OK, let's work through this together. First of all, the maths. Take a small, top quality marine air conditioning
unit like the Cruisair
Turbo Stowaway. Take the smallest unit available -- assume you will be cooling
one small cabin
for sleeping on a hot night. The 18,000 BTU model draws 5.5 amps at full load at 230 volts. Let's assume a 30% duty cycle over 12 hours -- you need 4.5 kW/hours of power delivered at the unit, to get from 20:00 to 08:00 on battery
4.5kW/hours of power is 360 amp/hours of power at 12.5 volts. Let's increase that by 20% for the inefficiencies of inversion, storage
, and transmission
-- 432 amp/hours.
Let's assume you are rapid charging
, so you won't get the bats beyond 80%. You have the range of 80% to 50% to work with -- 30% of the nominal capacity (and this assumes that the batts are brand new and providing 100% of their nominal capacity). So in order to supply 432 amp/hours of power you need 432 * 100/30 = 1440 amp/hours of battery capacity. Now that is just the power for the aircon --
this is what you need on top your capacity for ordinary loads like lighting
So besides the massive battery bank, you will need a way to get that power into those batts every day. At a 25% acceptance rate (and that's probably somewhat optimistic), you will need a battery charger
(on top of what you have for ordinary purposes) of 360 amps of power. That's about 5 kilowatts, and with inefficiencies will draw probably 6 kilowatts of power to run, maybe more. Depending on the type of genset, you will need 7 to 10 kilowatts of generator
capacity (a heavy duty 1500 rpm
genset can be run safely at 80% to 90% of nominal capacity; a 3000 rpm
genset much less; a cheap
frame genset even less). This will put into the batts the necessary power in about two hours, I guess.
So I think we can agree that this doesn't look too good, right? Namely running air conditioning
on inverted power.
So if you want to run the aircon from a genset, the question is what type and how big.
frame genset you showed will be extremely noisy and will vibrate a lot. It is designed for running construction equipment
or water pumps on an intermittent basis; it is in no way designed to run for long periods of time while people are sleeping. I don't think putting it in any amount of soundproofed room will help much, especially considering the vibration. You can get the dB numbers and figure it out for yourself -- remember, the dB scale is logorhythmic.
A Honda 2.0kW suitcase gen will be probably 10x quieter and will vibrate less. This is in fact designed to run for long periods unobtrusively. I think it is rated for 1600 watts, so you should be able to run a load which is 80% of that without any problem -- 1280 watts. Well, the small Crusair aircon draws 1265 watts at full load -- bingo. On a 30% duty cycle, I think the little Honda should do fine (but double check with people who have actually tried it). I think this would be a much, much better solution than a Yanmar construction generator
. You might require an inverter/charger with power boost to deal with startup loads, in order for that genset to work comfortably.
But far, far better would be a real marine genset, a heavy-duty 1500 rpm one like a Northern Lights
. The smallest one they make would be enough for this application (I think it's 4.5kW). This one has a three-cylinder Lugger engine
which you will hardly hear when running, as it lopes along at 1500 rpm, and which will not produce any kind of harsh vibration. And it's made to be run continuously, so 10,000 or 20,000 hours will not be a problem -- you can just run it whenever you need it and for however long you need it (but make sure to keep a load on it). Yes, it's expensive, but don't compare such a piece of equipment
to a crappy construction genset. You won't fit within your 100kg budget
for weight -- this thing will weigh probably 250kg after you add the weight of the sound enclosure and exhaust
system. It will be expensive to install, too -- you will need raw water
in and out, an exhaust
system, an antisiphon loop, etc., etc.
But if I needed aircon (I don't have it), I wouldn't even consider any other way to power it.
I don't have aircon, but living off shorepower (my boat is on a mid-river mooring) and anchoring
out a lot, I find our 6.5 kW heavy duty Kohler genset to be an absolutely essential piece of kit. At anchor, I run it for a couple of hours every day at the time when we are using AC power for other purposes, or even just to heat water with the immersion heater, and it gets the batteries up and simply deals with all of our electrical
needs on board. The biggest benefit of this is you don't have to constantly worry and manage power -- you just use what you need with confidence.
I hope that is at least somewhat helpful.