Volts on Voltmeter ?

Status
Not open for further replies.
jrpla

jrpla

.
Apr 10, 2007
34
Beneteau First 32 Fajardo, PR
How many volts should I read on my voltmeter? My question is because I have read people said they read 13 or 13.xxx on their voltmeter when batteries are fully charge. My batteries are 2 new Trojan 6 volts T105 and I have a new Xantrex 40 amps charger. When I unhooked the shore power batteries go down to 12 volts or less, Is this normal or I have a problem on my system? Also the charger is working because I see the voltmeter reading near 14 volts during the charging process. Prior the Trojan T105 I used to have 2 group 31 that read > 12 when unhooked. Thanks;
 
Don S/V ILLusion

Don S/V ILLusion

.
Sep 25, 2008
7,374
Alden 50 Sarasota, Florida
check voltage at batteries first

to make sure each bank is fully charged. Presuming you have no battery problem, the voltage drop is somewhere along the wiring connections to wherever you are seeing 12V. Unfortunately, as you are seeing 14v while charging, it sounds like a battery rather than a connection problem. A fully charged bank should indicate close to 12.6-12.8 v depending on the precision of your voltmeter.
 
sailaway78

sailaway78

.
May 11, 2005
3,431
Seidelman S37 Slidell, La.
You didn't say

whether or not you have a digial voltmeter, or one of the standard analog types. I don't think the analogs are particularly accurate. Most of them are pretty hard to tell exactly what you have. My first recommendation would be to get a good digital voltmeter, so you can tell for sure what the voltage really is before you start worrying about other things.
 
jrpla

jrpla

.
Apr 10, 2007
34
Beneteau First 32 Fajardo, PR
Analog Volmeter

I have a analog Voltmeter. next week I will install a digital one I found on Ebay. A Vena: http://venaengineering.com/vena/index.php?id=10070&url=html/acdc.html Is this good?
 
sailaway78

sailaway78

.
May 11, 2005
3,431
Seidelman S37 Slidell, La.
Should be fine

Any of the digitals are better than the analogs. The analogs even if dead accurate are hard to read to less than half a volt or so. You may or may not have a voltage problem, but it's better to know for sure before you start contemplating changes, or trying to diagnose a problem.
 
sailaway78

sailaway78

.
May 11, 2005
3,431
Seidelman S37 Slidell, La.
Should be fine

Any of the digitals are better than the analogs. The analogs even if dead accurate are hard to read to less than half a volt or so. You may or may not have a voltage problem, but it's better to know for sure before you start contemplating changes, or trying to diagnose a problem.
 
B

BobW

.
Jul 21, 2005
456
Hunter 31 San Pedro, Ca
Less than 12 volts would indicate a problem....

and if the batteries are actually fully-charged, you shouldn't see that low a voltage anywhere. Wiring should be sized so that the voltage drop is less than 3%, meaning less than .4v anywhere on the boat. Having said that, you would likely prove me a liar if you climb the mast and measure, or perhaps at the bow lights, but hopefully not at the distribution panel. When your batteries are fully charged, either shut off all loads (if you can be sure) or disconnect the batteries and measure them with a good meter. It's not impossible that new batteries might have a bad cell, or that the electrolyte might have been badly mixed. If the specific gravity is not high enough, the battery won't ever get to 'fully charged'. Not too likely that two batteries would have this same problem, but if they were shipped dry to where you are and filled/charged by a local vendor, they might. Cheers, Bob s/v X SAIL R 8
 
jrpla

jrpla

.
Apr 10, 2007
34
Beneteau First 32 Fajardo, PR
Hi, Bob

I will messure the batteries volts, with a voltmeter directly. What should be a good messure for a individual 6 volt battery? Also what should be the correct specific gravity of each cell? Thanks;
 
Stu Jackson

Stu Jackson

.
Feb 26, 2004
23,012
Catalina 34 224 Maple Bay, BC, Canada
Try this link

from a Google search on battery specific gravity: http://www.batterystuff.com/tutorial_battery.html The information is out there.
 
B

BobW

.
Jul 21, 2005
456
Hunter 31 San Pedro, Ca
Battery voltage measurements...

Your 6 volt batteries should read 6.3 to 6.45 volts. This is a function of the individual 'cells' inside the battery. Each cell will read 2.1 to 2.15 volts when fully charged, and a 6 volt battery has 3 cells and 12volt has 6 cells. Emphasis should be added to the term 'fully charged' - it takes a long time for a charger like the Xantrex that you (and I) have to fully charge a set of batteries, because as they approach the goal, the charging rate keeps dropping. At 90%, the reading will be about 12.5 volts, and that is well within the error range of most volt-meters. Specific gravity (SG) is actually a measure of the percentage of sulphuric acid (SG 1.8) mixed with the distilled water (SG 1.00). The SG of a particular battery is a function of two factors: 1. The SG of the electrolyte (mix of sulphuric acid and water) that was originally put into the cell. 2. The state of charge. The SG and voltage of a battery are equal measures of state of charge, but ONLY if the baseline SG and voltage are known, and most people (myself included) don't bother to test the SG of a brand new battery. :) Fully charged in terms of SG is defined as the state where all of the sulphur in the cell (which adheres to the plates as sulphur dioxide during the discharge process) has been 'pulled' off the plates and is back in the electrolyte as sulphuric acid. A fully charged battery should have a SG of about 1.265. Since it is devilishly difficult to get anything close to an exact SG reading (and I have taken literally tens of thousands of them), the common type of hydrometer found in auto parts stores has a 'green range' that probably extends from 1.250 to 1.280. A fully-charged reading in the green range means the battery is OK. If you check the SG and find it is low, and you are reasonably sure your battery is fully charged, DO NOT attempt to remedy this condition on your own! First off, if you do try to fix it, you will definitely void any warranty on your new batteries. Second, the ONLY way to increase the SG is by substituting highly concentrated sulphuric acid for electrolyte in the battery, and you do NOT want to mess with that process, especially inside a sailboat. Your best bet would be to take the batteries back to wherever you bought them, because most likely they were left sitting dry for too long - they have a shelf life of about a year before they start to deteriorate. Cheers, Bob s/v X SAIL R 8
 
M

Mike

I would use a digital Volt meter

and not trust the volt meter at the panel, through resistance in the conectors/lines/even the analog meter itself could result in a voltage drop in as much as a volt. When you unhooked the shore power did you have anything on?
 
Ross

Ross

.
Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
Echoing Mike here, If you don't have a digital

multimeter you should. They can answer a lot of questions when trouble happens.
 
Bill Roosa

Bill Roosa

.
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
check the terminals

99.44% of all voltage related problems (charge and discharge) are to be found at the battery terminals. The close proximity to battery acid is a real challenge to keeping them clean and tight.
 
D

DanW9494

.
Aug 30, 2006
118
- - -
Idle time

For accurate voltage readings, batteries must remain idle (no charging, no discharging) for at least 6 hrs, preferably 24 hrs.
 
Status
Not open for further replies.

Top Bottom