Digital Multimeter Replaces Analog Volt Meter

This just seems like a no-brainer.  We all know that everything with “marine” stamped on it means it cost 4-5 times as much as it ought to.  Sometimes this is justified – bronze or high-quality stainless hardware is pricy, and things that are made to last use high-dollar components.  Other times, though, those high prices are just an attempt to soak boat owners for more money.  I think that’s the case with volt meters for boats.  Earlier, I posted about my analog volt meter made by Blue Sea that costs $45.  It is has been on the boat as long as I’ve owned it – installed perhaps by a previous owner.  It was definitely better than nothing, but that doesn’t mean it was a quality piece of gear.  I’m learning now just how inaccurate it is, as I use my digital multimeter in its place.

I glued up a small bracket from scrap teak and .25″ plywood to hold the multimeter in place.  I mounted it today by drilling two small holes in the plywood back, counter sinking the holes for flathead screws, and screwing it into the bulkhead.  Here’s a photo of the bracket again:

DSC_2670

Multimeter mounted in the bracket.

Multimeter mounted in the bracket.

After cutting off the probes, I installed new ring connectors on the leads and attached the positive lead to the middle pole of the battery switch, and the negative lead to the negative bus bar.  I’ve attached hook-and-loop fabric to either side of the unit to hold it securely in the bracket.  Now I can test each battery’s state of charge and get an accurate figure.

Low-cost volt meter for your boat.

Low-cost volt meter for your boat.

The state of charge at any given time is subject to interpretation.  The meter can give you a rough idea of current usage, and let you know when the voltage is getting very low.  It can give you a more accurate picture of the state of charge in a battery after the battery has been unused for 24 hours.  The multimeter can also give you an idea of the rate of charge acceptance for your batteries.  This information is useful in determining the health and status of your battery bank.  And, the information is a lot more accurate with a digital meter than your typical consumer-grade analog meter – I discovered through this project that the old analog meter was reading several tenths higher than was true.

The meter cost me about $10, and I’ve just ordered another from Amazon for under $10.  I would have ordered just a new set of leads and continued to use the meter as a tool also, but the with shipping costs, it made sense just to order a new meter for – literally – a dollar or two more.

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9 comments
  1. David said:

    Doesn’t the 400 watt inverter put a heavy drain on your batteries? I have a 400 that I put away and use a 100 watt to run my notebook on. It even put a good drain on my battery. I’m running 80 watts of solar to keep my system charged up. I do have a 10 amp battery charger when 110 is available.

    Nice wood work on you cabinet.

    • David, the inverter does pull on the batteries pretty strongly. I use it with one battery bank at a time, so the amperage drain is limited. And you are correct, I don’t need 400 watts to power a phone charger or computer – 100 watts would do. But I can’t run an electric drill with a smaller inverter, or any other AC electric tool. With the 400 watt inverter I can power the drill and my dremel and a soldering iron, and probably some other smaller tools as well. And of course, I don’t keep the thing turned on all the time – only for the duration required to use the tool, or charge the lap-top. It’s an acceptable trade-off for me. Before we go cruising for a longer term than a week or two, we will install a solar panel, which will help keep up with our DC power needs. We’ve cut back our DC requirements to bare bones – no pressure water, no radar (although the newer radar technology is much more efficient wrt power consumption), no refrigeration, installation of LED interior lighting – so I think an 80-100 watt panel will help a great deal.

      Thanks for the nice comment about the locker!

      • … and the 400 watt inverter doesn’t pull 400 watts (+ inefficiencies) out of the batteries unless the load on the 110V side is 400 watts. In fact, for a 100 watt load, it could be that the 400 watt inverter will draw less power than the 100 watt inverter, since you won’t be running it at max load…

      • Bob, I didn’t realize that a larger inverter could be more efficient for smaller loads than a smaller inverter. Interesting. . .

  2. Paul L said:

    Rick, are your battery banks single batteries? I have two batteries for my house bank and sometimes I even hook up a third for long trips, I use to have two for my starting bank,but have gone to one single bigger battery, however I do have a second cranking battery that I can hook up, again for long cruises. I’m wondering how if you have two batteries on a bank, you can test the state/status of each battery without isolating it first. I really like the idea you using a volt meter.
    Paul L
    ALso hope you are getting in some quality sailing.

    • Paul, I have one battery per bank. It’s a simple matter of moving the battery selector switch from 1 to 2. If I had more than one per bank, I’d just have to crawl down in the hole and check it with a volt meter.

  3. Just a question, Rick, but how do you know that it is the digital meter which is the more accurate?

    • Ah, you found me out. I’m assuming a lot here – I don’t know for sure, and I realized that when I wrote that it is more accurate. But in my defense, I will say that if I tap on the analog meter, the reading changes – sometimes as much as 2 tenths of a volt. So, to say that the digital meter is accurate – well, I don’t really know. I guess I’m hoping that it is!

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