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Old 24-05-2013, 16:39   #31
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Re: battery charging from my generator

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Originally Posted by sailinglegend View Post
The charger doesn't lower the current, the battery resistance increases at it charges - this lowers the current.

Sometimes a picture helps:
You are being pedantic on this point.

I will stand by my statement - the charger does control the average current. The regulation circuits keep a constant voltage on the battery. The voltage is maintained by limiting the time current is supplied to the batteries. So while the absolute current at any precise MOMENT in time is that which the battery will accept, the current OVER time is controlled by the charger by limiting the amount of current it lets the battery have.

If it was left solely to the battery resistance, the voltage would approach very high values as the battery accepted current. So the only way your statement is correct is when the voltage of the battery is controlled.

And that voltage is controlled by the charger controlling the amount of time it allows the battery to draw current from it. Thus, the charger controls the current going into the battery.

This pulsing control of current is what causes the electronic noise generated from these switching regulators.

Solar regulators work the same way, as do alternators. When an alternator regulator goes, the battery accepts current until the saturation point of the windings, which is 15-17V (or more) for many alternators.

Mark
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Old 24-05-2013, 16:47   #32
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Re: battery charging from my generator

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Originally Posted by btrayfors View Post
Hold steady the voltage (the charger does this). The battery itself will determine how much amperage it will accept, and this depends on several factors, most important is it's state of charge and its chemistry.

Bill
But it all comes down to how the charger holds steady the voltage. It does this by controlling the amount of current over time the battery is allowed to take from it.

Yes, it can't force acceptance greater than what the battery will intrinsically accept, but it does throttle back the amount of time the battery is allowed to draw the current. And the battery can ALWAYS accept more current in our world because we do not want it boiling.

So the charger DOES control the current into the battery when the battery can accept more current than the voltage setpoint will allow.

While this is a pedantic point, in practical applications, the battery does not generally determine how much amperage it will accept for two reasons:

1. it is a current pig
2. our charging systems cannot exceed the current acceptance rates of batteries at recommended bulk and absorption voltages.

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Old 24-05-2013, 23:35   #33
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Re: battery charging from my generator

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Originally Posted by colemj View Post
You are being pedantic on this point.....
We are ALL being pedantic, and we are all correct - but I fear confusing a lot of people.

The bottom - simplistic line - is that the charger can't - as much as we would like it too - put any more amps into the battery whilst maintaining that constant voltage. The battery decides what current it wants and the controller controls how much it gets by limiting the voltage. (Thanks Maine Sail).

This is why, in the constant voltage absorption phase in my graph, the current falls away very slowly and the battery takes a long time to get the amps in that it needs to get to 100%. That graph is all to do with what the battery will accept in terms of current, and what it needs in terms of voltage.

If only we could force more current in and maintain the same voltage we could get our batteries fully charged faster - but we can't get the charger to do that.
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Old 25-05-2013, 01:30   #34
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Re: battery charging from my generator

I just wanted to post his topic by Rick How "fast" you can reliably charge your battery.

Thought some of the readers here might like to read.

Lloyd

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This discussion applies to deeply discharged house batteries and not start-only start batteries. A deeply discharged battery is one which is "missing" 10%, or more, of its potential capacity (note that I did not say "rated" because an aged battery will not exhibit a fully charged potential capacity equal to its rated one).

The answer: A charging current equal to the value of the number of Amp-hours missing from the battery will not excessively gas or heat the battery. This is the so-called "Amp-hour Law" which was proposed many years ago in the literature. Now what's interesting about this concept is that a charge curve following this "law" forms what is called the curve of Epsilon, an ever decreasing curve of charge current. What is also interesting is that when using 3-step chargers having an appropriately set absorption voltage and a sufficiently large charge source the resulting curve will almost approximate the Amp-hour law. When precisely following this curve you can safely recharge an 100% discharged battery in 3 1/2 hours with many AGM and GEL cel batteries and closer to 4 hours for flooded batteries. All lead-acid batteries designed to deliver heavy discharge currents (like you need for cruising with a microwave oven, etc) will be capable of folloing this "law".

If you have, for example, a 400 A-hr bank which is discharged 50% then you can safely begin charging at 200A. Immediatly, of course, the current begins to drop to follow the curve. If you have a battery monitor and an adjustable voltage setting for your acceptance charge voltage you can observe the A-hr value missing from the battery and switch to observe the charge current setting the charge voltage until the current equals the missing A-hr value. Guess what? If you do this you might notice that for your system the voltage required to do this initially might be close to 14.7 to 15 Volts for ambient temperatures of about 70 degrees F. If you keep watching you might notice that with some AGM and some GEL batteries you can leave the voltage there and the battery charge acceptance prevents the charge current from greatly exceeding the Amp-hour law. Note that the Amp-hour law does not dictate that the curve should not be exceeded merely that if you want to GUARANTEE no excessive temperature rise or gassing you may follow it.

Obviously 14.7 Volts is higher than the "normal" setting of 14.4 V for 70 deg. F, yet not by much. You WILL notice, however, that a mere 100 milli-volt change can cause huge current changes, which is why a well regulated source is desirable. Why am I telling you this? Because when Ample-Power and Cruising Equipment (They influenced Heart Interface as well) began promulgating the concept of using 3-step charging they picked a first-approximation to this Amp-hour curve which would, in general, be relatively easy to implement yet safe for the batteries. The IMPORTANT result is that capacity lost to a dischargte cycle can be immediately recovered. Charging a deeply discharged battery at voltages always below the recommended acceptance voltages DO NOT result in capacity recovery on a repeated cycle basis and equalization cycles are required to do so. Using higher acceptance voltages resulting in a closer Amp-hour curve CAN recover lost capacity (unless permanent sulphatation has occured).
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Old 25-05-2013, 04:56   #35
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Re: battery charging from my generator

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Originally Posted by motion30 View Post
In other words at what charging amps displayed on my panel should I call it a day for.charging, and shut down the generator ?o

Are you wishing you hadn't asked yet?

I assume you have wet cells.

My opinion is that once you get to absorption voltage you are pretty much charged. If you stopped at that point you would be fine as long as every once in a while you charged fully and equalized.

Or; get a battery monitor and charge to 85% state of charge in the morning and every few weeks do the full charge and equalize.

I ain't no expert but can answer a question without a bunch techno talk.
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Old 25-05-2013, 08:19   #36
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Re: battery charging from my generator

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Originally Posted by sailinglegend View Post
The battery decides what current it wants and the controller controls how much it gets by limiting the voltage. (Thanks Maine Sail).
How does the charger limit that voltage? It does so by limiting the amount of time the battery takes current from it (decreases the duty cycle) - thus controlling the current going to the battery.

Note that your graph is a relationship of current vs time. In the absorption part of your graph, the current falls away because the charger does not allow the battery to receive as much current over time as it did during the bulk phase. This is how it controls the voltage on the battery.

You postulated that the charger does not control the current. That is wrong. It limits the amount of current the battery draws from it through limiting the voltage it allows the battery to reach. It controls that voltage by limiting the current drawn per unit time (the operational duty cycle).

The amount of instantaneous current drawn within any microsecond will not be any more than the battery can take regardless of voltage, but that is true for bulk, absorption and float modes, as well as for an unregulated supply. It is similar to that in which only a set amount of water can flow through a hose of a given length. While a nice physics and chemistry point, it is not very meaningful when talking about how chargers work and how batteries are charged.

To make this topic practically clearer for most, one should think of battery charging as the charger supplying constant current without regard to voltage until a set voltage is reached and then modifying that current supply to keep the voltage constant until the batteries are full. After which, it only supplies a small amount of current to keep the batteries at a voltage slightly higher than nominally full.

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Old 25-05-2013, 08:24   #37
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Re: battery charging from my generator

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Originally Posted by Don L View Post
Are you wishing you hadn't asked yet?

I assume you have wet cells.

My opinion is that once you get to absorption voltage you are pretty much charged. If you stopped at that point you would be fine as long as every once in a while you charged fully and equalized.

Or; get a battery monitor and charge to 85% state of charge in the morning and every few weeks do the full charge and equalize.

I ain't no expert but can answer a question without a bunch techno talk.
Don, you have stumbled into CF - did you mean to?

Regarding your point about reaching absorption equaling mostly charged. I will dispute this. The absorption point is a voltage setpoint where the batteries are still accepting close to bulk current for quite a while yet.

You bring up a good point, though, regarding monitoring. It is probably fair to state that once the current in absorption mode has dropped in half from that in bulk, you have reached 85% charged or so. So one could broadly monitor charging based solely on charger output.

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Old 25-05-2013, 08:26   #38
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Re: battery charging from my generator

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Originally Posted by FlyingCloud1937 View Post
I just wanted to post his topic by Rick How "fast" you can reliably charge your battery.

Thought some of the readers here might like to read.

Lloyd
Lloyd, Trojan recommends a bulk and absorption setting of 14.8V for their batteries.

The problem with Rick's thesis is that with most of our larger banks, most of us cannot supply the charging current that meets his reasoning.

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Old 25-05-2013, 10:03   #39
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Re: battery charging from my generator

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Originally Posted by colemj View Post
Don, you have stumbled into CF - did you mean to?

Regarding your point about reaching absorption equaling mostly charged. I will dispute this. The absorption point is a voltage setpoint where the batteries are still accepting close to bulk current for quite a while yet.
I've been watching my solar controller compared to my battery monitor. I have noted that the solar controller goes into absorption mode right about the same time that the amp-hours out of the battery hit 0.

But it was my opinion and of course would depend on each persons definition of charged as far as practical boat battery use goes.
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Old 25-05-2013, 10:14   #40
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Re: battery charging from my generator

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Originally Posted by Don L View Post
I've been watching my solar controller compared to my battery monitor. I have noted that the solar controller goes into absorption mode right about the same time that the amp-hours out of the battery hit 0.

But it was my opinion and of course would depend on each persons definition of charged as far as practical boat battery use goes.
Agree with the personal definition of charge thing -that is relative and situational.

I think your battery monitor may not be calibrated well. It is very tricky to keep the Ahr meter correct - I adjust our parameters continuously and still need to reset it regularly. So I suspect when yours reads "0", it still has a lot of lost capacity in the batteries.

Check the amps going into the batteries when the controller says it reaches absorption - I bet it is still putting out close to full output at this time.

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Old 25-05-2013, 10:23   #41
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Re: battery charging from my generator

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Originally Posted by colemj View Post
Agree with the personal definition of charge thing -that is relative and situational.

I think your battery monitor may not be calibrated well. It is very tricky to keep the Ahr meter correct - I adjust our parameters continuously and still need to reset it regularly. So I suspect when yours reads "0", it still has a lot of lost capacity in the batteries.

Check the amps going into the batteries when the controller says it reaches absorption - I bet it is still putting out close to full output at this time.

Mark
When my solar controller goes into absorption around noon on a sunny day at 14.6V the batteries are accepting around 3-4 amps (460 AH bank) and my 290W panel is only putting out around 7 amps (with the stereo and frig running)! This meets my definition of charged (specific gravity also said they were charged 2 weeks ago when I checked them).

But I ain't no expert.
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Old 25-05-2013, 10:32   #42
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Re: battery charging from my generator

Yep, that would meet my definition of charged also. Our batteries reach absorption voltage while still accepting a lot of amperage.

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Old 25-05-2013, 10:57   #43
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Re: battery charging from my generator

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Originally Posted by colemj View Post
Lloyd, Trojan recommends a bulk and absorption setting of 14.8V for their batteries.

The problem with Rick's thesis is that with most of our larger banks, most of us cannot supply the charging current that meets his reasoning.

Mark
Hi Mark,

Amp Hour Law of charging is not Rick's thesis, it's been about since 1920, and almost every proper charger try's it's best to emulate it. In the battery industry it is considered "Best Practice"

Try this link it's a combined editorial for how to set up an On-board Power System. To get the most efficient system you can.

Everything installed to a boat is a compromise of some sort. But understanding how it all works together allows the owner/designer to achieve the best compromise.

Lloyd
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Old 25-05-2013, 11:27   #44
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Quote:
Originally Posted by Don L View Post

When my solar controller goes into absorption around noon on a sunny day at 14.6V the batteries are accepting around 3-4 amps (460 AH bank) and my 290W panel is only putting out around 7 amps (with the stereo and frig running)! This meets my definition of charged (specific gravity also said they were charged 2 weeks ago when I checked them).

But I ain't no expert.
Yep, your batteries don't accept a charge anymore. A 460Ah bank should be at a much higher charge current when switching from bulk to absorption phase, say at 10% of Ah rating, so 45A in this case. The 3-4A current is normally only seen when changing from absorption to float charge for this size bank.
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Old 25-05-2013, 11:48   #45
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Re: battery charging from my generator

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Yep, your batteries don't accept a charge anymore. A 460Ah bank should be at a much higher charge current when switching from bulk to absorption phase, say at 10% of Ah rating, so 45A in this case. The 3-4A current is normally only seen when changing from absorption to float charge for this size bank.
Yep,

But its also seen in highly sufated batteries. A 460 amp hr bank depleted to 50% should be charging at the max output of the charging source until the Absorption voltage set point is hit.

So as an example 460-230 amphr with a bulk charger rated at 100 amps. The bulk phase should be about an hour at 100 amps charge, and then once Ab...voltage set point is reached you should see the charging amps fall down the curve until 3-4% of bat amp hr capacity is reached, then Float Stage is reached.

Lloyd

Lloyd
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