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by **29a** » Sat Apr 21, 2007 11:52 am

I went with Nicd because they last longer (get to cycle them more times), or do you :?:

what causes this :?:

by **TylerDurden** » Sat Apr 21, 2007 12:24 pm

Looks like the leads shorted together right where they enter the pack. Most the heat damage is on the leads and surrounding area.

When did the event occur?

Were they flexing at that area?

:?:

by **TylerDurden** » Sat Apr 21, 2007 12:29 pm

Looks like all the battery bars got hot. A short in mid-pack might spare some cells, but they all look fried... full pack damage would support main leads being shorted.

by **Ypedal** » Sat Apr 21, 2007 1:07 pm

Wowzers..

.. i can almost smell it from here !! ( gotta add that to the " damaged components " thread for sure !

I'd take the time to check the individual cells.. might be a few good one's left. maybe..

So.. yeah.. what's the story behind it ?

by **knightmb** » Sat Apr 21, 2007 1:18 pm

I'm surprised to see them in the upside down configuration rather than all of them with the positive at the top. It's really hard to tell exactly what happened short of someone connecting the positive to the negative and leaving it to sit on a table to see what happens :evil:

That kind of thermal runaway would take some serious current, so it must have happened at a full charge and something touched somewhere that it shouldn't have. I take it the pack didn't have a thermal fuse?

by **TylerDurden** » Sat Apr 21, 2007 2:05 pm

Looks like the current never made it out of the pack. The 30A fuse is intact.

I've only seen thermal cutoffs in series with early NiCd trickle-charge relays and LiPo BMS circuits.

:?:

by **29a** » Sat Apr 21, 2007 2:16 pm

It happened this morning (Sat 21st Aprill)
This was one of 4 24v 8AH packs (to give 48V 16AH) none of the others wher damaged except for a little heat transfer to a touching pack and melted through my batt bag.I was only doing about 25-30Km/h on road with a 406 at 48V using 72V 35A controller. I had allready travelled 11km the bike was still working when i stopped at a light i noticed smoke.
I think i stopped just in time as ive since heard of a guy whose 5Ah Nicd pack had exploded on him sending hot cadnium scrapnell into his legs the blast was heard two blocks away. :!:

If you look in Cmelt 2.jpg you can see the thermal 55C cut out thermister (small,oblong,white undamaged)

by **Matt Gruber** » Sat Apr 21, 2007 2:29 pm

be sure to check the parallel pack for shorted cells!
.
extra fuses needed.

by **Ypedal** » Sat Apr 21, 2007 2:53 pm

It looks like the short happened between the positive and negative power leads before the fuse.. hense the fuse did not burn..

The temp fuse is only on the charging wires.. the power leads to the motor do not have this temp safety device.

Not fun.. at all.. that's a lesson for all of us, aka: regularly check all wires and conections. :oops:

Can you imagine if that was a Lithium pack !!!

by **29a** » Sat Apr 21, 2007 4:13 pm

Now the pack has cooled down I took a closer look .
It looks like the most damage is top row left cell below
with most leakage damage in the center of the pack.

by **Matt Gruber** » Sat Apr 21, 2007 4:23 pm

WOW! Great pics!
what does DVM say?
any show life?(volts)

by **NickF23** » Sat Apr 21, 2007 4:34 pm

Ypedal wrote:It looks like the short happened between the positive and negative power leads before the fuse.. hense the fuse did not burn..

If that's true then in its totally preventable. The fuse should be always be in the middle of the pack, right? My nimh packs I got from china are like, isn't that always the best place?

29A,

Can you confirm where the fuse was? where did you get the packs from?

by **Nimbuzz** » Sat Apr 21, 2007 5:46 pm

Well 'C melt 2.jpg' only shows part of the pack and the other pics don't quite get the essential part. It looks to me like the leads did not exit the pack straight to the fuse as they definitely should but instead wrap around to the other side across the cell tops then exit the pack. It looks like the red lead was on top of the cell and perhaps rubbed through its insulation causing the short.

Leads should be soldered so they aim straight out of the pack and should never be running across a cell top -- unless you like fireworks.

Please take a pic that clearly shows the route of the red lead from its origion to its exit to see if I'm correct.

by **D-Man** » Sat Apr 21, 2007 5:54 pm

Where did you buy this nicad pack at?

by **Mathurin** » Sat Apr 21, 2007 6:45 pm

Beautiful!

by **fechter** » Sun Apr 22, 2007 12:10 am

Oh yeah. I can almost smell those from here.
Post a coulple of those pics over in the "failed component pics" thread.

I'm surprised the damage was so complete. usually the sort just burns away and only frys a small area. I guess your cells were well balanced.

Some of the cells might still be good.

by **TylerDurden** » Sun Apr 22, 2007 8:38 am

Nimbuzz wrote: It looks like the red lead was on top of the cell and perhaps rubbed through its insulation causing the short.

I agree w/ Nimbuzz (except methinks the black lead). I'd be lookin real close at the other packs to see if the same thing is starting to occur.

If it is faulty construction, you may be entitled to a replacement. At the very least you may save your other packs and help others do the same.

(Shucks, you might save somebody's life...)

by **Nimbuzz** » Sun Apr 22, 2007 8:46 am

Yep -- could be the black lead but the pics don't quite show it for certain. It looks to me like both leads might come up the side of the pack then over the top of the cells then out.

If so, I would also call it "faulty construction" and I would advise us all to peek under our shrink wrap for such 'entanglements' An application like ours, with a pack bumping along in a bag can definitely wear through insulation that is bending over metal, sharp edged tabs.

by **29a** » Mon Apr 23, 2007 7:19 am

Hi guy's
These are the standard 24V 8Ah Nicd packs manufactured by Sanforce which recently have been reported to have cells explode.
The damage is so extensive i can't tell if the cell blew causing the black to short or the insulation on the black melted causing the short,
Your dead right the output wires wrap round the pack over the top of cells to the output cells,seems a real stupid design. I'm thinkink of putting output tabs direct from the output cells so no output wireing inside pack on the remaining 3 good packs any thoughts :!:

I would allso like to put some sort of thermal protection in pack any thoughts ideas :?:

Any other suggestions to stop this happening again :?:

by **TylerDurden** » Mon Apr 23, 2007 8:57 am

You might want to determine which happpened first: the heat or the short.

You could take the shrink-wrap off the other packs and look for abrasions on the leads.

Then you could also do a test under load, and use a thermometer to read those battery-bars. The bars look kinda thin and the tack-welds can be high resistance.

by **Nimbuzz** » Mon Apr 23, 2007 9:02 am

I've used hundreds of Nicad packs over the years in RC racing. I agree with your original post that they are very robust. Of course in RC we use the very best Sanyo cells -- they pick the cream of the crop for us. I've seen a few melt down about 1/4 as bad as yours from overcharging now and then. Some racers would even solder the pack into a dead short to totally drain it after each race to eliminate any memory. But then these were nearly dead packs, top quality cells and sponsored racers that got free packs.

I'd just make the leads out of the heaviest, best quality = most expensive 12 (or 10) ga, fine strand wire and simply solder the wire to go straight out of the pack to the fuse -- that's easy to do and the way it is done 99.9% of the time.

Do your other packs have the 'wrap around bomb-fuse' method? What brand are they -- so others can check?

by **fechter** » Mon Apr 23, 2007 9:23 am

It seems like it would be good if there was a strong, thin, non-flammable insulating sheet to cover the ends of the cells. The wires could go over the insulator. I've seen this sort of hard cardboard stuff they use for that. 1/16" polycarbonate sheet might work OK, you can cut it with tin snips.

A mid-pack fuse of some sort might be a good backup safety.

by **29a** » Mon Apr 23, 2007 9:36 am

All the packs are the same wireing
I opened one and there is no abrasion marks/damage anywhere, The wires are glued to the plastic covering on the cells, I guess to prevent any movement abrasion.
Could any of u guys give me a basic buzzer 24V schematic i could put in pack for over heat warning :?:

It would be greatly appreciated.

Any sugestions on packing these for return, so they dont short out on mail trip.

by **RatoN** » Mon Apr 23, 2007 11:46 am

Geewiz. Didn't know that nicads could burn like that or explode! Maybe the batts you added were not exactly the same?

Anyway get her back on the road 29a.

Be gone April

by **Ypedal** » Mon Apr 23, 2007 12:20 pm

For a temp monitor, i have a few Radio-Shack digital Indoor/Outdoor thermometers, they have a thin wire-probe you slip under your window jam to record outdoor temps.. this could be placed under the shrink wrap and the display mounted to the bars... Not very convenient for 4 packs tho.

I have 4 of these packs as well.. i'm going over them tonight checking every inch of wire !!!

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