Rayovac Sports Headlamp - First time mod advice

I am looking to try my very first mod. I would like to mod a Rayovac Sportsman Headlamp. I would like to replace the existing LEDs with 3 white nichia LEDs. Using the search function turned up some good advice so far, but most of the posts had to deal with installing a LS or regulation circuit. SO, a few questions.

1. Am I looking for 3mm or 5mm LEDs as replacements?
2. If I removed the limiting resistors would using NIMH batteries blow the new nichia LEDs?
3. Any suggestions on where to purchase the nichia LEDS? Radioshack? Online?
4. Any other things I should know about before attempting this mod?

Thank you in advance.

Re: Rayovac Sports Headlamp - First time mod advic

White Light LED is a good online source for LEDs.

I don't have the expertise to answer your other questions. I've used 5mm LEDs so far but some people use the 3mm ones to fit smaller diameter openings.

Re: Rayovac Sports Headlamp - First time mod advic

Make sure not to overdirve the Nicia's. They do not dissipate the heat like an LS. I recomend 5mm LED's. Use ohms law to find the appropriate amount of resistance. Try www.ledwarehouse.com $1.89 for 7200mcd is really good. Ask if you need more info on the mod.

Re: Rayovac Sports Headlamp - First time mod advic

Thanks for the help.

I assume the forward voltage is the MAX input voltage? The nichia at Led Warehouse has a forward voltage of 3.6 volts and a max current of 55ma. Using alkaline batteries I would need at least a 17 ohm resistor, though that is a non standard size. I can get 10 ohm resistors at Radio shack. 20 ohms of resistance should drop the voltage 1.1 volts. Leaving 3.4 volts to the LEDs. Which sounds like the perfect voltage to use. Does all of this sound correct?

Now the harder problem. I will probably be using NIMH 99% of the time and only alkaline during emergencies. Using NIMH would only give me 2.5 volts with the 20 ohms of resistance. How do I obtain a happy medium using both types of batteries??

Re: Rayovac Sports Headlamp - First time mod advic

Well after lots of reading I now see that forward voltage is the voltage required to turn the LED on. If this is the case, slightly worn nimh batteries will not work with the nichia leds. Dang it, I found this out after finding a constant current circuit that only uses 2 resistors and 2 transistors. Now I am really stuck!

Re: Rayovac Sports Headlamp - First time mod advic

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electronics4life said:
Well after lots of reading I now see that forward voltage is the voltage required to turn the LED on. If this is the case, slightly worn nimh batteries will not work with the nichia leds. Dang it, I found this out after finding a constant current circuit that only uses 2 resistors and 2 transistors. Now I am really stuck!

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Not a bit of it.. Your problem is the regulator you're using, not the idea.

There's a specification that's important here, "Drop out voltage", that is the minimum voltage between supply (battery) and load (LED).that the circuit will work at. Notice that the circuit in question 'drops out of regulation' at about a Volt and a half. That is for LEDs that are perhaps 3.4 Volts at working current, the circuit is 'getting in trouble' (current is starting to drop) at five volts or so.

There are, however, "Low Drop Out" regulators. My current favorite uses a LM334 (a 'transistor case" IC, 3 leads), a PNP transistor, four resistors and a small cap. A very small increase in parts count, but now the drop out is .1 Volt or less. I get 50 solid hours at 30 mA from *three* 1750 mAh AA cells. Time after time.

This means, "truly dead" alkalines (.8 Volts a cell) in a four cell battery will still have .3.2 Volts less .1 available for 'direct drive'. You'll get every last drop....

Doug Owen

Re: Rayovac Sports Headlamp - First time mod advic

[ QUOTE ]
Doug Owen said:
This means, "truly dead" alkalines (.8 Volts a cell) in a four cell battery will still have .3.2 Volts less .1 available for 'direct drive'. You'll get every last drop....

Doug Owen

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Oops...this is a three cell light, this means *three* times .8 (not four). Still, works just fine on *three* NiMH cells....honest....

Doug Owen

Re: Rayovac Sports Headlamp - First time mod advic

I would use 5mm LEDs. I know the Moonlight has a 3.7ohm resistor, and runs fine with alkalines or NiMHs. I removed the resistor in one altogether, and 1 LED went bad after a while (using NiMHs), so I would definitely use some resistance.

If you don't want to bother with a regulator, then I wouldn't bother with the calculations, since the Vf varies with LEDs anyway. I would hook them up to a pot, then adjust the pot for max brightness and check for excess heat. Then measure the resistance of the pot, and go out and buy a resistor with that value (or close to it).

Re: Rayovac Sports Headlamp - First time mod advic

[ QUOTE ]
Doug Owen said:...There are, however, "Low Drop Out" regulators. My current favorite uses a LM334 (a 'transistor case" IC, 3 leads), a PNP transistor, four resistors and a small cap. A very small increase in parts count, but now the drop out is .1 Volt or less. I get 50 solid hours at 30 mA from *three* 1750 mAh AA cells. Time after time...

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Doug,

Can you modify this circuit to run at 200ma? Do you just change a resistor value?

Re: Rayovac Sports Headlamp - First time mod advic

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Lux Luthor said:

Can you modify this circuit to run at 200ma? Do you just change a resistor value?

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Yeah, sorta. The transistor I use ('cuz it's cheap and an old friend) can make it to 100 mA and a bit more and stay under .1 Volts, but past that I use a different part. It raises the adds nearly a buck to the cost.

But, yes, it works fine at 350 mA for Luxeons. With them the sense resistor is a bit over a foot of wire wrap wire. Now it's a seventy five cent IC, three resistors, a 15 cent cap, a nearly dollar transistor and a piece of wire.

Doug Owen

Re: Rayovac Sports Headlamp - First time mod advic

Hmm, I simulated the circuit I was thinking of using in EWB. The LEDs were only getting micro volts???? How did this circuit ever work in the first place? Here is a link to where I got the idea. Constant current circuit Would the circuit suggested by Doug fit in that little space? In my simulation even with only 1V cells 19ma was still supplied. On the website it states only 1ma. Maybe Electronics Workbench doesn't have the right specs for a diode to accurately simulate? I'd really like to use some sort of regulation if possible. That would keep my battery options more open.

Re: Rayovac Sports Headlamp - First time mod advic

http://www.lsdiodes.com/ 75cents for 8000mcd white led 15deg viewing angle /ubbthreads/images/graemlins/wink.gif

Re: Rayovac Sports Headlamp - First time mod advic

[ QUOTE ]
electronics4life said:
Would the circuit suggested by Doug fit in that little space? In my simulation even with only 1V cells 19ma was still supplied. On the website it states only 1ma. Maybe Electronics Workbench doesn't have the right specs for a diode to accurately simulate? I'd really like to use some sort of regulation if possible. That would keep my battery options more open.

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Er, yes (or I wouldn't have suggested it). It uses a PNP transistor (the same size as the 2N2222), a TO-92 case IC (same size again), three resistors and a very small cap (smallest part of all). If you go to 1/8 watt resistors (rather than 1/4) you'll actually end up with *more* room.

I don't know what the problem is with your simulation (I suspect you're using a regular diode not an LED?), but for sure you know that it won't run at all on 1 Volt. Somehow I've always favored actually making these sorts of things. Having made several dozen such regulators in the past months I can assure you that's not what happens in the real world....... 3 NiMH AA cells drive 30 mA for 50 hours straight with 'rock stable' output (this on 1750 mAh cells). Time after time. Then it reverts to 'direct drive' and the light level drops off over the next half hour or so. Sometimes a little longer.

Doug Owen

Re: Rayovac Sports Headlamp - First time mod advic

Thanks for the continued help doug. Any idea on the runtime of only 3 NIMH AAAs. And could I just divide that by 3 since i will be using 3 LEDs. Or would 3 LEDs affect the circuit in a way I am unaware of.

Re: Rayovac Sports Headlamp - First time mod advic

You'll get slightly less total at the higher rate, I'd guess something over 8 hours from 750 mAh cells driving 3 LEDs at 25 mA each.

Doug Owen

Re: Rayovac Sports Headlamp - First time mod advic

Okay, I think I am set to purchase the components. I was thinking of using mouser.com as my source. If this is not the best choice please let me know. So I will need;

1. The LM334 (plan on using the TO-92 package)
2. A 300 ohm limiting resistor for the Vin on the LM334.
3. A .2uf cap (film okay?)
4. A 470 ohm resistor for R.
5. A .71-.85 ohm resistor for Rset. To get 75ma-90ma. For 25ma-30ma per LED. Problem is I can't find any of these. Mouser has a .68 ohm resistor though. I believe this would allow 31mA to each LED. Which should be OKAY?
6. A transistor, this I am stuck on. Any specific recommendations? Preferably available from the same place I am purchasing my other parts.

One more question. Does this absolutely have to be put on a circuit board? I currently don't have any but could run wires and shrink tube. I think that is about it. Thank you in advance.

Re: Rayovac Sports Headlamp - First time mod advic

Yes, that's about the list. FWIW, I use 390 ohms for both the V+ to base lead and the negative feedback R (in series with the cap). .1 MFD as well.

I'd probably use 1 ohm and 2.2 in parallel for a sense resistor (both values I have in 1/8 watt resistors).

At the currents we're talking about, I generally get good results with 2N3906s. Higher currents (like for Luxeons) call for a hotter part.

Mouser's a good outfit, but Jameco gets more of my money these days (better prices generally and faster delivery to my house). However, this is a very small buy, you'll take a beating on shipping etc.

Send me a PM, let's see what we can work out.

Doug Owen

Re: Rayovac Sports Headlamp - First time mod advic

[ QUOTE ]
electronics4life said:

One more question. Does this absolutely have to be put on a circuit board? I currently don't have any but could run wires and shrink tube. I think that is about it. Thank you in advance.


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Oops. Forgot this one. No, not for five parts. At least I didn't in the one I built today (I just did the white LED, for the time being I like the reds....). The two 'transistors' fit next to the LEDs just fine (on the back of course). PM me and I'll see if I can send you a photo (no, I can't post it here.....).

Doug Owen

Re: Rayovac Sports Headlamp - First time mod advic

Thank you for the pictures doug. This mod does indeed fit on the LED board. I may just have to build another constant current circuit for the LS I am also going to transplant. Now that the LED mod doesn't use up that extra space something has to right... /ubbthreads/images/graemlins/smile.gif I'll let you know if I run into any trouble with the actual assembly. Your help has been invaluable.

Re: Rayovac Sports Headlamp - First time mod advic

[ QUOTE ]
electronics4life said:
This mod does indeed fit on the LED board. I may just have to build another constant current circuit for the LS I am also going to transplant. Now that the LED mod doesn't use up that extra space something has to right... /ubbthreads/images/graemlins/smile.gif

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Yup, that's why I tucked it down below the battery tube, I wanted the extra space for the LS Driver. I can't make up my mind just how to do it, though, 'cuz I intend to put a switch through the wall somewhere to select between several levels for the Luxeon (I'm thinking like up to 100 or maybe 120 mA). While the main body seems like a good place (above and behind the main light), that's the back of the assembly and a PITA to wire. I'm now thinking of through the wall of the black part with only a clearance slot in the main body (electronics in the 'bowl' behind the LS)..

Anyway, with such a set up, white LEDs below seem all wrong. That's why I left the red LEDs in for the time being. I think I'll swap the factory white for the Nichia wide angle (IMO a very neat part) driven at 30 mA with the existing regulator.

Funny how different guys get on the same track, isn't it? As the Polish folk saying goes, 'fools seldom differ'.

Doug Owen