30 amp service and you have a severe overload and low voltage which spikes the amps even higher by Ohm's law. I wondered if your WM was possibly belt driven maybe you could have changed pulleys to slow it down, use a smaller motor, like 3/4 HP, that came more in line with the supply of power you have?

Thanks Transaxial,

I intended to only use the inverter while underway. The DC power would come off off the house bank but only when it was supported by the main engine alternator (+/- some contribution from our 550W of solar power...) The house bank was not supposed to be drawn down by this load. OTOH, the 12 Amps AC represents ~100 Amps of DC draw which is going to be a workout for my alternator. (More wear and tear and heat etc.)n If the battery bank were in a partially depleted state after a night on the hook, the draw on the alternator would be significantly larger and potentially more than the alternator could handle.

So using the WM underway would have to be confined to times when the battery bank was fully recharged.

Compounding this issue is the fact that I am finding the WM starts to be intermittently erratic when the WM is wired to the Inverter supplied AC bus. As djmarchand has pointed out, I may have a poor connection somewhere in the system that is limited the current draw through the inverter; but, even if I fix that I would still be left with the above limitations.

Wiring the WM to the main Generator / Shore Power bus gives me flawless starts and would not be too taxing to the 9 KW generator and AC system; even when charging the house bank at180+ amps.

As twistedtree has posted, I would have preferred to run the WM while underway, and still can; but, with the generator running.

A DC watermaker might have been a good choice after all, as a slow and steady product flow would have been just fine and on days when we are doing longer travel legs, I could leave the generator off. OTOH, I bought this used AC WM ( 140 hours on it) for a price less than half of what you are quoting above. For that, I think I can live with these limitations.

-evan

 

[eheffa]

12 vt Spectra Newport 400 Mk2. Supposedly makes 400 gpd. To be honest, I have never found the need to run it. FW seems to always to be available.

I opted for the 12vt so I can run it underway or off the gen via the batteries.
I have 3x200 amp house batteries and 2x130 amp solar panels and a 150 amp engine generator.

Alas, I only have approx 150 gal water tank so if I want, I can flush the bilge with fresh water. Suuuuuure. LOL

As Sunchaser notes, on the South Coast of BC & Northern Washington State, getting FW is not an issue. Ironically, though once you get into the rainforests North of Port McNeill, it is a big problem getting good FW. Compounding that, as we prefer the more remote areas and anchorages, coming to marinas to load water interferes with our preferred itineraries. It is quite freeing to not have to come into port just to refill the FW tanks and to be told that they are "out". (This happened to us in Shearwater last summer.)

-evan

 

[twistedtree]

Despite the pros and cons of AC vs DC water makers, the best one is the one you have, so it seems you are taking the best course of action.

That said, I would emphasize what Dave has suggested re carefully checking the wiring into and out of the inverter. Even if you never run the WM of the inverter again, the behaviors you have seen suggests there may be a wiring weakness that should be checked and addressed if needed.

 

[dhays]

Despite the pros and cons of AC vs DC water makers, the best one is the one you have, so it seems you are taking the best course of action.

Yes!

Of course being TF, I’m surprised we haven’t yet told him that he needs to buy a different boat (with a different anchor) in order to solve his watermaker issue.

 

[eheffa]

Despite the pros and cons of AC vs DC water makers, the best one is the one you have, so it seems you are taking the best course of action.

That said, I would emphasize what Dave has suggested re carefully checking the wiring into and out of the inverter. Even if you never run the WM of the inverter again, the behaviors you have seen suggests there may be a wiring weakness that should be checked and addressed if needed.

Thanks.

Yes, Dave’s recommendation and steps to checking the AC wiring makes good sense.

I plan to do that. ( I’m quite sure the wiring is all quite adequate as to specs /gauge / quality but need to ensure all connections are sound.

I will report back.

- Evan

 

[twistedtree]

Thanks.

Yes, Dave’s recommendation and steps to checking the AC wiring makes good sense.

I plan to do that. ( I’m quite sure the wiring is all quite adequate as to specs /gauge / quality but need to ensure all connections are sound.

I will report back.

- Evan

Wiring connections can be sneaky buggers, looking great visually, but still have impaired contact, bad crimps, etc. Lots of stories of great looking connections that have been smoked under load.

 

[OldDan1943]

Yes!

Of course being TF, I’m surprised we haven’t yet told him that he needs to buy a different boat (with a different anchor) in order to solve his watermaker issue.

That might work. What kind of WM on the new boat, DC?, amp draw, capacity.

Anchor, a 400# barrel of concrete should do nicely.

 

[SteveK]

Thanks.

Yes, Dave’s recommendation and steps to checking the AC wiring makes good sense.

I plan to do that. ( I’m quite sure the wiring is all quite adequate as to specs /gauge / quality but need to ensure all connections are sound.

I will report back.

- Evan

May I suggest a new piece of wire (test wire) be strung direct to WM from inverter, eliminate the middle connections and see if it works. Even use a wire 2 sizes more than you have now.