Battery Charging Questions.

[goboatingnow]

The fundamental reason to retain large single banks is that the discharge % on a larger bank will be less and hence life cycle will be much improved.

Dave

[Exile]

Originally Posted by Adelie

A group 24 can start a a 125-150hp gas car engine regularly. Gas engines draw less than diesel when starting but not that much less. I wouldn't worry about it if the rating works.

Three banks seems to me like you are begging for an argument with Murphy.

Agreed, although with separate charging for each bank & separate switches for consumption it has thus far been flawless. Then again, I've unfortunately been mostly tied to a dock & plugged in since replacing the batts a couple of years ago. Once out cruising, it would be nice to have the 3rd 8D tied in as part of the house & eliminate the third bank. I should still be able to isolate in the event of a bad batt.

Good info on the G24's start capacity -- thanks. It looked OK on paper but with Murphy always lurking one never knows.

[noelex 77]

Originally Posted by goboatingnow

The fundamental reason to retain large single banks is that the discharge % on a larger bank will be less and hence life cycle will be much improved.

Dave

Two banks can be linked with the flick of a switch when this is advantageous. Two banks used for half the amp hours will have essentially the same discharge. Pukets equation is not much of factor with a large marine bank at the sort of discharge currents generally used. If you want to power the microwave link them.

[mitiempo]

Originally Posted by noelex 77

Two banks can be linked with the flick of a switch when this is advantageous. Two banks used for half the amp hours will have essentially the same discharge. Pukets equation is not much of factor with a large marine bank at the sort of discharge currents generally used. If you want to power the microwave link them.

It is always advantageous to have the banks linked.

If you are using 100 AH per day it is better for the batteries if it comes from the linked bank instead of half or it - the large bank ends up at a much higher SOC at the end of the day.

Battery life - AGM batteries can last a long time but they are a lot fussier about charging than flooded. Flooded batteries tolerate not being fully charged more than AGM batteries do.

[noelex 77]

Originally Posted by mitiempo

It is always advantageous to have the banks linked.

.

Not when they are different chemistries or even ages.

Originally Posted by mitiempo

If you are using 100 AH per day it is better for the batteries if it comes from the linked bank instead of half or it - the large bank ends up at a much higher SOC at the end of the day.

B.

50 AHrs a day out of each bank. It makes no difference if they are linked, providing the discharge current is not high in relation to the battery size.

[mitiempo]

Originally Posted by noelex 77

Not when they are different chemistries or even ages.

Agreed - a large bank should be the same chemistry and ideally age as well.

50 AHrs a day out of each bank. It makes no difference if they are linked, providing the discharge current is not high in relation to the battery size.

If you are switching midday to even the loads from each bank that is true. If you forget to switch at a certain time the half bank gets drawn down farther.
Much better to have one large bank without any switching required.

[noelex 77]

Originally Posted by mitiempo

If you are switching midday to even the loads from each bank that is true. If you forget to switch at a certain time the half bank gets drawn down farther.
Much better to have one large bank without any switching required.

This is true a lot of the time. This is as easy as switching both battery switches on.
For the price of an extra battery switch and cable you can separate them if needed.

This is very useful as a diagnostic test, to isolate a defective battery, or to utilize different types of batteries. Overkill if you can buy suitable batteries and have them delivered the next day, but very useful or the long distance crusing boat.

[Pblais]

Battery life - AGM batteries can last a long time but they are a lot fussier about charging than flooded. Flooded batteries tolerate not being fully charged more than AGM batteries do.

That is pretty much the reason when not to use AGM,s. Good charging is good for all batteries but the charging profiles are not the same. An AGM will have a higher acceptance longer in the profile so they will require less engine time to recharge. This is where the savings in cost comes from but it's all out the window with a poor charger / alternator / regulator. For the ultimate the LiFePo batteries have the best acceptance rate but at a very high cost.

[mitiempo]

AGM batteries last longer if they are fully charged on a very regular basis - and if they are Lifelines equalized monthly.

How many cruising offshore do this or even are able to?

[Strygaldwir]

I have 2 banks, a House bank (850 AGM amp hours), a Starter batter (AGM also). My alternators are connected to the starter batter. The reason being they have small output demands and the alternator will bring them back up quickly when they are used. The Solar panel, and wind generator are conected to the house bank. The logic being that is where most of the sustain load is taking place, I want to be able to replace as much of this as possible.

I REALLY like my portable generator Honda/Kipor, it allows me to make up any charging deficit in a very cost effective manner. I store the portable in my sail locker when not using it. I pull it out on deck when I need to use it. Some folks I have seen suspend it from their booms. A LOT of flexibility due to the size and ready handling. I agonized for months about the danger of gas then I realized, I have a dinghy that needs gasoline, so I am stuck anyway. Several year, no issues, LOVE the solution.

When I go cruising again (Weeks without shore power). I intend to get more solar panels. They have been the most trouble free/usefule/cost effective item on the boat. They just sit there and supply Power. I have concluded 600 watts will supply 95% of my power requirements. Any lack will/should be made up by the wind generator, and if necessary the portable.

If you want to maximize utility of panels, get and MPPT controller. It gives you so much flexibility and efficiency it is difficult to imagine going without. I use 24 volt panels in my 12 system. The MPPT allows this. That also means when my panels are shaded or there is very indirect sunlight I can still generate voltages necessary to supply useful energy to my systems. I was seing 1 amp at 6am in the morning and 7pm in the evening. Great stuff.

[goboatingnow]

Originally Posted by noelex 77

Not when they are different chemistries or even ages.

50 AHrs a day out of each bank. It makes no difference if they are linked, providing the discharge current is not high in relation to the battery size.

You have no real way to control the distribution of the 50ah. Big banks are always better the split banks.

[noelex 77]

Originally Posted by goboatingnow

You have no real way to control the distribution of the 50ah. Big banks are always better the split banks.

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.

[Ex-Calif]

Originally Posted by Exile

OK, got it -- thanks. I suppose the only downside is that the 2 house batts will pull the presumably less stressed start batt down to their level when all 3 are paralleled. If there's a dedicated start batt used only for starting the engine, it's likely to stay healthier since it's generally topped off. As always, pros & cons must be balanced . . . . I still think my 8D for eng starting is overkill & wasteful, but I rarely worry about being able to start my engine!

Yes. Sometimes after start if the house is down we will switch to house only until it comes up towards the start battery state.

Need to make sure you have a make then break switch as the alternator doesn't like running with no field feedback. i.e. blown diodes.

[Adelie]

Originally Posted by noelex 77

I would advise the opposite. AGM and gelled batteries have a longer life, but at a greater cost. If you are are crusing developed areas flooded batteries are usually the cheapest option, but if you need to replace the batteries in underdeveloped areas the cost is much higher. Transport costs are a significant part, batteries are very heavy and flooded (but not AGM and Gel) batteries are classified as hazardous goods. The longer life of AGM or gel can make them cheaper than replacing them in underdeveloped countries.
Having your house battery bank set up so it is possible to separate them into 2 banks ( giving 3 banks including the start batteries) is helpful when crusing any areas where deep cycle batteries are difficult to get. If batteries fail you can pick the best old batteries to form one bank. In underdeloped countries it is very difficult to get deep cycle batteries at short notice, but car start batteries can be got anywhere. This can form a cheap second bank. This combination will last untill you can get somewhere where deep cycle batteries are cheap, or at east available.
Even better if when leaving on your voyage if you replace half the batteries with new ones, the two house banks will be different ages, which makes sudden complete house battery failure unlikely.

I think a completely separate start battery that is used only for starting ( or possibly the anchor winch as well) is good insurance.

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.

[mitiempo]

I agree with most of that posted above, but not all. If the primary charge source is the alternator then AGM's will seldom be fully charged - nor would flooded batteries either. Yes AGM batetries will accept more current, but the last 15% or so is just as slow as with flooded.

Below is an expert's opinion of AGM lifespan with different charging regimes. It is from Justin at Lifeline. MaineSail originally posted it on another forum.

There is also an interesting quote from Trojan batteries - who manufacture AGM and gel batteries as well as flooded.