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Amp and Voltage Meters

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Bortiquai
1st Mate

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88 Posts

Initially Posted - 09/07/2008 : 22:02:09

I am redoing the electrical in the my 1980 Catalina 25. Really, i'm starting out very simple with just the basics - lights, radio, stereo... I want to put a n analog Voltmeter in to be able to see the status of my battery.

What is the advantage/purpose of having the ammeter in addition to the Voltmeter? I thought I would be able to tell the condition of my battery charge by using the Voltmeter.

Thanks
Matt

Edited by - on

pastmember
Master Marine Consultant

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Response Posted - 09/08/2008 : 06:44:50

What would you do with the info if you had it? Many power panels come with dual battery status voltmeters, they are adequate info for a health status. Amp draw could tell you if you were over drawing some component in your system but if you design your improvements with the right components you do not need to worry about that. The biggest single thing to insure a safe electrical system is using the correct wire. Do not scrimp on wire, used tinned stranded marine wire. Most use ANCOR brand, use the correct gauge or larger.

Here you can see a white/red light, nav light power panel with battery status, and 110 volt outlet I installed.

I added a large buss bar for comon ground terminations as an upgrade over the very minimal buss bar Catalina used. (My electrical were in a different place on my year boat, yours are on the powerwall, (back wall of the galley).

yours, note old buss bar at bottom and new buss bar (still empty) on right.

Edited by - on

Jefffriday
Navigator

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USA
198 Posts

Response Posted - 09/08/2008 : 07:04:55

I put in a 15v volt meter on a switch when I redid all my electrics last year. I do not have any shore power available all season and use a 15 watt solar panel with a charge controller wired in to the battery selector for keeping my two batteries up. I find knowing the voltage has been really handy when determining if I need to use the solar more. Sometimes on long days with everything on, autopilot, GPS/depth-finder etc. I can get low (I like to keep them above 12.0 v, fully charged is about 13.5V Be careful when you look for a stereo, the one I put in sucks power, looking for a replacement this fall. I think it is going to be difficult to find power draw specs on these things...

Edited by - on

Stu Jackson C34
Admiral

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Response Posted - 09/08/2008 : 20:27:24

An ammeter is a VERY handy tool. You can buy a 0-25A ammeter from Blue Seas with a built in shunt. Your batteries are measured in amp hours. Wouldn't it be nice to know how many amps you are drawing at any given time. It's a simple install, like a voltmeter but in series with the load so all the current goes through the ammeter. Alternatively, you could get a Link 10 or a Xantrex unit that will measure amp hours and give you time remaining on your house bank.

Between the voltmeter and the ammeter, plus a hydrometer you can keep very good track of the batteries' condition.

With the ammeter you can determine the power draw of any appliance, including stereos!

Edited by - Stu Jackson C34 on 09/08/2008 20:29:51

Dave5041
Former Mainsheet Editor

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Response Posted - 09/08/2008 : 20:46:37

Every piece of electronic equipment I have bought has had power consumption specs on its technical spec sheet - divide the watts by the voltage to get amps. It is basically a matter of output power plus varying amounts of overhead to run the circuitry. Smaller speakers produce more volume for a given wattage at the expense of base, but to much volume increases distortion; they are also separated by higher and lower efficiency types Look at the specs and test with your ear.

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Dave Bristle
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Djibouti
10005 Posts

Response Posted - 09/08/2008 : 21:50:49

After I installed a 12V outlet in the galley, I picked up a digital car volt meter at Wal-mart (for something like $7) and left it in the outlet. Worked like a charm.

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ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 09/09/2008 : 08:55:57

"analog Voltmeter "

Why analog? You're only interested in voltages between 11 and 14 VDC. Most small analog VM's won't have the proper range to accurately see the difference between 12.3 and 12.1 volts that tells you about your battery state.

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Bortiquai
1st Mate

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88 Posts

Response Posted - 09/09/2008 : 16:38:43

Well... from what I've seen so far, the digital ones are significantly more expensive... so there's that. But also, I acutally like the way the analog ones look a little better. The digital ones kind of add a little space aged-ness that doesn't go with the rest of my very non-digital, non-modern, frugally outfitted boat. I see your point about the accuracy though...

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Dave Bristle
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Djibouti
10005 Posts

Response Posted - 09/09/2008 : 16:45:30

$7 is significantly more expensive than what? (I dunno, maybe I paid more than $7...

)

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OLarryR
Master Marine Consultant

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Response Posted - 09/09/2008 : 19:41:28

If a solar panel is being considered in the future, then you may want to hold off getting a voltmeter and then just opt for a solar controller that has a digital readout. My Morningstar Pro-15M reads the solar panel amps and voltage when the sun is out. When I kick in the outboard, then the solar controller cuts off the panel and so no amps are displayed but the voltage charge from the outboard is displayed. When there is no sun and I do not have the outboard on, then the controller reads the battery voltage.

The other thing to consider is that some (maybe many) fishfinders display the battery voltage on one of the viewing options.

The thing is that the voltage is not one of those things that you are going to get mesmerized over it for long periods of time. (At least my perception is that most people do not.) You may take a quick glance at the battery voltage and then may only view it once or twice or not at all during or at end of your sailing outing. So...if a fishfinder or solar panel will make it onto your boat, then you may not need a switch panel with a voltage readout.

Edited by - on

Voyager
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5418 Posts

Response Posted - 09/10/2008 : 22:36:58

While the digital voltmeter has a nice readout, I've been concerned about its calibration. It appears to read that the battery becomes moderately discharged very quickly. Some time ago, I stopped into the Defender store and found an LED charge indicator which provides a pretty accurate reading relative to my digital voltmeter. It is made by Pro-Mariner.

Here's the listing: http://www.defender.com/product.jsp?path=-1|328|49758|319689&id=724566

It has six LEDs - a red one that turns on solo when the battery is mostly discharged at 11.8V, the amber one that comes on when the battery is 1/2 discharged at 12.2V, the green one the when the battery is fully charged up to 12.6V. It has three more, another amber for 13.2V, which is nominal charging voltage, the green for 14.4 with peak charging voltage and the last at 15.5 or over voltage, which means your voltage regulator is no longer operational and should be replaced.

Nice thing about it, is it's pretty much idiot proof and its only ten bucks (not as good as $7 though)

And it has a magnetic strip on the back, so you can slap it up onto just about any steel object. I've velcro-ed it up on the back-board next to the settee near the battery compartment. At a glance, I can see the battery's charge status, even without my glasses!

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Dave Bristle
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Djibouti
10005 Posts

Response Posted - 09/11/2008 : 08:03:48

I know you know this, Bruce, but we should all remember that if anything is "turned on" and no charge is being introduced, the voltage on a meter will be lower. To get a true reading of battery condition, turn off all radios, depth sounders, surface-to-surface PWC missile radar, etc.

Edited by - on

Voyager
Master Marine Consultant

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5418 Posts

Response Posted - 09/11/2008 : 22:44:36

One other item to keep in mind is that the original C25 buss bar and supply cables to the switch panel need to be replaced from time to time as they age and corrode. With all circuits on, I found a 0.4V drop from the positive terminal on the battery to the (+) terminal on the lighter plug. I assumed I have a similar drop on the negative side.

That's borne out when I power on the running lights, radio, interior lights, etc and note almost a one volt drop at the plug. The battery monitor, connected directly to the battery, shows a much smaller drop which quickly recovers after I turn everything off.

Bottom line, I plan on spending the coming cold winter months rewiring the switch panel and associated circuits to and from the battery and replacing the ground buss bar.

Edited by - on

ilnadi
Captain

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452 Posts

Response Posted - 09/12/2008 : 00:42:54

If you have a current meter, you can make instantaneous readings to extrapolate your battery usage and eventual charge level (do I get a point for pretentious word bingo?). That way you can see if you are living within your means.

However, over a longer time the current will change when people are turning things on and off, the VHF draw changes when it wakes up, etc. Unless you have a dedicated individual that never gets seasick (or a house-elf) to read the current all the time you will not know exactly how much the battery was drained. As Stu said, a more sophisticated battery monitor would constantly read the current and integrate it to see how much charge you have used up.

Any in-line device like the current meter will cost you voltage drop (assuming you do not buy an expensive one. You may be better off having a more accurate volt meter to know when your battery is getting low. All the current meter will tell you is how fast you are getting there.

Edited by - on

Stu Jackson C34
Admiral

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844 Posts

Response Posted - 09/12/2008 : 01:57:22

Whenever "the battery becomes moderately discharged very quickly" happens it means the batteries aren't doing very well. It should be time for an equalization, because the voltage is dropping on a load. See www.amplepower.com, and download and read the Ample Power Primer. Battery maintenance and proper usage is not just for boats with inboard engines and alternators.

Edited by - Stu Jackson C34 on 09/12/2008 01:58:18

ilnadi
Captain

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Response Posted - 09/12/2008 : 09:16:13

Stu, thanks for the link. I am an Electrical Engineer and can get my brain around current and distribution but the understanding the battery part of the equation has been my weak point. I clicked around a bit and now I have many more things to read.

When I rewired Enka I made a spreadsheet that calculates wire gauges from length and draw. Is that something anybody is interested in? I guess I am looking for help mustering up the energy to clean it up and post it.

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JohnP
Master Marine Consultant

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Response Posted - 09/12/2008 : 10:58:58

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by ilnadi
 When I rewired Enka I made a spreadsheet that calculates wire gauges from length and draw. Is that something anybody is interested in? I guess I am looking for help mustering up the energy to clean it up and post it.
<hr height="1" noshade id="quote"></blockquote id="quote">We all should be interested, since it is important to use wire of adequate gauge for each load and distance from the panel. I learned about that in general terms from Don Casey's excellent book [url="http://www.amazon.com/Sailboat-Electrics-Simplified-Don-Casey/dp/0070366497"]Sailboat Electrics Simplified[/url]. Then I rewired my mast and felt good about applying those concepts. Any info you prepare specific for the C-25/C-250/Capri-25 would be well appreciated.

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Voyager
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USA
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Response Posted - 09/12/2008 : 16:11:13

Stu -
I read through several of the articles on the Ample Power site, this is a wonderful resource. Thank you.

I purchased the battery in June this year, and I have not been very impressed with it. It's supposed to be good for 80 AH, but as I mentioned it's voltage begins to sag quickly, however it continues to deliver current at about 12.2 V for a long time.

My most critical drain scenario is using the inverter with my Laptop battery charger. The PC requires about 90W, and if I measure the 12V powering the inverter, I get about 7-8A, so there's some inefficiency in the inverter. I used the PC onboard for 5 hours last week, so that would have been 40 AH of drain. Battery voltage was quite low at that point. Several days later after recharging on the solar panels (2A), it apparently made up the deficit, because the solar panel regulator was toggling between charge and full, and the voltmeter read 13.2V.

On the Ample Power site, I checked the "equalization" article and what I have not done so far is allowed the battery to fully discharge down to around 11.5 volts. I have a 6A battery charger in the garage and during the next stretch of rainy weather will pull the battery, discharge it at say 10A down to 11.5 volts, then recharge it using the 6A auto charger.

Once it hits 16 volts (which seems like an insane level), I'll take it off the charger and put it back in the boat. I'll post my results.

PS: and yes, Ilnadi, I'd like to see the spreadsheet. Since I plan to spend a little while redoing the cabling, I'd like to use the right wire gauge the first time.

Edited by - on

Stu Jackson C34
Admiral

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Response Posted - 09/13/2008 : 15:38:31

Bruce, as part of the Ample Power information, you should have read the 50% Rule. So you used 40 ah of an 80 ah bank, which is about the most you'd want to draw it down before recharging anyway.

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Voyager
Master Marine Consultant

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Response Posted - 09/13/2008 : 22:08:36

Stu -
Yes - I read several more articles after the "equalization" article, and it was interesting to see that their charging/discharging and battery conditioning advice changed in some of the other monographs.

In fact, the author said that it could be destructive to the battery to discharge beyond 50%. I believe overcharging the battery (to 16V) would be descructive as well.

I believe I will return to my simple-minded approach that Amps x Time is equivalent to "filling" the battery, It's quite straightforward to predict discharge rates, provided you can estimate the amperage and duration of use.

I will continue to use voltage readings of the battery as a measure of "fullness" (once the voltage settles down after charging or discharging).
13.2V . . . . . . Solar panel charging voltage (per my solar regulator)
12.6V . . . . . . Battery Full
12.4V . . . . . . 3/4
12.2V . . . . . . 1/2
12.0V . . . . . . 1/4 (do not go to this level of discharge)
11.8V . . . . . . Completely discharged

Using this approach, I'd expect the battery to last for the expected 3-5 seasons.
Thanks

Edited by - on

OLarryR
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Response Posted - 09/14/2008 : 07:44:46

Bruce,

I have seen info similar to what you posted before but not sure where. In any case, I do not have it written down but looking at the voltage readings you listed (solar panel, battery full, 3/4, etc and expectation to go 3-5 years)....that has been my thinking as well. My experience with solar panel charging and battery full voltage readings is similar to yours. My solar panel charging voltage and my battery full is a bit higher but within ballpark to your table of values.
My 2 batteries were not new when I bought the boat...perhaps 1-2 years old. Now I have had the boat for 3 years...so the batteries have a minimum of ~ 4 years use on them and possibly more. They seem fine so far with battery full readings. By the way...these batteries are on the boat all year and I use them all year. I do not pay for electrical service to my dock, otherwise, they would charge me $20/mo more. I find my 20 watt panel is sufficient to charge the 2 batteries for the daily trickle discharging, electric starting the motor to get in/out of the marina and the occasional use of navigation/cabin/fan lights.

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Voyager
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Response Posted - 09/14/2008 : 22:05:59

Larry --
Just to remain 100% kosher, the voltage numbers I quoted are from Don Casey's Sailboat Electrics Simplified, who says that these values apply to wet cell batteries, but not AGMs or Gels, which often read about 0.2V higher.

I too opt NOT to purchase shore power at the marina, as I don't have any electrical appliances like a microwave oven, TV set or thermo-electric cooler. I use the battery primarily for lights, the VHF, depth and for a 10 Watt CD/FM stereo, and use ice in my 5 day cooler for keeping beverages and snacks cold. That thing works great!

My solar panels (I have two 18W units) are wired in parallel into a purpose-built solar regulator that came with the solar panel when I bought it. While I got mine from Amazon, a similar unit is available from West Marine. The regulator allows the battery to charge up to about 14.4 V, then it disconnects the panels from the battery. When the voltage drops back below 13.4, it resumes charging. This prevents overcharging the battery and boiling off the electrolyte.

As I said, I ran the laptop for about 5 hours last week and discharged about 40 AH, and since then, the battery has been recharged back up to 12.6V, which ought to be nearly 100%.

But, one more day of bright sunshine ought to restore the battery up to full with power to spare.

Edited by - on

josgood
1st Mate

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USA
57 Posts

Response Posted - 09/15/2008 : 10:33:32

I try to use my laptop's battery to almost 0 % before plugging it into the inverter and stealing the boats power.
It buys me an hour or two before starting any drain. I can easily recharge that battery when I get home.

Edited by - on

Voyager
Master Marine Consultant

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Response Posted - 09/15/2008 : 20:44:28

John -
I take the opposite tack. I fully charge the computer before going to the boat, then it only takes minumum current to maintain the full PC battery. Otherwise, the boat battery needs to replace the entire charge of the PC battery if you spend any time on the boat using the computer.
But that's me.

Edited by - on

piseas
Former Treasurer

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USA
2017 Posts

Response Posted - 09/15/2008 : 22:04:43

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by OLarryR
 My 2 batteries were not new when I bought the boat...perhaps 1-2 years old. Now I have had the boat for 3 years...so the batteries have a minimum of ~ 4 years use on them and possibly more. They seem fine so far with battery full readings. By the way...these batteries are on the boat all year and I use them all year. I do not pay for electrical service to my dock, otherwise, they would charge me $20/mo more. I find my 20 watt panel is sufficient to charge the 2 batteries for the daily trickle discharging, electric starting the motor to get in/out of the marina and the occasional use of navigation/cabin/fan lights.
<hr height="1" noshade id="quote"></blockquote id="quote">

Larry, I have an 2003 boat that had original batteries. Both went bad about a month ago and I replaced them. I thought they were ok and I used shore power to recharge them as well as the motor. But one day they went dead. I have a volt meter I plug into the cig plug to verify and sure enough...
Also re using shore power, I plug in all year long and the bill comes with my slip fees, about $.20 extra per month! Is the $20 charge you speak about a service charge? I charge my GPS, cell phone, handheld VHF and a few other odds and ends.
Bruce, I am like you, I fully charge my laptop and other stuff I dont keep on board so I dont need to use my shore power for those items. I also have a multi purpose power system that has inverter, jump starts batteries, air hose and and has couple of plugs for running stuff and a couple of other things. It comes in handy when away from slip.
Steve A

Edited by - piseas on 09/15/2008 22:14:43

OLarryR
Master Marine Consultant

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Response Posted - 09/15/2008 : 22:31:35

Many marinas include shore power in with the cost of the slip. My marina does not do it that way. They charge for the slip monthly, semi-annually or annually. It's less cost per foot if you sign up annually. I believe the cost of electricity starts at $20/month and then over a certain boat size, the cost is then $25/month. If you want to use the electricity for a day or two, then they have a $3/day charge. There are a lot of motorboats in my marina. Their bilge pumps are constantly spitting water and I suspect that a number of the boats, they have their AC running frequently. This may explain why the electricity cost seems high.

Of course, they could just raise the slip fees $200+/year and then include the electricity. The electricity is not free for those that have it included in their slip fees...The slip fees were adjusted accordingly to provide the electric service whether one is a low or high user of it.

Since I do not have a bilge pump that needs to run frequently (or at all for that matter) and I have light electricity needs, a small solar panel worked out best for me. However, I have hard-wired a battery charger into my AC circuit for charging both batteries for those times I stay as a transient in a nearby marina. My thought was that I would tend to use the cabin lights, etc a lot more in that situation and could then benefit from charging the batteries overnight.

Edited by - OLarryR on 09/15/2008 22:32:50

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