Driver for SSC P7 LEDs

[wquiles]

Thanks, but truth is I am just a hack. I learn from blowing things up!

A hack would not care about the projects as much as you do. Not only you do very good work, but there is a lot of though behind your mods, and you take care on making sure everything is right. Keep up the good work

Will

 

[wquiles]

I got one of these, running of a 9.6volt pack, so far I like it better than the 8 7135 chip driver. Not sure if I'll really use the modes in the crappy PNW vis, but it's nice to have. It's a good idea to heatsink the chip, I understand they can overheat pretty easily. Much cheaper than the drivers from TaskLED, but I'm thinking you get what you pay for.

Jake

Both drivers will do the job and will work great. I like the drivers from TaskLED is because they are more efficient, so more power from the battery is used for the LED, than being dissipated as heat by the driver. The difference in efficiency might not be large enough to justify using the more expensive driver from TaskLED, but I have been using his drivers for almost 4 years now, so in the end I use what I am most familiar with

Will

 

[nwbrewer]

I have always heat sinked them, untill the other night.....

I hooked one up to a 12v battery and a 2.8amp 7.4 v load.
It melted the Fet off the board then the fet blew.

They really do need sinking.
I use the 3 modes alot.
Low is for peering under the dash of cars during work. Mid and high are for diving.

I was thinking low was going to be nice for cleaning up after night dives this winter.

 

[Packhorse]

Low is actually really good for use post dive ( as I found out this weekend). Its enough to provide light for SOS ( Sorting Out S***) on the boat with out blinding people.

 

[adm3745]

Thanks for advice. Since you guys seem to know a bit about Lights:

I am now looking at different batteries for the P7. I had originally decided on a 12V 4.5Ah NiMh because of the cost, but it seems Li-Ions are worth the extra money.

Could I direct drive a P7 on a 3.7V 9.6Ah Li-Ion Bat pack? (It looks like its made of 4 x 18650) If this is not recomended I am also looking at a 7.4 V 6Ah Li-Ion...



Is 2.8A to high of a draw for these batteries? Do NiMh work better with high current draw?

Thanks

 

[wquiles]

Thanks for advice. Since you guys seem to know a bit about Lights:

I am now looking at different batteries for the P7. I had originally decided on a 12V 4.5Ah NiMh because of the cost, but it seems Li-Ions are worth the extra money.

Could I direct drive a P7 on a 3.7V 9.6Ah Li-Ion Bat pack? (It looks like its made of 4 x 18650) If this is not recomended I am also looking at a 7.4 V 6Ah Li-Ion...



Is 2.8A to high of a draw for these batteries? Do NiMh work better with high current draw?

Thanks

I have done several direct drive on P7's with 3xAA, 4xAA cells, 1x18650, and a 1x A123 cell, and I would not recommend a direct drive on a P7 with that much mAH - it is likely to overdrive the P7.

Most of these LED's have a vf that vary between 3.5 and 3.7 volts, but the problem is that the charged cell is not sitting at 3.7Volts, but at about 4.1-4.2 volts (with no load). As soon as you put a load in the battery(or pack), the voltage drops due to the internal resistance. But in a larger pack with 4x cells, the voltage will sag less, and since LED's have a non-linear relationship of voltage vs current, a small increase in voltage will result in a significant jump in current. A high mAH pack might only drop to 3.8-3.9 volts, which is a significant overdrive condition, most specially if the vf was on the low side (3.5v for example).

If you still want to use this pack (for longer runtimes), you would need an in-line resistor to drop the voltage "somewhat" to prevent overdriving the P7. The resistor would need to have the right wattage rating for the specific voltage/current/value chosen.

Will

 

[nwbrewer]

Or just add a 8 x 7135 linear driver..... ($7-8)

 

[martzak]

I'm currently using a dive light made with a spiderfire flashlight which uses a ssc P7 LED.
I was using a SLA battery with a cheap driver that limited current to about 2A, it's bright enough.
But I also tried direct driving using 2x18650 pack, works fine with ~2.7A when the battery pack is freshly charged, dropping to ~2.4 after ~30min, and so on.
I can see how using a high mAH pack could stress the LED. However, I'm going to try it anyway. I have another set of 2x18650 on the way, so I'll be testing a 4x18650 pack soon.
I'm hoping that with good heat sinking and in-water (cold water, especially) operation the LED can safely handle more current.
By the way, with the 2x18650 pack the battery voltage (while powering the LED) started at 4.17V, after about an hour of continous operation the pack voltage was at 3.2V. The flashlight was submerged in a bucket of water for this test.
I'll post some pictures of my light tomorrow...it's really 'ghetto'.

 

[wquiles]

Just keep in mind that the LED can/will die in two ways:
- exesive heat, even when working within the current rating of the LED (which will of course be less of a problem working under water)

- too high a current through the very thin internal gold wires - this is the one I am warning folks about.

If you over-drive the LED even for a short period (easy to do then the batteries are fresh and you are in a direct drive mode with no driver/regulator to control the current), you run the risk of exceeding the max. current through the LED, which will permanently damage or destroy the LED. In these P7/MC-E's with multiple individual dies in a single package, damage could be as little as loosing one or two, up to loosing the whole array of LED's, which means having to replace the assembly. At the CandlePowerForums some folks have over-driven the LED and it appeared to work well for a little while, and then the LED died completely, so the failure from an over-driven situation could be quick/instant, or take a little bit to take effect.

Just my 2 cents.

Will

 

[martzak]

wquiles,

I'm in complete agreement with you. There is a good reason why most dive lights regulate voltage/current to the LED/bulb.
I wanted to get the most Lumens possible out of my light with the least amount of hardware, that's why I tested it without a regulator...but now that I had some time to think it over maybe I won't push my luck again.