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Open Roads Forum  >  Do It Yourself Modifications and Upgrades (DIY)

 > Adding a Digital Volt Meter to show battery state of charge

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NetBoy

Portland, OR

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Posted: 07/02/12 06:01pm Link  |  Quote  |  Print  |  Notify Moderator

Hi, I decided to add a digital volt meter to my motorhome to show the state of charge of the batteries - it will be handy when dry camping.

Here is a table from the web site "The 12 Volt Side of Life" that shows voltage vs state of charge (a great web site to learn about living on 12 volts):


I ordered a digital volt meter from eBay for $5 including shipping:



I mounted the meter, and a momentary contact switch, in a piece of plastic from an old car litter basket:




I will mount the meter in some convenient location in the motorhome tomorrow. And I'll include a printout of the above voltage chart.

Pretty cool for five bucks!

Note that battery voltage should be read when the batteries are at "rest" -- that is, wait a half hour after any big discharge (for example, such as running a microwave on an inverter).


NETBOYâ„¢
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Visit Netboy's Camper Project's Page = Lots of mod projects to my truck and camper.

My newest rig -- 2004 Thor Chateau 21RB:


tenbear

Northern Vermont, USA

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Posted: 07/02/12 06:38pm Link  |  Quote  |  Print  |  Notify Moderator

Hi NetBoy, great minds think alike, etc. Having a voltmeter is a great help when camping without electric hookup.

Here is where I installed my battery monitor some time ago. The switch below the meter is a SPDT to select either the converter output or the battery voltage. Since then I also installed a 120vac meter.


* This post was edited 07/03/12 04:48am by tenbear *


Class C, 2004/5 Four Winds Dutchman Express 28A, Chevy chassis
2010 Subaru Impreza Sedan
Camped in 45 states, 7 Provinces and 1 Territory


Jerry9n

SE Michigan

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Posted: 07/02/12 07:05pm Link  |  Quote  |  Print  |  Notify Moderator

I did the same thing but added a 120VAC meter with it to monitor shore power--I very seldom dry camp.

Here's my setup:

(I wasn't plugged in to shore power when I took the pic so top meter is dark).




Jerry9n
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Normk

Canada's Wet Coast

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Posted: 07/02/12 07:38pm Link  |  Quote  |  Print  |  Notify Moderator

The 120 volt meter is such an obvious that I'm embarrassed..... I typically check at some point using a hand held meter if we're staying somewhere for any time and using AC. The $5 meters are such a deal that I will be addding one also. Thanks for the idea.

FWIW, the 120 volt meter should be consulted when the AC load is at maximum useage to reference voltage drop/loss.

The most exciting aspect of this thread is that I've been looking for my Stanley tape measure for over a week, NetBoy! If you're done, please return it.

Norm

helperzack

Treasure Coast Florida - East Tennessee

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Posted: 07/02/12 08:28pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks so much for posting this.

I have been thinking about doing this for a while, just haven't gotten a round tuit. This will get me moving.

Are there any special requirements on the 120VAC meter?
What gage wire and any special requirement for a switch, or is the 120v meter always on if you have 120v power?

Off to ebay now..


Coachmen Mirada 310DS named "The Corporate Headquarters."
When camping I just tell clients that I am working at "Corporate Headquarters"

Jerry9n

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Posted: 07/02/12 08:38pm Link  |  Quote  |  Print  |  Notify Moderator

On both meters I mounted them in a switch plate for the flat decorative wall switches. I used push switches generally used on lamps and fans for each so I could turn the meters off (they are terribly bright at night. Both meters are fused with inline fuses and both have appropriate power sources right next to them that I could tap into. Right now I don't exactly remember the specifics.

The AC meter is helpful, especially with the AC to keep a check for low voltage. The DC meter doesn't do a whole lot since I don't dry camp, but it does let you know if your convertor is working. I like them, but I'm a natural tinkerer and gadget nut.

NetBoy

Portland, OR

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Posted: 07/02/12 08:39pm Link  |  Quote  |  Print  |  Notify Moderator

Norm, nope, I like the Stanley tape.

helperzack wrote:

Are there any special requirements on the 120VAC meter? What gage wire and any special requirement for a switch, or is the 120v meter always on if you have 120v power?


You can leave the meter on all the time, or include a switch to turn it on only when you want to view it. In my case I am just using a momentary contract switch that I will push when I want to read the voltage.

For either 12v or 120v, it doesn't matter what gauge wire you use.... the meter uses virtually no power, so very small gauge wire is just fine. You can also use just about any switch for the same reason. You will want to connect the wires near the power source (ie, near the battery or near your 120v circuit breaker box) and not at the end of a circuit which has other devices hooked to it, as those devices may pull the voltage down a little.

If you dry camp, having a good 12v meter and that voltage chart in my original posting is quite important -- those will let you know when you are getting in trouble.

* This post was edited 07/02/12 09:34pm by NetBoy *

tenbear

Northern Vermont, USA

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Posted: 07/02/12 08:59pm Link  |  Quote  |  Print  |  Notify Moderator

helperzack wrote:

Snip...

Are there any special requirements on the 120VAC meter?


The last I knew there were 2 kinds of 120vac meters, one required a 12v power supply to power the meter, the other uses the 120vac that is being measured to power the meter. I recommend the self powering type even though you won't be able to measure low voltages, but who cares. The 12v power type may require that the 12 V is isolated from the ac being measured which may be difficult in the RV. It also requires 2 more wires.

Normk

Canada's Wet Coast

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Posted: 07/02/12 09:09pm Link  |  Quote  |  Print  |  Notify Moderator

On a related subject, it is well worth the time to take one's hand held voltmeter and check the voltage to any heavy loads on your RV, such as the AC. Test as close to the unit as it possible to ensure that the voltage is not significantly lower than at the power distribution panel. Load such as AC must be at full load for the test to be meaningful.

Regardless of whether one has a panel voltmeter for AC, one should use a hand held voltmeter to check voltage in the RV with all power loads on and compare the reading to that with all loads off. If one is seeing a difference (loss) of more than a couple of volts difference (loss), it would be worth investigation as to which section has the loss.

A high voltage drop (loss) always points to a high resistance which means heat. If the loss is over a short distance the heat could be enough to melt/burn a connection. This type of testing is an ideal item for one's semi-yearly maintenance checks to find problems before they become a failure.

Likewise, the power distri


"You will want to connect the wires near the power source (ie, near the battery or near your 120v circuit breaker box) and not at the end of a circuit which has other devices hooked to it, as those devices may pull the voltage down a little."

ScottG

Bothell Wa.

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Posted: 07/02/12 09:23pm Link  |  Quote  |  Print  |  Notify Moderator

I have a whole set!
ACV/ACA/DCV/DCA (for some reason the pic isn't legible but they are clear and easy to read.




Scott, Grace and Wesly
2003 Dodge 3500 4x4, 6 speed Cummins (lightly bombed),
2004 Forest River 25RKS many, many mods.
POS H0NDA eu2000i

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