Can Downboy 'spoil' and regulate at different current?

[LEDcandle]

Just messed up another mod when I was 95% done. Everything was in place and it was a matter of screwing on the bezel with optic. Screwed on a little too tight, trying press the Luxeon again heatsink with thermal epoxy.

I adjusted everything and the light turned on, but it smoked out in about 30 secs and I burnt out my WW0S!!

$44 down the toilet. I'm guessing the messing around made 'holes' in the thermal epoxy and the Lux V was not getting sinked properly. Esp driven at 1000ma.

After that, I replaced the setup with a TV1K lying around, and it seems the current draw is only 600 ma now. (2 x R123as) Could the DB1000 have 'shorted' a little when the Lux V burnt out and now regulate differently?

Also, it's supposed to be regulated (the current remains at 600 ma) but when I shine it thru my litebox, the output starts at about 50 lumens then quickly drops to 40 and stay there. Switching it off and on has the same results. Brighter first then drops and maintains. Something wonky with the DB?

Am tempted to try another LuxV with a DB500 (heard about the LuxV's extremely high efficiency at low ma), but am very afraid to smoke it again. Can't afford it.. heh...

 

[Nitroz]

Can you give some more information on the heat sinking and what type of light this was. I have ran a Lux V with a DB1000 in a mag with a good heat sink and never had a problem with my VVOT. Maybe the heat sinking was not good enough or you shorted something out?

 

[LEDcandle]

Yeah, I think twisting the optic too tightly prob dislodged the LuxV from the thermal epoxy and left 'holes' below, but I didn't notice.

It is a cheapie chinese flashlight hollowed out. The Lux V emitter is mounted onto a filed down coin with silicon thermal epoxy (not Arctic) which is in turn thermal epoxied to another bigger chunk of aluminium (I think its alu) that came originally with the light.

I guess it was because of dislodging that I didn't notice that burnt out the Lux. I'm just wondering about the DB1000 now running at 600 ma.

The TV1K now sitting in place of the burnt WW0T "seems" to work fine, except for the 'drop in lumens' syndrome that it's going thru, although it should be flatly regulated.

 

[wasBlinded]

I don't have specific knowledge about the Downboy, but there is a good chance the convertor was damaged when the LED failed.

 

[Shark]

If I remember correctly if power is applied to the regulator board and there is no LED connected or if the LED burns up and opens the circut then the regulator board will be damaged quickly.

Im so sorry to hear this, I hope you have better luck on the next one.

 

[LEDcandle]

I was guessing that

Prob some damage to the convertor. I still have a few spares lying around, but I'm deciding hard if I wanna redo the whole mod again. I don't really need the flashlight (even after its modded) and I know I won't really use it either; but just have the urge to mod it... haha..

Am now wondering if I should disassemble this one (TV1K running on 'spoilt' DB1000) that works pretty fine and puts out around 40 lumens or start from scratch and try out a DB500 with LuxV. $$$ is the issue though, and no guarantees I won't burn another LuxV!!

 

[PeterB]

The downbiy regulates the output current, iince you swapped a LuxV vs. LuxIII, the output voltage has decreased and the regulator needs less input current to supply the same output current (the 600mA sound reasonable to me). Therefore everything is fine.
A downboy is not damaged by open or short output!

 

[LEDcandle]

But isn't the DB1000 supposed to supply 1000ma all the time as long as Vin is higher than Vf?

What if I wanted to drive my Lux III at 1000ma?

Previously, I had a DB1000 with a Lux III and it ran at 1000ma.

 

[HarryN]

I learned the hard way that a Lux V needs to be VERY well heat sinked to run at 1000ma, and be useful. Lux IIIs and K2s are a bit more abuse tolerant.

All of the modern coins are pretty poor heat sinks. An old silver one might be ok if you smoothed it out. Now of course, I need to say publicly that defacing currency is not really allowed.

 

[PeterB]

But isn't the DB1000 supposed to supply 1000ma all the time as long as Vin is higher than Vf?

What if I wanted to drive my Lux III at 1000ma?

Previously, I had a DB1000 with a Lux III and it ran at 1000ma.

Yes, but if I understood you correctly, the 600mA are the current draw of the battery. A step down converter like the downboy has typically less current consumption at the battery than output current to the LED:
Vout*Iout = Vin*In* Efficiency => In = (Vout/Vin)/Efficiency * Iout

In your example Vout decreased and therefore In is reduced.

 

[LEDcandle]

I learned the hard way that a Lux V needs to be VERY well heat sinked to run at 1000ma, and be useful. Lux IIIs and K2s are a bit more abuse tolerant.

All of the modern coins are pretty poor heat sinks. An old silver one might be ok if you smoothed it out. Now of course, I need to say publicly that defacing currency is not really allowed.

Ahem, what currency?
If anyone asks, it was an arcade token! heh...

PeterB, sorry, I kinda lost you.

I understand the DB1000 to put out 1000ma as long as the Vf of the Luxeon is less than the voltage supplied. In the case of the WW0S-bin, 6+v Vf requirement powered by 2 x R123a (7.2v), it runs at 1000ma. (Vin > Vout)

Replacing the LuxV with a Lux III TV1K (3.5+v Vf) and using the same batt config (7.2v) should still run at 1000ma (still Vin > Vout).

Anyhow, I was soooo tempted to get another WW0S to remod, but then I came across Dae's thread that a 7w Golston that can accomodate Li-ons is coming. I guess if its $30+, is it worth sticking to my original mod?

Mod costs with shipping :
WW0S - $42
DB1000 - $20
Flashlight host - $10
Thermal epoxy, contact spring, time

The satisfaction of succeeding (and the pain of failure ) cannot be found in purchasing a flashlight of course (only modding), but I wonder at what price is this satisfaction worth it

P/S Just ran a runtime test with the TV1K light. 1 solid hour exactly and it switches off. The bezel area maxes at around 43ºc and after the light switched off, I immed opened up the head to take the temp of the slug with my infrared thermo. 40+ ºC too...

Not sure if the lux cooled down rapidly, but if not, it seems the heat is well managed now, esp since its running at 600 ma and not 1000 ma anymore.


Another thing, do Li-ons always run out earlier than their mah ratings? I seem to get closer figures with NiMhs than Li-ons.

In this mod, 2 x R123as 750 mah (I believe its more like 600 mah) should theoretically get about 2 hours runtime.

Previously, I did a runtime test on a 1000ma Lux V with 2 x 17500 1100mah. That should last 2 hours too, but switched off at 65 mins.

My NiMh's seem to hold up closer to their ratings. Anybody else concur?

Nvm this, I've asked it before. Totally forgot and rambled on!! Haha

 

[Christoph]

What the guys are saying is the output is 1000ma with a 600ma draw which is the way a buck converter works higher Vin than Vout means lower draw as long as the Vin is greater than Vout the Iin will be less then Iout.
C:thinking:

 

[the_beast]

How are you measuring the current draw? Unless you have a resistor or your meter connected in series with the LED AFTER the downboy then you aren't measuring the LED current. You are probably measuring the draw from the batteries.
Your S bin LuxV will be pretty much direct driven on 2 123s, so the battery draw will have been around 1000ma.

Your K bin Lux3 will be running around 3.6v. At 1000mA this will need 3.6Wh out of the converter (voltage*current output). The converter is around 80% efficient, so this therefore requires 4.5Wh input to the converter. At 6v from the 123s, this is a current draw of 750mA from the batteries. The lower battery current you mention (600ma) could be caused by several factors. you might either be making a measurement error or the batteries can't put out the required current. Also if the led Vf is lower you would need a lot less current (leds burn in over time and the vf goes down, if the led has seen some reasonable use it's vf could be below 3.5v, and the current from the batteries would be closer to 600ma.

As for the battery capacity, you have your cells in series, not parallel. You use up the juice from both batteries at the same time (getting 6v total), so the actual capacity of your pack (ie both cells together) is the same as the capacity of 1 cell (you get twice the voltage from the 2 cells, but the same capacity). If you connect your cells in parallel (which is almost never done in flashlights) you would get twice the capacity but only 3v output. Basically the run time for the light is consistent with the capacity of the cells, and is exactly what you should expect.

What I am saying is that it looks really like your downboy is fine, and you are running ok at 1000ma, and your batteries are performing they should. How bright is the led? A T-bin at 1000ma should be obviously brighter than a T bin at 500ma. You might have fried the Lux5, which is an expensic mistake, but you have seemingly got everything else ok. I hope the Lux3 stands up to the current (you will need that well sinked too or it will fry with time). If you do decide to do things again I would consider a 750ma limit for the Lux5 to be safer as they are easy to cook at the higher drive levels.

I hope this helps.

 

[HarryN]

I have destroyed as many or more Luxeons than anyone else, but one thing is for sure. After you get used to a Lux V light, going back to a 3 watt solution is really hard.

 

[LEDcandle]

Beast, oh yeah, I forgot about the series thing! I've asked this before even. How dumb Capacity is fine then. What was I thinking.

In that case, if I decided to swap to a H/J Vf bin eventually, 1 batt would be enough to run it at 1 hour rite?

Seems to me the 2nd batt would be redundant (unless I can wire it up parallel) except to boost the voltage and make the converter work harder for nothing. (In the case of a low Vf that is)

Or does chucking in more batts reduce the current draw on the batts and thus make the runtime longer?

Oh ok, yeah, it could be current draw from batts. I'm using the 10A port and setting on my DMM to connect the back of the batt to the body of the flashlight.

It's just that so far all the time I've seen the 'correct' draw from the batts in reference to the converter. Like ArcMania's 1A turbo module reads 1.09A from the batts. A previous DB1000 Lux III read 1.1A.

For a T-bin at 600 ma (near spec), its pretty 'dim'. I mean its putting out good light and all but its not 60-80 lumens. Comparing it with my other lights via my milk carton litebox, it is only around 40 lumens.

And the weird thing is the output dips 30-40% in the first 10secs! (but current is constant) That's what makes me suspect the DB is spoilt. It should be a constant output right?

Thanks guys.

Harry, yeah man, you hit the nail on the head

 

[wasBlinded]

Using an H voltage bin Lux with a Downboy and Li-ion will work fairly well. At 500 mA, the light will run in regulation until the cell is nearly exhausted. You could use a DB700 or DB1000, but they will fall out of regulation sooner as the cell voltage drops.

The more voltage you deliver to a Downboy (above Vf), the less current it will draw. So putting cells in series will prolong runtime, though the Downboy gets a little less efficient as Vin rises.

The Downboy is designed to deliver a constant current, it has no way to control what the LED is putting out beyond that. If the current is remaining constant, but the output of the LED drops 30-40% within the first 10 seconds I would suspect the LED is not getting good thermal relief. Is the contact between the LED slug and the heat sink good? There might be an air pocket or something else preventing good transfer of heat.

 

[the_beast]

What wasBlinded said. LED output is always quoted at 25 degrees celcius die temperature. This will never be the case in a flashlight, so the output will always be slightly below the ratings, but if it is dropping so fast in the first few seconds that indicates the heatsinking is very inadequate. If you keep driving the Lux under these conditions you will damage it quickly (the life is shortened at higher temperatures and it will age very quickly). There is a graph of output vs die temp in the datasheet you can look at - the change with temperature is very obvious. If the sinking was the same (or worse) for the Lux5 it is no surprise it popped - they are far less tolerant of temperature than the Lux3s.

As for the battery life - 1 600mah battery will not last an hour. If the LED Vf is 3v and the battery voltage is 3v, then it will deliver 600ma for 1 hour. This will be the current out of the battery however, and the current to the LED is supposed to be 1000ma (from the downboy). This would probably last about 30 mins with losses. Note that this will not work with the converter you have - the downboy needs a HIGHER input voltage than the LED Vf. With 1 battery you would just be direct driving the Lux. You need 2 cells to keep in regulation.

As you said, adding extra batteries (and therefore voltage) reduces the current draw and hence increases runtime. However there is a limit to the max input voltage for the downboy (of the top of my head I don't know what it is - prob 12v or so - check the Shoppe site). If you exceed this limit you WILL damage the converter.

Quoting battery draw currents really isn't much use, as they are completely dependent on the batteries. It will not be constant either - if you use drained batteries you will increase the current (lower battery voltage = higher required current for constant input power). There is no easy way to measure the actual current going to the LED in a fully assembled light - you need to get a low value resistor in series with the LED and measure the voltage drop across it to get the current, but this is often impossible without a lot of work and probable damage to the board or LED. It is usually OK to assume that if the LED lights it is getting the rated output current (if the batteres are able to deliver it). If there is no light then the converter or LED is blown, or you have a faulty connection. As I said, the Lux5s are pretty much direct driven if the voltage in is the same as the LED Vf, so the current you measure will be the same. However it does not have to be, and this isn't a good way of checking what is happening to the LED itself.

I would suggest you rethink the heatsinking in the light. Check it's connection to the coin (or whatever you have as a sink) first, as the rapid decrease in brightness suggests that the die isn't thermally connected to anything. If this is ok, consider adding more metal (to slow down the temp increase - more metal takes more energy to heat up, so it will be cooler longer). The next step is to sor out a path for the heat to get out of the light. Usually the best conductor is the users hand, so a good thermal path to the flashlight body is required.

Basically - sort out the heat, and the Lux3 will fly again. Then when you have nailed this setup, bite the bullet and buy a new Lux5. Then build the light you want, and be proud of yourself...

Good luck and have fun.

 

[the_beast]

One more thing - about the single cell/low Vf combination you mentioned. If you are driving an LED with a voltage slightly too high to be safe you will be more efficient using a simple resistor setup or a low dropout linear regulator than trying to use a fancy switching regulator. For small drops in voltage switchers are inefficient. IIRC an H-bin should direct drive ok on a single 123 cell (trying to remember my bin ranges here, so this may be wrong).

The only problem with the direct drive setup is the lack of regulation. The output will drop with time. For a low Vf Lux3 (3-3.5v or so) I would aim for a regulator running off a Li-ion cell (nice long runtime, rechargeable and should give a nice tail as the Li-ion cell gets low. Gives you an indication to charge but won't leave you in the dark or damage your cell).

 

[LEDcandle]

Thanks wasBlinded, I will check out the setup.

Beast, thanks for the detailed reply. I see what you mean. I'll have to relook the heatsinking and stuff.

But there is some possibility that the DB got damaged when the Lux V burnt out right?

I guess I might try out another mod from scratch and maybe use of 'em more affordable K2s. With a 2 cell setup, the Vf bin of the K2 doesn't matter too much.

 

[the_beast]

The downboy is fully open output protected, so it should not be damaged when the attached LED dies. The Lux is also more sensitive to temperature than the circuit, so the heat should not have been a problem. Personally I would assume the DB is fine. If you ever remove the Lux (as you will need to do to sort out the heatsinking), attach your meter to the DB and check the output. I would say if the current is anywhere between 900 and 1100 ma then it is probably fine (I don't know the actual tolerance on the DB output, the resistors used are probably +/- 5%, so a perfect DB will give anywhere from 950 to 1050 ma anyway). There will be tolerances on the other components too, so +/- 10% would not be unexpected. This would also explain the seemingly low current draw.

As for the K2 - getting a bagful of them and playing is exactly what I intend to do! At about $3.50 each it'd be rude not to! And they are even more heat stable than the Lux3, so heatsinking will be easier. The early samples people have received seem to be poor performers with high Vfs though, so they still won't match the Lux5 and will use quite a lot of power (hence more heat management etc). If they bring them out with the same Vf ranges as the Lux3 I'll be a very happy man though. Just gotta play the waiting game. While the 2 cell setup will run any K2 bin, the lower the Vf is the longer battery life will be - a higher Vf for a given current = more power = more heat + less battery life.