Help with Current Sense Resistor Modding

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adrenalnjunky
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Thanks, Chris

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

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

garrybunk
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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?  Laughing

-Garry

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

Rufusbduck
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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.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

Rufusbduck
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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.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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

-Garry

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Rufusbduck
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No worries Garry, just doing the sense resistor mod might satisfy your needs and doesn’t preclude the more complex slave mod so you could just take baby steps here. The leap of faith comes when you strip the FET and resistors and things start getting ugly. The good news is that there are firmwares available for mom switches to 105C drivers if it goes south on you.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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Here is a pic of the backside of the driver. Not much going on as expected:

S

-Garry

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wight
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Rufusbduck wrote:
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.
Good thinking.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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Rufusbduck
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Could you post consecutive images of the top and bottom please. Hard to tell but if you measure the resistance between the bottom left pin of the FET and the top left pin of the mcu and get ~270 ohms then I think you have your pwm trace. The question then becomes is that 270 ohm resistor needed for use with 7135’s? I think some of that row of chips in the middle has to do with powering the indicator LEDs on the back side but the traces on the lower half are shadowed.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

wight
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I don’t see why the 270 would be needed for that, I’d solder my PWM wire to the side of it which face the MCU.

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garrybunk
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Probing those two pins gives me 26.6 ohms. 

-Garry

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wight
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garrybunk wrote:

Probing those two pins gives me 26.6 ohms. 

-Garry

Eh, it’s actually a 27 ohm resistor (27 + zero zero’s is what the marking means). I think many of us make that mistake on a regular basis. Someone else just mentioned the same problem in a PM to me and I know it happens to me. (EDIT: and it definitely happened to me this time LOL

IOW that’s definitely the PWM pin. 27 ohms doesn’t matter one way or the other, you can solder your PWM wire wherever is convenient.

EDIT 2: Here’s a link to help with decoding SMD resistors. http://www.marsport.org.uk/smd/res.htm

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garrybunk
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Great! Thanks for the help! I'm actually working on this right now. This is extremely difficult work for me and I might have to postpone it because I have other chores I need to get to. 

-Garry

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Rufusbduck
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Thanks wight! I’m in deep water without a vest here so it’s nice to have back up. When the FET is removed it should be obvious which is the pwm trace I was just trying to see if I was seeing things correctly first. I mentioned above that the resistor might not be needed for the slave mod. Thanks for the correction on the “0”.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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Remember Garry, you don’t need to bring + power to the slave. Just the pwm signal, led-, and gnd. The last two will carry the full current so decent wires (awg24 or better for 3A).

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

wight
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Really you don’t have to remove any components.

  1. Take the existing driver and detach LED-.
  2. Attach LED – to the 7135 based driver in the normal place
  3. Add a heavy jumper wire for GND between the existing driver and the 7135 based driver.
  4. Add a PWM connection between the existing driver and the 7135 based driver (it goes to the righthand pin on a 7135 when the tab is away from you). EDIT: You may get the PWM from the FET’s gate pin if you want.
  5. You are done.

Am I missing anything?

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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So no connection for "Led+" coming in/out of the 105c? I've already attached it. And in fact I used the existing wire that came with the 105c as the "PWM" line as I couldn't get my 20ga attached (too big). Not sure what gauge these stock wires are. Anyone know off hand?

-Garry

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wight
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I forgot to mention that in my list. Small wires are fine for the PWM lead, no harm there. I don’t know what AWG the stock wires are, but they are fine for PWM.

No LED+ is necessary coming in/out of the 105c. It’s fine to use it, but all the 105c does is pass BAT+ directly to LED+ so it’s just extra connections and resistance. Not a big deal.

Side note: Note that while I’m very confident that you can get away with leaving the FET in place, eventually if you hook enough stuff up to an output pin of an MCU, whether that stuff is being used or not, the MCU will struggle to send out a strong enough PWM signal.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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garrybunk
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I'll remove the FET. I also got the Attiny13a removed too (that was tough!). I've not got all 22ga wire installed ready to mount to the existing driver. I even piggybacked another 7135  My first attempt at that ever! And I found that to be MUCH easier than attaching these darn wires!  Just hope I didn't burn up any of the 7135s. 

Im gonna have to quit for now. Thanks for the help!

-Garry

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wight
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FWIW, and I don’t do as many of these as others, I’ve never burned up a 7135 or had a “bad” one that I noticed. I’ve torn legs off of them several times, but it’s always been pretty obvious that I had physically damaged the thing.

A heat gun makes all this much better!

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Well I couldn't leave it alone, so it's connected! 

A

 

Best at pic I can post until I get a chance to upload my high res macros. Not too bad of a job! Now I hope it works! Wait - let me test quick. Well it works, however I'm getting 2.35A measured in each mode (it still ramps down then back up between modes) with 2 unprotected cells in parallel at 3.99v. Ugh! Why'd I lose mode levels? 

Ill probably post high res pics Monday. I'm done for now. 

-Garry

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wight
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I am unable to see the PWM lead in your picture.

I took a closer look at the stock driver. It appears to be setup for current sensing after all. It’s probably still just doing PWM to the FET and using an RC circuit to smooth the sense voltage out.

so err, sorry! If I’m correct I’d say that this is not really a common setup. I’m not sure that the best solution is not to re-assemble the driver and do a sense resistor mod. EDIT: hold that thought. I’m taking an even closer look now. EDIT 2: OK, I’ll stand by that for now. Forgive me but this driver is only so interesting and I won’t stare at it all day. It looks like what I wrote in strike-through text may be the case.

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Well I already broke the old FET getting it off Sad .

-Garry

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wight
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Hmm, I’m not making much sense here. Why would you be limited to 2.4A if you bypass the sense resistors? They’d have zero voltage drop across them and thus the driver would attempt to run full blast. Maybe it never provides a 100% duty cycle no matter what. Your 105c is fully populated with 8×7135?

Anyway you can probably just use a normal FET like the 70N02 or AOD510 if you have those.

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My 105c has 9x7135's now. Possible I burned some up? I don't have any FETs here at all on me. I did connect the GND directly to the incoming NEG lead (connected across those resistors where they connect to GND. The PWM wire is connected to FETs gate pad (lower left). LED- from new driver to to the FETs drain pad. I also checked for shorts on the 105c while wiring up. 

-Garry

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wight
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If you would like to do an experiment let’s move the Nanjg 105c’s GND connection over to the right of the sense resistors and see if modes come back. I do not expect to see more current, but I do expect to see modes / levels.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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You're right! Modes now show:

L-1.06A

M-1.38A

H-2.08A

Too closely spaced though. And low & medium fluctuate a good bit on the meter while high is steady at 2.08A. 

-Garry

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wight
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Sorry for the mixup earlier. So it’s as I said: this driver appears to use current sensing through an RC circuit to do “CC” (not really) PWM. I’d drop an FET in and do the resistor mod to get the desired current.

How badly did you damage the FET when removing it? I’ve been doing some serious bending on one or two DPAK FETs over here and they aren’t dead yet..

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
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