Ohm’s Law Simplified and Stuff We Are Testing

I know I can be a bit of a pain in the ass about the importance of understanding Ohm’s Law.

A “bit” John?

OK, a lot of a pain in the ass.

Anyway, Al over at Wakespeed, designer of the WS500 that I’m so excited about, sent me a very cool and fun graphic that helps in understanding Ohm’s Law. I was not able to use the one Al sent me since copyright was not clear, so I grabbed the one above from iStock.

It’s fun, but it may also help in visualizing this vital law, the understanding of which will make every boat electrical problem easier to solve.

That said, to really understand Ohm’s Law to the point you can apply it to your boat, you will still need to read the first three chapters of our Online Book—don’t look so sad, you would have feared for my cognitive state if I had abruptly stopped being a pain in the ass.

Testing a WS500 Regulator

Talking of Wakespeed, Al’s partner Rick is sending us a WS500. I will install it on Morgan’s Cloud, unless she sells first, in which case on whatever new boat we buy, and report.

Nice of Rick, but then I guess he feels bad about being the guy behind calling stupid regulators “smart” while in charge of marketing at his previous employer.

Seriously, I just love that we are seeing a small company run by two real cruisers making things better for the rest of us. Back in the day there were a bunch of those around, but these days it seems that much of the gear we buy is manufactured by bigger companies who are a lot more into how much gear they can sell at the highest possible margin, rather than into actually making the best gear possible for task.

Here’s Rick on the same subject:

It’s funny, this area (Seattle, north to Vancouver BC) was always a hot bed of clever guys that hung out and developed great charging technology. Rick Proctor, Dave Smead, Mike Frost (who developed the Max Charge regulators for Balmar) who started great companies like Trace Engineering and Heart Interface, Cruising Equipment and Ample Power. We feel a bit like we’re the beginning of a new generation that’s taken up the sword, as so many small, awesome companies have disappeared to big holding companies.

Programming Not-Smart Regulators

Way back in 2010, I wrote an article that identified the problem of stupid regulators wrecking batteries—a first, as far as I know—and outlined how to reprogram them to at least ameliorate, but not solve (it’s not solvable with stupid regulators), the problem.

That article is now long in the tooth, particularly since the regulator in question is no longer made. So I’m going to delete it since our recommendation is now to upgrade to the WS500.

Yes, I know, throwing out a perfectly good regulator that cost several hundred dollars sucks, but trust me, you will save money in the long run since your batteries will last longer with a truly smart regulator and you can always keep the old stupid one as a spare.

That said, if you just can’t stand to throw your old regulator away, Rod “RC” Collins over at Marine How To has a good programming guide.

Testing Ewincher

Ewincher demo rig. Sorry about the camera strap. Sheesh what a newb mistake.

Talking of testing cool stuff from small innovative companies, Ewincher have sent us an evaluation unit, which Phyllis and I are really looking forward to working with.

Testing SeaAngel

And if that were not enough, SeaAngel has sent us one of their AIS person overboard beacons to report on.

More From Maus

And, I also have an interesting new fire suppression gadget from the folks at Maus in Sweden sitting on my desk that I need to investigate more.

Busy, Busy

And I haven’t forgotten that I need to finish (mostly written) the next chapter on keels. To that end I’m off to take a look at one that’s just been removed by our friends at East River Shipyard.

And, yes, I know, I still need to finish our review of the Outbound 44/46. And our broker is beating on me to write more about Morgan’s Cloud as well as shoot more video.

Not to worry, it will all happen, just not today…or tomorrow…as I need to finish up installing the new commercial quality engine room fire suppression system on Morgan’s Cloud…and I will write about that, too. (I wrote this a few weeks ago, now finished).

To think I used to worry about not having enough to write about!


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Meet the Author


John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

19 comments… add one
  • Alastair Currie Aug 5, 2020, 6:02 pm

    Really looking forward to the Wakespeed WS500 test. My plan next year is to removed the two ancient Lucas alternators and modernise the battery charging system by converting to single large case alternator etc. Your articles and advice are appreciated and will form the basis of the design of the new system.

  • Murray Fitzgerald Aug 6, 2020, 2:49 am

    G’day John,
    We have Ocean Signal AIS MOB devices fitted to our jackets/harnesses and as we are always two up they allow the off watch to rest. We have tested the unit and there is no way the off watch could ignore or sleep through the alarm.
    Thanks for your site.

    • John Aug 6, 2020, 11:19 am

      Hi Marry,

      Yes, we have and use the MOB1, and I have written a bunch about it in our online book: https://www.morganscloud.com/series/staying-aboard/

      That said, we did identify several issues with the MOB1, so it will be interesting to see how the SeaAngel stacks up.

      • Douwe Gorter Aug 7, 2020, 11:37 am

        Hi John, as an owner and user of MOB1’s it would be interesting to know the issues you experienced with this product. Thank you! Douwe

  • Brian Sutton Sep 1, 2020, 5:17 pm

    This electrical stuff doesn’t sink in easy with me and it makes my head hurt.One thing that I haven’t been able to figure out.Say I had a 220ah 4d deep cycle bat.If I was getting a battery charger,how would I determine what size or how many amps the charger should put out, 10,20,30,40,50,60.If I had two batteries would I just double the size of the charger? What is the determining factor for the size battery charger I should install?

    • Ernest E Vogelsinger Sep 1, 2020, 5:36 pm

      Brian, John has put a lot of detail into this eternal question here: https://www.morganscloud.com/2016/06/25/how-hard-can-we-charge-our-lead-acid-batteries/

      This said, there is no “amperage” (John, please say sorry to your late high school physics teacher) limit, as the charging source only controls the voltage, and in the end it is the voltage that makes the current flow. So your charger will throw as much amperage to your battery as it accepts (and the charger is able to deliver) at a given voltage – usually 14.4 volts in bulk mode.

      This said, if your current charger/alternator puts its max. ampere into the battery in bulk mode it is probably to small. You might want to throw as much amps into the batteries as possible, as much as they accept for a given voltage – you cannot ruin your batteries by throwing too much current at them.

      But take care of thermal issues – batteries will heat up when being charged, the harder you charge the hotter they get. Put temperature sensors at the right places and have your regulator programmed to the battery manufacturers specification regarding charging voltage at given temperatures.

      All this is discussed in great detail in Johns aforementioned “Electrical Systems For Cruising Boats”, Chapter 3 (link above)

      • Brian Sutton Sep 1, 2020, 10:52 pm

        Thank you for the reply.I re-read the obove link and it appears to me that the limiting factor for how fast you can charge a battery or how “big” of a battery charger you could use is based on the amount of heat that will be generated while charging.Like Dick S below says if charging by using a generator your going to want to charge as quickly as possible.It sounds like a “big” charger with a built in heat sensor would be the way to go.Iv’e been trying to figure this one out for to long.If im missing something please comment.Thanks again

    • Dick Stevenson Sep 1, 2020, 5:39 pm

      Hi Brian,
      My take:
      Most of the answer depends on how fast you want your battery charged. A 10a charger will do the job (over time) if plugged into shore power. A 100a charger may not be too big (depending on battery chemistry) if using an on-board generator where you want to minimize running time. Same, or similar, thinking leading to answer for a larger bank.
      My best, Dick Stevenson, s/v Alchemy

    • John Sep 2, 2020, 8:12 am

      Hi Brian,

      That depends on how you use your boat and whether or not you have, and rely on, an AC generator. If your boat is regularly on shorepower then the size of the charger does not much matter. 40 amps at 12 volts is probably a good option up to a 800 amp hour bank. But if you plan to charge off an AC generator charger size becomes very important. This chapter explains how to size for that scenario: https://www.morganscloud.com/2018/06/29/reducing-ac-generator-run-time/

      And this chapter will help you figure whether of not you need a generator: https://www.morganscloud.com/2014/04/24/do-you-need-a-generator/

      • Brian Sutton Sep 2, 2020, 2:13 pm

        Ok , I should have stated at the beginning that I will be doing all my charging from an ac generator.That was quite a bit of reading (informative reading) for what I thought was a relatively easy question.While I do understand that their are variables I did finally find a sentence that i believe answered my question,it read; “Most batteries can be charged at a rate of 30% of rated capacity”.Now we’re getting somewhere.This is something that is not confusing to me ; )

        • John Sep 3, 2020, 8:35 am

          Hi Brian,

          Sorry about the amount of reading, but the only way to get a good electrical system is just that, thinking about it as a system, and that takes a lot of explanation. Decisions make piece meal based on simple rules rarely work out well.

          Not sure where you got “Most batteries can be charged at a rate of 30% of rated capacity” but that’s overly simplistic. For example LifeLing AGM batteries can theoretically be charged at 80% or more of capacity, but that would not be practical due to wire size and the number of chargers it would take, as well as generator load. Also, that’s only true during bulk charging, not acceptance.

          Since you have a generator, this chapter has the key information you are looking for: https://www.morganscloud.com/2018/06/29/reducing-ac-generator-run-time/

  • Brian Sutton Sep 3, 2020, 8:56 pm

    Yes thank you.I did read that.Under “Why 20%-30%” is where I read “Most battery types can safely accept a charge of 30% of capacity,(some AGMs can take far more,even up to rated capacity)”.
    Their just seems to be a lot of variables.Wish it was a little simpler.

    • Brian Sutton Sep 4, 2020, 8:31 am

      In my situation where I would like to charge batteries as fast as possible and the battery bank is not oversized (say two 200ah 4d bats) would the main concerns be; 1) charge up to the recomended charge rate recomended for that particular size battery from battery manufacturer, and 2) monitor batteries for over heating with a shunt attached to the chargeing cable or battery? Thanks for any thoughts.

      • John Sep 4, 2020, 8:43 am

        Hi Brain,

        Shunts don’t monitor batteries for temperature, they measure current (amperage).

        Since you are charging with a generator, simply take the recommendation in the chapter I already linked you to for charger sizes.

        That said, the chargers should monitor temperature. Most manufactures provide sensors to do that so just make sure that the chargers you buy have that feature.

        One other thing, given that you have a generator, I assume that your boat is quite large. Assuming that’s true two 4Ds would be a very small bank so you will be starting your generator several times a day.

        See this series of chapters (three) for how to calculate proper bank size: https://www.morganscloud.com/2019/01/09/cruising-boat-house-electrical-system-design-part-1-loads-and-conservation/

        You need to settle on bank size before you can decide on chargers.

        Yes, I know you want this simple, but if you don’t take the time to take a systems approach to this I can guarantee a bad outcome.

  • Dick Stevenson Sep 4, 2020, 9:02 am

    Hi Brian,
    You describe yourself as quickly getting overwhelmed when reading about electrical systems. This is not a good state to be in when making decisions for your boat and I would put off making decisions at this time if you can.
    I suspect you would benefit greatly by immersing yourself in Charlie Wang’s “Boatowners Illustrated Electrical Handbook” and/or Nigel Calder’s “Boatowners Mechanical and Electric Handbook”. Both live on my shelf. Couple that reading with John’s articles and you are likely to make good decisions in this complicated, but far from rocket science, area.
    My best, Dick Stevenson, s/v Alchemy

  • Brian Sutton Sep 4, 2020, 3:32 pm

    Thank you all, I guess their is no easy way our of this.I really have a very simple situation, 29 ft fishing boat that I run only a fishfinder and a 800 gph pump for the bait tank while I am at anchor.I have a Pro mariner, pronautic 40 amp dual battery charger that charges two sportsman 220ah 4ds.I usually start the honda 2000 gen a couple times a day and run for around 1/2 hour.This has been working out fine so far just trying to figure out if I could move up to a larger charger if I decided to move up to a larger size bait tank with a larger pump.I only work off one battery at a time.The battery bank issue is much more important/complicates in your situation.Ill put my time in.Having a better understanding of all this certainly isn’t going to hurt anything.Thanks Again

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