7880 Driver catches on fire!

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DBSAR
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7880 Driver catches on fire!

So i was doing a run-time test of my well-used Black Shadow modded PadMe. This Padme came with a dead original driver, so i modded it back in the fall with the 20-mode / 1.5 volt 7880 driver and a Nichia 219B.
I used this light quite often after the mods, and it worked great with great tint & modes on three AA NiMH cells in Parallel. I t had a great run time in all modes, and good throw & output on Turbo mode, so i decided to test the run time on Turbo with three freshly charged Ladda 2000mah NiMH cells.
Fortunately i had the light apart and in my view while it was running, ( with the main driver plate held to the cells on the flashlight body with a rubber band) to monitor heat build up on the custom LED aluminum pill plate, and after running for roughly 20 minutes i heard a “pop” sound and when i looked at the light there was a visible candle-sized flame flickering off the driver, with the torrid coil glowing red hot. After i blew the flame out and turned off the light, i checked the cells and LED and the volts were still at 1.31 V, and LED survived, but the driver is literally cooked with the smell of burned wiring and thermoplastic in the room.
This is the first time i had a light “burst into flame” , and its not even a “xxxfire” light. Silly
*+
Edit Update: – i discovered the solder joint and resistor near the Emitter leads has de-soldered and shorted together, causing the driver failure. (You can barely see the resistor near the red wire lifted off the board on an angle in the second photo, and the solder on the red lead is now contacting the black wire shorting the connection.+*

That Canadian flashlight guy & Lantern Guru -Den / DBSARlight

Edited by: DBSAR on 01/19/2015 - 22:00
Bort
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That is very unexpected, what would have happened if it was in the light
Glad your ok, battery powered fire is serious business

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DBSAR
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Bort wrote:
That is very unexpected, what would have happened if it was in the light Glad your ok, battery powered fire is serious business

its likely the light would have built up pressure, and most likely would blow the tail cap switch boot off, or the lens out.

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It might be a test worth doing, perhaps it would extinguish the available oxygen and put itself out, or overheat and blow a li ion (or NiMH), its something i think worth testing (outdoors)

Is there a way to determine which component on the board failed?

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wight
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DBSAR wrote:
Bort wrote:
That is very unexpected, what would have happened if it was in the light
Glad your ok, battery powered fire is serious business
its likely the light would have built up pressure, and most likely would blow the tail cap switch boot off, or the lens out.
I think the most likely conclusion to this fire is that it would put itself out quickly once a component “failed open”, ending the shenanigans. I could be wrong about that though!

Thanks for posting this, it’s interesting stuff.

I think that I have some of those 7880 drivers. In fact, now that I think about it… I think I even tested one some. It may be in an SK68 right now. As I recall the efficiency was low. Maybe very low, I don’t recall. I do recall that input current would increase with voltage while output current remained stable – that means that efficiency was dropping like a stone above a certain voltage.

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wight
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Bort wrote:
It might be a test worth doing, perhaps it would extinguish the available oxygen and put itself out, or overheat and blow a li ion (or NiMH), its something i think worth testing (outdoors)

Is there a way to determine which component on the board failed?

I’d say it’s most likely an FET failed.

FWIW, I’ve just pulled a 7880 driver out and taken a look at it. I think that it may be a flyback driver. I’m basing this on the fact that the inductor has 4 leads rather than 2. http://en.wikipedia.org/wiki/Flyback_converter

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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DBSAR
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Bort wrote:
It might be a test worth doing, perhaps it would extinguish the available oxygen and put itself out, or overheat and blow a li ion (or NiMH), its something i think worth testing (outdoors)

Is there a way to determine which component on the board failed?


its difficult to know what failed first, as the glowing-red hot coil burned everything underneath it.

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DBSAR
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wight wrote:
Bort wrote:
It might be a test worth doing, perhaps it would extinguish the available oxygen and put itself out, or overheat and blow a li ion (or NiMH), its something i think worth testing (outdoors)

Is there a way to determine which component on the board failed?

I’d say it’s most likely an FET failed.

FWIW, I’ve just pulled a 7880 driver out and taken a look at it. I think that it may be a flyback driver. I’m basing this on the fact that the inductor has 4 leads rather than 2. http://en.wikipedia.org/wiki/Flyback_converter

The torrid coil definitely has two windings on it, (four leads) i have used this light quite often with no problems. And have other lights with the same driver modded in it. I like the modes settings it has, regardless if its inefficient of not. Though it did have really good run times on the lower modes with the three NiMH cells in parallel.

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Now you can rename it to PadmeFire Big Smile

 

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Sirius9 wrote:
Now you can rename it to PadmeFire Big Smile

+ 1

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I had my 7880 running on single d cell and they burn as well.

Its probably a forced boost driver and they limit it to small single aa cells only.

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power911 wrote:
I had my 7880 running on single d cell and they burn as well.

Its probably a forced boost driver and they limit it to small single aa cells only.

its probably what happened here, with the three NiMH cells in parallel the current supplied might have been to high. I also use this same driver in single-AA lights with no problems at all.

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wight
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DBSAR wrote:
power911 wrote:
I had my 7880 running on single d cell and they burn as well.

Its probably a forced boost driver and they limit it to small single aa cells only.

its probably what happened here, with the three NiMH cells in parallel the current supplied might have been to high. I also use this same driver in single-AA lights with no problems at all.

Can someone link me to anything that explains the term “forced boost driver”? Thanks.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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DBSAR
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wight wrote:
DBSAR wrote:
power911 wrote:
I had my 7880 running on single d cell and they burn as well.

Its probably a forced boost driver and they limit it to small single aa cells only.

its probably what happened here, with the three NiMH cells in parallel the current supplied might have been to high. I also use this same driver in single-AA lights with no problems at all.

Can someone link me to anything that explains the term “forced boost driver”? Thanks.

I’m not familiar with the term “Forced-Boost” driver either, as i known this 7880 as a Regulated standard boost type driver. ( steps the voltage up from 1.5 to the voltage needed to drive LEDs.

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DBSAR wrote:
wight wrote:
DBSAR wrote:
power911 wrote:
I had my 7880 running on single d cell and they burn as well.

Its probably a forced boost driver and they limit it to small single aa cells only.

its probably what happened here, with the three NiMH cells in parallel the current supplied might have been to high. I also use this same driver in single-AA lights with no problems at all.

Can someone link me to anything that explains the term “forced boost driver”? Thanks.

I’m not familiar with the term “Forced-Boost” driver either, as i known this 7880 as a Regulated standard boost type driver. ( steps the voltage up from 1.5 to the voltage needed to drive LEDs.

honestly I’m just blabbering words here but it gets to the point lol

I’m glad I didn’t use the word overclocked boost driver
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wight wrote:
DBSAR wrote:
Bort wrote:
That is very unexpected, what would have happened if it was in the light Glad your ok, battery powered fire is serious business
its likely the light would have built up pressure, and most likely would blow the tail cap switch boot off, or the lens out.
I think the most likely conclusion to this fire is that it would put itself out quickly once a component “failed open”, ending the shenanigans. I could be wrong about that though!

Oh but not all components fail open! Biggest reason I avoid tantalum caps. They are not only fond of exploding & shooting flames but also fail short.

This 7880 driver explosion is probably not due to tantalum. Though don’t know what under the coil.

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I modded an old plastic incan billy light last year.  The type that took a 6V lantern battery.

It's now running an XM-L and one of these drivers - powered by 8AA Eneloops in parallel for runtime.

The emitter is mounted on a PC chipset heatsink but the driver is simply sitting in place held by hot-glue.

I don't often run it at max, but perhaps I should do some spot checks on the driver temperature before leaving my latern unattended.  Thanks for the warning DBSAR!

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Quote:
a visible candle-sized flame flickering off the driver, with the torrid coil glowing red hot. After i blew the flame out and turned off the light …

Do you mean to say the light was still working, until you turned it off?

wight
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Halo… wrote:
Oh but not all components fail open! Biggest reason I avoid tantalum caps. They are not only fond of exploding & shooting flames but also fail short.

This 7880 driver explosion is probably not due to tantalum. Though don’t know what under the coil.

Of course not! Fortunately only one needs to fail open. Or desolder itself, or whatever. Like I said, maybe I’m wrong… but that’s where my money would be: I would bet that the driver (as a unit) would fail open rather than build up enough pressure to pop the tailcap.

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How much current is running to the LED on turbo? (and how much current draw from Battery) With rough estimate of driver (in)efficiency may be enough to glow a toroid.

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gadabout wrote:

I modded an old plastic incan billy light last year.  The type that took a 6V lantern battery.

It’s now running an XM-L and one of these drivers – powered by 8AA Eneloops in parallel for runtime.

The emitter is mounted on a PC chipset heatsink but the driver is simply sitting in place held by hot-glue.

I don’t often run it at max, but perhaps I should do some spot checks on the driver temperature before leaving my latern unattended.  Thanks for the warning DBSAR!

Are you using the same 7880 Driver ?
I believe i discovered what happened in this case, the lead wires to the LED solder points are so close it loos like heat build up caused them to short together, meaning its not a fault in the driver. (Though it would be a good idea to check how hot yours is running considering eight Eneloops in parallel can send a lot of amps into a driver.

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LowLumen wrote:
How much current is running to the LED on turbo? (and how much current draw from Battery) With rough estimate of driver (in)efficiency may be enough to glow a toroid.

The specs stated 800ma, though i measured 1.02 A on fresh charged cells to the 219 on highest mode.

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hank wrote:
Quote:
a visible candle-sized flame flickering off the driver, with the torrid coil glowing red hot. After i blew the flame out and turned off the light …

Do you mean to say the light was still working, until you turned it off?

The LED went out when i heard the “pop” sound, then i noticed the glowing inductor coil and the flame from burning insulation and resin.

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wight
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Good find DBSAR. That appears to jive with what I found previously with the efficiency dropping as input voltage went up. Maybe it’s more along the lines of efficiency dropping as boost ratio is reduced decreases. A dead short at 0.8A on the output would more than flip the ratio on it’s head.

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Could just be a cold solder joint and with the leads being so close to each other, when it came loose, it just touched up against the other. 

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Old-Lumens wrote:

Could just be a cold solder joint and with the leads being so close to each other, when it came loose, it just touched up against the other. 

could be that too. ( as visible in the second photo you can see the red lead lifted up off the board (with the nearby tan-colored resistor) and contacting the black – lead.

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DBSAR wrote:
LowLumen wrote:
How much current is running to the LED on turbo? (and how much current draw from Battery) With rough estimate of driver (in)efficiency may be enough to glow a toroid.

The specs stated 800ma, though i measured 1.02 A on fresh charged cells to the 219 on highest mode.

A modest drive level… Smile
…so that’s about 2.6 Amps from a 1.25V Battery at 100% eff. 80% driver eff would put battery current at 3.1+ amps.

wight
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A few minutes ago I took a brief glance at CPF and saw mentions of 75% eff. I assume measured. So a little higher battery current even.

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LowLumen
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A measure of the battery current will tell how much energy is lost as heat into the driver.

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LowLumen wrote:
A measure of the battery current will tell how much energy is lost as heat into the driver.
? No, a measure of the:
  • input current
  • input voltage
  • output current
  • output voltage

all at basically the same time would tell you that. Just measuring battery current doesn’t get us very far.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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LowLumen
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We do have a measure of LED current at about 1A. A 219B runs about 3.25 watts at 1 Amp. …just curious if there is enough wasted heat on the driver to melt a solder joint and cause the short. Knowing current from the battery would get a close approximation at this point.

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