Oct 19, 2020 > Watermakers
Rainman’s 115V 36gph watermaker is awesome, but is my 12v battery bank a reasonable way to power it?
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Product review Rainman Watermaker 115v
REVIEWED BY Alan Jacobson
Reviewer did not receive an incentive to post this review.
27 reviews, 1 follower
Beneteau 40CC Imagine
For some, “cruising” means leaving a home port and docking at a distant marina. That’s not for me. For me, the whole point of cruising is to anchor near uninhabited beaches where there are no services whatsoever. To do so, you need to be 100% self-sufficient. So you could spend days, weeks or even months sailing to an isolated anchorage in beautiful, crystal-clear water – only to endure hours humping 5-gallon Jerry cans of potable water to sustain yourself while you enjoy paradise. I tried cruising without a watermaker. I won’t do it again. I spent part of my first cruising season in the Bahamas’ Berry Islands – it’s about as close as you can get to the uninhabited, pristine beaches I sought. But I learned the hard way that a watermaker is almost essential, unless you want to monitor your fresh water consumption constantly, line your gunwales from stem to stern with Jerry cans of water and/or hope for rain to refill your tanks. ◉ Tap to add a comment or post a review Potable water is not merely essential to cruising – it’s essential for life. A watermaker is the practical way to visit secluded islands or endure extended passages at sea. But which watermaker? And how to power it? As I began my search for a solution, I discovered that Spectra offered a high-end system, but Spectras were expensive and complicated, and more prone to failure because of their complexity. Of all the sophisticated systems on cruising boats –  including refrigeration, navigation and autopilots – watermakers were cited as the most likely to fail according to Beth Leonard’s Voyager’s Handbook, from which I have learned a lot and highly recommend. With that in mind, I had settled on the “Little Wonder” from Village Marine. According to Practical Sailor, you can’t go wrong with a Little Wonder: “The heart of the Little Wonder (LWM-145) is a single-piston, belt-driven, low-RPM titanium high-pressure pump,’’ which is advertised as being reliable, impervious to corrosion, field serviceable, quiet, and designed for maximum efficiency, producing more water with less battery power. “If space is at a premium, and you need maximum installation flexibility, the Little Wonder has a lot to offer. Its simplicity, compact design, lower power draw, and installation options were its strongest attributes in our tests. We recommend it for those who use less water and those with very limited available mounting space.” Village Marine recently was purchased by Parker, a leading manufacturer of filters, so I was confident that I could count on ongoing support. I was sold on the Little Wonder (LWM-145) – or so I thought. In the meantime, I kept hearing good things about Rainman. Rainman’s watermakers have multiple configurations for both membranes and power sources, depending upon your space limitations and available power. They can be powered by gasoline, 115V AC or 12V DC. You can get more details here, but in a nutshell: more power + larger membranes = more potable water. Most of the press cites Rainman’s “portability,” but its high-pressure pump weighs 54 pounds and its high-output membranes measure 40 inches long. I couldn’t imagine storing these components in a lazarette and hauling almost 100 pounds of gear on deck each time I wanted to make water. Nor did I see myself leaving the watermaker on deck and subjecting it to salt spray. So I wasn’t interested in using the Rainman as a portable. The video, below, demonstrates the portable configuration using a Honda generator. But you can also use the gasoline-powered Rainman, or if you have a genset, you can use your genset as a source of 115V AC. There is also a 12V powered Rainman, but it doesn't deliver the high output of the other power sources.
Unlike the portable configuration, above, I wanted a seamless integration with my existing fresh water tanks. And Rainman supports permanent installations, which they refer to as “naked” because the permanent installation kit does not include the carrying cases that make the components somewhat more portable. But the naked kit includes the fittings necessary to facilitate a permanent install. It’s the same price for either the “portable” configuration or naked install kit. Not sure which way to go? As they say Down Under – which is where Rainman is made – “No worries, mate!” If you buy the portable configuration then decide later to install it permanently, you can convert your portable configuration to a permanent install by adding some valves and fittings to integrate it into your boat. Here’s why: both the portable and naked versions use the same high-pressure pump and membranes. The seamless integration I sought would require a source of 12V DC, 115V AC, raw water input, raw water discharge, integration with existing fresh water tanks and a means of testing and disposing of product water – that’s so you can test the potable water produced by the watermaker before diverting it into your fresh water tanks. The install is highly doable, but it’s not for the faint of heart. And in my case, it was too much for even an ABYC-certified mechanic. And one more thing: for an additional $245, Rainman offers an “auto-flush” system so you never need to pickle your system. This appealed to my desire for a hassle-free “one-button” operation of the entire watermaker system. But none of these considerations motivated me to change gears and opt for the Rainman instead of the Village Marine. Instead, it was Rainman’s 36 gph output versus Village Marine’s 7 gph output – for roughly the same cost as Village Marine’s 7 gph output. Maybe it’s the sailor in me, but I couldn’t pass up a 36 gph system for a 7 gph system for roughly the same price. But there’s no such thing as a free lunch. Nor is there such a thing as boosting your fresh water output by more 500% without a cost. And here it is: To make 36 gph, you need a source of 115V AC. This wasn’t a dealbreaker for me because I have a 6kW Northern Lights Lugger on board. But I did not want to be 100% dependent on my genset for fresh water. No genset = no water. So I needed an alternate source of 115V AC. The simplest solution for a backup was a Honda EU2200i generator. This meant spending an additional $1,000 and losing significant space to store the Honda in the lazarette. But according to Rainman: “Originally designed to run off of a minimum of a Honda 2kW generator, it will be easily powered by your inbuilt generator or a quality 2kVA inverter.” But what does Rainman mean by a “quality” inverter? According to Chris Burton at SeaTask, which is one of the companies that markets the Australian-built Rainman in the U.S., an inverter made by Mastervolt or Victron will work. Enboldened by Rainman’s endorsement of a “quality” inverter, I came up with another idea: I was already planning to upgrade my 40A 115V AC battery charger because it was inefficient to use a 6,000W genset to recharge my batteries with a puny 40A charger which only delivers 560W. So I looked into battery chargers from Mastervolt, made in the Netherlands. Mastervolt has a “PowerCombi 2000,” which is both a 100A battery charge and a 2kW inverter. And for barely more than the cost of a charger, I could get a 2kW inverter at virtually no additional cost. Retail is $999, but you can get it for hundreds less if you search online. So now I had a plan. I could use my Mastervolt PowerCombi 2000 2kW inverter to run my watermaker for short periods of time (15 to 30 minutes) without putting excessive demands on my bank of five 90Ah AGM batteries (450Ah). This would produce 9 to 18 gallons of potable water, which is much more than I need daily. If I ran my watermaker for 30 minutes, it would require 12 amps * 115V AC = 1380W / 12V = 115A * .5 hours = 57.5A. At the same time, I would use the sun to power my nine 100W solar panels, which should produce at least 30A to mitigate the demand on the battery bank. After running the watermaker, the solar panels should restore the AGM batteries to full power in a few hours, and never deplete the batteries below 50%. And if this system failed, I still had my genset. But several sailors on Facebook’s “Boat Electrical Systems” Group took issue with my plan. They said I would destroy my battery bank by drawing so much power to drive the watermaker’s high-pressure pump. Others said that my inverter would not provide sufficient power to start the high-pressure pump – even though my Mastervolt 2kW inverter provides peak power of 4000W for three seconds. Now before you pummel me with Peukert's Law, let me stipulate the following: I acknowledge that lead-acid batteries do not discharge at a “flat” rate. Instead, at high levels of discharge, available energy is depleted at a greater rate. But I am proposing a high level of discharge for minutes, not hours, and I don’t plan to delete my batteries below 50% capacity. Furthermore, I take issue with those who claim that high discharge rates will ruin my batteries, because a battery that has been discharged at a very high rate will recover over time, and the remaining capacity can be retrieved after the battery has been left at rest for several hours or a day, according to Wikipedia. Furthermore, most of the doubting Thomases on Facebook were using wet-cell, golf-cart batteries, rather than the marine AGMs that I have. While significantly more expensive than wet cells, AGMs can accept a larger current to recharge faster than wet-cell batteries, and can be restored to full power more quickly when recharged by an external power source, such as a bank of solar panels. That notwithstanding, and Rainman’s assurances aside, I was still concerned about that start-up spike, which I measured in excess of 40A @ 115V AC. The solution could be a “soft starter,” which is often used on marine air conditioners to reduce the initial load on startup. Most such soft starters cost more than $300 and require direct integration with the compressor motor. Then I found a plug-and-play solution from RaymondInnovations for $139.
RaymondInnovations’ GS11 soft start
So let’s talk about Locked Rotor Amps (LRA) – something I didn't know anything about until some sailors generously shared their knowledge with me on Facebook’s Boat Electrical Systems group page. To explain, I need to offer a quick explanation of electrical power. For those of you who already know this stuff, I beg your indulgence. What follows is a brief description of volts, amps, watts and batteries – because to run my 115V watermaker via an inverter, I must convert 12V DC from my batteries to 115V AC with my inverter. So let’s start at the very beginning. It’s a very good place to start according to Julie Andrews.
AC volts and DC volts are different, but watts are watts regardless of AC or DC, and: Volts * Amps = Watts The Rainman 115V Watermaker draws 12 amps when it is running. The following calculation shows how much power, in watts, my battery bank must provide: 115V * 12A = 1380W 1380W / 12V = 115A So, I need to draw 115 amps DC from my battery bank to power my 12 amp watermaker at 115V via my DC > AC inverter. Now, I’ll explain how I get that 115 amps from my battery bank. But first, I need to talk about batteries. While watts are watts, batteries vary a great deal regardless of their amp hour (Ah) rating. With a 100Ah battery, you should be able to draw 1 amp for 100 hours or 100 amps for one hour and every permutation in between. But I said should  – this never happens in real life – because no battery should ever be discharged 100%. And the extent to which you can safely discharge a battery without shortening its useful life depends upon what kind of batteries you have. To keep things simple, I will only describe three kinds of batteries, and suggest why the kind of batteries found on the boats of cost-conscious cruisers may not be up to the task, regardless of the battery’s Ah rating. Let me emphasize again that the following description is succinct for purposes of illustration. Your mileage may vary.
● 100Ah wet cell ~ $100
● 100Ah AGM ~ $300
● 100Ah Li-ion ~ $1000
All three batteries are rated at 100Ah, but you can’t discharge 100Ah from any of them. To do so may shorten the battery’s life. Other factors that affect the life of a battery include how often you discharge it, how much you discharge it and how quickly you recharge it. But I won’t get into that here. For illustration purposes, here are some guidelines:
● 100Ah wet cell > do not discharge below 75% | useful power = 25A
● 100Ah AGM > do not discharge below 50% | useful power = 50A
● 100Ah Li-ion > do not discharge below 90% | useful power = 90A
As you can see, you get what you pay for. The more costly AGM and Li-ion batteries are also safer and maintenance-free. Now back to the illustration. I have five 90Ah AGMs in my house bank. 5 * 90 = 450A * 50% discharge rate = 225 useful amps. In the beginning, we determined that the Rainman watermaker needs 115A, so I should be good to go with my 225 useful amps for at least an hour, right? Sorry, no. Because that 225A is based on the power requirement to run the watermaker, but not to start it. To start a powerful electric motor, such as those used in watermakers or air conditioners, you need to overcome the initial, momentary power requirement which is referred to as “Locked Rotor Amps” –the power required to get the rotor to turn. Typically, the LRA is 5x the working load. My working load is 12 amps, so the LRA is 60 amps for .5 seconds. I confirmed this value on my ship’s ammeter. On start, my watermater pegs the gauge past the maximum indication of 40 amps. So I have reason to believe the watermaker’s LRA is 60 amps. A moment after start up, my ammeter indicates 12 amps, which is its rated working load. This is where a soft start comes in. A soft start reduces the initial load, typically by 50%. To confirm this value, I started my watermaker with the RaymondInnovations GS11 Soft Start between my source of 115V AC and the watermaker. I saw that adding the GS11 reduced the LRA from 60 amps to 30 amps on my ship’s ammeter. 30 amps * 115V = 3450W My Mastervolt inverter is rated at 2000W, so the 3450W seems to be a problem. But the inverter can provide a peak output of 4000W for up to three seconds, so the inverter can satisfy the watermaker’s LRA for .5 seconds. So what does it take to make a lot of water? A lot of math.
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