Testing AGM Battery capacity? - SailNet Community

   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
 Not a Member? 
  #1  
Old 08-28-2008
T37SOLARE's Avatar
Tartan 37C
 
Join Date: Feb 2008
Location: Chesapeake Bay - HHS
Posts: 501
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 7
T37SOLARE is on a distinguished road
Testing AGM Battery capacity?

With the help of a good electrician it appears I've finally worked out the bugs on the PO's battery upgrade on SOLARE. (4 group 27 = 440 amp hours)

He and the Link 20 manual say to do a battery condition test, to run 5% or your capacity until you get a 10.5 voltage reading. Then you can determine what your real available capacity is.

But, somewhere I recall reading that AGM's don't like to be fully discharged, and by doing so I'm shorting both the life and capacity.

Is this a good thing to do, or is there a safer way to determine actual capacity?
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

SOLARE
T-37 #442
Reply With Quote Share with Facebook
  #2  
Old 08-28-2008
Senior Member
 
Join Date: Jul 2001
Posts: 1,174
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 14
k1vsk will become famous soon enough
If you are unsure how to accomplish this properly, it may be best to simply input the stated battery capacity of your bank as a good approximation.

Out of curiosity, how do you get 440 amps out of four Gr27 batteries? Do you really have them all paralleled?
Reply With Quote Share with Facebook
  #3  
Old 08-28-2008
camaraderie's Avatar
moderate?
 
Join Date: May 2002
Location: East Coast
Posts: 13,878
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 15
camaraderie is a jewel in the rough camaraderie is a jewel in the rough camaraderie is a jewel in the rough
k1vsk...that's a fairly normal house bank with all parallelled. Mine is 1000+ with 4x8d's.
group 27's are generally around 90-100ah's each and 110 is actually quite high. I would simply use 90-100 ah's as my amount per battery IF they are new. It doesn't hurt to err a bit on the low side as extended battery life will be the result of charging before you reach 50% discharge.

SOLARE...you are correct...do NOT do what Xantrex suggests. If you are not content with estimates then you can do the following.
1. EQ the batteries.
2. Fully charge the batteries.
3. You have approximately 400ah capacity at the 20 hour rate which means that at a 20 amp load you should get 20 hours before you reach 10.5 volts. 4. Get a 20 amp test load and run the batteries down to 12.2V. (50%). They SHOULD last 10 hours before reaching 12.2V. If they only last 8 hours...you have 80% of rated capacity...5 hours is 50% etc.
5. Again...if the batteries are new...no need to go through this.
__________________
No longer posting. Reach me by PM!
Reply With Quote Share with Facebook
  #4  
Old 08-29-2008
hellosailor's Avatar
Plausible Deniability
 
Join Date: Apr 2006
Posts: 10,447
Thanks: 1
Thanked 76 Times in 74 Posts
Rep Power: 10
hellosailor has a spectacular aura about hellosailor has a spectacular aura about
Cheap test load: Automobile headlights, or similar 12-volt lamps or heaters that are rated as high as you can get them.

Batteries are nominally rated at a 20-hour discharge rate, so if they are rated 105AH each, that's based on 20 hours at a 5-amp load. (Ratings for higher and lower rates are usually also available from the maker.) One automotive high beam lamp (~65 watt rated) is a conveniently close load for one battery at a 20-hour rate.

And I'd agree with Cam--cycling them down to the 50% point should be enough.
Reply With Quote Share with Facebook
  #5  
Old 08-29-2008
T37SOLARE's Avatar
Tartan 37C
 
Join Date: Feb 2008
Location: Chesapeake Bay - HHS
Posts: 501
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 7
T37SOLARE is on a distinguished road
Quote:
Originally Posted by camaraderie View Post
SOLARE...you are correct...do NOT do what Xantrex suggests. If you are not content with estimates then you can do the following.
1. EQ the batteries.
2. Fully charge the batteries.
3. You have approximately 400ah capacity at the 20 hour rate which means that at a 20 amp load you should get 20 hours before you reach 10.5 volts. 4. Get a 20 amp test load and run the batteries down to 12.2V. (50%). They SHOULD last 10 hours before reaching 12.2V. If they only last 8 hours...you have 80% of rated capacity...5 hours is 50% etc.
5. Again...if the batteries are new...no need to go through this.
Thanks Cam!

These batteries were installed by the PO age unknown, and the fact the boat was keep on a mooring, I had no clue of their condition.

Good news is, I ran a 20+/-amp load on the bank and got it down to 12.2V at 12 hours, in addition the Link told me that I had consumed 215 amps.

So it looks like these batteries will be around for a bit longer!
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

SOLARE
T-37 #442
Reply With Quote Share with Facebook
Reply


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

 
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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Installing a Automatic Battery Selector Switch artbyjody Gear & Maintenance 24 07-08-2008 07:07 PM
Choosing Batteries Kevin Jeffrey Gear and Maintenance Articles 0 04-07-2003 08:00 PM
Choosing Batteries Kevin Jeffrey Cruising Articles 0 04-07-2003 08:00 PM
Installing a New Battery Bank Sue & Larry Gear and Maintenance Articles 0 09-26-2002 08:00 PM
Boat Battery Power East Penn Manufr. Gear and Maintenance Articles 0 01-18-1999 07:00 PM


All times are GMT -4. The time now is 01:24 AM.

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.