Help me locate the sense resistor on this board please....

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1

Hi,

I was wandering if anyone can tell by looking at this if there is in fact a sense resistor on this driver. It powers the halo leds for a car.

Thanks in advance.

2

I would guess the bank of 15Rs are the sensing resistors…
The only thing which confuses me a bit is that, if they are in parallel they still would have 2.5ohm which is high…

Check if these are parallel and if it is regulated at all….

3

It could be that they wanted approx 2.5ohms. Doing it this way you get 6 times the wattage, still using the small resistors. IF that is true, then I would suspect they are the sensing resistors as there would be significant current flowing thru them. Only 1 amp would generate 2.5 watts, that is a lot of heat

4

may be that 15R0 x 6

5

Your board seem to be lacquered by the way, it’s normal for car-specific board. You need to do some additional work to take those off in order to add anything.

6

I think you guys need to learn the difference between a ‘sense’ resistor and a current limiting resistor.

A sense resistor is used in a feedback loop for controling an output. A current limit resistor limits the current by creating a voltage drop.

7

That thing is huge..

I mean that picture!

8

+1

Thanks for pointing that out!
(Except the Ilim creates a Current drop; and the Sense circuit detects Voltage…)

9

I’d like to know what MCU they’re using, to be sure, but the traces make it look to me as if this is it:

Solder a Pot over it & see!

10

Thanks to all who have responded.

Dimbo, I was sort of thinking that when I first saw the board too ( not that I know squat about them LOL)

Its been a while since I have worked with a pot, can you remind me which of the pot leads I would solder to the ends?

EDIT: Also what pot value would you recommend?

11

If you really wanna try something, then try to test if it is regulated at all first.

If you really think this 1.5k has something to do with the regulation than choose something bigger like a 10k pot, trimmed to maximum resistance.

1÷(1÷1500+1÷10000)=1300 ohm resulting…

There are 3 legs on a pot, you can imagine a pot is like a big wire and the legs are connected to the wire.
Two legs are on each end fixed. And the third leg moves over the wire.
Between the outer legs you have the whole resistance which is printed on the case.
Between a outer leg and the middle leg there is a selectable resistance, more wire has more resistance shorter wire has less resistance.

For example a 10000 ohm trimmer:
A——————M—————-T.

Between A and T 10k
Between A and M 05K
Between M and T 05k
……

AM———————————-T
Between A and M 0k
Between M and T 10k
Between A and T 10k

….
A——-M—————————T
Between A and M 3K
between M and T 7KBetween A and T 10k

So you have to use the middle leg and one of the fixed ones, solder one to each side. Start with the maximum resistance first because two parallel resistors have always a resulting resistance which is smaller than the smallest resistor used.

12

That’s almost certainly not the sense resistor (1.5K is way too large of a value) and probably not an MCU…