The case for multiple small inverters

[Tupaia]

Fridges and freezers typically use Danfoss compressors that are available as 12 volt units. There is a simplicity aspect to using domestic units but these don't fair well in a marine environment and being air cooled are not very efficient in the closed confines of a boat. 12v keel cooled units are much more efficient and you have increased the reliability by eliminating the need for a separate inverter failure of which will render both fridge and freezer useless.
There is very little benefit in Pure Sign nowadays even electronic equipment can cope well with Quasi Sign Wave. QSW are less than half the price and more importantly less than half the weight of a PSW unit.
Do you really need a clock on the microwave that adds to internal night time light pollution. Units that have mechanical timers that are actually off when the say they are off, are more appropriate on board.

Just some things to consider.

[Culwatty]

get one of these, or two once for fridge one for freezer
https://www.amazon.co.uk/Laqiya-Temp...286653&sr=8-12

wire the trigger to a relay for your inverter on off switch then idle current .80a ish

i run a ring pro 3000w pure sine wave. hardly touches my small bank at idle and is on 24/7 i should really switch it off as all draw adds up!

cant tell you exact power use yet but i only have 300w solar and rutland 914i and 300ah of batteries. moving the battries to facilitate better balance for the boat and fit t105s (separate thread)

hth

[Chotu]

Originally Posted by Tupaia

Fridges and freezers typically use Danfoss compressors that are available as 12 volt units. There is a simplicity aspect to using domestic units but these don't fair well in a marine environment and being air cooled are not very efficient in the closed confines of a boat. 12v keel cooled units are much more efficient and you have increased the reliability by eliminating the need for a separate inverter failure of which will render both fridge and freezer useless.
There is very little benefit in Pure Sign nowadays even electronic equipment can cope well with Quasi Sign Wave. QSW are less than half the price and more importantly less than half the weight of a PSW unit.
Do you really need a clock on the microwave that adds to internal night time light pollution. Units that have mechanical timers that are actually off when the say they are off, are more appropriate on board.

Just some things to consider.

Well, no. I definitely don’t need to be powering microwave clocks. That was just something a different poster said I responded to.

The home refrigerators have too much going for them to even consider building a pit in the galley and running a standard marine refrigerator. I definitely don’t want that.

I’m just trying to choose inverters in a way that minimizes losses.

1400 watts solar and 440 (maybe 660) amp hours of batteries.

The less you use the batteries the longer they last so I’m looking at running bigger power consumption (water maker, laundry, dishwasher) during daylight hours and having just the refrigerator and freezer on at night without other loads.

[noelex 77]

Originally Posted by Palarran

I agree with this. If you can't afford the small amount of standby power loss, you need to look at your battery bank harder.

I do not agree. These small loads add up and become significant. Reducing loads that serve little, or no purpose is one of the steps to elctric happiness .

This is easy to show with some simple maths. For example a continal parasitic load of 15w tranlates to over 200AHrs (at 12v) after a week. If you run your generator or main engine once a week for couple of hours to make up a shortfall in solar production, even if you have a large alternator or battery charger capable of delivering a continual 100A then the generator or main engine run could be completely eliminated, simply by getting rid of this one small parasitic load.

There are many other parasitic loads on most cruising boats. Eliminating or reducing these can be very worthwhile. Who wans to listen and service a generator, or even fit one in the first place, when some small tweaks and careful choice of equipment could povide the same usable power.

Having said the above I am not sure multiple small inverters are necessarily the way to go. Some of the large inverters have sophisticated software that reduces the stanby current when no power is drawn. This technology is harder to find in small inverters. However, you do have to shop carefully for example the Mastervolt inverters are much better than the Victron inverters in this regard. The table shows the Victron 3000w inverter has a parasitic load of 20w at no output. The Mastervolt 2500w inverter draws 0.6w. There are a couple of caveats. Functions like a clock display often force the inverter to power up and there can be some delays starting the inverter with low loads at these maximum power savings settings. Nevertheless, careful choice of equipment can make a very significant power saving.

[atoll]

Originally Posted by Chotu

I don’t think this is right.

Inverters are sold based on their continuous output oddly enough. Most can handle near double their rating for brief intervals like the LRA of a compressor.

So a 300 watt model is supposed to be able to deal with the lra of 600 watts, yes?

Wouldn’t that work just fine for the compressor startup?

you would think so,but i have just fitted a 250w 24v pure sine inverter to run my 95w fridge,the inverter runs my drill that is 400w fine and should be able to handle surges to 500w, the inverter is located next to the batteries so no voltage drop,but the fridge stops it dead.

when running on the larger inverter which is 1200w the fridge runs fine,but you hear the fans start up momentarily when it switches on which indicates a fairly high load on fridge start up.

[Chotu]

Originally Posted by atoll

you would think so,but i have just fitted a 250w 24v pure sine inverter to run my 95w fridge,the inverter runs my drill that is 400w fine and should be able to handle surges to 500w, the inverter is located next to the batteries so no voltage drop,but the fridge stops it dead.

when running on the larger inverter which is 1200w the fridge runs fine,but you hear the fans start up momentarily when it switches on which indicates a fairly high load on fridge start up.

Well, that kills my theory.

Thanks for the recent real life experience data point.

If I can find the right big one, maybe that’s the best way. Checking out the Mastervolt.

Still, some of these ideas about using a thermostat to trigger the inverter for just the refrigerator and freezer have merit.

Or maybe I just need to forget it and cycle the batteries a bit more with the parasitic load of inverter and refrigerator electronics.

Never an easy decision when picking your poison.

[Matt Johnson]

The chart from Victron is watts not amps.... AES is 7w.

Matt

Originally Posted by Chotu

Where are you getting 15 watts?

I see 36 watts as the absolute lowest the 2kva unit uses when it’s completely off and looking for current to turn on.

Next level is AES mode and that’s 7 amps or 84 watts on standby.

24 hours of power completely off with no clocks on is 72 AH wasted.
24 hours of that AES is 168 AH wasted.

These are big numbers to just waste no matter how large your battery bank is.

This type of inefficiency is what I’m trying to avoid.

[Chotu]

Originally Posted by funjohnson

The chart from Victron is watts not amps.... AES is 7w.

Matt

Ok. Thanks. I was definitely misreading that.

In my defense, it’s nearly impossible to see the full width of pictures on the forum on my phone. They get cut off.

[Palarran]

Originally Posted by Chotu

Where are you getting 15 watts?

I see 36 watts as the absolute lowest the 2kva unit uses when it’s completely off and looking for current to turn on.

Next level is AES mode and that’s 7 amps or 84 watts on standby.

24 hours of power completely off with no clocks on is 72 AH wasted.
24 hours of that AES is 168 AH wasted.

These are big numbers to just waste no matter how large your battery bank is.

This type of inefficiency is what I’m trying to avoid.

The numbers are in watts already. So standby is 7 watts - nearly nothing.

[Jammer]

Originally Posted by Chotu

I had been looking at getting a big inverter (3kw) to run a refrigerator, chest freezer and whatever else, including microwave, dishwasher, washing machine.

The more I have looked into this, the more it seems that’s not the best way to do it.

Large inverters idling can use quite a bit of power.

Instead, I’m looking at getting a few small inverters. One for the refrigerator, one for the freezer, one for the microwave and whatever else, since they don’t run simultaneously.

Anyone have any thoughts as to why this is a bad idea?

The grand fallacy here is the idea that you can achieve an electrically efficient system by running a 120v household fridge and a 120v household freezer through an inverter. There's no way to do that regardless of what kind of inverter you use, or how many of them there are.


You'll be money ahead to get a 12v fridge and freezer, because you won't need inverters for them, or as much battery capacity, solar, etc. Running household fridges is houseboat thinking, and it works for those guys because they run a generator 24 hours a day if they're not on shore power.


I'll post my experiences with cheap 12v fridges on another thread.

[Palarran]

Originally Posted by noelex 77

I do not agree. These small loads add up and become significant. Reducing loads that serve little, or no purpose is one of the steps to elctric happiness .

This is easy to show with some simple maths. For example a continal parasitic load of 15w tranlates to over 200AHrs (at 12v) after a week. If you run your generator or main engine once a week for couple of hours to make up a shortfall in solar production, even if you have a large alternator or battery charger capable of delivering a continual 100A then the generator or main engine run could be completely eliminated, simply by getting rid of this one small parasitic load.

There are many other parasitic loads on most cruising boats. Eliminating or reducing these can be very worthwhile. Who wans to listen and service a generator, or even fit one in the first place, when some small tweaks and careful choice of equipment could povide the same usable power.

Having said the above I am not sure multiple small inverters are necessarily the way to go. Some of the large inverters have sophisticated software that reduces the stanby current when no power is drawn. This technology is harder to find in small inverters. However, you do have to shop carefully for example the Mastervolt inverters are much better than the Victron inverters in this regard. The table shows the Victron 3000w inverter has a parasitic load of 20w at no output. The Mastervolt 2500w inverter draws 0.6w. There are a couple of caveats. Functions like a clock display often force the inverter to power up and there can be some delays starting the inverter with low loads at these maximum power savings settings. Nevertheless, careful choice of equipment can make a very significant power saving.

I agree with you too :-)

If we could avoid it, we would. I don't need any clocks running. But my refrigerator has a microprocessor that it requires to run so I have to have inverted power to it 24/7. I've often thought about a small inverter to run just the refrigerator so the 3000 watt Victron could be turned off. But IMO your really dealing with a 1000 watt standalone inverter and so maybe it would save 4 watts. I have an 1100 AH bank and it really shouldn't make a difference between charging when the solar kicks in.

[Chotu]

Originally Posted by Jammer

The grand fallacy here is the idea that you can achieve an electrically efficient system by running a 120v household fridge and a 120v household freezer through an inverter. There's no way to do that regardless of what kind of inverter you use, or how many of them there are.


You'll be money ahead to get a 12v fridge and freezer, because you won't need inverters for them, or as much battery capacity, solar, etc. Running household fridges is houseboat thinking, and it works for those guys because they run a generator 24 hours a day if they're not on shore power.


I'll post my experiences with cheap 12v fridges on another thread.

the thread is about selecting either one large inverter or multiple small ones to power given loads. In the case if refrigeration, a cyclical load. In the case if everything else, user controlled loads.

marine refrigerator pits absolutely suck in every way and are just a tad more efficient than the best land refrigerators. The galley is the focal point of my life. Digging in a pit to find all the food is wasteful in terms of time spent, aggravation and even efficiency. How much heat is absorbed by putting the whole contents of the pit on what’s left of the counter when you’re trying to find something at the bottom? More than opening a door for 5 second for sure.

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

I’m off grid. Always. No shore power. Generator is only used for HVAC purposes. The rest is 1400 watts solar. 440 (I hope) or maybe 660 AH battery bank for night time loads. The less you drain the batteries the way longer they last, so I’m trying to maximize evening efficiency given the design parameters.

Another idea might be to just knock off the power to the refrigerator and freezer from say 3AM to 7AM each night. Not sure how good the insulation is on the house units. Probably not so great I’m assuming.

[rslifkin]

If really good refrigeration efficiency is key, you'd probably want to build your own setup rather than using something off the shelf, as you could likely do better than any store-bought 12v or 120v fridge.

But on the inverter thing, even within a size of inverter, the idle draw varies. So it's worth shopping around between brands to see if one brand / model jumps out as having a lower idle draw than another. Depending on how low an idle draw you can find and how much it changes between sizes of that inverter model, that will drive whether one or multiple makes sense. What you want for a power distribution layout may drive some decisions as well.

[Chotu]

Originally Posted by Palarran

I agree with you too :-)

If we could avoid it, we would. I don't need any clocks running. But my refrigerator has a microprocessor that it requires to run so I have to have inverted power to it 24/7. I've often thought about a small inverter to run just the refrigerator so the 3000 watt Victron could be turned off. But IMO your really dealing with a 1000 watt standalone inverter and so maybe it would save 4 watts. I have an 1100 AH bank and it really shouldn't make a difference between charging when the solar kicks in.

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.

[AndrewA2]

Im no expert here. But very interested in the idea of having a dedicated inverter for your always on devices (fridge/freezer etc), and then another inverter(s) for your infrequently used devices (tv, microwave, coffee maker, etc etc etc).

Maybe the cost of a super running efficient inverter for the always on stuff is worth it. and then inverters(s) that can be less efficient/costly but with very low/zero standby for those infrequent devices.

What i am hearing is that small draw can often trigger the inverter into full power mode, loosing the efficiency. Curious what the typical threshold is for that ?
Something like:
Sleep: .5%
Idle: 1%
Running: 100%
Overpowered: 200%
?