AC or DC (both?) For the Small Seastead/Homesteader Philosophy


#61

Note the appeal for “low-cost seasteading (as opposed to mega-city projects)”.


#62

Even on up to 48 VDC is easy to tinker with. Just need to mind a few basics, such as polarity. Gets dangerous when you reverse polarity and blow up a large battery, things like that, but Heck, swallowing a dead zinc/air cell can kill you… A little common sense is required…

There is no human endeavor without an element of risk. Seasteading is more of a leap into the unknown.


(Larry G) #63

Neither AC nor DC are inherently more dangerous. People electrocute and burn themselves with simple car batteries all the time.

Not much could be simpler to rewire than an electric lamp, it seems an odd example of danger. My dad had me rewriting things like that and much more complex things as a pre-teen. I was running AC house wiring by 9 or 10, about the time I was strong enough to string 10g and 12g wire through holes drilled in studs.


(Larry G) #64

Indeed, it is not difficult to make large temp differences in insulated areas from input temps that don’t differ much. It does involve pumps for compression and a refrigerant that is more efficient than water. But the heating and cooling performed by my home heat pump using ambient air temp is many times less efficient than what you could get from the denser water.

Heat pumps would require maintenance of input lines, but a closed system minimizes it.


#65

Not to put too fine a point on it, but not many people wire ANY electrical device using live wires… Jumper cables generally being the exception for autos and extension cords for AC…


(Larry G) #66

48vdc is a common voltage in telecommunications equipment and is the baseline voltage to telephone systems in US “central office” facilities.


#67

The point being - on experimentation - that few, if any, people are really in danger of hurting themself with a 12v DC battery pulled out of a car.

Experiment away.

But please don’t suggest to inexperienced people that they should play with a 120v AC outlet in the house.

When we talk about seasteading, that includes the smallest experimenter who turns a floating island made out of recycled plastic bottles into a homestead. (hat/tip to Richie Sowa for doing just that)

So we should distinguish between professional applications requiring extensive safety precautions and simple experimentation that even a child can do.

And there are MANY applications of 12v DC power suitable for experimentation by the untrained person who simply want to try something.

Clear?


(.) #68

I think, it is clearer to me if it is 12V DC or 120V AC.
I think, I am going to use both.
I am going to have a converter from 12V DC to 120V AC. I am going to
place the inverter really close to the battery pack, and I am going to place
the 120V AC consumer very close to the inverter.
I am planning to use low power consumption 12V DC devices where ever I can. Protecting circuits with fuses is a good idea, so it seems to me.


(Larry G) #69

Overall, the future looks bright for battery and hybrid power. As the technology advances, smaller, more powerful and clean charging options continue to emerge (such as onboard fuel cells) that, when combined with high performance energy storage, will make battery power feasible for a wider variety of vessel sizes, types and operating profiles.

As for heat exchanges:


(Alex B.) #70

My thoughts about DC vs AC so far(not about the voltage level)

  1. Pros and Cons of DC
    + it is easier for non electricians to work with DC (esp. low voltage)
    + sharing DC power into a power grid is way simpler than AC
    + good for small “island-type” systems with solar charging system
    - RCD (residual-current device, a protective device) Type B (for DC+AC) is way more expensive than a Type A (AC)
    - if DC-Current flows through saltwater, hydrogen (explosive) gas generates…

  2. Pros and Cons of AC
    + Power generation with turbines/generators will generate AC
    + AC Voltage transformers are way simpler and less error prone than DC/DC Converters
    + AC devices are more common, AC is used everywhere
    - additional losses when converting to DC for storage and converting back to AC for usage

I would not use DC for power distribution, but for power storage and maybe for the end-devices.

Alex


(Larry G) #71

Technically through any water, if you have anode and cathode in separate air chambers and you give it long enough to build up. It actually takes a bit of work to gather enough quantity to have a chance of explosion. Then you need a spark and you need a mixture somewhere between LEL and UEL

This is not different between AC and DC. In fact, generators come in both AC and DC. In most cases, you can simply use a DC motor with some mechanical force driving it (like a turbine) and make DC (at varying voltage per input horsepower) with little to zero modification.

Not sure why you have come to that conclusion. The main purpose of transformers in the AC grid is to prop up voltage levels over long transmission distances, not to specific AC voltages at point of use. AC voltage from the grid can be pretty “dirty” and vary quite a bit over time and geography. It’s actually pretty common to see voltages anywhere from 108 to 130vAC on the US power grid. Most of the “wall-wart” transformers in use inside the home are also rectifiers providing a specific step-up/step-down DC voltage.

Depending on the size of the distribution, I don’t think it really makes sense to have an AC leg in the middle for a home-scale distribution, or really even for 4-5 homes clustered wall to wall.

Start running hundred of yards and AC becomes more practical due to safety factors (heat from resistance at high wattage) and cost of conductors.


(Alex B.) #72

they do not need to be in separate chambers. Separate chambers are only needed if you want to separate Oxygen/Hydrogen. Also a damaged wire from Home A to Home B is hard to find, if that damaged wire is somewhere where gas can build up without being distributed by air it can easily cause an explosion.

If these generator work with magnets, they will only produce AC voltage, just with an commutator that rectifies the signal built in. I don’t know any way to generate DC power except for photovoltaics (solar) and thermocouples(seebeck-effect). But I will look if i have missed something there, not sure since I’m not an power electrician

yes! i was thinking about bigger seasteads with >100 homes

both reasons you listed are only voltage dependent, not AC or DC


#73

Problem with ac in seawater is it also releases Chlorine gas, along with the Oxygen and Hydrogen, all mixed, but still deadly.


(Bob LLewellyn) #74

Why, would that be a problem? Chlorine is a pretty good natural cleaning agent. Waste treatment plants use it to kill bacteria and stuff.


#75

Humans can smell chlorine gas at ranges from 0.1–0.3 ppm. According to a review from 2010: “At 1–3 ppm, there is mild mucus membrane irritation that can usually be tolerated for about an hour. At 5–15 ppm, there is moderate mucus membrane irritation. At 30 ppm and beyond, there is immediate chest pain, shortness of breath, and cough. At approximately 40–60 ppm, a toxic pneumonitis and/or acute pulmonary edema can develop… Concentrations of about 400 ppm and beyond are generally fatal over 30 minutes, and at 1,000 ppm and above, fatality ensues within only a few minutes.”


(.) #76

Seasteading is going to be a technological development.
Lots of old and new technology will be needed for survival out there
on the high seas. Sooner or later it will have to be the high seas for
political autonomy. Special economic zones are good too (IMHO).
Many of these technological developments, as research and development
will have to be done out there; in location of the seastead; on the high seas.
All these dangers are there; such as gas, and explosion an fire.
Just like in case of scuba diving, there are lots of dangers, and technology
and science is important to avoid the bends.
Some people can do it.

For example of a danger; landlubbers do not see: a spiral bound note book
on a boat. If that note book is placed on a 12V DC battery the way that
the metal spiral short circuits the battery, the spiral will glow, and the paper
will burn = fire danger. Is a 12V battery bad? Is a spiral note book bad?
Yes, there is a place where that combination can be deadly: 1000 miles
away from nothing.

Yes, technology is dangerous.(IMHO again)

It reminds me of a line from the kids movie ‘Indian in the Cupboard’:
“You should not do magic, you do not understand.”

Cars use very dangerous liquid: gasoline. Gasoline is flammable and explosive.

(IMHO again)Seasteading will have to use certain things that are
dangerous to people who do not understand the science of it.


(Larry G) #77

!!! Yes. This. !!!

There is not much point in worrying about this stuff. The marine industries have already solved these problems, such as they are (very little problem in any event.)


(.) #78

One thing I forgot to add.

We can all talk about chlorine gas. It is true. Electrolysis of seawater
produces chlorine gas at one electrode and sodium hydroxide at the
other electrode. Sodium hydroxide reacts with the chlorine gas
to end up with sodium hydrochloride (bleach/chlorox) in solution .

There is a lot more about this seawater electro-chemistry, and
the more a seasteader knows about it, is the better (IMHO).


#79

The answer to the AC/DC question is both. I would rather tell you the best way to design a system, from a practical standpoint.

First start with solar panels large enough to power your typical big loads, like the RO water maker, washer and dryer, refrigeration and oven at the same time while the sun is shining and only plan on running those systems while the sun is shining. The battery systems should be large enough to handle the low load stuff like lights, microwave, Computers, TV refrigeration (yes I included it twice), auto pilot, etc for a a couple of days with no sun. A generator larger than the solar panel system is also required as backup (mandatory).

And yes it will cost from $30k to $50k, prices are coming down though especially the panels and Batteries (I am looking at ultra batteries right now, they look promising). The Battery bank also needs to be large enough to handle the large loads temporarily if there is a cloud or something in the way.


(Gordon Hoffman) #80

There are some good design ideas on this thread, but I don’t see a consensus of the sea village size - A lot of the power supplies and usage not be known until the village is up and running, and needs assessed.

I currently have a 24 volt PV on my house (3 - 165 watt panels, 4 - 6 volt batteries wired in series for 24 volt storage) that I use to run a freezer in the basement. Long Winter days requires that plug into a battery charger when I have no sun for more than a couple of days. Most of the time I produce more power than I can use, which ends up getting wasted. I checked into a grid tired inverter to try and sell power back but it cost more than the amount I would get back. I was excited to see the current issue of Home Power Magazine with a thorough article on micro-inverters which might make it affordable to good connect (but I also didn’t need the complications of code requirements of interconnection). Managing community power with one’s home power can be complicated, depending on how communal one would want to be. A bigger community might have some large moment of power requirements if they intend to do some manufacturing - welders and such. (Running away from a storm, maybe).

I would love to experiment with using cool seawater for space cooling. I was a solar hot water heating contractor for a while and know something about heat exchangers, radiant floors, and backup systems.

From experience, I know that DC pumps (motors) use less power for a certain load than AC.

A heatpump will deliver about 3 times more BTUs per watt than resistance heaters.

Sewage is going to have to be processed - methane production is a no brainier - maybe it can be coupled with hydrogen gas from natural power systems (solar, wind, and wave) food production is primary, so yes to fertilizer. I would like to know more about a gigantic seawater flow-battery that can also be used as ballast weight.

So what is the minimum size of village would it take to support a small medical facility?

I vote for more DC power systems than AC, and I would plan for times when the power is low - and try to not use fossil fuels, if at all possible.