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Renewable Energy Questions/Discussion => Solar (heating or electric) => Topic started by: off the wall on April 11, 2015, 05:25:56 pm
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I have been testing capacity of a bank of lead acid batteries for someone. In fact a major problem is the insulated connectors which are bolts not of stainless steel but of galvanised iron, which sit upon a 1mm ring of copper attached to the connectors and buried in insulation, and which need tough screwing down to make proper contact. But that's not the problem today . . .
It's a 1000ah bank of batteries and after a full charge I took out 600ah down to around 11 volts. Sun has not been brilliant in England so whether they've had 10 days of 12 amps or so for 6 hours is a moot point and the batteries have been gassing nicely at around 28.5volts during charges with the specific intention of equalising them. Some show specific gravity at full charge density whilst a few are still lagging behind a bit.
During charging today, we were connecting together another row of batteries adjacent. There was no circuit made, merely inserting the interconnecting links. Perhaps this caused some vibration.
Without the presence of a spark two batteries in the centre of the bank exploded, rupturing the top four inches of the casing and spilling a considerable quantity of acid on the floor.
I can only think that the caps which should be capable of allowing gas to exit simply didn't do so, allowing undue pressure to build up.
Has anyone had any experience in this sort of direction?
Best wishes
OTW
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My experience of lead acid batteries exploding is a very loud bang (12 gauge volume) as the gases (in the perfect ratio!!) burn. Overpressure I'm sure would be more of a pop and less spray of acid (if that can be determined after the leak).
I'm now restricting my use of an angle grinder to just setting my trousers on fire :)
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I'm with Frackers on this one..... the stoichiometric conditions in the cell are ripe for explosion...not a pop.
Somehow an ignition source has turned up, maybe a fracture in the plate to collector or something, but a pressure response will be a whole lot less energetic than a nice explosion of one of the fastest burning gasses there is.
Been there and done that a few times with industrial traction machines from time to time...... the noise is a very serious crack... has a sound barrier feel about it. Frackers description is apt.
Ditto on the angle grinder, although I also include my windcheater in that.
...............oztules
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It's a 1000ah bank of batteries and after a full charge I took out 600ah down to around 11 volts. Sun has not been brilliant in England so whether they've had 10 days of 12 amps or so for 6 hours is a moot point and the batteries have been gassing nicely at around 28.5volts during charges with the specific intention of equalising them. Some show specific gravity at full charge density whilst a few are still lagging behind a bit.
Something does not quite add up here, a 1000ah bank receiving 12A for 6 hours/day over 10 days? Then discharging down to 11V for an apparently 24v bank?
Is this a 12v bank or 24v bank?
Almost sounds like a 12v bank has been supercharged to 28.5V if that is possible, and two batteries have protested.
Nah every which way I look at this there is some miss information. Were the batteries gassing with only solar input? or...............
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Hi!
Sorry - I think of a 12V system with the 11-14V range as standard - so there is a typo in the above - I discharged down to 22V - (being the 11V equivalent) so there's no anomaly.
I have been hosting over the past couple of days a meeting in England focussing on battery charging and rejuvenation.
Some time ago I sold an inverter to someone setting up tea rooms by a lake without grid power. He's finally got the grid connected and so he sold me his battery bank. This is a 48V bank of batteries, again 1000ah, and although shorter and fatter than the bank which suffered the explosion, bear similarities. I have yet to look at the specific similarities of castings, but the plate separators are the same plastic material inserted in the same way, and the cases are the same plastic material and colour but with a different colour vent cap. Three cells had been rejected and replaced by (OUCH) 600ah cells - and the retailer who recommended that needs to be shot. The "dead" cells were given to me in addition, and presented a 1.5V reading. Why they were dead we don't know.
For fun, we connected the dead cells to a rejuvenating charger over night, and this brought the three cells up to 2V, 1.9V and 2.1V. At lunchtime yesterday I presented to them a 12V incandescent bulb and on 2V cell caused it to glow dimly, the 1.9V just slightly less strongly and the other 2V cell at first not at all and then nearly as the others. Specific gravity was at the low charge end of the scale. We connected the charger to the three cells over lunch covering the cells with plastic and underneath a table. We went off to lunch and within 10 minutes an assistant nearby to the workshop reported an explosion . . .
This was another situation where there was no external spark and where gas was ignited internally. What by? Upon inspection there is no obvious cause and this is worrying.
Interestingly the second exploded cell is showing the top of one of the plates and the plates are quite thin . . . and a grid containing paste. I thought that this construction was only used for car batteries and not deep cycle batteries.
These battery banks were reported to have been bought "cheaply" and are without manufacturer markings nor ratings indications - and I suspect that there is a flood of them on the market in England, probably imported from China.
Clearly they should only be used in a situation that provides for acid containment, well vented and possibly with the vent caps open, although an ignition of one could then spread to any other gassing cells.
Best wishes
OTW
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OTW -
A second explosion? It's time to reevaluate *something* from the sound of it. While you could theoretically get just so unlucky, the likelihood of two independent and unrelated events near back to back like that is less than nil.
At the very least, buy out 3 stores worth of baking soda and maybe get a fire truck on standby (couple birds with one stone?) until you have checked, rechecked, and checked everything again for any possible connections between the two events. And above all else, keep yourself and anyone else safe in the process!
Good luck... I hope a reasonable explanation comes to light before something else happens :-\
Steve
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Dear Steve
Thanks
I do assure you that the thing in common with both explosions, apart from charging at 12 amps - clearly don't ever ever ever charge 1000ah batteries at 12 amps ever - is cells bought cheaply on the UK market in black and grey cases with neither manufacturer's marking nor capacity identification.
The second explosion was "achieved" with wholly different equipment. The first was a charge from my solar system charging on 12 amps togather with other banks of batteries in parallel at the same time, the other batteries having the same charging regimes for two years. The second was on a dedicating recycling monitoring charger which desulphates and charges on a monitored basis.
Best wishes
OTW
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clearly don't ever ever ever charge 1000ah batteries at 12 amps ever
Are you suggesting that this is too much, or too little current?
If "too much", I can't believe that C/100 is "too much", and for 10 years I've run typically C/10 and higher (500AH and 1000AH banks at 50-80A charge).
If "too little", I can't believe that they require more than that, and for 10 years when sun has been less than great, significantly less than 12A for hours on end has been common.
As Steve says, I suspect that there's something else at play - even if its only "dumb luck".... but I have great doubts that 12A charge for a 1000AH bank is "bad" (except for probably being not enough!)
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Allan tips his hat and bids this thread a duh, confusion reigns.
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clearly don't ever ever ever charge 1000ah batteries at 12 amps ever
Are you suggesting that this is too much, or too little current?
Apologies. My sense of humour - to demonstrate that there was nothing unreasonable about how these batteries were being treated. There is some capability of this design of battery to self ignite gas internally.
[attach=1][attach=2][attach=3]
What I believe to be in common is a cheap and poorly made battery with a design or manufacturing flaw.
The two batteries have in common the same plastic plate separators and clearly come from the same stable.
Best wishes
OTW
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Johny cool pants reborn?
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Here are the photos of the other similar cell which exploded.
[attach=1][attach=2][attach=3][attach=4]
Best wishes
OTW
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It seems to me that you may be using a charger that has a high voltage pulse, if this is the case then bin it, the battery construction may be "cheep" , hard to say but looks fairly standard to me. Batteries can and do short out internally but in my experience this does not cause an explosion
I worked for 27 years in the power industry where the generators are filled with hydrogen (as a cooling medium), explosive limits for hydrogen are 4-74% in air, much more in a oxygen rich environment. Leaving the caps in place ensures a hydrogen rich mixture in the battery, should an ignition source ignite venting gas then the flame should stay external to the battery.
Can you please define over what period of time you discharged 600 ah, and how you measured/ achieved this this?
In one of your pics of your handy work (sorry my sense of humor) I see what looks like 4mm sq wire and both red (a recipe for confusion and disaster), this goes to the above question. What are you using these batteries for or are you just using them as a learning experience? There are lots of outcomes here, just whether they have been a learning experience remains to be seen, or maybe not.
You stated that the bolts were not stainless steel, in one of your pics, the one where we see the red trolly, that remaining bolt look stainless steel to me.
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Going by other clues, the cell in the second set of pics also looks like it may possibly be swollen, indicating extra stress on the separators, potentially leading to an internal short (closely following gassing, this could easily lead to an explosion)... It's hard to tell exactly tho because of the vantage point of the pics.
The first cell doesn't seem as cramped inside, but as A of J mentioned, there are other issues that potentially could have caused the demise of that one.
Lead Acid isn't a toy, and particularly when you get up into the larger cells. The potential for disaster increases notably as size goes up. Use proper wiring, terminators, etc or this type of thing might be a regular occurrence. I'm not saying explicitly that either or both are your fault, but it's difficult to rule that out going by the pics.
You've seen what they can do to themselves, please know that it can (and does) get worse from there. Imagine the top of that cell being the ceiling of a battery room... Google has a fair collection of pics illustrating the latter. None of them are pleasant scenes.
Steve
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Thanks
I have been managing a 300kWatthour battery bank now for a couple of years and so am not a complete newbie when it comes to batteries, but am somewhat perplexed by the experience.
My own personal battery bank is colour coded red for positive and black for negative, arranged in switched banks, fused and arranged using with connecting wire and bus bars appropriate to expected currents, fuse ratings and out of preference I like stainless steel connecting bolts and washers.
One of the major reasons for failure in my experience of banks of traction batteries is the insulated bolts clamping down on a 1mm ring of metal resulting in a good recipe for bad contacts: I'm aware of these sorts of issues and for that reason in testing this bank I replaced them by stainless steel and ensuring good contact with connecting wires held securely by washers.
The first cell that blew was in a bank that someone asked me to look at. Its major problem had been poor connections. I charged it as one of the subsections of my battery bank on which the charging currents per section are not much more than a ball park of 12 to 15 amps maximum. For this connexion with 6mm cable is perfectly adequate. For discharge as a test load I have a 22V to 30V 600W grid tie inverter which from a 24V battery bank on a continuous basis puts a constant 500W into the grid, so discharge at 20 amps. No-one can say that a C50 rate is mis-use of a battery . . .
That discharge to 22V was a few weeks ago and from memory it was over 30 hours, thus 600ah
On the day that the cell blew, there was good sun, giving a 12 amp charging rate at around 28Volts which should be fine even if overcharged as an equalising charge . . . and as you say with the caps on, the hydrogen concentration should not have led to ignition, but there was ignition from some source inside the cell and the explosion was violent. The explosion was internal and not external.
With regard to the second cell which blew under a desulphation charge the specialist charger used, developed by someone in the battery business for over 20 years, does not use a high voltage pulsing regime. It so happened that the developer of that charger was here and it was he who had set up the three cells to be charged. The sources of ignition were internal rather than external and it's for that reason that this is of particular concern. Were an identifiable cause in terms of a loose wire, external spark to have caused an external explosion, those are comprehensible circumstances.
Best wishes
OTW
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And here is one pic to start you off.............
[attach=1]
That was taken from this artical http://www.daintree-holidays.com.au/daintree-pollution.htm, if you read it take it with a grain of salt. I have lived here for just short of 4 years using solar and I have an air conditioned house, cook off electricity etc. The pic is from before I moved to this area. This to me is a classic example of a wiring fault, perhaps even the connection at the lead flapping in the breeze, an overheated/shorting/melting wire or joint is not your friend.
Just as interest I will give you another example of wiring faults, not batteries directly but part of the system. While visiting the home of an acquaintance and looking over the top of a shot of home-brew rum or was that several, I noticed his DC switchboard open and smoke trail, and charred wires. He told me it caught fire, the battery fuses blew, wires caught fire and his pl40 was no longer working.
I went back another day to effect repairs, now it is hard to get the true story sometimes but battery fuses blew, so a well meaning local chap bypassed this fault, somewhere this same chap extended the wires from the solar panels to the controller by about 200mm (8"). One connection is not tight, a blue point connector that was not flame proof was used and caught fire. Since the owner was home it did not result in a house fire, most of our homes up here are timber, ceder lined in and out. There are many house fires, I can only postulate as to how these fires occure.
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"I worked for 27 years in the power industry where the generators are filled with hydrogen (as a cooling medium), explosive limits for hydrogen are 4-74% in air, much more in a oxygen rich environment. Leaving the caps in place ensures a hydrogen rich mixture in the battery, should an ignition source ignite venting gas then the flame should stay external to the battery."
For the sake of completeness it is important to understand that the mixture in the cell has more oxidant in it than hydrogen.... simply because of the lightness of the H2 gas.
However, in an oxygen rich environment you only need 4% to be hydrogen, and it will detonate... not just burn.
So it is not true that a leak will/may have flame on the outside, and not progress into the cell from venting gas..... it will.... have no doubt at all..
It is not like hydrogen in the power station, where the gas has no oxidant mixed with it, and has to wait until it gets to the air around it........ Hydrogen mixtures with oxidant have exceptionally low energy requirements to ignite, in the range of only milli joules.... so any kind of even "so fine you cant see them " static sparks can cause total detonation.....it does not need to be contained to detonate, same with acetylene... they burn so fast that any mixture of gas and oxidant will explode rather than burn.... hence the bang you hear igniting the acetylene in the gas torch. ( yes still technically burning......., but more like an explosion than a rapid burn )...
Those cells exploded... either poor leads, internal break, or static spark.... but that was an explosion. I've been too close to too many of them to not recognise it when I see it. It is fortunate that the explosion did not spread to the whole lot. I have not seen that happen, usually only a few at a time.
edit:
Although energy to ignite is in the tenths of a millijoule range, the temp required is quite high comparatively. (>1000F)... so red ( dull not bright) hot wires may not cause ignition, but the melted plastic..... should it actually ignite and burn and / cause a plasma ( flame) of any kind.... then away she goes.
My 675AH battery box
It has 24 T105RE batteries in three strings. Separate leads of all the same length to each string with 100amp enclosed fuses inside the shed for each string (48v).
It is big on ventilation, and isolation from other flame sources.... never again I hope.
[attachimg=1]
[attachimg=2]
................oztules
Edit fixed up typing fault in AH figures... not 750ah... thats the 100 hr rate
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I've had similar experience, this is one I happened to be near, and able to document the aftermath.
Not the same as a larger or multiple detonation, but none the less it did not feel good.
http://www.anotherpower.com/board/index.php/topic,53.0.html (http://www.anotherpower.com/board/index.php/topic,53.0.html)
(http://www.anotherpower.com/albums/blownbatt/dscn2697.jpg)
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Gotta love that label too Wolv.... 8)
............oztules
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OUCH! Thanks - it's good to see others have experiences. My worry - and that of the family and helpers - is that the source of detonation in the cells we experienced was internal. Connexions were tight and there were no external ignition sources.
The solution that you're all appearing to be suggesting is . . . to keep batteries in a well ventilated bunker . . .
This thread is important because as more people get into the idea of solar power and battery storage, people are entering a realm in which they're unfamiliar with what they're getting into.
Personally my system, against all conventional advice, uses SLA batteries ejected from emergency power supplies and this has enabled me to put together a large system economically and so-far successfully. As a matter of interest, a useful material for bus bars is 3x25mm lightning "tape" and, again, I colour code this keeping copper for positive and alumiunium for negative, and doubled up where appropriate for current carrying capacity. All my connectors are similarly coded with brass for positive and zinc plate for negative. Using 12V SLA batteries in multiples for 24V and obeying the requirements for only gentle exercise on each battery, instead of conventional hefty connectors I use a piece of solder wire which melts at 7 amps. In this way there is current limitation at the source of each point of power. Because of cheap availability, I use 6mm red and black solar cable to connect groups of 10 or 12 batteries to a local connexion taking 5 or so such groups of batteries and each of these fused with a dozen strands of solder wire twisted together. From these groups two parallel 6mm cables (ensuring equal length cables throughout the system as far as possible) take the group connexion back to the bus bar and 9 or so such groups all switched add to the current carrying capacity of over 100mm cable. LED voltmeters at the group connexions show the voltage at each such junction and any differences between them, and the difference between those voltages and the voltage at the bus bars indicate any poor connexion issues and any high currents. This distributed system has the advantage that sharing among 9 or so groups of batteries there are no high currents in any individual places other than the bus bars to the inverter - and likewise minimising any risk of spark as in the case of a poor contact, there will always be an easier current source from the 8 other groups rather than a spark or dangerous current through a high contact resistance.
This system is unconventional but I believe avoids the safety issues leading to the photographs above.
Best wishes
OTW
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The solution that you're all appearing to be suggesting is . . .
.... to not use lead-acid!
This thread is important because as more people get into the idea of solar power and battery storage, people are entering a realm in which they're unfamiliar with what they're getting into.
All the more reason to encourage the use of "safer" technology. AGM (fairly safe, but not very forgiving), perhaps LFP.
Personally my system, against all conventional advice, uses SLA batteries ejected from emergency power supplies and this has enabled me to put together a large system economically and so-far successfully. As a matter of interest, a useful material for bus bars is 3x25mm lightning "tape"
I used copper busbar, cut to lengths and drilled. I think most of mine was 25x5mm and for the end bars I used 36x5
(from memory)
[/quote]
alumiunium
I would STRONGLY advise against the use of aluminium in ANYTHING around your batteries. It's a disaster.
instead of conventional hefty connectors I use a piece of solder wire which melts at 7 amps.
7 amps? On a 24 volt system? Thats so near useless as makes no difference. I pull peaks of near 150A PER BANK at 48V
And charging a system at a maximum of 7A? That'd be fine for pocket-sized cells, but it is chronic undercharge for anything in the 200+AH range.
This system is unconventional but I believe avoids the safety issues leading to the photographs above.
Please don't take this the wrong way... but most of what you've put forward is so far removed from any practical application as renders it either useless, or ok for some esoteric system with a peak demand of around 100 watts, and not much more than that in PV to charge it.
My system is NOT a showpiece, it's NOT best-practice, and it's NOT all new gear. It does run my home, 2 offices and workshop, and has done so for a decade with no problems. It's second-hand AGM (sealed lead-acid) cells, running around 1000AH capacity (faceplate would say 1500AH @ 48V).
(http://house.albury.net.au/23may2010/100_4463.JPG)
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That's a nice system
But my mention of aluminium is for intergroup bus to the inverter and solar controllers and nowhere near batteries.
When one is using multiples of 38 to 60 or 70ah batteries, limiting draw and charge to C10 or C5 at most, and therefore fusable wire at 7 amps per battery, is not inappropriate. The concept makes a lot of things non-critical which could be otherwise.
Best wishes
OTW
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That's a nice system
But my mention of aluminium is for intergroup bus to the inverter and solar controllers and nowhere near batteries.
Given the problems I had of connections constantly coming loose, high contact resistance etc, I'd never, ever, use aluminium again in this application.
When one is using multiples of 38 to 60 or 70ah batteries, limiting draw and charge to C10 or C5 at most, and therefore fusable wire at 7 amps per battery, is not inappropriate.
I hadn't realised you were using such small cells, but I would still contend that "fusible wire" is a bad choice. Should you have a fault (which may cause significant gassing), then a fusible wire/link may well prove to be just the ignition source you DON'T want around! Far far safer to use HRC fuses, keep the arc fully contained and rapidly quenched.
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Yes - thanks - it should be pointed out that my personal system is a world away from the traction wet cell explosion experiences the subject of this thread. The busbars I'm describing are nowhere near the battery end of things and the aluminium works well in the context chosen as well as providing visual identification of the negative rail.
Because I'm using SLA batteries offgassing is neither allowed nor happens. On the solar controllers I set the maximum charging voltage to 28.8V in cloudy weather to take advantage of any available peaks of sun and 27.6V in continuous sun. Any risk is an accidental short and the interbattery fusing provides the best failsafe protection in the context.
The cells which exploded were not being operated as part of this system and the matter of concern is what internal source of combustion can have caused ignition.
Best wishes
OTW