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

(Larry G) #21

Gonna be pedantic for a moment, because these ideas matter a lot.

DC is used in automobiles because it’s what you get out of a battery. If you have more electrons on one side of a gap than on the other, you have a DC voltage. DC is entirely natural, AC requires a system to produce it. AC generators are more complicated than DC. AC devices are more complicated to build than DC devices. AC requires a means of stabilizing frequency in addition to voltage. DC doesn’t have a frequency.

[quote=“ForexBob, post:14, topic:2591”]
But I’m thinking that DC is also safer around water. [/quote]

I’m not sure why you think this. Marine systems on yachts and larger commercial vessels have a combination of systems.

P=I*E (Power equals current times voltage.)
If you’re using “DC” as short hand for “12vDC” then think about a 100w incandescent bulb (available for both 12vDC and 120vAC.

100w/12vDC= 8.3A 100w/48vDC=2.083A 100w/120vDC=.83A

100w/120vAC = .83A

As you can see, it’s not AC or DC that determines the Amps, it is the voltage. If you stack (QTY)10 x 12vDC batteries in series (cable positive to negative one after the other until you put a load across the positive terminal of battery # one and the negative terminal of battery # ten), you get 120vDC.

Resistance is a physical characteristic of the conductor or insulator. Current is where HEAT comes from. Heat is movement. More electrons moving = more heat. More resistance, means less movement, means less heat. Put too much voltage to a small wire without a lot of resistance, you get so many electrons moving that the physical size of the wire cannot dissipate the heat to the air (a poor conductor of heat) before it melts.

High amperage applications need thick wires to dissipate heat, whether AC or DC. You get more power at lower amperage (and less heat for the same power “the ability to do work” output) with higher voltage. The load is what determines wire gauge- how much current do you intend to draw and how much power are you consuming? Your 12vDC input on your computer doesn’t need 000 gauge, it’s not drawing that much current.

DC voltage tends to drop off over long runs due to the wire’s resistance. So does AC, but not as abruptly and it can be regenerated with transformers. DC voltage drops measurably over the distance a typical house wire might run. It’s not enough to prevent using it.

I agree, and I think the only reason that most land-based homes with solar/wind power supplementing grid power don’t go all-AC is because they retain great benefits of convenience in being grid-tied for heavy loading, avoid the cost of implementing a system that is capable of supporting all maximum conceivable loads, and avoid conversion costs in their appliances and end-user devices. It’s a different matter to design from the bottom up for a location where grid power is not even an option.

I have built lots of electronic systems. I was just doing some wiring on my boat the other day. Both of our boats have DC systems, AC shore power inputs for AC outlets inside for user convenience, with DC outlets in the cockpit area. I am working on converting some of our user devices to 12vDC, like the tv.

One boat has a built-in on-board generator, Kohler 7.3kW gas genset, marine grade, low CO emissions, non-sparking, and currently, inoperable. We use a Honda 2kW portable plugged into the shore power input for now while I’m troubleshooting the on-board genset.

(.) #22

I had used a 12v DC TV, it works. The power consumption of
the TV is 30W. I only used the 120V shore power for soldering and
some heating, and for power tools. I used an extension cord for that.
I charged the batteries with solar panels.
An electric grill is about 1000W power consumption.
For me, a generator takes up too much space and the exhaustion of
the generator is a problem, particularly in high wave action.
Things, that work well in dock and in no waves, turn a different thing out there.
On one of my boat a 9HP honda engine would generate 12V and it fed into the batteries.
Each to it’s own.
An 800W honda generator is a good deal. And there is a 2000W honda
generator too. One is none, two are one.

(.) #23

The problem with the TV was that after being out there in rough waves,
some of the internal parts of the TV broke off. It could not stand the shake.

(Larry G) #24

Which brand? The one I posted is designed for semi-trucks, but the way I have my current tv mounted in the boat is on a swing-arm wall mount with a bungee cord for securing it under way. I have pondered several means of securing such things in a shock-absorbent manner, and it doesn’t seem too difficult.

Our worst day on the Columbia is not going to shake quote like the open ocean, but we do hit some pretty big wake from ships passing and jet boats/jet skis.

(Bob LLewellyn) #25

Hi Larry, Before you went through all that hassle of rewriting my physics books I should have said approximates and generalities were taken as I didn’t want to teach a course in electronics just discuss the power problems of long distance distribution of 12VDC. For a floating village there would be a power grid of a sort but still home generated power will be cheaper, less dangerous (higher voltage = higher death by shock potential).

I have built several systems for different things but one weird one was that I bought an older chev. van to drive from Pittsburgh to Coasta Rica. I put two 1000amp deep cycle batteries in the back of the van and charged them from a high amperage truck alternator. I had to use an isolater (bought off the shelf) to have the truck run off the car battery which gets charged first, then the 2 deep cycles. A 1500 watt inverter gave us ac when we needed it. We could run the batteries dead but never touch the truck battery. Drove it the whole way down to CR then all around Nicaragua where I had built a lake house. Yep, did the electric for that too.

(Larry G) #26

OK Bob, and no disrespect intended, but words mean things and when they’re used wrong people can get hurt. Many people do not understand electricity at all and incorrect details confuse them even further. When people are trying to back-yard engineer a system that will have to support life hundreds of miles from help or solid land, it’s that much more important to be PRECISE. This is a problem the more actively-inclined potential seasteaders have when they encounter this forum. Incorrect and imprecise statements, math that often doesn’t pencil out because it was estimated, not calculated, and worse when the estimation is not explicitly acknowledged.

Incorrect details like this are dangerous:[quote=“ForexBob, post:25, topic:2591”] (higher voltage = higher death by shock potential).[/quote]

It is current that is more dangerous. I was trained in the USAF that as little as 50 milli-amps (50 thousandths of an amp, .050 amps, not thousands of amps) can cause your heart to fibrillate if it takes the right path through your body. High voltage and high resistance still equal low current, but it really doesn’t take much. If someone proceeds on the assumption that low voltage (like 12vDC) means they can’t get hurt, bad things can happen.

Your body is not a great conductor, but water and sweat (and possibly physiological conditions but it’s so complex no one can really predict it) can make a difference. Different AC frequencies can have different likelihood of travelling through your body vs along the surface of your sweaty skin but likewise, it’s very hard to predict. The turn of the 19th->20th century hype over whether AC or DC is inherently “more dangerous” has been largely discredited a long time ago.

(.) #27

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(.) #28

Any pictures of those many wonderful electric systems?


I like the simplicity of DC. Simplicity makes experimentation more probable.

Plus … battery power is pretty universal, especially 12v (just about everywhere cars are found).

I’d like to see some discussion threads on adapting DC projects to low-cost seasteading (as opposed to mega-city projects) … perhaps with some links to DIY sites like or maker sites.

(Larry G) #30

And any multiple thereof: DC power stored in car batteries can be connected in parallel (positive to positive, negative to negative terminals) for more depth of power, as in more available amps for longer periods of time, or they can be connected in series (positive to negative) for more voltage. 2 x 12vDC batteries connected in series provide 24 vDC (like a semi truck system). 4 of them in series provide 48vDC which is a standard voltage for telecom equipment.

(Bob LLewellyn) #31

Of course you would have to use deep cycle batteries. Car and truck batteries won’t last long with any significant amount of discharge. They develop memories and won’t charge beyond its memory.

(Larry G) #32

For consideration: Tesla Powerwall 2.0

Deep cycle batteries are better, yes. Forklift and golf cart batteries as well. Deep cycle designs have thicker plates:

  • A car’s battery is designed to provide a very large amount of current for a short period of time. This surge of current is needed to turn the engine over during starting. Once the engine starts, the alternator provides all the power that the car needs, so a car battery may go through its entire life without ever being drained more than 20 percent of its total capacity. Used in this way, a car battery can last a number of years. To achieve a large amount of current, a car battery uses thin plates in order to increase its surface area.

  • A deep cycle battery is designed to provide a steady amount of current over a long period of time. A deep cycle battery can provide a surge when needed, but nothing like the surge a car battery can. A deep cycle battery is also designed to be deeply discharged over and over again (something that would ruin a car battery very quickly). To accomplish this, a deep cycle battery uses thicker plates.


No, you want to convert DC to AC as close to the batteries as possible. You will need massive amounts of cabling if you convert your 12VDC to 120/230VAC close to the every consumer, not to mention the amount of inverters you would need. And you want to stay away from any automotive, trucker or RV equipment. Marine grade stuff is what you want.

I do engineering for ship electrical systems for a living. :slight_smile:

AC and DC have the same complexity when it comes to wiring and designing the system. No difference at all.

My general advice would be to keep it simple. For low budget small scale simply stick to 120VAC or 230VAC for your consumers, DC is just for energy storage and maybe some small emergency consumers. The risk of shock etc will be exactly the same as in your landbased home (depending a bit on how your electrical system in your home works off course). ANd you can use regular appliances Put in a system like a Victron Energy Multi or Quattro to charge your batteries and invert it back to AC. Solar/wind can be hooked up to either AC or DC depending on the controller. It’s a proven system design that is working in thousands of setups, no need to start from scratch and try to reinvent the wheel.

If you have a bit more money to spend on your electrical system go full on yacht/offshore vessel style for your energy needs.

(Larry G) #34

What do you think of the EMerge Alliance link here:


Safe DC sounds great, but it you look at what they actually do is putting a 24VDC power supply in each room to power things like the lighting and some other small consumers and give an option to hook up solar directly to the DC grid. So yeah… not really useful… it’s a solution for a problem that doesn’t exist.

When designing an electrical system you start with the big consumers, those determine the backbone of your electrical system. In a seastead I guess those consumers would be a stove, oven, A/C, heaters, etc. For those you’re going to want something like 120VAC or 230VAC since they consume at least 1kW, might as well connect the smaller consumers to it as well and try to keep everything at a single voltage level.


(Larry G) #37

GPersonally, I wouldn’t use resistive heating for anything in an off grid situation like seasteading. Methane would be the way to go for stove, oven, and heat if necessary.

I’ve been around the world a good bit, and had to deal with issues of 110-120vac, 220-240vac on both 50 and 60 hertz, designed and built a lot of UPS installations in various data centers.

The AC vs DC issue doesn’t really seem all that cut and dried to me. The only real adapvantage AC seems to have is massive base of consumer/retail appliances dominating the market, but when you get to specialized applications and off grid use cases, things start to change the equation where purpose fit is more important than ubiquitous.

Especially where PV solar seems likely to be a large part of the local micro grid strategy. The energy-expending model of transoceanic shipping doesn’t necessarily translate into seasteading.

(.) #38

Lots of hot air that is not generated by electricity but about electricity.


But on the other hand you want to go full electric so you can be fully self sustainable as far as energy goes… That’s a choice to be made which indeed can impact the choice for AC vs DC.

If it’s only 120VAC and 230VAC you have to deal with you’re a lucky guy. :smiley:
But 50Hz vs 60Hz doesn’t really seem to be an issue these days, most new things can handle both just fine.

True, I think the main difference between AC vs DC at the moment is the voltage level. DC (not taking into account some exceptions) seems to be mainly focused at 12VDC and 24VDC, in my opinion if you want to go full electric without burning fossil fuels that voltage needs to go up. It’s simply impractical to power heavy consumers at 24VDC let alone 12VDC. So if you decide to use fossil for heating and cooking you can probably get away with a 100% DC system for all your electrical needs if you can find all the appliances you want. But spare/replacements parts and maintenance is something that needs to be taken into account.
If you want to go full electric right now AC simply seems to be the best option because of the higher voltage and availability of stuff.

PV doesn’t really have anything to do with a choice for AC or DC. Even in an AC system you can hook up the PV to the DC storage part of the system, or choose to connect it to the AC part of the system.

(Larry G) #40

Good points, but methane isn’t fossil fuel, and it doesn’t require supply lines. It can easily be produced at the farm scale or individual household level.

Agreed on voltage levels, but this can easily be achieved with batteries in series. And new battery tech is making a lot of things feasible that required a serious hobbyist to achieve before. The Tesla Power Wall and its soon to be reverse engineered copies are sgnificant in this space.