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Old 09-08-2009, 20:53   #1
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New House Bank Charging Too Slowly

We just installed a new house battery bank and charger. After spending hours reading all of the information on this site about batteries and charging systems, I thought I had a good set-up figured out but I guess not. My house battery bank is taking much longer to charge than I thought it would and I do not understand why.

Here is the set-up: Four Trojan T-105's wired in series/parallell to make a single 12 volt 440 ah house bank, a 75 amp Iota charger w/IQ4 smart charge controller, Honda Eu2000i generator, Link 20 battery monitor. We use the Honda generator to run the Iota charger at anchor. We use about 60 amp/hours per day and with this set up I thought we could run the generator/charger two hours every two days or three hours every three days and keep the battery bank somewhere between 3/8 and 7/8 full (down 260 ah to down 80 ah). I have read here that it is not a good idea to let the batteries completely discharge and it is not efficient (i.e. more charging time for fewer amps) to fully charge them.

But here is what actually happens: We started charging when the batteries were down 262 amp/hours. The charger initially produced about 70 amps, but after about 20 minutes it dropped to 45 amps. Then, over the course of the next 3 1/2 hours or so, the output slowly dropped to 28 amps. After four hours, I stopped charging. According to the Link 20, batteries were now down 134 amp/hours which means that in four hours, we only put in 128 amp/hours - an average of 32 amps per hour. (which doesn't make any sense because the charger was putting out 32 amps or better for all but the last 20 minutes).

After this disappointing performance, we tried again the next day. This time we started charging with the batteries down 178 ah. The charger initially put out 70 amps, but within 20 minutes the output had dropped to 28 amps. For the rest of the charging time, the output slowly decreased to 16 amps. I shut it off at 4.5 hours at which time the monitor showed the batteries were down 100 amp/hours which means in 4.5 hours, we only put in 78 amp/hours or an average of 17 amps per hour.

I am thoroughly confused. I thought a battery bank of this size would accept the full 75 amps of the charger output until it was about 3/4 full.

What have I done wrong here? Or am I just expecting too much from this system?
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Old 10-08-2009, 01:45   #2
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The maximum acceptance of your bank will be more than 100A; for lead-acid batteries, I always assume 25% of their Ah capacity. You can probably find the charging characteristics in the Trojan documentation.

About the Ah's going in: you compare the Ah delivered from the charger with the Ah that are stored into the batteries. But that assumes the charging process is 100% efficient which, unfortunately, isn't so.

About the charger: does it have a temperature sensor that is attached to one of the batteries? If not, charging times might well be longer because the charger will assume a high temperature to be safe. If there is a sensor, check it's reading if you can show it on the charger's panel (compare with thermometer reading).

Also, you have new batteries. These will not be up to full capacity yet. You should give them a couple of good deep cycles first (check the documentation but I would say down to 25 or 30%). I think this is mentioned in the Trojan documents too.

Next up is the specific gravity of the electrolyte. You should measure that and, after correcting for temperature, compare that to the reading of the Link20 monitor. In other words: you put too much trust in that monitor for the conclusions you make.

And last: did you equalize the batteries? You must do this with new batteries. I would suggest you give them a couple of good deep cycles and next fully charge them, followed by equalizing. Measure the electrolyte during that process as it will tell you when the process is finished and it will show any weak cells if there are any.

So, I think you are dealing with a combination of factors which, combined, make a big difference with the expected results.

good luck!
cheers,
Nick.
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Old 10-08-2009, 02:41   #3
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Unhappy CTEK Smart Chargers

Great thread guys, always good to see folks demystifying the voodoo of the ions.
I too have been wrestling with keeping batteries up to par, and because of a couple of accidental flats, I recently got hold of CTEK Multi X series smart charger.
The Chargers have a Reconditioning Mode (for deeply discharged batteries) as part of their sequencing but I have never seen the little light (#6 in their manual) come on? The manual doesnt really detail how this function actually works and when.
According to the program description it should occur between the Absorbtion(peak charge) and Float(maintainance charge) part of the programme. Anyone have a thought on this??
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Old 10-08-2009, 04:44   #4
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I generally agree with Jedi (for once!), except for the temperature thing. The Iota charger doesn't have or need a temp sensor, due to its PWM design.

With the info you provided, it's really not possible to say whether or not you have a real problem. At least, not yet.

Don't trust the Link monitor implicitly, at least until you've lived with it awhile and know it's telling you the truth.

Exercising the batteries a few times is a good idea with new batteries, as is checking the specific gravity of each cell. The Iota has a kind of "equalization mode" which it will automatically go into after awhile. It would be good to be plugged into shore power for a couple of days to get a good full charge, so you know for sure where you're starting.

Finally, check all the cable connections carefully. They should be clean and tight...tighter than you normally think is right. I assume that the cables are sized correctly, too, including the ones from the charger to the batteries.

Bill
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Old 10-08-2009, 04:44   #5
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A study done by Sandia National Laboratories describes this problem. We all think the efficiency of battery charging is around 80-85%. It is for a fully discharged battery to a full charge.
The problem is what happens at the upper 25% of charge. The efficiency of charge dramatically reduces. At a state of charge (SOC) of 70% the incremental charge efficiency is 83%
80% SOC incremental charge efficiency is 70%
90% SOC incremental charge efficiency is 55%
95% SOC incremental charge efficiency is 45%


This has nothing to do with Peukert Effect
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Old 10-08-2009, 04:53   #6
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Yes, this is an excellent point. SNL has exposed the reason why all of us wonder at how long it takes to attain a really full charge -- and, why batteries on a cruising boat only rarely get there :-)

Thanks, mesquaukee.

Bill
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Old 10-08-2009, 05:43   #7
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Originally Posted by mesquaukee View Post
A study done by Sandia National Laboratories describes this problem. ..
A Study of Lead-Acid Battery Efficiency Near Top-of-Charge and the Impact on PV System Design
by John W. Stevens and Garth P. Corey, Sandia National Laboratories


http://photovoltaics.sandia.gov/docs...atpapsteve.pdf
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Old 10-08-2009, 06:38   #8
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I do not know what is your configuration, how far is the charger from the battery, what voltage is the charger sensing.
One thing you could do is when charging, is to check the voltage at the battery terminals and any point allong the wiring from the charger. If the charger see a higher voltage it will trotle down. Just a thought. Good charger have special sensing leads which connect to the battery terminal.
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Old 10-08-2009, 13:55   #9
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Thanks to everyone for the great responses! I feel better now.

Jedi and btrayfors: I will "exercise" the batteries a few times, check specific gravity, and give the charger time to do an equalization. btrayfors is right about the Iota - there is no temp sensor. I will also re-check all the connections - they are all new so they should be clean, but I may have failed to tighten something. I believe the wiring is correctly sized. I used a wiring chart for 5% voltage loss to size the wires.

Many thanks again and I will report back later.
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Old 10-08-2009, 14:39   #10
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It sounds like you are drawing down pretty far before charging? How do you measure tha AmpHrs? What is the voltage level? Most fancy meters are notoriously wrong for AH's unless constantly monitored themselves IMHO. If you have refrigeration I would question your 60 AH per day...? One of the things most of us miss is that a big battery bank only does any good if you have a BIG way of putting the amps back in.... which we dont for the reasons mentioned above. However, a long motoring voyage can do it. Like an 8 hour motor trip. It may help to run the charger for the high rate charge portion and then do it again a few hours later etc....
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Old 10-08-2009, 15:04   #11
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Cheechako: All the readings came from the Link 20. I was not paying much attention to the volts, but it was under 12 volts (maybe 11.8 or so) at the beginning of the charging on day one, 12.6 volts about halfway through, and 12.8 volts at the end. These were the readings on the Link 20 while the charger was charging.

On day 2 we started charging at 12.4 volts, it was up to 13.9 volts after 20 minutes, hit 14 volts at two hours and stayed there for the rest of it. Keep in mind it was 90 degrees out and we were still using power while charging. Most of the usage was for the refrigerator. We have a medium sized Engel that draws about 30-35 amps per day. The rest goes for lights, anchor light, water pump, stereo, grey water pump, etc.

I hear you on the big bank/big charger thing. I thought that's what this was going to be. It beats the old 20 amp charger/220 ah bank, but it was not the quick/big charge I'd envisioned. Hopefully it will get better after exercising the batteries and some of the other things suggested above.

The more we sail, the more we realize how little we know. But we're learning..... And this forum is a huge help.
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Old 10-08-2009, 15:24   #12
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That makes sense with the Engel. I think for the casual user, too much focus on adding/subtracting AH's can be bad because realistically 50% of your AH's are unuseable.... meaning you should never be that low. Now if you could set your meter to say you are 50% down when you are really 25% down it would be more for the layman! At 12.0 volts with no draw on a battery at rest you should be about 23% charged. At 12.5 volts you should be about 70% charged. In a perfect world you might want to be 12.3 volts minimum... like you need one of those K mart blue lights to go off when you get that low! In reality, my refrig would sometimes get me down to below 12V overnight, depending on my charging and other usage the previous day. Although they are a lot of clutter, the advantage of wind and solar is they just keep trickling it in all day. I dont know for sure but I would imagine the batteries dont heat up much with those units.... There are others who are more astute on the theory on this board, so take it with a grain of salt. I'm more the practical type (my hero is Dr Feynman on the shuttle disaster commission...he's the guy who put the oring sample in the glass of ice water while everyone else was expounding theory, then pulled it out and noted that it breaks apart when cold!)
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Old 10-08-2009, 21:16   #13
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Dr. Feynman

I enjoyed Feynman's book about his time on the shuttle disaster commission. He seemed a little put out that most of the commission's time was spent having meetings rather than talking to someone who might know something about what happened such as the person who installed the o-rings or the engineers who designed them.

Feynman's books are great. Most of it sails right over my head, but I somehow feel smarter after reading them. For a little while, anyway.
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Old 11-08-2009, 00:05   #14
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I also installed a much larger AGM bank and played with how many amps I should deplete to find optimum zone for operating Ö. so as to minimize charging/ generator time needed to replace used Ahís

From that I found that with my chosen bank capacity I basically consume in 24 hrs only 10% at anchor and if I keep it in the 70 to 80% SOC (State of Charge), my generator cycle is about 2 hours a day.

Here are some early tests which have proved fairly consistent.

With AGMís I donít worry about stratification
Attached Files
File Type: doc Charging LOG.doc (170.0 KB, 70 views)
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Old 11-08-2009, 09:01   #15
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Yea Feynman was a funny guy for such a genious. I read his books also, he was also on a couple of programs on PBS.
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