Reply
 
Thread Tools Search this Thread Display Modes
 
Old 03-25-2013, 12:44 PM   #1
Wise Elder
 
Jammer's Avatar
 
2010 30' Classic
Vintage Kin Owner
South of the river , Minnesota
Join Date: Dec 2009
Posts: 4,119
How to drain test a battery

Spring will be here someday even though we still have snow on the ground.

Some of you may find that you have batteries of doubtful provenance or uncertain age. While it's tempting to just replace questionable batteries out of hand, it's expensive and possibly unnecessary.

The best way to know whether your batteries are still good is to run a drain test on each one. It's simple to do:

1) Charge the battery.
2) Connect a load that draws a known, consistent number of amps.
3) Measure the time until the voltage drops significantly.

By multiplying the amps the load draws by the number of hours the test takes, you can find out the actual amp-hour capacity of the battery. If it's less than around 75% of the rated capacity of the battery, it's time to go shopping.

I made a load test setup with two 12v 50W light bulbs, which draws around 9 amps, because 12 volt light bulbs draw around 10% more than their rated current at the 12.6 volt discharge voltage. I used a porcelain lampholder and one of those y-shaped adapters to allow two bulbs in a single socket. The parts cost less than $10 at a home center. Not voltage or current measurements are required, since it's obvious when the lights become dim. I put the whole thing in a ceramic dish to protect the floor from heat.

The group 31 starting battery that the PO put in my Cayo camper ran for just under 12 hours, for around 105 amp-hours, better than I expected.
Attached Thumbnails
Click image for larger version

Name:	photobucket-20284-1364232875078_zpsbc035cb0.jpg
Views:	68
Size:	58.8 KB
ID:	181821  
__________________

__________________
To learn to see below the surface, you must adjust your altitude
Jammer is offline   Reply With Quote
Old 03-25-2013, 09:13 PM   #2
2 Rivet Member
 
Dobber's Avatar
 
2012 25' FB Flying Cloud
Queens , New York
Join Date: Jul 2012
Posts: 68
How to drain test a battery

Great info.
Thanks, Jammer
__________________

__________________
Dobber is offline   Reply With Quote
Old 03-26-2013, 05:07 AM   #3
Rivet Master
 
wayneskid's Avatar

 
2010 22' Interstate
Anchorage , Alaska
Join Date: Mar 2010
Posts: 515
Images: 1
Interesting idea. But, any decent battery dealer (Costco, Sears, Interstate Batteries come to mind) will test your battery for free using a tool designed for the purpose; a battery load tester.
__________________
- wayne
2010 Interstate 3500 Twin Bed
(2008 Freightliner CRD Sprinter)
AIR #44779
TAC AK-1 !!
wayneskid is offline   Reply With Quote
Old 03-26-2013, 12:08 PM   #4
Wise Elder
 
Jammer's Avatar
 
2010 30' Classic
Vintage Kin Owner
South of the river , Minnesota
Join Date: Dec 2009
Posts: 4,119
Quote:
Originally Posted by wayneskid View Post
Interesting idea. But, any decent battery dealer (Costco, Sears, Interstate Batteries come to mind) will test your battery for free using a tool designed for the purpose; a battery load tester.
The load testers used by battery dealers will identify a battery that is completely shot, reasonably reliably. They won't always identify a battery that is 50% shot. A drain test is more accurate. The dealers don't use it because it takes too long.
__________________
To learn to see below the surface, you must adjust your altitude
Jammer is offline   Reply With Quote
Old 03-28-2013, 06:02 AM   #5
Wise Elder
 
Jammer's Avatar
 
2010 30' Classic
Vintage Kin Owner
South of the river , Minnesota
Join Date: Dec 2009
Posts: 4,119
The marine dual purpose batteries that the dealer put in my Airstream, now 3 years old, are testing out ok.

The conventional wisdom is that dual purpose batteries are no good. Maybe the conventional wisdom is wrong.
__________________
To learn to see below the surface, you must adjust your altitude
Jammer is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



Virginia Campgrounds

Reviews provided by




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 11:56 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.

Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.