Mechanisms that decrease the Lifespan of Lithium-Ion batteries and how to avoid them

[reed cundiff]

Extreme cold degradation while charging

wb9k

Thanks for response. The solar system on 5th wheel is 1420 W of panels which three panels are in series then both strings are parallel to provide 90 V to MPPT and a 48 V nominal battery suite of 16 CALB cells (Manzanita Micro fabrication and BMS). The capacity is 8.6 kW-hr (48 V nominal and 54.4 actual)

We left rig at son's place two winters when we flew down and spent the winters in Guatemala/Honduras and then Ecuador/Peru. The temperatures went down to a minimum of -20 C and battery suite was not disconnected. Inverter was disconnected since it has a parasitic draw of around 50 W. The other parasitic draws are about 20 W so that the daily discharge would have been around 500 W and perhaps 300 overnight. Early morning charging rates would have been around 200 to 400 W, or about 0.02 C. Son checked on this and battery was fully charged at these low rates by mid-morning We have discerned no loss in capacity.

We have had charging rates of over 1400 W in mid-June and high elevation (2700 m) according to Tri-Star MPPT-45 and Manzanita Micro BMS monitors.

Have always appreciated the responses of Karnak and PNJunction as well.

Reed

[Sunking]

The bottom limit is really around 300 mV. A123 states 500 mV for additional safety margin. Below this voltage, the Cu anode plates begin to dissolve.

So on a 4S. 8S pr even a 16S battery with LVD set to 12, 24, and 48 how would it ever be remotely possible to get a cell down to .5 volts when you set the cut off at 3 vpc? You are are biased manufacture and only have one side, otherwise you are in conflict. Just so everyone is properly warned you are a Shill and came here to just make trouble and generate sales. You would also have to explain whey many EV and gizmo manufactures do not monitor at the cell level or 1SxP. They monitor and balance at 1S to 4S. That tells me and the world BMS is not required on lower voltage systems. If one stops and think about it chew on this. A 12 volt system is 4S, 24 volts is 8S or 4 cells in series at 12 volts and 8 cells in series at 24 volts. If you have an Inverter, it has a Low Voltage Disconnect aka LVD. Default is 10.5 volts or 2.625 vpc. The operational range of a LFP battery is 3.0 to 3.4 volts on 12 volts. Critical voltage on a lithium cell is 2 volts or 8 volts on a 12 volt system. The chances of ever over discharging a 4S, 8S, or even a 16S system is so remote you have a better chance of winning the lottery. Even without a LVD your battery operated equipment would quit working long before you ever get the voltage low enough. Now on something like even a 45S 144 volt EV system a BMS is nice to have and takes some workload off the driver. A difference of 3 or 6 volts (1 or 2 bad cells) can go noticed. That is not the case with 12, 24, and 48 volt systems used in solar. Nor do you take all your cells, cram them into a tin can, and set them out in the sun to bake while you charge and discharge them. So in a properly designed Solar System do you have BMS. You most certainly do have a BMS, it is called the LVD in your Inverter, and Set Point voltage in your Charge Controller. You can add more automation if you wish and afford to, but not necessary with a sound strategy of passive fail safes. If you know little about LFP batteries and do not want to learn anything or just the conveyance or piece of mind a BMS may afford you, get a BMS. But just remember Balance Boards are known to destroy cells. I say get rid of them.

[wb9k]

To return to the question of mechanisms that decrease lifespan of LFP.

It has been stated quite often that LFP should not be charged below 0 C. Is this true for the quite low C charge rate of solar. Have not seen this discussed elsewhere.

What is the mechanism that would cause degradation in CALB cells?

The bottom limit is really around 300 mV. A123 states 500 mV for additional safety margin. Below this voltage, the Cu anode plates begin to dissolve. The Cu goes into solution in the electrolyte. It happens even faster when the cell is driven negative. When you recharge such a cell, Cu plates onto the cathodes, forming dendrites that can eventually puncture the separator, causing a short inside the cell. The result is a cell that holds no capacity. Kept in place, this usually results in a hot cell in the stack that increases series impedance of the whole pack. Occasionally, the damaged cell will go out in a "blaze of glory", and that's the worst case you're trying to avoid, and the reason OEM's do not tolerate no protection against this scenario.

At low (discharge) C-rates these limits are actually "harder" than with higher currents where a cell might fall this far under load, but then spring back to 2 Volts (for example) once the load is removed. This is a safer condition than slowly pulling down to, say 200 mV and the cell only bouncing back to 300 mV when the load is released. For two cells that show the same loaded voltage but are loaded differently, the cell with the lighter load is more completely discharged than the heavier loaded cell. Charge rate makes no difference to the outcome in this case. Make sense?


[EDIT] I just reread your post and realize you are talking about temperature, not SOC, sorry. The mechanism for damage from charging at very low temperatures is Li plating permanently onto the cathodes, causing rapid and permanent capacity loss. Slower charge rates ARE safer at low temps, so it may or may not be an issue for you. 0 degrees C isn't really that cold....safe charge rates for A123 LFP don't fall off much until you're down to -10 or colder, falling off really far around -20 and below. By the time you hit -40 degrees C, safe charge current is down to a trickle. Bear in mind that at warmer temps, A123 cells are rated to handle 4C of continuous charge current. Ideally, you should be able to get data from CALB showing what the safe charge rates are as temperature falls. If your solar rig can never source more than the worst-case safe current, then you're OK.

Sorry for the confusion.

dh

[reed cundiff]

What is mechanism that causes LFP cell degradation in charging below 0 C?

To return to the question of mechanisms that decrease lifespan of LFP.

It has been stated quite often that LFP should not be charged below 0 C. Is this true for the quite low C charge rate of solar. Have not seen this discussed elsewhere.

What is the mechanism that would cause degradation in CALB cells?

[wb9k]

Like I said lets see what you got to show. You keep threatening to show it, play your hand. A123 battery may certainly have something inside. But there is nothing in the docs to indicate so. But even if it does, does not change the fact you kind find dozen just like it that do not have anything other than cells inside the box. At 4S is silly to think you could get any one cell so far off without the pack voltage being way below what any equipment can operate with just 7 to 9 volts on a 12 volt system.

And I was being so nice until you showed up to make trouble.

I rest my case. Goodbye.

[Addendum for the benefit of confused onlookers]

P2250001.JPG

Above is a photo of the BMS pcb for the A123 gen II starter battery. Note that there are no relays here (or anywhere else in the battery), switching instead being done by the two banks of large FETs. Current can be cut off for only charge, only discharge, or both. 550 CCA rated, every unit is tested to deliver that amount of current. Cells are Amp 20's in 4S4P or 4S3P. The main microprocessor holds thousands of lines of code. The product specification is 93 pages long, and includes several state diagrams, some of them quite large and complex. A few features:

1) Low volts cutoff. If pack voltage falls below 10 Volts, discharge current is interrupted until battery is charged back up over 10 Volts. If any cell falls below 0.5 Volts, the pack is permanently disabled, since it is no longer safe to charge. THIS IS A REQUIREMENT FOR EVERY OEM.

2) High volts cutoff. Charge current is shut off if any cell reaches 3.9 Volts. THIS IS A REQUIREMENT FOR EVERY OEM.

3) Cell balancing. All four cell voltages are monitored directly. Above 3.6 Volts, balancers are turned on full for 300 mA of balance current. Below this, balancers are PWM'd for lower current until the cell voltage reaches 3.585 Volts. (Error margin in the voltage measurement dictates a number just below 3.600.) Safety and reliability requirements make this a de facto OEM requirement.

4) Temperature sensing. Two thermistors in the module and two on the pcb provide thermal protection for the cells and FETs respectively. Charge current can be limited at extreme low temps, and the pack can be completely disabled if too hot to guard against permanent failure. Safety and reliability requirements make this a de facto OEM requirement.

5) Communication. In OEM applications, the pack communicates with the car over LIN (Local Interface Network). Alternator output will be adjusted to optimize battery performance based on data streaming from the pack to the car's main controller. Error/service messages for the driver are also supported.

6) Data logging. There is an extensive list of histograms, event counters, and other data capturing tools that provide all kinds of historical data for the unit in case it is needed for troubleshooting or failure analysis. When not in use, the battery goes into a sleep mode, but still wakes up periodically to make sure nothing has gone awry and log data.

There are indeed LFP 12 Volt batteries out there with no electronics in them. Most are sold as motorcycle/racing batteries. They can do this because there are no real requirements for the aftermarket--until you manage to kill a few people. Then, beancounters who recognize the cost of a wrongful death lawsuit, or government regulators step in to stop the irresponsible behavior of the manufacturer/designers. As stated in the thread at ES on Ballistic's motorcycle batteries, this has been a disaster for users of these packs, who are experiencing huge failure rates and a shorter life span than the LA batteries they replaced. I've seen others that have balancers and nothing else inside. There is nothing preventing gross overcharge or damage by overdischarge in those batteries. It's a recipe for abysmal performance or worse.

Our friend SK apparently believes his knowledge is so great that he can divine operational details of very complex systems simply by reading the advertising copy for them, or from media reports that give the most scant technical details. Reality strongly suggests otherwise. You have been warned.

[Sunking]

You're changing the subject because you stepped in a pile of sh%t with claims you realize you can't back up, and in fact are in danger of being proven extremely wrong. What's inside that A123 battery...since you claimed to know? Put up, or STFU. I will not waste my time on a fraud any longer.

Like I said lets see what you got to show. You keep threatening to show it, play your hand. A123 battery may certainly have something inside. But there is nothing in the docs to indicate so. But even if it does, does not change the fact you can find dozens just like it that do not have anything other than cells inside the box. At 4S is silly to think you could get any one cell so far off without the pack voltage being way below what any equipment can operate with just 7 to 9 volts on a 12 volts.

Many commercial EV's DO NOT MONITOR or CONTROL at cell level voltages. They range from 2S to 4S level. Example Nissan Leaf is 2S or what Nissan calls a Module which is 2s2p. That clearly indicates you do not need to monitor and control at cell levels.



And I was being so nice until you showed up to make trouble.

[wb9k]

You're changing the subject because you stepped in a pile of sh%t with claims you realize you can't back up, and in fact are in danger of being proven extremely wrong. What's inside that A123 battery...since you claimed to know? Put up, or STFU. I will not waste my time on a fraud any longer.

[Sunking]

The more you edit this post, the worse it gets for you. Selling a product that can kill somebody for being negligent or ignorant...IS NEGLIGENT! There's nothing stopping the user from the possibility of burning his house down if he accidentally puts his 12V battery on a 24 V charger.....or a "12V" charger that really makes up to 17 Volts. Now you really are advocating no supervisory electronics on an LFP pack. If this were my forum, you'd be on vacation for advocating dangerous practices and banned if you repeated. But of course, it's not. The moderators here can do as they please, but to me, you smell like a saboteur.

You are full of chit too. If anyone can say anything about me, Dangerous is not one of them. That is a fact that can get you in trouble here because every moderator and the site owner know for fact safety is my top priority. If anyone stinks it is you my friend as a Shrill.

No supervisory my foot. What the heck do you think any Inverter or Solar Charge Controller has built into it?

[Sunking]

you'll see an unanswered question from me about what you actually mean by when you say "BMS". This is needed before any debate can continue there, which I'm open to.

I answered that already here because the other thread is locked. But to recap any system that uses Balance Boards or By-Pass Charging. It is the vampire boards I take issue with.

I know of several programs (mostly hybrid buses) that do in fact allow packs to go to 0% and will allow brief excursions ABOVE 100%. Every plug-in car I'm familiar with takes the pack to 100% or very close to it on every charge cycle that runs to completion. "Middle balancing" doesn't even exist. LFP cells must be balanced at either top or bottom of charge to be balanced at all. If you're not at one of the extreme ends of the charge curve, you cannot discern SOC using voltage with any hope of accuracy.

Sure you want to stick with that statement? Because Tesla and Nissan do not allow owners to have access to all the battery capacity. In fact Tesla just upgraded all their Roadster mileage from 240 to 400 miles with nothing more than a Over The Air Up Grade to firmware to allow customers to access more capacity that was always there to start with. Tesal sends out alerts to customers warning them not to charge to more than 90%.

Chevy Volt uses a 16 Kwh battery and limits access to only 10.4 Kwh usable.

The Nissan Leaf uses a 24 Kwh and limits to 21 Kwh usable.

Between Tesla, Nissan, and Chevy make up the majority of the market.

I never said you bottom balanced every cycle. In fact, I think the lack of regular resetting of balance is the single largest liability in your system. You have no means of dealing with developing imbalance, except by leaving margins for error wide enough to drive a truck through at both the top and bottom of charge--putting over 1/3 of capacity permanently off limits. Yes, it's cheap to bottom-balance cells just before assembling a pack, but it is any cheaper than paralleling the cells and charging them to exactly 3.6 Volts? I see no reason to trumpet this virtue for this part of the process because so far, you've gained nothing at all.

You would be incorrect, I would use my Powerlab 8 to re balance if it ever became necessary like anyone who BB thier EV pack.

Not sure what Holes you are are talking about and loss of capacity. When I drop to 10 to 15% SOC all my cell voltages are equal all the way down to 2.5 vpc. I cannot see anyway hole sin those voltages.

My cells are 100 AH Prismatic, Chi Com Prismatic GBS to be exact. Their actual capacity ranges from 101 to 110 AH or about a 9% tolerance. Regardless the weak cell of pack means the pack is only 101 AH. That last 9% is not accessible like any battery pack be it Lithium or Pb. When I am fully charge (85 to 90 AH, I use Coulomb Counter Gas Gauge), my lowest cell voltage 3.36 and highest is 3.41. So I have no idea what holes of loss of capacity you are referring too.

In a pack made of decent cells, there should be very little difference in capacity from cell to cell.

That maybe true if you use a good manufacture, and have a manufacturing at either at the battery manufacture plant , or Auto Manufacturing to match cells. But what I have been trying to tell you a DIY Solar System is going to use inexpensive Chi-Com cells and only LFP. If cells were matched up as close as you imply, there would be no need for any monitoring needed outside what the charger and inverter already have built in. All that would be required is the initial Balance at either the Top or Bottom. Set your charger to say 3.45 vpc and set LVD to 2.9 vps and you would never even come remotely close to either edge making it a Middle Balanced system.

We are not talking about any other battery, only Chi-Com LFP in a DIY Off-Grid Solar System. The batteries get treated like babies and never see the extremes an EV will see. In a properly designed solar system, a LFP battery will never be fully charged. Just not enough sun hours in the day. Charging rates are relatively low in a Solar system and discharge rates are even lower. On the charge side it would would be rare to ever see a charge rate in excess of C5 with C/8 to C/10 being the norm. Discharge rates are similar. Couple that with a controlled environment of room temps and all the need for a BMS vanish.

Look I am not saying DO Not Use BMS. I am saying You Do Not Have Use a BMS. Regardless if you like it or not, there is a Market being born for BB. BMS manufactures are just now starting to offer equipment, but all one really needs is a Powerlab 8, and good strategy. Run Between the Sheets of either 10/90 or 20/80.

[wb9k]

Lets see it, nothing in the documentation that indicates there is anything inside. . Then IJ wil show you dozens of 12 volt Lithium batteries with no form of BMS. There are more than I can count. A 12 volt 4S battery is kind of a waste having any BMS. If a cell failed you would be in the 9 volt output range. That woul dtake catastrophic failure and gross negligence on the user.

The more you edit this post, the worse it gets for you. Selling a product that can kill somebody for being negligent or ignorant...IS NEGLIGENT! There's nothing stopping the user from the possibility of burning his house down if he accidentally puts his 12V battery on a 24 V charger.....or a "12V" charger that really makes up to 17 Volts. Now you really are advocating no supervisory electronics on an LFP pack. If this were my forum, you'd be on vacation for advocating dangerous practices and banned if you repeated. But of course, it's not. The moderators here can do as they please, but to me, you smell like a saboteur.

dh

[wb9k]

Lets see it.

Oh no...you first, Mr Expert. A relay, you say? Running LVC? Any other capabilities in this thing at all? Tell us, what are the real-world requirements for this battery. I'll even give you this...that's the same battery we have been selling to Daimler and Ferrari for a couple years now. So...what's needed in such a battery?

[Edit:] Those "no BMS" 12V batteries are unreliable, dangerous pieces of crap that will eventually be illegal. Search the ES forum for "Ballistic" for my posts regarding one example. Are you consulting for these guys?

dh

[Sunking]

WHOA That statement is complete BS....totally untrue. How to you pretend to know what is inside that battery? Tell you what....you tell us what's in there, and then I'll post a picture of one torn down and we can all see how full of it you really are. Your trousers are ablaze.

dh

Lets see it, nothing in the documentation that indicates there is anything inside. . Then IJ wil show you dozens of 12 volt Lithium batteries with no form of BMS. There are more than I can count. A 12 volt 4S battery is kind of a waste having any BMS. If a cell failed you would be in the 9 volt output range. That woul dtake catastrophic failure and gross negligence on the user.

[wb9k]

[*]Many battery Manufactures make 12 volt LFP batteries as drop in replacements for Pb and most do not have any type of BMS other than a LVD Relay. That includes the almighty A123 LFP 12 Volt Car Battery. Why would a manufacture do that without a BMS? Because it is NOT NEEDED.

WHOA That statement is complete BS....totally untrue. How to you pretend to know what is inside that battery? Tell you what....you tell us what's in there, and then I'll post a picture of one torn down and we can all see how full of it you really are. Your trousers are ablaze.

dh

[wb9k]

Like I said you are a manufacture and only have one point of view. The claim that Top Balance and a BMS must be used is completely false and made up by manufactures with BMS and Top Balance products.

I work for a company that is a cell maker first and foremost. The company does also make BMS systems, but they are not for sale to the general public, and I don't expect A123 to ever sell any electronics to any member of the GP. So, I reject the idea that I'm on some kind of sales shill mission regarding control systems. I never said packs MUST be top balanced, but I think there are plenty of good reasons for opting for that arrangement. Bottom balancing requires compromising performance and control over certain aspects that I think are not worth any perceived benefits. Others in this thread and the one at ES have covered most of these things already.

There is nothing dangerous with Bottom Balancing, it is safer than Top Balance. As to responding I would have loved to continue a debate, but you shut the thread down. So do not give us that crap I would not answer questions. You do not want questions answered unless it is you are th eone giving answers. You cannot have your way here. Now you come here hoping to shut the debate down here. Simon like like you are manufactures, you have to tow the company line. Simon couldn't win the debate here, so went crying to you looking for help. I expect you and Simon both to say exactly what you are saying. As manufactures if you said anything else is Conflict of Interest. You are here to protect your Invested Interest. I am here to tell floks there is another way and you do not like it.

You're teetering off the rails here. I am not a moderator at ES, or any other forum nor have I ever been. I had nothing at all to do with the temporary locking of that thread, in fact when I saw it was locked, I sent a note to the moderator (Ypedal in this case) to make sure I wasn't the one being complained about (I wasn't). I have no idea who complained or what exactly they complained about, and I don't really care. As Simon (who you falsely accuse of being a mfg.) pointed out, the thread is open again, and if you look, you'll see an unanswered question from me about what you actually mean by when you say "BMS". This is needed before any debate can continue there, which I'm open to. I suspect the locking of the thread was about the acidic comments of one member there, but I don't know for sure. I'm confident it had nothing to do with technical content...where several posters (not just me, not just people in the industry) expressed a feeling that you were deficient on that front.

Fact is EV manufactures do not Top Balance, they all Middle Balance never touching 100% and never getting close to 0%. Exact same thing I do with my NEV. I charge up to 80/90%, and only discharge down to 20/30%.

You keep repeating that first point as though it is gospel, and I know for certain that it is a totally incorrect statement. I know of several programs (mostly hybrid buses) that do in fact allow packs to go to 0% and will allow brief excursions ABOVE 100%. Every plug-in car I'm familiar with takes the pack to 100% or very close to it on every charge cycle that runs to completion. "Middle balancing" doesn't even exist. LFP cells must be balanced at either top or bottom of charge to be balanced at all. If you're not at one of the extreme ends of the charge curve, you cannot discern SOC using voltage with any hope of accuracy. NEV is a mighty highfalutin' term for a souped up golf cart. Is it even street legal in any sense? Regardless, in a purely recreational vehicle, you can afford to not use 30-40% of your battery capacity. In a real car, this would be considered an enormous waste of resources and no OEM I am aware of operates this way to my knowledge. Perhaps if you could share how you come by this belief, we could discuss it more detail.

What you guys did on EP is distort what I said. Batteries are not Bottom Balanced every cycle as was implied by yourself and others. They are only Bottom Balanced initially when assembled like any dang battery assemble has to be done. Does not matter if it is Top, Middle, or Bottom because any will work once you pick the end means. . Any lithium battery must be equalized with his mates before assembly. You know that as well as I do. I just do it at the bottom when the cells arrive. Wire then all in Parallel and drain then down to 2.5 vpc resting over night. All it takes is a real simple cheap circuit made from a dollars worth of parts and nichrome wire.

I never said you bottom balanced every cycle. In fact, I think the lack of regular resetting of balance is the single largest liability in your system. You have no means of dealing with developing imbalance, except by leaving margins for error wide enough to drive a truck through at both the top and bottom of charge--putting over 1/3 of capacity permanently off limits. Yes, it's cheap to bottom-balance cells just before assembling a pack, but it is any cheaper than paralleling the cells and charging them to exactly 3.6 Volts? I see no reason to trumpet this virtue for this part of the process because so far, you've gained nothing at all.

You say it has to be at the top 100% where you only really know voltage, but AH is unknown. I reference at the Bottom where I Know exactly where 0% and 00 amp hours are located. From there once charged they never see anything below 20% or above 90% which is spot on for maximum lithium battery life. Everything I said has been factual.

In a pack made of decent cells, there should be very little difference in capacity from cell to cell. This is one good reason for paralleling smaller cells when building a pack....the capacity difference between cell groups tends to get averaged out and be less of an issue than if you use one giant cell for each series element. Your system seems to be targeted very specifically at fixing this problem which you really shouldn't have in the first place, unless you're building from recycled/recovered used cells.

Your method is to charge lithium cells to 100% every time, and it is well know that is not good on for lithium batteries and can cut battery cycle life down some 50%. That is good practice from a manufacture POV as it generates more battery replacement sales. Me I never go above 90%, so not something I have to worry about is over charging, I eliminated the possibility, where Top Balance does it every cycle if set to 3.6 volts.

I'd like to see data showing that 50% loss of lifespan vs charging to 80% with LFP. This would need to include specific details on the charging and usage routines to be really meaningful. My own experience and the data I'm familiar with suggests a difference of more like 5 or 10%. Top SOC isn't the only thing that affects this. Charge rates and soak voltages are important to consider as well. A cell that loses half it's life for going to top of charge is not fit for automotive use, IMO, and I think the OEM's feel much the same way.

With Top Balance you also set the batteries up for a over discharge and reversing a battery cell polarity. With Bottom Balance I eliminated the possibility because all cells arrive at 0 at the same time. No adjacent cells have any energy left in them to drive a cell into reversal. Cell Reversal is the most destructive thing you can do to a lithium and you know it.

Top or bottom balance has nothing at all to do with robust protection against overcharge or overdischarge. Those things can only be properly addressed with cell-level voltage monitoring and controls that stop the show before a cell can be destroyed. Yes, I say all the time that overdischarge is bad, there has never been any argument about that. Apart from gross overcharge, it is the most dangerous thing you can do with an LFP cell.

Is Bottom Balance for everyone. Nope especially the uniformed public. For them, I send them to you to lighten their pockets with Automation and not a thought in their head. . That is good for both if us.

See the deal is I do not represent any company or technology. I got nothing to sell you or anyone else. Just 35 years as a professional electrical engineer in battery plants and power transmission. Retired and giving something back to the public. Endless Sphere is a commercial site, that was my only mistake. You guys do not want anyone there that does not have a commercial product solution and I understand and respect that.

Where we left our conversation before you had it turned off is, I said is some level of monitoring is required and a Strategy is needed with LFP. You replied calling that BMS. That is when I said you cannot define what a BMS is other than something you sell or recommend as a manufacture. We get it. You sell lithium batteries. As a manufacture you can only warrant your product if a BMS of your approval is used.

Have I missed anything?

I think you've missed plenty and added some things as well. ES, as far as I know, is NOT a commercial site, any more than this forum or DIY EC. You're strawmanning me and Simon by painting us as having agendas that we don't have. I am not a sales guy. I sometimes go to bat for the company on forums when I see misinformation or sabotage by certain individuals, but that's as far as it goes. A123 has already sold every cell it can possibly make through 2017...I really don't care whose cells you use, and you can't buy an A123 BMS, so this is just noise on your part. You're oddly narrow definition of "BMS" makes me wonder what product you may have waiting in the wings and how you plan to differentiate it in the market. Just a hunch...trying to make sense of your odd assertions.

[solar pete]

please argue nicely

Hi All,

I was a bit worried about this thread but I am very pleased that the argument can continue in a civil manner. People will disagree on many things, lets face it there is more than one way to skin a rabbit. I, like some of the other posters think these things need to be debated but in the most civil and polite way, cheers all