Battery Charging Questions.

[sww914]

We have a lot of watts of solar and we use a lot of electricity. If it's sunny we have no problems but if it's cloudy we run out of juice. We can cut back on usage but when the weather report says the gray will burn off in the afternoon and we use all we want but then it stays overcast all day, we have problems. I very much prefer having an entirely seperate starting battery so that I can use the engine after it's been cloudy and we've wasted electricity to recharge before the fridge dies and our food spoils or say the anchor drags and we need to move fast, well the engine is good for that too.
I am not a fan of Optima batteries. 4 times in a year I had a customer bring me a good used (ran when I parked it) Optima battery that was junk after sitting for a couple of months. I wasted an hour or two installing and charging these junk batteries by marrying them to a lead acid battery so that the charger could sense a draw and then allegedly charge the Optima garbage, but it never worked and just wasted my time and my customer's money.
Once an Optima goes dead it's a door stop. You'd think they were made in England.

[noelex 77]

Originally Posted by Adelie

I just did a Google search for "agm vs flooded battery life". On the first 5 pages these are the sites I found that were not trying to sell batteries.

FLA AGM Battery Life Span - Moderated Discussion Areas
AGM Absorbent Glass Mat (AGM) Battery Information - Battery University
FLA http://www.pureenergysystems.com/PES...el-battery.pdf
FLA http://undercurrentaffairs.com/survi...ry%20types.pdf
FLA About RV Batteries
AGM AGM battery takes primary role for idle stop-start in microhybrids - Vehicle Electrification - SAE
No direct statement- Frequently Asked Questions - Batterytender.com

This site indicates that flooded gets better cycle life than gel or AGM at the cost of regular maintenance. However although the site is an alternative energy emag, the actual answers were from an interview with Trojan battery employees:Alternative Energy eMagazine - Batteries for Alternative Energy Systems | AltEnergyMag

This site was a reference for the Wikipedia article that appeared in the first 5 pages:
FLA Sterling Power Products: What is the best battery to use for an auxiliary charging system?

This site indicates that Gel gets more cycle life than AGM when cycled deeply (>80%DOD): Battery Tutorial | ChargingChargers.com

The count was about 6 to 2 that FLA gives more life cycles.

The technician's comments from the first site listed are consistent with my experience as an engineer, just because something is advertised as maintenance-free and manufactured that way doesn't make it so.

Total life cycles is not the only part of the story, there is also the maintenance required, the charging regime and the use conditions.

Use on a sailboat is not particularly rough except perhaps in regards to temperature. Sailboats are relatively low in vibration and if they turn upside down the batteries will be among the least of your worries. Consequently AGM has little or no advantage here.

FLA's require monthly maintenance to get the better cycle-life. AGM are maintenance-"free". Advantage AGM. As a world-class procrastinator this is the primary reason I would chose AGM.

If the boat is going to be unattended and not have any charging source for long periods (months) then the AGM with the much lower self-discharge rate has a big advantage. If the boat has solar panels then the FLA's will survive just as well or better provided you can check densities and water levels every 2-4mo.

If running the engine is your primary charging source, then the AGM has the advantage, charge acceptance rates are 50-75% faster meaning the engine can be run for about 2/3 the amount of time as FLA batteries saving engine wear and fuel costs.

If you are going to spend a lot of time away from any civilization and worry that the whole battery bank will die all at once and you will have to have batteries shipped out on short notice to an out of the way place, then the AGM's have the advantage.

For run of the mill cruising and living aboard with solar panels in the US, Caribbean and Europe, FLA's have the advantage in price and longevity IF you can do the maintenance regularly.

If you do a search of crusers forum you will find lots of information on battery life and you will find that the majority view is gel and AGM batteries give a longer life than flooded batteries. Certainly this has been my experiencience.
Of course you can find contrary views views expressed, but I would not put too much faith in information from sources such as Trojan battery employees.
I do agree that if you can replace them easily flooded batteries will generally give the the lowest cost per cycle and will always give the lowest initial cost, an important consideration for most crusing sailors.
The maintance on flooded batteries is very minimal and I don't think this should be much of factor unless battery access is very difficult. Gel and AGM batteries are slightly safer. If flooded batteries get covered by sea water they can vent toxic chlorine gas.

Hopefully Litium boat batteries will fulfil there promises. There much lighter weight and non hazardous nature will mean they can be ordered and shipped to out of the way places like crusers do with other boat parts. I am skeptical of the very long cycle life claimed for these batteries, but it should be better than existing technologies which will reduce the chance of failure in remote places.

[goboatingnow]

Originally Posted by noelex 77

I do not understand why there is "no real way to control the distribution."
There are only two switches needed to control distribution.

Both on = banks joined draw from both battery banks
1 on = draw from battery bank 1 only
2 on = draw from battery bank 2 only

A battery monitor will tell you how much has been drawn from each bank.

The only difference when compared with single battery bank is the first option is the only option you have when you have a single bank.
Two banks gives versatility, you can suggest its unessary or overkill, but it's not worse.

The lifetime of any bank is related to the depth of discharge and the rate of such depth of discharge. A battery subjected to 50AH capacity in 30mins is far more depleted then one subject to 50AH ever 10 hours. Hence splitting a large bank up into smaller banks allows each bank to be subjected to a bigger proportional discharge "shock" then a larger bank. Battery monotors merely tell you the totsl they do not profile the rate There is no advantage to having Ah capacity distributed into smaller banks.

Dave

[noelex 77]

Originally Posted by goboatingnow

The lifetime of any bank is related to the depth of discharge and the rate of such depth of discharge. A battery subjected to 50AH capacity in 30mins is far more depleted then one subject to 50AH ever 10 hours. Hence splitting a large bank up into smaller banks allows each bank to be subjected to a bigger proportional discharge "shock" then a larger bank. Battery monotors merely tell you the totsl they do not profile the rate There is no advantage to having Ah capacity distributed into smaller banks.

Dave

I think we better agree to disagree on this one.

To answer your questions yes the Pukets equation does need to be taken into account for high discharges, as I mentioned in an earlier post. Batteries are better linked if high discharges are needed.

With separate battery banks they can be linked easily for as long as you like.

The only difference is they can also be split when this is an advantagage.

Situations where it's helpful to sptit the batteries are for example failure of one battery. This often occurs offshore as the this is when the depth of discharge is higest and the physical abuse tends to cause mechanical failure. Disconecting and swapping battery leads is not much fun in these conditions and is prone to accidents. Flicking a switch is much easier.
Two battery banks enables batteries of different makes ages even chemistry ( with limits) to be run. Want to try Litium batteries, you can replace half your house batteries while the industry sorts itself out.
Another important advantage is also much easier to detect a defective battery.

To me the these advantages justify the minor extra cost and complexity of an adittional battery switch, but not everybody has the same needs.

[goboatingnow]

Originally Posted by noelex 77

I think we better agree to disagree on this one.

Why listen to just me

Nada’s systems are fairly standard, with a few interesting twists. Nigel feels that electrics are the source of most problems on modern cruisers. Nada has a single, large battery bank, consisting of 8D marine gel batteries, with a smaller engine-starting battery isolated from the main bank. This arrangement reduces the daily draw on the batteries, as a percentage of the total capacity, from what it would be were there two banks. "The greater the depth of discharge, the shorter the battery life," Nigel explains. And, because the maximum charging rate is a percentage of the total battery capacity, higher rates can be used, reducing engine running time. Small solar panels keep the batteries charged when the boat’s in storage, and a wind generator helps when at anchor. Nigel prefers gel batteries for the on-again off-again type of cruising he does, because they don’t need to be monitored when the boat is in storage for prolonged periods.

Cruising World August 2002

Dave

Im not saying your shouldn't have a separate starter battery, but don't split your domestic bank.

[Exile]

Originally Posted by goboatingnow

Im not saying your shouldn't have a separate starter battery, but don't split your domestic bank.

I'm reading consensus, not disagreement here: It's generally best not to split the house bank in most instances, but having switches to do so in the few circumstances described can't hurt but could help.

A fair sum-up?

[noelex 77]

Originally Posted by Exile

A fair sum-up?

Yep that's a good summary.

[goboatingnow]

Having switches to split a large house bank just introduces the possibility that inadvertently you deeply discharge a single side of the bank and that you will not recharge the other bank ( this isn't good). Its also more switches wires and points of failure for virtually no gain. ( i would argue , actually no gain). Its also not common practice. In practice without sophisticated splitters or combiners, there is a risk that the part of the house bank will not be recharged if you forget to parallel them. I suspect that anyone using such a system in practice just leaves the paralleling switch closed.

This leaves aside the part that one large bank will provide more cycles before failure then two smaller banks. In addition a large bank is more resistant to unexpected high discharge. Given say a 200 Ah daily discharge, taking bank 1 to 100AH and bank 2 to 100Ah is worse than taking a the combined bank to 200Ah.

But hey if you want all the extra electrickery ....

Dave

[Fuss]

Originally Posted by Adelie

If running the engine is your primary charging source, then the AGM has the advantage, charge acceptance rates are 50-75% faster meaning the engine can be run for about 2/3 the amount of time as FLA batteries saving engine wear and fuel costs.

I have not seen the results of a test with numbers that show this so I am not sure how true this is.... Especially when taking a real live situation.

Does anyone know of one????

For example, lets say we are at anchor with 500ah of batteries. Our alternator has the potential to generate 50% of the battery bank making 250 amps the figure for this example.
48 hours later we have used 40% giving a status of 60% full.

Ok, lets charge them up to 80%.
How long does this take when they are AGM.
How long does this take when they are FLA.
What % faster were they.

Now lets charge them to 90%
How long does this take when they are AGM.
How long does this take when they are FLA.
What % faster were they.

Now lets charge them to 100%
How long does this take when they are AGM.
How long does this take when they are FLA.
What % faster were they.

In a real life situation we might only take them to 100% once every 2 weeks.... or ..... even less frequently.... or even ...... not ever!!!!

How are they both coping after 2 years???

This would be a very interesting test for the magazines

[goboatingnow]

In my opinion, the cost of AGMs are not balanced by their usefulness in a boat. They contain many advantages, however few of them are applicable to yachts.

(a) Higher charge acceptance, Yes, but few people can actually generate such high charge currents in the first place, certainly not with solar or wind and rarely with battery chargers. Even high powered alternators struggle to keep up with AGMs.

(b) Sensitivity to overcharging, unlike FLAs , they are damaged by overcharging or too aggressive overcharging and this can result in a permanent loss of electrolyte.( FLAs are also damaged but at least you can replace the water/electrolyte)

c) Self discharge, yes its better, but on a boat these issues are rarely pertinent. Most people have some sort of constantly attached standby charging system, hence self discharge is irrelevant.

(d) AGMs were developed for fighter planes and the the like, in that environment they have some specific advantages, few of which translate to boats

(e) No inspection ability, FLAs with accessible cells , allow proper cell SOC inspection.

Maintenance, If you have a charging system that requires maintenance on FLAs, i.e. you are suffering periodic water loss, you will actually damage AGMs. SO its a toss up between maintenance and battery replacement.

While carefully charged and used AGMs can provide longer cycle times, there is plenty of evidence around the boating industry that equally there have been poor user experiences.


In practice I would suggest it is much better to pay the difference of the AGM and put that into into better quality FLA's this actually delivers real tangible advantages.


Of course as Ive found LiFePo4 blows all this away.
DAve

[Exile]

Originally Posted by goboatingnow

Having switches to split a large house bank just introduces the possibility that inadvertently you deeply discharge a single side of the bank and that you will not recharge the other bank ( this isn't good). Its also more switches wires and points of failure for virtually no gain. ( i would argue , actually no gain). Its also not common practice. In practice without sophisticated splitters or combiners, there is a risk that the part of the house bank will not be recharged if you forget to parallel them. I suspect that anyone using such a system in practice just leaves the paralleling switch closed.

This leaves aside the part that one large bank will provide more cycles before failure then two smaller banks. In addition a large bank is more resistant to unexpected high discharge. Given say a 200 Ah daily discharge, taking bank 1 to 100AH and bank 2 to 100Ah is worse than taking a the combined bank to 200Ah.

But hey if you want all the extra electrickery ....

Dave

All excellent points, some of which I had not thought of -- thanks.

For better or worse, my boat came to me set up with a switch for the 2-batt house bank where I can select either battery, but I thus far have always just kept it on ALL. Then there are two separate ON-OFF switches for the eng start batt & the gen start batt. The nice thing (I think) is that the switches only affect the consumption/discharge side. All of the batts charge off both the alts & the charger regardless of the positioning of the switches.

From what I've been reading, this set-up sounds rather unusual. But I suppose there's nothing "unusual" about how any particular system is set up on a boat!

[noelex 77]

Originally Posted by Fuss

I have not seen the results of a test with numbers that show this so I am not sure how true this is.... Especially when taking a real live situation.

Does anyone know of one????

For example, lets say we are at anchor with 500ah of batteries. Our alternator has the potential to generate 50% of the battery bank making 250 amps the figure for this example.
48 hours later we have used 40% giving a status of 60% full.

Ok, lets charge them up to 80%.
How long does this take when they are AGM.
How long does this take when they are FLA.
What % faster were they.

Now lets charge them to 90%
How long does this take when they are AGM.
How long does this take when they are FLA.
What % faster were they.

Now lets charge them to 100%
How long does this take when they are AGM.
How long does this take when they are FLA.
What % faster were they.

In a real life situation we might only take them to 100% once every 2 weeks.... or ..... even less frequently.... or even ...... not ever!!!!

How are they both coping after 2 years???

This would be a very interesting test for the magazines

I dont have any firm answers, but in general most boats will only see a slight reduction in charging times from the main engine when changing to AGM batteries.
However in your example with an output of 250A from the engine alternator ( this is larger than would be typical for a boat with a 500AHr battery bank). The gains would be more significant and I would expect something in order of 1/3 less running time in the sweet spot when charging from 60 to 80%, but this is nothing more than an educated guess.

[goboatingnow]

All of the batts charge off both the alts & the charger regardless of the positioning of the switches.

How through diode splitters? my experience is that gen start batteries usually just charge of the specific generator or , in fact don't get charged at all from the genny ( unless you use a mains charger, which is what mine does).

[noelex 77]

Originally Posted by Exile

All excellent points, some of which I had not thought of -- thanks.

For better or worse, my boat came to me set up with a switch for the 2-batt house bank where I can select either battery, but I thus far have always just kept it on ALL. Then there are two separate ON-OFF switches for the eng start batt & the gen start batt. The nice thing (I think) is that the switches only affect the consumption/discharge side. All of the batts charge off both the alts & the charger regardless of the positioning of the switches.

From what I've been reading, this set-up sounds rather unusual. But I suppose there's nothing "unusual" about how any particular system is set up on a boat!

It is not an unusual system for a custom designed crusing boat, but few production boats go to the slight adittional expense of wiring a boat like this.
It's normall for all banks to be charged automatically from the main engine and generator.
FWIW I think you you have got the best system, lots of versitity and redundancy, always a good thing for a crusing boat. Even humble battery switches fail more often than you would imagine.

[Exile]

Originally Posted by goboatingnow

How through diode splitters? my experience is that gen start batteries usually just charge of the specific generator or , in fact don't get charged at all from the genny ( unless you use a mains charger, which is what mine does).

Yes, the gen start batt charges off the gen alt when its running and when not, it charges through a BEP VSR (echo-type charger) off the eng batt. The gen or shore power run the 110v batt charger, who's 3 ports are wired to each of the 3 main batts (2 house, 1 eng start). There are 2 alts running off the eng, one dedicated to charging the eng start batt, the other to charging the 2-batt house bank.

Except for probably being undersized with a 50A charger, it seems like a good system and has thus far been working well (2 yrs), except for a 8D for eng start which seems wasteful. That's why with what I think would be fairly minimal re-wiring, I could bring the eng start batt over to the house bank, and then use the gen start batt for starting both the gen & the eng. I'm considering the Balmar 612-Dual regulator which is supposed to be good for charging 1 bank off 1 engine using 2 alts. Would love to hear that this step (& expense) isn't necessary!