Help with Current Sense Resistor Modding

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ImA4Wheelr
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The modes compressing like that indicate that something else is limiting current.  You may be able to just short the sensor bank and still get under 2 amps (probably in all modes).  We know that FET is capable of very high currents with low resistance. 

I'm having trouble reading the traces.  It appears that the top left pin of the MCU in the picture below is the PWM output.  It feeds into a 27 ohm resistor (may also have a 10k ohm resistor going to ground) on the way to the FET's Gate.  You could try to bypass the MCU's PWM by using a paper clip to bridge the Vcc (bottom right Pin in the pic below) to the PWM Pin.  This will be equivalent to a PWM of 255.  If current increases significantly, then the MCU may be somehow governing the current to just under 2 amps.

Rufusbduck
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Adding more resistors does seem to be bringing up the lower modes more than raising high. The two LEDs will pass whatever current their relative Vf’s allow. If they’re exactly the same then 1/2 total each. The difference in current measurements isn’t loss in the wires but the additional current used by the rest of the circuit. Voltage drops occur all through a circuit but the current in every part of a given path is constant as long as you account for any branch circuits.

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

Scott

garrybunk
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I bridged the upper left MCU pin to the lower right MCU pin and current only increased slightly to 2.196A @ LED wire (still stock wiring). So what does this tell us? 

Edit - 2 cells at 3.98v now. 

Edit#2 - I get 1.88A prior to bridging. wiggled my connector from battery pack and got 2.24A after bridging now. 

-Garry

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garrybunk
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Ledoman suggested I take voltage measurements both at the battery pack and at the PCB (where battery wire connections are soldered). Perhaps he's onto something! Here are my results:

Low @batt: 3.87v @PCB: 3.67v

Med @batt: 3.80v @PCB: 3.48v

High @batt: 3.76v @PCB: 3.37v

I'm now going to unsolder the power cord from the PCB and solder thicker wires in place and remeasure. 

-Garry

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ledoman
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Ok. If we assume there are also some losses in the circuit you might get voltage to the leds to low. As you probably know leds needs enough voltage to run at certain currents. In your case the voltage at leds might be below Vf (forward voltage). If this is the case there is no way to get desired current.

Also you need to know: more current means more resistance in the wires ie. higher voltage drop unless the wires are thick enough.

At DX forum discussing about some driver I've been advised there can be significant loss in the connector. It is much more powerful driver pulling up to 6A from the battery pack. At that current minimum 20AWG wire is needed. I've been advised to use Deans Ultra connector instead of tipical 5.5x2.1mm which can have resistance of 100 mOhm or more. Unfortunately Deans Ultra connectors are not waterproff.

So every bit can count. Wink

garrybunk
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Bingo! 2.74A after temporary swap of power lead to 18ga wire. Here are my results:

Low @batt: 3.85v, @PCB:3.79v, @LED 1.00A

Med @batt: 3.75v, @PCB: 3.66v, @LED 1.70A

High @batt: 3.64v, @PCB: 3.50v, @LED 2.74A 

      So now I don't know if the problem is the connector or the power lead wires themselves. Outer cable says 22 AWG and it looks like they could be 22ga. Think I'll still replace the LED wires. 

-Garry

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wight
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garrybunk wrote:

Bingo! 2.74A after temporary swap of power lead to 18ga wire. Here are my results:

Low batt: 3.85v, PCB:3.79v, LED 1.00A</p><p>Med batt: 3.75v, PCB: 3.66v, LED 1.70A

High batt: 3.64v, PCB: 3.50v, @LED 2.74A 

      So now I don’t know if the problem is the connector or the power lead wires themselves. Outer cable says 22 AWG and it looks like they could be 22ga. Think I’ll still replace the LED wires. 

-Garry

This makes a lot more sense than my crazy esoteric suggestion assertion.

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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Whoopee!

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ledoman
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garrybunk wrote:
Bingo! 2.74A after temporary swap of power lead to 18ga wire. Here are my results:

Low @batt: 3.85v, @PCB:3.79v, @LED 1.00A

Med @batt: 3.75v, @PCB: 3.66v, @LED 1.70A

High @batt: 3.64v, @PCB: 3.50v, @LED 2.74A 

      So now I don't know if the problem is the connector or the power lead wires themselves. Outer cable says 22 AWG and it looks like they could be 22ga. Think I'll still replace the LED wires. -Garry

I told you, I told you so Wink.  If you would like to know if the most looses are in connector then try to solder same type and lenght of cable directly and measure again. I would be very interested in the results as I'm in the same boat many times.

Alternatively I would use better and/or shorter cable. Where I can I use THIS one from DX hopefuly 20AWG. Still, connector is not good for very high currents as I've explained in my post above.

wight
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As you mentioned above, Deans Ultra is good for high current. It’s certainly not waterpoof, but I don’t think getting it a little wet would be a problem.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

Nightbird95
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ledoman wrote:

garrybunk wrote:
Bingo! 2.74A after temporary swap of power lead to 18ga wire. Here are my results:

Low batt: 3.85v, PCB:3.79v, LED 1.00A</p><p>Med batt: 3.75v, PCB: 3.66v, LED 1.70A

High batt: 3.64v, PCB: 3.50v, @LED 2.74A 

      So now I don’t know if the problem is the connector or the power lead wires themselves. Outer cable says 22 AWG and it looks like they could be 22ga. Think I’ll still replace the LED wires. -Garry

I told you, I told you so Wink.  If you would like to know if the most looses are in connector then try to solder same type and lenght of cable directly and measure again. I would be very interested in the results as I’m in the same boat many times.

Alternatively I would use better and/or shorter cable. Where I can I use THIS one from DX hopefuly 20AWG. Still, connector is not good for very high currents as I’ve explained in my post above.

The cable I ordered from DX finally arrived after 110 days. :bigsmile:

I’ll be using it to upgrade my Pannovo battery case and maybe I won’t need to use 3S2P anymore for the X6. Smile

ledoman
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Nightbird95, try to fix your springs with copper braid just like some other guys are doing with flaslights at the switch end. Hope you know what I mean.

This way you might lower resistance. And think of connector issue!

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