Time It Takes To FULLY Charge Batteries

[CWayne]

That's true, battery charge/care needs to be studied as there's more than you think to it. I have 15 years battery maintenance on large power systems and sailed the world for 22 years.I lived at anchor as much as possible but to fully charge my battery bank I had to plug in somewhere even though I had solar, wind, 100A Alternator with manual control.
One helpful thing I did was use an old style 100amp simple battery load tester, an accurate digital voltmeter and a clamp-on ammeter to measure/record the voltage and current for one minute under load. Then a graph of the results will enable you to determine the decrease in ampacity and the approximate end of useful battery life. Then I would adjust my charge time until my readings were satisfactory. All this takes time and study. Good luck and enjoy the sailing life.

[lituya1617]

In any 12 volt system, the batteries control the charge rate, not the alternator. A huge alternator is nuts. A typical large battery (like an 8 D heavy equipment battery) will accept a high amp charge for only a few minutes and then will taper down the amp scale to something like 40 amps. A few minutes later the battery will accept only 20 amps. If you really want to do it, use your computer to generate a series of superimposed graphs showing how quickly you can charge your batteries given an initial state of charge. It takes a certain amount of time to "pump" electrons into the battery to "fill the spaces left" when the battery is drained. This takes much longer than most people appreciate. You have to fill the bucket with a small hose, so to speak. It will depend on the battery and how much charge it will accept at a given state of charge, not on what the alternator can produce. You cannot achieve 100% charge because that point is approached as an asymptote in the charging process. What you do achieve is a point beyond which the battery will not accept any additional electrons you are trying to cram into it. At that point the alternator will only be generating electricity to overcome resistance of the circuit and internal resistance of the battery - not charging the battery further.

[a64pilot]

Originally Posted by s/v Jedi

You can not use voltage. Instead, use the SOC value on your battery monitor, it shows you the exact percentage.

When you have full batteries and run the microwave, the voltage may show 11.8V but the batteries are still full.

You can use voltage, its likely more accurate than most battery monitors because most aren’t reset frequently or correctly.
Now there is a caveat to that, you can’t be running your water heater off of the inverter while you use voltage, you need to be at a normal house load, which most often ought to correspond to a 20 hour discharge profile.
This is the lifeline vs SOC under load chart that’s in their manual that I printed out.

Now thats Lifelines chart, but you can make your own from observations of your own bank, you really can monitor your bank with nothing more than a voltmeter, and some knowledge of batteries, you don’t need anything else, other things are nice, but not required.

[barnakiel]

Originally Posted by lituya1617

In any 12 volt system, the batteries control the charge rate, not the alternator. A huge alternator is nuts.


(...)

No. The batteries may LIMIT, not regulate the charge rate.


And while a huge alternator will be nuts on a small battery, it may be a good buy when the bank is big too!


A well sized alternator shortens the time required to charge the bank. (Unless the bank is never seriously (30-50%) discharged in a cycle).



Real life example: our house bat is 100Ah. Our alt is 60A. It basically does a fine job in this case. But how well is it suited for a 400Ah battery - in case the owner likes to discharge deep then recharge? Answer: sub-optimally.



We may also look at life of the alternator. I would guess that a big one may be less stressed given a fixed bat bank size.



Cheers,
b.

[a64pilot]

Originally Posted by gamayun

What voltage do you people let the AGMs discharge to before charging? Asking for myself as I'm working out an issue related to charging. In other words, what's your critical 50% point? Lifeline says 12.2 v. But if solar ain't doing it, do you run auxiliary power at that point to get some charge in or do you let it discharge a little more? If so, how low and how often is this acceptable to you?

Most ought not get close to the 50% point, it’s best to use a shorepower charger or alternator to charge the bank first thing in the morning, because that’s when a bank can accept large charge amperage. If you have an average bank and happen at 50% SOC, then if you have a large enough charge source it’s not hard to get to 85% SOC in an hour or so, whether that be a large alternator or a generator.


However I see most often people running their engines in the afternoon to get enough charge in to get them through the night, and if they have Solar that is very inefficient, the reason is because the bank won’t accept many amps, so your getting very little charge over time.
Use a generator or alternator to get to 85% SOC or so early in the AM, then let Solar spend all day polishing off the last 15% because that takes time more than amps.

Personally I wake up at 75% SOC or so, run the Honda for 30 min or so and get to 85% ish and shut it down and let Solar take me to 100% by end of the day.

[sailorboy1]

Originally Posted by a64pilot

Personally I wake up at 75% SOC or so, run the Honda for 30 min or so and get to 85% ish and shut it down and let Solar take me to 100% by end of the day.

Really? Your KW of solar can not do it without the added 35-50AH of a 30 minute generator and battery charger run?

[barnakiel]

Originally Posted by a64pilot

(...)


Personally I wake up at 75% SOC or so, run the Honda for 30 min or so and get to 85% ish and shut it down and let Solar take me to 100% by end of the day.

I too think that in many boats, it is best to deploy the heavy hammer when the batteries are lowest and at the end of the discharge circle. Pump it hard for a brief time, then switch off and let the sun or wind top off.


Wind is very nice to have where it is windy, as it will also produce overnight while the boat systems keep on doing without solar input. This often helps avoid the morning Voltage blues.



b.

[a64pilot]

Originally Posted by sailorboy1

Really? Your KW of solar can not do it without the added 35-50AH of a 30 minute generator and battery charger run?

Not in the middle of Winter, and not guaranteed. It may be a cloudy day later, or rain, or maybe not.
The catch 22 is if you decide later in the day that your not going to get to 100% SOC but want to, it may take a couple of hours generator run time to get there, because all your batteries will accept is 6 or 8 amps or so.

However in the morning early, the Honda can charge them at a 100 amp rate, and the batteries will accept it, so in 30 min, I can get 50 AH into the bank, not quite 50 of course because nothing is 100% efficient, but at low SOC it’s pretty efficient.

To get 50 AH into the bank at the end of the day will take hours.

So a 30 min Honda run in the morning pretty much guarantees a full charge even if it gets cloudy or we get some rain.

With a Firefly bank, I wouldn’t be so anal about getting to 100%, so I’d skip the generator run and if I only made it to 95%, so what, maybe we will make 100% tomorrow.
However as I make water twice a week, and I’m my case that means generator runs, that guarantees I will make 100% SOC twice a week, which ought to be ideal, for a FF bank?

It’s not, not making it to 100% everyday that might be a concern, it’s not quite putting back in what you took out every day, that of course would mean each day your walking your SOC down, the twice a week watermaking sessions would eliminate that concern.

[a64pilot]

The numbers work out sort of like this.
I use 150 AH overnight
My Solar is capable of 300 ish AH a day
We probably use 150 AH during the day, the day is shorter but we use more power during the day.
So throwing in 50 AH first thing in the morning means Solar only has to cover house loads and add 100 AH back into the bank, not the whole 150.

Plus getting to absorption early means we have excess power, power that I can then use to run the inverter, make ice, vacuum the boat or maybe wash clothes with the clothes washer or even watch some TV.

Besides a 30 min run on the Honda is maybe a quart of gas?

[FlyingScot]

Originally Posted by a64pilot

Not in the middle of Winter, and not guaranteed. It may be a cloudy day later, or rain, or maybe not.
The catch 22 is if you decide later in the day that your not going to get to 100% SOC but want to, it may take a couple of hours generator run time to get there, because all your batteries will accept is 6 or 8 amps or so.

However in the morning early, the Honda can charge them at a 100 amp rate, and the batteries will accept it, so in 30 min, I can get 50 AH into the bank, not quite 50 of course because nothing is 100% efficient, but at low SOC it’s pretty efficient.

To get 50 AH into the bank at the end of the day will take hours.

So a 30 min Honda run in the morning pretty much guarantees a full charge even if it gets cloudy or we get some rain.

With a Firefly bank, I wouldn’t be so anal about getting to 100%, so I’d skip the generator run and if I only made it to 95%, so what, maybe we will make 100% tomorrow.
However as I make water twice a week, and I’m my case that means generator runs, that guarantees I will make 100% SOC twice a week, which ought to be ideal, for a FF bank?

It’s not, not making it to 100% everyday that might be a concern, it’s not quite putting back in what you took out every day, that of course would mean each day your walking your SOC down, the twice a week watermaking sessions would eliminate that concern.

We now have 900 ah @ 12v FF and 1440wp solar.
I agree that the best time to run the Honda is in the morning.
Once or so per week, I turn the Victron 'master' controller float voltage to the same as absorption. Run the Honda for an 1.5 hours or so in the morning almost guarantees I can watch for trailing amps to get low enough in the mid afternoon to be 100% SOC.
We use about 300ah overnight.

Solar is unpredictable. Yesterday we had our record low solar harvest of 1.63kwh. Our normal is 5-6kwh. Max record is 8.5kwh and normal low is 4kwh.

People still seemed to be confused that batteries are either charging, doing nothing or discharging. Power doesn't flow through the battery to the house loads while it's charging. If voltage is steady at absorption level and amps are low enough, that's what matters, not how much house loads you have when looking for trailing amps.

[sailorboy1]

Originally Posted by FlyingScot

We use about 300ah overnight.

[sailorboy1]

I have running my generator a lot lately. Yesterday was a good sunny day plus i ran the battery charger for hours.

Still didn't get my batteries FULLY charged. In fact i don't think they have gotten to 100% in the last 14 days.

[Tonali99]

Originally Posted by StuM

So if I have a constant 1 Amp load on a 100Ah battery and run it down from 100% to 50%, it will take 50 hours to charge?
And if I pull 50 Amps out of it for half an hour, it will only take half an hour to charge back up?




So if I'm drawing 5 Amps house load and I have a 30 Amp smart charger, I cant charge my batteries?



Somehow I doubt your claims.

No, you misunderstood them. I never mentioned any specific time frame.
How long did it take to run them down?

[motion30]

Originally Posted by Wotname

It works the other way around down under - jus' saying....

He may have those new bipolar solar panels.. then that would make sense

[akopac]

Not looking for critique, just putting my situation, data forth.
Location : La Paz, MX - anchored
Air Temperature - 27.6C
Water Temperature : 23.4C
Charging source : 400W directional solar
Charger Controler : Tracer 4215bn temp. Compensated - 2 stage charging program per ocean planet.
Battery Bank - 4 31-Firefly’s
Usable battery Capacity -464amphrs
Refrigerator - isotherm sp thruhull condenser cooled 5.75 cubic foot, 5-7 inch blue foam relatively well constructed. Isotherm sp2551.
Lighting - LED
Navigation system - Opencpn on Raspberry Pi

I included some info on the main loads on board as I think it’s critical to understand why my case might be interesting.
Typical battery consumption from dusk 6pm to dawn 6am 12Hrs with no audio video use is ( includes frig. Lighting, Raspberry Pi Nav/WiFi access point, AIS Transponder, LED Anchor lights) :
Total:
28-30 amphrs

If I’m programming or watching a movie I will be using a 200w inverter usb charger with another Raspberry Pi on it and a 24 inch Supersonic TV/Monitor plugged in for a couple hours. Around 10amphrs.
Total :
~40 amphrs overnight with entertainment.

My batteries are generally floating by 10-11am at 13.3-4 volts 4-6 amps.

I experienced similar numbers in Sacramento delta with 38C air temps. and 20C water temps.

No claim here for full bank at 10am, but I will put forth that efficient use of power makes a BIG difference in how much you have to put back in. Specifically the insulation in you frig. A lot of the power being put back into your bank in the morning is being used to remove heat leaking into you frig./freezer box all day and that doesn’t even matter what kind of batteries or charge system you have.