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gijoe460
28 October 2012, 2020
3734

Hey everyone, So i got my batteries in finally...80 X 63 Ah SLPB110255255H DOW/KOKAM. I am only going to be able to use 34 at a time for the first attempt at a battery box that will fit in my bike. I would like to match the best of them up for that task. I have a ThunderPower TP-1010c charger.....It is working perfectly to charge and discharge.
I have the ability to set the discharge rate up to 22 Watts, which rough math i came up with is a 6 Ah discharge....using this, can i take the no load voltage, and the stabilized voltage during 6 Ah discharge and use them to get a decent IR measurement?
Is this accurate enough to at least get an idea which batteries are closest matching ?

Thoughts?

Thanks

lugnut
28 October 2012, 2229
3734

Hey everyone, So i got my batteries in finally...80 X 63 Ah SLPB110255255H DOW/KOKAM. I am only going to be able to use 34 at a time for the first attempt at a battery box that will fit in my bike. I would like to match the best of them up for that task. I have a ThunderPower TP-1010c charger.....It is working perfectly to charge and discharge.
I have the ability to set the discharge rate up to 22 Watts, which rough math i came up with is a 6 Ah discharge....using this, can i take the no load voltage, and the stabilized voltage during 6 Ah discharge and use them to get a decent IR measurement?
Is this accurate enough to at least get an idea which batteries are closest matching ?

Thoughts?


I think you mean 6 A discharge, not 6 Ah. And 63 Ah cell or that part number does not show up on the Kokam web site. But if it actually is a 63 Ah cell, then 6 A or 22 W is a pretty low discharge rate and would require 10 hours or more to fully discharge. Which would be a C/10.5 rate.

You should measure internal resistance closer to the rate you intend to use the cells. And I find it best to measure the actual cell voltage at 2 different current levels and use the delta V / delta I. Using an open circuit voltage can cause error. Also the difference in voltage between 0 and 6 A will be a very small value which will also introduce error. I'd use 30 and 60 Amps, or 50 and 100 A.

podolefsky
28 October 2012, 2229
You should be able to set the discharge current exactly with that charger. You want to do two measurements at two different currents, but not zero. Cells behave differently at rest than under load.

You want to do the tests with the cells at the same state of charge (fully charged is good, after letting them sit for 30-40 minutes). Also make the tests quick and close to each other, so the cells don't discharge much.

Try 0.5A and 5A. Then IR = (V2 - V1) / (I1 - I2)

Just to be sure, you could try at 1A and 3A, or something like that just as a double check to make sure your method is working.

podolefsky
28 October 2012, 2233
Oh, yeah - I missed that you have 63 Ah cells. Lugnut is right, you won't see much voltage sag at 5-6A. I've been using 5Ah lipos, so 5A is 1C, which gives me decent IR measurements.

My iCharger has an IR test function which seems to work pretty well.

gijoe460
28 October 2012, 2243
Yeah....thats what i was wondering too( draw being too low)......yes you are right i meant 6 Amps...

So am i screwed? how do i draw that much current to get a good test?

gijoe460
28 October 2012, 2249
http://edisonpower.co.jp/product/pdf/Tech_spec_SLPB110255255H_60Ah_A1.pdf

There is the link if anyone wants to check them out. From checking my military acquisitions websites, it seems these were made for some very specific military purpose. Probably good that i got more than enough for a few to be bad....

Any ideas that i might be able to do with things around the house, or cheap.......i use this ThunderPower charger for my RC planes as well...not really looking to buy another charger, on top the the Manzanita charger i already have for bike.

lugnut
29 October 2012, 0750
Yeah....thats what i was wondering too( draw being too low)......yes you are right i meant 6 Amps...

So am i screwed? how do i draw that much current to get a good test?

You can use a resistor load with an accurate voltmeter and ammeter (either sensor type or current shunt with millivolt meter). Maybe a braking resistor or length of wire or cable. Just get the V & I measurement at the same instant as the values change as the load heats up.

podolefsky
29 October 2012, 0859
If you can't find a suitable load resistor, nichrome wire works. 15 AWG is about 0.2 Ohm / ft. If you put a fan on it it will keep it from heating up as quickly (still heats up, just gives you a bit more time).

If your charger has a "regenerative" charge function, you can draw more amps. The way that works is that you use a larger battery as a power source (like a car battery). The charger can then draw more current as it is dumping it into the car battery instead of having to dissipate it. I can pull 20A that way with my iCharger. That's still be a little low, but it would get you closer.

Last option would be to get a charger with an IR tester built in. A $100 iCharger 106B+ will do it...might be worth it to save those thousands of $$ in Kokam cells.

gijoe460
29 October 2012, 1354
OK,
So now i am pretty confused.
So, my charger doesn't have a IR feature, but it has the same charging, and dis-passitive features as chargers that do. So i am assuming here (you know what that can do) that if the load i can put with mine is too low like we talked about in earlier post, then how does a charger that does have the feature accurately read. It should have about the same load capability( for a battery as big as mine 6/10/20 amps are all about the same).... The charger is currently hooked to a very nice power supply, so i can shove any more voltage to it, and the discharge rate is a firmware thing, i think i am screwed on that.

Also i agree that a larger load would be good.
http://www.harborfreight.com/100-amp-6-volt-12-volt-battery-load-tester-90636.html
this would be 100 amp load (ish) since its only a 3.7 volt battery, and i could take pretty good measurements? with my digital multi-meter of course..lol

Also the other wire and load stuff, everyone mentioned sound good too.....but unfortunately i am not familiar with making a wire or braking resistor....maybe some pointers or websites to get me up to speed.

Thanks a ton.

yes...Noah...I would like to not ruin them now that i am broke...ha ha ha

podolefsky
29 October 2012, 1704
I believe my charger uses an AC impedance measurement rather than a DC resistance measurement. The AC measurement doesn't require large currents.

I've checked the measurement from my charger against a high current DC load test and they were very close.

I'm not sure about your charger, but on mine the dissipative (or regenerative) discharge is requires a special setting. When you use it, the charger lets you draw higher current. You need a source that can take a charge current, like another battery. You can't use it with a power supply, though. The current coming from the charger will likely destroy the supply.

gijoe460
29 October 2012, 1915
ahhhhhh....
Now that makes sense....

I was sooo confused...which isnt hard

gijoe460
29 October 2012, 1918
just for $h!ts and grins.....
I went ahead and did the discharge method using just the charger....the calculations gave me 60 milliohms...

i was thinking if i used a ammeter clamp, and my digital multimeter, and used that harbor freight battery load tester for 6 volt batteries.....i could take accurate measurements......right?

gijoe460
29 October 2012, 1929
Noah,
I checked our chargers against each other...same exact specs...as long as i got the right user manual...just seems like mine doesnt have the screen menu to get IR

Going to call thunderpower tomorrow see if they can do anything for me

picaroon
30 October 2012, 0840
I'm in the same boat as you are gijoe, I have a bunch of cells to test too that I want to build into a pack.
Without even doing a test for
$h!ts and grins..... (nice saying! where does that come from? :) ) I realised that I wouldn't be able to repeat the test consistent enough to be certain. All connections and temperatures of wires, cells, loads etc would have to be the same for every test
I don't really know but I think this is more important for you because your large cells have such a low internal resistance, it says 0.6 milliohms in the spec sheet, one cell could have 50% higher resistance than another but measures just 0.3 milliohms difference.
I have an icharger like Noah, I think the IR measurements are pretty consistent so it should be good for comparing cells. Its easy and quick, you could measure a cell every 10 seconds easily. Mine was a second hand ebay buy so it was cheap.
Before I bought it though I bought an ESR/IR meter from a chap called Wayne Giles. Its the one sold in these links, but mine has a mod to able me to test single cells. The mod is to power the meter by a 2s lipo and can done by the owner if they can solder.

http://www.progressiverc.com/esr-meter.html

http://www.f3aunlimited.com/webstore/index.php?main_page=product_info&products_id=572

You may be familiar with it anyway because you fly RC planes? So you may still find the manual an interesting read as it explains IR causes and effects, and about winter flying etc...

The icharger and the ESR meter do read the same cell with slightly different measurements, from what I have read and can work out I think the ESR meter is more accurate. But if just comparing cells for a pack then there is probably no difference.

Hugues
30 October 2012, 1155
...

Also the other wire and load stuff, everyone mentioned sound good too.....but unfortunately i am not familiar with making a wire or braking resistor....maybe some pointers or websites to get me up to speed.

....

hi,

you can find a link to a video i made showing my discharge rig, building on an idea from Noah. I just bought some Nichrome wire, turned it around a concrete block, that's it.

I managed to dissipate 2'700 watts. The only tricky part was to switch it on without creating too many sparks. You can see in the video a very simple switch i made with a piece of wood and 2 copper brackets. The trick to avoid sparks is to be able to connect and disconnect very quickly.

good luck,


https://www.youtube.com/watch?v=HlWAeu6jDHs

podolefsky
30 October 2012, 1221
Just to add more ideas, here's a nichrome discharger that I built. The thing about using nichrome is that you don't have very good control over current. It varies with voltage and the wire's resistance changes as it heats up.

http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/high_current_close%20(Small).JPG

HOWEVER, you can still do pretty well. If you use a parallel wire system like I have, then each wire will carry roughly the same current, so they will all heat up and change by the same resistance. That is, if you have 5 wires each carrying 20A (total of 100A), and switch to 1 wire carrying 20A (total of 20A), the relative change in resistance due to heating should be the same. So you can figure the 5 wires will have 1/5 the resistance of the 1 wire.

It takes some math to prove it, but with this setup you can just estimate the resistance and substitute V/R for I in the formula for Ri. The reason you can estimate is that you only care about the relative Ri to sort the cells, not the absolute value.

Put another way - if you get Ri = 10 mOhm for 2 cells this way, then you know they are matched. If the real value is 12 mOhm, it doesn't matter because if you had the exact value they would have both measured 12 mOhm. They're still matched.

Clear as mud?

gijoe460
31 October 2012, 0653
Yup....thats exactly what i am trying to do....
Just match them..

Thank you for all the great ideas....
I'm on it

Side note.....poor little thunder power charger
cells came half charged, each cell is taking 4 hours + to charge to full, 80 cells to match= 2013 ish before i am done....ha ha

liveforphysics
31 October 2012, 1050
I went ahead and did the discharge method using just the charger....the calculations gave me 60 milliohms...

If your measurement is even in the same order of magnitude of the cells resistance, throw them all away, they are useless for an electric motorcycle.

They should be something closer to 0.6mOhm each if they are modern cells designed for EV use and 63Ah each. 1mOhm would be poor, but still possible to make a decent motorcycle batter with.


I've owned and tested most every RC chargers Ri (it's not IR, that would mean current times resistance, you want R, resistance, sub internal to show what resistance). They all worked with acceptable accuracy in >20mOhm cell measurements (like 18650's, old low C-rate 2Ah RC packs, etc). Once you start to get below 5mOhm, the accuracy becomes uselessly poor with all models I've owned/tested. They are great tools for RC toys, not so great for EV sized packs.

AC impedance readings taken at 1kHz are not much more than a measurement of the cells internal capacitance resistance (ESR) rather than DC resistance, and you can have some fantastic AC impedance numbers on cells that will fall on there face when drawing DC (which is all we care about). AC impedance numbers perhaps does have a place, and it's certainly the industry standard for better or worse (because it takes about 10mS to take a reading vs 5-10sec to do a proper DC reading).

Charging these things up 1 at a time sounds like a nightmare, and an analogy seems like trying to fill a whole room full of 2 liter bottles with a drip line that you have to move to each new bottle after hours it it dripping to fill.

My recommendation would be to buy a real power supply, like a sorensen 8v 125amp or even a 5v 300amp supply, crimp 20-30 piece of 10awg wire into a couple big terminals you bolt onto the back, put clip leads on the end of each wire, connect to 20-30cells, set the supply for 4.15vdc, and crank the current up. Then I would let it sit until current drops below 1A (this could take a week). Then I would let it sit all clips connected for another few days at minimum, then unclip each cell, take a precise voltage measurement and write it with a sharpie gently on each pouch (I can't emphasis how important it is for long term life of a pouch to not be rough with them, the damage takes months to show up, but it shows up). Then let them all sit a week or two, then check voltage again. Any cells that dropped substantially more than the average drop should be culled.

From there, you could take a resistance measurement (the way to do this is with 2 resistors, wait 5sec after loading to take the voltage drop readings, the resistors don't have to be big as they are only loaded for 5 seconds at a time, so a 20w resistor works fine even for 100w of heat for 5sec). Do the math just using the measured voltage across the resistor value as your current, because actual current doesn't matter for binning, you just need to make sure the method of connecting is perfect for each cell.

However, you're likely going to have a greater measurement error than the difference in Ri if these are new Kokam pouches from a modern line. Culling from the self-discharge test is going to give you a lot better end results for finding the cells that will become puffy problems in your pack if you're starting from a quality cell. If you're starting from a thunder-sag-esque cell, you really need to measure everything, because you can't really take anything for granted.

gijoe460
01 November 2012, 0050
OK...just to make sure my math isn't messed up before i start this.

Open voltage minus loaded voltage divided by total amps drawn times 1000

Does that sound right?

Thanks btw

frodus
01 November 2012, 0813
Don't do open voltage. Its not as accurate. Use two current points and their voltage at each point.

(V1-v2)/(i1-i2) = R

gijoe460
01 November 2012, 0823
hmm, ok, soooo
two different load points....
I think i can do around 2-6 amps, will measure to see what it comes out to be
and then i can do 100 amps now....
Will post a result this afternoon and see if it sounds right.
The first cell i charged has been holding 4.06 for a week.....and i sharpied it.

podolefsky
01 November 2012, 0846
Don't do open voltage. Its not as accurate. Use two current points and their voltage at each point.

(V1-v2)/(i1-i2) = R

Note that if you use this formula you will get a negative resistance. This is because lithium chemistries have a negative permittivity, so their dielectric constant results in an impedance phase reversal.

I'm totally kidding...

Just do Ri = (V1 - V2) / (I2 - I1) and you'll get positive resistance (switch the order of I2 and I1)

frodus
01 November 2012, 1042
Oops. Yeah. Typo.

Really should be:
|V2-V1|/|I2-I1| = R
Where || is absolute value.

:D

liveforphysics
01 November 2012, 1256
The first cell i charged has been holding 4.06 for a week.....and i sharpied it.


For doing a self-discharge test over a short time period (like a week), you need more digits on your meter than that. I use 6.5digit meters for this, but 5.5digit meters are much cheaper and would do the job.

The reason you care about self discharge is because that energy isn't just lost as heat (that's possible for some types of cell issues, but it's unlikely with a quality cell), it's lost to electrolysis processes happening to the solvent/electrolyte from impurities or damage in the separator caused from mfg or rough handling etc. These processes evolve a gas in the sealed pouch, and even if it's just a teeny tiny bubble per week, over the course of a year or two, your cell is puffed and splitting apart. The self-discharge is an easy to measure predictor of this so you don't end up sad down the road.

I don't know the history of these cells, but if they are healthy new modern Kokam pouch cells, the capacity and Ri will be matched to a higher precision than you're even going to be capable of measuring with the equipment you've got. If the cell history is something used and pulled out of whatever packs and shipped and handled with human hands etc, then STILL self-discharge is going to be the most important test.

gijoe460
01 November 2012, 1903
I just ran into another brick wall....
aside from the fact that my meter isn't accurate enough...


so that battery discharge tester i have (the schumaker car one), which is basically a big resistor wire inside that heats up says that it is 100 amps for 6 volt tests, and 50 amps for 12 volt tests....
is there a formula to find out what it would be for 4 volt tests which is the range i am in....reading the resistance through the heating wire doesn't seem to be working out to a number i would expect.

I guess what i am asking too, is if there is equipment i need for all this testing that has a name and brand and such that i can purchase.....this seems to be getting way more accurate than tools i have for car/airplane/house electricity work i normally do...
If there is a particular meter i need, and better battery tester and such.....within money reason...i seem to be having a lot of trouble with this even though i am an electrician and the concepts aren't foreign to me.

lugnut
01 November 2012, 2110
so that battery discharge tester i have (the schumaker car one), which is basically a big resistor wire inside that heats up says that it is 100 amps for 6 volt tests, and 50 amps for 12 volt tests....
is there a formula to find out what it would be for 4 volt tests which is the range i am in....reading the resistance through the heating wire doesn't seem to be working out to a number i would expect.

My guess is that the tester has two 0.12 Ohm resistors. For 12V, it uses them in series for 0.24 Ohms yielding 50A. For 6V, it switches them to parallel for 0.06 Ohm yielding 100A. Both cases give a total of 600W or 300W per resistor. Using 4V on the 12V setting should get you 16.7A and 67A on the 6V setting. Wattage will be lower either way for 4V. 17A and 67A would be good targets for measuring Ri.

I have a Fluke digital multimeter which is great. I also have other decent digital multimeters which work pretty well. And a couple of cheap ones which proves you get what you pay for. For voltage, 4 significant figures like 3.823V would be good. You will need to measure current. Some decent clamp-on digital DC ammeters are available for reasonable money, under $100, or maybe half that. Or use a current shunt and millivolt scale on the multimeter.

liveforphysics
02 November 2012, 1212
I have a Fluke digital multimeter which is great.

Just as an FYI, this is kinda like telling someone you have a Honda car and it works great. They offer meters that are totally useless for taking these readings, and they offer some meters that are very well suited towards it. There are no meters that are hand-held that are properly suited towards this work that I've ever seen. I've got a Fluke 289, but I wouldn't bother wasting my time trying to measure self-discharge with it (cause it's realistically a 4.5digit meter).








I also have other decent digital multimeters which work pretty well. And a couple of cheap ones which proves you get what you pay for. For voltage, 4 significant figures like 3.823V would be good. You will need to measure current. Some decent clamp-on digital DC ammeters are available for reasonable money, under $100, or maybe half that. Or use a current shunt and millivolt scale on the multimeter.

If you're binning Ri, you don't care what the current is, you just care that your setup's connections and resistance is repeatable between cells. Your goal isn't to measure the Ri with accuracy when you're binning, it's to measure it with precision and repeat-ability.

lugnut
02 November 2012, 1402
If you're binning Ri, you don't care what the current is, you just care that your setup's connections and resistance is repeatable between cells. Your goal isn't to measure the Ri with accuracy when you're binning, it's to measure it with precision and repeat-ability.

He's using a Harbor Freight battery tester. I figure it would be prudent to check the current magnitude.

liveforphysics
02 November 2012, 1445
He's using a Harbor Freight battery tester. I figure it would be prudent to check the current magnitude.

I hear you, and I agree that it's sketchy at best. It's also going to be making a difference in his Ri readings if he counts to 4.5sec of load on one test and 5.5sec of load on another test, or if one cell (or the load) is a few deg warmer in testing than another, or if it isn't quite sitting perfectly flat so some layers have larger gaps etc.

That's why I ask the cell history. If they are all perfectly flat and have never been handled by human hands (because a 60Ah pouch is too large to carry in your hands without damaging IMHO, gotta set it on something flat to move it), and they are modern Kokam pouches, then his thread is the mechanical equivalent of someone saying, "I just bought this 30 piece Starrett machinist block set, and I've got a tape-measure, how do I sort the good from bad?" The answer is, the limit of the precision of that tape measure will absolutely have a greater measurement error range by perhaps 3 orders of magnitude beyond the maximum deviation you would ever expect to see in that machinist flat set. You would be heading the the right direction to be calibrating your tape measure based off the machinist flat set rather than trying to bin the thick and thin blocks with it. For myself to bin those cells, I would be using $10k in equipment, and I would tell the person it's going to require 3 weeks to do it (of that 3 weeks, it would only be perhaps 4-5hrs of work, the bulk of the time is just sitting looking for the deltaV over time. This is much like if you told someone to bin the Starrett blocks, they would say, ok, but I'm going to need a precision temp controlled metrology room, and either a $100k CMM system or an extremely good fixture setup with a $1k micrometer. To attempt to bin the Starrett blocks with anything less would just be an exercise in wasting your time.


However, if they are used and/or perhaps damaged cells, and you're looking to cull the ones with the most damage, I think you've got a real chance at doing it with the tools you've got.

gijoe460
02 November 2012, 1650
These were said to be brand new...
I have put eyes on about half of them so far, and no tabs were bent or even looked handled...
There were a few that look like they have had a clamp on them...i assume to check voltage.

They are in the original box they came in from kokam.

Thank you for all your time on these guys...i read each post very very carefully

gijoe460
02 November 2012, 1653
Some one mentioned to me taking them to a engineering department at a college, and seeing if they would do it with their equipment as a like a class or something....
That way everyone benefits...

Thoughts?

liveforphysics
02 November 2012, 1830
Some one mentioned to me taking them to a engineering department at a college, and seeing if they would do it with their equipment as a like a class or something....
That way everyone benefits...

Thoughts?

That sounds like an excellent idea! The right lab will have the right meters, and if you have a school teaching a EV/hybrid powertrain class, or just the right EE professor, they would love to make analyzing the cells a project for students to learn, and they should have the equipment to do it.

gijoe460
07 November 2012, 0027
Just a thought.....what do you guys think of these

http://www.westmountainradio.com/product_info.php?products_id=cba4

and with the 500W amplifier..
http://www.westmountainradio.com/product_info.php?products_id=cbaamp

and a craigslist or ebay 5.5 or 6.5 meter

Will that get me accurate enough?

gijoe460
08 November 2012, 0941
Also was thinking....The internal resistance goes down after a few of the initial charges take place..if i do all this work to get the batteries matched, they very well could be not matched after a few of the first charges. right?
so would it be better to build the pack start charging it with my PFC-30, and as i catch a few cells not as strong as the rest, swap them from the extra pool i have..

What do you guys and girls think?

gijoe460
15 November 2012, 1012
Little bump?

lugnut
15 November 2012, 1045
Also was thinking....The internal resistance goes down after a few of the initial charges take place..if i do all this work to get the batteries matched, they very well could be not matched after a few of the first charges. right?

What is your objective? With 63 Ah cells I assume you will not parallel connect cells so matching isn't required AFAIK. You would do well to avoid cells with Ri values way out of the norm. Hopefully someone else here can explain any benefit to closely matching series connected cells by Ri.

lugnut
15 November 2012, 1050
Just a thought.....what do you guys think of these

http://www.westmountainradio.com/product_info.php?products_id=cba4



I have one of these. I like it. Easy to use and seems pretty accurate. I do not have the amp but know a guy who does and he likes it.

moon
15 November 2012, 1843
I have a CBAIII and I like it for the graphs and ability to set current very precisely. I don't like that it overheats way way before hitting the specified wattage limit and it could really use a Kelvin sensing setup as it reports voltage incorrectly. That said I have used it to do Ri measurements and as long as I use an external multimeter to get the voltages they seem to be reliable numbers.

gijoe460
26 November 2012, 1331
i read an re-read all the posts..

So is this a huge concern for me? I am putting all 32 in series....is it that critical to match new batteries? when and if i add the second pack i could see it being an issue.

What do you guys think? I am going out to get a 6.5 meter so i can get a good starting point for sure...but beyond that, i was going to keep building the pack, and save for the CAB III or IV

liveforphysics
26 November 2012, 1448
i read an re-read all the posts..

So is this a huge concern for me? I am putting all 32 in series....is it that critical to match new batteries? when and if i add the second pack i could see it being an issue.

What do you guys think? I am going out to get a 6.5 meter so i can get a good starting point for sure...but beyond that, i was going to keep building the pack, and save for the CAB III or IV


I will give you the condensed version.

Properly check for self-discharge.

If no cells have abnormal self-discharge, build your pack.


The build-your-pack step is not easy to do right with large pouch cells, and just handling them with your hands results in layers cracking off the foils, making failure prone points, and your tab-attachement method needs to not get the tabs hot where they enter the pouch, or the hot-melt-glue seal there will be compromised.

lugnut
26 November 2012, 1537
i read an re-read all the posts..

So is this a huge concern for me? I am putting all 32 in series....is it that critical to match new batteries? when and if i add the second pack i could see it being an issue.

What do you guys think? I am going out to get a 6.5 meter so i can get a good starting point for sure...but beyond that, i was going to keep building the pack, and save for the CAB III or IV

I agree with LFP's post. He did not address the Ri question. I do not think it is critical or necessary to try to match Ri on series strings of cells. I would check Ri on each cell and avoid using cells with excessive Ri or at least put those at the end of the stack so they can cool better.

I suggest that you charge all the cells to an equal SOC or open circuit voltage before assembling a series string.

As for running a second string in parallel later; that can be done. It would be best to parallel at the cell level. Running parallel strings will require twice the BMS effort. And adding the second string later will mean a difference in age and capacity and Ri of the 2 parallel strings. But I think that would not be too terrible.

gijoe460
26 November 2012, 1859
Sounds good....yes been handling very carefully