New Batteries, Second Alternator or New Chargers ?

[Hugh Walker]

OK so I need some help upgrading/understanding our power generation.

The boat is a 2009 Beneteau Oceanis 46 with a 560amp battery bank (we think damaged so holding less). We have a standard 80amp alternator on the Yanmar 75 and a 5.5 KVA genset with two 40amp chargers. Our daily usage would be around 110amps per day. We rarely if ever go to marina's for shore power (maybe once a month or less) so we need to be able to generate everything onboard. We move around quite a bit (currently cruising the Med) so definitely getting a lot of use from the main motor. When not motoring we use the genset twice per day for about 1.5hrs (I shut it down when the charge rate gets less than 15amps for efficiency sake).

Our current problem is the batteries seam to be giving us less and less output. We have a Xantrex Link Pro and I changed the settings to reflect 400amp capacity (about 2 months ago) but recently our fridge has been turning off overnight due to low voltage when the link pro is still reading 63%, something is amiss.

I was talking with another owner last night and with a slightly larger yacht and he said his life changed when he installed a second alternator. I've done some research this morning and yachtwork.com in NZ advertise we can add a 165amp alternator giving 245amps total. Sounds pretty good but got me thinking, if the batteries can take charge at that rate, does this mean our genset chargers at just 80amps combined are woefully undersized? Maybe upgrading them is a more efficient solution, are they sized correctly?

So I think we have 3 possible solutions;
1. Replace the battery bank.
2. Install a second high capacity alternator to the main engine.
3. Install new higher capacity charger for the Genset.

Which is the best option for a limited budget?

[Dockhead]

Originally Posted by Hugh Walker

OK so I need some help upgrading/understanding our power generation.

The boat is a 2009 Beneteau Oceanis 46 with a 560amp battery bank (we think damaged so holding less). We have a standard 80amp alternator on the Yanmar 75 and a 5.5 KVA genset with two 40amp chargers. Our daily usage would be around 110amps per day. We rarely if ever go to marina's for shore power (maybe once a month or less) so we need to be able to generate everything onboard. We move around quite a bit (currently cruising the Med) so definitely getting a lot of use from the main motor. When not motoring we use the genset twice per day for about 1.5hrs (I shut it down when the charge rate gets less than 15amps for efficiency sake).

Our current problem is the batteries seam to be giving us less and less output. We have a Xantrex Link Pro and I changed the settings to reflect 400amp capacity (about 2 months ago) but recently our fridge has been turning off overnight due to low voltage when the link pro is still reading 63%, something is amiss.

I was talking with another owner last night and with a slightly larger yacht and he said his life changed when he installed a second alternator. I've done some research this morning and yachtwork.com in NZ advertise we can add a 165amp alternator giving 245amps total. Sounds pretty good but got me thinking, if the batteries can take charge at that rate, does this mean our genset chargers at just 80amps combined are woefully undersized? Maybe upgrading them is a more efficient solution, are they sized correctly?

So I think we have 3 possible solutions;
1. Replace the battery bank.
2. Install a second high capacity alternator to the main engine.
3. Install new higher capacity charger for the Genset.

Which is the best option for a limited budget?

You probably don't want to charge at more than 20% or so of your bank's capacity. More than that, and you run into problems of heat and gassing and you can reduce the batteries' life. They don't like to be charged too fast.

So I would say 80 amps of shore power/ genset charging is probably more or less ok. I have 70 amps (albeit at 24v) for 440 amp/hours of batteries and it seems to be ok. At that rate, I don't usually have more than a couple of hours of charging at full power anyway.

I would definitely upgrade the alternator. 80 amps of power from a shore power charger is NOT the same as 80 amps of alternator power. Your alternator will only put that out when it is running at full speed. At cruising speed it is probably not putting out much more than half of its rated power (depends on your cruising speed and how the pulleys are set up, and the power curve of the alternator).

Separate alternators for domestic batteries and starting batteries are always a good idea -- separate them completely if you can. Put both shore power chargers on the domestic batteries and buy a smaller separate trickle charger for the start battery.

A 165 amp alternator sounds good. You would be likely to get around 80 amps out of realistically (but you need to calculate that based on your realistic cruising RPM), and your batteries can take around 120 amps without any big problems. Make sure it is smart regulated.

Sorry about your dying batteries. I am in the same situation. Lead/acid batteries are easily killed by leaving them discharged for a long time. You might try equalizing them -- do your chargers have that function? If not, you can buy an automotive charger with that function and equalize them one by one, which is probably better.

Don't rely on your amp-counting Xantrex meter for state of charge of your batteries. They don't take account of the real capacity of your batteries. You need to use voltage and specific gravity to really know what the state of charge is.

I had the same problem with my Victron meter -- said I had 70% left but the batteries were almost dead according to voltage. I made that mistake over and over again and let the batteries get way too far down, which made them even worse. I learned not to pay too much attention to it -- rather, I learned to use the part which shows how many amps have been consumed, which is useful information, while ignoring the % charge part, which is useful only with new batteries.

So in summary, I would:

1. Start monitoring the state of charge of the batteries differently. It could be that you are never charging them up enough and you are letting them get lower than you think. Go into a marina and hook up or let the genset run a bit and get them up to 100%. Then don't let them get below 50%, measured by SG and voltage, NOT by Xantrex. It may be that your batteries are better than you think.

2. If not, then you need to replace them.

3. If you have the money after that, then a new, separate, high capacity alternator is an excellent idea.

Good luck and let us know how it all works out.

[Hugh Walker]

Wow Dockhead, what brilliant response. I'll take some time to go through all the detail you've outlined. Thank-you!

[Dockhead]

You're welcome! Please be sure to let us know how it works out -- we all benefit from your experience.

[Dockhead]

By the way, I forgot to mention the other benefits of a separate high output alternator:

You will no longer be charging anything through a splitter. You will have one alternator directly charging your domestic batteries, and another alternator directly charging your engine start battery. Folks on here who understand electrickery better than I do can explain why splitters are bad -- for one thing, you get a voltage drop but I think there is more to it than that. Also, less to go wrong.

The other advantage, rather obviously, is redundancy.

[Dockhead]

And read this: http://rollsbatteryne.com/docs/A%20S...%20Battery.pdf

About sulphated batteries. That is my problem -- batteries fully charged according to voltage, but half-discharged according to specific gravity. According to this, it means the plates are heavily sulphated.

I am trying to unsulphate them by applying an equalizing charge to them. My Victron battery charger does this, although I am not sure that the current is enough to be useful with eight 110aH batteries in my domestic bank. Maybe someone more knowledgeable could comment on that, for the benefit of all of us.

[Lars_L]

The equalization current is only 4% of the battery capacity. For a 110 Ah battery it means 4.4 A, and that can any charger make. You push on this current until the voltage stops rise. But it could mean that the voltage reaches more than 16 V and therefore you should have the batteries disconnected during equalization.

You can have the batteries in series without any problem, ever cell gets the same current.

You can’t have the batteries parallel during equalization since you don’t know which cell that’s get the current.

[goboatingnow]

The reason diode splitters are bad is not really the voltage drop, which can easily be accommodated. It's that you can only sense one battery yet you are charging two.

Hence one is either undercharged or the other is overcharged.

Dave

[Mark Zarley]

Sounds like your shutting down the charge cycle at 15 amps has definitly sulphated your batteries. You can do that for a few cycles but then you need to bring them all the way back to a full charge (when the voltage drops from 14.2 volts down to the 13 volt range it is fully charged). Care should be taken to make sure your batteries have thick plates if you are going to equalize them. Thin plates will be damaged. Checking specific gravity is the best indicator of your individual battery cells.

[Hugh Walker]

Thanks again for all the help, I've just read the document on equalization but I don't think I can manually select anything like that on my chargers which are 2 x Dolphin 40A. The user manual does say there is an equalization mode as indicated by a flashing orange light and I've seen the orange light often when the chargers first come on. Is this a similar thing? I though it was just the normal charging process, equalization then absorption then float.

We motored 9hrs today and the batteries just reached full charge, sounds like we'll have to get the second alternator because 9hrs to full charge is just not reasonable via the generator alone. I've spoken to Scott Fracture from yachtwork.com who has given me some good information on the second alternator configuration and install.

One quick question I can't understand, I see the charge amps going in today slowly dwindling. I understand this to be the resistance of the batteries increasing as the state of charge increases. If it is the batteries that limit the charge amps then how does the bigger alternator change anything? Does the bigger alternator just force more amps in? How doesn't this cook the batteries?

[David M]

Some alternators can put out their full load at low RPM's. I installed ammeters shunts (I have two engines) inline with my alternators so I could see just how much current they are producing. This helps to create an image of just how much charge the batteries are receiving and after they are fully charged helps to see just how much is the true house load when the engines are running. I think it is a smart thing to be able to see how much current your alternator is producing.

[DeepFrz]

A larger alternator wont help much unless you have an external regulator that will keep the charge voltage constant until it goes into float mode. Even then the current will drop off as the internal battery resistance increases.

There is another factor, and that is the hot rating of the alternator. As an alternator heats up the regulator should reduce the output. A high output alternator should be able to maintain a higher power output.

[Hugh Walker]

Thanks all,

I finally did a capacity test a couple weeks ago and found I only had 250Ah, down from 560Ah. I'm needing to run the generator morning and night at the moment. I've decided to get a new bank of around 560Ah again, simple wet cels is what gets recommended on here most.

One quick question, as mentioned before I don't often get into marinas to do an overnight charge and mostly I charge with the genset in the 50-80% range. How often should I bring the bank up to 100% so as to avoid damage? Also is time spent on float important or is just getting to 100% the important factor.

[Maine Sail]

Originally Posted by Hugh Walker

One quick question I can't understand, I see the charge amps going in today slowly dwindling. I understand this to be the resistance of the batteries increasing as the state of charge increases.

It's called the "acceptance" rate of the batteries. Below about 80% state of charge, on a healthy bank, you'll be in bulk charge which means the alt or charger has not yet been able to bring the bank voltage up to the acceptance voltage set point and is running wide open or is limited by the acceptance rate of the batteries.. The most current flows in bulk at about 25% of capacity/bank with deep cycle wet cells. Some banks take slightly less in bulk as a % and some slightly more but they average around 25% or so unless AGM, GEL or TPPL.

At around 80% SOC the bank starts limiting and taking less than the 25% or so it would accept in bulk. By the time your into the high 80's low 90's your probably accepting less, 12-13% or so and for all intense and purposes when your bank is taking less that 2% of "C" / capacity you can consider it full. Based on simple battery chemistry you're not going to charge your batteries to "FULL" much shorter than what you just saw. This is why most cruiser cycle between 50% SOC and 80-85% SOC. You may change the time you spend in bulk mode with a bigger alt, if you're not already up against "C/25%" but you won't drastically cut much off how long it takes to get back to 100%. The remainder of charge, the last 15 - 20% is most efficiently put in via shore charger or solar or wind and not necessarily by running an engine to do so.

Originally Posted by Hugh Walker

If it is the batteries that limit the charge amps then how does the bigger alternator change anything? Does the bigger alternator just force more amps in? How doesn't this cook the batteries?

Alternators do not "force" current in, batteries, based on internal resistance, take it and accept the current or allow it to flow. I can hook a dead 60 Ah battery up to my 90A charger and watch a brief in-rush spike but it then happily settles down to about 23-24% of its capacity in current it accepts in bulk.

One example I will use to demonstrate acceptance is to run the customers alternator on the house bank only via their 1/2/BOTH switch. The alt may be putting out 40-70A +/- at that point feeding a large discharged house bank. I then switch the charge source to their single smaller starting battery, by passing through the BOTH position. This battery is very often at or near full charge and the alt quickly goes from about 70A+/- in the HOUSE or BOTH position to about 1-2A output on just the single start or reserve battery... This always seems to put "acceptance" into perspective for them..

I think this quote by Balmar sums it up well..

"Forget the rumor that an oversized alternator will destroy your batteries ... the truth is that the acceptance rate of your batteries will dictate how much amperage the alternator will provide."

[Jon Hacking]

Be careful getting Deep Cycle batteries. In South Africa we were offered local "deep cycle" batteries that could be cycled to 50% "up to 250 times!" But 250 cycles is less than a year. We went with Sonenscheim batteries that can be cycled to 50% 2,500 times.

The higher you are in your state of charge, the longer your batteries will last. Therefore, a bigger bank will last longer. We seldom discharge more than 10% of our 660Ah bank overnight, & our solar panels usually fill that back every day. But bringing batteries to full charge (getting into "float" mode on your charger) is difficult without solar or a marina, as the last 10% takes a long time.