DC Powered Air Conditioning. The Bucket List Trip.

[scottinsydney]

Hello All, This is a new thread about achieving the goals of DC power
for existing aircons for our Antipodean Big Loop trip. Its not about the pros and cons of lithium batteries.

++

Following on from the 2021 lithium battery installation we'll now power the OSR, galley and twin cabin air cons via an inverter. There would be a switch somewhere to select Generator or Inverter power for these three units. The Victron lithium system is fantastic reducing genset usage by 75% so far and we have our "silent ship."

The purpose of all this is to have aircon available at night and sometimes during the day without running the noisy generator.

This is all part of the 2025 bucket list plan to go up to the Great Barrier Reef, on to Papua New Guinea and across to New Caledonia. The Admiral is in favour of getting me out of the house and already declared herself to be a FIFO wife... Fly In Fly Out. Kids will be in last years of school and holiday adventures await them.

It seems that moving to a 10,000 or 15,000 watt inverter and doubling or tripling the size of the lithium battery bank to a minimum of 400 or 600 amps at 48 volts (20kwh or 30 kwh hours) will provide enough power to get though a hot humid night. The solar farm on the flybridge roof will average 6300 watt hours a day.* Genset would still need to run to charge batteries.

The seven old Cruisair units may not be as energy efficient as newer units, but they are installed and working. Two aircons and pumps operating should use 10 Amps at 240 volts when compressors are running. The total cost of two additional custom made batteries is about US$8500 which will be less expensive overall and simpler than installing new or additional aircons. Plus the cost of the larger inverter.

On a hot day we could also run the galley aircon to take the sting out of the galley, wheelhouse and salon. We can also run the genset if we need to really cool the boat down. Big dehumidifiers will also work too.

So these are our initial thoughts and work could be completed by November. Does anyone have any comments about the plan or its execution?

*Apologies if I have my wh and kwh nomenclature incorrectly termed.

 

[SKYCHENEY]

I think the plan you laid out would work. I am guessing that you don't want to run the generator at night and that is the reason for this??

I enjoy not hearing the generator when at anchor and we usually don't need air conditioning so I limit my genset time to a couple of hours in the morning and evening with the inverter in use the rest of time.

But with the noise of the air conditioner units running anyway, I guess I don't see the need for large inverter when you can just run the generator. However, most places we go it is a common courtesy to shut down generators from dusk until dawn so maybe its the same where you travel.

 

[scottinsydney]

Hi SKY, Thanks. I have edited original paragraph 2. But yes you are correct, we do not want to have the noisy genset running at night. It now seems the Victron technology will allow us to power the aircons by inverter and using an auto transformer provideing both 240 and 120 volt circuits at 60hz. The inverter system was pre wired with 10mm cable for each load circuit so it should easily handle a couple of aircons. (A wiring diagram will be completed by an electrical engineer, as we did with the original battery/inverter install.)

 

[JD5652]

The inrush current when large pumps start is usually the limiting factor in any type design.

Are you incorporating "soft starts" on your AC units and raw water pumps to limit the inrush current?

 

[rustybucket]

The air conditioners and the large pump(s) required to run them are going to suck a ton of power. Add to that the load of the fridges, freezers, tv's, lights...etc.....

You gonna need to fill one of the state rooms with batteries lol.

Best of luck to you with all this, but I'm not sure the juice would be worth the squeeze. Maybe a generator sound shield? Or new/better ER sound insulation? Heck for the cost of this you could throw in a brand new generator and a quiet run muffler or something?

 

[cww]

This seems like a LOT of effort and expense to avoid running a generator. The owner before me put in a new northern lights 20kw with a sound shield on it. I'm not exaggerating when I say you can't even tell it's running unless you happen to be standing right above it in the galley, and even then it has to be a quiet day with no radio, TV, or anything else on.

I put a new Phasor 12kw in my Chris-Craft and skimped on the sound shield, I used to think they were unnecessary. That one you can hear running inside the boat but it's not loud or offensive. Now that I have a soundshield on the new boat, I don't know that I'd ever not want to have one again. The difference is massive. My boat came to me with a 5kw inverter and a large additional battery bank to power it. The former owner put it in. In the year I've had the boat, I've used it exactly one time, and that was when the generator was broken.

To each their own I suppose.

 

[rustybucket]

This seems like a LOT of effort and expense to avoid running a generator. The owner before me put in a new northern lights 20kw with a sound shield on it. I'm not exaggerating when I say you can't even tell it's running unless you happen to be standing right above it in the galley, and even then it has to be a quiet day with no radio, TV, or anything else on.

I put a new Phasor 12kw in my Chris-Craft and skimped on the sound shield, I used to think they were unnecessary. That one you can hear running inside the boat but it's not loud or offensive. Now that I have a soundshield on the new boat, I don't know that I'd ever not want to have one again. The difference is massive. My boat came to me with a 5kw inverter and a large additional battery bank to power it. The former owner put it in. In the year I've had the boat, I've used it exactly one time, and that was when the generator was broken.

To each their own I suppose.

Agreed on the soundshield. My old boat had a westerbeke without sound shield, the hatt has sound shield, the difference is quite substantial, and I probably would not have a gen without an enclosure on future boats.

 

[oscarvan]

Second the soft starts on the AC's. Other than that you seem to understand the math and have the wallet to support it, so go for it.

Lots of pictures and a schematic or two would be nice to see.

 

[rustybucket]

Second the soft starts on the AC's. Other than that you seem to understand the math and have the wallet to support it, so go for it.

Lots of pictures and a schematic or two would be nice to see.

Def post a build thread as you go through the process. Would be super cool to follow along with you!

 

[VieEnRose]

Based on my limited knowledge and looking into this for the sail boat, the only way this makes sense is with something like the 12v Mabru units. Otherwise the complexity and cost makes no sense and it's better to run a generator.

 

[Boatsb]

I'm sure nobody wants to know how the last boats I did this on worked out but I'll post it anyway.

Properly designed and installed inverters can and often do support Air Conditioning.

From a small unit in the owners cabin on a sailboat to the ability to run 4 or 5 units over night it is just dependent on the design.

Addie-cat ran 4 or 5 units and started to cook dinner on inverter power. Yes it was a test to see if we could pull that much and is not a daily occurrence but it worked.

Another vessel I setup up has 3 AC units and when on inverter can run them. But he can't turn on the induction cook top burners and the oven at the same time.

I have 3 customers with small owner units in sailboats running off inverters. I also setup a grand banks with a 5k AC in the master on an inverter with generator auto start.

I'm not too excited about the marbu as it's only 12 volts and I'm not sure how efficient it really is. My buddy has Installed a bunch of dometic units that have always worked well when we do these projects.

So there it is. Its not only possible but can be easy to use. If a system is designed and implemented correctly it's a fantastic upgrade.

 

[scottinsydney]

So the decision is made to make the existing aircons operate off DC, genset and shore power. No turning back. This is a DC project and thread.

I guess it comes down to how you use your boat. We are on a swing mooring with no shore power. Sometimes we are on board for only a few hours on a humid day and it would be nice to have aircon for that amount of time knowing the solar panels will replenish the battery the next day.

We have a newish 2010 #2 Phasor 20Kva with sound shield, but its noisy throughout the lower levels of the boat. Its been run for 500 hours a year since 2017. The Phasor uses up a heap of fuel and significantly reduces the range of the boat before refuelling. My guess is it uses 1/3 of our available fuel each year.

In February 2021 we cut a hole in the roof and craned out the already broken 40 year old Kohler #1 genset. The real estate was already marked for the inverter and single 48v/200amp lithium battery. The lithium battery / Victron gear proved itself very successful as a genset replacement during our Christmas holidays. It makes sense to now complete the covid delayed solar farm on the flybridge roof, get rid of the old 32 volt Furuno TV radar and its 6' whirligig antenna array and replace it with a simple Furuno wifi radar and Ipads.


#1 Kohler Removal

These projects all take a year or so and the costs are spread out over time. Implementation is easy but working out how to do it is the hardest (most interesting) part. A younger electrician who might have done the work could not understand my reasoning for wanting 48 volts, a big stainless single battery with a 250amp BMS or grasp the system's future expansion to include a 48 volt bow thruster and possibly more big batteries.

Using new DC technology, boats like our Hatts can now operate as off grid homes when at anchor or living on a swing mooring thanks to lithium and Victron type products. The galley appliances, power outlets and AC lights all work perfectly. DC air conditioning on its own dedicated circuit should work too, but as pointed out by HOF members, you need to power it all and it needs to be well designed. A genset will always be required until there is a replacement technology.

I looked at additional 12v air cons but 48 volt power would have to drop down to 12 volts. Its easier to make use of the 240 and 120 volt aircons already installed. Only the switch board wiring needs to be modified. With a 15000 watt inverter there would be limited issues of overloading if compressors cycled at the same time.

The surge current required for a smaller air con appears to be 36 amps or 8500 watts. The Victron website indicates our existing 5000 watt inverter can maintain this for 5 seconds which is fine. Soft start upgrade is definitely an option too.



The question of what to do with the old AC #2 and #3 panels is an interesting one as most of the circuit breakers are to do with aircons and pumps. If the project proceeds / succeeds, these great old panels will become mostly redundant. At this stage it looks like each aircon will have a 3 way selector switch located near each existing AC panel with GEN-OFF-INV and a new 2 or 3 pole circuit breaker. A grounding consideration is that the AC panel grounds to its own buss bar and the auto transformer / inverter ground through the inverter's grounding relay. (However both grounds and the neutral bar for the 110 volt circuits end up at the boat's ground/engine block.)

My estimate for the 240v cable, wiring, circuit breakers and switches is about US$400 or so. I can add a new battery or inverter from there.

And of course its just as easy to upgrade all seven air cons with the DC option as it is to wire just three. (I think I just supersized myself!).

 

[Boatsb]

No need to add the 3 way switches. I have installed a bunch of systems that use the existing wiring and switches.

 

[JD5652]

The surge current required for a smaller air con appears to be 36 amps or 8500 watts. The Victron website indicates our existing 5000 watt inverter can maintain this for 5 seconds which is fine. Soft start upgrade is definitely an option too.

With multiple air conditioners and other "heavy" pump loads, the electrical design challenge is to ensure that none of these loads start at the same time, or if they start at the same time, you have taken that into consideration in your design. Timing circuits, soft starts and interposing relays will most likely be required to ensure you avoid overload conditions due to inrush currents.

 

[52CMY]

Following with great interest. I'm currently upgrading my 52CMY with 30KWH of LiFePro (6 x 48v rack batteries in parallel), dual Quattro 5KW inverter/chargers (split-phase 240VAC) and 2KW of solar (8x160w flex panels on the sundeck + 800w of bifacial panels on my aluminum tube radar arch.

My two (American voltage) Victron Quattros will be about as powerful as my 20KW Onan GenSet and my upgrade is sized to power the whole boat electrical load. Also with the Quattros' power assist feature, I can program the Victron system to use battery and solar to partially power the boat pierside when shorepower is limited.
On the hook, this will be enough capacity to run 1 (or maybe 2) stateroom 240VAC Dometic HVACs (6,000 & 8000BTU units with softstarts) overnight with minimal GenSet use.

In the next few years, variable speed compressor HVACs will be introduced that are much more efficient than the current ON/OFF cycling units that we're used to-- several start ups are developing 12, 24, & 48VDC HVAC units-- Marbu, IntegralSolutions and Termodinamica are three companies in the hunt. I'll wait till the dust settles regarding their actual reliability and value before I consider buying, but it's a promising technology to pair with big battery banks.

 

[drburke]

With multiple air conditioners and other "heavy" pump loads, the electrical design challenge is to ensure that none of these loads start at the same time, or if they start at the same time, you have taken that into consideration in your design. Timing circuits, soft starts and interposing relays will most likely be required to ensure you avoid overload conditions due to inrush currents.

Since this thread is fundamentally about applying new technology, I would respectfully point out that such surges are trivially accommodated by so-called "Ultracapacitors" or "Supercapacitors" across the load.

Obliviates the need for elaborate sync operation, soft start, inrush accommodation, or other; probably just initially rely on the over-capacity designed into the inverter, then as warranted add caps (<$50) each where required.

DAN

 

[drburke]

I guess I should explain myself a little more. Those who, like me, may remember "old school" capacitors may not get what I said.

Basically, there is a new generation of capacitors based upon kind of a furry dielectric of carbon surface which can therefore hold *enormous* numbers of electrons thus energy.

But there is a catch (isn't there always?). The max voltage is around 2.7V, so they generally exist in banks. Because they can charge unevenly, some sort of balancing circuit is beneficial as well.

The payback is a group of 5 or 6 will support standard 12V systems (with headroom for charge voltages--not completely necessary if using a well regulated DC-DC like our Newmars).

Nowadays they are appearing as battery replacements for automobile starting (at least one member has such a system) thus capable of hundreds of amps for a brief period.

Without endorsing any one supplier, check eBay for "supercapacitors" for a sample offering.

This came up in the context of supporting some potentially undersized cables for a powerful macerator on a new head installation--easy to eliminate voltage sag this way.

I wonder if Scott has paired any with his numerous Victron installs?

DAN

 

[drburke]

For the anal like me:

Energy in a capacitor
=1/2 C V [SUP]2[/SUP]
=0.5⋅1 Farad⋅12V⋅12V
=0.5⋅1 F⋅144V[SUP]2[/SUP]

for 1 Farad at 12 Volt = say 72 Watt seconds per Farad.

Car starting = 12V⋅500A⋅1 second as above
= 6000 Watt seconds.

So capacitance required to supply this energy at 12V =
6000/72= 83F.

Thus, 500 amps for 1 second is around 83 Farads, and such a system on eBay is for full battery replacement which is not our goal.

Rather, we want about 20% or perhaps 100A (generously) so 16F as a buffer is fine. One just wires it in parallel at the load end of the cables (at the AC unit).

DAN

 

[SKYCHENEY]

My friends 1978 60C has a bank full of capacitors for his ships service that runs all of the air conditioners. I liked that idea as you don't see those spikes when the compressors turn on. Hatteras thought to do that in 1978. I know its not new technology, but I was impressed as I had never seen another boat of that vintage with a bank of capacitors.

 

[scottinsydney]

Could you please provide an example product and how and where do you wire this in to the AC circuit? I am curious. Need to see a picture of the part and drawing to understand.