May have bought the wrong bulb

[3D black mag]

Hi I'm new here and I'm not sure if this is in the right spot to post this but about 2 months ago I bought a CSXPI P7 LED from 4sevens.com. I've recently learned about binning and labeling and if I'm correct that means that the bulb I have has an input voltage of 3.25 to 3.5 volts please correct me if I'm wrong. But I am making a direct drive 3D maglite with with rechargable NiMh batteries that equal 3.6 volts so if I drive my P7 with 3.6 to possibly 4.0 volts when batteries are fully charged will it blow my bulb or make it not work at it's full capacity? please help.

 

[Seiko]

I dont think it will "blow" the led. It will shorten the lifespan of it for sure if you are over running it at 4v. It will be brighter at the higher voltage. All the way up to the point that it stops working. Heat is a bigger killer in LED's then voltage.

I have been running a C bin P7 at 4.2 volts (at 3.68A) for around 3 months with no ill effects. It sees around 20-30 mins of use per day so far so good.

Not knowing what light you re putting it in, but do you have room for a driver? If so might want to think about it. In my light there was no room so just went ahead with the direct drive.

 

[3D black mag]

Thank you for the help seiko. I do not have room for a driver but I do have a large heatsink so I guess I'll just hope for the best. Just out of interest what is the recomended input voltage for your P7?

 

[Al Combs]

:welcome:

I think in depends on how lucky you are. Many people have used P7's with the "I" voltage bin and have had no problem. Although the "J" bins (3.50-3.75 volt) are safer for direct drive. Every now and then you see a post from someone saying first his light turned blue and then everything went black. It's called cascading thermal runaway. Take a look at the P4 Emitter Specs. On page 15 there is a graph called, "Forward Voltage Shift vs. Junction Temperature at IF=350mA". I used the P4 as an example because the P7 specs have no such Vf vs JT graph. But all LED's exhibit this behavior. What happens is as the LED's junction gets hotter, it takes less voltage to make it draw the same amount of current. Since the batteries without a constant current regulator don't know anything about this, you're in trouble. If you go direct drive and your LED turns blue, turn it off and go buy a regulator. If you have a DMM with a 10 or 20 amp scale, or know someone you can borrow one from, just wire it up in series with the tail cap removed and see what it reads. Leave it there for a few minutes while watching the readout. If you're going to have a drop in Vf because of rising heat, that might take several minutes to happen.

I have the exact same CSXPI that I also bought from 4Sevens. I have a 0.1 ohm 5 watt resistor wired in series with the P7. It draws 2.7 amps with freshly charged 3*NiMH D cells. While I was testing it, I shorted the resistor out with a clip lead just to see what would happen. The current level rose to a little over 3.3 amps. I didn't bother to wait and see if it was stable because there was only a barely perceptible increase in output. I decided it wasn't worth the risk. If you really don't want to use a good constant current regulator, a resistor is a good low cost substitute. You can do a search from DealExtreme or KD for, "P7 regulator" and find several in the $10 range. The bad news is the free shipping means you'll have to wait a month.

But I am making a direct drive 3D maglite with with rechargable NiMh batteries that equal 3.6 volts so if I drive my P7 with 3.6 to possibly 4.0 volts when batteries are fully charged will it blow my bulb or make it not work at it's full capacity? please help.

 

[3D black mag]

Thank you for the info Al Combs. I think I will just not fully charge my batteries to be safe. But I have one more question the more Amps or mah I put on a bulb the brighter it will be and the hotter it will be?

 

[Al Combs]

Yes both brighter and hotter. But it's more hotter than brighter beyond a certain point. Have a look at the P7's spec sheet. Page 6 has a graph for Normalized Relative Luminous Flux. They consider 1.4 amps to have a hypothetical output value of 1.0. And an increase to 2.8 amps only causes a 75% increase in brightness. If the response was linear, you would expect the output to double from drawing twice as much current, which it doesn't. Also that's at an ambient room temperature of 25°C. That's much cooler than it will be inside your flashlight.

The next graph on page 7 is full power output vs junction temp. If the LED is 75°C @ 2.8 amps, it will only put out 90% of its rated maximum. Further along the curve at 140°C, it looks like about 67% output. Of course at that kind of temperature, you could cook dinner.

I mentioned already that many people say the light from the LED turns from some shade of white to noticeably blue just before it blows. So you might get some warning if you overdo it.

BTW, what heat sink did you come up with that you have no room left for a regulator in a MagLite? Did you cut off the bulb tube part of the plastic switch body? That should leave plenty of room for something like this.

 

[3D black mag]

Thank you on again Al combs I did not think of cutting off the post.I am using the D sized P7 heatsink from 4sevens.com. What Amperage do you think would run my bulb at it's max output? I do not think heat is going to be a problem due to the size of the heatsink. And also what driver would you suggest to run my bulb at it's max output incase I can't direct drive it due to high amperage? I would like it to be less than 15.00 dollars. I don't know whether this will help or not but for my batteries I am using two D sized NiMh CTA 12,000 mah batteries and one D size NiMh 4,500 mah raioshack battery. Hopefully I will be getting one more CTA battery to replace the radioshack one.

 

[Al Combs]

I saw your other post about using different types of batteries. You indicated you were aware it is never a good idea. Either get the other CTA or 2 more Radio Shacks. Nuff said on that subject.

I have the exact same 4Sevens heatsink. Imagine a 10 watt light bulb. OK so that's not very big for a light bulb. And now imagine it in a sealed metal box that has no air holes for ventilation. What's going to happen if you grab a hold of this metal box? It was hard for me to imagine LED's as generating heat. But 10 watts is 10 watts. You would be surprised how much heat the thing can generate. Since it is theoretically possible to generate[FONT=Arial, Helvetica, sans-serif][SIZE=-1] 683.002[/SIZE][/FONT] lumens from 1 watt of energy. Kind of like absolute zero for LED's. And since SSC claims the P7 generates 90 lumens per watt. That means the P7 is only 13.2% efficient. Which is way better than an ordinary incandescent light bulb that is only 2% efficient. But another way of looking at that is 8.7 watts of the P7's ≈ 10 watt input is wasted as pure heat.

If you only want to spend 10 or 15 dollars on a regulator, that pretty much leaves you with the Chinese guys (DX & KD). Did you search their sites? Here's a very instructive link with a good example of DX driver. Notice how he potted the boards right inside the DHS heatsink with thermal epoxy. The Litemania heatsink you bought from 4Sevens is very similar. StefanFS points to a NetKidz link where he got the idea. The 3rd post from NetKidz shows hooking 2 of the 1,400 ma boards in parallel for 2.8 amps. So that's another way to do it.

The good news is the 5 mode regulator only costs $3.19. The bad news is the 1,400 ma slave only comes at a minimum in packs of 10 for $17.83. So if you're building 10 MagLites, they are only $1.78 each. The worse news is they are always on back order. Perhaps you can find one on the B/S/T forums. Or maybe you can post a want to buy over there. There must be more than 1 person that bought 20 of these things thinking they'd use them eventually.

KD sells a pre-made version of a the NetKidz paired 1,400 AMC7135 boards for 2.8 amps output. At $5.99 this is easily the cheapest P7 regulator available. KD has had a lot of complaints lately. They are not the best on customer service. The good thing is you are only risking 6 bucks if you want to look at it that way.

Another way to look at it is for a few dollars more than buying 10 1,400 ma boards you can get a really good regulator that won't take a month to ship from China.

TaskLED also sells the d2Flex many people have successfully used with the P7. The d2Flex isn't really a regulator but a pwm dimmer. As it pulses on and off at a few hundred times a second, it's drawing the full 3 amps. Or whatever your P7 draws in direct drive. Since it's not a full duty cycle, heat build up and a possible thermal runaway doesn't become an issue. Unless you run it at full power all the time. It also requires a modification to the MagLite's switch so it can always have power to remember what mode the user interface was in.

 

[Al Combs]

Oh I almost forgot, 2.8 amps is the number you are shooting for. That is what SSC calls, "Absolute Maximum Rating". If your LED direct drives at 3.5 amps without blowing, you'll get a little more light and a lot more heat. It will also dramatically shorten the LED's life to run at a higher junction temperature.

 

[3D black mag]

OK I think I will go with the KD regulater showed in your link. The two boards are already together right? And do you know if it is prewired?

 

[Al Combs]

Yes the boards are already together. As far as the wires, sometimes yes, sometimes no. You always get the wires, just not necessarily attached to the board. From user comments I've seen on their forum in the past, wires thrown in the bag instead of attached could be their way of doing you a favor. Read the comments on their forum.

They only have two at the moment. One reviewer says without the bridge his regulator was only putting out 1,400 ma. But from both the StefanFS and the NetKidz post you can figure out how it should be wired for yourself. Read them both CAREFULLY. Half way down the StefanFS post thread he shows how to bridge the reverse polarity diodes. I believe this is the Q1 and Q3 missing bridge the reviewer mentioned. The only real advantage to this KD board is it's cheap. Buying 10 from DX and doing it yourself might be a better bet in the long run.

 

[3D black mag]

I think I will stick with the KD board because of the price. I doubt I will be making many more P7 lights. so as long as the KD board works I think I'll stick with that.