Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 18-12-2023, 03:56   #1
Registered User

Join Date: Oct 2023
Location: UK, Solent
Boat: Jeanneau Sun Odyssey 35
Posts: 44
Will my alternator overcharge AGMs?

My current house bank needs to be replaced. It consists of 2 85Ah SLA batteries which are basic wet flooded chemistry. I am considering replacing with AGMs for all the known advantages. However, my alternator outputs a regulated 14.5V and I am concerned this may overcharge my batteries and so shorten their life. My shore charger outputs 14.5V for 6 hours after powering up as well, then drops to 13.5V. Again a potential source for overcharging. The charging setup was designed with FLA in mind with any overcharging compensated for by topping up with water.

I keep the boat in the UK and the batteries stay cool much of the time, eg <20C, should that make any significant difference.

Whilst at anchor I intend to use a separate LFP bank, topped up with solar, so the AGMs should stay at a fairly high SOC most of the time, just used for instruments and auto pilot under sail, and when using the windlass.

Should I be concerned about my alternator overcharging, or just replace and not let it bother me?
Sailing Paul is offline   Reply With Quote
Old 18-12-2023, 05:06   #2
CLOD
 
sailorboy1's Avatar

Join Date: Jul 2007
Location: being planted in Jacksonville Fl
Boat: none
Posts: 20,491
Re: Will my alternator overcharge AGMs?

well yes if you use voltage higher that you suppose to it will be a problem

why don't you adjust the voltages to be correct?
__________________
Don't ask a bunch of unknown forum people if it is OK to do something on YOUR boat. It is your boat, do what you want!
sailorboy1 is offline   Reply With Quote
Old 18-12-2023, 05:13   #3
Registered User
 
Kettlewell's Avatar

Join Date: Jul 2006
Location: Massachusetts
Boat: Finnsailer 38
Posts: 5,614
Re: Will my alternator overcharge AGMs?

Check with the battery manufacturer for their optimum charging voltages. 14.5 is in the range that some recommend for an absorption charge. And yes, temperature does make a difference. This article covers things pretty well. https://workshoppist.com/agm-battery-charging-voltages/

And, here is an article on typical alternator charging problems with AGMs, if you don't have some sort of smart regulation. https://workshoppist.com/car-alterna...e-agm-battery/
__________________
JJKettlewell
Kettlewell is online now   Reply With Quote
Old 18-12-2023, 05:32   #4
Registered User

Join Date: Apr 2022
Posts: 249
Re: Will my alternator overcharge AGMs?

First question is NOW LONG are you running the engine.


14.5 VDC for an hour or so, particularly with discharged batteries is fine and very much like bulk mode on a smart charger or smart inverter/charger.


Motoring all day long (like long ICW trips) is a different matter.


There are some smart regulators that will have your alternator following the basic 3 stage charging that would be more battery-friendly.
Wolfe10 is online now   Reply With Quote
Old 18-12-2023, 06:37   #5
Registered User

Join Date: Jan 2023
Posts: 1,652
Re: Will my alternator overcharge AGMs?

None of the answers you have gotten have asked you an important question: is your alternator internally regulated? If it is, then the output voltage into a full battery is going to be about 13.4 to 13.7. (Most certainly NOT 14.5V!) For routine motoring of a sailboat that’s going to be fine. My AGM’s live a long and happy life with an internally regulated engine alternator. I don’t need more sophisticated alternator control because other charging sources are normally used.

If on the other hand you have an externally regulated alternator, then just adjust the regulator to the battery manufacturer’s specifications for absorption and float voltages.
SailingHarmonie is online now   Reply With Quote
Old 18-12-2023, 07:28   #6
Registered User

Join Date: Oct 2023
Location: UK, Solent
Boat: Jeanneau Sun Odyssey 35
Posts: 44
Re: Will my alternator overcharge AGMs?

Quote:
Originally Posted by SailingHarmonie View Post
None of the answers you have gotten have asked you an important question: is your alternator internally regulated? If it is, then the output voltage into a full battery is going to be about 13.4 to 13.7. (Most certainly NOT 14.5V!) For routine motoring of a sailboat that’s going to be fine. My AGM’s live a long and happy life with an internally regulated engine alternator. I don’t need more sophisticated alternator control because other charging sources are normally used.

If on the other hand you have an externally regulated alternator, then just adjust the regulator to the battery manufacturer’s specifications for absorption and float voltages.
Interesting question! I have a Yanmar 3GM30F with a standard 55A Hitachi alternator. No external regulator and I believe internal regulation is essentially temperature regulated. So as it gets hotter the voltage is reduced. Is this what you mean by internally regulated?

This makes we wonder whether AGM batteries would be more at risk of under charging than overcharging.
Sailing Paul is offline   Reply With Quote
Old 18-12-2023, 07:38   #7
Registered User

Join Date: Oct 2023
Location: UK, Solent
Boat: Jeanneau Sun Odyssey 35
Posts: 44
Re: Will my alternator overcharge AGMs?

Quote:
Originally Posted by Kettlewell View Post
Check with the battery manufacturer for their optimum charging voltages. 14.5 is in the range that some recommend for an absorption charge. And yes, temperature does make a difference. This article covers things pretty well. https://workshoppist.com/agm-battery-charging-voltages/

And, here is an article on typical alternator charging problems with AGMs, if you don't have some sort of smart regulation. https://workshoppist.com/car-alterna...e-agm-battery/
These are really helpful links and expand upon my concerns. A dumb alternator setup as described both under and over charging AGMs.

The articles say that AGMs are more sensitive to over/under charging than flooded, but I would not be interested in buying traditional flooded batteries that require topping up with water. The alternative to AGM would be still be sealed VRLA type batteries, just using flooded construction. So the question then is whether AGMs are more sensitive to over/under charging than sealed VRLA flooded batteries? If they are then I may not get improved longevity from AGMs with my existing charging kit. Could AGMs wear out even more quickly?
Sailing Paul is offline   Reply With Quote
Old 18-12-2023, 07:45   #8
Registered User

Join Date: Oct 2023
Location: UK, Solent
Boat: Jeanneau Sun Odyssey 35
Posts: 44
Re: Will my alternator overcharge AGMs?

Quote:
Originally Posted by Wolfe10 View Post
First question is NOW LONG are you running the engine.


14.5 VDC for an hour or so, particularly with discharged batteries is fine and very much like bulk mode on a smart charger or smart inverter/charger.


Motoring all day long (like long ICW trips) is a different matter.


There are some smart regulators that will have your alternator following the basic 3 stage charging that would be more battery-friendly.
We aim to use the engine as little as possible! There are though times when we will have to motor all day. I guess I could, maybe should, turn off the lead acid bank in such circumstances to prevent it being overcharged. The instruments, etc. could then run straight from the alternator.
Sailing Paul is offline   Reply With Quote
Old 18-12-2023, 07:51   #9
Registered User

Join Date: Oct 2023
Location: UK, Solent
Boat: Jeanneau Sun Odyssey 35
Posts: 44
Re: Will my alternator overcharge AGMs?

Just had a thought about how smarter alternators and other chargers are supposed to work. When charging AGMs I believe you are supposed to lower to float voltage once the absorption phase finishes. But if the batteries are connected to a load, how can the "smart" charger detect the end of the absorption phase?
Sailing Paul is offline   Reply With Quote
Old 18-12-2023, 07:56   #10
Registered User

Join Date: Jan 2023
Posts: 1,652
Re: Will my alternator overcharge AGMs?

Yes AGM batteries are more sensitive to undercharging. That would be a problem if your only, or principle, charge source was your engine alternator. That is not the system you described.

Yes, AGM are damaged by overcharging. However, a properly set up alternator does not go high enough in voltage to cause this. Think about this for a second. Lots of cars use AGM batteries with dumb alternators. They can spend many more hours running than your boats engine.

If you want to regularly charge your batteries with your engine alternator, you need to have a smart regulator. That’s true for any battery, not just AGM. If you just pump some extra energy into the batteries as a side effect of running the engine, a dumb alternator will work fine.

My Lifeline AGM bank lasted 7 years, cycling virtually every day, charging from a dumb alternator when the engine was running. We move a LOT, and our engine runs about 500 hours a year. Is that good enough for you?
SailingHarmonie is online now   Reply With Quote
Old 18-12-2023, 08:19   #11
always in motion is the future
 
s/v Jedi's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 19,185
Re: Will my alternator overcharge AGMs?

If you motor for more than a couple of hours you simply -must- have an externally regulated alternator with a smart regulator. Every other option is technically flawed.

I can recommend a kit from Balmar, they have them for every engine.
__________________
“It’s a trap!” - Admiral Ackbar.

s/v Jedi is offline   Reply With Quote
Old 18-12-2023, 08:44   #12
Registered User

Join Date: Apr 2022
Posts: 249
Re: Will my alternator overcharge AGMs?

Do NOT turn off alternator B+ output to at least A/one battery with the engine running. Likely to blow the alternator diodes.
Wolfe10 is online now   Reply With Quote
Old 18-12-2023, 09:15   #13
Registered User
 
Stu Jackson's Avatar

Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 9,732
Re: Will my alternator overcharge AGMs?

Overcharging with Combiners or ACRs The MYTH:
http://c34.org/bbs/index.php/topic,7052.0.html
__________________
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, SR/FK, M25, Rocna 10 (22#) (NZ model)
Stu Jackson is online now   Reply With Quote
Old 18-12-2023, 10:05   #14
Registered User

Join Date: Mar 2007
Location: Santa Cruz
Boat: SAnta Cruz 27
Posts: 6,853
Re: Will my alternator overcharge AGMs?

Quote:
Originally Posted by s/v Jedi View Post
If you motor for more than a couple of hours you simply -must- have an externally regulated alternator with a smart regulator. Every other option is technically flawed.

I can recommend a kit from Balmar, they have them for every engine.
Balmar regulators are good kit, unless you put them in the engine compartment--they don't like it hot. You can get a plug and play dumb regulator from NAPA for $25 as a backup if you fry the Balmar.
donradcliffe is online now   Reply With Quote
Old 18-12-2023, 10:56   #15
CLOD
 
sailorboy1's Avatar

Join Date: Jul 2007
Location: being planted in Jacksonville Fl
Boat: none
Posts: 20,491
Re: Will my alternator overcharge AGMs?

Quote:
Originally Posted by donradcliffe View Post
Balmar regulators are good kit, unless you put them in the engine compartment--they don't like it hot.
Probably true, but my Balmar regular is in the small engine enclosure and about 1 foot away for the engine and it has been fine for 22 years. Just saying.
__________________
Don't ask a bunch of unknown forum people if it is OK to do something on YOUR boat. It is your boat, do what you want!
sailorboy1 is offline   Reply With Quote
Reply

Tags
agm, alternator

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to put Solar, Wind, Alternator into AGMs beebopbogo Electrical: Batteries, Generators & Solar 14 08-05-2014 08:00
Overcharge event on new lithium batteries retired Electrical: Batteries, Generators & Solar 6 07-06-2013 05:13
AGM overcharge Shamancat Electrical: Batteries, Generators & Solar 5 27-04-2013 17:31
Does Alternator Need Protection from AGMs? batkins61 Electrical: Batteries, Generators & Solar 14 24-05-2012 07:45
Will My Outboard Overcharge My Battery ? Please Help ! OrangeCrush Monohull Sailboats 14 22-06-2010 20:21

Advertise Here


All times are GMT -7. The time now is 12:23.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.