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Old 30-09-2008, 07:46   #1
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Battery Selection Question

I would like your opinion of my proposed battery and charging selection in case I have missed something (I haven't used a boat battery in 12 years).

It is time to start thinking about the wiring aspects of my refit as I expect to start the rewire in a few months time. I am starting with an almost clean slate, the only electrical item in the boat is the 55 A alternator (Hitachi) which is new - part of the Yanmar 2GM20.

So first I have to chose the heart of the system - batteries (and charging).

The electrical loads are modest being LED nav and anchor lights, a couple of internal LED lights, compass light, sounder/log combined (Furuno smart transducer and RD 30 display), bilge pump, VHF and HF Coms, Radar, GPS and CD/AM/FM receiver

There is no chart plotter, watermaker or refrigeration. Primary self steering is windvane (with autopilot when motoring).

As the boat will not always have access to shore power when unattended for long(ish) periods, I have elected to fit AGM batteries for their limited self discharge characteristics with the bonus of having sealed batteries that I don't have to be able to reach to check electrolyte levels and add water etc.

Primary (perhaps only) charging will be via the existing 55 Amp Hitachi alternator. I plan to replace the internal regulator when an external 3 stage "smart" regulator. I am assuming I will be able to do this and I will be pulling the alternator apart next week to confirm this aspect. I am working on being able to extract 40 amps (semi-continuous) from the alternator for charging purposes.

Starting battery to be 50 to 70 AH capacity AGM which will be ample for the 1KW Yanmar starter motor.

House battery to be a AGM with a capacity of somewhere between 100 and 200 AH and probably either 150 AH or 200 AH depending on room, costs (and your opinions ).

Perhaps I will fit a battery combiner but more likely just standard manual 1/2/both switch. I prefer having the manual control as I thinks it helps with general all round situation awareness of the vessel's systems. Having said that, I have, at times in the past, forgotten to change over to the house battery after recharging the starting battery

Have I missed something basic or is there a better solution for my proposed needs?

Can anyone recommend a good external "smart" regulator (and perhaps a good battery combiner - if I go that route)?

Should I fit SLA (not AGM) batteries and a small solar panel to provide trickle charging to overcome their inherent self discharge?

BTW, although I have always had solar panels in the past, I have elected not to go that way this time for cost and space reasons. Also, my electrical loads are much more modest this time around due to LED's and no refrigeration.
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Old 30-09-2008, 08:32   #2
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For what it's worth, I tossed those red 1-all-2 switches because they leak and will over time drain both batteries even if you are on 1 or 2. I know, happened to me. Took it out and put a meter on the terminals to prove my theory. If you aren't near help that sucks.

Blue Sea Systems has better switches and I have never had a battery issue since buying from them. Just a personal experience to share.

I have no experience with AGM batteries but I do know getting 90% of rated output from an alternator doesn't happen for long.
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Old 30-09-2008, 10:19   #3
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I am a fan of AGM's but in your case I think you will get reduced life since you will not be able to fully charge them to 100% regularly. I'd go with wet cells in your proposed set up. A nice big 8D or a pair of T-105's would allow you to make good use of your alternator and be more tolerant of abuse.
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Old 30-09-2008, 13:12   #4
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"SLA (not AGM) "
SLA, sometimes called Sealed Valve Regulated (SVR) and other names, mean AGM and Gel.
Instread of "SLA not AGM" why not just say "gel" if that's what you mean?

There are still some gel fans out there but the world (telecom backup supplies, etc.) has mainly abandoned gel in favor of AGM. Higher energy density, conventional charging voltages (or real close to them), and companies that literally buy them by the truckload for backup power installations, seem to believe the story that they are better in every way--except of course, cost. Wet lead is still the cost leader, if you don't mind splashing acid around.
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Old 01-10-2008, 01:31   #5
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Originally Posted by CaptHead View Post
.......
I have no experience with AGM batteries but I do know getting 90% of rated output from an alternator doesn't happen for long.
Thanks for the info on switches. As to the alternator, I was expecting it to perform reasonably at 73% load but I understand what you are saying about running at 90%.
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Old 01-10-2008, 01:45   #6
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Originally Posted by camaraderie View Post
I am a fan of AGM's but in your case I think you will get reduced life since you will not be able to fully charge them to 100% regularly. I'd go with wet cells in your proposed set up. A nice big 8D or a pair of T-105's would allow you to make good use of your alternator and be more tolerant of abuse.
If I understand you correctly, you are suggesting that as I won't have regular access to shore power, I won't be able to fully charge the AGM's on a regular basis.

I admit to zero experience of AGM and charging - I was thinking (but don't know) that with an external smart regulator and the alternator that I would come close to fully charging them. However that is why I am seeking your experience and knowledge.
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Old 01-10-2008, 02:11   #7
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Originally Posted by hellosailor View Post
"SLA (not AGM) "
SLA, sometimes called Sealed Valve Regulated (SVR) and other names, mean AGM and Gel.
Instread of "SLA not AGM" why not just say "gel" if that's what you mean?

There are still some gel fans out there but the world (telecom backup supplies, etc.) has mainly abandoned gel in favor of AGM. Higher energy density, conventional charging voltages (or real close to them), and companies that literally buy them by the truckload for backup power installations, seem to believe the story that they are better in every way--except of course, cost. Wet lead is still the cost leader, if you don't mind splashing acid around.
Bear with me Hellosailer, I am on a steep learning curve with current battery technology (no pun intended). Last time I messed with batteries, you could get FLA or FLA and as for alternators, the only options were standard regulator, raising charging voltage by way of the diopde trick or running an external reostat to manually control the field current and therefore output voltage (and by default, charging current). I had a switched system where I could manually control the field current or revert to the regulator .

The "SLA (not AGM)" is what the battery dealer told me, I wasn't sure if he meant Gel or something else. The next battery dealer offered AGM and "Maintenace Free FLA". These weren't sealed (or valve regulated), rather they were FLA without any access to the cells. Supposedly had extra volume for acid and some way to "help" keep the acid (water?) from escaping when charging. He also told me that there were no conventional FLA deep cycle batteries around anymore. You either used "maintenace free" ones or AGM.

Not sure where I am at the moment but all information is helpful (I think ).

One concern with FLA is the potential for sea water to enter after capsize and thus produce Chlorine as the only place I can fit the batteries are inside the cabin with this boat.
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Old 01-10-2008, 04:29   #8
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Seems like you should be looking at some kind of auxiliary charging system irrespective of the battery type - though I would agree that AGM is the way to go, especially if you're "living with it" at close quarters, as it were.

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Old 01-10-2008, 05:11   #9
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You might look at the threads on batteries we already have. Each battery type has a charging profile. The rate you can add amps based on the discharge state. AGM's use a different profile so treating one battery type with a wrong profile leads to problems that shorten the lifespan of a battery. Mistreatment always means they wear out faster.

This is easily solved by using a proper regulator that can control the charging rate throughout the charging cycle.

The bigger issue for all battery types is getting the battery fully recharged. The more batteries you have the more recharging you need to do. Having too many batteries makes the problem worse not better. Charging back the last 10% is pretty hard to do with an alternator. You would normally not discharge any battery to less than 50% of capacity to get the longest life. That means you take the daily amp hour total and see if that is within the battery bank capacity of 90% - 50%. The plan is you would use 40% per day and recharge to 90% everyday. At 90% capacity the acceptance charge rate is down to several amps. AGM's can take more amps faster than other types but even AGM's at 90% capacity is not as high a rate as when at 50% capacity.The last mile as it were is the longest for all batteries.

In this way 2 group 8D batteries might have a whole lot more power but the day won't be long enough to recharge the batteries the way you operate and you will be using a zone of maybe 70% to 50% over time. The problem of not getting them fully charged is worse when your battery bank is too large. Your last mile is a lot longer. Batteries can be "equalized" with a shore power charger over a longer charge period. This can seemingly bring back capacity since you end up at a full 100% capacity when it's over. You might want to do that every 2 or 3 weeks with anything you have aboard.

From what you describe your daily load it looks to me like 1 group 4 AGM would provide all you need OR two golf cart 6 volt batteries like a Trojan T105. You would then add a marine starting battery on a combiner. If you add a fridge you'll need to double the bank size. Your alternator may be adequate but it's not overly adequate. Cooing is a problem with alternators. They have to run pretty hard to recharge a battery bank. The heat eventually wears them out. They get less efficient as they get hot and that makes them get hotter. They become a toaster and the repeated heating just makes them die quickly.

Quote:
One concern with FLA is the potential for sea water to enter after capsize and thus produce Chlorine as the only place I can fit the batteries are inside the cabin with this boat.
I'm not sure of many boats that keep batteries any other place except large ones within an engine room. Not everything possible is worth laboring over. FLA batteries need containment and easy access since fluid levels have to be monitored. They also should have venting since the problem of Chlorine while it may be possible is not as serious as sulphuric acid that vents and can corrode those things near over time when you are upright every day. Being cooler means that they accept charge at a higher rate too! AGM's have all the advantages except cost. There is a tendency to deride those things that cost more as not being better in order to believe the cheaper product really is better. Such is the case with AGM's.

All batteries must have a proper regulator for the charging profile management based on the type. Your batteries are not like the ones in your car that use a dumb regulator that works well enough for a car starting battery. Deep cycle batteries are very different.

If you search the archives you can find several whole system plans that have been discussed by some of the more electrically blessed members. Use the new search tool. We now have a Google style search engine connected with the last software upgrade. This subject has been covered a lot.
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Old 01-10-2008, 05:19   #10
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Don’t forget the “brains” of the system which is a smart battery monitor, so that whatever you start with you are able to see if that is a good solution in both capacity and charging, by monitoring the State of Charge and voltage levels during the cycles.

I just redid mine and went with AGM because they are installed under the dinning area where I got fumes in the past. Also I wanted to increase Ah capacity, which I could …if I did not need to regularly service them.

My advice is to get as much Ah for house load as you can practically fit so that the % deficit is as small as possible in one user’s cycle. That means you can charge back faster at higher voltage, because you are doing mostly surface charging rather than deep charging.

Not sure if the experts would agree, but I am testing out the system and it seems to support that a low deficit will charge back proportionally quicker.


p.s Paul I note we seem to differ and as I am doing cycle tests at the dock, I will know when it is done
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Old 01-10-2008, 07:37   #11
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If I understand you correctly, you are suggesting that as I won't have regular access to shore power, I won't be able to fully charge the AGM's on a regular basis.

I admit to zero experience of AGM and charging - I was thinking (but don't know) that with an external smart regulator and the alternator that I would come close to fully charging them. However that is why I am seeking your experience and knowledge.
Some time ago I got into a discussion with Rick over economical advantages versus other advantages of AGM versus flooded. In post #27 of thread
AGM?
Rick has a warning about AGMs.

Rick is definitely an AGM fan, but says don't bother with AGM, unless you can keep them topped off properly. In your application IMO this means at least enough solar to maintain a proper float charge using a smart controller.

John
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Old 01-10-2008, 07:50   #12
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Rick is definitely an AGM fan, but says don't bother with AGM, unless you can keep them topped off properly
You have the same problem with flood batteries too. They do need full charging or they need regular equalization. Using a flood battery charge profile with AGM's is not a good thing. I had AGM's on the last boat because I had the right charge controller. The current boat would require some all new expensive controllers since the controller I have now also handles the solar panels and the alternator. I went back to golf carts because the charging system would not support an AGM profile.
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Old 01-10-2008, 08:48   #13
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Thanks to All, especially to Paul

Thanks everyone for taking time to comment - I appreciate it.

After reading ALL the battery, regulating and charging threads back to 2004 on CF, reading quite a few manufacturers websites and your current replies I think I can make the following generalizations between FLA and AGM batteries:
  • FLA self discharge much faster than AGM
  • FLA are quite a bit cheaper than AGM
  • If left idle for any time, both should be fully charged
  • Both will fail early if left dischaged (or partially discharged) for any length of time
  • If correctly charged, AGM will have much longer life
  • AGM requires no other maintenance other than a very good charging regime

So if I can't assure a good charging regime, I am better off killing cheaper FLA's.

If I can arrange a good charging regime and can afford AGM's (and associated equipment to charge etc), then the AGM's have a much longer lifespan and are "maintenance free"

Am I close to the mark?
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Old 01-10-2008, 10:38   #14
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I would say you are very close. The devil is left in the details of how you do all the connections and other details.
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Old 01-10-2008, 18:36   #15
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Quote:
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I would say you are very close. The devil is left in the details of how you do all the connections and other details.
Thank goodness the actual details of connections, layout, general wiring won't be a problem in my case given some 35+ years in the avionics industry.

What was lacking for me was any real knowledge or experience of modern battery technology and charging methods, especially in a cruising application - again thanks to CF, this is slowly been addressed.

FWIW, In my telecommunications days in the 70's, I still remember installing 50 V, 2,000 AH FLA battery banks that we charged at 200 Amps and floated to 2 decimal places. When you have a room full of gassing 2 volts cells (that each takes two people to lift) and hundreds of amps moving through uninsulated copper bussbars, you get to real careful with tools and sparks . Working in the battery rooms meant destroying a set of clothes per week. Nowdays I am more used to big NiCad's that also need careful handling.

Thanks again all.
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