Size of Battery Charger

[Cpt Pat]

You're being "upsold" by the sales guy.

I have two battery banks: 200 A/H of Odyssey batteries, and 200 A/H of Lifeline batteries.

When cruising, I keep them charged with solar panels that output 20 amps MAXIMUM. 20 amps will charge all 400 A/H to 100% just fine. All I need is a little patience and frugality. I've been doing this for 2 years now with no loss of performance.

As long as your charger is able to produce more than the self-discharge current of the batteries (which should be very small), you will eventually recharge the batteries. It's just a question of how long you are willing to wait.

There is a maximum charge current rating for your batteries, but no minimum.

[twinboat]

The point of paying 3 to 4 times as much for AGM's, as Lead Acid, is to reep the benefets of them.
One of the benefits is that they can charge up faster, but you need a big charger to do that.
If you are not doing that, then the other benefit is, not having to check and maybe add some water every month. I decided to deal with that.

I feel that the upsale started with the batteries.

[Capt Alfex]

Originally Posted by twinboat

Amp output from a charger and Amp Hours in or out of a battery are 2 different things.

If you have 600 Amp Hour bank and you want to charge it at C/10 then you need a 60 "AMP" charger.

If you run down your battery bank to 80% then you need to replace 120 Amp Hours.
That mean you need to run your 60 AMP charger for 2 hours to replace 120 Amp Hours.
That is the simple explanation. Of course it will take longer because the charger Amp rate drops off after the battery nears full charge.

Well said twinboat.

Odyssey® make batteries that "try" to be both a deep cycle and a start battery. This is fine for most inshore, weekenders and marina hopping boaters. They don't make a "golf cart" size battery at all! Most coastal and offshore boaters use "golf cart" batteries for their house banks. As has been discussed, no one makes a 200 amp charger. So you can never have an Odyssey® based house bank larger than 400 Ah. 400 x 40% = 160 Amp charger.

Many long term (away from dock) boater house banks are in the 500-1000 Ah size. These boats use 100 A chargers and alternators as standard equipment. These house banks would take 5-8 hours to recharge from 50% depending on lots of variables. We keep our batteries (lead-acid) between 60-90% when underway and anchoring. Takes too long to charge that last 10%, so why bother.

Many posters have already stated they have had no problem using smaller than recommended chargers so this 40% "requirement" is obviously not required, just nice to have and brings out the full potential of these batteries.

[Patacha]

Originally Posted by twinboat

If you run down your battery bank to 80% then you need to replace 120 Amp Hours.
That mean you need to run your 60 AMP charger for 2 hours to replace 120 Amp Hours.
That is the simple explanation. Of course it will take longer because the charger Amp rate drops off after the battery nears full charge.

Apologies for my confusion, and thank you Twin for noticing.

To avoid future confusions, I suggest we use the SOC SOD acronyms (state of charge/discharge); 80% SOC is 20% SOD :-)

[Cpt Pat]

Originally Posted by twinboat

The point of paying 3 to 4 times as much for AGM's, as Lead Acid, is to reep the benefets of them.
One of the benefits is that they can charge up faster, but you need a big charger to do that.
If you are not doing that, then the other benefit is, not having to check and maybe add some water every month. I decided to deal with that.

I feel that the upsale started with the batteries.

In a sailboat, there is one other BIG advantage to AGMs: they don't leak electrolyte when they are tilted. Sailboats heel and they sometimes even end up inverted for short periods (one tries to avoid that, but it does happen).

And if there's any flooding, battery electrolyte (sulfuric acid) and seawater don't play well together. Ask any submariner about that. I don't like the idea of having to abandon my otherwise intact sailboat because it is now filled with poisonous gas.

The proper way to mount flooded conventional batteries in a sailboat is to place them in a big tub that pivots when the boat rolls so they are always horizontal. In my boat, there's no room for that. For the same money, weight and space, flooded batteries do offer more capacity. But now that AGMs are available, flooded batteries really have no place in a sailboat that doesn't have a proper pivoting mount. And for me, the cost of providing that space is greater than the cost differential of the AGMs.

[Patacha]

I feel lucky to own a Catamaran...

[Cpt Pat]

By the way, the problem of lead-acid batteries producing chlorine gas has been known for some time. Here is an article from 1915 quoting no less of an authority on the topic than Thomas Edison:

DEADLY GAS IN SUBMARINES. - Edison Calls Attention to Danger When Lead Batteries Are Used. - View Article - NYTimes.com

It takes a great deal of pressure to force seawater into an AGM battery (enough that the vessel will have already sunk), but no pressure at all to cause seawater to react with the electrolyte in a flooded battery.

[Cpt Pat]

Originally Posted by Patacha

I feel lucky to own a Catamaran...

True. They don't heel - they just capsize and turtle...

[Patacha]

Originally Posted by Cpt Pat

True. They don't heel - they just capsize and turtle...

[sailinglegend]

Just to clear up a few confusions - or maybe add some more?

If a battery manufacturer recommends C/5 or 20% of the full capacity for the charging rate then that is the rate going into the batteries. It would be better to go to a Charger or Alternator that can deliver C/4 or 25% of C to account for the current going to boat loads and the losses in the cables.

AGMs don't need the extra high charging current to charge faster - that's a real bonus if you do have a large charger - they charge faster than other batteries anyway because their charge efficiency is much better. To put 100Ah into a FLA battery bank may take as much as 130Ah. To put 100Ah into an AGM bank may only take 102Ah. So they charge 30% faster with the same charger. If I had a huge charger and put the maximum I can into my Lifeline AGMs - that is 5 X C - 500 amps into a 100 Ah battery - then they charge even faster. That rate is only maintained for a short while, but they will then settle at 40% of C. Btrafors produced some graphs that showed a C/2 or 50% charger would raise a bank to 80% in 30 minute - a C/5 or 20% charger would take over 70 minutes. That's twice as fast to add to the 30% increased charging speed you get anyway. So AGMs do have a place on a boat even with a normal charger. A bigger charger will keep AGMs happier and give even more value for money with even faster charge times.

If you only go into a marina for one night to recharge batteries then a small shorepower charger may not do the job. If you have an AC genny then a bigger charger will cut down on the genny run time. A 30 amp charger will require the genny to run three times as long as a 100 amp charger.

[goboatingnow]

Originally Posted by sailinglegend

Just to clear up a few confusions - or maybe add some more?

If a battery manufacturer recommends C/5 or 20% of the full capacity for the charging rate then that is the rate going into the batteries. It would be better to go to a Charger or Alternator that can deliver C/4 or 25% of C to account for the current going to boat loads and the losses in the cables.

AGMs don't need the extra high charging current to charge faster - that's a real bonus if you do have a large charger - they charge faster than other batteries anyway because their charge efficiency is much better. To put 100Ah into a FLA battery bank may take as much as 130Ah. To put 100Ah into an AGM bank may only take 102Ah. So they charge 30% faster with the same charger. If I had a huge charger and put the maximum I can into my Lifeline AGMs - that is 5 X C - 500 amps into a 100 Ah battery - then they charge even faster. That rate is only maintained for a short while, but they will then settle at 40% of C. Btrafors produced some graphs that showed a C/2 or 50% charger would raise a bank to 80% in 30 minute - a C/5 or 20% charger would take over 70 minutes. That's twice as fast to add to the 30% increased charging speed you get anyway. So AGMs do have a place on a boat even with a normal charger. A bigger charger will keep AGMs happier and give even more value for money with even faster charge times.

If you only go into a marina for one night to recharge batteries then a small shorepower charger may not do the job. If you have an AC genny then a bigger charger will cut down on the genny run time. A 30 amp charger will require the genny to run three times as long as a 100 amp charger.

Well have a look at http://www.trojanbattery.com/tech-su...selection.aspx

AGMs have about an 8-12% improvement in charge efficiency , mostly in absorption phase. They also typically have 10-20% capacity reduction, weight for weight and case size. They are in fact not optimised for deep discharge applications and can exhibit early death from poor charging regimes especially if not regularly returned to a100% charge.

They therefor are suitable for the weekend sailor. Light duty use and back on the shorepower on Sundays.

Of course then there is the cost premium

They have low self discharge , so one other group of users might bebefit , ie thosevthat leave the boat unused with no float charger might find them useful.

Electrolyte spills and chlorine gas etc is all a bit of nonsense. Submarines had vast banks of batteries and had real flooding risks. Sailboats have a couple of Small batteries.
Ordinary lead acids batteries cant work on their side , but electrolyte spills are very slow and in most cases hardly any seeps out

For deep cycle marine use, good quality , preferably tubular , flooded accessible LA batteries are best . The premiums paid for AGMs are far better deployed buying higher quality flooded batteries

Dave

[ranger58sb]

Didn't mean to help spur side discussion of AGM versus other battery types.

I think I'm deciding "it ain't broke" for our situation. We are indeed "light duty" coastal cruisers, but mostly that means we're tethered to marinas most of the time (for now). And the "too-small" 40-amp charger seems to do fine, even when we've been lucky enough to anchor out for 3-4 days at a time.

I'll eventually upgrade the charger, but probably only to a 60-amp version, when that bubbles up to the top of my wallet. If that means I can full recharge the battery banks in 3 hours instead of 4... whoop-de-doo. In the meantime, our oldest AGM bank is going on 8 seasons old, seems to be fine, no problem. (With a "too-small" 40-amp charger.) And I don't have to deal with the pain from contortions required to check our batteries all the time.

-Chris

[Patacha]

Originally Posted by goboatingnow

Electrolyte spills and chlorine gas etc is all a bit of nonsense. Submarines had vast banks of batteries and had real flooding risks. Sailboats have a couple of Small batteries.
Ordinary lead acids batteries cant work on their side , but electrolyte spills are very slow and in most cases hardly any seeps out

For deep cycle marine use, good quality , preferably tubular , flooded accessible LA batteries are best . The premiums paid for AGMs are far better deployed buying higher quality flooded batteries

Dave

I second that, Gobo.

Thuogh the Chlorine issue is not nonsense, it is a marginal, theoretical and somewhat on the paranoid side factor for our small crafts.

I myself am an avid fan of Flooded batteries.

[sailinglegend]

Originally Posted by goboatingnow

Well have a look at Trojan Battery Company.....They therefor are suitable for the weekend sailor. Light duty use and back on the shorepower on Sundays.
...........

Dave, you are looking at a Trojan site - they say "generally" and then offer their thoughts - based on their batteries. Trojan are good, but look deeper into their AGM range.Their "OverDrive" batteries are described by them as true Deep Cycle.

You guys out there who continually knock AGMs without knowing the facts need to get out a bit more. May I direct you to the Lifeline AGM site and suggest you download their 37 page AGM manual.

http://www.lifelinebatteries.com/manual.pdf

Remember - NOT ALL AGMs are the same. Some are designed as starter bats, some as dual purpose, some as Telecom and Solar standby bats, and others like Lifeline are designed for long life and are robust enough for repeatedly falling off 3 metres waves.

We have been permanently living aboard our 42ft Hunter Legend for the last 7 years and our AGMs are now in their 10th year.

[Cpt Pat]

Originally Posted by sailinglegend

To put 100Ah into a FLA battery bank may take as much as 130Ah. To put 100Ah into an AGM bank may only take 102Ah.

An excellent point! My solar array cost $1,000 and is just enough to replenish my AGM batteries. If I substituted flooded cells, I'd have to spend $1,300 to accomplish the same task.

Actually, since I have no more space for PVs on deck, I'd need a larger boat, which would cost a lot more.