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Old 24-08-2020, 13:17   #1
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Time It Takes To FULLY Charge Batteries

Even with all the battery talk, posts, threads, and obsessive behavior here I can not believe how many times I read a cruiser on anchor/mooring post "my batteries are fully charged by 10am". This is just so misinformed and mostly just impossible. If you ran your refrigeration all night on the batteries you are not to be 100% FULLY recharged at 10am unless maybe if you have a 2000AH bank and only used 50AH last night (or some other crazy capacity to use ratio). And it matters little to nothing if you believe this because you have 1000W of solar and some "superfast" to charge in your mind GEL/AGM batteries. Even if you got full sun from 7am-10am, ran your engine with your 200A alternator, and ran your generator and 150A charger ALL AT THE SAME TIME you are not going to be 100% at 10am. Most of us might get there by 2-3pm.

To quote MaineSail: "Even the fastest charging AGM batteries require approximately 5.5+ hours to go from 50% DOD to 100% SOC, and this is in lab conditions with no chance of premature float and with 20% to 40% of Ah capacity in charging current. Flooded & GEL batteries charge even slower so absorption times will need to be adjusted to suit the batteries. The worst efficiencies for charging are from 85% SOC to 100% SOC and this duration alone, the last 15%, even with AGM batteries, often takes 3 – 6+ hours depending upon battery state of health."

If you are one of those that feels you are getting fully charged by 10am, do yourself a favor and research it so you understand. Meanwhile you have been sliding down the partial state of charge ramp a while.

I feel better now and am going back to the project I was working on that triggered this rant
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Old 24-08-2020, 13:41   #2
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Re: Time It Takes To FULLY Charge Batteries

My comment/question would be, do you ever get to 100% if you are constantly pulling amps out of you batteries (refrigeration, etc.) while you are charging an AGM or FLA?
Mathematically you could say you are putting in more amps than taking away, but does your battery (AGM/FLA) accept all of that?
We do go into float mode early (low daily usage and large house bank) and holds at 12.8V for a while after the solar input is 0, but you are still constantly drawing from the batteries.
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Old 24-08-2020, 13:58   #3
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Re: Time It Takes To FULLY Charge Batteries

I am not going to argue with people about their batteries, because why should/would I care?

But, what does "holds at 12.8V for a while after the solar input is 0" matter far as a measurement of the batteries getting to 100%? I don't believe it means much of anything.
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Old 24-08-2020, 14:47   #4
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Re: Time It Takes To FULLY Charge Batteries

If by fully you want 100% then the answer is NEVER.


If by fully you understand a specific Voltage or (older technology) density, then you can get them charged fully. Also you can achieve 99% or something like this and call it 100% (this is what instruments do).



I think most instruments display 100% when you are 99 something % full, others let you specify the offset.


In practical terms, when our boat is anchored in tropical Caribbean sun, our batts are back at 100% (my our monitor's standard) before noon.


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Old 24-08-2020, 14:51   #5
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Re: Time It Takes To FULLY Charge Batteries

The general concept of SOC using battery voltage for a 12V system is "100%" at 12.73V (or greater) measured w/no load or input.
If we are living on our boat, we are always measuring the V (or s.g.) with some sort of load on it, so is that measurement of SOC using V (or s.g.) accurate?
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Old 24-08-2020, 15:32   #6
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Re: Time It Takes To FULLY Charge Batteries

Quote:
Originally Posted by Bill O View Post
My comment/question would be, do you ever get to 100% if you are constantly pulling amps out of you batteries (refrigeration, etc.) while you are charging an AGM or FLA?
Mathematically you could say you are putting in more amps than taking away, but does your battery (AGM/FLA) accept all of that?
We do go into float mode early (low daily usage and large house bank) and holds at 12.8V for a while after the solar input is 0, but you are still constantly drawing from the batteries.

If you are "pulling amps out of your batteries", you are NOT charging them you are drawing sufficient amps from them to make up for the shortfall in what your charging sources are generating.

If you are generating more amps than your house loads are drawing from your charging sources, you are not pulling anythiing out of your batteries. The excess is going into your batteries.
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Old 24-08-2020, 15:40   #7
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Re: Time It Takes To FULLY Charge Batteries

Quote:
Originally Posted by Bill O View Post
The general concept of SOC using battery voltage for a 12V system is "100%" at 12.73V (or greater) measured w/no load or input.
If we are living on our boat, we are always measuring the V (or s.g.) with some sort of load on it, so is that measurement of SOC using V (or s.g.) accurate?
There is no load on your battery bank if you are generating sufficient energy to power your house loads. In that situation, you will be measuring the voltage of your generating source, not your batteries.
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Old 24-08-2020, 15:49   #8
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Re: Time It Takes To FULLY Charge Batteries

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Originally Posted by sailorboy1 View Post
Even with all the battery talk, posts, threads, and obsessive behavior here I can not believe how many times I read a cruiser on anchor/mooring post "my batteries are fully charged by 10am". This is just so misinformed and mostly just impossible. If you ran your refrigeration all night on the batteries you are not to be 100% FULLY recharged at 10am unless maybe if you have a 2000AH bank and only used 50AH last night (or some other crazy capacity to use ratio). And it matters little to nothing if you believe this because you have 1000W of solar and some "superfast" to charge in your mind GEL/AGM batteries. Even if you got full sun from 7am-10am, ran your engine with your 200A alternator, and ran your generator and 150A charger ALL AT THE SAME TIME you are not going to be 100% at 10am. Most of us might get there by 2-3pm.

To quote MaineSail: "Even the fastest charging AGM batteries require approximately 5.5+ hours to go from 50% DOD to 100% SOC, and this is in lab conditions with no chance of premature float and with 20% to 40% of Ah capacity in charging current. Flooded & GEL batteries charge even slower so absorption times will need to be adjusted to suit the batteries. The worst efficiencies for charging are from 85% SOC to 100% SOC and this duration alone, the last 15%, even with AGM batteries, often takes 3 – 6+ hours depending upon battery state of health."

If you are one of those that feels you are getting fully charged by 10am, do yourself a favor and research it so you understand. Meanwhile you have been sliding down the partial state of charge ramp a while.

I feel better now and am going back to the project I was working on that triggered this rant
Don't tell people that. No one wants to hear they burned a hole in their wallet for nothing. After all, that 200 amp externally regulated alternator driven by the new serpentine belt and two acre solar farm must do something------------right? They are even FULLY programmable.
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Old 24-08-2020, 16:09   #9
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Re: Time It Takes To FULLY Charge Batteries

Yeah, I had the engine rep try to sell me a new high capacity alternator, because, well, it'll charge faster, right?

With the current (is that a joke?) setup, we'll be down 45 Ah after a night at anchor. I start the engine and the battery monitor shows 45 A charging current. So I'll be good in an hour ... except 15 minutes later the batteries are only taking 25 A.

And a 200 Amp alternator would fix this how?
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Old 24-08-2020, 16:20   #10
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Re: Time It Takes To FULLY Charge Batteries

*shrug* when someone tells me that their battery bank is fully charged by 10AM, I assume they mean that it’s out of bulk. I say, “cool, man... wanna beer?”
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Old 24-08-2020, 16:51   #11
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Re: Time It Takes To FULLY Charge Dp

Quote:
With the current (is that a joke?) setup, we'll be down 45 Ah after a night at anchor. I start the engine and the battery monitor shows 45 A charging current. So I'll be good in an hour ... except 15 minutes later the batteries are only taking 25 A.

And a 200 Amp alternator would fix this how?
Well, it kinda depends on why the current has dropped off. Lots of stock alternators, Hitachi for one, have thermal sensors that back off the output as the alternator heats up. Many people here on CF have reported that this severely limits the output for them.

So, the 200 amp job might well charge faster... but, if your bank is small (you don't mention its capacity) you might well be correct and it wouldn't help all that much.

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Old 24-08-2020, 16:56   #12
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Re: Time It Takes To FULLY Charge Batteries

We pretty well always, run the motor to put most of the overnight Amp hours back in, then top off with solar. On a sunny day, fully charged is by midday. How do we know? Batts are at 14+ volts and input amps are around 2A on a 500 amp hour bank. For me it’s all about what the batteries are accepting.
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Old 24-08-2020, 16:56   #13
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Re: Time It Takes To FULLY Charge Dp

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Originally Posted by Jim Cate View Post
Well, it kinda depends on why the current has dropped off. Lots of stock alternators, Hitachi for one, have thermal sensors that back off the output as the alternator heats up. Many people here on CF have reported that this severely limits the output for them.

So, the 200 amp job might well charge faster... but, if your bank is small (you don't mention its capacity) you might well be correct and it wouldn't help all that much.

Jim
Thanks for the nuance, Jim, I didn't specify: our bank is 210 Ah so I'm pretty sure that counts as small by the standards of most people here.
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Old 24-08-2020, 17:16   #14
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Re: Time It Takes To FULLY Charge Batteries

My battery "bank" is 180 ah.

So when I sailed off at 5:30 am Sunday I had 11.8 volts. Fans run all night and lights when I wake up several times a night.

So I used my handheld compass and tiller autopilot only for the first few hours sailing home.

Got back to the marina at 1400.

My 115 watts worth of panels still don't have the bank in float yet due to the cloudy day we had.

Was running only 65 watt panel after returning to the dock as the other panel was facing away from the sun and partially blocking the 65 watt panel. I pulled out another 20 watt panel today at 5 pm so batteries should be fully charged by tomorrow noon.

Lots of variables here

50 watt panel is hooked to a PWM controller and the 20 watt and 65 watt panel to the Victron 75/15 controller

All power is off when not sailing

If I was sailing, I'd hookup my other 20 watt panel directly to the batteries no controller to give me 155 watts worth of panels

Solar is the only charge for the batteries on my boat. The outboard doesn't have an alternator......and I do not hookup to shore power
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Old 24-08-2020, 17:29   #15
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Re: Time It Takes To FULLY Charge Batteries

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Originally Posted by anotherT34C View Post
*shrug* when someone tells me that their battery bank is fully charged by 10AM, I assume they mean that it’s out of bulk. I say, “cool, man... wanna beer?”

10 AM will be a challenge. How hard a challenge, depends on many things.


If they are somewhere in the latitudes that the Sun is up at 05:00 ...


If they drew only small amt of juice the night before ...


etc.


In the Caribban this would be a challenge: it is winter, the sun pops-up late and you are "behind" an island - most anchorages are on lee sides and many islands are very tall.


Also, measuring anything by 'bulk' is not measuring at all. Bulk is a state of the charger, not a state of the battery.


Almost all battery monitors (except for very basic ones) have remote shunts and measure Amps out and Amps in and remember the size of the battery. So when they say 100% they normally imply you have by now charged as much as you were Amps short before you started charging. Off course 100% does not mean 100% but much rather something like +99%. Some monitors let you define what that mystic 100% actually is. (Ours does, we have a Bogart.)



Let alone other factors - like your battery technology. Mind some of us are already on Lithium banks. These will suck whatever Amps you throw at them. You may be fully up at 10:00 too.


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