Interesting article on air conditioning and inverters

[HawkX66]

This article is a bummer, but nice to see a definitive answer to the question of whether you can run a/c for any amount of time using an inverter. The answer is effectively no.
"Self-sufficiency with solar is a wonderful thing, but it has its limits. You can easily keep up with LED lights and efficient refrigeration at anchor, and can come close to keeping up with an autopilot underway, but running air conditioning or any large load with an inverter is just too much.
Traditionally air conditioners required about twice the running current to start them, so a unit with a 12-amp running current could take 24 amps to start the compressor. This high starting current made air conditioners hard to run from small generators and even on docks with significant voltage drops. The new more efficient units have far lower starting currents.
An inverter allows you to run a 120-volt load from a 12-volt battery. It doesn’t do this for free. To be able to provide the 120-volt power it must draw 10 to 11 times more current from the battery. A midsized air conditioner will draw 10 amps when it’s running, plus another amp for the water pump. This theoretical 11-amp load will require roughly 120 amps from your batteries.
To sum it all up, your inverter and batteries would likely be able to start and run a new efficient air conditioner, but not for very long. Your 600-amp-hour bank can efficiently supply maybe 400 amps of power. Drawing current at 120 amps, your charge will last a little over three hours. Replacing that 400 amps will require you to run your engine for hours, and this is with the air conditioner turned off.
Your best bet for air conditioning in a marina is to plug in and underway you will need a generator. Enjoy your time in Grenada and look forward to cooler weather in fall up island."

https://sailingmagazine.net/article-2136-can-i-run-air-conditioning-from-an-inverter-.html

 

[WV 320 Dancer]

Good info thanks for sharing

 

[J Hopsalot]

In the article they don't discuss Lithium battery banks.
LiFePO4 are more efficient and while not meant to replace a generator they provide a nice environmentally and acoustically favorable option. Also, they are starting to drop a bit in price, but just a bit.
Here is nice article that had me intrigued. https://becomeacruiser.com/switching-to-lithium-batteries-on-a-boat/
Have a project to install a 600 amp bank on my boat (no Gen). Will see how it goes in regards to running my AC for few hours and allowing me to have cup coffee in the morning

 

[hughespat57]

This article is a bummer, but nice to see a definitive answer to the question of whether you can run a/c for any amount of time using an inverter. The answer is effectively no.

This is a yes and a no...
Given the situation described no it's not practical.
Sailors by nature don't want to run their engines just to produce electricity.
Thus primarily solar charging. And you just cant put 4+ Kw of solar panels on a boat, not enough surface area.
The second issue is trying to do this at 12v; the current requirements at that low voltage are huge complicating cabling, fusing, switching and charging.

But when compared to a dedicated AC generator there are alternative designs. I am going to undertake this over next winter.

First it will not be integrated at all into the existing 12v systems. They will remain as is. (KISS)

Think of this as similar to an engine driven generator which is a purpose built AC power source.
The inverter/charger will be true sine wave 240VAC split phase (240/120), 48VDC, 6Kw; not that I need that much power but it is required for the HVAC startup load. The battery pack will be a purpose designed LifePo4 with BMS in a custom aluminum battery box.

This will be phase one, shore power charging only.
I am going to test this for run time ability and general function.
If this proves workable, then phase two will be underway charging.

Underway charging will be a dedicated 48VAC 3Kw PMA (Permanent Magnet Alternator) with external rectifier and MPPT charge controller.

Trying to integrate these functions at 12VDC just gets to complicated with such high DC currents required. 48VDC requires 1/4 the current, smaller more manageable windings, wiring, fusing, switching. The inverter electronics at 48v are more reliable since each Mosfet carries less current. Internal transformers are more reasonable again since 1/4 the voltage/current differential.

The reason for the "custom aluminum battery box" is because thermal control/protection of the LifePo4 batteries is the single greatest risk. Both risk of thermal run away (low with LifePo4 but still possible) and battery longevity. This is a key safety part of my design as it will insulate the batteries from engine room heat and be separately ventilated. It will have both manual and automatic power disconnects.

 

[HawkX66]

Sounds like a couple of interesting projects you guys are thinking about. I'll be interested to see them. For my purposes I'll just end up with a generator. My boat came from the factory with one, but the PO removed it. The wiring and plumbing is all there. I already have an 8eozd I bought that's a diesel, but I want to sell it and get something smaller. Around 4.5kw-5.5kw.

 

[ttmott]

I'm way down the road on this. What I'm dealing with is after I had all of the desired loads tallied is we need over 1345 AH in Lithium batteries to make it work. That is essentially run the boat's refrigeration, normal receptacle loads, the DC loads and the two forward 18K BTU AC units including the raw water pump for 8 hours. In other words all night without the generator running. The con ops was to allow a depth of discharge to 80% on the batteries then the system will command the generator to start for a charge cycle. That left a 10% margin in the battery bank for engine starting. As it ends up starting the engines is rather insignificant in the battery AH size but the battery must be able to carry the initial locked rotor load as well as the cranking load which for my Cummins QSM's is 350 AMPS at 12 volts DC. There is no house bank or engine bank just one large battery bank. Another essential reliability thing is to have individual BMS's for each battery in the bank so should a BMS crap the bed the balance of the bank is still there. I think the direction that @hughespat57 is going on a single BMS will end up being a very large risk. My boat systems are 120/240 volt; I will have dual 3KVA inverters running in split phase to provide the higher voltages but yet as there are dual inverters I still have the redundancy to get the batteries charged rapidly should one be lost. The second challenge is to have the engine alternators a part of the charging circuit which is very difficult on two fronts - the first is the current demand from Lithium batteries will overheat and fry the alternators so a dedicated charge control system which measures the alternator temperature is needed. @hughespat57 plans to have a standalone alternator (if I read the above correctly) that is moderated using a MPPT charge controller however I haven't seen an MPPT charge controller big enough to really support rapid charging that Lithium batteries really excel in and one of the big benefits of them. Alternatively my QSM11's will be fit with 150 amp Balmar alternators and Balmar charge controllers that can safely provide 90 amps of current for each alternator. The problem then becomes using two alternators to charge a single battery and alternators tend to compete for charge priority and end up not living up to the potential. Balmar makes a device they call a Centerfielder that fixes the issue. The second big issue is should the battery BMS trip the battery bank off line and the alternators are charging they will go extremely high in voltage and not only fry themselves but take out anything connected in the circuit (MFD's, stereo, radar, you name it). This is why I have a BMS for each battery and a Sterling APD on each alternator. Anyhow, anyone that says a lithium battery is a drop-in is doomed to disappointment sooner or later. So where an I at on this project? The engineering company that is doing the design finished up the load analysis and will be wrapping up the drawings this month. We have been discussing the system with Battelborn Batteries over the last year with the intent they will provide not only the batteries but all of the Victron and Balmar components. The below is the preliminary sketch we put together before getting the engineering in place. Right now to do this we need five Battleborn GC3 batteries... Go look them up.. I have the calcs also if anyone desires to see how this is done.
So to address the original post - to do it right it is an eye opener on how much energy is required.
Tom

 

[ttmott]

Regarding the batteries themselves. I've learned a lot on lithium in our engineering discussions and with technical discussions with Battleborn. I think BTW that from a technical aspect and customer technical discussions Battleborn leads the pack by a significant margin; and, we've looked at all the batteries.
There are specific operating parameters that lithium batteries need and that is primarily temperature; the crux of it is keep them within 20 Deg F and 140 Deg F and you'll be ok. They will not be damaged below 20 degrees but they cannot be charged at or below that temp. Temperatures higher than 140 will simply take life away and for what these cost high temperature is a non-starter. A quality battery will perform continuous cell balancing, protect it's self from under voltage, over charge, over current, and under temperature charging; that is the purpose of the BMS. Remember, the BMS is not to protect the boat's systems but solely there to protect the battery. It is amazing however that these batteries will pretty much give a steady state voltage until the battery is depleted and a good lithium battery will give around 5000 cycles at consistent discharging to over 80 percent of the rated capacity. Compare that to lead acid which, if we are lucky and really baby the battery will give 700 cycles limited at a 50% discharge. Really, if you were to own a boat long term the lithium battery becomes quite cost effective.
Anyhow - thats it...

 

[TheDudeAbides]

Don't know if you've come across this article but it might offer some possibilities, at least in application.

https://panbo.com/dc-air-conditioning-comfort-on-the-water-no-generator-required/

The biggest draw in A/C units is the initial ramp up of the compressor. Essentially it's a motor and typically only has an on/off operation. The VAST majority of the draw comes when the unit kicks on and the enormous amount of amperage required to get that compressor from 0 to full run in a matter of seconds. That's why in many houses the lights dim for a second when the AC first turns on. Most modern A/C unit designs (for home) these days use inverter compressors and ECM motors, which means they have speed control on them to slowly ramp from stop to the required speed that is necessary (i.e. demand only calls for 62% instead of 100% in a particular situation). You consume 1/3 or less amps initially and your total amp draw is much lower. Think of it like a car accelerating from stop by slowly applying the gas pedal rather than flooring it from a stop. So you need less amp capacity because of the starting current required and it is much more efficient because it can throttle back to where it is actually needed rather than banging on & off to maintain temperature setpoint.

 

[HawkX66]

The ramp up was a big feature of our new HVAC system at our house. I had to install both an upstairs and downstairs heat pump including registers and ducts. Home was built in 1730...
It'd be nice to have a system where you didn't need a generator, but the expense involved doesn't make sense for me. I was thinking purely from an underway standpoint. Not for overnight or while stopped. I'll just go with a genni for that.

 

[Pirate Lady]

Interesting discussion. I have found that most nice destinations on the bay have rooms on premise or within walking distance. Annapolis, St Michaels, Oxford, Chester Town. So I’ll get take the zodiac ashore and leave the boat to the mosquitoes til the weather cools enough to sleep comfortably onboard.

 

[Craig]

On my previous 270 I had 300ah dedicated house bank that would last 5hrs to 50%. T stat set at 78. 5k btu Marinaire unit. 1000 watt pure sine wave inverter. The old cruiseair wouldn't even start up with that set up.Cabin wasn't ice cold but kept it bearable on the hook.

 

[ttmott]

Don't know if you've come across this article but it might offer some possibilities, at least in application.

https://panbo.com/dc-air-conditioning-comfort-on-the-water-no-generator-required/

The biggest draw in A/C units is the initial ramp up of the compressor. Essentially it's a motor and typically only has an on/off operation. The VAST majority of the draw comes when the unit kicks on and the enormous amount of amperage required to get that compressor from 0 to full run in a matter of seconds. That's why in many houses the lights dim for a second when the AC first turns on. Most modern A/C unit designs (for home) these days use inverter compressors and ECM motors, which means they have speed control on them to slowly ramp from stop to the required speed that is necessary (i.e. demand only calls for 62% instead of 100% in a particular situation). You consume 1/3 or less amps initially and your total amp draw is much lower. Think of it like a car accelerating from stop by slowly applying the gas pedal rather than flooring it from a stop. So you need less amp capacity because of the starting current required and it is much more efficient because it can throttle back to where it is actually needed rather than banging on & off to maintain temperature setpoint.

Inductive load inrush current is a concern but fortunately the inrush loads really isn't an impact to the AH size of the battery, however, that inrush must be not only managed by the inverter but also the conductors to the battery bank and the current capability of the batteries themselves. Most modern inverters can manage much higher peak loads for things like motor starting. The Victron Quattro 3KVA can manage a 6KVA peak load for example. The issue becomes, in the case of lithium batteries, can the battery manage such high peak current. Most lithium batteries assemblies cannot manage high current starting loads due to their inadequate BMS controllers; they will trip off line. It interesting that except for Prismatic cells the individual cells that make up the battery assemblies can discharge at incredible current, you can arc weld with the battery cells, however, the manufacturers simply don't utilize a BMS than can deliver the high currents - they are expensive. Multiple batteries can be gained in parallel to up the current capabilities but the means and methods to tie in parallel becomes problematic to ensure the bank is drawn equally across each battery. You could imagine that if one battery in a parallel arrangement is the first in line to the load and it trips on over current then the next trips and next; they will cascade to a total failure. 90% of all lithium battery assemblies are designed for constant steady state discharge loads; very few have robust enough BMS to manage say 200 amp discharge currents. On one of my 18K BTU cooling units the start current was measured at 26 amps and the run current 4.7 amps. That 26 amps is at 240 volts which equates to a whopping 520 amps from the 12 volt batteries which is a coincidental 6.2KW demand for a fraction of a second on the inverter.... Now in my case the HVAC units on the inverters will have soft start modules installed which reduces the inrush to less than 12 amps at 240 volts. All of this must be a consideration in the design.

 

[J Hopsalot]

I'm way down the road on this. What I'm dealing with is after I had all of the desired loads tallied is we need over 1345 AH in Lithium batteries to make it work. That is essentially run the boat's refrigeration, normal receptacle loads, the DC loads and the two forward 18K BTU AC units including the raw water pump for 8 hours. In other words all night without the generator running. The con ops was to allow a depth of discharge to 80% on the batteries then the system will command the generator to start for a charge cycle. That left a 10% margin in the battery bank for engine starting. As it ends up starting the engines is rather insignificant in the battery AH size but the battery must be able to carry the initial locked rotor load as well as the cranking load which for my Cummins QSM's is 350 AMPS at 12 volts DC. There is no house bank or engine bank just one large battery bank. Another essential reliability thing is to have individual BMS's for each battery in the bank so should a BMS crap the bed the balance of the bank is still there. I think the direction that @hughespat57 is going on a single BMS will end up being a very large risk. My boat systems are 120/240 volt; I will have dual 3KVA inverters running in split phase to provide the higher voltages but yet as there are dual inverters I still have the redundancy to get the batteries charged rapidly should one be lost. The second challenge is to have the engine alternators a part of the charging circuit which is very difficult on two fronts - the first is the current demand from Lithium batteries will overheat and fry the alternators so a dedicated charge control system which measures the alternator temperature is needed. @hughespat57 plans to have a standalone alternator (if I read the above correctly) that is moderated using a MPPT charge controller however I haven't seen an MPPT charge controller big enough to really support rapid charging that Lithium batteries really excel in and one of the big benefits of them. Alternatively my QSM11's will be fit with 150 amp Balmar alternators and Balmar charge controllers that can safely provide 90 amps of current for each alternator. The problem then becomes using two alternators to charge a single battery and alternators tend to compete for charge priority and end up not living up to the potential. Balmar makes a device they call a Centerfielder that fixes the issue. The second big issue is should the battery BMS trip the battery bank off line and the alternators are charging they will go extremely high in voltage and not only fry themselves but take out anything connected in the circuit (MFD's, stereo, radar, you name it). This is why I have a BMS for each battery and a Sterling APD on each alternator. Anyhow, anyone that says a lithium battery is a drop-in is doomed to disappointment sooner or later. So where an I at on this project? The engineering company that is doing the design finished up the load analysis and will be wrapping up the drawings this month. We have been discussing the system with Battelborn Batteries over the last year with the intent they will provide not only the batteries but all of the Victron and Balmar components. The below is the preliminary sketch we put together before getting the engineering in place. Right now to do this we need five Battleborn GC3 batteries... Go look them up.. I have the calcs also if anyone desires to see how this is done.
So to address the original post - to do it right it is an eye opener on how much energy is required.
Tom
View attachment 110756View attachment 110754 View attachment 110755

Thanks ttMott,
I learn something each time I read your posts. This time the comments regarding the "centerfielder". I'll be sure to discuss this in detail with my installer. We already have plans for a charge controller, not sure about the APD.
I'll take notes as I get closer to install.
Right now trying to decide if I should go with Victron 200 amp or Battleborn 270s. Not sure if the Battleborns are compatible with the Victron Energy GX Touch 50 and Cerbo GX which my installer recommended. We are investigating to see if the GX touch will display the BMS from each Battleborn battery.
It's a journey for sure!

 

[ttmott]

Thanks ttMott,
I learn something each time I read your posts. This time the comments regarding the "centerfielder". I'll be sure to discuss this in detail with my installer. We already have plans for a charge controller, not sure about the APD.
I'll take notes as I get closer to install.
Right now trying to decide if I should go with Victron 200 amp or Battleborn 270s. Not sure if the Battleborns are compatible with the Victron Energy GX Touch 50 and Cerbo GX which my installer recommended. We are investigating to see if the GX touch will display the BMS from each Battleborn battery.
It's a journey for sure!

Since we started the design the Cerbo/Touch came out; that is the direction we are going. The Cerbo or any GX device really doesn't care about the batteries, Battleborn or any other; you really need a shunt however to make the system work correctly as designed. Now the Victron batteries have a data interface obviously with their BMS controller but also with their GX devices which really opens the field on battery management and visibility and also now the GX devices have NMEA 2000 compatibility so the system can fully integrate with the boat's MFD's like Garmin and Raymarine. But to your question you do not need to have Victron batteries with their GX control systems. The Battleborn batteries have no external interface to monitor their BMS; this is another reason I have individual BMS for each battery - that redundancy thing. One thing to be aware of is ABYC is considering code language for use of lithium batteries which includes the requirement to have a data interface with the boat's systems to alert of an impending BMS malfunction or trip. The Victron batteries have this feature intrinsically with their integration into the GX devices. The only down side to the Victron batteries is they are very limited in the current they can deliver; make sure to read and understand all the manufacturer's specifications for batteries.