SailNet Community - Reply to Topic

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > On Board > Gear & Maintenance > Voltage puzzle
 Not a Member? 


Thread: Voltage puzzle Reply to Thread
Title:
  

By choosing to post the reply below you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Message:
Trackback:
Send Trackbacks to (Separate multiple URLs with spaces) :
Post Icons
You may choose an icon for your message from the following list:
 

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below


Additional Options
Miscellaneous Options

Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below


Topic Review (Newest First)
06-01-2012 12:37 AM
hellosailor
Re: Voltage puzzle

Gary, if it is ten years old, guaranteed it has drited out of calibration. As the Mad hatter said "But it was the best of butter!" and even the best components shift as they age.

If you had one bad cell, that should have been reflected in a significant change in the voltage measured from that battery, and a calibrated meter should have picked it up.

I know, "should". If the turkey baster works for you, great. I found that calibrating my meters was cheaper than replacing anything the acid splashed onto, acid loves me but I have different feelings about it.
05-31-2012 11:30 PM
travlineasy
Re: Voltage puzzle

I thought the OP was talking about standard, lead-acid, marine batteries. I have a very expensive battery monitor on the boat. And, when I had a totally dead house battery (1 of 4, 6-volt golf-cart batteries in a series parallel rig) that battery continued to provide readings that would have been consistent with a fully charged battery. Even with a light load, it still provided good readings. The hydrometer, however, quickly revealed one cell was sub-par and failed when under a heavy load.

Granted, you cannot test gel batteries with a hydrometer, but the vast majority of folks that I know don't use them. I guess some folks like sealed wet-cell batteries, but I'm not among them. Kinda' like the "no maintenance" car batteries that tend to die much faster than the traditional batteries that allow you to add water. As for getting battery acid on your clothing--I think I may have done that about 10 years ago, but it may have been longer than that.

I also have a very high-quality digital multi-meter here in the office, one that I use for measuring minute changes in line outputs of audio systems. It was very expensive when I purchased it a decade ago, and I don't take it near saltwater--too darned expensive. I also have an old-fashioned load tester from back in the 70s when I owned a service station. It still works, but I rarely use it anymore.

I guess I'm a bit old fashioned--I'll stick with the hydrometer. I've never had one that failed, and you cannot beat the price.

Cheers,

Gary
05-31-2012 11:29 PM
hellosailor
Re: Voltage puzzle

david-
If you have no heavy loads to use, disable the engine and crank the starter a bit, use the starter as a load. It should be good for a 15 second run, ten minutes of rest, another 15 second run, that way there's no danger of overheating it but you'll certainly knock off any surface charge on the batteries. And of course, make Real Damn Sure the raw water inlet is closed when you do that, so you can't hydrolock the engine.
If for some reason that's impractical, get any high-wattage auto headlamp or bulb i.e. 65-100 watts, and some jumper wires or alligators. Connect to batteries and leave it on for 5 minutes, check again at 10 minutes. If you don't mind dumpster diving, you can often find a dual-beam headlight behind any auto parts store, with the low beam burned out and the high beam (what you want) perfectly good.
05-31-2012 10:46 PM
davidpm
Re: Voltage puzzle

Thanks Maine?
I was hoping you would weigh in on this one.
Yes these are brand new batteries.
I can't think of anything to put real load on them. The boat has very little to turn on.
Maybe all the cabin lights together would do something.
The engine panel on for 24 hours brought it down to 60%
I will test it every time I get on the boat just to learn what to expect.
05-31-2012 06:16 PM
btrayfors
Re: Voltage puzzle

Quote:
Originally Posted by hellosailor View Post
bill, my impression was that the $50 load testers (electronic, not pile, and typically good for 1000-1200 cca ratings at that price) wre also a good way to measure real capacity. While they are "just" in theory measuring how much of the batteries rated CCA capacity is left, isn't that the same thing? If you're expecting a battery to put out xx amps into a starting load, and it only has half that capacity let...? Same same?

I thought they were measuring internal conductance and the price had just ramped down because they were a little less sophisticated, lower power rated, and some electronics had dropped in price.
Not sure which new meters you're referring to. Can you be specific about makes/models? Have you tested or used any?

The good ones still cost a bundle. My MDX-650 still costs $650-$750 new. The cheaper ones that I've seen all have some limitations.

But, hey...it's always possible. The Chinese have a "conductance tester" that sells for $10 :-)

Bill
05-31-2012 02:29 PM
hellosailor
Re: Voltage puzzle

bill, my impression was that the $50 load testers (electronic, not pile, and typically good for 1000-1200 cca ratings at that price) wre also a good way to measure real capacity. While they are "just" in theory measuring how much of the batteries rated CCA capacity is left, isn't that the same thing? If you're expecting a battery to put out xx amps into a starting load, and it only has half that capacity let...? Same same?

I thought they were measuring internal conductance and the price had just ramped down because they were a little less sophisticated, lower power rated, and some electronics had dropped in price.
05-31-2012 12:02 PM
btrayfors
Re: Voltage puzzle

denverd0n, Hellosailor, and MaineSail are absolutely correct.

Accurate open circuit voltage measurement, done correctly, is an accurate method of determining the state of charge (SOC) of all lead-acid batteries....flooded, AGMs, gelled, etc. Much, much better than attempting to use a hydrometer, for the reasons cited by MaineSail.

For the OP: 12.9 or even higher OC resting voltage is very common with AGMs and gels, but not with flooded batteries. Your battery appears to be a flooded "no maintence" type, so I'd guess that your voltage measurement device is inaccurate. Or, just maybe, there's some charging device still connected, like a solar panel?

Note that the SOC is not the same as capacity. Batteries typically begin to lose their rated capacity practically from the date of manufacture, and they continue to lose capacity throughout their useful lifetimes.

The best way to measure capacity is with a controlled, purely restive 20-hour load test, with the load being 1/20th the ampere-hour (AH) rating of the battery and the load test continuing until the battery reaches 10.5VDC. This is not possible for most users, lacking the time and/or equipment necessary.

The industry standard for measuring battery capacity these days is with a device which measures internal battery conductance and resistance, such as one of the Midtronics series. These cost upwards of $600 and more, so are not available to most users.

For measurement of SOC, however, IMHO you'd be hard-pressed to find a better way than an OC voltage measurement directly at the battery terminals with a calibrated voltmeter after a suitably long resting period.

BTW, this includes the fashionable-these-days "battery monitors", which are only accurate if they have been properly installed and calibrated -- and recalibrated as the battery ages.

Bill
05-31-2012 11:42 AM
hellosailor
Re: Voltage puzzle

"The only true method of determining the charge state is to use a hydrometer."
Consider this, Gary. If that were so, then there would be no way to determine the charge state of AGM, gel, and sealed wet cells.
So, how do you think battery makers, distributors, and warranty services are done on all these other batteries? Right, with digital voltmeters, and internal resistance testers, aka electronic "load" testers.
The main purpose of a hydrometer is to burn acid holes in fabric, so folks can sell you new clothing and upholstery. It has some other minor uses, but that's the main one these days.
The electronic tools are easiily misused, but you can't blame the tools for poor workers.
05-31-2012 11:40 AM
Maine Sail
Re: Voltage puzzle

Quote:
Originally Posted by travlineasy View Post
The only true method of determining the charge state is to use a hydrometer. If it reads 1.275 specific gravity the battery is fully charged. It's that easy.

Gary
As written that is not even close to the reality. Contrary to popular misconceptions many people use hydrometers incorrectly too, no make that most people.

The electrolyte still needs to settle out over time just like any OCV reading does. 24 hours rest, no loads, no charging is what should be the ideal minimum for an accurate SG reading. You then need to drain and fill three times per cell to get a clean cell reading and correct for temperature. Testing a battery shortly after charging will yield false SG readings. SG reading also tell you nothing about the batteries actual capacity at a given point in its life-cycle.

SG is best used to determine cell imbalances.. It is generally far safer to conduct an OCV test rather than risk acid spillage, burned clothes or a spill than to conduct regular SG readings. Once or bi-yearly is often a good protocol for wets to determine internal cell balance and to determine when to equalize the batteries. In a healthy battery all cells will have a nearly identical SG reading. Also "cheap" hydrometers can be VERY, VERY misleading. I personally use a far more accurate sight refractometer and when compared to a cheap EZ Red hydrometer it shows just how inaccurate they really are. I have seen people throw away perfectly good batteries because of erroneous errors from cheap hydrometers. The floating ball version is a complete and utter joke, the EZ Red style not much better.

The 12.9v reading after 24 hours may not have been enough "rest" time or your meters resolution is bad or it's just a "new battery".. Some battery types can take well over 24 hours to fully settle out, especially when new.

With many wet cell deep cycle batteries 100% state of charge corresponds to 12.7-12.74V not necessarily 12.6. 12.6V is only 90% SOC for many wet cells.. The batteries that DavidPM bought are Deka Deep Cycle batteries, same as Sam's Club, West Marine, NAPA or O'Reilly Auto sells. Deka says any voltage above 12.6 can be considered full. Kind of non-committal..

I have however tested MANY Deka/East Penn batteries and found a resting voltage for "full" to be 12.7-12.73V.... With a new battery 12.9V after 24 hours is not out of the question. Apply a decent load for 5 minutes and then test and you'll be closer to reality or, just let it sit for a few more days..

These are Trojan's OCV numbers and I find they match up darn close to the DEka/East Penn deep cycle batteries: Note the 10% capacity difference between 12.6V and 12.7V!! On a 400 Ah bank that is 40 Ah's or a full day or more of capacity for many boaters....

Battery SOC at Resting Voltage and 80f (Source Trojan Battery)
100% = 12.73
90% = 12.62
80% = 12.50
70% = 12.37
60% = 12.24
50% = 12.10
40% = 11.96
30% = 11.81
20% = 11.66
10% = 11.51
05-31-2012 10:50 AM
travlineasy
Re: Voltage puzzle

The only true method of determining the charge state is to use a hydrometer. If it reads 1.275 specific gravity the battery is fully charged. It's that easy.

Gary
This thread has more than 10 replies. Click here to review the whole thread.

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


All times are GMT -4. The time now is 06:14 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.