Modifying Coleman Sentinel - Add your info Here *Pics added*

[Quickbeam]

I am going to modify a Coleman Sentinel (3.6V 3 x AA NiMH rechargables, charges via crank handle) to use nichias.

4.17 volts are produced on a full charge from the + to - terminals at the bulb connector.

If I plug in a Nichia directly, it only draws 10.7 mA and produces only about 6 LUX. The voltage across the LED is 3.5V - quite a drop.

If I plug in an LM2621 board, I can adjust the voltage up to 4.04V output and the LED is drawing a little less than 27mA (around 30 Lux) with no voltage drop. After frying one board by accident I found one more that I had in the bottom of a box... Gotta be careful with this one!

I think I can rig it so that "low" directly drives the LEDs and "high" pumps the board to boost the output for the same LEDs.

More to come...

I've moved the Mod process out of the general LED forum thread about the Sentinel being on sale.

If you are also modifying a Sentinel, please post your ideas and progress here!

 

[LoneRebel]

Quickbeam, I ordered a sentinel also. It should be here by next monday. So I'll be modding it soon also. Anyways, I bought a am/fm radio/flashlight solar/dynamo. I used my multimeter to check out the voltage it was putting out and it read at 2.8 after having been cranked a bit. I put an LED in it and it was glowing. Not bright, but still glowing alright. Anyways, I soldered the LED into the lamp assembly. I started cranking the dynamo while the light was on and it went dim. The LED was pretty much ruined. Anyways, I just thought I'd share this with you as apparently with the light I have, it lets alot of excess voltage across while winding. I guess we may or may not run into this same problem with the sentinel.

Quickbeam, shouldnt the LED be brighter running while being plugged in directly? It doesnt make sense to me why it would be dimmer than with a voltage regulator, a regulator that would at best drop the voltage.

 

[James S]

Doug, is there any difference between the high and low pins as far as voltage or current available? I doubt that would be the case, but I can't account for that fantastic voltage drop with a load of only a few ma. Could they be putting a resister on the low pin or something like that?

How are you measuring that amperage? My meter will not accurately measure low currents like that, it always adds too much resistance to the circuit and I can plainly see that the LED is brighter and drawing more power when I remove it from the loop.

If it were my meter that would very easily jump up to 25ma or so after removing the meter and plugging it directly.

 

[Quickbeam]

Voltage is identical regardless of which pin is used (high or low)

To measure mA, I just put the meter in series with the LED. Make the connections, flip the switch and watch the mA go up and down as I adjust the voltage on the LM board. Lux output is identical if I have the meter in the loop or not.

Now I just need to figure out a way to support the board in the head of the light without the reflector in there. Oh yea, and how to build the LEDs onto a board and support that, too...

 

[Quickbeam]

Well, the LM2621 is a boost circuit and a regulator. Input voltage is variable (I forget what it's limits are) and by changing 1 resistor (I replaced it with a pot. and a resistor) you can change the voltage out. Turn the pot. and you can make the LED brighter or dimmer.

http://www.national.com/pf/LM/LM2621.html#Availability

I saw no variation in LED brightness whether cranking or not when an LED was plugged in directly, so it seems to charge the batteries independently from the lighting circuit.

 

[LoneRebel]

Quickbeam, ahh I just thought the board was a plain regulator. That board almost costs as much as the sentinel itself (ouch). I might have to try making a one transistor step up circuit and see how it works out on this light. It sucks that radio shack nor fryes carries ferrite beads:/

 

[LoneRebel]

I just got my sentinel a couple hours ago. I'm quite impressed with how solid and rugged it feels. Even with the standard bulb it looks to be quite useful. So far I think this is quite a good deal for $24.99. I cant wait to get a good LED mounted in this thing:) Quickbeam have you tried running a luxeon star in yours?

 

[Quickbeam]

No luxeon stars - at least not yet. I got the LEDs for the mod and I think I'm going to go that route just for fun. Plus the LM booster board can't handle the mA requirements of the LS.

 

[Orion]

My EXTREMELY MILD moddification just involved taking the original tri pin bulb out and putting a 9200 mcd white LED in. I only have one level of brightness (hence only one of the on selections will work), but it is plenty bright if it were dark in the room, and it should last a good long while. It's the only think I can do at my level of skill. Oh well, it works as a good wind up light.

 

[LoneRebel]

Quickbeam, I made the same observation as you. The light is extremely dim with a direct drive LED. Do you have any idea why this is? I just tested it with my multimeter and it showed a voltage of 4.2v and the amperage was showing 5.73. From my limited knowledge of electronics I cannot explain this. It seems downright weird

 

[Quickbeam]

Well, I built the board during lunch, 10 LEDs draw about 110mA direct from the batteries (low setting, set the LM2621 voltage to allow the LEDs to pull around 200mA for the High setting... I'll add some pics later.

I tried it at 250mA, but it kept creeping up as the LEDs heated up. Since there is no internal resistance in the LM2621 like there is with alkaline batteries, it just keeps giving more and more current as they heat up, heading toward thermal runaway...

73 Lux at 1 meter on low, 120 lux on High!!!

 

[James S]

I"m not sure I'm seeing the same problem as you folks. I haven't really done anything to it yet as I am awaiting the next credit card bill before I order the parts I want for this

I did run the same tests as you guys and I see the same amperage and voltage. But, when I tested at the ma range instead of the amp range I only saw 300ma. This used a different, higher value resister in the meter to measure the voltage drop.

When I placed an LED in it I can't tell that it's significantly less bright than when I connect it directly to other batts.

But the amount of current you can pull from this does seem variable by the load. Perhaps I need to take it apart again and see if there is something else going on in the circuit.

 

[Quickbeam]

James- I found the problem - I was using my meter on the mA range, which doesn't seem to read accurately - once I switched it to the Amp range, the readings went way up. My post - 2 above - has the accurate amp readings.

 

[Quickbeam]

CRAP - I don't believe it! I smoked my last board... DAMN!

OK... forget it. It'll run directly off of the batteries.

70+ Lux isn't bad at all... Guess I'll have to live with it.

 

[Orion]

 

[Quickbeam]

DONE!!! Pictures!

More here on the mods page from my site:

http://thelightsite.cruxial.com/mods/coleman_sentinel_mod.htm

 

[x-ray]

Very nice work, thought of going into business ?

 

[Clouddancer]

I should have delivery of my Sentinel in the next few days and been following what you guys have been doing. It should be very interesting to see what your best results are. Quickbeam I take it that board you've been trying to use isn't a regulator board, is that right? Would that make a difference?

 

[Quickbeam]

New board design - 2 leds on low, 10 on high, all direct driven off of the rechargable batteries.

Final count - with lens in place 50 lux on 10 LEDs, 10 lux on 2 LEDs.

Sorry if this thread is a bit of a monologue, hopefully others will start some serious modding on theirs soon.

Now that the lm2621 boards are all fried, I should have the mod done by this evening along with pics since not cramming a board in there makes things a lot easier. The mod will be completely reversable as well.

Lonerebel - sorry if I missed your question. I really don't know why the LEDs are so dim running on 3.6V. Seems like something is limiting the current....

Cost for the completed mod:

$33.00 - Sentinel flashlight
$18.50 - 12 white LEDs
$2.00 - waferboard
$2.00 - misc parts
______
$55.00

Add the fried LM2621 boards at $22 each = $99.00! Ouch!

I should have just bought a KL1 and a bunch of 123A batteries!

 

[Quickbeam]

The LM2621 is a boost regulator. Check out the Nat. Semi. link above (under the big picture of the board) for details.

And no, I'm not making any more of these - In fact, now I remember why I stopped moding and started focusing on reviews!