Dan’s Boat Tools, The Battery Operated Kind


Dan Corcoran:  In the fall there were a lot of magazine articles on tools everyone should have on their boat including favorite tools, tools distance cruisers should have, unusual tools, multi purpose tools, and so forth. In this article I bring some focus to tools of the battery operated kind I use on my boat.

The most frightening tool to use is the Electrophysics CT-33 Moisture Meter in the top left side of the picture. If the meter on this tool moves much to the right, it’s a good predictor of unpleasant drilling, epoxy, and sanding work in my future. Place this tool against the surface of a fiberglass deck, and rather quickly the contact sensor on the backside utilizes a capacitance based measurement to indicate how much moisture is on the other side of the fiberglass, in the wooden core below. Move this around the fiberglass and you can find how extensive a water penetration is and possibly trace it to the source. As unpleasant as the meter reading might be, it’s far better to detect and resolve water leaks early, than have a boat surveyor warn away buyers or knock many thousands off the value of your boat when you go to sell it later.

The black analog multimeter above is a Radio Shack model 22-223. A very inexpensive piece of gear worth keeping aboard at all times. I like this one because the big display makes the volt and ohm markings readable from 3 feet away. If you’re not a master of this $20 device, the rest of this article will be tough to follow although I do include below a good book recommendation.

Next is a digital multimeter. I strongly advise against the use of digital multimeters on boats, as they will waste your time with false readings. An exception is the Fluke 117 multimeter pictured above. This product has a low impedance measurement feature (Fluke LoZ) which overcomes the reasons most digital multi meters provide false readings on boats (induced voltages between wires in the same conduit). For $190 you get an absolutely solid digital reading, automatic range selection, back lit display, and so forth … but it does do exactly the same function as the $20 radio shack meter.  

Both analog and digital multimeters above have a DC and AC current measurement feature, but they are a real hassle to use. First because most are limited to 10 Amps, which I find is not enough 20% of the time, and second (unlike for measuring voltage) these meters require the user to disconnect boat wiring to insert the multi meter in the middle of the circuit before current can be measured. In the cramped wiring areas of a boat, this is often tough to do, and creates significant opportunity for burns and electric shock.

An alternative for measuring current quick and safely is an ammeter with a clamp which measures the current without ever disconnecting the wire. Beware the typical clamp on ammeter which reads up to 600 Amps and is near useless for boat applications. This white Amprobe LH41A low current precision ammeter pictured above is a specialty ammeter appropriate for most boat applications up to 40 Amps. While it won’t measure your starting engine current, it excels at everything else with a high sensitivity to the very low currents that can slowly kill batteries or plague your boats anode protection. 

The right most yellow test device in the above picture, the Ideal SureTest Circuit Analyzer, is useful for testing the quality of AC connections both dockside and inside your boat, and is about as simple as a testing device can be. For my purposes, it tells me if the dock pedestal is wired correctly and has not been compromised by corrosion. With the simplicity of plugging in a blender, the SureTest allows a boat owner to perform the same tests within seconds, that a qualified electrician invasively disassembled the pedestal would take an hour to perform.

Moving to the picture below, the gray tone generator and wire tracer (receiver) boxes are the second most important electrical tools I have on my boat. Ben wrote here about a similiar product, the Foxhound from Triplett, that would be a more compact choice than mine. Next in the picture is a Marinco adapter to allow the household polarity tester (attached in this picture) and my Ideal SureTest above to connect to a dock style 30 Amp outlet.  The little white Shakespeare ART-3 VHF tester (Panbo tested here) is useful for measuring the VHF losses in a mast antenna, confirming each season the antenna has been correctly installed.  Finally there is that yellow pointy probe (DesignTech Deluxe LED Test Light w/12v adapter); all of what this 12 volt tester can do is covered by multimeters; it’s limited value is in poking around live circuits and fuse panels to confirm everything that should be connected to ground or battery, really is.

Before poking around any circuits, live of otherwise, I recommend reading “Boat Owner’s Illustrated Electrical Handbook” by Charles Wing. In addition I have a narrow recommendation for Ed Sherman’s excellent book, “Advanced Marine Electrics and Electronics Troubleshooting“. Unlike other books that help you apply a multimeter to trouble shooting various applications, Ed covers the use of specialty testers to troubleshoot various boat systems. Beware, it is a rather expensive read as each chapter requires yet another expensive testing product.

– Dan Corcoran is an avid sailor and leads ServiceSPAN a back office work center automation technology company. Dan has 950 hours of classroom electical and electronics training. While such training is not required to work on boat DC systems, some education and safety precautions are necessary. Amateurs must always leave AC boat systems to the professionals.


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18 Responses

  1. Sandy Daugherty says:

    Sorry for the off-topic intrusion, Dan, but Kudos to Ben for his two awards from EXCELLENCE IN BOATING JOURNALISM contest!
    Now, as for your article….
    Thanks. I needed that.

  2. Dan – excellent article and great personal advice. I know that I wouldn’t leave the dock without my Fluke a single step away from my helm!
    There’s only one thing I’d add to your list – a high quality silver/silver-chloride electrode for the Fluke. Given that, it’s quite easy to check the bonding and zinc protection of your boat. I do that every few months on my boat and often do a quick check of other friend’s boats. It gives you a good indication of how your zincs are doing, points out bonding wire corrosion that’s hard to see, and shows if any DC wiring is putting current into the bilge, so common with bilge pumps as they age. I usually find a couple of problems on most boats I check that are trivial to fix – long before they get to do damage.

  3. Scott Cadle says:

    Jeffrey – would you mind sharing your source for the silver/silver chloride electrode? When I looked at them last year there seemed to be a significant range in price/quality.

  4. JonM says:

    Although my Electrochemist friend offered to help me build one, I got my Ag/AgCl reference electrode from boatzincs.com
    {added by editor}

  5. Silver/Silver-Chloride electrodes…the company I got mine from 4 years ago is no longer in business. It was an industrial company. I have seen the BoatZincs.com page on their product. It’s less expensive than the one I bought. Mine was about $250 and has 75′ of wire which is really nice.
    I figure that the BoatZincs one has less sliver in it and might not last as long. I always rinse it after every use and that might help to prolong its life.
    I looked around for some other reference electrodes but couldn’t come up with any quickly.

  6. Sean says:

    UHHMMM you don’t specify where you got that “pointy probe” piece which as luck would have it – is something I’m looking for. FTA -“Finally there is that yellow pointy probe; all of what this 12 volt tester can do is covered by multimeters; it’s limited value is in poking around live circuits and fuse panels to confirm everything that should be connected to ground or battery, really is.”
    Love your work – can you provide linkey ???

  7. Dan Corcoran (b393capt) says:

    Jeff, yes, that Ag/AgCl reference electrode from boatzincs.com would be an excellent addition to this set of battery operated tools. In fact, placed an order yesterday. It�s on sale for $119.
    Sean, UHHMMM I was hoping nobody would ask !! The link was omitted as the product has no model number labeled and I couldn’t remember where I got it. Since you asked, I dug a little and found it. The article above has been modified to provide a link to Autobarn where you can purchase it. Before you purchase it, let me say I only used it once last season and if I could do it over again, would have saved the $30 and have not purchase it as the multimeter can cover the same functionality.

  8. Chip says:

    I have a Fluke 117 myself, but you can adapt a set of plain multimeter leads to give the same “Lo-Z” functionality for damping down “ghost voltages” to a regular digital multimeter. Still, the 117 is a really nice meter…
    The Lo-Z input of the Fluke is 3000 ohms. Find yourself a 5 or 10 watt 3000 ohm power resistor (from Mouser.com perhaps) and wire it in parallel across the test leads. Be sure to insulate the bare leads well. Now you have a multimeter with a 3000 ohm input impedance just like the Fluke. I would only use these where “ghost voltages” are expected, and not on curcuits above 120 volts that could deliver significant current, but even at 120 volts the resistor will only draw 40 milliamps and need to dissipate 5 watts.

  9. Adam says:

    Dan, Ben, and Panbots: I’m wondering if anyone can recommend a good battery tester for assessing my 6 x 8D AGM house bank (and the other smaller banks). Steve D’Antonio recommends a carbon pile tester but I don’t know what specs I should be looking for regarding CCA capacity, etc. for my particular bank configuration. Thanks all!

  10. Dan Corcoran (b393capt) says:

    There are two tests that I think are valid for batteries, but nothing is quite like having a LINK 20 or equivalent real time battery monitor (I have not tested, but I believe the Maretron DCM-100 is the latest of this type of product, featuring NMEA-2000). This product helps you understand if your battery and charging system are working well, take care of your batteries, manage a power budget, and gives much more information than a carbon pile tester.
    The two tests below are less expensive alternatives:
    The first test is free, and that is your level of tolerance for your current batteries. No matter what a battery tester says, its possible the use of your boat has changed, the power consumption of the devices aboard has increased, and battery capacity has dropped (battery age and a little negligence on your part will shave off 15% of capacity each year) such that your batteries appear to be faulty but they are not. No amount of testing is going to fix a mismatch between what you need and what your getting from your batteries, better just do the testing you can do with any multimeter using the book I recommended above.
    However, if you want a sanity test for your batteries, here is a recommendation I wrote long ago for the E-Z Red S101 Battery Hydrometer that appears in Amazon.com for less than six dollars.
    Great Product, January 4, 2007
    By D. W. Corcoran “b393capt” (Huntington, NY United States)
    Spend the couple of extra dollars on this. The wide range of movement on the dial makes it easier to see small differences between individual cells in a battery. It doesn�t say so on the web-site, but on the box it states that it is self compensating for temperature.

  11. Adam says:

    Thanks, Dan.
    So reading the Lifeline AGM manual, they basically say that the best test is to measure the time it takes a 25A constant-current discharge to run the battery down to 10.5V. I’ve been trying to find a reasonably priced 25A discharger/analyzer, but haven’t had any luck so far…

  12. Dan Corcoran (b393capt) says:

    Ugh, an AGM battery, and you don’t have a Link 20 I imagine that would have been real helpful in the care and feeding of this type battery.
    When a story begins with AGM battery and �how to I test�, there is never a happy ending. But, there is no reason for the test you want to perform to cost you anything.
    It’s probably not apparent at first, as most multi meters don’t go beyond 10 Amps, but you can do this analysis with almost any multi meter. (although the LH41A in the article above would have made quick work of this !)
    To do the test with a multi meter that doesn�t go up to 25Amps:
    1. Confirm everything is turned off in you boat.
    2. Disconnect your +12V at the battery
    3. Using your 10Amp capable multi-meter to measure the current your boat is drawing when off (usually your going to have at least something pulling current), call this your base current.
    4. Turn on just one light at a time. Measure how much additional current is draw for each light. Subtract the base, and write that down for each light, turn it off and move onto the next light. Do the same for your VHF radio and some other small devices (e.g. not your autopilot or inverter if you have one).
    5. Remove you multi meter, hook the battery back up.
    6. Figure out what combination of VHF radio and lights will consume 25 Amps (I don’t know where you got 25 Amps from, that sounds like a round number, normally you choose an amount that is the total battery capacity in Ahr of your battery at the C20 rating, and divide by 20)
    7. Turn on that combination of C20 power sources for 10 minutes, then turn it off.
    8. Let you battery sit at rest for an hour.
    9. Measure your battery voltage again. This is the voltage that you can use to determine if your battery is fully charged.
    10. Again turn on that combination of VHF radio and lights to consume C20 in current.
    11. For the first hour write down the battery voltage under load every 10 minutes. If you get past one hour, write down every hour, and measure total time it takes to get down to your target voltage you were aiming for.
    If you don’t have a multi meter now and know how to use it, I would purchase the one I recommended above from radio shack and have someone who has worked with the meter assist you.

  13. Adam says:

    Dan: Makes sense! Just build a 25A resistive load from stuff I already have.
    As for the 25A number, that came from Lifeline’s own docs. They spec the battery capacity in minutes at 25A draw.

  14. Dan Corcoran (b393capt) says:

    That’s pretty much it Adam. The rest of the detailed steps catch a little more diagnostic information and deal with the overall difficulty in determining the battery charge state by measuring DC volts.

  15. norse says:

    Adam said: “So reading the Lifeline AGM manual, they basically say that the best test is to measure the time it takes a 25A constant-current discharge to run the battery down to 10.5V”
    I would say that this is on the verge of destructive testing and it is certainly battery abuse.
    Almost exactly a year ago there was a Panbo item “Battery Bugs, new monitoring tech?”. I think that would be the easiest and cheapest first step. Is there an update on how well those work?
    The a better way to do a load test might be to run a space heater off of an inverter for the load and get a battery monitor to watch the amp-hours and voltage while you do this… and only go to a normal depth of discharge.
    The Link series of battery monitors are no longer available.

  16. Dan Corcoran (b393capt) says:

    Borders on destructive testing, yes it certainly does. Considering how battery capacity is decreased with use and abuse (most owners are guilty), and how runtime is further reduced by adding more gadgets each year, its easy to have the appearance the battery is diving off a performance cliff, especially after you rule out any charging problems using a multi meter. The upside of the test I suppose is that it definitively demonstrates to the owner that the battery is some measurable % close to rated capacity, and while that might not change a decision on replacing the battery, putting the number against the age of the battery could indicate if further investigation is warranted of the (i) charging system, (ii) the battery itself, (iii) battery abuse, or (iv) a mismatch of the battery to the load.
    Using an inverter and a heavy load for such a test is the wrong move. The amount of energy that a lead acid battery (including AGM) provides varies based on how quickly you take the energy out. The faster you take it out, the less energy you get. For a 180 Ahr battery you can get something like 30% less energy (measured in amp hours) if you put a 150Amp load on it like an 1800 watt heater, vs a 20 Amp load. That would make the battery appear to have 30% less capacity. Instead for this test you need to discharge the battery at the same steady amount the vendor has rated the battery for (usually rated battery capacity / 20 hours), in this case Adam indicated this battery was rated based on a discharge rate of 25 Amps.
    Link 20 discontinued, so it is! Why? Competition or did the cost of providing technical support to people who install them wrong (typically screwing up the grounding system) and people that had to high an expectation on % charge accuracy make it not worth while to sell the product?
    Who is a worthy competitor ?

  17. Adam says:

    I have a Maretron DCM100 on order so we’ll see how well that works. But I need to say frankly that you guys have scared me that the installation will be a bear.

  18. norse says:

    I didn’t mean to suggest using a 1800 Watt heater! For 25 Amps at 12 Volts, 300 Watt would be the right size. Those exist, but it would be easier to just use light bulbs to get the desired load, or use something on your boat in that range if you have it.
    I think the Maretron DCM100 is a good choice. It uses NMEA 2000 and it does not use a shunt — that makes it much easier to install.
    The Link 10 was replaced by the Xantrex XBM. There is no replacement for the Link 20. Then the XBM was replaced by the LinkPRO. There is also a LinkLITE. The competition includes Newmar DCE and Victron BVM.

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