450 AH vs 675AH charging question

[brianlara 3]

Love Solar, love Wind too. But sometimes there is neither...for days. What to do? Turn off the freezer?
There is no substitute for a very! good quality charger. I've had my Sterling Pro 12/60 now for 6 months and so far....just brilliant.
For those who have never been told: Charging batteries from your engine, unless you are in gear and running loaded, wrecks engines by glazing the cylinder walls...can't get hot, inefficient combustion, fuel particles turn into solids and imbed themselves into the cylinder wall cross hatching/cylinder block micro-porosity.
Sure, occasionally it may be that engine running without load can be convenient but do it rarely.
Diesels MUST be fanged ie minimum, say, 30 to 40% load. They have a governor for a reason....governed speed equals no damage.....sure, increased fuel consumption & servicing frequency....nothing worse than that FWIW. And, I charged you nothing for this, as we pros usually do and if it sunk in I saved you big dollars.

[btrayfors]

Depends on the SOC. Obviouly, the higher capacity bank will accept more charging amperage.

The 10% is a rule-of-thumb for flooded lead-acid batteries. It is predicated on the fact that a FLA battery at 50% SOC will only accept 10-15% of its rated capacity (C/10 - C/15) in charging amperage so long as the voltage is limited to the normal acceptance charge, i.e., 14.4-14.8VDC.

Will smaller capacity chargers fully charge your batteries? Yes, of course, it just takes longer.

Will larger capacity chargers fully charge your batteries faster? Not necessarily.

Here's the rule: so long as charging voltage is controlled within recommended levels, a lead-acid battery will accept a given level of charging amperage no matter the size of the charger.

Say, for example, it's now accepting 15A with a 20A capacity charger (@ 14.6VDC). How much amperage will it accept with a battery charger five times as large, i.e., a 100A capacity charger?

The answer is, 15A. That's right, the larger capacity charger will NOT charge the battery any faster than the smaller one, so long as the smaller one is capable of furnishing all the amperage the battery will accept at any given state-of-charge.

Can you have too small a battery charger? Yes, of course, but not because it's incapable of fully charging your batteries but because it's just too inefficient, and will take much longer than a properly-sized charger.

Can you have too large a battery charger? No, you can't. Provided, of course, that charging voltages are properly controlled.

Another way of putting this is that LA batteries are self-limiting: they'll take whatever charge they're gonna take, and no more, provided you control the voltage correctly.

Of course AGMs and gelled batteries change the equation somewhat. Gels can take 20-25% of their capacity in charging amperage when at a 50% SOC. AGMs can take over 100% of their capacity when at 50% SOC. And, when discharged to 20% SOC, AGMs can take five times their capacity in initial charge. That's right, a 100A AGM @ 20% SOC can take 500A initial charge.

And, this may surprise you: this incredible high amperage is actually good for them.

What won't surprise you is that very few boats (none really) have anywhere near enough charging capacity to take advantage of AGMs incredible charge acceptance profiles. For most cruising sailors, switching to AGMs without a thorough review and upgrade of your charging systems is just throwing $$$ away.

Bill

[brianlara 3]

Btrayfors. I have given thousands of customers free advice re their cars over the years. I and others like me try our hardest to help save people money and minimise the frustrations of car ownership.
But, I have never, and I'm gettin' old, seen anyone try to help people as passionately and expertly as you do.
Whoever you are....you're supremely knowledgeable, a bloody good teacher, and seriously caring.
Sorry about the thread drift (like hell I am).

[btrayfors]

brianlara 3,

Very much appreciate the kind words.

That Sterling Pro 12/60 is just about the best charger on the market, IMHO. Have installed several of them on client's boats, and have had occasion to test them on the bench in my shop. As you say, brilliant!

Cheers,

Bill

[Rusty123]

I've long since lost the reference, but I once read that the 10% thumb rule for a shore charger (actually 10% + normal loads) is based on getting back to full charge overnight, while the 25% thumb rule (plus loads) for alternators is based on maximum acceptance (for FLA).

[GILow]

Well thank you all. From reading this I am getting the impression nobody is worried by my limited rate of charge, but more concerned that I can get the bank back to full charge.

On balance, I think I will go with the larger bank then, on the logic that the lower depth of cycle will be better for the batteries, and should I have some unexpected situation where I use a lot more power than normal it will be nice to have the extra capacity.

Matt


Sent from my iPad using Cruisers Sailing Forum

[brianlara 3]

Matt. Further to all this, and in what I'm about to suggest I am NOT an expert.
But, minimalists aside who I suspect are probably 5% of distance cruisers, dare I suggest the the majority of vessels have a dedicated charging system that is not reliant on wind, sun OR running a main engine IN NEUTRAL to charge the bank.
A great charger is essential and you've read what the Guru said about Sterling. Sure he sells and installs Sterling, but can sell Xantrax or Victron (or crap) if he chooses also. This guys livelihood depends upon being able to walk into ANY group of previous customers and not have to wear sunnies and a hood.
To me a charger is essential and it needs a source of clean pure sine wave energy.
Your Swanson presently doesn't have a dedicated diesel genset. And unless you install an A.C. cooking range you'll NEVER need one.
But, a Honda or Yamaha sitting outside, under a fabric cover and sprayed inside & out with Lanox is something I think you'll need when you head off. Surely in our waters we find many days of no wind and no sun. So if you're hanging off the hook, not motoring, not on the marina....a charger and genny need to be on the list.
Btrayfors...thank you.

[Krilleonnova]

Some basics from an old submarine engineer Pig boat Diesel electric
your whole life center around batteries and charge of same.

You can not regulate the charge amps it a function of the potential (voltage)
at the charging source generator or batt charger versus the potential Voltage is the batts.
Think of it as two buckets One is empty (Zero volt)and on the floor One has a hose fitted in its bottom it is full. Lift the full bucket a bit (put it on a stool) a certain flow rate in Gal/Min( AMPS) starts into the empty because the full one has higher potential(12Volt) Differential is 12 volt but decreases as water fills up the lower bucket.
Move the bucket with it hose to a table the difference in potential increases the flow increases (13 Volt) going down as the lower fills up. Keep topping up the upper bucket so it stays full to reduce confusion.
This discussion assumes you have a batt-charger or generator with unlimited capacity. So there is no drop in voltage delivered when the current AMPs go up.

Batts are low say 10 volt It now depends on how many batts you have in parallel
that means Ah say 100 Ah You set the Generator to deliver 13.6 Volts the amps
in the beginning as say 60 as the batt volt comes up=batt are more charged
Amps goes down When Batts are 13.6Volt = both buckets on the floor the pot.differance is Zero and the AMPS are Zero
Your batt supplier tells you the max charge voltage is 14.8v that means the rate of acceptance to charge AMPs is 100% and if you increase the voltage all extra amps will cook the batteries.
Acceptant is usually about 25% So if you have 100Ah your max charge should be below 25 AMPs Put two such batts in parallel and it will be 50AMPs which in these batteries corresponds to 14.8 Volt
Batteries after long exposure to voltage (moderate or High or trickle) To do an equalisation put them back in shape expose them to 16 Volt for 1/2 hour in repeated cycles the will gas -ventilation and get warm-- stop before they overheat lots of gas bubbles up it explosive no flame around. Batt supplier tells you max allowable temp and recommended equ. volt. Top up water .You will see
they charge and discharge better.
In subs you spend days under water moving slow and silent that build up sulphur.
What you do on the surface with good ventilation runs 5-6 Hours without the diesel to make the batt bank flat this is best done in an archipelago like Stockholm in the summer when all the chick are basking nude in the sum and you come around the corner at 18 knots dead silent-it will be a bit of a fight around the periscope alright.

[brianlara 3]

KRILLEONOVA....you plenty genius person. IMHO.

[TheThunderbird]

Your charging set-up can not match a big house bank

Split it in TWO banks
Advantages have been described thoroughly in another post

[GILow]

Originally Posted by TheThunderbird

Your charging set-up can not match a big house bank

Split it in TWO banks
Advantages have been described thoroughly in another post

Which post please? Also, can you elaborate on the charging setup not matching the big house bank?

[mitiempo]

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 absorption 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 !

A battery charger can not be too large in output. The battery determines the current it accepts, not the charger, for a given voltage setting.

[mitiempo]

Originally Posted by TheThunderbird

Your charging set-up can not match a big house bank

Split it in TWO banks
Advantages have been described thoroughly in another post

One large bank is always more efficient that the same size bank split in two.
This applies to charging efficiency as well as the fact that a larger bank is drawn down less with the same loads. This translates into longer life of the batteries.

One thing to consider is that regardless of how large the battery bank is the daily usage will be the same. The AH required to charge will not be different for a 675 AH bank than a 450 AH bank.

[brianlara 3]

All good input Mitiempo.

[TheThunderbird]

I can't remember... some 1month ago...


Unless you are a motorsailer pottering for hours, your alternator of 60A would take hours to charge a big bank. Mostly so with AGM, absorbing up to 1/3 of capacity nominal value approx (100Ah .... 30A charging)

Less so on FLA batteries, but still at least a 15/20% approx.

Your solar is just good for floating topped up bank (10A)

These are rule of thumbs, please verify my numbers/% further :-)