Lithium (LiFePO4) Battery Build

[OverEasy]

Hi Inquisitor

We just got home from a beautiful day out on the Beaufort River and Coosaw River Estuaries.
Clear day, light breeze and an out going tide.
About 6 hours and a Gorgeous Day!

The portable A/C EER and your heat pump SEER are a little bit different in absolute terms I believe but that’s a nuance issue.

The portables are claimed to be 14000 BTU which they claim ‘should’ cool 450 sq.ft. (That equals a room ~21 ft x ~21 ft.)
A/C is a 3D problem so multiply the 450 sq.ft. by ~8 ft to get a volume of 3600 cubic feet.
A Mac26X or Mac26M has a maximum interior volume of only about 750 cubic feet. {Ballpark estimate: 750 cu.ft.= ((26 ft long x 6 ft tall x 8 ft wide x 0.6 cf to account for hull/deck/cockpit geometry. It’s probably less volume but it’s definitely not larger... }

So if we suspend disbelief and go with advertised values an approximation would be to take the 14000 BTU divide by the volume of the advertised room 3600 cu.ft. to get ~3.88 BTU/cu.ft. Then take this 3.88 BTU/cu.ft. X Mac26 volume of 750 cu.ft. to get ~2910 BTU anticipated to cool a Mac26. Continuing with suspended disbelief we take the unit capability of 14000 BTU and divide it by the Mac26 “need” of 2910 BTU we get a ratio of ~4.81:1. All of which means the A/C unit would only need to work approximately a 5th of the time to cool a Mac26 vs the 450 sq.ft. reference room advertised. So the estimated cooling power requirement is considerably less in a Mac26. Now granted a Mac26 isn’t insulated and expectedly sits fully exposed to the sun, and the bottom wetted (cool) surface is insulated from the cabin by the liner so it wouldn’t be quite that low and much more likely to be a 4th (rather than a 5th) of the work required for a 450 sq.ft. room.

The point of all that is the actual anticipated energy draw is considerably smaller than what one would assume based solely on advertised capability specifications. This is a good thing as far as generator/battery/inverter demands.

What would help is if they provided the electrical peak surge current and the steady state current at 120VAC.
KNOWING THAT would allow a better estimate of relevant power supply needs.

Hoping to find time to get that from the manufactures sometime before we aim at the Florida Coasts or Keys.

The inverter generators are REALLY QUIET!!!
The A/C is probably louder!

[Be Free]

I've not been in the Keys in a few years but in Central and North Central Florida I've seldom needed anything more than a wind scoop mounted over the forward hatch to sleep comfortably at night. If someone is in the aft berth I have been known to set up another scoop over the companionway to direct some wind down there. If you are not going too far south that may be all you need.

Keep in mind that I grew up in Miami and never saw an air conditioner until I was in high school. My "thermostat" may be set a little differently. These days, if I were going to take an extended trip to the Keys I might be looking for some way to stay a little cooler.

P.S. My wife says I'm crazy and won't spend the night on the boat if the temperature is over 80.

[Inquisitor]

P.S. My wife says I'm crazy and won't spend the night on the boat if the temperature is over 80.

I'm about in the same shoes. The very few times it was too hot for me to sleep (Flamingo in June) I'd just sleep up top. For me... it to is about marital bliss. My Admiral seems to have similar temperature constraints.

Also... it may be more about the challenge of the project. I'd like to see if I could cobble together a DIY, $300 A/C unit that can run on a relatively small solar / battery system without a generator. Maybe even with water chilled condenser. Just sounds like a great science project.

[pleb222]

We have a windscoop for the evening and a zerobreeze mark two rigged for the night. It really works well enough for the 5 of us

[OverEasy]

Yes, marital bliss is more important than project complexity!!!
Happy Admiralty makes for a Happy Life!

My Admiral must be related to your Admirals in the elevated thermal environmental and humidity aspects.


The wind scoops are great ideas for ventilating the boat!
They would really probably take care of making things tolerable and comfortable in in a lot of locations.

My Admiral sort of wilts when she overheats and the humidity climbs.
So traveling into the waters much further than where we are now in SC is gonna be a non-starter in the Spring or Summer seasons.
We might utilize a less efficient portable A/C unit that we already have (given we can just drop it n when needed for a particular trip.

The generator is the cost challenge and that will have to wait until the actual trip gets closer to a reality.....we’d like to anchor out on that kind of trip and not be tied to having to use marinas regularly just to have shore power.

[pleb222]

For the ac, I recommmend the zero breeze II. It will run on your lifepo4 bank with a 24v converter. It's super light and small. That's what we do. I can get quite a few degrees down on the small macgregor with it.https://www.zerobreeze.com/products/zer ... _QQAvD_BwE

The other idea i toyed with, was to get a mermaid ac with reverse cycle. The way I thought to hook it up without putting a hole in the boat: I would only use it at anchor at dock. I would have left the ballast fill port open, and hook up the ac intake to the ballast vent. Since after filling there is no air pocket, and the fill port is way bellow the waterline, there should only have a siphon getting water from the sea into the ballast, through the AC. I would have teed the outflow line into the galley drain, with a valve.

My brother in law is a mechanical engineer who designs satellites and a regular very prudent sailor. He looked at my idea and didnt see much of a problem with it.

[Chumpy36]

Reviving to ask the question...

Taking aside the cool DIY aspect and the learning... would you build a DIY battery again knowing how cheap (250$ for 100ah) they are at this point?

I like the idea of building a battery is cool but I have A LOT of projects for the boat so I wouldn't mind skipping this one if there wasn't a huge cost savings.

Thanks for documenting everything!

[dlandersson]

Got room on your sofa?

We just got home from a beautiful day out on the Beaufort River and Coosaw River Estuaries.
Clear day, light breeze and an out going tide.
About 6 hours and a Gorgeous Day!