need help starting 4d resistored mag build

i've got plenty of direct drive mags under my belt. i'd like to delve into a 4d resistored mag. can anyone start me in the right direction. i assume i mount the resistor on the bottom of heatsink with glue epoxy, run the + and - to that, forward them through the heatsink holes to the led and walaa, :candle:

that sound about right?

Yep, it's that simple.

how do i pick the right size resistor. i guess it would be smart to pick a high vf led, then a small resistor. or could i just get one of those dx limiters where you can pick 350ma/700/1050mah. wouldn't that adjust the voltage to MAKE the drive voltage be right, even if i had 5 or 6 batteries in there, it would just be working harder to drop the power.

LED Pro
Norm

jasonsmaglites said:

i've got plenty of direct drive mags under my belt. i'd like to delve into a 4d resistored mag. can anyone start me in the right direction. i assume i mount the resistor on the bottom of heatsink with glue epoxy, run the + and - to that, forward them through the heatsink holes to the led and walaa, :candle:

that sound about right?

Click to expand...

Sorry if I misunderstand, but when you wrote "run the + and - to that" did you mean running BOTH wires to the resistor?

you tell me how it goes.

The resistor goes in series with the LED not parallel.
Norm

I'm no expert, having only done two Mag mods, one resistored and one with a driver. This thread was the recipe I followed for the resistor mod. The resistor will work on either side of the circuit, but I took the following advice from IssacHayes:

For the resistor, I have used a 1ohm 1W before too. I solder it to the positive wire, (that way if the led somehow gets connection from the negative through the heatsink, it's not bypassing the resistor, call me paranoid.

Click to expand...

thanks for the thread. it was very helpful.

oops. not out of the water yet. someone verify my calculations. i have an h bin led, going into a 4d maglite, i want about 700mah to save alkaline batteries since the build is for a non-flashaholic, and i plan to use a 2 ohm resistor.

does 2 ohm sound right and where do i buy one?

Assuming Vf=3.3V@700mA drive current, and a Vbatt=4.8V, I get 2.14 ohms and 1.05W for the resistor that you need. With a 2 ohm resistor, you will get 750mA drive current and 1.12W of power through the resistor.

jasonsmaglites said:

thanks for the thread. it was very helpful.

Click to expand...

You're welcome. It was very helpful for me too. Let us know how your mod works out. :wave:

Don

cool. the vf is 3.0-3.25 but if the drive ends up being a little higher thats ok. at what point will the d cell alkalines start becoming inefficent?

jasonsmaglites said:

cool. the vf is 3.0-3.25 but if the drive ends up being a little higher thats ok. at what point will the d cell alkalines start becoming inefficent?

Click to expand...

A P4 (I assume that's the emitter under consideration) H voltage bin is 3.00V-3.25V at 350mA drive. Vf will be higher at higher drive current.

huh. i thought each led had a certain voltage that was considered its "vf" and that they varied so they binned them in categories like h(3-3.25) i(3.25-3.5) j... and so on. so the vf used in that forumula someone linked me to can vary with drive. i knew that the voltage going in varied the output of the light, but i didn't know... well im not sure what i didnt know. i thought vf was fixed on each light and they were thus categorized that we could pick from.

well whatever, you guys still recommend 2ohms resistor? where can i find a small small one for this 4d mag for my buddys camping light.

No. Read the SSC P4 datasheet and binning and labeling datasheet.

The If vs Vf curve in the P4 datasheet clearly shows that Vf is not a constant.

The table for the electro-optical characteristics clearly states that the values are for If = 350mA at 25C.

Pretty clearly, H voltage bin is the Vf range at If = 350mA and 25C.

I bought the 1ohm resistor for my Mag mod at Fry's Electronics. I checked on Radio Shack's website and didn't see any 2ohm, 1 watt rated resistors. Parts Express has some and they ship USPS so the shipping is not too bad - especially if you have other stuff to order at the same time.

Hi, if you can solder 1206 size resistors, I can help you out with some 2 ohm, power resistors. I had some custom made by a firm that makes aerospace grade resistors some time ago. (They already made high power, 1206 resistors, I just had them make some for me in 2 ohms)

They can handle way more than 1 watt.

The original purpose was the circuit board for my "Project Breeze" light in my sig line. That project is sidelined, but I still have lots of parts.

Send me a pm if you want to buy / trade for a couple.

Take care,

HarryN

harry n, i do believe im gonna take you up on that. but first guys, i was just at radio shack and they didn't have the ones i needed. can you help me understand what the ohms rating and the watts ratings are for. i assume the ohm is how much resistance it gives you, thereby reducing the power flow by a certain amount. and the watts rating is the amount of power it can handle before going poof, and the only drawback to getting one too big is the waste of money or difficulty in installing it. or does the watts have more meaning than that and is also a factor in resisting? help

also im assuming that since i got a h bin low vf led bulb, that if i want it to be on the conservative side (500-700mah) that i would need more of a resistor than if i had an i or a j bin? do i understand the mechanics of it right?

harry n, thanks for your offer of hooking me up with some resistors for some 4 d mag mods. your pm box is full. i could use 3 or 4, how much do you want each, and for shipping if i decide to go this route?
jason