The case for multiple small inverters

[a64pilot]

I have two inverters, a 130W one to run my TV and Satellite so it’s on for hours at a time.
And a MS2812 to run any big loads we may have, the bigger loads are almost always short interval, to vacuum, make toast or similar. To wash clothes for example we run the generator because we are making water anyway, washing machine uses a tremendous amount of water.

Leaving a big inverter on, even in sleep mode consumes more power than you think over time. An inverter is inherently inefficient, first they consume power and just being on, then they are only on average about 88% efficient, to run an anyways on device like a fridge with an inverter is very inefficient, better off to spend the $$ on a DC one.

I started out leveling mine on, but soon realized ho much power that was, now we push a button, use the inverter, push the button to turn it off.

[Jammer]

Originally Posted by Chotu

marine refrigerator pits absolutely suck in every way

The point behind them is that they make best use of available space. Some of the better installations open both on top and at the front.

12v front openers?? Maybe. If there are reasonably priced, large enough ones. Still need to run the long term storage chest freezer though.

::shrug:: What is reasonable. What is large.


Household fridges are way cheaper, particularly in large sizes. When cost is what matters most that's what people use. You have to add an inverter and do some amount of marinizing -- figure out a way to fasten it in place, at least, and some way of latching the door. It still comes out cheaper but perhaps not as much as you think.



The marine fridges run on DC out of the box, and have latching doors, and are shaped to fit spaces on boats. They are designed to be fastened in place, most of them having a mounting flange for attachment to cabinetry. Some of them have flexible lines and a compressor and condenser that can be located a few feet away from the fridge. In most cases the shelves have ledges or retainers that keep food from flying onto the cabin sole when you open the door on a heel or in heavy seas.

[s/v Jedi]

I’ve done it all, trying to achieve the best option without looking at budget. The system we built in 2004 with 3 custom boxes with 4-8” insulation and the newest tech keel cooler based compressors. That cost $10,000.- and it has served us until 2019 so 15 years.

Looking at replacements I decided to do energy consumption tests of the Snomaster boxes we have now vs our custom boxes from 15 years ago. I found almost identical consumption figures despite the new system being air cooled and only having 3” of insulation.

The final decision was easy and we ripped out the old system and built new cabinets. We’re now on our first trip with them to evaluate the system. The modern construction in stainless steel, organized interiors efficient gaskets, compressors etc. seems to outperform the old system.

These take either 12V, 24V or 120V, but efficiency tested best for 12V with 24V closely 2nd and AC considerable behind. Domestic units however are optimized for AC so that’s another picture.

[AndrewA2]

Originally Posted by Jammer

Household fridges are way cheaper, particularly in large sizes. When cost is what matters most that's what people use. You have to add an inverter and do some amount of marinizing -- figure out a way to fasten it in place, at least, and some way of latching the door. It still comes out cheaper but perhaps not as much as you think.

Home fridge: $200
Marine Fridge: $1000

No way $800 in a latch and inverter loses will come close to that !

[doog]

didnt thoroughly read all but just logging in to comment that our little "DC" appliances like a small refrigeration unit are not DC at all, but that they have a small built in inverter to make the AC power that runs the compressor for exactly the reason you state. And Ive been told, oh just buy a big inverter for your boat and then you can use power tools and AC appliances but no way, just having one item working would be an enormous drain. This is the best idea Ive seen here and its right on. You want the smallest inverter possible, not the biggest you can afford. And integrated right into the item you want to power with it, and making the needed AC whether full sine wave or just a simple AC with minimal draw on the DC power bank.

[transmitterdan]

Most modern home fridges have built in inverters that convert 120VAC to some other voltage and frequency. The compressors use a variable frequency drive as this improves efficiency and lowers peak power consumption.

That doesn’t change the fact that distributing 120V uses less weight and is more efficient than distributing DC.

[Grimgrak]

I've been seeing some nice fridge and freezer combos meaning they can run as both a fridge or a fridge based on how you set the temp they are usually stainless and stack one on top of the other on newer boats. Any idea the brand/model and if they are DC?

[Palarran]

Originally Posted by Chotu

I feel like this is where I’m probably headed given the reality of the situation.

I was hoping to squeak out a little more electrical efficiency, but in reality, the electronics you’re talking about here will keep the inverter awake in (hopefully) a low power mode that isn’t horribly inefficient.

I’m attempting to minimize night time loads so battery usage isn’t much. Unless I cut the refrigerator and freezer power for a few hours each night and can do that without any repercussions in the food, I’m probably just going to have to live with this drain.

My refrigerator draws a lot of power. It's somewhere around 4 amps at 120v so 480 watts plus the 8% loss of inverter for a total of 520 watts. It also runs quite a bit, at least 50% of the time. But it's also huge, keeps the freezer as cold as -7f and the fridge at 38F. We make ice in trays, quite a bit of it. It's awesome and cost $900. With my old holding plate unit I had to run the generator twice a day for over an hour, mostly 90 minutes, at a time to get a freezer temp to average below freezing and a refrigerator that went from high 30's to low 50's. Nothing was ever totally frozen and fresh food didn't hold well. With the 1100 amp hour bank and 1350 watts of solar, we don't need to run the generator except to make water or run the A/C units.

[roland stockham]

Makes sense to me, I have a 400w inverter at the chart table that runs things like the laptop and battery chargers for torches etc. Very low drain and very efficient. I had a 1500w Sterling power for the main inverter which was great until a circuit fault blew it! Looking at a replacement for that I want around 3kw mainly to run tools and domestic stuff like a bread machine and vacuum (fridge is 12v). This size is expensive. I also want split phase as some tools nee 230v and that can only be done with low frequency inverters. LF inverters seem to be very robust but have higher standby currents, fine for intermittent use but not for continuous small loads. I have also tried a few very small inverters over they years and found big differences in both quality and efficiency, some give poor quality power and draw more current both in standby and supply mode so one issue is to ensure you get decent units. This seams to be particularly an issue at 800w or less where the market is very competitive and price sensitive.My approach is to look at the current draw. The 400w unit at the chart table can draw current from the general DC supply to the chart table and loads are plugged in direct (through a multi socket extension lead). That's fine but anything bigger would need direct and close connections to the batteries and I don't want multiple AC circuits on the boat. Having two inverters both of which supplied the general A/C sockets sound like a recipe for problems.

[Nicholson58]

We run one 3.5 kw inverter only as needed. We have a high efficiency true sine wave inverter for small users. The parasitic loss for the small one is a lot less than the large one. 300 watt Samlex.

[atoll]

Originally Posted by Grimgrak

I've been seeing some nice fridge and freezer combos meaning they can run as both a fridge or a fridge based on how you set the temp they are usually stainless and stack one on top of the other on newer boats. Any idea the brand/model and if they are DC?

this would be my choice,as it will work either as a freezer or a fridge,or both,uses about 4-5 amps when running 12v or 2-3A 24v.
various sizes available,think 80L is the largest

https://www.marinesuperstore.com/ref...kaApHUEALw_wcB

The Dometic CoolMatic CRX 50 E offers 45 l of cool storage and an optional 4.4 l of freezer space. Providing a 3-in-1 solution, you can choose between having: a fridge, freezer or both at the same time! By automatically adjusting its fan speed to the ambient temperature the CRX 50 E also generates minimal noise. It boasts an intelligent electronic control of the compressor speed making it up to 25% more efficient. With temperature control via the soft touch control panel and a bevelled back edge for a close fit – this is one seriously efficient, intelligent fridge.

[wingssail]

It seems to me that this pursuit for maximum electric efficiency by using multiple smaller inverters (and using one to power an AC house hold refer and maybe another to power an AC household freezer) plus a switchable bigger one for washer and dryer(!) is adding a lot of complexity for probably little gain.

In my case simplicity is a very important consideration.

We have decided that the main Inverter/Charger should be hardwired into the boats AC outlet system. The AC outlets around the boat have shore power, if present, and Inverter power if shore power is not present. We can simply ignore the power source and depend on reliable AC. This is a simple use case.

The main Inverter/Charger does not run the refer/freezer (see below) and can be switched off when no AC loads are required. Even turned on it's "search" load on the DC side is only 5 watts, however we turn it off when at anchor unless it is needed.

There is a smaller, 170 watt, inverter in the nav area, wired to the DC accessory breaker, supplying power for electronic gadget's battery charging needs. The continuous power drain is not measurable and is not listed on the inverter's specs sheet, but it is low. We can turn this unit off at the DC distribution panel if we want to but rarely do.

Otherwise, we rely on keeping our AC electrical needs low.

Washer? Dryer? AC water maker? We don't have them. (Live lightly)

Refer/Freezer? I am still not convinced by the miraculous efficiency claims for some of these dorm fridges and there is no room in our boat to fit one in an a graceful way anyhow. Maybe in a 50 foot cat or a 60+ boat undergoing a major Galley area refit it could work, not in our small 43 ft boat.

Our 12v Dometic refer/freezer unit has technology which sounds exactly like the inverter fridges (it varies the speed of the compressor in response to cooling needs and DC voltage availability by varying the frequency of the three phase AC electrical output, and further compressor speed control is available), however it cannot run on zero power which some of the dorm fridges seemingly claim to do. But I think it is efficient.

Anyhow, it runs on 12v DC and it's always on and we monitor the power usage and on/off cycles carefully and it does not require an external Inverter.

Yes the 12v DC refer system costs more and is a top loading unit, but this is a boat after all, not a condo.

We've adhered to this simpler and smaller approach throughout our boat, and it pays dividends by being reliable and easy to operate and maintain, as well as resulting in a lighter and faster boat.

[Chotu]

We all make our choices and compromises.

A lacking galley is not one I’m putting up with. A 50’ cat with a 70ft air draft, currently weighing around 12,000-14,000lbs,, props that retract out of the water, Dagger boards, every possible pound saved? Yes. I already made my sacrifices. But tiny dorm fridges and pits to dig through when cooking? Hell no.

I think I’ll be plenty fast with 300-400 lbs added to have a real refrigerator and freezer, laundry and dishwasher (dishwasher is already on board).

My entire propulsion system and 6kw generator weighs a grand total of 492 lbs. 2 engines and a generator. 492 lbs.

I’ll be fast enough. Lol

[atoll]

re power usage
,i have a 12v fridge freezer 30liter which running draws 5A as well as
the 230v freezer 40liter running off the 24v system through the inverter which uses 2.5A total
both freezers cycle about 50% of the time
(inverter in standby,0.2A)

happy with the system,batteries are fully charged by 10 am on both 12v/400w pv and 24v /500w pv systems

[BjarneK]

If you want a small 200 VA inverter with low standby power, consider this:

https://www.studer-innotec.com/en/pr...aj-275-12-4834

Make sure to get the solar (-S) option even if you are not going to use it as a solar regulator. With this option, the 12 V version of the inverter has a stand-by power consumption of 0.3 W (that is Watts, so around 25 mA).

It is quite expensive, but good quality. I have had one in a leaky outhouse in Denmark all year round for ten years and it still runs. I have another newer one on the boat.

On the boat I have wired a transfer switch, so when I turn on the big inverter, that powers everything and when the big inverter is off, this little one powers the outlets. This means that I can leave the small one on day and night and always have 230 V in the power outlets for the small consumers.

We don't have anything on the boat that uses much 230 V power continuously. Only intermittent use like power tools, heat gun and such. For those things I turn on the big inverter with a conveniently located remote switch.