How big of an inverter for your RV, Boat, or non house powerwall--Inverter Sizing

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Riplash

Member
Joined
May 27, 2018
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71
Greetings everybody.

My progress on the boat is going well. I am trying to get the bottom fiberglassed, and painted soon, so I can flip it over and work on the inside. I have 2100 cells tested and probably 500 ready for testing. I don't NEED the Inverter yet, but I want to get the inverter, use it, experiment with it and learn about it. I can also use the inverter to run the power tools, and lights when I am building the boat, rather than firing up a generator each time I need to use a power tool.

When the boat is completed, a lot of the stuff will be either be propane powered, or DC powered, and the boat's main motor voltage will be anywhere from 12S to 100S. (It is a tradeoff between Crazy high Amperage or crazy high Voltage) depending on which motors and companies I go with. I don't know what all I will want to run yet. I know will probably run a microwave occasionally, and lots of small appliance chargers (most could be charged off of a 5V DC bus.

I realized during construction of the boat, and during use of the boat, I will probably only use 1 big AC thing at a time. All of my portable powertools are 15A or lower at 120V which would be 1800W . There are some that require 20A at 120V (2400W) , but I don't have any of those. So I am thinking of getting a 2000Wcontinous/4000W peak at 24V input 120V output true sine wave inverter, or for $20.00 more US dollars, I can get a 2500W continuous/ 5000W peak. Do you think I am on the right track?


So what size inverter did you pick for your mobile power wall and are you satisfied with the size?

Here are two pictures taken a few weeks ago. The overall appearance hasn't changed much because I am doing alot of trimming/ plugging/ fairing, etc, so tons of small stuff gets done, but the pictures from a distance still look the same.
20210524_071309.jpg
20210524_071243.jpg


Take Care,

Ryan
 

OffGridInTheCity

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Dec 15, 2018
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1,657
Sounds like you want a solar generator. I use a MPP Solar "PIP" https://watts247.com/product/pip-3048lv-mk/ It's 3000w (120v@25a) on 48v battery and I can atest that it handles 25a@120v.

They make other variations for 24v battery instead of 48 and up to 6000w. Here's a youtube where @LithiumSolar made one on a 'cart' for portability with a 24v@2000w model to give you the idea.



There are also GroWatt all-in-ones - very similar in functionality/price to MPP Solar PIP.

I mention this because its the heart of my cargo trailer -> camper conversion. It's an all-in-one and you can charge the batteries thru incoming 120v or Solar. I use a Honda ue3000is and it can sustain 2,200w of charge.

You might find that once you're finished with the portability aspect/work - you can repurpose it as a permanent part of your boat's electrical system. :)
 

Riplash

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May 27, 2018
Messages
71
Hi OffGrid, thanks for the Idea. How often do you pull 3000W from your inverter when you are using your camper conversion?

You might find that once you're finished with the portability aspect/work - you can repurpose it as a permanent part of your boat's electrical system. :)
This is exactly what I want to do. I mainly want the inverter for when I am using the boat. If I can use it when I am building the boat, that is a bonus, and gives me another excuse to go ahead and buy it.

The boat I am building is a 27' electric ski boat. It is based on a design that used a Marinized Chevy 350 small block. So the Main battery system for the Motor will be Electric Vehicle size.....Huge, and I haven't picked a definite motor system yet so the Voltage of the main battery is unknown. I am planning on making a smaller "house battery" that will be 7s x 40p for the inverter. But if I go larger than 2500W I will probably do 14S x 40p.

I will be using Stuart Pittaway's DiyBMS for both batteries, and I am working on charging systems, both through solar, and through AC. So I don't really need an all in one unit. A stand alone true sine wave inverter This is the inverter I am considering. I am just trying to figure out if this one will be large enough, or if I should get one bigger.

-Ryan
 

OffGridInTheCity

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Dec 15, 2018
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>Hi OffGrid, thanks for the Idea. How often do you pull 3000W from your inverter when you are using your camper conversion?
A few times so far - for example the heat-pump + shop-vac (often) is over 2000w and this morning the hotplate + toaster + k-cup all at once went to 2999w on the meter :) The MPP Solar PIPs have a good rep - so if its rated for 120v @ 25a continuous then I would expect it to be pretty close.

My home system is independent components and I use AIMS 12,000w pure sine wave inverters - 2 years (every day) so far and no problems - just reached 22,000kwh consumed (from the AIMS output) yesterday :)

There are a lot of choices that seem pretty good these days. You can always bump up to 4000w or 6000w and leave head-room. One key issue in choosing an inverter is whether its low-frequency or high-frequency. Low frequency (like AIMS) are heavier but can do 2x or 3x power spikes to handle tools like saws and shop-vacs. High-frequency ones are lighter but cannot stand surge/overload at all - the surge has to be below the max limits.
 
Last edited:

floydR

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Aug 23, 2017
Messages
1,224
The Reliable inverters are reliable until they are not. Power tools often have large inrush current. Enough to kill a 3000w/6000w peak Reliable inverter (yes it was my inverter). 15amp load
later floyd
 

Roland W

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Oct 9, 2017
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130
The Reliable inverters are reliable until they are not. Power tools often have large inrush current. Enough to kill a 3000w/6000w peak Reliable inverter (yes it was my inverter). 15amp load
later floyd
As floyd said, if you want to use power tools, you need to use an inverter which can handle inrush. That will typically be a Low Frequency Inverter (those are the heavy ones). A 800W electric drill can trip my 4000W High Frequency inverter if I press and release the trigger a few times after another. You can go with a 2000-3000W LFI. Surges will be no problem.
 

ajw22

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Nov 16, 2018
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The boat I am building is a 27' electric ski boat. It is based on a design that used a Marinized Chevy 350 small block. So the Main battery system for the Motor will be Electric Vehicle size.....Huge [...]

Awesome project. When you say "ski boat", do you intend to actually use it for water skiing?
Would love to hear some numbers about your main propulsion & energy options, and expected speeds & ranges.
 

GoneDiving

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Jan 17, 2020
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I'm also setting up a solar generator system for my boat. I've used two PIP 5048MKs and 48 280ah Lifepo4 cells. Note that it's a pretty big system because it's a 54ft live aboard ex commercial trawler. Loads are a residential galley, dive equipment and a 7.5kw anchor winch (only intermittent use).

I'd agree with previous comments that too big is better than too small (if you have the space and battery capacity). No one ever complains about having too much capacity. Lol

The only issue I've come up against is consider how you will handle safety earth/neutral bridging and shore power. If you want to connect to shore power for supply or charging you need to be able to disconnect and bridging within your inverter.
 

Riplash

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May 27, 2018
Messages
71
The Reliable inverters are reliable until they are not. Power tools often have large inrush current. Enough to kill a 3000w/6000w peak Reliable inverter (yes it was my inverter). 15amp load
Thanks for the feedback about Reliable inverters not being reliable. I looked at AIMS website and they seem like a more reliable company. Most of their 2000W to 4000W low frequency inverters are sold out, unavailable at the moment or way larger than I need with lots of bells and whistles that I don't need. I will keep my eyes on their website for when one becomes available. Do you know of other similiar brands that sell Low Frequency inverters that I can keep my eyes on?
Awesome project. When you say "ski boat", do you intend to actually use it for water skiing?
Would love to hear some numbers about your main propulsion & energy options, and expected speeds & ranges.
Yes, I do intend to use it for waterskiing. I currently slalom ski the course at 28 or 30 miles per hour. If I get better, I might have to ski at 34 or 36 miles per hour in competition. The boat is based on Glen-L Caypso design found here. But I will be using an electric motor, and I am reducing the cabin size, adding a hardtop, and making it look and function like a modern dual console, such as a sailfish 276DC except with an inboard motor.

95% of the time I use my current boat once or twice a week is for about 15 miles, spread out over 2hours. I drive the boat to the area we ski about half at idle and half time at cruise speed. Then we ski normally 3 to 5 people ski and the engine is on about 50% of the time. Then we cruise back home. The rest of the time the boat is sitting on its trailer in the sun, or in the water in the Sun. So I want to put enough solar on the boat, that I hardly ever have to plug it in to charge. The other 5% of the time we use our boat it is for group poker runs, lunch runs with boat building clubs, and groups. These are about 60 miles round trip.

So that means I need the boat to go more than 36 miles an hour with the boat lightly loaded for short runs. And eventually I want enough battery capacity that I can go 60+ miles slower but fully loaded.

I have looked at lots of motors such as Hyper 9 by Netgain, AC-51, Motoenergy Motors, too many more to list. Right now I am leaning towards an EMRAX 268 if I go with a single big motor. This motor has Thrust bearings built into i so I could run it direct drive, but if I don't gear it down it spins a little bit faster than I want it to.

The other option I am thinking about is buying smaller 35KW PMAC watercooled motors from Alien motors, and building a transmission bracket that will let me add more motors and power as I need it and as I can afford it. Once I get the hull flipped over, even though it will basically be a boat shaped shell, I will probably put it in the water and drive around with a trolling motor, and a little bit of ballast so it sits somewhat into the water.

Rough calculations for the motor size show that I need about 92 kiloWatts of power to go 36 miles per hour at a weight of 3500 lbs. So 3 of the 35 KW PMAC motors would be the minimum. Then for the range at 6000 lbs, cruising at 25 miles per hour, I need 79 KW of power, so for 60 miles I need 190 KWh...So it will be a while before I have that much capacity.

-Ryan
 

prepared1

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Jan 17, 2021
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Very interesting project! I was going to chirp in with a suggestion to go all electric, until I saw your last post. I'm not into boats at all, but I hear people talking about using Leaf motors, or other regular DC motors to re-power nearly anything. So many possibilities.

I think you are on the right track...start with the motor, and get that nailed down. Work backwards for requirements of batteries, and then select the equipment that mates up best with those components/requirements. If it were my project, I'd be spending my money on very reliable inverters. It is bad enough to have equipment failures on land, but out on the water, it is another story. Victron might come to mind in this scenario. Take a look a the new Multiplus 2, 48v unit.

In your exterior hull pictures, it looks like the joints between sheets are some sort of wavy "dovetail". Or are those some sort of giant biscuit? I haven't seen those before. I'm obviously not a wood boat guy.....

Fun project..keep up the good work.
 

Riplash

Member
Joined
May 27, 2018
Messages
71
Prepared1,

The joints in the plywood for the boat are fat finger joints. I made a router guide and then I cut them out with a router. I thought it would be easier than a conventional 8:1 scarf joint, but I can do scarf joints now really easy too. There are 2 pieces of plywood stacked in the picture below. Between work being busy, the weather being too hot to work with epoxy, or big thunderstorms, my pace has slowed down in June. I still work on it a lot, but I have to get ready and then pack up before much gets done because it is too hot, or wind and thunderstorms.

-Ryan




20210228_122233.jpg
 

prepared1

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Jan 17, 2021
Messages
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Riplash: Nice! Are you using West System epoxy? I have a buddy who builds wood kayaks, and he uses nothing but that. I think your fat finger joint is a great idea, and likely to be really strong. Would you fiberglass over the inside of that joint?

Just a fun comment about wood boats...I once saw a gigantic wood boat on cribbing in a guys backyard. It was for sale, over 50' long. he had been working on it for years, and had not gotten to the engine stage. It was a work of art. Wish I had it sitting behind our house as an "office away from home". I could be a modern age Noah...

Keep up the good work!
 

Riplash

Member
Joined
May 27, 2018
Messages
71
I am using RAKA epoxy. Their headquarters are 60 miles south of me, and a lot of companies private label their epoxy. I have used West System epoxy if I have a small project on a Sunday, and I am out of epoxy, and I don't want to wait. Since I began building the boat, my stockpile of epoxy and supplies has gotten larger, and I have done a better job of managing the supplies.

Right now I am a frustrated because the weather isn't cooperating. It is too hot to apply the epoxy during the day, and during many of the late afternoons and evenings when I have time and it cools off, it is is raining. We are looking forward to buying a better house with an area for covered boat building, but we are not quite able to just yet.

-Ryan
 
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