battery question

[Ken Heyman]

I currently have two somewhat marginal deep cycle batteries. Other than an extended cruise this summer (where I often have AC hook-up), we are on a can and the only charge they get is periodic, albeit  brief, engine runs.

I've been operating house with either batt 1 or 2 but using the selector switch to achieve a parallel connection on "all" which I use for starting. Whats interesting is the only way I get sufficient cranking amps to start the engine is to have the switch on "All". Neither battery independently will start the engine.

Why is this? I thought a parallel hook-up just increases amp hour capacity without increasing voltage or current?

thanks in advance,

[APACHE]

Ken : What you are doing is combining two "marginal" batteries, that together have enough amps to start the engine.
Look on this site and you'll find MANY posts on 4 golf cart 6 V batteries or 3 AGM/Gel batteries for your house bank.  There are a number of posts on the addition of a separate starting battery.  All kind of info on this site and in the Mainsheet C34 tech notes for a 1988 MKI.  
Some thoughts.  

[Ray & Sandy Erps]

Ken,

You are right.  The parallel switch combines amperage, but not voltage.  I was in the same situation as you for several years with my boat out on a can with no way to keep the batteries in good condition.  In good condition, either one of your batteries should start the engine, although as others have pointed out in past discussions, the starting circut is marginal, with long runs of cable that are on the small side.  There is quite a bit of info in past discussions on how to improve the stock battery charging system and different ways to improve the starting circut.  I've done both this past year and am very pleased with the results.

Ray

[SteveLyle]

Ken,

It doesn't just take volts (potential) to turn the starter, it takes current (amps).  When you combine two batteries, you get essentially double the available amps.  I tend to use the hydraulic analogy for electrical systems - the pressure in the pipe (volts) can be a little lower as long as you've got enough volume available (amps) to flow through the system.

Steve

[Stu Jackson]

Ken

For all you guys on a can, what is stopping you from getting a solar panel?  It is SOOOO simple.  Your batteries will last longer, stay charged and work.

There is an incredible amount of this information on this website message board (I know, you know that already, but...).

I also know that this answer/post is beyond your original question, but offer the ideas for your consideration and possible use.

Do a search on "C34 Electrical Systems," which, in many cases, I've added to posts enable you to find them quickly.

Sure, you can get away with two batteries if you plug in when you're traveling.  Your boats, your choices.

BUT: that's not the problem.  The real issue is: you ARE killing your batteries by letting them self-drain (even gel cells will over time).

The amount of $ you spend on a solar panel will have a 2 second payback, because your batteries WILL last longer.  Read Calder and Ample Power Primer.

You (OEM) alternator is doing SQUAT, and this is something you may be aware of already, unless you've upgraded to a new alternator with an external three stage regulator.

Good luck, and hope to have Santa help you consider upgrading your electrical system, or at the very least, getting a solar panel.

BTW, Catalina is pretty much still making NEW C34s with the same old very, very basic electrical system - I just was introduced to a brand new boat:  my understanding is that there are just (2) 8Ds. It certainly would be appropriate to include a separate start battery, parallel the two that Catalina installed, all of which could be done reasonably easily at the factory, instead of people complaining a year later: "Why does my electrical system fail after I've only been on the hook for one night?"  It seems to me that people buying new boats may not have yet determined how they plan to use them, so the basic system is OK: ONLY as long as you plan to stay at a dock, plugged in, every two days; that is, of course, ALSO unless you don't load up with stereo, TV, radar, refrigeration, and the other power consuming gadgets, like computers, interfaced GPS, etc,. that have interested so many boaters.  An energy budget is a good first place to start.  Two separate 8Ds would simply last a lot longer if they were paralleled with the same daily load.  

Here's one for you to answer your original question: (link updated 9/2007)

http://www.c34.org/projects/projects-slow-starter-fix.html

A search on SOLAR finds this, among many:

http://www.c34ia.org/phpbb/viewtopic.php?t=1563&highlight=solar

(Note: This link doesn't work anymore since it went back to the last board software.  Try a search on SOLAR, lots of material available)  9/2007

Jim Moe's great long article about upgrading the alternator charging system has been posted on Projects at:  http://www.c34.org/projects/projects-electrical-system-upgrade-2.html

[Stu Jackson]

This is a two year old thread, but Ken and I were discussing the issues by phone yesterday, and I thought I'd update this one since it still seems to be an issue for many: "Why do I have to use BOTH to start my engine?"  Ken since the first post on this has replaced his marginal batteries with 4 Trojan T-105s, in two banks.

Ken installed a small solar panel, but leaves it disconnected unless he's on the boat.  He's also on a mooring. I suggested that he check all of the wiring connections including the ground at the engine.

After reviewing this thread and our discussion yesterday, it appears that the mooring location of his boat does not afford him time for adequate charging from a dockside and the OEM alternator is not producing enough input amps to ever get his two T-105 banks up to a full or at least 80% charge.  Over the course of the season the banks are experiencing the "steadily diminishing law of return" (see reply #8 at: http://c34.org/bbs/index.php?topic=2143.0) and, hence, Ken needs to use BOTH to get his engine started.

The solutions (not necessarily mutually exclusive):

1.  Get a bigger solar panel and connect it for use during the week.  An 11 watt panel would be just barely enough to offset the wet cell drain, so the next larger panel would work.

2.  Install a larger alternator and new three stage regulator to maximize input amps to the banks.  (see Projects, Jim Moe's noted in the reply above and my Nov. 2006 Tech Notes Mainsheet alternator/regulator upgrade)  Consider relocating the alternator output from the 1-2-B switch to the house bank directly, using a relay (combiner or switch) to charge both banks.  With Ken's two equal T-105 banks, an echo charger would not be appropriate since it limits current to the second bank.

3.  Plug in more often - many times NOT an alternative because of cruising plans.

[Wayne]

I used to own a boat with a solar panel permanently hooked into the battery.  Worked great.  Never a problem with the battery; hardly ever even needed water.

[Footloose]

Ken,

We are in a similar situation in the we are at a mooring.  When we first purchased our boat I could not get it to start even with both batteries.  If you haven't replaced the terminals on the cables do that first.  It is cheap and easy.  Small amounts of resistance can be problematic at the high currents needed to start the engine.  It is similar to putting a kink in a hose and trying to get and trying to get a large volume out of the end.

The high output alternator with a three stage regulator is what we did next.  I don't have any scientific evidence that the regulators make any difference but they sure make a lot of sense to me.  The best analogy that I have is that it is similar to how we used to fill our gas tanks.  Pour it in like crazy when the tank is full and the slow down when you get to full so you don't over fill.  You can try to fill it at the slower rate but it takes much longer.

We have never gotten the solar panel (and I am probally going to hear about it).  The sun isn't very strong here in Vermont.

Generally we are on our boat three time a week or more during the summer.  I run the motor for a half an hour or so going out to top off the batteries.  If we are going out for a week I will motor for a couple of hours the first day.  I never need to have the switch on both to start.  We don't have a refrigerator but I do have a family that is not energy wise.  We will stay up playing cards or watching DVDs.  Last month we spent two days out without starting the engine.  On the third day the engine fired right up on the same three year old group 31 battery that we had been living off of.

Because we are hardly ever at a slip I installed a 10 amp three stage charger just to make me feel like I am getting my moneys worth after paying the big bucks. 

Finally you have to have some idea of your energy demands.  Ours are probally smaller than most, but you can be on a mooring and have a reliable starting system.