Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 12-11-2014, 09:32   #1
Registered User
 
admiralslater's Avatar

Join Date: Sep 2014
Location: Toronto summer rest somewhere else
Boat: Outremer 45/pdq36
Posts: 678
Adding batteries 1

We have just purchased a boat which is in Grenada .it has 4 120 amp agm batteries which are at least two years old .they have tested in good condition and have been kept charge via the solar pannels .
Now the question ,I would like to add another battery to the house bank ,a local tech said that it was not a good idea . Sub question can the extra battery have a different ampre rating than existing . I know that it needs to be the same style I.e. Agm
Thanks David
__________________

__________________
admiralslater is offline   Reply With Quote
Old 12-11-2014, 15:38   #2
Registered User
 
GrowleyMonster's Avatar

Join Date: Dec 2012
Location: New Orleans
Boat: 1976 Cal 2-27
Posts: 1,298
Re: Adding batteries 1

Ideally you want all batteries in a bank to be the same, and same conditiin. Don't add a new batt to your 2 year old bank. What you COULD do is install one or 2 batteries in a separate bank, as a reserve.
__________________

__________________
GrowleyMonster
1976 Cal 2-27, MR WIGGLES
Now with clean, dependable electric propulsion!
GrowleyMonster is offline   Reply With Quote
Old 12-11-2014, 17:28   #3
Registered User
 
admiralslater's Avatar

Join Date: Sep 2014
Location: Toronto summer rest somewhere else
Boat: Outremer 45/pdq36
Posts: 678
Re: Adding batteries 1

as a matter of interest why does it matter
__________________
admiralslater is offline   Reply With Quote
Old 12-11-2014, 18:34   #4
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,033
Re: Adding batteries 1

That sheds light on your other question.

Two year old batteries will be partly depleted. If you charge the old ones and the new ones together, one set gets overcharged or the other set gets undercharged. It is like hitching two slow horses and two fast horses to the same wagon, there's no way to keep them all working together at the same pace.

For more technical information, look at the MANY existing threads about this. Your best bet for now? Adding just "one" more battery isn't worth doing. At all, in any way. Spend the money on extra insulation for the reefer, LED replacements for the lights (all the lights) or an extra solar panel or an MPPT controller for the existing one. You'll get more bang for the buck.
__________________
hellosailor is offline   Reply With Quote
Old 12-11-2014, 19:02   #5
Registered User
 
GrowleyMonster's Avatar

Join Date: Dec 2012
Location: New Orleans
Boat: 1976 Cal 2-27
Posts: 1,298
Re: Adding batteries 1

Quote:
Originally Posted by admiralslater View Post
as a matter of interest why does it matter
Essentially, as HelloSailor said. Capacity and internal resistance will be different due to age and usage difference. They will charge and discharge differently and you will have a very inefficient system. With two isolated banks, each having a different age or type of battery, there is no problem. In fact, twin banks with different ages is a great system. As the older bank ages and eventually needs replacing, the newer bank can be relied on more and more. If you get 6 or 7 years of good use out of your batts you are doing pretty good. So a new reserve bank now will stagger the replacement date nicely.
__________________
GrowleyMonster
1976 Cal 2-27, MR WIGGLES
Now with clean, dependable electric propulsion!
GrowleyMonster is offline   Reply With Quote
Old 13-11-2014, 10:08   #6
Marine Service Provider

Join Date: Dec 2003
Location: South Carolina
Boat: Philip Rhodes Custom
Posts: 395
Re: Adding batteries 1

Quote:
Originally Posted by admiralslater View Post
as a matter of interest why does it matter
It doesn't. All the paranoia about non matching batteries in parallel is a misconception derived from batteries in series where size, age, chemistry etc., is very important.

But batteries in parallel all charge at an equal rate because the are all at the same voltage. Part of the misconception relates to assuming, for example, that 4 batteries in parallel will get 5 amps each from a 20 amp charger so a smaller capacity battery would be overcharged before the larger ones reach full charge. However the current divides according to the capacity of each battery so a low capacity battery will take much less current than the larger one.

If one battery were to be overcharged it would have to be at a higher voltage but since they are all connected together at the same voltage this can't happen.

Think of it as two water tanks of the same height, one 100 gallons and one 10 gallons connected together at the bottom. If you pour in 110 gallons to either tank (battery) both will end up at 100% full without overflowing the smaller one.

Add the extra battery in parallel. By having them at different overlapping ages and condition they won't all reach end of life simultaneously and you can smoothly replace dead ones as needed without the whole bank giving poor performance for weeks before failure.
__________________
Andina Marie is offline   Reply With Quote
Old 13-11-2014, 10:13   #7
Moderator
 
carstenb's Avatar

Cruisers Forum Supporter

Join Date: May 2012
Location: Copenhagen
Boat: Jeanneau Sun Fast 40.3
Posts: 4,936
Images: 1
Re: Adding batteries 1

Quote:
Originally Posted by Andina Marie View Post
It doesn't. All the paranoia about non matching batteries in parallel is a misconception derived from batteries in series where size, age, chemistry etc., is very important.

But batteries in parallel all charge at an equal rate because the are all at the same voltage. Part of the misconception relates to assuming, for example, that 4 batteries in parallel will get 5 amps each from a 20 amp charger so a smaller capacity battery would be overcharged before the larger ones reach full charge. However the current divides according to the capacity of each battery so a low capacity battery will take much less current than the larger one.

If one battery were to be overcharged it would have to be at a higher voltage but since they are all connected together at the same voltage this can't happen.

Think of it as two water tanks of the same height, one 100 gallons and one 10 gallons connected together at the bottom. If you pour in 110 gallons to either tank (battery) both will end up at 100% full without overflowing the smaller one.

Add the extra battery in parallel. By having them at different overlapping ages and condition they won't all reach end of life simultaneously and you can smoothly replace dead ones as needed without the whole bank giving poor performance for weeks before failure.
Unfortunately, when I added a battery a few years ago (in parallel), I ended up damaging the old battery and had to replace it. So while others here have much more theoretical knowledge than me - my practical experience is that adding a battery is bad news.
__________________
I spent most of my money on Booze, Broads and Boats. The rest I wasted - Elmore Leonard
carstenb is offline   Reply With Quote
Old 13-11-2014, 15:09   #8
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,033
Re: Adding batteries 1

Andina-
"But batteries in parallel all charge at an equal rate because the are all at the same voltage"
Wouldn't they charge at different rates, dependent on the internal resistance of each battery? I readily admit to knowing just enough electrical theory to be dangerous (G) but IIRC when there are multiple "loads" set up in parallel, the flow of current through them will be dependent on the resistance of each one, no?

I'd still rather use 'em up faster and replace the entire bank with a bigger uniform one, faster too.
__________________
hellosailor is offline   Reply With Quote
Old 13-11-2014, 20:38   #9
Marine Service Provider

Join Date: Dec 2003
Location: South Carolina
Boat: Philip Rhodes Custom
Posts: 395
Re: Adding batteries 1

Quote:
Originally Posted by hellosailor View Post
Andina-
"But batteries in parallel all charge at an equal rate because the are all at the same voltage"

Wouldn't they charge at different rates, dependent on the internal resistance of each battery? I readily admit to knowing just enough electrical theory to be dangerous (G) but IIRC when there are multiple "loads" set up in parallel, the flow of current through them will be dependent on the resistance of each one, no?
You are correct, the internal resistance controls the amount of charging current.

It could have been worded better. By equal rate I meant that each battery will match the other batteries for their "relative" amount of charge, they will all be (approximately) at 50% at the same time, 75% at the same time and fully charged at the same time. The amount of amp-hours in each will be in proportion to their actual capacity.
__________________
Andina Marie is offline   Reply With Quote
Old 13-11-2014, 21:18   #10
Registered User
 
Sun and Moon's Avatar

Join Date: Nov 2009
Location: Colorado
Boat: Bristol 29
Posts: 273
Re: Adding batteries 1

Quote:
Originally Posted by Andina Marie View Post
It doesn't. All the paranoia about non matching batteries in parallel is a misconception derived from batteries in series where size, age, chemistry etc., is very important.

But batteries in parallel all charge at an equal rate because the are all at the same voltage. Part of the misconception relates to assuming, for example, that 4 batteries in parallel will get 5 amps each from a 20 amp charger so a smaller capacity battery would be overcharged before the larger ones reach full charge. However the current divides according to the capacity of each battery so a low capacity battery will take much less current than the larger one.

If one battery were to be overcharged it would have to be at a higher voltage but since they are all connected together at the same voltage this can't happen.

Think of it as two water tanks of the same height, one 100 gallons and one 10 gallons connected together at the bottom. If you pour in 110 gallons to either tank (battery) both will end up at 100% full without overflowing the smaller one.

Add the extra battery in parallel. By having them at different overlapping ages and condition they won't all reach end of life simultaneously and you can smoothly replace dead ones as needed without the whole bank giving poor performance for weeks before failure.
Andina's got it right. When connected in parallel, different batteries will behave correctly. The voltage is common across them, so the charge and the load will be distributed according to capacity.

The batteries must, however be of the same type. Different type batteries (flooded, gel, agm) have different acceptance, float and equalization voltages and currents, and so cannot be charged together. I believe they could in theory be discharged together, though I can't see how this could be reasonably implemented.
__________________
Sun and Moon is offline   Reply With Quote
Old 14-11-2014, 10:11   #11
Marine Service Provider

Join Date: Dec 2003
Location: South Carolina
Boat: Philip Rhodes Custom
Posts: 395
Re: Adding batteries 1

Quote:
Originally Posted by Sun and Moon View Post
Andina's got it right. When connected in parallel, different batteries will behave correctly. The voltage is common across them, so the charge and the load will be distributed according to capacity.

The batteries must, however be of the same type. Different type batteries (flooded, gel, agm) have different acceptance, float and equalization voltages and currents, and so cannot be charged together. I believe they could in theory be discharged together, though I can't see how this could be reasonably implemented.
Sorry can't agree that the different types have to match. Each battery sees a voltage on its terminals that is higher than its "internal" voltage so charging current flows into the battery depending on the internal resistance at that time. A battery doesn't "know" that there are other batteries in parallel, all it sees is a charging voltage. It doesn't care or react differently because other batteries may be taking a different share of the current at a particular voltage, it just charges with what is supplied.

It is true that the profile of a smart charger may not match the consolidated profile of the bank so it may not be possible to choose a charging profile to please all the batteries but the only downside is a second order reduction in charging time. Most batteries don't have the privilege of a smart charger but charge just fine from the "dumb" ones.
__________________
Andina Marie is offline   Reply With Quote
Old 14-11-2014, 10:39   #12
Registered User
 
Sun and Moon's Avatar

Join Date: Nov 2009
Location: Colorado
Boat: Bristol 29
Posts: 273
Re: Adding batteries 1

From wikipedia:
Lead-acid batteries
Accepted average float voltages for lead-acid batteries at 25 ░C can be found in following table:
Gel battery 13.05
Flooded lead–acid cell 13.4
Absorbent glass mat 13.6

I believe other charging parameters differ as well. I know my charge controller asks what kind of batteries I have. And I think it effects battery life, sometimes severely, if you get this wrong. The OP has solar panels, therefore I presume he has a decent charge controller as well.
__________________
Sun and Moon is offline   Reply With Quote
Old 14-11-2014, 10:45   #13
Marine Service Provider
 
Maine Sail's Avatar

Join Date: Jan 2007
Location: Maine
Boat: CS-36T - Cupecoy
Posts: 3,060
Re: Adding batteries 1

Quote:
Originally Posted by Sun and Moon View Post
From wikipedia:
Lead-acid batteries
Accepted average float voltages for lead-acid batteries at 25 ░C can be found in following table:
Gel battery 13.05
Flooded leadľacid cell 13.4
Absorbent glass mat 13.6

I believe other charging parameters differ as well. I know my charge controller asks what kind of batteries I have.

And we all know Wikipedia is always right.... Every battery maker has different requirements. They simply can't be summed up into 3 float voltages for three types.

The most commonly available GELS for the marine market (Sonnenschein & East Penn) actually want 13.8V for float, temp compensated, so Wikipedia is wrong by nearly .8V, caveat emptor.........
__________________
Marine How To Articles
Maine Sail is offline   Reply With Quote
Old 14-11-2014, 10:55   #14
Registered User
 
Sun and Moon's Avatar

Join Date: Nov 2009
Location: Colorado
Boat: Bristol 29
Posts: 273
Re: Adding batteries 1

Quote:
Originally Posted by Maine Sail View Post
And we all know Wikipedia is always right.... Every battery maker has different requirements. They simply can't be summed up into 3 float voltages for three types.

The most commonly available GELS for the marine market (Sonnenschein & East Penn) actually want 13.8V for float, temp compensated, so Wikipedia is wrong by nearly .8V, caveat emptor.........
I'm merely trying to make the point that it's a bad idea to mix battery types, in part because the charge profile can be radically different. Surely you agree with this, no?
__________________
Sun and Moon is offline   Reply With Quote
Old 14-11-2014, 11:46   #15
Marine Service Provider
 
Maine Sail's Avatar

Join Date: Jan 2007
Location: Maine
Boat: CS-36T - Cupecoy
Posts: 3,060
Re: Adding batteries 1

Quote:
Originally Posted by Sun and Moon View Post
I'm merely trying to make the point that it's a bad idea to mix battery types, in part because the charge profile can be radically different. Surely you agree with this, no?
I don't mix types in the same house bank but I do and have mixed them for charging, when it can work.

I also have a few banks out there with mixed sized batteries. One of them is a series pair of Lifeline 6CT's in parallel with a series pair of Lifeline 4CT's.... Going strong at year three and this was done after consulting with Lifeline's engineer Dave V.

On my own boat I parallel an AGM with a LiFePO4 to put some charge back into the AGM when it needs it.. The LiFePO4 charge voltage is lower than ideal for the AGM but it works. I will probably slap a GEL in place of the AGM eventually, but the AGM is still testing at 97% of capacity after three years (because it is really never used). About bi-monthly I give the AGM reserve battery a good boost charge to 14.4V.

So the answer, like everything, is it depends. What Andina is saying is actually correct technically speaking but no battery manufacturer recommends it be done. Course they want to sell you new batteries too....
__________________

__________________
Marine How To Articles
Maine Sail is offline   Reply With Quote
Reply

Thread Tools
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
Adding distilled water to batteries GalaxyGirl Powered Boats 22 22-07-2014 18:30
Adding solar to 5 batteries, 3 banks. How's my wiring diagram? beebopbogo Electrical: Batteries, Generators & Solar 9 30-03-2014 19:52
Adding Bow Thruster and Windlass . . . What to Do with Batteries geoffr Electrical: Batteries, Generators & Solar 26 20-09-2010 05:26
Golf Cart Batteries vs Marine Batteries Bill Estes Electrical: Batteries, Generators & Solar 52 27-01-2010 00:28
Adding More Batteries Randyonr3 Electrical: Batteries, Generators & Solar 30 25-09-2009 15:27



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 04:34.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.