The Offshore Voyaging Reference Site

One Simple Law That Makes Electrical Systems Easy to Understand

Yea, I know, you don’t have time for a lot of theory BS. I get that, we are all busy. But I can absolutely guarantee that you will have better results and happier cruising if you break a half hour or so free for this, and the next two chapters.

Can’t I just pay someone else to get my cruising boat electrical system up to cruising standard, you ask? I wish, but, sadly, it never ceases to amaze me how ignorant many, perhaps most, technicians around boatyards are about how electricity works. Yes, even those who have worked on boat electrical systems for years.

And the ignorance of said technicians pales into insignificance when compared to the pure unadulterated rubbish spouted by many people who sell marine electrical equipment.

And don’t even get me started on the level of BS that flies on the forums when things like batteries and charging are discussed—you could drown in the stuff.

The point being that we can waste a boatload of money and still end up with an inefficient, unreliable electrical system if we don’t have this basic knowledge.

The good news is that if we understand just a little bit of electrical theory we will immediately be able to detect the rich aroma of marine electrical BS before any harm is done. And the even better news is that this stuff is not that hard to grasp.

Let’s do it.


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More Articles From Online Book: Electrical Systems For Cruising Boats:

  1. Why Most New-To-Us Boat Electrical Systems Must Be Rebuilt
  2. One Simple Law That Makes Electrical Systems Easy to Understand
  3. How Batteries Charge (Multiple Charging Sources Too)
  4. 5 Safety Tips For Working on Boat DC Electrical Systems
  5. 7 Checks To Stop Our DC Electrical System From Burning Our Boat
  6. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  7. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  8. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  9. Balancing Battery Bank and Solar Array Size
  10. The Danger of Voltage Drops From High Current (Amp) Loads
  11. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  12. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  13. Battery Bank Separation and Cross-Charging Best Practices
  14. Choosing & Installing Battery Switches
  15. Cross-Bank Battery Charging—Splitters and Relays
  16. Cross-Bank Battery Charging—DC/DC Chargers
  17. 10 Tips To Install An Alternator
  18. Stupid Alternator Regulators Get Smarter…Finally
  19. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  20. Smart Chargers Are Not That Smart
  21. Replacing Diesel-Generated Electricity With Renewables, Part 1—Loads and Options
  22. Replacing Diesel-Generated Electricity With Renewables, Part 2—Case Studies
  23. Efficient Generator-Based Electrical Systems For Yachts
  24. Battery Bank Size and Generator Run Time, A Case Study
  25. A Simple Way to Decide Between Lithium or Lead-Acid Batteries for a Cruising Boat
  26. Eight Steps to Get Ready For Lithium Batteries
  27. Why Lithium Battery Load Dumps Matter
  28. 8 Tips To Prevent Lithium Battery Black Outs
  29. Building a Seamanlike Lithium Battery System
  30. Lithium Batteries Buyer’s Guide—Part 1, BMS Requirements
  31. Lithium Batteries Buyer’s Guide—Part 2, Balancing and Monitoring
  32. Lithium Batteries Buyer’s Guide—Part 3, Current (Amps) Requirements and Optimal Voltage
  33. 11 Steps To Better Lead Acid Battery Life
  34. How Hard Can We Charge Our Lead-Acid Batteries?
  35. How Lead Acid Batteries Get Wrecked and What To Do About It
  36. Equalizing Batteries, The Reality
  37. Renewable Power
  38. Wind Generators
  39. Solar Power
  40. Watt & Sea Hydrogenerator Buyer’s Guide—Cost Performance
  41. Battery Monitors, Part 1—Which Type Is Right For You?
  42. Battery Monitors, Part 2—Recommended Unit
  43. Battery Monitors, Part 3—Calibration and Use
  44. Battery Containment—Part 1
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Marc Dacey

“More than a little shocked” is covered in a future chapter: “Careful Where You Put Down Your Spanner”.

This is all timely as I’m getting six L-16s next week that will comprise our house bank. Your labelled lugs look excellent.

Alastair

Looking forward to the rest of the chapters as I am not that comfortable with electricity and the concepts around it.

Marc – A really good way to label is to use a standard Dynatape label, the printed ones, not the stamped letters, slip under some clear adhesive shrink wrap, then shrink the shrink wrap. A water tight joint and solid label.

Marc Dacey

Thanks, yes…I am trying to source clear heat shrink…maybe I can find it in the States online as locally it’s proving a bit of a unicorn.

Dave Lochner

Genuinedealz.com, waytexwire.com, and McMaster.com all have clear heat shrink and other products.

Enno

Just a small correction: If I remember my highschool physics right the symbol for votage is U. V is the symbol for the unit (Volts) that voltage is measured in. So Ohms law is I=U/R while the basic units are Volts (V) Ampaere (A) and Ohms(Omega). Another Law that one should really know is P=U * I. P being wattage. The unit is Watt(W). So Ampaere is a measurement of Power only if the Voltage is known. Likewise Ah (Amphours) is a measurement of energy only if the Voltage is known. For example if an appliance uses 10A on a 12V system this is 120W while it is 240W on a 24V system. Not only tecnicians but also Journalists also get this wrong all the time.

Frans

That’s correct!

Enno

OK. I see this seems to be language dependent. The german and french wikipedia uses U while the englisch uses V. (The norwegian wikipedia got it mixed up 😉 I wronly assumed that this would be the same across languages.

Foster Lee

When I was in school voltage was E. E=IR.

Jim R

Any lithium tidbits would also be appreciated.
Jim

Dick Stevenson

Hi John,
A very nice start and I look forward to the next installment.
I love pictures of wiring and yours is most elegant and a distribution area to aspire to. A couple of comments: I believe that most rules/regs (ABYC for ex.) limit the number terminals to a post to 4, with the one carrying the most amps on the bottom. Your post carrying 5 terminals could have one or more distributed to the other posts easily. It is hard to tell from the picture, but the large amperage wire looks to be on top of a smaller terminal: again easily remedied.
In the lower left of your photo is a particularly nasty bit of cut off wire tie waiting to scratch an arm as it passes through. A wonderful addition to one’s tool chest is a small flush cut diagonal cutter made by Xcelite which will leave the ends of wire ties smooth as the proverbial baby’s bottom.
Finally, and only because I am on a roll here, I would suggest securing the grey colored cable carrying multiple wires so that it does not rest/chafe on the threads of the adjacent post it passes next to.
My best, Dick Stevenson, s/v Alchemy

Dick Stevenson

Hi John and all,
With respect to your “good enough” response to my comments about electrical practices, number of terminals on a post etc. I should have made my thoughts clearer. It is my take, that rules and regs (guidelines) vary widely in their practicality (and even in their wisdom) so “good enough” for sure has its place in many/most projects.
I pay most attention to rules & regs when I am at my most ignorant, when I do not have the experience to judge good enough. Generally, I like to follow the accrued wisdom, the guidelines if you will, until they start to make little or no sense when compared with experience. Most of us are, and will remain, amateurs in the electrical work we do on board. And many of us do a lot of electrical work for a variety of reasons. It is good to know what is recommended practice.
I believe the event that scares my most on a boat is fire and way too many fires start electrically. The down side of electrical problems can be a catastrophe, so “good enough” has to be very good. The ABYC guidelines for electricity on board are the accumulated knowledge of experienced marine electrical people, and, in my read of them: they make a lot of sense. One of their primary purposes is to promote practices that make it unlikely for heat to build up: for fires to start.
Many distribution posts are tall enough to fit far more than 4 terminals and there can be a strong temptation pile them on when it can save work and time. Similarly, it can be easy to put a high amperage terminal on top of a lower amp carrying terminal. The results can be more heat. Knowing the guidelines can allow you to make wise “good enough” calls
As said in my first email, your distribution area is to be admired and emulated. It is certainly better executed and safer from fire than the vast majority of boats out there and even brand new just-out-of-the-factory boats could benefit from an electrical survey.
My best, Dick Stevenson, s/v Alchemy

Rob Gill

Hi Dick,
I am severely electrically challenged, but know just enough to agree completely with your thoughts on electrical fires on boats. Hence we have always engaged competent electrical guys to work on our boat, homes and businesses. I do not trust myself with any high load DIY electrics, even 12V DC, but that’s me!

2 years ago we had the standard bi-annual electrical survey done in our workplace, and we’re offered ( at no extra charge) an extra survey using a heat sensing camera. The camera picked up a faulty connection in one of our server racks that was over 70 degrees centigrade, in normal mode. The inspector suggested that this was a possible/likely pre-cursor to further deterioration and a fire hazard, so we quickly replaced the offending junction.

I wonder if such an addition to boat electrical surveys should be part of the guidelines for boats, given the horrendous record of marine electrical fires on boats and the highly corrosive atmosphere our electrical systems endure?

Rob

steve d'antonio

Rob:

Indeed more and more folks in the marine electrical world are relying on IR cameras to identify hot spots. These have dropped dramatically in price since they were first introduced, and are now within reason for any yard or independent marine electrician. While there are stand alone products from Fluke and others, in the interest of keeping my traveling kit bag as light and compact as possible (my checked travel bag typically weighs in between 50-65 pounds as it is) I use a tiny product called SeeK; a camera that plugs into the USB port of my smart phone, it cost about $200. I routinely use it to inspect the backs of electrical panels and battery banks. It’s well worth the price.

Dick Stevenson

Hi Rob,
I very much agree with your comments and feel that your use of competent marine electricians is likely wise. You also mention electrical surveys. Both, however, depend on finding people who can do the work well and that, to me, is a problem. There is only one person I know who I would trust to do a competent survey on the electrical system of Alchemy and it is Steve D’Antonio who has added the recent contributions here to AAC.
I have had one superb marine electrician in my time and I played surgical assistant (handing tools, making coffee) to him for some major jobs on Alchemy and learned a great deal in the process. Since then I have done the majority of DC work on my boat and, casual observation of the work of electricians on friend’s boats have not made me change my mind. Let me also say that that is not solely the competence of the electricians. Good electrical work takes time, both to design and think through, and then to execute properly. One must also have an impressive array of parts etc. Many boat owners go for those who do jobs for the least amount of money and do not want, expect or know what a good electrical installation entails.
With respect to pyrometers, IR temp sensors, I have used one for years that I got for diagnosing some refrigeration issues. Since then it has proved quite handy for a variety of diagnostic chores on Alchemy: base line temps on various parts of the diesels, heat leaks in insulation, testing thermostat opening temps and checking out terminal connections. When/if you buy one, make sure it has the range to do reefer work as well as the heat level diesels can generate.
John has talked wisely in the past about taking regular deck walks on offshore passages. I would suggest regular visitations to the darker hidden regions where our electrical connections often reside for a thorough inspection including a fingers-on-push to those connections to see/feel whether they have loosened and visually whether everything looks to be in order. The best thing any owner can do for his/her electrical system is to do a complete schematic. Doing so will immensely speed trouble shooting when its necessity rears its head, but also stimulate thoughts about designs that might not make sense or practices that should be changed.
My best, Dick Stevenson, s/v Alchemy

Marc Dacey

As a sort of adjunct to the best practice Dick mentions of checking the securing of various studs and terminals, when commissioning in spring I go stern to bow giving every hose clamp a quarter-turn (the average) and every terminal screw or securing nut a check. I also look for loosened or worn cable ties, as one of the worse things to happen is a loom of wires coming loose near a moving or hot engine part.

This can take an hour or two, but it gets one to rarely seen parts of the vessel, hopefully to preventative effect.

Rob Gill

Thanks Guys for your comments,
Steve – what a great gadget for the smartphone – how accurate is the heat calibration in your experience? Have you used it also on your own boat, say approaching an anchorage on dark cloudy nights? How does it perform? Have you used it for low temperature applications also as Dick marvellously suggests?
With regard to our own install, we have a full schematic of the electrical systems, and I have traced every circuit. But I rely (and trust) fully our excellent provider here in NZ (Enertec Marine) to do any major work or upgrades.
best regards,
Rob