I'm sorry if this post is too long but I think it may shed some light on the subject for the OP.
My cat a 2007 Leopard 40
is setup to run air conditioning
on batteries alone. We have a 900 AH lifeline AGM
housebank. AIMs power 4000 watt pure sine industrial inverter
with a max surge rating for 20 seconds of 12000 watts. My Northern Lights
6kw genset bit the dust last summer and I had been contemplating going DC anyway if in fact I had to replace the genset so after a ton of research
I decided to give it a shot. One of my initial contacts was John from ZRD out of Stuart Florida
who I had several lively discussions with during the last few Miami
boat shows. John had insisted that not only is it possible but if done correctly this type of system would actually pay for itself in fuel
savings in a short time. He had a ton of charts
and graphs to backup his claim and I was impressed. There is at least one yacht manufacturer installing his DC systems as options on their yachts and having great sucess. I ultimately went with the AquaMarine AquaGen because that system is very similar to ZRDs but also has designed in a HP pump for a water
maker and if the need arises a second compressor
. Of course you cant run all at once so the HP pump and compressor
are on clutches for the times the Generator is working real hard to charge the batteries. That unit can be seen here,
Anyway we replaced the 445 pound Northern lights
M673L3 genset with a 140 pound AquaGen and wired the boat for DC charging
which makes a ton of sense in my mind do to the inefficiency of converting ac to dc for charging
and so far I am mostly happy with the results but it is not perfect. Here is my take on the good and the bad of our new system starting with the positive stuff. The Northern lights took up a large amount of storage
space in our port side forward locker, so much so that we had very little room for anything else beyond a couple of fenders. Oil
changes and any maintenance on the NorthernLights to the starter, heat exchanger
or simple water
pump impeller changes were extremely difficult and had to be done mostly by feel. Now With the AquaGen we have gained that huge space back which allows us to keep all of our dive gear
, 5 tanks
, 5 BCs and all the other scuba
paraphernalia one could want as well as the Aquagen in that same space. When Its time for MX on the Aquagen its very easy to accomplish do to the small size and easy access without all of the sound shielding to dig through of the previous Northern Lights. I empty the dive gear
step inside and sit next to the unit with access to all 4 sides. The AquaGen recharges our House Battery
Bank from 12.2 volts back to 90% 12.85 volts or there abouts state of charge in about an hour. The AquaGen literally sips fuel
using about .3 of a quart at full RPM
2800 which only has to be maintained for only a short time maybe 20 minutes. Once the amps drop to 90 we can throttle the unit back to 2200 for another 20 minutes or so. At 60 amps going into the house bank we can further reduce the rpm
to 1800 or so for the last 20 minutes. Once the amps drop below 10 we shut the unit down and we are good for the rest of the day. The NorthernLights took forever to get the house battery
bank charged even with a state of the art Magnum 2800 watt inverter. Basically as the amp acceptance rate drops the genset still runs at its governed 1800 rpm which result in the engine being to lightly loaded causing black soot all over the side of the boat and the exaust elbow
to need regular maintenance to clean out the build ups. A real P.I.T.A!
Now for the not so good
Running the air conditioners is not as simple as just turning them on like we did with the NorthernLights running.
If the boat is hot it takes quite a while to cool down so we have to plan for the need for cooling
and it much more involved than before.
Here is how we do it.
Step 1 about an hour before we want to run the air conditioners we complete a charge cycle.
Step 2 once the charge cycle is complete we leave the AquaGen running and turn on a single
16k btu unit and the genset is now basically keeping the batteries topped off while the initial cool down takes place. Our AquaGen puts out 150 amps continuous and our CruiseAirs need about 10.5 amps AC each which equates to 105 amps DC per unit at full locked rotor amps. Thats a huge power draw hence starting with a full battery bank so the generator is not trying to fill up a rapidly depleting battery bank.
Step3 once the first unit has cooled the worst of the heat we start the second 16kbtu air conditioner and set it about 1 degree higher than the 1st one so that they both don't cycle on at the same time.
Once both units are cycling on and off we can turn off the genset and the air conditioners will run for about 4 hours before we need to charge the batteries again. If its just myself and my wife onboard we really only need to run one unit so we can get about double the runtime between charge.
There are a couple more items I'm not really excited about in the system we went with. One is the unit comes standard with a 12 volt lift
pump for cooling
water flow to the fresh water heat exchanger
and the wet exhaust
. If it quits we have no way of knowing until I install a sensor in the raw water
line. It is on my list of things to do but for now I check under the bridge deck
for water flow from the unit when we start it. Another downside is we can no longer heat water electrically unless I tie into the inverter which I don't really want to do do to the complex wiring
that will have to be done. The last item is subjective and we knew full well going in that this is a hands on system. We have to control the rpm manually via a remote
throttle and pay attention to what the amps are doing in order to achieve the efficiencies John from ZRD was talking about, on the one hand you have to pay attention but on the other it really makes you aware of how much energy you are using where as the NorthernLights you simply turn it on and forget it.
Hope this helps.
Sent from my iPad using Cruisers Sailing Forum