voltmeter question

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voltmeter question

Postby exminnesotaboy » Fri Feb 18, 2005 2:15 pm

12v electrical newbie here....for keeping an eye on the juice in my marine battery, is all I need is a meter like this wired on it's own circuit from my galley mounted fusebox? is it that simple? or am I missing the whole concept - which is entirely possible...

12v only system running only a couple of lights, a Fantastic fan, and a really small inverter(300w) that will be used rarely. The battery will probably be the largest available from WalMart
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Postby angib » Fri Feb 18, 2005 2:48 pm

A 0-15 volt meter will not be much use to you. At 10.8 volts, the battery will be effectively dead and full charge on a brand new battery will be around 13.5 volts, so you are only interested in this 3 volt range.

A volt meter will tell you the approximate state of charge. However if you are drawing any current, the reading will change and so you can only really use it with nothing switched on.

Andrew

PS The voltages above are from memory - if anyone can chip in with corrections, please do.
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Postby Woody » Fri Feb 18, 2005 6:49 pm

I mounted the same gauge in my tear and it is big enough to watch the range. I would have prefered a digital for greater volt range for accuracy
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voltmeter

Postby ahjones3 » Fri Feb 18, 2005 9:50 pm

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Postby Q » Fri Feb 18, 2005 9:58 pm

You didn't say what system you are using to charge the battery, and that makes a difference. In my solar powered home I use a digital amp hour meter which works sort of like a gas guage in a car, but it's a pretty expensive gadget to use in a teardrop.

I have no meter at all in my solar teardrop electrical system. The solar module usually keeps the battery slightly overcharged. On those rare occations when I'm not sure about the battery's state of charge, I carry a cheap and small $3 Harbor Freight VOM to check it.

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Postby mexican tear » Fri Feb 18, 2005 10:35 pm

I have the Radio Shack meter. It is a good thermometer and a good clock. I have yet to finalize the location for the hole for the temp sensor.

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Postby exminnesotaboy » Fri Feb 18, 2005 11:26 pm

thanks to all for the responses - I will probably go with this one for a while and if it gets annoying, I will switch to a digital one. I probably won't spend the $$ to get the digital amp/hour meter

Q, I am just going to charge the battery at home and see how it holds out for long weekends with my minimal usage. If that doesn't work, I will look at alternatives - solar is preferred but I will have to learn more about it first
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Postby Q » Sat Feb 19, 2005 12:38 am

Here's a good article and chart to help determine the state of charge of a lead acid battery using a volt meter.

http://www.homepower.com/files/battvoltandsoc.pdf

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Postby angib » Sat Feb 19, 2005 8:02 am

Excellent post, Q.

So the actual voltage range of a battery is just 1.0v - 11.7v (10% charge) to 12.7v (100% charge)!

Andrew

On edit: Looking for something else, I came across Exide's state of charge guide which gives:

Regular lead-acid batteries:
12.6v=100%
12.4v=75%
12.2v=50%
12.0v=25%
11.7v=0%.

Sealed AGM or gel batteries:
12.8v=100%
12.6v=75%
12.4v=50%
12.0v=25%
11.8v=0%
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Boat fuse box/volt meter

Postby OkieSailor » Mon Feb 21, 2005 9:20 pm

I picked up a 12v fused panel for my project last fall. It has like six (6) fused circuits and a meter for checking voltage on the battery. Check West Marine for the different panels they carry. I am going to install all LED lighting so the only real drain will be the vent fan. By the way make sure you do not buy an auto type battery for the camper. You want a marine style that will handle being fully discharged several hundred times with out failing. An automobile type battery is not made to do slow complete discharges like you would do while camping. Also if you put a marine type 110v ac charger on your battery it will keep the battery charged without over charging. If you are connected to 110ac and you put on say a 5 amp charger, but are pulling 10 amps (with lights and ect) the charger will supply 5 amps the battery the other 5 amps without hurting the charger(this is per the manufacturer of the charger). I double checked this before I bought the battery and charger from Bass Pro here in Oklahoma City. :D
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Postby campadk » Tue Feb 22, 2005 8:03 am

I chuckled at this...

Will adding aspirin or other additives to my battery prolong its life?

There is no real evidence that aspirin will prolong life. However, some other additives will clog up your hydrometer. Top of Page


Never knew aspirins had so many uses!
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My Home Build Volt Meter

Postby Dee Bee » Sat Feb 26, 2005 6:57 pm

Grace happens...
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Postby myjeepcherokee » Wed Mar 02, 2005 6:34 pm

I've installed one of these gauges in my boat last year to monitor my deep cell that runs my trolling motor. I'm planning on putting one in the tear to...can't beat the price either only 30.00, I think its well spent!

http://www.basspro.com/servlet/catalog.TextId?hvarTarget=search&hvarTextId=5197&hvarAID=inktomi&cm_ven=Performics&cm_cat=Search&cm_pla=Overture%20SMX%20%28Inktomi%29&cm_ite=DDI%20Link
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Postby wlooper89 » Mon Aug 04, 2008 12:06 pm

I installed this in my electrical compartment. Just for fun I also put in some ammeters. The round meter at top right is the voltmeter. A voltmeter can give one a general idea of the state of battery charge.

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The switch on the right is DPDT with center off. Up displays battery voltage and down converter output.

Bill
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