Size of Battery Charger

[Stu Jackson]

Chris, I don't know what analog gauges you have, most likely amps and volts. Neither will tell you without a battery monitor or reading time and amps. Try read the Battery Acceptance link I provided. Less than 37 pages - yeah, I know it wasn't you.

[ranger58sb]

Originally Posted by Stu Jackson

Chris, I don't know what analog gauges you have, most likely amps and volts. Neither will tell you without a battery monitor or reading time and amps. Try read the Battery Acceptance link I provided. Less than 37 pages - yeah, I know it wasn't you.

Yep, correct, one for amps and one for volts on each bank. When I really want to know, I go down below and use the multi-meter, and just did that yesterday after 4 hours rest from charging. 12.84v.

When I get around to doing the upgrade, I'll also include a real battery monitor.

Thanks for posting the links

-Chris

[Cpt Pat]

Because they have lower effective series resistance, expressed as their Peukert exponent, AGMs recharge faster and require less energy to recharge.

Here's a comparison. Taking two batteries, each rated at 105 AH (20 hour discharge rate), here are the Peukert exponents:

Trojan model 27TMX: 1.24
Lifeline model GPL-31T: 1.11

(A "perfect" battery would have a Peukert exponent of 1.00.)

Assuming you have a limited and modest amount of recharge current available, the Lifeline AGM will recharge in 90% the time with the same charge current, and require 90% the amount of energy as the same capacity Trojan flooded battery to recharge. The difference becomes even more dramatic with larger batteries. In the size I'm using, it's a 30% difference after factoring in the self-discharge rate that's 30 times greater in flooded batteries. If I used flooded batteries, they would eat up 10% of my solar array capacity in just self-discharge drain.

Because they waste less energy in effective series resistance (heat), the AGMs can also accept a much higher charge current compared to flooded batteries. That doesn't factor in with my implementation however since I can't generate anywhere near that amount of current. It would be a factor for anyone using a large current capacity charger or alternator.

But... you have to know what you're doing with AGMs since you can't just pour in more water to correct your mistakes. As we say in the computer business: RTFM! Read The Freakin Manual.

[pbiJim]

Originally Posted by Stu Jackson

Sure, and one's on acceptance, too

AGM Battery Issues (from Maine Sail)
AGM Batteries - Making The Choice - SailboatOwners.com

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
Darn AGM Batteries - SailboatOwners.com

That was a pretty interesting read. Thank you for that.

Do you, by chance, have links to similar information on gel cells?

Thanks,
Jim

[goboatingnow]

Originally Posted by Cpt Pat

Because the charge efficiency of AGMs is greater than flooded batteries. That's because - digging deep into the physics of batteries - AGMs have a lower Peukert exponent. Peuket's law applies to both discharging and charging lead acid batteries.

A larger percentage of recharge energy returned to a flooded battery is converted to heat, and so, a larger solar array is needed to recharge flooded batteries of the same capacity. Given the costs of both money and space for a solar array, the savings in using AGMs is substantial for those of us who don't have or don't want to use engine-driven alternators. You also save fuel if you do run the engine to recharge AGMs, but the offset isn't as obvious.

I recommend reading this very excellent document for a detailed description of all the other variables: Battery Types: Flooded versus AGM and Gel.

Peukerts law and his exponent only apply to discharge cycles.

The charge efficiency of aGMs over similarly priced flooded LA is about 8-10 % , and primarily in absorption phase , not enough to make any significant differences to charging economics.


Equally the requirement to return to 100% means longer is spent actually charging AGMs.

Any engineering review ( like the links specified ) will show you AGMs are the wrong fit for boat domestic s
Dave

[Stu Jackson]

Originally Posted by pbiJim

That was a pretty interesting read. Thank you for that.

Do you, by chance, have links to similar information on gel cells?

Thanks,
Jim

Jim,

You're welcome. Specifically on gel cells, no, sorry. IIRC, there was mention of them in Maine Sail's post. The "issue" with gel cells is that they require, require, don't just like but require, a much lower charging voltage. This "may" be difficult for some alternators to accomodate without an external regulator like a Balmar MC-614 or even an ARS5, which can adjust the voltages as long as the battery sense wire is run to the house bank (as should all installations with external regulation). Also, IIRC, gel cells are "less popular" these days because for long distance cruisers they "may" be less available when something breaks.

The real "issues" and comparison is simple between wet cells and AGMs:

-- safety - true or a perception if knocked down
-- acceptance/charging - yes AGMS are "better" but require a support system to assure regular back to 100% SOC
-- ability to completely recharge regularly to avoid sudden and catastrophic failure without warnings

Like everything else in boating:

Your boat, your choice.

[pbiJim]

Originally Posted by Stu Jackson

The real "issues" and comparison is simple between wet cells and AGMs:

-- safety - true or a perception if knocked down
-- acceptance/charging - yes AGMS are "better" but require a support system to assure regular back to 100% SOC
-- ability to completely recharge regularly to avoid sudden and catastrophic failure without warnings

Like everything else in boating:

Your boat, your choice.

My big issue with a sail boat battery is that I want something spill proof. I'm the type of idiot that goes out even when things are rocking & rolling a little more than most people feel comfortable with. To somewhat complicate things, I'm not going to have a monster charging system & I really don't want to invest a lot of money in a fragile solar system if I can possibly avoid it.

That leaves me still scratching my head a little. I may work on better containment for a flooded battery. I may bite the bullet & get a small solar system to top off an AGM. I may take the time to learn more about gel cells. I may just get a cheap sealed battery & accept that it will not last that long.

Decisions, decisions, decisions. At least I'm starting to improve my knowledge base a little so that my decision making can be a bit more informed.

This read has been very useful for me. My previous experience with AGM batteries was limited to a single use on a motorcycle & my previous assumptions and conclusions about AGM based on that experience, now appear to be a bit off. I am now guessing that the characteristics of a small starting AGM may be far different from the characteristics of a deep cycle AGM.

At the same time, I'm also doing some similar research on electric forklift batteries for a different project. There are some parallels, but those too seem to be a bit of their own phenomenon. For one thing, they get drawn down to 20% charge as a planned standard daily practice. They also get equalizing charges about every 10th cycle & they tend to last for more cycles than boat batteries do.

I think that I still have a lot more reading to do, but this information looks to have provided a useful piece of the puzzle for me.

Thanks again,
Jim

[goboatingnow]

Tubular traction batteries , like some forklifts , would be excellent , if only for the price. For my bet , outside a Li ferrous bank the next best thing are single cell tubular traction batteries

Dave

[btrayfors]

Interesting discussion.

Here's a little meat for chewing, based on actual AGM research and measurements:

1. AGMs can indeed accept a LOT more charging current than can flooded or even gelled batteries;

2. AGMs have less internal resistance and therefore less loss due to heat during the charging process; that means that they are more efficient in accepting charge current.

3. No matter the size of the charging current, AGMs still take many hours to reach 100% state-of-charge (SOC) due to lower charge acceptance as they come up to high SOC. And, we know that it is very important to reach this 100% SOC frequently with AGMs to avoid much shortened life.

What can we glean from these facts?

That AGMs are a better bet for most boaters? NO, not at all. In fact, for many boaters they may be a bad choice.

That AGMs are cheaper to recharge, due to their higher charge acceptance and lower internal resistance/increased charging efficiency? YES, this is true up to a point. It is particularly true during the part of the charge regime between about 40% - 80 or 85% SOC, as in the case of most cruising sailors when not connected to shorepower or without large solar/wind generator power.

These benefits (better charging efficiency and higher charge acceptance) are only really capitalized upon IF YOU HAVE A VERY SUBSTANTIAL CHARGING CAPABILITY.

Look at the following charging curves for four different size chargers. The graph shows charging current (battery acceptance rates) during the first two hours for a battery which was discharged to 50%SOC.



The next graph shows an estimate of how much capacity has been restored during charging, with three different size chargers.

You can see that with a large enough charger, a great deal of energy can be restored to the battery in just 30-60 minutes. Most boats have only a 10% of CA charging capability, though. That would be a fourth line much lower than the other three.



No way in hell flooded batteries can do this quick charging up to about 80% SOC, no matter how large your charging capacity.

BUT.....there are lots of factors in play here, and the fact is most boats with AGMs simply are not set up to take maximum advantage of their unique capabilities.

Having been involved in battery research for several years now, what would I choose?

Easy peasy. Last week I just put six new $99 flooded golf cart batteries and one $109 group 31 flooded starting battery aboard my boat :-)

Bill

[pbiJim]

Originally Posted by goboatingnow

Tubular traction batteries , like some forklifts , would be excellent , if only for the price. For my bet , outside a Li ferrous bank the next best thing are single cell tubular traction batteries

Dave

Dave,
Enlighten me please. What is a tubular traction battery?

Thanks,
Jim

[goboatingnow]

Originally Posted by pbiJim

Dave,
Enlighten me please. What is a tubular traction battery?

Thanks,
Jim

Cells are designed for deep discharge , with tubular plate construction , google is your friend

Dave

[zboss]

So,

I have also done some research since I last wrote.

With 500 amp hours of either AGM or Wet Cell we would need either a large alternator or a large charger or both.

In any case, based on a new calculation of available battery space we are limited to either (4) T-145 Plus Trojans with a total of 520 AMPS or (4) GPL-31XT Lifelines with a total of 500 AMP hours.

We anticipate using about 40% of our available battery capacity on a daily basis - 200 AMPS.

So we have decided that since we anticipate being a close proximity to the US for the next few years that we should learn toward AGM's. So in the end, we will be looking to equip the boat with:

a) 280 watts of kyocera solar power (2 x KD140SX-UFBS) with MMPT chargers TBD (blue sky maybe)
b) Balmar 200 AMP Alternator and MC-614 Regulator
c) Wind Generator (maybe, currently have a non-functional Four Winds II) - with a 200 AMP alternator I can produce as much amps in 20 minutes as I would generate with the wind gen all day long and do it will much more regularity.
d) Charger - 100 AMPs for sitting at the dock.

Originally Posted by btrayfors

Easy peasy. Last week I just put six new $99 flooded golf cart batteries and one $109 group 31 flooded starting battery aboard my boat :-)Bill

Which batteries did you go with?

[btrayfors]

Originally Posted by zboss

................

Which batteries did you go with?

Crown Batteries (made in Ohio). From Steven's Battery Warehouse in Annapolis.

Bill

[sailinglegend]

Originally Posted by goboatingnow

Peukerts law and his exponent only apply to discharge cycles.

I think Cpt Pat's post that you shot down was absolutely correct.

Peukerts effect does apply during charging but it is impossible to calculate or quantify. So a lower (AGM) Peukert value makes charging more efficient.

Any increase in charging efficiency during bulk stage must be worth having - especially if running an engine or generator.

FLA batteries NEED decent charging facilities and NEED to get back to 100% regularly - but many boaters don't bother - just equalize later. If an owner appreciates these points then AGMs (Lifeline's can also be equalized) are very good for him.

Some quotes from the SmartGuage.co.uk site:

There are 3 separate effects that combine to produce Peukert's effect:-
A. The resistance of the battery due to the interface between the plates and the electrolyte.
B. The resistance of the electrolyte itself and......
C. The bulk resistance of the electrolyte due to the bubbles being produced within it.
These three effects combine to produce the overall Peukert's exponent for a particular battery.

The three effects also apply during charging. But they are impossible to calculate because of the way charging causes the chemicals reactions to take place. Yet the effects can be dramatic.

[colemj]

Originally Posted by zboss

b) Balmar 200 AMP Alternator and MC-614 Regulator

What size engine do you have? A 200A alternator is going to require a serpentine belt and will lug down smaller engines. If your engine is less than ~75hp, you may want to research this a bit if it is to be a primary charging method.

Mark