Help with Current Sense Resistor Modding

I would just bridge it if it was me garry. I mean think your pushing 4s in parallel into two xml2 u2 emitters in parallel from the looks of it. You can run in medium, low modes and have the high for when you need it. Maybe reflow onto a couple of noctigons and redo the tim. You should have plenty of light in the lower modes.

Or put in the 120s you already have and see where high takes you. That’s the cheapest way right now. Those u2 aren’t going to blow up on dd- just keep it in the lower modes until you can get the noctigons and tim mailed out to you

Just my 2 cents anyways… :stuck_out_tongue: * disclaimer I take no responsibility if those emitters are mounted badly or have no pill and go blue on high

But seriously the four 120s should be good even with crappy sinks, that’s less than half what those leds can take… You can then add more resistance or take away after playing around.

Yes. And… now I can also see the photos… Dwarf mischief :smiley:

That's all I have for heatsinking in stock form! Emitters on a 2mm thick aluminum board only making contact at those triangle shaped contact points (not even around the edge of the board!). I plan to fully "pot" the area behind the board out to the driver. Even then I don't want to produce a huge amount of heat.

-Garry

^ At least it appears to have a copper layer to spread heat and transmit to the host. Might not be all that bad. Need to check for thermal sag to know.

I looked at the photo gallery. It looks like those resisters have traces going to more than just the FET Source Pin. Are there any components on the switch side of the board?

Yeah I would bridge it man… You don’t have to worry about the limiting resistors going out. I think, well from what I’ve gathered here on the forums… That’s not the correct way to limit power. I’m no expert by any means but I know what those emitters can do. Try bridging it and put it on medium- check the heat. The pwm should keep it cool and you’ll have high for blasting your buddy in the face when he looks back

*Edit yeah 4wheel guess could cut the trace to the source and ground the source on the FET… That would be the safe way to do it

Ugh! Do I really have to tear it down again? I figured the backside didn't look like it had anything important. Should have known I should have taken pics. Will try to get to it soon (like tonight).

-Garry

I like the way you think! All or nothing!

-Garry

BTW - am I okay gauging LED current by the input current on this driver? Or do I really need to check current at the LEDs? I guess I could pull that emitter board back out and screw it down on a big CPU heatsink while trying to tweak the driver. That way if I hit 4A/emitter it doesn't go "POOF".

-Garry

You should be ok in dd… I was thinking like this but someone might have a more elegant solution that involves giving you the 1.5a per emitter your looking for

Cut the trace at the red line, connect a wire from the fet to gnd, (blue line). That’ll keep everything like it was and put it in dd

*edit actually just unsolder the leg on the fet- probably a better idea before connecting the wire

GB wrote:

Ugh! Do I really have to tear it down again? I figured the backside didn't look like it had anything important. Should have known I should have taken pics. Will try to get to it soon (like tonight).

You don't have to for me bro. I am curious how you planned to resistor mod the light without opening it back up.

Unless you are a tinkerer and willing to risk failure it’s probably best to start by just stacking or bridging the resistors to see what that gives you. However, if like me, you can’t leave well enough alone I’m willing to lead you astray.

This is essentially an adaptation of the master/slave mod developed by Techjunkie and posted here by Oldlumens.

First a bit of identification.

On that FET the big tab at the top is called the drain and it’s connected to Led-.

The smaller pin bottom left is called the gate and is how the mcu turns the FET rapidly on and off(what’s called pwm). The amount of (on) time is called the duty cycle and gives you your modes.

The other small pin bottom right is called the source and is connected through those resistors to V-.

7135’s have the same 3 connections but they have different names. Don’t ask me why, maybe an EE could tell you.

The large tab is instead called ground and is equivalent to the source pin.

The bottom right pin is called Vdd and has the same function as the FET gate pin.

The bottom left pin is called Led out or Led -.

The middle pin is the same as ground and is often left unconnected without consequences.

All the 7135’s on a typical driver are connected in parallel so if you make those 3 connections between this board and any of the 7135’s on the slave board then all the chips are used.

What you would need to do is remove the FET and the two resistors and solder in 3 wires to connect the slave board there instead.

If you’re not comfortable soldering and desoldering smallish stuff then you shouldn’t try it but here’s why you should consider it. The difference between the two is in regulation and resistance. The FET is either fully on or fully off and will always pass as much current as the voltage allows during each (on) cycle with the maximum controlled by those resistors. As the battery voltage falls since the resistors are fixed value the current falls as well and the LEDs get dimmer in every mode. With the 7135’s, when they are on each one passes a fixed amount of current with the maximum controlled by the number of 7135’s. As the battery voltage drops the resistance of the 7135’s drops as well to maintain current level. The lights won’t begin to dim until the battery voltage drops down close to the forward voltage of the led and stays constant until then in all modes.

The FET/resistor combo would be more similar to the 7135’s if instead of fixed value resistors a pot were used instead that automatically lowered it’s resistance as the batteries drained.

If you’re interested I can post a sketch later showing the connections but you would need a slave board or a stack of 7135’s to do this.

Thanks for such a clear detailed description RBD! I understand how to wire a slave board up without a sketch. Now the question is, do I want to try adding resistors, or try the slave board method? Hmm . . . I think I'll try the slave board method, but I need to make an order. RMM stock those? I'll go have a look.

-Garry

Ok, seems Mountain is out of stock on them .

-Garry

subbed

Maybe buy a driver something like this http://www.fasttech.com/product/1186301-8-amc7135-2-group-25-modes-led-flashlight-driver-n all the wired up already

I wish we had that buck ck is working on… Use that for everything! xd

I do have some 105c's somewhere. You mean to use it as a slave board (removing everything else)? Or do you mean as a total driver replacement? I don't want to lose the battery voltage indicator if I can help it. (But then again, the 105c would have low voltage protection with it's switch to low & flash.)

Aren't you supposed to be getting those solar panels finished up fellfromtree?

-Garry

Yeah it’s raining man :)… Just wire it up like rufus was sayin

To use a 105C as a slave just clip the power pin and the pwm pin on the mcu or desolder and lift them up. You don’t need to remove anything.

If all you do is replace the FET/resistors with the 7135’s on the slave board you shouldn’t lose any other features on the stock board. The lvp on the 105C won’t be functional.

Ok, thanks. Not sure when I'll get back to this, but I'll try to post back.

-Garry