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


(Larry G) #1

One thing that can make a big difference in planning is very much a common concern for the land-based off-grid homesteader. Electrical systems benefit from lots of prior planning.

Catalog of DC Appliances and Power Systems (Berkeley National Labs)


(.) #2

Both.
I would go with 12V DC and to convert it at the location it is needed to
120V AC. The 120V AC devices are mass produced and cheap and
available. Power generators usually have 120V AC output too.
Solar panel usually charge at 12V with DC. Well to charge a 12V battery
full more than 12V is necessary, so solar panels max at about 19V, but
still DC. There are lots of DC appliances available, because of the
automobile cult and the trucker cult and the RV cult.
My personal favorite is the 12V DC rice cooker.


(Larry G) #3

[quote=“spark, post:2, topic:2591”]
The 120V AC devices are mass produced and cheap and available. Power generators usually have 120V AC output too.[/quote]

True, but often the standard retail consumer version is not robust in the marine environment, and the more robust marine versions cost as much as dedicated DC systems. Generators can be specified for DC output too. I want to get this one for an experiment entirely unrelated to Seasteading.

You can connect in series for higher DC voltage too. Telecoms industry standards are generally 48VDC and I recently found a mini-split heat pump designed for this voltage, which would be VERY useful in the subtropic-tropics. The condenser units can typically run more than one area cooling unit.

www.hotspotenergy.com/DC-air-conditioner/

www.hotspotenergy.com/solar-DC-air-conditioners/

www.tradezz.com/buy_9421865_SplitCool-DC-18.htm

There are also refrigerators, freezers, grills, stoves, sandwich makers, coffee pots, fans, TVs, radio/stereos lots of things. I think there are even microwave ovens. Most consumer computing/communications electronics and phones run on DC and use an AC adapter which could be eliminated in the right circumstances.

In the book “Sailing the Farm” there are various means for making cooking and food prep/preservation more “cost-effective per watt” for the small electrical budget. There are many forums with discussions of ways to do this for sailboats cruising long distances and living aboard.

EMerge Alliance Occupied Space standard, platform model for low-voltage DC power in commercial interiors


#4

Meanwhile … I’m learning to brew beer, to sell to those electricians who will be needed on seasteads. :wink:


#5

LOL,…I’ll buy your beer and sell it to those electricians in all my bars around the seastead. :blush:


(.) #6

I agree. I do not know much about electric systems.
I am trying to learn. So far my understanding is that for a heat producing
electric appliance, such as a grill, the current is important (ampers).
The way to get more current (amps) through the device is to make the
voltage higher. 120V devices are more successful than 12V.
The same way for boat electric engine a 12V motor might be not as
strong as a higher voltage motor. This kind of manifests in the voltage
of the Torqedo electric engines and motors.
Though Tesla car might be a contraindication to it.

I do not know that much about electric engeneereing.
I am also interested about 12V DC appliances just for hobby reasons too.


(.) #7

Beer brewing is very useful.
Moonshine distillation is also useful because it can double up as a
water distiller to make drinking water out of seawater.
Both activity can be done with the same equipment. When the officials
show up it can be called a drinking water maker. After official business: party on.


#8

I agree w/both too, but marine grade. Much higher corrosion resistance, longer life, better quality.

Solar, wind, battery bank, inverter, done.


(.) #9

Yes, the much higher corrosion resistance is necessary. I think.


(Larry G) #10

Not exactly. Heat comes from electrons moving, which is Amps- so far so good. The way to get more Amps flowing is to either increase Voltage (motive force) or decrease Resistance. For example, an electric stove element has low Resistance, allows lots of Amps to flow from (typically) 220vAC.

An electric cigarette lighter in a car, has low resistance, and 12vDC input. Still gets hot.

Current (measured in Amperes) is generally represented in formulas by "I"
Voltage is “E” (sometimes V but traditionally E)
Power (measured in Watts) is "P"
Resistance is “R”. There are additional impedances in addition to pure resistance, these are grouped together as “Z”.

To get the power, remember “PIE”: P=IE
From this, you can derive the rest through basic algebraic substitution:
To get the current, I=P/E or E/R
Voltage E = I
R or P/I

http://www.angelfire.com/pa/baconbacon/page2.html

http://www.sengpielaudio.com/calculator-ohm.htm

The way motors work with voltage is a bit more complicated. You get AC motors and DC motors with different characteristics. For example, it’s generally easier to make a DC motor variable speed, while AC motors are designed for particular speed settings or narrow ranges. With DC motors you can simply vary the voltage applied. Lower voltage, lower speed (obviously there is a maximum and a range where they are designed to work without excessive heat.)

DC motors have instantaneous torque with a pretty consistent torque across their speed range. Internal combustion engines have a much narrower power band where they develop maximum torque. This is why internal combustion engines stall out when load is applied at low rpms. AC motors have somewhat different torque characteristics than DC motors.

The main reason AC is more prevalent is because it is easier to transmit AC long distance at more consistent voltages due to the way transformers can regenerate the voltage (at a cost of drop in power gone to heat from resistance and impedance of capacitance and inductance qualities of wires and transformers) while DC voltage drops primarily due to the resistance of long wires, with loss in power also gone to heat. Some of the AC power loss (inductance in transformers) is used to “prop up” the voltage level for consistency of use by retail electrical devices designed for a narrow range of AC voltage. So transmission of AC electricity consumes some of the power but delivers a consistent voltage. This is kind of a “dumbed-down” explanation, and it has been 20 years since I formally studied electricity and electronic circuits in USAF technical school to get my Associate’s Degree in Electronic Systems. I haven’t tried to teach electronics, so I hope my explanation helps.

It’s a worthy area of study for a backyard engineer.


(.) #11

Good luck with all of that. Hehe-))).


(Alex Smith) #12

actually i am very interesting of the wave power => https://en.wikipedia.org/wiki/Wave_power


(Larry G) #13

That’s fine, but wave power doesn’t directly power your blender, toaster, or TV. Whatever mechanical systems generate electricity, it still has to be delivered to a point of use as either AC or DC. That’s what I am trying to get folks to consider and collaborate on in this thread.


(Bob LLewellyn) #14

No, really its a good question. DC is used in automotive because it is easy to store and transport. But I’m thinking that DC is also safer around water. To power something it will take 10 times more current with DC than 120V ac. And of course the current is where the resistance comes from. The more current that goes through the wires, the more you lose to heat. So do we wire the entire village with 000 gauge wire or use the standard 12/14 and risk serious shock with 120V.?

There are plenty of DC equipment available and inverters for the occasional appliance that doesn’t have a DC counterpart. The real problem is in the transmission. If every home generated their own power, the the answer is simple, DC. But is there a way to transmit AC to substations that convert to DC into the home or boat.

Most boats are set up for AC plug-in to the shore so at the shore connector is where the choice will have to be made. Eventually we will be able to offer a choice at the connection until then we have 3 AC generators on the Marinea barge and nothing for DC so our minds have been made up for us for phase one, However, phase two is another story.
Bob


(Mariusz) #15

There are few things that need to be considered here.

  • corrosion
    I believe, although I’m not an expert on this, that AC systems will generally be less corrosive,

  • safety
    Up until about 60V dc tends to be safer.

  • efficiency
    A lot of energy is wasted when we convert from AC to DC, but a lot of our devices run on 5-12V. (computers, cellphones, etc) .

  • cost
    hard to estimate, probably comparable when you take everything into consideration.

It’s possible the it would be the best to have mixed system. Use AC when you need more power, and DC when you can power for your small electronic devices, or lights.
This way any solar or wind power generation system could be feed into the system without having to go through the inverter, and convert it into AC only when really needed, or when the safety requires it.


(.) #16

Has anyone actually built any electronic systems, or
we are just here to discuss it?

Is there an intent to build anything? What have you tried so far?
How did that work? Write that down.


(.) #17

So far, I did try this:

The cable and the plug heat up more than the cup of water.


(.) #18

The 120V version works better.

That is my experience.

Thank you for the US Airforce version of Ohm’s law.


(.) #19

https://images-na.ssl-images-amazon.com/images/I/61I73wb-kGL.SL1363.jpg

It is for sale on Amazon. Customer reviews can be found at the end.
Other 12V appliances can be found too, and the reviews can be read.
Or you can just try google search, and 12v toaster, 12v grill.
You know how google works.


(.) #20

Though, I find it strange that a heating device is called Koolatron.