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Old 07-05-2019, 07:51 AM   #1
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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 donít 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.
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Old 07-05-2019, 08:01 AM   #2
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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
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Old 07-05-2019, 08:05 AM   #3
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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.

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Old 07-05-2019, 08:17 AM   #4
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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
Thanks Ted.

I will look into that.

-evan
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Old 07-05-2019, 08:22 AM   #5
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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
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.
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Old 07-05-2019, 09:19 AM   #6
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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.
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Old 07-05-2019, 09:20 AM   #7
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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.


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Old 07-05-2019, 09:31 AM   #8
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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).
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Old 07-05-2019, 09:55 AM   #9
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Exactly. Heís 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.
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Old 07-05-2019, 10:11 AM   #10
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I have the same MS2812 inverter/charger but donít 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 doesnít do it you have added additional money to a system that wonít 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, Iíd likely just resign myself to running the genset while underway when I needed to make water.
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Old 07-05-2019, 10:15 AM   #11
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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.


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Old 07-05-2019, 10:48 AM   #12
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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.
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Old 07-05-2019, 10:53 AM   #13
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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.
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Old 07-05-2019, 11:19 AM   #14
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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.
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Old 07-05-2019, 11:24 AM   #15
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Hmmmm, I guess that is why I opted for a 12vt water maker.
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Old 07-05-2019, 11:28 AM   #16
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Quote:
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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.
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
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Old 07-05-2019, 12:34 PM   #17
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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

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.
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Old 07-05-2019, 12:51 PM   #18
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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.
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.
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Old 07-05-2019, 01:08 PM   #19
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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
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Old 07-05-2019, 01:10 PM   #20
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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

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.
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