Aircon Without a Genset?

[rickbase1]

Further to requests from members viewing the Alpha 42 thread I thought I would share some of my ideas WRT onboard gensets and blue water cats.

I am currently 12 months into the build of a new series of Catamarans, with another 3-4 before we splash. The Architect is Roger Hill from NZ and the design is based on the 42 ft Montebello from AU built in 2010. Phil of Multihulls and Roger worked to create a second generation of the boat. It was great because we were able to closely critique the first generation, which was a very nice boat in itself, and build on that success to create a new series called the Balance 451.

I was fortunate enough to be able to design my own electrical and mechanical systems. My challenge was that I wanted a fast, light cat while still wanting some of the creature comforts that would allow my wife and I to enjoy the boat for years to come and that means having ample electrical supply and some air-con for tempering and de-humidification.

Together with the builder we decided on a 24V system as this significantly reduces the copper requirements and 24V products are readily available now.

Then I decided to go with a Lithium LiFePo4 based battery system. The Boeing event caused some reflection but with a good enclosure, a complete BMS (battery management system) and redundant banks, each fully independent, I feel we are in good order(I hope I don't have to eat these words) This gave me over 800 amp hours (1600 at 12V) of power, while weighing the same as just 4 8D AGM batteries.

The real beauty of lithium batteries is their ability to accept a high rate of charge, right up to 95%. These batteries can be charged at up to 3C. That means that if a battery has a 200AH rating it can be charged at up to 600 Amps, or fully charged in just 20 minutes.(to be safe I have kept it to 1C)

Many of you know there is nothing worse than having your genset screaming away for hours and watching your charge rate drop to almost nothing, because the system has gone out of bulk mode.

And even better, they can be discharged to 20% vs AGM which is 40-50%, thus significantly increasing our effective capacity.

They do seem to be more intolerant of complete discharge, but with a good monitoring system and full redundancy we should be ok. After a few months on the water I will try to give everyone an update.

For shorepower charging and A/C I am using a 24/3000 Victron multiplus.
For charging while at sea I decided not to use a small genset.

I looked closely at the Panda 4200, and several other 4-5K gensets, but it just didnt make sense to add yet another engine to the boat. Why add another 400-500 lbs when I already had two great 39HP Yanmars available?

After doing a series of daily load calculations, allowing for refrig, instruments and 3-4 hours of aircon, I determined I could add a high output (4kw) 24V alternator to each of my propulsion engines and running one of them for only 1-2 hours per day would yield me all of the power I needed. This is only made possible because the batteries can easily take such a high rate of charge. And now instead of a tempermental genset that needs maintenance, spares, oil changes, etc... I have a fully redundant charging system for the house batteries as well and it was still significantly cheaper than a genset.

And with almost a kilowatt of solar, and 300 watts of wind, in favourable conditions I may not have to run an engine for several days. The challenge with the solar was in boosting voltage up to 28.4V and getting a Lithium hi output charge profile. Bruce Schwabb was a great help here and recommended the Genasun Solarboost. I am also using his External alternator regulators with the 28.4V LiFePo4 charge profile on 2 x 28V 160A APS alternators so I can minimize engine charging run times.

For aircon I chose two 9KBTU mermaid units. I have them Y ducted to either the salon or the cabin, with one in each hull. I chose these as they were capacitor start units with a slow startup current (lock rotor) and both should be able to run happily off the one Inverter. (If not, I will add a second inverter) They will not keep it cool in the heat of the summer but they will temper and keep the humidity levels down. Beer will do the rest!

If anyone is interesting in more detail just let me know.

Cheers!

Rick

[Dockhead]

I've often thought that three diesel engines on board a catamaran, which is mass sensitive as it is, does not make sense.

With the very high rate of charge possible with LiFePo batts, I would think that you could make good use of high capacity alternators on the main engines in the manner you propose.

However, there are a couple of bottlenecks in your system you might think about:

1. You are completely dependent on one Victron Multiplus charger/inverter. You have no AC power without it. I have a lot of Victron equipment on board, and have found it to be quite unreliable, including my Multiplus charger. These things can be paralled; you might want to consider wiring up two in parallel. Or you could add a separate inverter.

2. You are completely dependent on one battery bank. What if something goes wrong with it?

One beautiful thing about a separate AC generator is that it is entirely independent of the rest of the boat's electrical system.

On the other hand, you have beautiful redundancy of two high capacity alternators, so you in effect have two completely redundant generating systems -- very cool.

Since you don't have Peukert issues with LiFePo batts, maybe you should consider breaking up the LiFePo bank into two separate ones (and maybe add capacity while you're at it?)? So each alternator charges its own separate bank with its own separate Multiplus? How cool would that be? That would make for very deep redundancy and reliability. You could easily wire it to charge both banks from one alternator, so as not to have to run both engines.

[Dockhead]

By the way, one other point --

be very conservative about what you expect from those inverters. Mine Multiplus is a 3000/24/70 unit which leads you to believe that it's a 3kW inverter -- hah. That's 3000VA, not watts, and at a low temperature. In real life at real temps (even up here), it does not like loads of much more than 2kW, although I have a big 24v battery bank and good wiring so minimal voltage sag. I guess you will somewhat over 1kW for each of those Mermaid units with the seawater pump, with startup load of nearly double that. So I don't think two of them would run happily off one nominally 3000VA inverter, not to speak of other AC loads on board. I think you would want at least double that amount of inverter capacity.

[sigmasailor]

Did you think of designing an all electric propulsion/regeneration system (Hybrid drive)? Now that would add to the fun wouldn't it? As long as you're sailing you will have ample electrical energy. In theory you would just need a single diesel engine with a generator and lots of batteries to store the energy.

[rickbase1]

Hi Dockhead, you make some salient points here, and I think I have addressed most of them in my design.

1) I agree with you and think the Victron is the weak link in this design. I have roughed in power for a second inverter, in case the Victron Multi does not live up to my expectations, and you are right, it requires about 1 kw running and 1.5 times(according to the literature) for lock rotor capacitor start. I wanted to use the 24/5000 but it is only available in 50hz/220. The upside is that worst case I loose AC and my wife looses her hair dryer, everything else is 24VDC powered.

2) I have actually designed two completely separate 400AH/24V battery banks, each with its own BMS, LOAD bus and CHARGE bus configuration. It is set up to run either one or both banks concurrently using a small display panel at the nav station. The BMS monitors every cell for voltage and temperature and reports it back to both the salon TV using the AV video input and the Raymarine E127 MFD. In addition there are local hardwired alarms for over and under voltage that disable either the CHARGE or LOAD bus respectively. I have also linked the alternator fields to the circuit breaker and BMS so as not to blow my diodes on an overvoltage trip. I am trying to program the BMS cpu's to talk CanBus/NMEA2K and send out some PGN's that I can use for redundant monitoring with my Maretron network, but that will have to wait. (This is the plan anyway; I'll report back on it after I have done full in situ testing)

3) Because I will be inducing a significant parasitic load onto the engines, I have included 2 Alternator disable switches at the helm that allow me to shut them off when I need full propulsion power. Additionally I have wired in independent fresh air blowers onto the alternators themselves. Based on a quick review, by keeping the winding temperature down I can pretty much make up for the blowers current draw, and hopefully increase the life of the alternators at the same time.

And to Sigmasailor, I did indeed consider a hybrid system. I found the regenerative charging possibilities intriguing, but ultimately decided against having one big genset and a single point of failure for all of my systems.

Thanks for your insight. I hope I have covered as many angles as possible but fresh eyes are always welcome !

Cheers,

Rick

[djmarchand]

Rick:

You have obviously thought through your electrical system well and have an intelligent design. I would challenge you on one point however: I don't think you are saving much if any money with your high output alternators.

Those two alternators, regulators, mountings, dual or serpentine belts are going to cost about as much as a small, compact, 200 lb genset like the Next Generation 3.5.

The genset will run your A/C all night long and will be a nice backup source of power.

David

[beiland]

Originally Posted by rickbase1

....
For aircon I chose two 9KBTU mermaid units. I have them Y ducted to either the salon or the cabin, with one in each hull. I chose these as they were capacitor start units with a slow startup current (lock rotor) and both should be able to run happily off the one Inverter. (If not, I will add a second inverter) They will not keep it cool in the heat of the summer but they will temper and keep the humidity levels down. Beer will do the rest!
Cheers!
Rick

Well I must admit you guys lost me on much of this electrical and monitoring discussion...just a little mental block situation & old school

But what did catch my attention was the capacitive start AC units. I do know that in the past most 'electric storage systems' needed to be oversized in order to supply those significant start up peak loads required for most AC units.

So now you are telling me they are (have) developed AC units that will start up with less power requirements due to a 'capacitive storage device' assistance??

Thanks, Brian

[rickbase1]

Hi Brian,

In an Ac circuit, as I understand it, the start cap acts as a phase offset device, allowing the motor to get a better magnetic push and pull (60 hz sine wave) during startup, reducing the startup current needed to get the motor turning. After a few seconds a relay diengages the capacitor and the motor spins normally. Lock rotor current (armature is not turning) is typically 5-7 times normal current. This is what dims the lights or trips your inverter when you first turn on a big A/C motor. If I am not mistaken this is sometimes referred to as a variable torque device with a high inrush current.

Whereas a DC type motor is always pushing in the same direction with its magnets (DC= direct current vs AC alternating current) so it is called a constant torque device.

Have you ever tried to use a plugin AC drill as a screw driver? It sits there and hums and then spins the head off of the screw but with a DC the torque is constant and you can slowly install the screw while having maximum torque.

Here is a good excerpt borrowed from Erin.

Most smaller, single phase motors usually have a permanent magnet armature that is pushed / pulled around by the rotating inductive field produced by the stator (outside) windings. The inductive field rotates simply as a result of the positive / negative alternations of the 60HZ AC current flowing through the windings. The problem is that when the voltage is applied, the 60HZ is applied immediately, the rotation of the field through the windings begins immediately, and the armature has no chance to react (or catch up, as it were) to the field.

The start cap provides that electrical "push" to get the motor rotation started. It does this by creating a current to voltage lag in the seperate start windings of the motor. Since this current builds up slower, the armature has time to react to the rotating field as it builds up, and to begin rotating with the field. Once the motor is very close to it's rated speed, a centrifugal switch disconnects the start cap and start windings from the circuit. Watching a single phase motor starting you can see that this all happens very quickly.

Without a start cap (such as when one burns up) when the voltage is applied, the motor will just sit and hum. But if you were to grab the shaft and give it a spin, the motor would (usually) start and run normally.

Hope this helps,

Rick

[Capt Hugh Wilde]

Check these out, they run on 12 and 24 volt

Marvair - Marine - DC Air Conditioner

[rickbase1]

Originally Posted by djmarchand

Rick:

You have obviously thought through your electrical system well and have an intelligent design. I would challenge you on one point however: I don't think you are saving much if any money with your high output alternators.

Those two alternators, regulators, mountings, dual or serpentine belts are going to cost about as much as a small, compact, 200 lb genset like the Next Generation 3.5.

The genset will run your A/C all night long and will be a nice backup source of power.

David

Hi David,

I thought I had replied to this one earlier but it seems my post got lost.

You make a good point here but I figured that after we added an exhaust system, thruhulls, fuel lines and filter, a mounting pad and sound shield it would be a bit more than that. The two alternators give me full redundancy with more than 8kw of charge capacity, and will weigh in around 60 lbs total with wiring for about $ 3,500.

Having spent many hours scooping out water pump impellers and servicing my old genset I frankly just wanted to try something different.

Interestingly enough hull #2 is going your way with a small genset.

I am eager to see if my concepts prove themselves. I will try to follow up with an objective update after a few months of use.

[rickbase1]

Originally Posted by Capt Hugh Wilde

Check these out, they run on 12 and 24 volt

Marvair - Marine - DC Air Conditioner

These look great !! I especially like the brushless DC motors. They tend to be very efficient, easily speed ajustable and long lasting. I wish I had found these last year when I was spec'ing out the boat. Never fails, there always seems to be a better mouse trap just around the corner !

Thanks for the info. Has anyone had good experience with these?

I found some 12VDC units but no 24V units in my searches.

[rickbase1]

Originally Posted by Capt Hugh Wilde

Check these out, they run on 12 and 24 volt

Marvair - Marine - DC Air Conditioner

ok, here is a possible show stopper. The pricing I found says that they are $ 6,800 each !

That is more than 3 times the cost of my units.

here is where I found the pricing.

DC Air Conditioner

Is this possibly a misprint ??

[beiland]

Originally Posted by rickbase1

Hi Brian,

In an Ac circuit, as I understand it, the start cap acts as a phase offset device, allowing the motor to get a better magnetic push and pull (60 hz sine wave) during startup, reducing the startup current needed to get the motor turning. After a few seconds a relay diengages the capacitor and the motor spins normally. Lock rotor current (armature is not turning) is typically 5-7 times normal current. This is what dims the lights or trips your inverter when you first turn on a big A/C motor. If I am not mistaken this is sometimes referred to as a variable torque device with a high inrush current.
...lots more

Hope this helps,

Rick

Thanks for that. I'll have to reread several times to digest it

[Kevin84]

Hey Rick, something to caution you about on your assumption that Lion batteries can be safely discharged to 20% capacity. I worked at Boeing on the Dreamliner during the battery problems. Those type batteries do not like high discharges. For example, Boeing recommends the battery to be scrapped and replaced if the charge drops too low. They are also sensitive to overcharging. Both being undercharged and overcharged can result in a thermal runaway. Be careful where you install them. I would also keep a temperature monitor on them with an audible and visual alarm I'm case the temp spikes on one. I will caveat thus by saying I have no direct experience with that brand of battery, only the ones Boeing uses.

Sent from my HTC6500LVW using Cruisers Sailing Forum mobile app

[s/v Jedi]

A couple of points:

- I have a CruisAir 18kBTU self-contained unit with a March pump, both at 240V/60Hz and I can run these of my Victron Quattro 12/3000.

- The 12/5000 is 220/50Hz. So is my 12/3000, but I reprogrammed it to 240V and 60Hz which is a 10 second job. I'm not sure if the 5kW also supports this but I would assume it does.

My genset outputs 240V/60Hz which goes into the Quattro (floating, ungrounded output). My shore power can be 110-240V and goes into a 3.6kW isolation transformer that outputs 220-240V which also goes into the Quattro.

The Quattro is a 12V EU model on which I have the computer interface and using the software from Victron, I set it to 240V and 60Hz; matched the charger profile to my batteries etc.

So the output is 240V 60Hz, which goes into a Victron Auto Transformer which creates a new neutral for 120-0-120 volt service.

I am now contemplating switching to induction cooking and thus 50A service…