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Forum Index : Electronics : Batteries
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| windlight Guru  Joined: 03/03/2007 Location: AustraliaPosts: 331 |
In May 2011 I "retired" moved to the Daintree rainforest, I put my hand in my pocket and outlayed $80k on a renewable energy system. 10 Kw of solar - great Selectronics inverter/charger -great 3x Zantrax solar controllers - great except it's a pity programing an equalize is next to impossible. And oh must I say it a bank of 1600 Ah Exide batteries, now here I must admit Exide seen me coming, in 4 years one failed, the day the installer (a very helpful and genuine guy) took away the offending battery I discovered another dead in the water. I predict 4-5 to follow based on readings, so obviously Exide is not my flavor of the month. Now here I will say they are replacing the dud batteries free, that part is good, but I have lost faith in their batteries that should have lasted me 12+ years ( I baby them). ATM I am running the generator on evening assist to try and stave off the inevitable. So what other brands are the rest of you using for total Re systems? Allan "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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| govertical Guru Joined: 11/12/2008 Location: United StatesPosts: 383 |
charging info for batteries Hi, I am still learning about battery maintenance, the above link may help. There is some info on the web that suggests pulse charging may help rejuvenate dead batteries but I have not tried it at this time. Has anyone tried a pulse charger? just because your a GURU or forum administer does not mean your always correct :) |
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| govertical Guru Joined: 11/12/2008 Location: United StatesPosts: 383 |
PDF on pulse charging older info, still searching for updated info just because your a GURU or forum administer does not mean your always correct :) |
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| windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331 |
Hi govertical, thanks for your interest, these batteries are defiantly not sulfated they are fully recharged each day, usually by mid to late morning. It is a manufacturing fault. Allan "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
How much do you generally suck out of them each day and then replace? You didn't mention what your system voltage is. At 1200A/H I am guessing 24V or higher. Are you generally keeping them above 70-80% SOC and equalising weekly or ? Do Exide provide any cycle life data? Have you seen a gradual decline or a sudden drop in capacity? Did Exide actually offer any suggestions why the batteries are failing? |
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| windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331 |
30 day average 10,5 Kwh 365 day average 12.35 Kwh System voltage 48v 1600 A/h Rarely drop below 80% Yes;1500 cycles to 80% DOD ◦2500 cycles to 50% DOD ◦3300 cycles to 30% DOD ◦>4500 cycles to 10% DOD Sudden They would not have received the first failed battery yet. Exide did recommend 2 monthly equalize but per their agent now say monthly, it happens anyway, they are never undercharged or under equalized. Allan "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Serious system. After spending many hours reading about LiFePO4 battery systems I had the impression that the cycle life of lead-acid was a lot shorter than that. Perhaps in their attempts to convince others that LiFePO4 is a much more economical choice. Which model of Exide batteries do you have? Also, you mention "based on readings", is that voltage, hydrometer or coulomb counting? I would expect with "sudden failure" that they should be able to come up with an explanation. |
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| windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331 |
They are Energystore batteries. Based on voltage and SG The current dud is still holding reasonable volts but practically zero SG, and when equalizing it has no activity, just as if the electrolyte is just water. I only do SG readings once a month. I usually notice it on overnight DOD. Allan "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Looked up the datasheet for these. I see their capacity is based on a 100hour rate. Thought a 20 hour rate was more common. However, the cycle life is based on a 10 hour discharge. So, going down to 50% DOD you can discharge these guys at ((48V * 1600AH) / 10hours) * 50% = almost 4KW/H and get 2500 cycles. I am impressed. So, you have seen the SG drop from 1.25 down to 1.00 over a short period. My Trojan equivalents are sitting around 1.20 and as very rough estimate I reckon I have about 25% of the original capacity. |
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| windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331 |
How old are your trojan's "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Around 6 years. They were previously owned (about 4 years). I did a discharge test on them on arrival and reckon they had about 30% of their original capacity. 8 * T-105 equivalent Thor brand batteries (24V at 440A/H) I never drop below 50% DOD. Do you have a graph of SG versus time (months/years)? The observation that seems to be trying to tell me something is that from a resting voltage of 24.5V and I apply a charging current of 3Amps the terminal voltage jumps up about 1.5Volts over a 15 minute period. When I remove the charging current the voltage drops back down to 24.5V in another 15 minutes. I suspect one could gain some insight into battery impedance from these measurements. |
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| windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331 |
I have not graphed my batteries SG, I see little point in it. Comparing SG and terminal voltage as read after equalizing with previous periods is adequate for me. When I say the cells have died rapidly, it could have been over the course of a month for all I know, I look at a system overview in my office but I do not take daily or weekly SG readings. I am not quite sure what your last sentence means, impedance as you would know is a term used to describe AC current flow. Neither do I understand your observations of voltage after a very brief charge, what you describe is what I would expect to see, a small surface charge and subsequent reversal of said charge. I would be interested in how you conducted your discharge test. I look after two sets of batteries other than my own, one is only 12 months old, Exide's like mine just bigger. The other is 10 years old and is the set these new ones replaced, their SG and voltage is impeccable and how I would expect an Exide battery to perform. Personally I am leaning towards my batteries being a bad batch, quite how a major manufacturer of a product that has basically been unchanged for over 100 years can have a bad batch escapes me, but................... Allan "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Battery impedance here and part way down the page (AC Conductance). I was trying to find a way that would give me more insight into the real condition of my batteries. A very crude discharge test at the 10hr rate using a 1KW heater down to the low voltage drop-out on the inverter (20Volts). Crude. The test lasted 3 hours so obviously, I needed to back off the load to say 300Watts. Maybe, at that rate I would have got to 10-15 hours, ie 3-4.5KW/H for a system that should produce almost 10KW/H, when new. My observation ... at a resting voltage of 24.5Volts (~40-50% SOC from a chart on the internet) I expected at a 3Amp charge would take about ... 440A/H divided by 3A times 50% equals 73 hours ... to get to the fully charged point. I will read more about surface charge effects. Cheers, Dave |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
This looks like a better way to test: here Found a bit of info on surface charge and how to remove it. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Hi Allan, If exide are replacing the damaged batteries i would try and get them swapped out sooner rather than later. I would think that if you removed the battery leads from the low SG cells apply a small load across the terminals and measure the voltage it would be very low or non existent. it sound suspiciously like the cells are shorting somewhere inside. I am reluctant to offer any advice that could void their returns policy. I guess you could swap the cells around in the string so that the dodgy ones are next to each other and stick a 6 volt charger across 3 of them and see if they come up at all. The handy-ist tool I have is a DC clamp meter, it is possible to "see" how much charge is going to each cell. In answer to your original question the battery i install the most is BAE secura gel, however I only buy them when there is a price discount on, they are quite expen$ive. I'm confused, no wait... maybe I'm not... |
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| windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331 |
Since this is a single bank all batteries see the same current, I am waiting on replacement #2 and hopefully feed back on the first failure. I tend to agree with your assessment of an internal short, but how many more? assuming they are all from the same "batch" happy days. "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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| windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331 |
OK just had the second battery changed this morning, still no feedback on what is happening. The agent did say that he doubts it's an internal short as they normally go reverse voltage if they short, this was still about 1.1V correct polarity but SG 1. Allan "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
when you consider 2.1v is charged and 1.7 volts is stone motherless dead flat, a measurement of 1.1 volts unloaded could be measuring any stray voltage, the cell is completely stuffed. if the current is getting from one terminal to the other when you have used them then for all intents it is low resistance somehow. I wrote a post on how I test cells however My computer hates me and I am trying to cut hay so I gave up. I have made a point of tracking down what is wrong with a cell with these sort of symptoms in the past and I can tell you that no-one wants a verdict in case it was their fault. I have found them bent inside from being squashed, dropped or dented, bits have come adrift, bus bars melted, somebody has added some special sauce or contaminated the acid somehow and there is scum or jellied crud inside, the list goes on. there is not much future in babying a set of batteries, it will make you paranoid after a while and that take the fun out of life! I'm confused, no wait... maybe I'm not... |
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| windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331 |
I suspect you are right about cause of failure. "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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