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Old 03-06-2017, 07:40 AM   #1
Obx
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Another Battery question

I have been schooled since I asked the 1st question on where to get a deal on a 8D battery,
Here is additional info and a question:: MY 89 42ft GB has 3208 TA's in it, the PO installed 8D GEL batteries in it for starting.
1 of the batteries is bad. I see that info is coming in talking about "make sure the charging system can charge GEL batteries".

My 3208 have the alternator that came when they were installed so if I go back with GEL or AGM am I messing up? also do the starting batteries get any other charge from anywhere or are they only charged when they are running.

I'm a newbie so I'm not familiar with the electrical system.
thanks
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Old 03-06-2017, 07:54 AM   #2
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I will never understand why people us 8D's for start batteries. A group 31 is more than enough in most cases. Check the manual.
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Old 03-06-2017, 08:18 AM   #3
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I use 8Ds for main starts and genset too. LAs though. Buy them cheap, battery boxes in place and great ballast. They have a separate charger from the inverter bank. Do the 8Ds make sense? Probably not but they sure do the job and redoing them to satisfy pundits isn't worthwhile.
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Old 03-06-2017, 08:25 AM   #4
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I've had premature failures of all battery types. Gel and AGM are sensitive to charging voltage. If the charging sources regulators do not specify GEL charging profiles, then very good chance of early death by overcharging.
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Old 03-06-2017, 09:41 AM   #5
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Quote:
Originally Posted by Obx View Post
also do the starting batteries get any other charge from anywhere or are they only charged when they are running.

Are the engine alternators the only charging source for your start batteries? Or do they also get charged by a separate charger too? These are key questions, much depends on (your) boat and how it was set up... so you'll likely have to figure that out before proceeding.

If latter, then probably more info required to understand the rest of your system. If former, then...

How long have the current gel starting batteries lasted? If long, then maybe your alternator charging is fine and you can go with gel should you choose to... or change to other alternative (flooded or AGM) if you choose that route.

I agree with folks who've suggested G31s instead, although your engines and starters will both have minimum cranking amp and reserve capacity (MCA/CCA/RC) requirements that you can look up and compare to candidate batteries. Maybe a pair of G31s could be required; depends. Either way, moving a G31 (or wven two, separately) is usually lots easier than moving one 8D.

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Old 03-06-2017, 09:45 AM   #6
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I will never understand why people us 8D's for start batteries. A group 31 is more than enough in most cases. Check the manual.
True...but my last 2 boats came with 2 8D batts, using one as a house bank too. One switch, utter simplicity till you need to lift one out/in.

But if setting up for cruising...I can see the switch to a dedicated start batt (group 31 if appropriate up or down) and a house bank of batts capable of deep cycling.
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Old 03-06-2017, 01:21 PM   #7
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True...but my last 2 boats came with 2 8D batts, using one as a house bank too. One switch, utter simplicity till you need to lift one out/in.

But if setting up for cruising...I can see the switch to a dedicated start batt (group 31 if appropriate up or down) and a house bank of batts capable of deep cycling.


If you have 2 x 8D, it is pretty easy to simply add a group 31 and echo charger. Then you have one larger house bank with a dedicated and isolation start battery.
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Old 03-06-2017, 01:42 PM   #8
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Because that is how the builder configured it

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I will never understand why people us 8D's for start batteries. A group 31 is more than enough in most cases. Check the manual.
I think most folks continue to replace batteries installed by the builder and subsequent owners.

Both of my engines have 8Ds. I will be rewiring things to start both engines off the same battery and use the additional 8D for the house bank.

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Old 03-06-2017, 02:32 PM   #9
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Obx:

Here is a quick tutorial on marine DC systems. But you really should get a copy of Nigel Calder's or Charlie Wing's book on the subject.

Most boats as delivered from the factory have two batteries connected to a 1,2,all switch. The simplest way to use them is one for start and one for house loads. Use the switch depending on what you are doing.

The batteries are charged either by a shore power charger which is often separately wired to each battery independent of the switch and the engine's alternator which is usually wired to the start battery but can be paralleled to the house battery with the switch.

Gel cell batteries were first developed for aviation use as they can be mounted in any direction and don't require water to be added. But they have a special voltage profile for charging that is different from flooded cell lead acid (FLA) batteries- the ones that have been around forever.

AGMs were then developed which have all of the advantages of gels, but their voltage charging profile is close enough to FLAs that most, well some- me, don't worry about it. But they cost 3 times what FLAs cost.

8Ds were developed to start 8-12 liter 18 wheeler engines and boat builder's just went with the flow. But as I said on your other thread and others have said here, 8Ds are too damn heavy to wrestle around in a boat and a good group 31 will start any engine installed in what we call trawlers. You can use an FLA or an AGM in this service.

I am going to call it quits now and not get on my soap box about all of the so called deep cycle batteries sold for marine use and all of the various combiner, ACR, Echo Charger solutions out there. Read one of those books to find out more.

So, back to your specific questions. If your engine alternators are stock then it is highly likely that they are not right for gel cells. So I would not replace then with gel cells. I would replace them with two group 31 FLA batteries. Most are sealed anyway so you don't have to worry about adding water and will last a long time. So save your money and buy them from Sams, Costco or one of the other recommended suppliers.

You also have a shore powered charger that charges these batteries. Those built in the last 10-20 years have a selection switch for Gel, AGM, FLA. Set it to whatever you buy, hopefully FLAs.

To know how your boat is wired beyond the simple explanation above, you need to hire a good marine electrician to walk through it with you. He can quickly confirm my theory that your Cat alternators are not right for gel batteries and also help you to understand how to keep the house batteries from running down at anchor and taking your starting batteries with them.

David
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Old 03-06-2017, 03:56 PM   #10
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If you have 2 x 8D, it is pretty easy to simply add a group 31 and echo charger. Then you have one larger house bank with a dedicated and isolation start battery.
Pretty easy...but not necessary for many boaters.

The more you cruise and anchor out the more you may want to complicate things to give you versatility and the ability to live off the grid. Much more complicated and better than what you suggest.

Many never do..... so 2 big batteries with 1, but generally 2 engines is as simple as you can get and get the job done with still the ability to conserve a start battery with enough juice to start 2 big, hard to start engines and have enugh amp hrs to spend a length of time, even the night off one big battery that is also dual purpose.

So many here are confused how their DC electric system is set up...the 2 battery and simple 4 position battery switch is as simple as it gets.
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Old 03-06-2017, 04:09 PM   #11
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DJ and PS
Thanks for the simple English on the" how this works" for batteries. I'm still learning this boats systems ie plumbing/elect/mechanical so I don't have everything down so I need answers to keep me from frying myself lol.
The PO installed a GEL 8D for each motor and the Genset and then has 2 group 31 for the house bank. I agree loading two group 31 is lighter than 8D and cheaper.

I'm going with what everyone has said and that is use 2 31 for cranking this motor.

Thanks to everyone for the ideas and answers.
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Old 03-06-2017, 04:16 PM   #12
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The PO installed a GEL 8D for each motor and the Genset and then has 2 group 31 for the house bank. I agree loading two group 31 is lighter than 8D and cheaper.

I'm going with what everyone has said and that is use 2 31 for cranking this motor.

Thanks to everyone for the ideas and answers.
Lee
That seems backwards. Are you SURE that the two group 31s are for the house bank?
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Old 03-06-2017, 04:44 PM   #13
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That seems backwards. Are you SURE that the two group 31s are for the house bank?
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Old 03-07-2017, 04:43 PM   #14
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I'll check when I get back to the boat this weekend but I'm pretty sure the 3 8D are for starting
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Old 03-07-2017, 07:58 PM   #15
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I'll check when I get back to the boat this weekend but I'm pretty sure the 3 8D are for starting
Yeah, generally you would use large, deep cycle batteries like the 8Ds for the house and the smaller group 31s for starting batteries. The group 31s would make a terrible house bank. Could be the PO may have reversed them accidentally at some point?
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Old 03-08-2017, 06:29 AM   #16
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". Could be the PO may have reversed them accidentally at some point?_"

Probably just a matter of selection with the rotary switches.
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Old 03-08-2017, 08:36 AM   #17
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I'll check this weekend when I get to the boat
Thanks for throwing that out there for me to check
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