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Old 15-07-2007, 01:16   #1
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Maxing out the batts

First, I want to say thanks to everyone out there who is so helpful in helping me learn my way around my new tub. You guys are awesome. So much so, in fact, I thought I'd throw another one at you:

If batteries are 50%down at 12.2 volts, 12.8 is "full, but 13.6 is the limit of what you can put in without damage, why do all the chargers I see shut down at what they think is 100% (12.8), when I still have a fridge and lights to use, and even a movie to check out later? I could use the other 80 amps!

Thanks in advance!
Jack
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Old 15-07-2007, 02:53   #2
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That is why you need a "real" marine charger. One that is multi stepped as in three independant charge cycles. Bulk charge, Absorbtion charge and float. This is a minimum and a charger with temperature sensing is even better.
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Old 15-07-2007, 13:50   #3
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Battery Voltage vs. Charging Voltage

Jack,

Your batteries are fully charged at 12.8.

A charging source has to deliver a voltage higher than the current battery voltage in order for your batteries to accept a charge from that source, so that's why input sources are over 13v. If the charging source were 11v, and your batteries half-discharged at 12.2, they would not accept a charge from that source.

Let's say, by way of analogy, that you have a soft tire on your car. You measure the tire pressure as 15psi. You have an old can of "Fix-a-Flat" that has 15psi left in it. What is going to happen when you stick that can on your valve stem? Nothing. To expect the tire to accept any air, the source must have more pressure than the tire currently has.

So, too, the charging source for a battery must be of a higher voltage than the battery's current voltage, or the electrons will not flow into the battery. Because your goal is a fully-charged battery @ 12.8v, the charging source must be higher than that, but not so high as to cause damage to the battery. So, depending on the type of battery, 13v and some change is the right charging voltage.

There are no additional "80 amps" to get into your battery. Battery storage capacity is measured in amp-hours, not in volts or amps. This seems to be the concept that is eluding you. Once that is understood, the picture gets clearer

I'll let someone smarter than I describe the details & toss out my crude analogy for something more technically accurate. I write for the uninitiated.
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Old 15-07-2007, 14:15   #4
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keep writing, you are doing well.
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Old 15-07-2007, 14:57   #5
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Well said, Jeff!! Bravo. I love the analogy.
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Old 15-07-2007, 18:41   #6
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And to build on what Alan said. When the batteries are very depleted a single step charger is like a firehouse filling a bucket. You have to stop well in advance of reaching the brim in order to not overflow.

A good quality charger will reduce the flow to a trickle as the bucket fills and provide a trickle charge as the battery leaks a bit of current.

There are other things going on as well such as the batteries heating up as they charge and a good quality charger accounts for these changes as well.
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Old 16-07-2007, 06:04   #7
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This is a good thread. Keep it up.
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Old 17-07-2007, 08:02   #8
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OK.... I will ditto the above and also say that a good 3 stage charger should also have provision for an EQUALIZATION cycle running at 15 volts or so to allow for de-sulfating the plates of the battery. (THIS IS FOR WET CELLS). My 15V statement is approximate and individual battery mfrs. will specify the EQ process for their models.
This is necessary in full time cruising use and constant cycling of batteries and charging to less than 100% often.

I also see reference to checking voltage after charging and reading 12.8.
12.8 is indeed "FULL" but you are NOT measuring actual charge state when you measure a battery that has just been charged. TIME must pass and no load must be on the battery. Wait at least an hour...preferably several more before checking voltage after charging or you will just be measuring surface charge. You can also remove surface charge by running a 20+ amp load on a 12V battery for a couple of minutes...it costs you a few amp hours but lets you measure quickly.
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Old 17-07-2007, 08:10   #9
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Originally Posted by camaraderie
OK.... I will ditto the above and also say that a good 3 stage charger should also have provision for an EQUALIZATION cycle running at 15 volts or so to allow for de-sulfating the plates of the battery. (THIS IS FOR WET CELLS). My 15V statement is approximate and individual battery mfrs. will specify the EQ process for their models.
This is necessary in full time cruising use and constant cycling of batteries and charging to less than 100% often.
One of the best things you can do to understand your battery/charging system is install a battery monitor that tracks voltage and current flow. Watch it as you turn on devices and as you charge. Most monitors will indicate a % charge for the bank. Since they monitor current flow, in addition to voltage, they are more accurate at reporting % charge than simply reading the voltage to deduce % charge.

Some monitors have temperature sensors and allow charge constants to be tweaked in their firmware for the real techie geeks.
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Old 17-07-2007, 08:29   #10
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Has anyone had any experience with the new Pulse Battery Desulphators? The unit "uses a sharp pulse of current forced into the battery suddenly to "jar" the sulfite crystals and cause internal resonances, both mechanical and electrical, to grind down the sulfite crystals that form so they can be recombined into the battery acid"

It all sounds good, but.....maybe it's better at removing $$ than it is removing sulphate?
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Old 17-07-2007, 09:26   #11
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Here's a prior discussion on pulse technology.
Battery Question
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Old 17-07-2007, 11:20   #12
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Thanks, guess I'll wait for btrayfors test results!
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Old 17-07-2007, 11:33   #13
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My report is anacodotal, but since I installed a "sulfator" which is a pulse device I purchased from JR Energy, my house bank as been doing very well. They are 2- 3 yr old 8d AGMs. I have also renew all the wiring and connectors and they batts are on 110 watt solar panels w/ a pv14 flexcharge.

After 5 days of sitting on the mooring they are alway 100% topped up!

jef
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Old 17-07-2007, 11:38   #14
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Originally Posted by defjef
...After 5 days of sitting on the mooring they are alway 100% topped up!....
Which is exactly what AGMs need to stay healthy. They cannot handle being discharged and then regularly only being brought back to 90% charge. Going to 100% charge is probably what is keeping your AGMs healthy, not the sulfator.

Paul L
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Old 17-07-2007, 13:48   #15
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All though we have many very good experts here, we are very fortunate to have the guy that vertually wrote the Book as one our members. I do hope you jump in here Rick. Rick was one of the cheif designers behind many of the top chargeign and monitoring equipment that has been mentioned here on the board. Problem is, he can not discuss mcu of the gear as he is bound by company policies. However, he can discuss the reasons behind the why's and wherefores.
Some key points I have ,earn't from past discussion with him are,
Batteries power supply/consumption needs to be measured in Watts. Few of us do so and using Amp/hrs although common practice, does not tell the whole story.
De-sulphating devices do not work in most situations. Nor the chemical additives. With the additives, seemingly a improvement occurs only to be shortly lived and a worse result reappearing.
At least that is what I learn't and I hope I was a good student and learn't correctly.
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