Yep, I'd just got the lipo bags the day before.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=170494884670&ssPageName=STRK:MEWNX:IT

I'd been hammering these little 3s-800's really hard mostly daily for months in a trex 250 getting about 4:30 minutes per. When I fly, I fly continuous, one after another for about two hours, because any more and my brain starts to hurt . I was using a polycharge4, so I usually have four packs going at their rated 2C charge. I'd been stating to catch up (charging slowly) on my 8 packs for a week or so. It was odd enough that I kind of gave it some thought to check all the packs for balance. They were fine, just puffy as heck. Still common for me so far.

This day was the hottest day of the year so far with an official 118F at the airport (Goodyear, Az) it was in the 120's in the shop. I closed down one of the big doors, checked all four packs on the charger, all were good and charging at 1.2C. I slipped two packs in each bag, and each bag sat on a 16'' slate tile, then I went in for lunch.

An hour later I go out to swap to other set of packs and I knew there had been a problem the moment I entered the breeze way. The burn smell was strong, but not hot smelling, so I knew there was no fire in progress. When I got there the contents on the corner of the table was burnt, including the plastic covering on one of the bags. It had not been sealed shut.

I have two theories. One is that the charger finally just failed into an overcharge condition which cascaded through each circuit in time because each battery had signs of high current failure. (melted wires to the point of seperation). Or two, the hot batteries in the sack could not cool enough and that caused the runaway condition. The polycharge4 had on occasion thrown an error during a charge, but a check of the pack showed nothing odd. I'd just restart and all was good again.

The 1000 hrs Polycharge4 is now in the parts bin and five newer chargers are going to be doing the job.
http://www.xheli.com/dysudc6dcmuf.html A little wiring, an old PC psu, some fireproof sound board, and a charging rack design is next on the list. Will the pp cut sound board? I hope so.

Oddly enough on the same table for a week now I've had a smoke alarm with a wired remote speaker built and ready to install from shop to house, and out back I have 160' of 1/2'' pvc and sprayers to mount in the shop ceiling and plumb to a valved water source. No charger, no fly, get projects done time :mrgreen: If anything this was a great wake up call to put safety even more on center stage. Attached files

 

Wow! Looks like that bag did it's job. Mark's sitting here looking over my shoulder. He is definitely going to do something about his batteries now. This is a great reminder and we are glad no one got hurt and nothing was seriously damaged. Thanks for sharing!

Mark and Trish

 

Wow , bad luck for your bats and depending on how you look at it, good luck for you. It really could have been much worse.

Glad to see nothing else was damaged. I think maybe I'll doing something different with my charging station, aka my work desk.

Thanks for the info TB.

 

I say free shop...
That's what we say at the field when something horribly goes wrong with a plane but somehow it comes back in one piece.
I am bad about not using something to keep the batteries contained if they start a fire. After seeing this, I know I need to get busy building a charging area in my shop.
Glad you made out ok though. That could have been really bad.

Oh... so has the awful smell gone away yet?

 

Glad it ended well for what it was. This is why I Never bring Lipos into the house. I do my charging in the driveway or yard

 

Further testing on the other puffy packs showed the bags prevented the hot lipo from cooling, where as per my usual hot pack 2C charge open air went fine while the hot bagged pack would of gone poof at 1C in 10 minutes. So I'll save my bags for storage and transportation.

What I am going to build is a charge rack from either Ceramic Tile Backer or PermaBase UltraBacker Cement Board with independent galvanized screen racks for cooling. If I need a lid, I'll add one. Probably add toggles for each unit and maybe an amp/volt meters and fan for the main psu.

The Good news is I've got my MK1.5 together and mostly wired. Just lights, limit bypass switches, fence mounting, weighted roller, more structural pinning and removable pinning here and there and its done. I mean ready for tweaking :roll: Attached files

 

I feel a lot better while charging now that I have (my god sent friend Kurt V. did all of the work) finished the charging station. It will keep the likelihood of a lipo fire from spreading onto my work bench. I did use the Permaguard 1/4'' sheet of cement backer board as the primary material. It score cut easy enough as long as you score both sides. I did the plans for a saw cut but couldn't find the blade in the end. i used the rest of the sheet to top the bench where I charge.

After cutting we used a belt sander mounted to the bench (60 grit) to pretty the edges a little. The edge wasn't to bad as per the pic. Also used 3/4'' sqr thin wall steel just because we have it. Fasteners were either sheet rock screws or wood screws depending on what was on top of the small screws box. Glue used was Gorilla Glue standard. I strayed from the plan a tad by using a piece of 1/4'' liteply to mount the chargers on. That piece is also hinged to help in viewing and wire control.

Power supply is a FeatherPower 30A@12V unit, from the BST on RCG, and the chargers are the Dynam Supermate DC6 unit from HobbypartZ at $30each. Nice thing is they come with all the connectors and more for charging just about anything. They even have a computer data port .

Unit is 21'' wide, 7-1/4'' tall and 11'' deep. It does a LOT more than my old Polycharger4 ever did and I still have charge rate control for charging my Hyperions at multiple C. I can run all the chargers at full tilt and still stay under %80 of the PS's max continuous. Now, finally I can get back to hammering out a couple hours of 450 thrashing each day I ran one pack to test the free flow cooling during charge and it worked better than just setting the pack on the table.

My note and plans are attached. Have any questions just PM Attached files Charger Rack build plans.ZIP (2.2 MB)Â Charger rack cut layout.zip (2.3 MB)Â

 

Nice work!
I have one suggestion. I've seen where a lipo when on fire can sputter in an upwards and outwards direction. I wonder if some kind of a boxed in lid would help even more to prevent any sputter if a lipo did catch fire. It looks easy enough to add on to what you have already.

 

Hi Shaun,

Your suggestion was in my original plan, but as the test burning of last seasons lipos went on I decided against a lid for a couple of reasons. Out of the half dozen or so lipos I hit with an arc welder dc supply while on open ground, only a couple moved close to a foot. Those were well hammered 3s-2200 packs btw.

None left the ground, they just kind of spun a little as the pressure released, some violent others not. The other half dozen I burned in a frame the same size as in my rack. Actually it was a little shorter made of wood. None jumped out or caught the treated wood a blaze, so I had a good feeling a lid was not needed.

As the build went on I realized there were a couple other factors in my favor. One is that the balance tap wires restrict the packs movement to only one dirrection. Then if it did go forward over the charger the length of the wire still prevents it from going below the bottom of the charger. The charger rack itself now sits on the large 3'x3' leftover sheet of cement board. So barring a major pack explosion that would separate the pack from the leads or into multiple flaming pieces I figure I'm good to go.

The con of a lid is that if it's going to flow air it needs to be an nonburnable rack. Metal is about the only thing I can come up with easily and if the leads get exposed for some reason whether via wear or accident the shorting probability is high.

So I went without but yes your suggestion was part of the design process.

John

 

I'd thought about Shaun's term 'sputter' before I wrote, and wondered about that. But my mind was on the the more obvious danger of battery movement because I've yet to see any ejection of liquid or oozing, on fire or not during a lipo burn. Maybe Shaun will chime in and shed a light on the term

 

I was meaning like what Yoram was saying (erupting) but you would probably be ok with the cement board under everything.