I found (a part of) the problem:

The soldered pin connections at start of the ribbon had leaking current. This was due to the soldering flux remaining around the pins. Rinsing the connection with water carefully solved the problem.

In earlier runs I soldered with flux and simply wiped it off afterwards. Also note that I am generous in flux usage. I do not know how people can make neat solderingwork without it. Just scraping, and wiping with tissues between the connections is apparently unreliable. The flux is water solutable, said the package, so I used tap water for cleaning, but I also tried alcohol at times. Of course by taking care not to make anything wet besides the connection, and drying careful afterwards.

Obviously I checked the look of my soldering earlier as well, and it looked quite neat in my opinion. Yet measuring resistance between pins gave varying results, also compared with unsoldered, which made me wonder why. Cleaning the area around the soldered pins seemed to remove this, which indicates that this may be due to the soldering flux that was remaining. I also heard that flux tends to start flowing again as it heats up under operation, which indicates why the connection seemed good right after soldering, but changed trough time. Perhaps this is why people use these ultrasonic cleaning baths or something.

About the led strips: They were one of the cheapest ones available.

About the power supplies: The first power supply is the 5v line from a PC power supply, which should be able to give quite some amps. ( i forgot how much exactly, but way more than I needed) The second power supply was a Lithion battery with regulator. The thing says it is able to supply 2 amps, but I stayed far away from this limit.

Thank you for your tips. You help me keep improving myself.

Any more tips on cleaning soldered connections are welcome.

I found (a part of) the problem:

The soldered pin connections at start of the ribbon had leaking current. This was due to the soldering flux remaining around the pins. Rinsing the connection with water carefully solved the problem.

In earlier runs I soldered with flux and simply wiped it off afterwards. Also note that I am generous in flux usage. I do not know how people can make neat solderingwork without it. Just scraping, and wiping with tissues between the connections is apparently unreliable. The flux is water solutable, said the package, so I used tap water for cleaning, but I also tried alcohol at times. Of course by taking care not to make anything wet besides the connection, and drying careful afterwards.

Obviously I checked the look of my soldering earlier as well, and it looked quite neat in my opinion. Yet measuring resistance between pins gave varying results, also compared with unsoldered, which made me wonder why. Cleaning the area around the soldered pins seemed to remove this, which indicates that this may be due to the soldering flux that was remaining. I also heard that flux tends to start flowing again as it heats up under operation, which indicates why the connection seemed good right after soldering, but changed trough time. Perhaps this is why people use these ultrasonic cleaning baths or something.

About the led strips: They were one of the cheapest ones available.

About the power supplies: The first power supply is the 5v line from a PC power supply, which should be able to give quite some amps. ( i forgot how much exactly, but way more than I needed) The second power supply was a Lithion battery with regulator. The thing says it is able to supply 2 amps, but I stayed far away from this limit.

Thank you for your tips. You help me keep improving myself.

Any more tips on cleaning soldered connections are welcome.

EDIT:

Oh boi! If it isn't the consequences of my own actions!

So this is what SN39 flux does to soldered wires in 2 years. This is a different object, soldered with the same acid based flux thats intended for copper piping, and not for electricals. I have quite some wonky soldering work to replace at my job. Don't be me lads, and only use flux thats intended for electricals.

I finally found the solution:

The soldered pin connections at the cable was leaking current. This was due to the soldering flux remaining around the pins. Rinsing the connection with water carefully solved the problem.

Just scraping, and wiping with tissues between the connections is apparently unreliable. The flux is water cleanable, said the cup. Of course by taking care not to make anything wet besides the connection, and drying careful afterwards. Perhaps it failed after a minute or so because the flux started flowing due to heating up.

Thank you for your tips. You help me keep improving myself.

Any more tips on cleaning soldered connections are welcome.

I found (a part of) the problem:

The soldered pin connections at start of the ribbon had leaking current. This was due to the soldering flux remaining around the pins. Rinsing the connection with water carefully solved the problem.

In earlier runs I soldered with flux and simply wiped it off afterwards. Also note that I am generous in flux usage. I do not know how people can make neat solderingwork without it. Just scraping, and wiping with tissues between the connections is apparently unreliable. The flux is water solutable, said the package, so I used tap water for cleaning, but I also tried alcohol at times. Of course by taking care not to make anything wet besides the connection, and drying careful afterwards.

Obviously I checked the look of my soldering earlier as well, and it looked quite neat in my opinion. Yet measuring resistance between pins gave varying results, also compared with unsoldered, which made me wonder why. Cleaning the area around the soldered pins seemed to remove this, which indicates that this may be due to the soldering flux that was remaining. I also heard that flux tends to start flowing again as it heats up under operation, which indicates why the connection seemed good right after soldering, but changed trough time. Perhaps this is why people use these ultrasonic cleaning baths or something.

About the led strips: They were one of the cheapest ones available.

About the power supplies: The first power supply is the 5v line from a PC power supply, which should be able to give quite some amps. ( i forgot how much exactly, but way more than I needed) The second power supply was a Lithion battery with regulator. The thing says it is able to supply 2 amps, but I stayed far away from this limit.

Thank you for your tips. You help me keep improving myself.

Any more tips on cleaning soldered connections are welcome.