450 AH vs 675AH charging question

[GILow]

Hello Cruisers,

I feel like this one has been done to death, but I still can't quite get my head around the charging question.

I have an option of putting in either 4 or 6 Trojan T105 batteries, so either 450 AH @ 12v or 675 AH @ 12 V.

The power consumption of the boat is pretty low. Main items are the Danfoss DB50 fridge compressor, the autopilot, plotter, windlass, pursurvivor 35 watermaker, TV and a few radios, VHF and HF. Lighting is 100% LED. I have been managing fine for weekend overnight sailing on a pair of very cheap 125 AH AGMs and they have never gone below 12.5 volts.

Power production comes from 280 watts of solar connected to a 420 watt capable MPS controller, an Aerogen 6 (300Watt) wind-generator and reasonable quality 100 amp alternator. (Hitachi, so I figure it is good for about 60 - 70 amps in reality, that may be optimistic.) In practice, we are never using the Aerogen or engine driven alternator because the solar panels are keeping the two 125AH batteries full all the time. We never plug into the mains.

Engine electrics are a totally separate 24 volt bank.

The previous owner lived aboard for many years with a 400AH battery bank and felt it was plenty, so I am inclined to think, with the advent of LED which he did not have, that 400 AH will still be plenty. But, I have the space to fit the bigger bank easily enough, so logic says it would be better to have the shallower depth of discharge and go the larger bank.

BUT, do I have enough charging capacity? I see the mention of 10% of battery capacity required for charging current and I realise that as it is, the solar will not be enough to provide that peak current. I could add panels, up to 420 watts, but I would rather not do so if is just to provide charge capability that I don't really need. Would short runs of the engine provide what I need to prevent sulphating from inadequate current or is it good enough to keep the bank fully charged to prevent problems?

Really confused, and I have read lots on C.F. without being any less confused. Can anyone enlighten me?

Matt

[El Pinguino]

Its late in the day and rather hot but here we go...
I have 2 x Trojans in the house bank and I think they are about 125 each.... plus the same as an engine start battery of the same size...... I always run them as a single unit because I am not a nong charterer and know that when I get up in the morning the engine will start...

Charging is either an engine driven Bosch 12/80 alt which puts out max 60 amps, or solar, or an Aerogen 4 ( the wind or water one).

The key to a having happy life - apart from not making a pretty woman your wife - is to have an ammeter on each so you know what it is doing.

I would put in as many batts as you can fit... lower percentage of discharge = longer batt life... working for me.

[btrayfors]

Matt,

If you have room for six T-105s, go for them. The shallower discharge will pay off in the long run.

Sulfation is not a function of charge amperage per se. Rather, it is a function of battery voltage and, especially, state-of-charge. Note that Trojan recommends 14.8VDC absorption voltage. Try to see that your charging sources (solar panels/controller, engine, wind genny, etc.) are set for such charging voltage.

Note also that sulfation can occur when batteries are "full" and at a resting voltage of 13.2 or so. That's why it's a good idea to:

- use a higher resting voltage....13.6-13.8; and
- periodically kick up the voltage to absorption levels, i.e., 14.8VDC or so.

In tests on my own boat with six T-105s in the house battery bank I found that kicking up the voltage every other day to 14.8VDC for a half-hour made a measurable difference in battery capacity and in longevity.

Be sure to watch the electrolyte level closely, and use Hydrocaps or WaterMiser caps to reduce water loss.

Bill

[GILow]

ElPinguino and Bill, thanks for the ideas.


EP, your marriage advice is noted, thank you. Very happy with the current model, not planning to upgrade.


Bill, I have a programmable controller for the solar panels, so I will look into what parameters may be set for the charge cycle.


I'd still love to understand where all the "10% of battery capacity" remarks come from when reading about charging systems though.

[brianlara 3]

MATT. FWIW. Been a mechanic and a Mercedes Benz service manager.
I've been on the hook non stop, no moorings/berths for 6 years on NSW coast, mostly pretty exposed...Eden Bateman's Bay Broken Bay SYDNEY etc and rarely well protected, mostly because I never...pick up anyone's mooring. 250' of 8mil chain, Supreme, 900watt windlass.
I run everything you do except the w/maker and HF. My Waeco freezer runs nearly 4amps @ about 30% cycle rate. 6 hours TV per day which includes Ocean South full HD tuner (together 4 amps). Occasionally I'll run the Sunbeam bread maker.
I anchor, 20 to 50 feet of water probably every 3 days.
What powers all this is 5x100 ah flooded wets, a solitary 135w solar and a Sterling Procharge 12/60 charger which runs off a 1600w genny sitting on the poop.
Soon I'll fit a good 900mm wind gen to cut down on gen noise and petrol dependence.
Generally am fuel, food and water sufficient for C. 21 days.
What stands out at me in your post is firstly....
the quickest way to kill a diesel is to run it (even at speed) unloaded to charge batteries....ie, unloaded gearbox in neutral.
This all to common practice keeps mechanics in business, not repairing worn out engines, rather the cylinder walls glaze over because of incomplete combustion (not getting hot!).
Been warned!
I think that you should spend the extra few quid on a bigger bank. My opinion, depends on how you use the boat....you didn't indicate current or intended vessel usage.
If motoring A LOT!!! then your alter and solar and wind, WITH WINDY, SUNNY DAYS 6 days out of seven may, ?? keep your batteries up.
How often are you anchoring eg...there's 1200watts or more.
In summary. Take care of the Swanson's motor re charging from the alternator.
As you've asked, I personally would increase the batt bank size and finally, consider a Honda or Yamaha 1600 watt (continuous!) genny pwith a top quality battery charger.
I do it the way I do because I have no choice, perhaps your usage is totally different to mine.
Feel free to pm me so that I can give you my mobile #.
cheers. Brian.

[twinboat]

I believe the 10% ( I hear 13% ) is the max capacity for not gassing the water out.

You could build in 50% charge capacity but once the volts reach the absorbsion setting in a good charger, alternator or controller, the amps are going to cut back. Be some water loss with a low bank though.

With shallow cycles you may never reach 10% rate of charge.

I could be wrong !

[brianlara 3]

Happy to explain the 10% thing....too lengthy & complex for internet... deserves two way dialogue as in class room.
Call my mobile.
Also licensed in NSW as auto electrician.

[GILow]

Thanks Brian you make some important points.

Absolutely agree with not running the engine to charge the batteries, a 3.5 litre 100HP diesel would die pretty quickly if I went down that path, plus the noise and vibration would be horrid.

No idea what sort of Amp Hours we will get through when we start sailing for real, that's a few years away and I had actually planned to put off installing this battery bank until we were ready to go. Alas my cheap and nasty AGM solution appears to have died after a year, so no more temporary solutions for me.

At this stage I am going to assume that we won't need to run the engine to charge the batteries, I just included it in the description because it is the highest current charging device on the boat. Otherwise I expect the Aerogen and the solar to manage quite well. Our refrigeration numbers are very similar to your figures but our charging setup is very different. I don't expect to use the watermaker when coastal cruising, but the previous owner ran it on long trips from the Aerogen without killing the battery bank, so it might get used from time to time.

In theory, according to my calculations, we have more than enough total charging capacity, just no high current charging capacity. Hence my concern about the bigger bank, which otherwise seems totally logical to me.

Matt

[GILow]

Originally Posted by twinboat

I believe the 10% ( I hear 13% ) is the max capacity for not gassing the water out.

You could build in 50% charge capacity but once the volts reach the absorbsion setting in a good charger, alternator or controller, the amps are going to cut back. Be some water loss with a low bank though.

With shallow cycles you may never reach 10% rate of charge.

I could be wrong !

And you could be right. I don't get it, and your logic makes as much sense as any I can determine.

[brianlara 3]

Matt, your original post and your reply deserve lengthy attention. But its getting late now.
Sounds like you have almost all of the wherewithal to sort this out.
For now, I'll just pick up on your current batteries....possibly your wind and solar, even combined weren't sufficient to save your new batteries. W & S are good for top-ups but often, depending on usage, only a good charger will "bulk" and then "absorb" batteries so that they reach 100%. If not full charged poor reserve capacity isn't the only price paid. Battery death is also common with no charger. Neither S nor W are substitutes for a charger & generator. Nor is an alternator the right device (on a boat, not car) for maximising batt longevity. Unless running v/long hours that is. Motor cruisers exempt.

[GILow]

Well, the current battery bank was a small AGM bank. The boat lives in the pen and is only used at weekends. The bank was fully charged all the time, as AGMs like to be, at exactly the voltages specified by the distributor using the programmable German MPPT solar regulator. They have NEVER gone below 12.5 volts according to both the regulator and the battery monitor system.


BUT, and it is a big but, the batteries were bought from a big Australian online retailer of rebadged no-name systems and they were suspiciously cheap. So I really think they died from being total and utter crap to begin with. I have gone over the whole charging and management settings from beginning to end, and on paper those AGMs were living in AGM paradise.


But I might have missed something. I sure hope not, don't want to kill the Trojans as well.


Matt

[ramblinrod]

Originally Posted by GILow

Hello Cruisers,

I feel like this one has been done to death, but I still can't quite get my head around the charging question.

I have an option of putting in either 4 or 6 Trojan T105 batteries, so either 450 AH @ 12v or 675 AH @ 12 V.

The power consumption of the boat is pretty low. Main items are the Danfoss DB50 fridge compressor, the autopilot, plotter, windlass, pursurvivor 35 watermaker, TV and a few radios, VHF and HF. Lighting is 100% LED. I have been managing fine for weekend overnight sailing on a pair of very cheap 125 AH AGMs and they have never gone below 12.5 volts.

Power production comes from 280 watts of solar connected to a 420 watt capable MPS controller, an Aerogen 6 (300Watt) wind-generator and reasonable quality 100 amp alternator. (Hitachi, so I figure it is good for about 60 - 70 amps in reality, that may be optimistic.) In practice, we are never using the Aerogen or engine driven alternator because the solar panels are keeping the two 125AH batteries full all the time. We never plug into the mains.

Engine electrics are a totally separate 24 volt bank.

The previous owner lived aboard for many years with a 400AH battery bank and felt it was plenty, so I am inclined to think, with the advent of LED which he did not have, that 400 AH will still be plenty. But, I have the space to fit the bigger bank easily enough, so logic says it would be better to have the shallower depth of discharge and go the larger bank.

BUT, do I have enough charging capacity? I see the mention of 10% of battery capacity required for charging current and I realise that as it is, the solar will not be enough to provide that peak current. I could add panels, up to 420 watts, but I would rather not do so if is just to provide charge capability that I don't really need. Would short runs of the engine provide what I need to prevent sulphating from inadequate current or is it good enough to keep the bank fully charged to prevent problems?

Really confused, and I have read lots on C.F. without being any less confused. Can anyone enlighten me?

Matt

Extra battery capacity is always a good thing, when balanced with budget, weight, and space considerations.

You will get the most battery cycles out of these batteries, with a charge cycle between 50 - 80%.

In which case, assuming your daily consumption is 100 Ah, and your solar and wind can always generate 120 Ah (considering charge efficiency) every 24 hour period, you would need about 300 Ah of batteries.

However, you will not always get 120 Ah of solar and wind, so the extra capacity will help you to avoid dipping below 50% and to go longer before having to start the engine or plug into a marina.

With the 675 Ah bank you are considering, your average charge cycle will likely be around 75% to 95%, so you will not get the maximum Amps possible out of the batteries over their lifespan.

However, you will be less likely to dip below 50% capacity too, so in reality it will likely be a wash in real life expectancy.

Only you can balance the weight, space, purchase price cost consideration over the extra reserve capacity benefit.

Ramblin Rod
About Sheen Marine

[Stu Jackson]

10% is minimum. Anything higher that includes appropriate control of the voltage is just fine. Battery type must also be included, since, for example, AGMs can take a lot more than FLA.

[a64pilot]

To some extent I believe the 10% is to ensure a re-charge in a reasonable time, Solar is good for what 1/3 of the time on average? 8 hours for an average day? If so then obviously you need to be able to charge at least three times your usage rate, actually higher, so if you use 10 amps continuously, then you have to have 30+ amp charge rate for Solar, probably 40 amps.
I believe you want a higher charge rate on a flooded battery as this promotes the electrolyte to be mixed or stirred, preventing stratification I think it's called, but you want the electrolyte to mix and higher amperage apparently mixes it.

[a64pilot]

What I don't know and I think maybe what your asking is, if I pull 100 AH out of a 1000 AH bank, and 100 AH out of a 500 AH bank, which one can I fully recharge faster?