Installing a digital Amps/Volts Meter - Fiberglass RV


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Old 02-20-2009, 09:45 PM   #1
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When you depend on solar power and a single battery to supply your juice it really helps to know what your battery condition is as well as how fast your are charging/discharging the system. I installed a digital Amps/volts meter and ampere shunt I found on eBay for around $55 so I could get Amps and Volts readings at the push of a button.

Here's a picture of the meter showing the battery is being charged at a rate of 3.18 Amps. There's a round button in the bottom corner of the meter that switches the display from Amps to volts. The switch just under the meter turns the meter on and off.


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I made a pressboard template of the hole I needed to cut in the side of the cabinet and test-fit my meter in the hole. Then I marked the outline of the hole on the fiberglass withe a fine-point sharpie and scribed just outside the lines with a sharp utility knife to prevent the fiberglass gelcoat from flaking off when I cut the hole. Next I drilled 1/16" holes at all four corners of the opening, and made 1/4" holes next to two of them so I coould get my saw blade in place.

The pictures here shows me using a coping saw hand-tool to cut the opening and a rotary tool (like a Dremel) with a sanding drum to smooth out my cut lines and slightly enlarge the opening in a couple spots. (Wear a dust mask when cutting or sanding fiberglass!)


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Amp meters require a special device, called a "shunt" to measure the amount of current flowing through the system. One side of the shunt connects to the wire heading to the negative (ground) pole of the battery; the other side connects to the rest of the ground wires for the trailer. An additional wire pair, with one wire connected to each side of the shunt, connects back to the meter.


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Old 02-20-2009, 11:52 PM   #2
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REEL nice work. I presume you must do a good deal of boon-docking to make use of such a device??
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Old 02-21-2009, 01:12 AM   #3
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REEL nice work. I presume you must do a good deal of boon-docking to make use of such a device??
I don't know if I'd call it "boondocking," but there are a lot of National Parks campgrounds that have a water spigot somewhere on the way in plus a toilet and a pay shower, but no hookups.

When we set up in one of those sites we depend on our solar panels and battery to keep the lights on and provide power for the furnace fan. Having a volt meter tells me how much charge our battery is holding, and that will help us make better power use decisions.

The amps readout is less vital, and I could do without it if I had to. I just think it's plain nice to know how much juice the solar panels are pumping out, how much electricity each additional light or appliance use.
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Old 02-21-2009, 03:23 AM   #4
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Actually, there is no such thing as an ammeter. What it is is a voltmeter which measures the voltage drop across some known resistance known as a shunt. Then using the formula E=IR or I=E/R. Since the resistance of the shunt is known R and the voltage drop across R is measured (E), then the meter knows what the amps flowing in the circuit are (I), and that is what it displays. Interesting, no?
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Old 02-21-2009, 06:19 AM   #5
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More trivia; Some ammeters use the Hall effect to measure amperage. Clamp meters are an example. Also, my boat's instrumentation uses what I believe is a ferrite coil through which one of the wires passes to measure the field generated which is proportional to amperage. These tend to be a bit pricey and shunts are usually a more economical solution.
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Old 02-21-2009, 03:11 PM   #6
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The metering system is one of the best mods a dry camper can do. My total money was less than $80.
I added meters to my 25RQ Bigfoot in much the same way. I got them on Ebay from Sure electronics. I power them from a 3 D cell pack for each meter. This provides total electrical isolation from either AC or DC system. This is important because the meters that I used, have a common sense and power connection. Meters are 5 volt input, but work from 4 to 6. The D cell alkaline packs provide long life, cheap and commonly available replacement. My batteries are almost 5 years old. The switch at the left is a 4 pole double throw small toggle. I have configured it so that when I turn the meters on, the toggle is up and when I close the overhead storage door, the toggle is mechanically pushed down to the off position. On the AC amp meter the shunt is enclosed in a metal duplex box for safety. The 8 conductor 22 awg stranded wiring to the meters are fused with a Pico fuses for safety.
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The meters are mounted and located along the top and very near the front of a storage area. They are also at eye level for easy reading. The meters are stuck to a wooden mounting strip with stick tape. This storage is next to the refrigerator. This provided easy access to the converter, breaker, and AC service entrance. Also the DC system is accessible. I also have the Charge Wizard in this location.

http://www.radioshack.com/product/index.js...oductId=2062245 I jumpered out one of the slots because I was just uning 3 cells
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Old 02-21-2009, 03:37 PM   #7
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Actually, there is no such thing as an ammeter. What it is is a voltmeter which measures the voltage drop across some known resistance known as a shunt. Then using the formula E=IR or I=E/R. Since the resistance of the shunt is known R and the voltage drop across R is measured (E), then the meter knows what the amps flowing in the circuit are (I), and that is what it displays. Interesting, no?
Very true. I didn't want to get how an ammeter works in my very basic how-to post, but the reasons I chose 16-gauge line cord to connect the ammeter to the shunt is that its resistance is less than half (.04 ohms vs .10 ohms) of the 20-gauge wire alternative I was considering.
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Old 02-21-2009, 03:43 PM   #8
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[quote]
Attachment 18031


Quite a setup! We don't have a generator, so we only need the volts/amps meter.
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Old 02-21-2009, 11:03 PM   #9
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Peter,
You did a good job on the meter install. Can you provide a link to the meter you used?

I've enjoyed reading your posts on this forum. They are most informative and entertaining.

I have just retired so now my wife and I plan on spending much more time in our NP, NFS, and other such campgrounds. Many of the best camping areas are the "no services", therefore the solar becomes more attractive. Of course living in a 12 volt world for weeks on end makes for some creative tinkering.
I have made all (12) of the 12 volt lamp fixtures into hybrid fixtures meaning that I can select with a 3 position single pole double throw switch either the LEDs or the incandescent lamp. Mine required some modification to replace the switch, other don't. I used a wide angle LEDs with a cost of $6 per fixture. I might start a new thread about how easy it is to make some of the common fixtures into a hybrid at a low cost.

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However, I think we (wife and myself) might be power hogs, meaning that we have too many gadgets. I am also a licensed amateur radio operator so I may pack my 12 volt gear along as well. I have added the double batteries and also have a Honda 2kw generator. The metering project has been very handy.

I have a friend Brad, also a member on this forum, who did a good job of installing meters in his Casita. He has also found them to be very valuable. Here are pictures of his meter project. His battery packs are mounted under the seat on top of the battery box.



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Old 02-22-2009, 12:14 AM   #10
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PeterH, as always, you have done some seriously good work, both in functionalism and fit/finish! I know I tend to overlook that sometimes, mostly because I expect it of you!
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Old 02-22-2009, 01:21 AM   #11
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. . . You did a good job on the meter install. Can you provide a link to the meter you used? . . .

. . . I've enjoyed reading your posts on this forum. They are most informative and entertaining . . .

. . . Of course living in a 12 volt world for weeks on end makes for some creative tinkering . . .

. . . I used a wide angle LEDs with a cost of $6 per fixture. I might start a new thread about how easy it is to make some of the common fixtures into a hybrid at a low cost . . .
Thanks for the compliments from you and Pete on both my installation and about my posts in general.

I am withholding judgment on the meter I bought because the unit in the picture works very erratically. A replacement is on its way, however, and if that one works I'll turn in a good report on it; meantime it came from the eBay vendor "e3b6ay5" who sells a wide range of meters and e-stuff. The shunt I ordered elsewhere . . . don't remember who from, but they're pretty much all the same. Just make sure the shunt you order matches the meter you're buying or your Amps readout will be off.

Living in a 12v world does require some adjustment . . . but then so does living in a trailer! The main thing, I think, is to do your best to find appliances that work on 12v to start with and limit your use of non 12v devices. A 12v DC to 120v AC inverter consumes a lot of power, even when its turned on but not connected to anything. My little 120 watt inverter, for example, eats half an amp all by itself.

I like your two-way incandescent light/LED light conversion. At $6/fixture that's a real bargain! Lynne and I have gone a different route, buying "warm white" LED replacement panels that put out an incandescent-like warm white light, but they're $20 each. Multiply that by the number of lights in a trailer and that gets pricey very, very quickly. Good job!
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Old 02-22-2009, 06:52 AM   #12
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This is the Ebay source for the digital meters that I used. I find the voltage meter, both DC and AC to be very accurate. The amp meters come with the shunts, so no guess work there. However the accuracy of the ampere meter, especially the AC is not as good as the DC. All are very satisfactory. I will mention that the AC amp meter can be calibrated with a standard if necessary.
These type meters must have independent 5 or 12 volt power supplies either from a regulator or batteries. When I purchased mine, they were 5 volt dc, so be cautious as to the supply voltage. The fact that it says 12 volts supply does not mean that you can hook to the coach battery directly. Research this as to any internal connection within the meters. D cell batteries will run them a long time as the current draw is ~50 ma.
They come in either read or blue display. Go to the Sure Electronics site on Ebay and Search for "panel meter red" or "panel meter blue". This is a dream world of neat electronics.
http://stores.shop.ebay.com/Sure-Ele...__W0QQ_armrsZ1
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Old 02-22-2009, 11:03 AM   #13
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I have configured it so that when I turn the meters on, the toggle is up [b]and when I close the overhead storage door, the toggle is mechanically pushed down to the off position.
I like that.
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Old 03-08-2009, 03:58 PM   #14
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Had a warm-ish day here yesterday and finished a couple projects. In the trailer I installed a Blue Sea 8247 AC multimeter. Gives me AC amps, volts, frequency and watts. Pretty cool. Uses a coil through which goes the AC black wire to measure amps based on the current induced in a field (coil). The field current is in mA so the gauge doesn't need a shunt. I also set a low voltage and high amperage alarm.

Pretty pricey, but it is "Castle Pretentious"! It replaces a unit that plugged in that gave voltage and frequency. I believe in the picture it's showing amps; I had a space heater going today when I went out to take the picture. A good check on campground shore power quality.


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AC meter on the bottom

Above it is the Link 10 DC unit. Tracks DC voltage, current and amphours. (I have a Battery Minder going during the winter. That's why the 13+ volts.) Very little current is going into the battery so the fluid doesn't boil away.) This is the more useful gage for when I'm boondocking. Amphours total up as negative. When recharging the amphours wind back towards zero as the battery recharges. For me, amphours is a better indicator of battery state than waiting for an hour with no battery loads for the battery voltage to stabilize.

As an aside, this is the gage that tells me what a minuscule amount of current the tow puts into the trailer battery to recharge it. In my study, the tow only kept up with the drain running the reefer on 12v. It never put back the roughly 10 Ah lost to running the reefer on the trailer battery only during lunch and comfort stops.

Both meters can be set to cycle through the readings and go into sleep mode after 10 minutes or until a button is pushed, or in the DC meter's case if an amp draw exceeds some arbitrary level that I set. In this case I've set it for 1 amp.
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