You've shown the resistors in parallel with the strips ,they need to be in series with them. IE: one resistor Inn series with each strip.

I'm sorry, but this is what confuses me. I remember from my basic electronics course, 15 years ago, that:
- In series, the current flowing though each element is the same
- In parallel, the current flowing through each element is summed (i.e. the sum of currents flowing through each parallel circuit equals the total current).

Again, pardon my ignorance,
but wouldn't connecting the resistors in series with the strips, reduce the voltage on each led in the strip, but maintain the same 150mA current ?

 

Each LED strip will have a voltage drop across it when it draws 150mA, the problem with having 4 strips in parallel is the one with the lowest voltage drop will draw more of the 600mA current source. If you know what strip needs the highest voltage to draw 150mA then you can work out what series resistance you need per strip by ohm's law. That way the currents will be balanced.

 

Don’t try anything else until you have verified that all 4 strips still work! From your description, it is likely one or more if them failed, so attempting to run the four strips at 600mA will likely just fail again, perhaps destroying more of them.

What equipment do you have? Do you have a bench supply capable of 30V or more?

Bob

 

Each LED strip will have a voltage drop across it when it draws 150mA, the problem with having 4 strips in parallel is the one with the lowest voltage drop will draw more of the 600mA current source. If you know what strip needs the highest voltage to draw 150mA then you can work out what series resistance you need per strip by ohm's law. That way the currents will be balanced.

Ooook, I think I got it.

So suppose I measure the voltage on the strip and find that the voltage drop is 30V. The Current which I want to obtain is supposedly 120mA.
then I=V/R, R=V/I=30/0.120=250 Ohm (To be connected in series with every circuit)

Hopefully my assumptions are right

 

Don’t try anything else until you have verified that all 4 strips still work! From your description, it is likely one or more if them failed, so attempting to run the four strips at 600mA will likely just fail again, perhaps destroying more of them.

What equipment do you have? Do you have a bench supply capable of 30V or more?

Bob

I have identified 2 LEDs that are shot, and ordered replacements.
I'm going to replace them and make sure the others work and the I'll connect everything together (for a very short time)

The only thing I have is the LED power supply unfortunately. I'm a noob in electronics and never needed to use transformers and this kind of stuff before. But I like learning about it

 

The two LEDs that are shot experienced too high a current. The others in the same group of 15 also experienced that same current and may very well be damaged.

How did you test them?

Bob

 

Ooook, I think I got it.

So suppose I measure the voltage on the strip and find that the voltage drop is 30V. The Current which I want to obtain is supposedly 120mA.
then I=V/R, R=V/I=30/0.120=250 Ohm (To be connected in series with every circuit)

Hopefully my assumptions are right

It won't work your adapter is a Constant Current output, whatever resistor you put in series , the adapter will give out 600mA, you need to put more led strips in parallel or put resistors in parallel to divert the current.

 

The idea of putting a resistor in series with each strip is to help balance the current among the strips. You would indeed still get the same current.

I don’t think it will work in this case though, because you would want it to drop a significant voltage, maybe 5V, and that might exceed the driver’s capability.

Bob

 

If I were to connect a resistor in parallel to the 4 strips, how would I go about calculating its value ?
Ohm's law, measuring the voltage drop on one of the strips, taking 120mA as the current and calculate the Resistance ?

 

How did you test them?

Bob

I just put my multimeter in resistance measurement mode, then connected to the led poles. The leds which were not dead, would light up a bit.
The ones which were dead would not (also they have a barely visible black dot on top, which AFAIK means they're shot)

 

HI Everyone,
Wanted to give a quick update.
I replaced the dead leds and connected everything and it works.
But it's not stable. After several minutes, some strips start flashing, or simply switch off.
So looks like the current is too strong.

I would like to bring the current per strip from 150mA, down to 120mA. This basically means adding one more strip. Except there is no room for a led strip, so I want to just add a resistor in parallel.
My deduction is that the resistor needs to have the same Characteristics as the strip:

I have measured the Voltage drop on the strips, V=47.5V
Having the current I=0.15A
The Resistance of a strip should be R(strip) = V/I = 47.5/0.15A = 316 Ohm
Assuming that the voltage drop on the resistor will be 47.5V, the Resistor is around 316 Ohm, the target current should be I= 0.12A
Therefore the Power rating P=IV = 47.5V * 0.12A = 5.7W

My conclusion is:
- I need a 300 Ohm resistor, with a power rating of 10W (to be safe?)

The question is:
- Are my assumptions correct ?
- Does this resistor risk to get hot ?
- On Amazon I found this one, would this be suitable ?

Thanks in advance
Alex

 

That resistor would be suitable but should be bolted to a heat sink. (Possibly the lamp casing.) It may be easier to use four 1.2K resistors (in parallel.) to distribute the heat around the unit. For example these. (This would also be cheaper.)
Was your test done with the original or the new power supply and did you measure the total current (600 mA.)?

Les.

 

Hi Les,

thanks a lot for the tips. I’ll listen to your advice and buy the cheaper option

i didn’t measure the current(for some reason I assumed this was a given). ButI will measure it tomorrow.
I connected to the old power supply. Haven’t tried the new one yet