Basic Electrical for a Boat?

[sailinglegend]

Originally Posted by Bill Seal

...You can change the voltage and the current will change, but you can't just arbitrarily change the current. Voltage pushes current, not the other way around.

I'm sorry but Ohms Law hasn't helped your full understanding of DC circuits.

An increase in current will push the voltage drop on a wire or across a high resistant switch (faulty - corrosion).

This does take a bit of brainpower - but consider a faulty house battery main breaker switch, which has a high fixed resistance. With a current through it there will be a volage directly across the terminals of the switch. Double the loads and so double the current and the voltage across the switch will double. This 'voltage drop' is being pushed up and down by the current.

This also happens along a cable run where the current is too high for the size of the cable. Finding these problems is one of the few times you really need to understand Ohms Law - otherwise the water analogy is the simplest explanation.

[Lake-Effect]

Originally Posted by sailinglegend

This will put anyone off electrickery for life.

The trouble is all books on DC for boats make the same mistake with Ohms Law on page one. It's not needed to understand the basics of choosing batteries, charging them, and monitoring their State of Charge.

What Gord said. If you don't understand Ohm's law early on, you lack a fundamental grasp of what electricity is. Sure, you can learn patterns and techniques for wiring a boat (monkey see, monkey do), but you won't understand the why, or be able to analyze or solve issues when they occur.

[HeinSdL]

A circuit diagram is a great addition to your boat documentation. I just got mine from the builder and each and every page of the 30 pages or so is worth studying. So I am very fortunate to now have an inventory of every cable, fuse, appliance on board with the corresponding cable size, fuse size etc.


But such a diagram may no longer be available, in which case, start your own (I say start because it's complicated and aiming to have it finished is a tough challenge). It's a great learning exercise and eventually will help trouble shooting.


But you do ultimately also need to know a thing or two about electrical circuits which I think is what this thread is about. So... first get the basics up to scratch from a book which are not boat related and then home in on your actual system.

[Stu Jackson]

Originally Posted by HeinSdL

A circuit diagram is a great addition to your boat documentation. I just got mine from the builder and each and every page of the 30 pages or so is worth studying. So I am very fortunate to now have an inventory of every cable, fuse, appliance on board with the corresponding cable size, fuse size etc.

But such a diagram may no longer be available, in which case, start your own (I say start because it's complicated and aiming to have it finished is a tough challenge). It's a great learning exercise and eventually will help trouble shooting.

But you do ultimately also need to know a thing or two about electrical circuits which I think is what this thread is about. So... first get the basics up to scratch from a book which are not boat related and then home in on your actual system.

This is very good advice. When we bought our boat, it had reasonably good documentation, augmented by the PO's own diagram.

Since I didn't know what he knew, or didn't know, I started out by following the wires in his diagram and found a few glaring errors!

There was also a rat's nest of wiring behind the nav station, where a VHF radio, cigar lighter outlet (used for charging various items), an Automac, dual bank analog voltmeter, and an ammeter had been installed. These were all aftermarket items not covered in the builder's wiring diagrams.

I made my own wiring diagram of that stuff (look at the date - 1998), which has come in handy many times over the years. Here's an example: On our cruise from SF to B.C. in 2016, our VHF stopped working. I pulled out the diagram and found that the shelving I'd installed in 1999 had come loose in a seaway and jiggled around enough to dislodge one of the wires to the VHF.

Without that diagram, I would not have known what wires I was looking at. There were a LOT of red ones!

While we had owned two previous boats, each had only one battery and rather simple 12V systems. This boat was much more complex, but the concepts were identical, just bigger, with more "stuff."

I was in the same boat as the OP. I spent the time to learn, and this was before the internet.

Now there's no excuse, but it still "takes some book learnin'" as my grandfather was wont to say.

Good luck, all of us were there at one time, 'cuz we weren't born knowin' this stuff.

The OP has to put his own effort into it.

[ve0hak]

Originally Posted by crybllrd

I saw that in the stickied post, but I don't see how, say, a 1000w coffee maker fits into it. If I have (for the sake of easy math) 500w of solar, 500amp battery bank, how would I know what else I can add to it? I see my (home) coffee maker says 1000w, how would I know how many 1000w appliances I could support with the system?

I think you might be a little confused about your batteries. Batteries are not measured in amps, they are measured in amp-hours. So if you have a 600AH battery, that means you can supply 600A for an hour (probably enough to melt your wires), or 60A for 10 hours (quite a lot) or 6A for 100 hours (reasonable).

To get watts (power), you multiply by voltage. So if you have a 24V battery pack, pulling 6A means 144W. Or, working backwards, if you want to run your 1000W kettle, that means about 40A (quite a lot). With a 600AH battery, you could run 15 kettles for an hour (see above about melting your wires), or one kettle for 15 hours.

Your solar is for charging your batteries, not for running things. 600AH of battery at 24 volts would need about 15kW to charge in an hour. That's unreasonable, and you only have 0.5kW of panels. That means that if you wanted to charge up your batteries from empty with those panels, under ideal conditions it would take about 30 hours of full sunlight.

A better way of thinking of it is that the batteries are a buffer. You use the solar panels to top them up. So if you run your 1000W kettle for an hour, it'll take your 500W panels two hours operating at peak efficiency to replenish the energy that you have used. They'll never be operating at peak efficiency.

Suppose the panels operate at 15% efficiency, on average. Maybe 30% during the day and 0% at night if you are in a sunny place. That means that the amount of energy that you can replenish without doing anything special is about 75W. That's your budget for things that run continuously. Add up the power consumption for everything that you keep running all the time and it had better be less than that, otherwise your batteries will slowly drain. If you keep enough headroom, say using 50W in steady state (whether that seems like a lot or a little depends on you -- for comparison a human or an old-style incandescent light bulb uses about 100W) then you can run the kettle for a few minutes to make tea and not worry about it.

If you are the kind of person that regularly has access to shore power, you can probably afford to deplete your batteries more. This means using more power than your solar panels can replenish but plugging into the shore at night (say) to replenish it much faster. Or you could similarly burn dinosaurs by running the engine or a generator from time to time to charge the batteries.

Hope this helps,
VE0HAK

[ve0hak]

Just to be clear as well, when your coffee maker says that it uses 1000W of power, that will be the maximum that it can use. In practice it will be less than that. Maybe it will use 800W when brewing and 200W to keep it warm. That's still quite a lot more than is usual to use on a small boat unless plugged into shore power.

[Boatwright]

Reading your original questions and your inventory of your boat's existing system:

It seems cruisers too often want to leave the dock with all the conveniences of a modern home. Electric stoves, coffee makers, hair dryers, air-conditoners, space heaters, refrigerators anything that produces or removes heat all use significant amounts of power (amps). Electric motors, winches, bow thrusters, washing machines, water makers -- ditto.

Suggestion: If you don't want to spend your days plugged in at a marina; if you don't want to spend big bucks on gear that requires maintenance and is prone to breakdowns, keep it simple. Make a list of those things you really need and compare it to your existing more than adequate setup. Make a list of the things you have on your wish list, tie it to a stone and throw it overboard.

[S/V Illusion]

Originally Posted by Boatwright

Reading your original questions and your inventory of your boat's existing system:

It seems cruisers too often want to leave the dock with all the conveniences of a modern home. Electric stoves, coffee makers, hair dryers, air-conditoners, space heaters, refrigerators anything that produces or removes heat all use significant amounts of power (amps). Electric motors, winches, bow thrusters, washing machines, water makers -- ditto.

Suggestion: If you don't want to spend your days plugged in at a marina; if you don't want to spend big bucks on gear that requires maintenance and is prone to breakdowns, keep it simple. Make a list of those things you really need and compare it to your existing more than adequate setup. Make a list of the things you have on your wish list, tie it to a stone and throw it overboard.

For many folks, boating isn't camping. Many of us enjoy some conveniences, our wives often insist on them to be happy and if the boat is big enough to accommodate them, there is no reason to live the minimalist life particularly for those of us who spend a great deal of time onboard.

Electric/hydraulic winches, water makers, refrigerators, coffee makers, air conditioning, etc... all make boating that much more enjoyable.



As to the fundamental issue of this thread, the problem here is the lack of effort some (don't) put into learning the basic principles of the systems on a boat but have no problem asking others to waste their time teaching.

[evm1024]

First off Bill is correct:

Originally Posted by Bill Seal View Post
...You can change the voltage and the current will change, but you can't just arbitrarily change the current. Voltage pushes current, not the other way around.

And you are incorrect or at least grossly misstating what is happening. In either case it appears that you do not understand what is going on.

Originally Posted by sailinglegend

I'm sorry but Ohms Law hasn't helped your full understanding of DC circuits.

An increase in current will push the voltage drop on a wire or across a high resistant switch (faulty - corrosion).

This does take a bit of brainpower - but consider a faulty house battery main breaker switch, which has a high fixed resistance. With a current through it there will be a volage directly across the terminals of the switch. Double the loads and so double the current and the voltage across the switch will double. This 'voltage drop' is being pushed up and down by the current.

This also happens along a cable run where the current is too high for the size of the cable. Finding these problems is one of the few times you really need to understand Ohms Law - otherwise the water analogy is the simplest explanation.

The voltage supplied to the circuit is fixed by the voltage source (e.g. 12 volt house bank). The sum of the voltage drops across all resistances in the circuit equals the supply voltage. The current in the circuit is equal to the voltage across the circuit divided by the total resistance of the circuit. That current passes through all parts of the circuit. The only way to increase the current in the circuit is to reduce the total resistance in the circuit. By reducing any of the resistances in the circuit then the voltage drop across each of the resistances in the circuit will change. The sum of the voltages drops will continue to equal the supply voltage.

Best that you study up on ohm's law.

It is easy to change the voltage (add an additional battery in series, not advised). It is easy to change the resistance (add more or less load, Turn the heater from low to high). But current is dependent on the voltage divided by the resistance. Simply if you add an additional battery in parallel (which increases the batteries ABILITY to supply current) will not change the current used.

N.B. Sorry for the digression.

[The Sun King]

The downloads section of Victron's website has offered some great information, including printed books, that you might find useful. I'm glad to hear you are wanting to learn. It sounds like you have a pretty nice setup, but it seems we always want more!

[Bill Seal]

Originally Posted by sailinglegend

I'm sorry but Ohms Law hasn't helped your full understanding of DC circuits.

An increase in current will push the voltage drop on a wire or across a high resistant switch (faulty - corrosion).

This does take a bit of brainpower - but consider a faulty house battery main breaker switch, which has a high fixed resistance. With a current through it there will be a volage directly across the terminals of the switch. Double the loads and so double the current and the voltage across the switch will double. This 'voltage drop' is being pushed up and down by the current.

This also happens along a cable run where the current is too high for the size of the cable. Finding these problems is one of the few times you really need to understand Ohms Law - otherwise the water analogy is the simplest explanation.

Ignoring your snide little comments, in your example, you are arbitrarily changing the RESISTANCE, and the current is ust folloeing along.

And yes, I have understood Ohms law since USCG ET school back in 1958. (I think I got the second highest grade ever achieved at that time)

[nofacey]

1) Calder’s book is a great start. You have to be able to calculate watts (=voltage x amps) and Amp-hours (= device amps x hours device is on). Don’t worry too much how the electrons flow, that detail isn’t overly important

2) Draw a wiring diagram of your 12v system...and a separate one of your 24v system, and another of your 120vac system. That is where the greatest learning will be - if you can’t follow wires while at the dock, you can’t troubleshoot, and you should not be adding anything.


A 120vac, 1800w hair dryer running off a 24v battery bank via inverter is a great example Of what you need to know. Going to stay basic and ignore all losses.

Watts = amps x volts, so amps = watts/volts = 1800/24 = 75 amps
That is a big load on your batteries....which is where time on comes in.
Let’s say she runs it for 15 min = 1/4 hour.

Amp-hours = amps x hours = 75 x 1/4 = 18.75....call it 19 amp-hours.

You’ve listed your house bank as 600amp-hr. At 24v that would be 6 x 8D batteries, which is highly unusual for your boat. Suspect it’s 600 amp-hr at 12v, 300 amp-hr at 24v, which is still very good.

Somewhere in Calder’s book, he’s going to tell you that you will quickly kill your batteries if you run them flat....I only let mine go down to 60% before recharging so that 300 amp-hr becomes 180 amp-hrs usable.

So in 15 min, your wifey has used 19/180 = 10% of your available battery capacity. No big deal during the day at anchor, where your solar will recharge, but at night on a passage, would likely have me firing up the genset after midnight.

Hope that helps somehow.

[Stu Jackson]

Originally Posted by S/V Illusion

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As to the fundamental issue of this thread, the problem here is the lack of effort some (don't) put into learning the basic principles of the systems on a boat but have no problem asking others to waste their time teaching.

Thanks, Don. Finally a wonderful summary of reality.


I have taken the path of providing links to previous writeups, 'cuz I got real tired real quick of retyping the basics. I admire the folks who have the patience to do so for folks who are too lazy to read a book. Bravo!

[Mauruuru]

Watts=Power
Volts --what pushes the current through your load
Amps (Amperes)--the amount of current running in the wiing, through the load and back to the source

Watts = Volts x Amps in the DC and single phase AC world....
1800 Watts at 120 V will drive 15 Amp load
10 amps DC @ 12 V DC is 120 Watts....if you run that for an hour you have consumed 120 Watt hours that is how much energy you have consumed...in other words power during some time equals energy

[captainwd40]

Good Day ... Fair weather and fair skies to you!

I am an Electronics Engineer and battery designer.

I totally understand how confusing ohms law can be.

However ...... a very simple way (maybe too simple) to explain boat electrics is:

If you have a 2000 watt (2 kw) generator you can only power 2000 watts of stuff at the same time. For example if your frig needs 1000 watts to run and your AC needs a1000 watts to run ..... your generator is maxed out if you run them at the same time. But if you only run one at a time you can use the remaining 1000 watts for something else. It is called power management and you will have to be careful that you switch off unused items with the circuit breaker to be sure they don't come on automatically and overload your generator.

Typically if you want run more stuff, you get a bigger generator. Sometimes OPs will enhance their electrical systems by adding additional batteries with an inverter (converts battery 12/24 volts DC to 120 volts AC) and a solar battery charger on a separate circuit (protected with additional circuit breakers) to provide more power to run additional stuff.

Good examples can be found on Google and YouTube and most .... if not all .... the hardware can be found and purchased reasonably on Amazon.

Hope this helps!

Cheers!