A Question on Charging

[svlamorocha]

Originally Posted by Maine Sail

It is a myth that batteries can't attain 100% SOC at less than their absorption voltage. They can hit 100% but doing this regularly will not be healthy for them owner the long haul.

Sorry for my sloppy wording and of course you are right. I should have clarified that at less than specified absorption voltage the batteries can eventually reach 100%.. .. but the owner will turn off the engine/genset or the sun will set before that happens, hence they will not reach 100%.

[Maine Sail]

Originally Posted by svlamorocha

Sorry for my sloppy wording and of course you are right. I should have clarified that at less than specified absorption voltage the batteries can eventually reach 100%.. .. but the owner will turn off the engine/genset or the sun will set before that happens, hence they will not reach 100%.

Heck most sailors rarely run 2 hours let alone 7 hours plus.....

[a64pilot]

A good thing about the smart Gauge is it seems to be a pretty good voltmeter, and of course tells you voltage at the battery terminal, so you can tell if you have any losses and how big they may be.



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[sailinglegend]

Originally Posted by Maine Sail

Once again thanks to MainSail for this test.

I offer some thoughts, please correct me if I am wrong.

1. This shows a 135Ah AGM battery charging at the absorption voltage of 14.4v until full. In practice this never happens as any charge controller will drop down to a Float voltage of 13.2v for this battery. Nearly all charge controllers work on some kind of time at Absorption before they drop to Float - because they don't actually measure the current going INTO the battery. So in practice maybe 4 to 5 hours into the charge cycle it could drop to the much lower Float voltage and so the current going into the battery at this point will drop considerably, so the time to 100% charge could go from 7 hours to maybe 10. Another test to confirm this with a real life controller would be worthwhile.

2. This is a test run on a Lifeline AGM which, depending on its age, had a much higher charging efficiency than an FLA battery. So a 135 Ah FLA will take even longer than this graphs shows. Another test with equally aged AGMs and FLAs to determine this difference would be interesting.

3. This test is at 20% of the battery capacity - recommended for FLA batteries - so if the house bank was about 400 Ah then a charge source of at least 75-80A would be needed to produce a similar charging time. Most solar set ups get nowhere near this so may never get to 100% full because there are just not enough hours in the day. Even if a little green light comes on to tell you they are full they may have dropped to Float too early, which depending on the time at absorption settings of the charge controller could only be 90% full or less!

Most people think their batteries get to 100% much quicker than actually happens in practice. Many never get to 100% often enough which leads to sulfation and premature death.

[svlamorocha]

Originally Posted by sailinglegend

Once again thanks to MainSail for this test.

I offer some thoughts, please correct me if I am wrong.

1. This shows a 135Ah AGM battery charging at the absorption voltage of 14.4v until full. In practice this never happens as any charge controller will drop down to a Float voltage of 13.2v for this battery. Nearly all charge controllers work on some kind of time at Absorption before they drop to Float - because they don't actually measure the current going INTO the battery. So in practice maybe 4 to 5 hours into the charge cycle it could drop to the much lower Float voltage and so the current going into the battery at this point will drop considerably, so the time to 100% charge could go from 7 hours to maybe 10. Another test to confirm this with a real life controller would be worthwhile.

2. This is a test run on a Lifeline AGM which, depending on its age, had a much higher charging efficiency than an FLA battery. So a 135 Ah FLA will take even longer than this graphs shows. Another test with equally aged AGMs and FLAs to determine this difference would be interesting.

3. This test is at 20% of the battery capacity - recommended for FLA batteries - so if the house bank was about 400 Ah then a charge source of at least 75-80A would be needed to produce a similar charging time. Most solar set ups get nowhere near this so may never get to 100% full because there are just not enough hours in the day. Even if a little green light comes on to tell you they are full they may have dropped to Float too early, which depending on the time at absorption settings of the charge controller could only be 90% full or less!

Most people think their batteries get to 100% much quicker than actually happens in practice. Many never get to 100% often enough which leads to sulfation and premature death.

Spot on. The key is to work out how long you need to run the engine/genset ***in the morning***** to reach the SOC you want in the evening (say 80% every day and 100% once a week), taking advantage of solar for the current "taper" in the top 25%.

If you run engine/genset the late in the day just to stop the monitor from beeping then you will never get to 100% or 90%.

[Maine Sail]

Originally Posted by sailinglegend

Once again thanks to MainSail for this test.

I offer some thoughts, please correct me if I am wrong.

1. This shows a 135Ah AGM battery charging at the absorption voltage of 14.4v until full. In practice this never happens as any charge controller will drop down to a Float voltage of 13.2v for this battery. Nearly all charge controllers work on some kind of time at Absorption before they drop to Float - because they don't actually measure the current going INTO the battery. So in practice maybe 4 to 5 hours into the charge cycle it could drop to the much lower Float voltage and so the current going into the battery at this point will drop considerably, so the time to 100% charge could go from 7 hours to maybe 10. Another test to confirm this with a real life controller would be worthwhile.

It was a 125 Ah battery based on as new specs. You are spot on that this test represents an ideal situation a .2C charge rate that stayed constant, 80F battery temp and 14.4V held all the way to full before it dropped to float. This is not going to be very representative of charging performance on perhaps 98% of the cruising boats out there due to premature floatulation, dumb but supposedly smart chargers, voltage drop, incorrect absorption voltage settings etc. etc. etc.. Even with AGM's charging time can exceed 7+ hours and can go upwards of ten+ very easily on a poorly designed system..

Originally Posted by sailinglegend

2. This is a test run on a Lifeline AGM which, depending on its age, had a much higher charging efficiency than an FLA battery. So a 135 Ah FLA will take even longer than this graphs shows. Another test with equally aged AGMs and FLAs to determine this difference would be interesting.

Charge efficiency is higher on AGM's but is still very dependent upon charge current for the best efficiency. Bulk on flooded or AGM is still very, very efficient but absorption charging is very inefficient. As batteries begin to sulfate getting them to full takes even longer.

Originally Posted by sailinglegend

3. This test is at 20% of the battery capacity - recommended for FLA batteries - so if the house bank was about 400 Ah then a charge source of at least 75-80A would be needed to produce a similar charging time. Most solar set ups get nowhere near this so may never get to 100% full because there are just not enough hours in the day. Even if a little green light comes on to tell you they are full they may have dropped to Float too early, which depending on the time at absorption settings of the charge controller could only be 90% full or less!

This test was done at .2C because the customer had an alternator capable of roughly .2C. A charge rate of .2C is the minimum charge current Lifeline wants to see. If I had charged it at .4C the bulk time would be shorter and the current taper would start earlier in the SOC curve.. Charging at low solar charge currents means hitting absorption much later in the SOC curve and higher efficiency charging because we are returning the bulk of the energy in bulk mode without needing voltage limiting until the very end....

Sadly we won't get around lawyer safe chargers and premature floatulation "egg timer" charge methods anytime soon. There are good controllers and regulators out there that allow full custom programming but most boaters don't fully understand them nor are they willing to spend the money on them because marketing says "smart is smart", right....????

Originally Posted by sailinglegend

Most people think their batteries get to 100% much quicker than actually happens in practice. Many never get to 100% often enough which leads to sulfation and premature death.

Bingo!! PSOC cycling of batteries is murder on them and dumb so called "smart" gear only leads to a false sense of actually being charged. Batteries don't die they are murdered by their owners.....

P.S. Just left a new customers boat at 3:00 for an autopilot issue and noted the batteries at 11.8V, and the boat is on a mooring..... When I mentioned it to the owner he thought that was normal and pretty standard for his use. He gets 2 years from the bank and was also fine with that.

[a64pilot]

So for a 660 amp bank of Lifeline batteries you need 120 amp charger? To power that would take roughly 20 Amps of 120V AC current?
I have currently a single 60 amp charger, but it seems that it's current tapers off after the first hour or so to less than 60 amps, so do I really need 120 amps of charger?
My plan is twice a week to run the generator early in the morning to make water and charge batteries, hopefully get them through the bulk phase and let Solar get them to 100%.
I believe my nightly consumption will be about 100 amp hours, so I don't think I will ever be close to 50% discharged.
Or would it be better to only use the 440 amp hour house bank to run house loads instead of a single 660 amp hour single bank?


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[EllisElectric]

Does anyone use the Hydrometer to test the fluid in the cells? That probably could be done during charging.

[capt ric]

hey all,,,I wouId like to retire on a 40ft or so cat with a good genset , ac ,watermaker...run the gen for couple hrs and top off with solar ...is this possible? I dont want to be crawling around with a voltmeter...any bulletproof monitoring/charging system u could recomend???

[capt ric]

I know the above comment question may be sound stupid but I want to keep things simple...just how do these smart regs work??? dont u need to let the bank rest after charge then measure voltage....12.7 is 100%....??? Seems like on a boat something is always on ....how can you ever get to 100%.....maybe close but isnt that unrealistic to get to

[cwyckham]

Originally Posted by capt ric

I know the above comment question may be sound stupid but I want to keep things simple...just how do these smart regs work??? dont u need to let the bank rest after charge then measure voltage....12.7 is 100%....??? Seems like on a boat something is always on ....how can you ever get to 100%.....maybe close but isnt that unrealistic to get to

Most people use battery monitors that measure and total up the amps going in and out of the batteries to keep tabs on how they're doing. They have their limitations, but I love knowing the real time flow of amps.

Mainesail has recommended a neat device that's more accurate and simpler to install, but doesn't show amps. You can read his in depth article about the Smartgauge here.

None of these need you to get to resting voltage. As you say, you'll never be able to actually read resting voltage because your batteries are never resting.

[daveNZ]

Originally Posted by Maine Sail

Charge efficiency is higher on AGM's but is still very dependent upon charge current for the best efficiency. Bulk on flooded or AGM is still very, very efficient but absorption charging is very inefficient. As batteries begin to sulfate getting them to full takes even longer.

Is there any guide as to what SOC a battery is at when it reaches the end of the bulk charging phase?

In a small, 150-200AH bank is the higher charge efficiency of AGM going to allow shorter engine charging time to reach either the absorption phase (by alternator) or fully charged (by solar); it should in theory but does it translate to actual experience on the water?

[exMaggieDrum]

This long thread, and all the different opinions, and the good information, points out that in the real world nothing is perfect. Most, maybe 99%, of cruisers never even come close to 100% charge of new batteries let alone ones in service for any period of time. IF - you had a big .2C AC chargers, and a big alternator, and you ran your generator or main engine for long periods of time (far longer than most want to run them), then you could do the "best" job, and even then that would not be lab conditions. Even in lab conditions batteries start deteriorating as soon as they are cycled.

So - replacing batteries and spending money, time, and energy on charging are legitimate, if unfortunate, costs of cruising. It sucks because all of this, especially batteries, are expensive. At least the charging equipment can last longer than the batteries, but like everything else on a boat (or a car or a house or whatever) has a useful life and then it has to be replaced.

Previously, we had a big heavy boat that did not go to windward worth a darn. I had 400+ amp-hrs of new AGMs. I had an inverter/charger that could pump 150 amps and my HD alternator was 125 amps with a reasonably good Balmar smart regulator (which I programmed the best I could for my setup). We had pretty good solar too - I routinely got 20-25amps, with a good (at the time) "smart" regulator. We also had very large fuel tankage. We motored a lot, far more than average cruisers, so the big alternator and Ford Lehman 80hp kept the batteries up pretty well. We got 6 years of good use of the batteries and the new owner got another 4 years before replacing them. I call that pretty good. I will not see that long of life on my current boat. It sails well and has a good alternator and large solar but I will never get the life out of my current AGMs that I got before. I will never, routinely, get them to as high a SOC as I did, routinely, on my previous boat. I have to accept that and get on with cruising. And save up to replace my batteries when they need to be replaced.

[daveNZ]

Apologies, silly question, the answer to my first question would be the often mentioned 80% (approx).

I'll rephrase the second part as well:

In a 200AH bank does higher charge efficiency of AGM lead to reduced Bulk or Absorbtion charging time; it should in theory but does it translate to actual experience on the water? (assuming best voltages etc)

[mitiempo]

Originally Posted by daveNZ

In a 200AH bank does higher charge efficiency of AGM lead to reduced Bulk or Absorption charging time; it should in theory but does it translate to actual experience on the water? (assuming best voltages etc)

Agm batteries will accept higher current in bulk, for a while anyway. Depending on the size of the charge source with a bank of 200 AH you may gain a little bit up to 80 - 85%. After that Agm batteries have increasing internal resistance same as Fla batteries. The last 15% will take 6 to 8 hours. The charging is best finished with solar.