Replacing Mode Indicator LEDs

[VitalComputing]

Hi all,

I have what should be a simple job but is causing me issues. There are three LEDs (yellow, green and red) on the indicator panel of a solar PWM controller and these have broken off. I need to replace them but I am unsure of the voltage drop across these. I don't want to replace with random LEDs in case they blow.

I took one of the LEDs out of circuit, put 19V across it with a 500 ohm resistor in series and there is a drop of about 13V across the LED, and this seems to increase as I increase the input voltage.

I thought I could just put a resistor in series with the LED and the LED would drop it's rated voltage. Should I just replace with a 12V LED?

Edit: I dont have any schematic

[eccerr0r]

Re: Replacing Mode Indicator LEDs

photo of the circuits involved would be helpful.

probably, a regular T1 or T1¾ LED probably would fry with 19V and a 500Ω dropping resistor.

Why did on whim did you test with a 500Ω resistor in case it was a regular ~1.7V LED? Not safe! Might have been able to solder jumpers!

[VitalComputing]

Re: Replacing Mode Indicator LEDs

photo of the circuits involved would be helpful. probably, a regular T1 or T1¾ LED probably would fry with 19V and a 500Ω dropping resistor.

I set it up originally with a 9V battery and 500 Ohm resistor, and tested with a spare LED and it worked fine - 2.6V drop across LED, remainder dropped across resistor.

When I swopped in the indicator LED from the board, it would not light up at all, so I had to increase the voltage. Only after I put about 14V across it, did the indicator LED from the board start to light up.

I'll see if I can remove the giant heatsink to view the other side of the board.

[stj]

Re: Replacing Mode Indicator LEDs

500ohm is better suited to maybe 5v

for 19v use atleast a 2k2
https://ohmslawcalculator.com/led-resistor-calculator

[eccerr0r]

Re: Replacing Mode Indicator LEDs

Well should always start with 2k2 and go down, those built-in resistor LEDs can be tricky.

However I think most of the built-in resistor LEDs I've run across actually mark on the body that they are indeed 12V or whatever voltage they were designed for. However assume standard voltages if not marked.

[VitalComputing]

Re: Replacing Mode Indicator LEDs

Okay I carried out a little experiment with the one LED that is still fully intact. I measured the 500 ohm resistor and it is actually 462 ohm to be exact. I started at 10V and worked my way up to 22V.



Any opinions would be welcome.

[eccerr0r]

Re: Replacing Mode Indicator LEDs

tbh perhaps a CC PSU at 5mA-10mA to pass through the LED and measure the voltage across it will be the easiest way to figure out the voltage.

strange though, looks like 14V is best, alas these things are annoying if one has to stock different voltage LEDs. Easier to stock regular ones and a bunch of resistors since likely you'll need resistors for other things anyway.

[stj]

Re: Replacing Mode Indicator LEDs

i would use regular leds.
if these leds have a linear regulator in them your gonna get them hot!
i dont know if that is whats in them - but it probably is.

[VitalComputing]

Re: Replacing Mode Indicator LEDs

Okay I thought there must be something else other than just an LED going on, so I hooked up directly to the voltage this time.



I'm gonna just buy a few different 14V through hole LEDs with built in resistor, see which performs closest to this and use it. I will just use the one colour and put labels beside each LED.

[sam_sam_sam]

Re: Replacing Mode Indicator LEDs

You need to know what the current requirements are for the type of LED lights you are using and try to stay a little bit lower than that for longevity of the LED lights you are using

They range from 2 milliamperes to 20 milliamperes

When I have used the 10 milliamperes versions I try keep them to the brightest that is need for the application but below the 10 milliamperes most of the time around 5 milliamperes