Run AC Watermaker off Inverter?

Hi,

I tried a search without success.

I recently bought & installed a used Village Marine Stowaway 600 Watermaker. (110V AC). We had hoped to run the unit off the inverter while underway.

It draws ~12 A when running. This is not an issue for our 9 KW generator but when I attempt to run it off the almost new inverter (Magnum MS2812 rated for up to 23 A ) it trips the over current breaker on the inverter.

It appears that when the high pressure pump on the Watermaker starts up, it has a brief spike of up to 90 A of draw which trips the inverter.

I understand that installing a soft start circuit might make the watermaker draw less when starting. These Soft Start modules don’t appear to be cheap & most on the market are designed for Air Conditioners.

Does anyone here have any experience in solving this issue?

Thanks for any feedback you can offer.

Might try a "Hard Start" capacitor. Basically it doubles or triples the capacitor on the motor reducing the surge draw on start. I have them on all my air conditioners and it prevents the main breaker from tripping when the generator is loaded and the AC compressor starts. They're about $20.

Ted

You might first try a Supco soft start capacitor. They are only $10-20 and can reduce inrush current by 30% or so. The next step is much more expensive, maybe a Dometic or Micro-Air soft start kit. These cost several hundreds but are reported to reduce inrush current by up to 75%.

I have never used one on a water maker but if yours is a 115V, single phase, capacitor start motor it may work. Contact the manufacturer to be sure.

You do realize that the inverter will pull more than 100 amps from your batteries while running the water maker, assuming it can start. You will need a big battery bank and a way to recharge it, presumably with your genset and shore power charger. So where is the savings? A big solar panel system might do it.

David

O C Diver said:

Might try a "Hard Start" capacitor. Basically it doubles or triples the capacitor on the motor reducing the surge draw on start. I have them on all my air conditioners and it prevents the main breaker from tripping when the generator is loaded and the AC compressor starts. They're about $20.

Ted

Click to expand...

Thanks Ted.

I will look into that.

-evan

djmarchand said:

You might first try a Supco soft start capacitor. They are only $10-20 and can reduce inrush current by 30% or so. The next step is much more expensive, maybe a Dometic or Micro-Air soft start kit. These cost several hundreds but are reported to reduce inrush current by up to 75%.

I have never used one on a water maker but if yours is a 115V, single phase, capacitor start motor it may work. Contact the manufacturer to be sure.

You do realize that the inverter will pull more than 100 amps from your batteries while running the water maker, assuming it can start. You will need a big battery bank and a way to recharge it, presumably with your genset and shore power charger. So where is the savings? A big solar panel system might do it.

David

Click to expand...

Thanks David,

Yes, I do recognize the draw is not insignificant; but we have a 160 A alternator, 550W of solar panels and 660Ah of Carbon Foam House Bank to feed the watermaker.

I thought that should be sufficient to make it all work.

I really dislike running the Gennie and the engine at the same time when we would have the capacity (in theory) without needing the Generator output.

-evan

PS Thanks for the Supco idea. I will research that.

If you start getting into fancier soft start devices, you might consider just upgrading the inverter instead. I don't know for certain, but it might be an easy swap out.

OK, but consider these realities:


If you run your water maker for 1 hour, probably making 30 gallons of water, you will draw 120 Ah nominal from your 660 Ah bank. That is 19% of the capacity in one hour, or about 4 times their rated 1/20 C Ah rating. Peukert's equation comes into play here and the amphours required to fully recharge the battery is approximately 160. Your solar panel will produce about 200 Ahs on a full sunny day, so it will take most of their power for a day to recharge the batteries.


So consider how many gallons you use each day, how much your water maker will make and if it is worth it to dedicate much of your solar power to recharging your batteries.


David

He does have a 160 amp alternator, note that he said he wanted to run the watermaker while underway. If he can overcome the start surge issue, why not? Just need to keep other loads on the inverter in line (like not running the microwave).

Exactly. He’s looking to do this while underway, so all loads supported (hopefully) by the alternator. But I agree with all Dave is saying regarding running off battery, should that come up.

I have the same MS2812 inverter/charger but don’t have a watermaker or AC. I know that with the wrong combination of AC appliances, I can trip the inverter. 90amp surge current is too much for any of the MS series of inverter chargers. Your MS2812 I think will handle about 32 amps of 5 second surge current. So you would need to reduce the surge current draw of your watermaker by about 66%. That is a big decrease!

So a soft start system may get you where you need to be but if that doesn’t do it you have added additional money to a system that won’t solve your issue. None of the MS series inverter/chargers will give you 90 amps of 5 second surge current so you would need to look at something else which would be really expensive. You might be able to try a difference watermaker that had less current requirements. Also an expensive option.

If I was in your shoes, I’d likely just resign myself to running the genset while underway when I needed to make water.

I missed the 160A engine alternator response, so assuming it is heavy duty and externally regulated, it should be fine supporting the 120A load on the batteries while underway.


David

We did the same thing for years, but with a cruiseRO sm30. The high pressure pumps starts with zero pressure, and very little current. Then you adjust the pressure up to operating, which sees all the current. Is your pump starting under full load pressure?

In this way, the watermaker is unlike alot of other loads, like A/C and refrigeration, etc.

There might be something wrong with your inverter, or maybe your alternator is not putting out 160A. I have the same inverter that runs a cruiseRO 30 GPH water maker without a problem. We have a 265A alternator derated to 200A that powers everything without the need to drawn on the batteries. We only run the water maker when the engine is at cruise RPM.
First check to see what your alternator is really producing, since even a brief heavy draw on the batteries will reduce battery voltage to below what the inverter will tolerate.

With my Victron inverter, I can start a large compressor on generator, switch to the inverter and turn off the generator. The Victron has the capability to transfer without disconnecting.

I don't remember if my previous Magnum 2812 inverter has the uninterrupted power function.

I'd try the switching function with a load to see if the Magnum will transfer without disconnecting.

Hmmmm, I guess that is why I opted for a 12vt water maker.

syjos said:

With my Victron inverter, I can start a large compressor on generator, switch to the inverter and turn off the generator. The Victron has the capability to transfer without disconnecting.

I don't remember if my previous Magnum 2812 inverter has the uninterrupted power function.

I'd try the switching function with a load to see if the Magnum will transfer without disconnecting.

Click to expand...

Yes you can do that with the Magnum 2812. My PC switches without blinking. Think I have also done that with the microwave, by accident.

Ted

O C Diver said:

Yes you can do that with the Magnum 2812. My PC switches without blinking. Think I have also done that with the microwave, by accident.

Ted

Click to expand...

A good feature, for sure, but I don't think it would come into play in this instance. I think he's running steady underway on inverter power with DC provided by the main engine alternator (mostly) and batteries (should only be for surges).


What he's doing should work, at least on paper. But pesky realities like surge loads, surge capability of the inverter, and sustained alternator capability can all muddle the pie.


Short of an economical way to reduce the startup surge, I think Dhays's suggestion is probably best - just run the generator. That's what it's for, and I think we generally have an unfounded aversion to doing so.

twistedtree said:

A good feature, for sure, but I don't think it would come into play in this instance. I think he's running steady underway on inverter power with DC provided by the main engine alternator (mostly) and batteries (should only be for surges).


What he's doing should work, at least on paper. But pesky realities like surge loads, surge capability of the inverter, and sustained alternator capability can all muddle the pie.

Click to expand...

Start the watermaker on generator, once underway, turn off generator and the inverter will run the watermaker off the 160 amp alternator.

It's not rocket science.

I appreciate the discussion points made above.

I have tried the start with the generator & switch to inverter only trick & with the brief lapse in power, the watermaker either quits or the inverter trips out over the surge...

Our microwave draws more current than the watermaker & runs fine on the inverter. (A brand new inverter unit BTW...)

I was thinking that the alternator & engine running at cruise speeds would be more than adequate without drawing down the house bank.

- evan

eheffa said:

I appreciate the discussion points made above.

I have tried the start with the generator & switch to inverter only trick & with the brief lapse in power, the watermaker either quits or the inverter trips out over the surge...

Our microwave draws more current than the watermaker & runs fine on the inverter. (A brand new inverter unit BTW...)

I was thinking that the alternator & engine running at cruise speeds would be more than adequate without drawing down the house bank.

- evan

Click to expand...

It's pretty certain that it's the startup surge of the WM pump. Your microwave won't have such a surge, which is why it works OK.

Yes.
It’s the abrupt startup surge current that is causing the problem. The microwave does not hit the system with the abrupt surge.

syjos said:

With my Victron inverter, I can start a large compressor on generator, switch to the inverter and turn off the generator. The Victron has the capability to transfer without disconnecting.

I don't remember if my previous Magnum 2812 inverter has the uninterrupted power function.

I'd try the switching function with a load to see if the Magnum will transfer without disconnecting.

Click to expand...

I have tried that without success but perhaps I was can try again with higher engine speed.

eheffa said:

I have tried that without success but perhaps I was can try again with higher engine speed.

Click to expand...

I don’t think it should matter. In my simple mind, the inverter is just taking the battery power and converting to AC. All your alternator is doing is replacing the amps that have been draining from the battery.

Your issue is that the inverter can’t handle the startup load, that shouldn’t have anything to do with what is feeding the batteries.

However, as with all things electrical, I could be wrong.

Sealife said:

We did the same thing for years, but with a cruiseRO sm30. The high pressure pumps starts with zero pressure, and very little current. Then you adjust the pressure up to operating, which sees all the current. Is your pump starting under full load pressure?

In this way, the watermaker is unlike alot of other loads, like A/C and refrigeration, etc.

Click to expand...

Thanks Sealife,

Good suggestion / question.

Yes, the Village Marine WM Ramps up to its working pressure of 800 PSI almost immediately.

It does have a pressure regulator with a hex key adjustable valve that allows one to greatly reduce pressure output for brackish water etc. Perhaps if I used that to reduce the startup load it could reduce the startup current demand to an acceptable level?

I will try that.

Thanks.

dhays said:

I don’t think it should matter. In my simple mind, the inverter is just taking the battery power and converting to AC. All your alternator is doing is replacing the amps that have been draining from the battery.

Your issue is that the inverter can’t handle the startup load, that shouldn’t have anything to do with what is feeding the batteries.

However, as with all things electrical, I could be wrong.

Click to expand...

I agree.

I didn’t think the problem was in the inverter demanding too much from the DC supply side. (The Firefly bank alone has the ability to provide very high currents & I haven’t skimped on the cabling. The alternator would only be a factor in resupplying the battery bank losses over the couple of hours of watermaker use.)

I can run my watermaker, windless. Incinolet toilets, and other items on my 48v Magnum MS_PAE inverter. But I don't use it for the watermaker. I have a big HP pump (5hp motor) because it doubles as a pressure washer. When you consider the charging time required to return a full charge to the batteries, it doesn't make sense to me. I use the inverter mainly to have AC power while running the mains w/o running a generator and have AC power 24/7 at anchor. I make water every other day and run the generator for an hour while also doing laundry and running the water heaters. More hours if I have a lot of people on board. Each main has a 48v alternator that keeps the banks up while cruising. While I have air conditioning, I rarely run it, preferring to avoid hot weather. No solar, yet, maybe a wind turbine as I usually anchor where there is wind.

I had an AC powered water maker that use the one horse motor. I replaced that motor with a 1 horsepower 12 volt DC motor. Draws 76amps. DC

Lepke said:

I can run my watermaker, windless. Incinolet toilets, and other items on my 48v Magnum MS_PAE inverter. But I don't use it for the watermaker. I have a big HP pump (5hp motor) because it doubles as a pressure washer. When you consider the charging time required to return a full charge to the batteries, it doesn't make sense to me. I use the inverter mainly to have AC power while running the mains w/o running a generator and have AC power 24/7 at anchor. I make water every other day and run the generator for an hour while also doing laundry and running the water heaters. More hours if I have a lot of people on board. Each main has a 48v alternator that keeps the banks up while cruising. While I have air conditioning, I rarely run it, preferring to avoid hot weather. No solar, yet, maybe a wind turbine as I usually anchor where there is wind.

Click to expand...

I was hoping to run the watermaker while at cruise speed / underway when the alternator was not needing to charge the battery bank and I could use its excess capacity to make water. There would, in theory, be very little deficit from the house bank capacity.

motion30 said:

I had an AC powered water maker that use the one horse motor. I replaced that motor with a 1 horsepower 12 volt DC motor. Draws 76amps. DC

Click to expand...

Hmmm.

That’s an interesting option.

Did you leave all the controls, low pressure pump etc running off the AC side?

eheffa said:

I was hoping to run the watermaker while at cruise speed / underway when the alternator was not needing to charge the battery bank and I could use its excess capacity to make water. There would, in theory, be very little deficit from the house bank capacity.

Click to expand...

You can stay ahead of the inverter bank, I do charge while running and do keep the inverter banks up, even running a water heater, electric toilets, etc. I designed my water maker to make 40+ gl/hr. So I could make more than enough water running a generator every other day for an hour. Longer if I've run down the battery banks or have guests. As much as possible, everything on the boat is AC except for bilge pumps, radios, and nav equipment & lights. One reason for the AC lights is I don't like the crappy, dim 12v lights available. I can go 3 days using AC lights, toilets, and running my reefer & freezers - w/o guests. I have supplied AC to boats rafting, but limit what they can run unless a generator is running.

MY experience with bigger 12v motors is they don't last as long as AC motors, cost much more, require much bigger cables, and tend to wear out contact points much faster. Most people skimp on the cable size and burn the motor out even faster. Before my time, the windlass had a 12v motor. I found 6 burnt out motors in the engineroom. Guess they figured it out.

When I bought my current boat, it had 2-14kw generators, both had badly glazed cylinders from running 24/7 mostly with light loads. Having the inverter, the generators only run medium to heavy loads, and saves ever having to rebuild them again.