Too much current?

[chelboed]

Alright...I'm in a pickle. I was told a couple of weeks ago that I could add as many single cells in parallel to a Direct Drive P7 as I wanted and it would just increase run time.

I built this bike light project with 4x 18650's in parallel and it caused my emitter to start to "blue out". I took two cells off and I'm direct driving only two 18650's now. I feel like I could do better with a driver.

Should I install a driver and run a 2s/2p 7.4v pack instead of a 2p 3.7v?


Where can I find a small enough driver to fit in the head of this MTE SSC P7 flashlight amputation?


Should I start over?

 

[chelboed]

Another option...could I mount the driver on the battery pack?

 

[Mettee]

Yeah I would say driver, the extra cells are providing a ton of current that needs to be regulated. I would add the regulation after the switch.

In the head if possible...not sure it would "behave" before the switch. Who knows maybe be an electronics guru will chime in.

The shinningbeam board might fit for you, they are out of stock I noticed in another thread, but you just have to wait a bit they get more.

That is a nice simple little light.

 

[65535]

Issue with running more than 1-2 18650's DD is that the voltage sag isn't enough to keep the LED from burning up.

I can't recommend a driver, my only thought would be that you are very near your Vf of the LED so you'll need either a buck/boost or a boost converter.

Running a buck converter and 2S2P configuration would be perfect.

 

[chelboed]

I would really like a driver that would fit on the backside of the battery pack...but if I can find one small enough to fit in the lamp head on the back side of the pill...I guess that would be fine. I'm not great at the tedious stuff, but I think I could get a small driver soldered up. Bonus of a 2s/2p would be alot more runtime I guess eh?



Driver recommendations anyone else?

 

[chelboed]

I ended up ordering 2x 1400 mA constant P7 driver boards to run in series for 2.8amps. They're single mode 17mm x 2.8mm...so they may fit inside the lamp head itself. (fingers crossed)

Should be here in 2 days:twothumbs

I'm kinda worried about heat though.

 

[chelboed]

Got the boards in!! I noticed that the emitter has 3 brown spots on the dies. (oops)

I have a new SSC P7 OTW. It's all put together and running really well for having 3 burnt dies.:naughty: I'll pop in a new emitter next week when it gets here.

I got some Weaver scope rings and a Weaver base to mount it to my Nitehawk QR mount:

 

[Mettee]

Nice, good work. Post a pic of the led in macro mode if you can I would like to see what it looks like.

ETA: the burnt one

 

[chelboed]

Sure...here:

It's probably ~1/2 as bright as my MagicShine with the new current limiting boards in there...I'm assuming it's because I have 3 smoked dies?


It was kinda comical man...it was like WHOOOOOAAHHH:naughty:...bright-as-crap for a while running 4 18650's direct drive in parallel...then it got really beautiful blue like the Aurora Borealis...then it changed to an odd shade of "incan":candle:...and now it's back to the normal "cool white" that the LED began as. It's just not nearly as bright. It's kinda like running a couple of Q5's instead of a 2.8amp P7.


I'm hoping that it'll be safer now with the new P7 and the current limiting boards.

 

[chelboed]

I had a little bit of concern with heat, so I added a heat sink from the local hobby shop. I think it's for an electric airplane motor.
I had to drill and tap the head to attach it, but I flattened out the lip on the head and added some heat sink paste. IMO it's a little uglier now...but it definitely has a bit of character and will be safer on warm nights.

(wish I hadn't put it in a vice back before the transformation...marred)

 

[chelboed]

Reminds me of these:

 

[HarryN]

Very nice light setup, and nicely done aesthetics.

There is one minor safety point related to putting cells in parallel - the potential for reverse charging. Its usually not a big deal, as we normally charge up a set and load them in.

If for some reason, one of the cells has a much lower voltage than the others, they will try to "charge it". If this happens very fast, life could potentially be exciting.

One way to prevent this is with a diode in the battery holder that is positioned to only allow "one way" movement of the power - discharge. The diode needs to be rated high enough to allow full current flow, and it will certainly use up 0.3 V or so of the supply voltage, which is unfortunate.

Since you built the light and are very familiar with the setup, the risk of you installing an untested, charged cell, or putting one in backwards, is probably low. If you think at some point others (like a GF / wife / kid) might install the batteries, then it is worth considering an upgrade at some point.

 

[chelboed]

I use protected cells...will that prevent it?

 

[AnAppleSnail]

I use protected cells...will that prevent it?

No.

 

[Mettee]

You really did burn those three die. That is crazy, pretty cool pictures. I have never burnt one out so I am always curious to see one.

And I like that new heat sink, adds a lot of character. Pretty cool.

How does it do on night riding?

 

[chelboed]

With the burnt dies...it was still adequate on the trail, but nothing special. Haven't had it on the trail since the boards and new P7. The MagicShine was great...this will probably equal the MS. I'm expecting it to be ample.

 

[chelboed]

Success!!!


I ran the light for a while yesterday with no fan blowing, and it started to heat up after a while. I turned a fan on med for a few minutes and I felt the heatsink fins and lamp head and it was noticeably cooler to the touch.


Looks like full blast on a trail ride will be no problem at all.:rock:



When compared to my Geoman light:
-equal volume of light emitting from the unit
-slightly spottier than the MS...the hot spot on the MS is broader
-the emitters are def. different...the MS is a warm white / this one is a cool white...nice contrast when ran together though...I like it
-the MS will obviously stay at full brightness longer b/c it's 2s/2p and this is 4p...but I don't think I'll notice any dimming while I'm on the trail b/c these two lights will have approx 3.5+hrs runtime...and I don't ride that long at night.


My next project will most likely take advantage of the buck boards that are out there giving me full voltage over the entire runtime, but for my first build...I'm happy with the end result.




I'd really like to build something rediculous next. Like a 4-5 p7 light...or maybe 2-3 Ostars...I dunno...I've been eyeballing the SST90 with that M-size LiFePo4 cell...run that sukka at 8amps...woohoo! I think since I don't have access to machine shop-type equipment...I'll have to go somewhat crude on the design. A huge block of aluminum for the heatsink. We'll see what comes along. For the price of an SST90, I can buy 3x p7's.

 

[chelboed]

Beamshots...I measured the shed from the lights with a tape...50 feet 6 inches:
Control

Magicshine

My own P7 creation

Both together

I'd like to take this time to show y'all a little light that I picked up recently. It's a Trustfire TR-1200. It has 5x Cree XR-E Q5's and will run on 3 RCR123a's, 2x18500's, 2x18650's, or 3x18650's:

This 50' beamshot doesn't do it justice b/c this light can throw a beam a couple of football fields. 50 feet is just rediculous for it:lol: