Forced to buy a 'dual purpose' battery. Now what? - 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 > Electrical Systems
 Not a Member? 
  #1  
Old 08-09-2012
Junior Member
 
Join Date: Aug 2012
Posts: 8
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
Downeaster is on a distinguished road
Forced to buy a 'dual purpose' battery. Now what?

Hi all - this is my first post so I hope you'll all be gentle with me :-). I've been studying this forum for some time now and learning a LOT. I know, however, that some of my question has been answered many times on this forum. But I'm not completely confident in my proposed plan (below) so would love to hear your thoughts.

My two 4D wet cells are 5 years old and one of them died on the first day of a multi-day cruise. In a bit of a panic I purchased one (1) 'dual purpose' wet cell 4D from West Marine. It has 135 Ah, 290 Res. Min. and 1050 CCA. Price was $368 plus tax. I knew 100% at the time that I was probably not getting the optimal battery for my needs - but it was a pressure situation and I had the admiral and kids staring me down... It was the only battery that came close to my needs anywhere local.

Here are my 2 questions:
- Are these 'dual purpose' batteries any good? I wanted a deep cycle but there weren't any in the area and the West Marine guy promised me that this was a good choice. They seem to have small capacity compared to size (135 Ah for a 4D?)

- What should I do about the 2nd battery? It still seems to be going strong but I know people say it isn't good to have old and new batteries comingled. Can I wait? And what should I replace it with? Deep cycle or dual purpose? I know enough to get wet cell versus other.

Here is my electrical situation:
- The old battery is a deep cycle with unknown capacity (stock with a Catalina sailboat). Standard 1/2/off switch setup. No starter battery.

- 100% on moorings or anchor (no shore power) with a 50 amp alternator and internal regulator (stock Westerbeke). We generally don't want to run the engine to charge the banks more than 60-90 minutes a day. This makes me think that we may not want huge Ah capacity since we may have trouble keeping the batteries topped off.

- Refrigerator on low, auto pilot, chart plotter (no radar), and very modest lighting needs. We use the bow thruster and windlass only with the engine running.

My hypothesis, based on reading this forum, is that I should:

- Buy a new companion battery soon. Thinking 2 6V wet cell deep cycle Trojans
- Use the Trojans as primary house battery
- Use the dual purpose for starting and as backup for the Trojans. So when the Trojans drop to below 50%, cut over to the dual purpose and plan to recharge soon.

Thanks in advance for your help!

Cheers,
Downeaster
Catalina 350 sail

Last edited by Downeaster; 08-09-2012 at 01:05 PM.
Reply With Quote Share with Facebook
  #2  
Old 08-09-2012
asdf38's Avatar
Senior Member
 
Join Date: Jul 2010
Posts: 664
Thanks: 1
Thanked 4 Times in 4 Posts
Rep Power: 5
asdf38 is on a distinguished road
Re: Forced to buy a 'dual purpose' battery. Now what?

You didn't make your setup entirely clear. Are your two batteries hard wired in parallel or are they on different sides of the 1/2/All switch?

What you really should avoid is either 1) Hard wiring the different batteries in parallel or 2) Flipping the switch to all (which is the same as 1) anytime when they aren't being charged.

In either of those cases you'll end up with one battery essentially charging the other as they will inevitably have different properties.

A dual purpose is a compromise battery that has ok deep cycle properties and good starting properties. The problem is that you're using it in an application where it's starting current is probably at least 2x more than your engine needs so versus a true deep cycle you've traded capacity and lifetime for cranking amps you have no use for.

So bottom line, I would avoid connecting those two different batteries. The set-up you propose (6v's) is fine except that 4D battery is way larger than you need for a reserve/start bank. The ideal setup here is to leave your 1/2/all switch but add an automatic charging relay that kicks in when the alternator is running and shorts the two banks to ensure they both charge. That means you can show up to the boat, flip to two (house) start the engine (there is no harm starting from a deep cycle) and use the boat with no additional switching. The start/reserve battery is there only in-case you leave the lights on and need to get the engine going again.

Your comment about limiting capacity is unnecessary - you only need to recharge the energy you use. Larger banks are, except for cost/size/weight, generally better as a mostly charged bank is a happy long lasting one. For this reason also consider a solar panel to help keep the banks topped off when you're not around.
__________________
1979 Contessa 26
Boston, Ma
Reply With Quote Share with Facebook
  #3  
Old 08-09-2012
Junior Member
 
Join Date: Aug 2012
Posts: 8
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
Downeaster is on a distinguished road
Re: Forced to buy a 'dual purpose' battery. Now what?

Thank you asdf38. The batteries are on different sides of the 1/2/All switch.

So I wonder... Given a 2 battery setup (no starting battery), I wonder if having one as a 'dual purpose' makes some sense. Deep cycle for house. Dual purpose for starting and reserve house. Given its design purpose - perhaps dual purpose will have better cranking amps at the end of life versus a 2nd deep cycle?
Reply With Quote Share with Facebook
  #4  
Old 08-09-2012
Stu Jackson's Avatar
Senior Member
 
Join Date: Jul 2001
Posts: 769
Thanks: 0
Thanked 6 Times in 5 Posts
Rep Power: 13
Stu Jackson is on a distinguished road
Re: Forced to buy a 'dual purpose' battery. Now what?

Your plan is very good. Use what you bought and shop wisely (unhurriedly) for a new house bank.

Charging: You wrote: This makes me think that we may not want huge Ah capacity since we may have trouble keeping the batteries topped off.

Think just the opposite way. Think of them as a reservoir that you can use. The bigger the reservoir, the longer you can have between charges.

Do an energy budget (See this link for a LOT of Electrical System information):

Energy Budget
__________________
Stu Jackson, C34, 1986, M25 engine, Rocna 10 (22#)
Reply With Quote Share with Facebook
  #5  
Old 08-09-2012
asdf38's Avatar
Senior Member
 
Join Date: Jul 2010
Posts: 664
Thanks: 1
Thanked 4 Times in 4 Posts
Rep Power: 5
asdf38 is on a distinguished road
Re: Forced to buy a 'dual purpose' battery. Now what?

Quote:
Originally Posted by Downeaster View Post
Thank you asdf38. The batteries are on different sides of the 1/2/All switch.

So I wonder... Given a 2 battery setup (no starting battery), I wonder if having one as a 'dual purpose' makes some sense. Deep cycle for house. Dual purpose for starting and reserve house. Given its design purpose - perhaps dual purpose will have better cranking amps at the end of life versus a 2nd deep cycle?
In some ways it makes sense. But on my boat I have two deep cycles, a group 27 house and group 24 start/reserve. I couldn't justify a dual purpose or starting battery because the group 24 deep-cycle still had 3x the cranking amps I needed. Extra cranking amps go to waste but extra capacity can always be put to use, if only in an emergency. Again start batteries are damaged when deep cycled but deep cycles are fine being used as starts. So that's my reasoning. I would have gone even smaller on the reserve except marine deep cycles just don't go smaller than group 24.
__________________
1979 Contessa 26
Boston, Ma
Reply With Quote Share with Facebook
  #6  
Old 08-09-2012
Junior Member
 
Join Date: Aug 2012
Posts: 8
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
Downeaster is on a distinguished road
Re: Forced to buy a 'dual purpose' battery. Now what?

Thanks gents - now I think my challenge is to find golf cart batteries that will fit alongside the 4D. The bracing could be a challenge given different heights and fill cap positions.

Now that I have the time to do further research it seems a lot of the 4Ds are actually dual purpose. I wonder why, however, as everyone seems to agree that they serve more of a niche role versus deep cycle and cranking batteries???
Reply With Quote Share with Facebook
  #7  
Old 08-09-2012
Maine Sail's Avatar
Senior Member
 
Join Date: Jan 2003
Location: Maine Coast
Posts: 5,247
Thanks: 9
Thanked 107 Times in 78 Posts
Rep Power: 15
Maine Sail is just really nice Maine Sail is just really nice Maine Sail is just really nice Maine Sail is just really nice
Re: Forced to buy a 'dual purpose' battery. Now what?

Quote:
Originally Posted by Downeaster View Post

Now that I have the time to do further research it seems a lot of the 4Ds are actually dual purpose.

Even if labeled as "deep cycle" 4D's & 8D's are still almost always a dual purpose battery and not a true deep cycle. Dyno is the only maker I know of with a true deep cycle 4D or 8D..

Quote:
Originally Posted by Downeaster View Post
I wonder why, however, as everyone seems to agree that they serve more of a niche role versus deep cycle and cranking batteries???
They work well for starting large diesels on 18 wheelers and for causing sailors to require back surgery.. Other than that there are probably better choices..

I just replaced two 4D's today with 4 6V t105's.... I HATE those calls... Hired a couple of young guns to get the 4D's out...
__________________
______
-Maine Sail / CS-36T


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




© Images In Posts Property of Compass Marine Inc.



Last edited by Maine Sail; 08-09-2012 at 08:30 PM.
Reply With Quote Share with Facebook
  #8  
Old 08-09-2012
Junior Member
 
Join Date: Aug 2012
Posts: 8
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
Downeaster is on a distinguished road
Re: Forced to buy a 'dual purpose' battery. Now what?

Maine Sail - you speak words of wisdom. Lots more18 wheelers than marine diesels out there. If I were a battery manufacturer I would optimize around that market...!

Thanks everyone - I now understand my situation, options, and (for me at least) an understanding of how the marketplace led me to my current destination. I really appreciate your help.

Cheers,
Downeaster
Reply With Quote Share with Facebook
  #9  
Old 08-10-2012
hellosailor's Avatar
Senior Member
 
Join Date: Apr 2006
Posts: 10,369
Thanks: 1
Thanked 72 Times in 70 Posts
Rep Power: 10
hellosailor has a spectacular aura about hellosailor has a spectacular aura about
Re: Forced to buy a 'dual purpose' battery. Now what?

Dwon-
Check out the many battery threads.

A starting battery ("SLI") generally has thin plates so it can pass a large current for a short time. A deep cell battery has thicker plates designed to withstand repeated deeper discharges. What's thick, what's thin? How long is a piece of string? So the dual-purpose design is somewhere in the middle.

By all means, use it as a starting battery and as for West's price...that's the price of not delaying a vacation. Assuming it was a wet lead acid type, any house batteries of the same wet lead acid construction will work with it. Odds are you can find a golf cart supplier and buy Trojan traction (golf cart) batteries from them. Pricing can be competitive and while we can all argue, no one would call Trojan a bad choice.

Then you want to look at your charging system, and possibly using an Echocharge or other device instead of manually switching for charging, to get the best life out of them.
Reply With Quote Share with Facebook
  #10  
Old 08-10-2012
Junior Member
 
Join Date: Aug 2012
Posts: 8
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
Downeaster is on a distinguished road
Re: Forced to buy a 'dual purpose' battery. Now what?

Yep. But I think I might as well take advantage of a few deep cycles on the dual purpose bank too. Maybe for the occasional long sail with the autopilot and chart plotter on. Might as well get some bang for buck for my pressure purchase...
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 Dual Batteries and dual battery switch lmddmc Gear & Maintenance 9 01-02-2009 01:51 PM
dual battery setup. dorourke Gear & Maintenance 16 06-07-2007 01:03 AM
dual group 27 battery box jackytdunaway Gear & Maintenance 5 04-23-2007 06:45 AM
Forced to Champaign SailinCowboy General Discussion (sailing related) 3 07-19-2006 03:30 PM
Dual Battery Installation Urband Gear & Maintenance 1 03-25-2002 08:57 PM


All times are GMT -4. The time now is 09:27 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