Battery Charging and Readings

[sailinglegend]

Originally Posted by Ahmet Erkan

....If anybody is pontificating "what if one battery gets overcharged" etc explain the mechanism that makes you so sure it could happen and I will be the first one who listens.

Since nobody's responded let me try!

Firstly you can mix the capacity of batteries to fit the available spaces. Use large cables to minimise voltage drop if the batteries are distributed around the boat. Recent research by Lifeline Batteries has proved that a bank can be made up of different capacities and that the life of the batteries was not compromised, as long as they are all the same make and the same age. This goes against most previous guidelines, but Sabre yachts, who use Lifeline batteries, regularly ship with different sizes to be able to get the maximum capacity from all the available space.

But mixing different types and ages means there will be unequal load sharing as one battery is always trying to top up the other one. This will shorten the life cycle of the new battery.

To understand this it can be helpful to use the water tank analogy.

Two water tanks (batteries) of different size (different capacities) and joined together in parallel by a common outlet pipe (cable), will have the same head of water (voltage). The smaller tank must have the same height (same nominal voltage) as the bigger one or I will overflow (overcharge). When the tap is opened they must discharge at different flow rates (current) to keep the head of water (voltage) the same. They will both lose the same percentage of their original capacity. The same works when filling (charging), so two different capacity batteries can happily work together.

Two take the analogy further to explain why different types and different ages of batteries don't work well together you have to consider how the batteries charge and discharge their energy. To do this imagine many smaller tanks (thick battery plates) within each tank (battery), each connected internally by small pipes. When charging the first internal tank fills first (surface charge) and water slowly percolates to the other tanks (deeper into the plates). This helps to explain why when a battery is discharged quickly it's voltage falls (the first tank) and when the discharge stops the voltage rises as it is filled from the inner tanks (deeper plates).

This really needs an animated graphic to make it easier to understand.

So apply this to batteries of different types and age. They will have different terminal voltages at different states of charge (so the height of the water in the tanks will be different) and their internal resistance will be different (the size of the small pipes between the inner tanks will be different). So when charging or discharging stops then the tank (battery) with the lowest internal resistant and/or higher nominal internal voltages will top up the other tank (older battery) to equalise the heights.

QED

[Dockhead]

Originally Posted by Ahmet Erkan

. . . What if you left a battery that measures at only 10% of its nominal capacity connected in the parallel bank as long as it is fused and temperature is monitored? Even the new batteries in parallel should be fused and temperature monitored anyway.. . .

Fusing and temperature monitoring won't help. In this scenario, the new battery will be wrecked in short order -- in weeks if not days.

The charger only sees the average between the two batteries. The worn out battery will reach a surface charge quickly, long before the new battery has gotten much of a charge. The battery charger will see system voltage which does not represent the state of charge of the new battery. It will either go over too early to float (which is what happens when the worn-out battery is connected by itself), or it might stay in absorb and on the contrary never go over to float. Both scenarios will wreck the new battery.

For health, lead acid batteries need to get a full charge and THEN they need the voltage to taper off. If they don't get a full charge, they will sulfate. If the voltage doesn't taper off, they will get overcharged, which will corrode and then destroy the plates.


In short, once again, don't mix old and new batteries!! A new battery CANNOT get a correct charge, mixed with an old battery in the same bank, whether it's parallel or series!

[Eder]

Originally Posted by WizardOfTheWind

However, recently I have noticed that when we are hooked up to shore power the battery voltage does not go much past the float (13.2V), usually about 13.3-13.4, but when we are on engine power we see about 14.4V on the battery monitor.

I have 400AH of Lifelines...my solar & alternator will hit voltages up to 14.5 when charging...my 60 amp Charles charger charges them on shore power & gen power more slowly ...rarely higher voltages than 13.6v

I use Xantrex battery monitoring to detect state of charge. Batteries are 7 years old but still give me 185 usable amp hours total before requiring charging. When charging off my 6kw gen I only charge till the charging amps hit about 15 amps and call it good enough, which results in about 135 usable amp hours.

We are often on the hook weeks on end without shore power. Trust your monitor once synchronized.

[WizardOfTheWind]

Originally Posted by Dockhead

OK. Some further comments:

7. Said before but worth repeating -- don't add new batteries to a bank of old ones. Get rid of the old ones -- sell them if they are still usable. Batteries combined in a single bank must be well matched.


Good luck, and let us know how you get on!

Well this comment has certainly raised some discussion with my technical advisors here!

The additional two batteries were actually installed a couple of days ago, before I saw this post, by my electrician. After reading this post, and subsequent ones, I contacted him about this and he was strongly of the opinion that, because the "old" batteries were relatively new that he did not believe it would create a problem at all but did recommend that:

1. Remove the shore power charging if I was going to be away from the boat for more than about 3-4 days & just allow the solar to trickle charge our fridge and freezer.
2. Check whether the "old" batteries were getting too hot on a regular basis by feeling the temperature.
3. As we had set each of the battery chargers (2 x Ultra pro 40A) to the max Bulk/Absorption rate of 14.4 (Range 14.2 - 14.4), I could reduce this to the min rate of 14.2.

One of my other local technical "advisors" said that we should have created two separate banks: one to power the boat's energy hogs (fridge and freezer) and one to power the rest of the house systems.

Not being technical enough to decide which way to jump, I am inclined to seek further advice on this matter. My thinking is that we should redo some of the (extensive) work that has already been done and create two banks to be on the safe side (and not have to pay about $2500 for new batteries that are only about 15 months young in operation). This most likely means another battery monitor as well but, if that is the case, so be it.

Whilst the forum comments have presented me with a real dilemma, I greatly appreciate the input and knowing about the potential problems now rather than in the future.

[btrayfors]

David,

Save your money. In most all cases, it is preferable to combine all house batteries into a single bank, not split them into two or more banks.

There are several technical and practical reasons for this, all of which have been discussed on this and other forums in the past.

In short, these include:

1. simpler and cheaper installation;
2. simpler monitoring;
3. simpler and faster charging;
4. lower average load on each battery;
5. greater overall capacity available (because of Peukert); and
6. much easier for you to keep track of (no switching, timing, etc.).

Possible exceptions include cases where there is a high amperage draw like a bow thruster or windlass located a long way from the basic house bank. Sometimes it makes sense to have a dedicated battery bank for these devices.

Bill

[sailinglegend]

Originally Posted by WizardOfTheWind

... I saw this post, by my electrician. After reading this post, and subsequent ones, I contacted him about this and he was strongly of the opinion that, because the "old" batteries were relatively new that he did not believe it would create a problem at all......

The "AGE" of the batteries has nothing to do with their state of health. He could and should have done some simple discharge tests on each battery, for even just 1 hour at the designed discharge current of C/20.

It sounds like they have not been charged properly.

Lifeline themselves have quoted their estimation of the life of their AGMs - and they have gone on to say that these figures apply to ALL Lead Acid Batteries:

Fully charged after each discharge (not feasible on a voyaging boat). Estimated life: 6-9 Years.
Fully recharged at least once a week and equalized once a month. Estimated life: 4-6 Years.
Only recharged to 85% and equalized once a month. Estimated life: 2-4 years.
Only charged to 85% and never equalized. Estimated life: 1 year.

You also have to understand what "FULLY CHARGED" really means, there are lots of posts on this forum, please do use the search tool.

I keep repeating my experiences with my current Lifelines of 12 years full time Liveabord.

[masonc]

Originally Posted by sailinglegend

Lifeline themselves have quoted their estimation of the life of their AGMs

FLA and AGM batteries are greatly affected by temperature. If you are somewhere cold, they will last a lot longer than here in the Caribbean. We see about five years for FLA and AGM, depending on how well they're cared for and how deeply they are discharged.
The most common problem with FLA is lack of maintenance. People start out well but forget to keep the electrolyte levels up. Because of this, AGM is often a better technology just because there is no maintenance.
AGM batteries can't be equalized, but most users never equalize FLA anyway. How do you equalize a solar charged battery anyway? Unless you have a serious alternator and do a bunch of motoring, how are you going to equalize?

[Suijin]

Originally Posted by WizardOfTheWind

3. As we had set each of the battery chargers (2 x Ultra pro 40A) to the max Bulk/Absorption rate of 14.4 (Range 14.2 - 14.4), I could reduce this to the min rate of 14.2.

If your charger was set to the max when you bought the boat, and has seen a lot of hot weather, that would be a bad thing. Ideally, you should have a temperature sensor that adjusts the rate automatically. If not, make sure you change the setting to what's appropriate for the seasonal temperature. Not something that is going to kill your batteries outright, but it certainly has an impact.

You said you bought the boat six months ago and the batteries are 2 years old. 18 months is more than enough time to ruin a battery bank poor charging habits. In other words, you really don't know what the health of the bank is unless you do a full capacity test, which is a bit involved, but probably worth your time at this stage as a "level set" to know exactly what you're dealing with.

I'll echo Dockhead's advice about the SOC monitor and take it a step further. It's worthless, and even worse can actually lead a boat owner into a routine of DoD and charging that kills their batteries. Simply hitting "synchronize" is not going to fix the problem. It's a bit more complicated than that. Ignore it's % reading and just pay attention to volts.

[sailinglegend]

Originally Posted by masonc

....AGM batteries can't be equalized, but most users never equalize FLA anyway. How do you equalize a solar charged battery anyway?

Lifeline AGMs can and are recommended to be equalised which has already been posted twice in this thread. Please read all posts first.

Correct, many people never EQ their FLA batteries - the only proper way to do it is with a shore power charger - for Lifeline AGMs it's 8 hours at 15.5v - temperature compensated.

If solar is all you use to charge batteries you will never get a bank fully charged, no matter what a little green light or a Battery Monitor tells you. Search this forum for the real facts on Solar Charging, and what "Fully Charged" really means. There are just not enough hours in the day or real estate on most cruising boats to get batteries fully charged with solar alone. The last 2-3% may take 10 hours!!!!

[01kiwijohn]

oops, my mistake then. sorry 'bout that.
Glad I keep mine simple. I'll take efficacy over efficiency every time.

[conachair]

Originally Posted by sailinglegend

Lifeline AGMs can and are recommended to be equalised which has already been posted twice in this thread. Please read all posts first.

Correct, many people never EQ their FLA batteries - the only proper way to do it is with a shore power charger - for Lifeline AGMs it's 8 hours at 15.5v - temperature compensated.

If solar is all you use to charge batteries you will never get a bank fully charged, no matter what a little green light or a Battery Monitor tells you. Search this forum for the real facts on Solar Charging, and what "Fully Charged" really means. There are just not enough hours in the day or real estate on most cruising boats to get batteries fully charged with solar alone. The last 2-3% may take 10 hours!!!!

What criteria are you using to determine fully charged? The most common looks to be well into 14v with 1%C current, easily achieved every sunny day with a property sized system, up to absorbtion by mid/late morning then full by the end of the afternoon.
And equalising is perfectly feasible with a genny, doesn't have to be all in one hit, you can split it over 2 days if the noise gets too much.

[ErikFinn]

Why folks seem to think equalizing with solar is not acceptable? Say you have <600W, and a good fully customisable controller such as a Midnite or Outback ? If not usable why do these controllers have the equalize function in the first place?

[conachair]

Originally Posted by ErikFinn

Why folks seem to think equalizing with solar is not acceptable? Say you have <600W, and a good fully customisable controller such as a Midnite or Outback ? If not usable why do these controllers have the equalize function in the first place?

Mostly just on the internet, not so many in the real world

[sstuller]

Increasing battery bank size without a corresponding increase in charging capacity will increase charging times versus a smaller bank with a higher rate of charge. This is based on the absorption calculation in the Rolls battery manual. Telling people that increasing bank size so you never get below 80% SOC for the sake of battery life always leaves their bank in the absorption state of charging.

[StuM]

Originally Posted by sstuller

Increasing battery bank size without a corresponding increase in charging capacity will increase charging times versus a smaller bank with a higher rate of charge. This is based on the absorption calculation in the Rolls battery manual. Telling people that increasing bank size so you never get below 80% SOC for the sake of battery life always leaves their bank in the absorption state of charging.

Would you care to show your calculations for that assertion?

Increasing the battery bank size will increase the Amps that the batteries can accept in absorption mode and make better use of your "charging capacity".