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Old 12-04-2004, 03:47 PM   #15
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The "equalization" voltage provided by the Charge Wizard isn't really high enough to provide true equalization. It's only the 14.4V bulk mode voltage. So I wouldn't worry about it with AGMs.
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Old 12-04-2004, 04:13 PM   #16
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Quote:
Originally Posted by Leipper
"Did you mean much better usable energy at higher current draws? "

no.

you get more energy out of a battery when you draw less current.

"The Peukert coefficients for the Lifeline and Optimas (both AGMs) are very close."
1.06 versus 1.2 makes a big difference when it is an exponent!
The first statement you make is true, but that is not what you said in you previous post. You said:

"This means that lower current draws will yield much better usable energy from an Optima that it will for most other batteries of equivalent weight."

What I am saying is that the effect is much more pronounced at higher current draws.

If you do the calculations using the Peukert coefficients that you provided, you get these results:

At low (3 amp) draw from 180 ah cells, the Optima will give 56 hrs reserve capacity, vs 48 hrs for a wet cell. The wet cell is 86% the efficiency of the Optima.

At high (25 amp) draw from the same cells, the Optima wil give 5.9 hrs reserve capacity and the wet cell will give 3.8 hrs. The relative efficiency of the wet cell is now only 64%.

Thats the point I was making, that at higher draws the Peukert effect is worse for wet cells than at low draws.

I think you will find the Lifeline AGMs have a similar Peukert coefficient to the Optima AGM, certainly less than 1.2 for flooded cells.
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Old 12-04-2004, 04:14 PM   #17
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A typical 100 amp-hour battery, by definition, gives 20 hours at a 5 amp discharge. One might think that it would give 100/25 = 4 hours at a 25 amp discharge. Looking at the Reserve Capacity rating (time at 25A) shows this clearly isn't the case. Most 100AH batteries have a RC of around 180 minutes or 3 hours, which only equates to 75AH. That's the Peukert Effect.

With two 100AH batteries in parallel you don't have to worry about the Peukert Effect if you keep discharge at about 10 amps or less. However, at its rated output, a small 500W inverter will draw about 25A from each battery.
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Old 12-04-2004, 09:58 PM   #18
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I calculated the Peukert Capacity (Cp) and Exponent (N), from the specifications above, for the yellow top Optima Group 31 and the smaller Lifeline Group 27.

Optima D31 Cp=83.4 N=1.08

Lifeline Group 27 Cp=129.3 N=1.16

Time = Cp/I^N

There's no reasonable amount of discharge at which the Optima's lower exponent would help it equal the smaller Lifeline, due to the Optima's much smaller capacity.
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Old 12-04-2004, 10:24 PM   #19
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Other sizes are slightly different. The Optima 34D has a coefficient of 1.11, and the Lifeline 24T has a coefficient of 1.15, close enough that I think personal preference or cost would be the deciding factor. I think I would prefer the Lifelines.

We need to keep in mind that the Peukert capacity is the capacity measured in a straight line to depletion. The 'missing' energy isn't wasted or lost. It just means that the voltage can't keep up with drawdown rate. If the battery is allowed to rest, it will recover the lost energy. It's a diffusion limited reaction.
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Old 12-05-2004, 07:32 AM   #20
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I theorize that each of us has at least one area of retardation. In my case, understanding the mathematics and principals of the previous posts would certainly be one of my areas. I have no problem in giving a speech before 1000's of people. I can recite most everything you would ever want to know about artificial insemination, embryo transfer techniques, and/or cloning of embryos with regard to bovine reproduction. I keep abreast of governmental, political, social and enviornmental issues both domestically and abroad. I have little trouble understanding 99% of the issues I see discussed here on the forum and often have found myself wondering how some people can seemingly be so dense at understanding some of the advice given here. On this issue, however, I find I am one of those dense people. I become totally lost in trying to comprehend the Peukert factor, exponents, relative efficiencies and to be able to truly comprehend the relative merits of utilizing one battery over another in the context of this discussion. I'm just grateful that there are those who do understand the concepts for which I find myself lacking.
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Old 12-05-2004, 09:20 AM   #21
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G,

My biggest blind spots are differential equations, interpersonal relationships, and organic chemistry.
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Old 01-09-2006, 12:30 PM   #22
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Hi to all.
In following this thread I see all have had the same experience as I; IE
1. Univolts and Megnetec converters kill yellow top Optimas.
2. The new technology convertor/chargers do a much better job of keeping batteries alive.
3. There is no subsitute for the weight of the battery when it comes to energy storage.
My solution was DIY like others; I use the battery disconnect switch while storing and 3 stage solid state charger. My lifeline G31 works great and only needs charging every 60 days or so.
WJ
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Old 01-09-2006, 12:50 PM   #23
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Now someones finally making sense

After all of the equations flying around, I was beginning to think we were running an '12-step' program for electricians.

I've been having problems with keeping a brand new deep cell battery charged. Someone recently told me that the Uni-Volts either work or don't work, is that true?

Mitch
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Old 01-09-2006, 01:07 PM   #24
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Quote:
Originally Posted by Swanny
Someone recently told me that the Uni-Volts either work or don't work, is that true?

Mitch
Mitch, You could say that about everything . Uni-Volts are still around after many years, but the newer convertors are much better. The Uni-Volts do not offer 3 stage charging like many of the newer replacements. The problems most often with the Uni-Volts are they hummmmmm alot and they will tend to over charge a battery if left connected for long periods (days). I am not sure how many amps are supplied to the charge circut, but it will take many hours to charge your battery. Have you put a volt meter across the battery and checked the voltage with city power and no city power?
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Old 01-10-2006, 07:56 PM   #25
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Here's the symptom

What's happening is the when I'm hooked up to city power, the interior lights will come on bright. Than after a while they will slowly dim to nothing.

When I listen to the Uni-volt it sounds as though something 'clicks' and than the lights come back on. As for the battery, I replaced it about 2 months ago and during a recent camping trip we used our generator.

It seems that the uni-volt will keep the lights on and operate everything when I take the battery out of the circuit, but once I put it back in we have the same problem. Could it be a bad battery already?

Mitch
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Old 01-10-2006, 08:06 PM   #26
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I would have te battery tested. It sounds like it may be pulling everything down. Just a guess.
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Old 01-10-2006, 11:04 PM   #27
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More Info

When I tested the converter with the battery removed, there was about 13.5 volts coming out of the leads.

Although I replaced the battery in November, when I put it in the loop all of the lights come on brightly and than dim.

So here's my question. When we went boondocking 2 weeks ago, I think we used the battery to a very low level. It appeared to recoup while we towed the AS home, but after leaving the AS hooked to shorepower overnight, the battery still pulls down the system. Is it possible for a battery to go bad that quickly?

Mitch
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Old 01-10-2006, 11:26 PM   #28
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Mitch,
Yes, it can happen. Any auto parts store should have a tester that they can hook to your battery and tell you in a few minutes if it is bad. Batteries do not like to be bounced around a lot and sometimes that will make them short out a cell. I have had batteries last for several years and others for a few months. In my autos I average less then 2 years, the Phoenix heat is tough on them.
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