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A lot of online resources never question the use of high amperage power supplies for powering LED Strips. As an example, 5 meters of low density (30 LEDs per m) WS2812B strips already use 30 * 5 * 0.06A = 9A at 5V. I have serious concerns about safety since the contacts and cables inside these strips have to be very thin and, to my knowledge, high amperage and thin wires don't mix very well.

My Question is: How many Amps are safe when powering LED Strips?

Side questions: Should I use 12V strips to lower the voltage? How would I safely power an arbitrary amount of LEDs (say 20m of strips, preferably only using one power supply).

Thank you for your answers!

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  • \$\begingroup\$ I'm pretty sure this question has been asked in some form several times. \$\endgroup\$ – Voltage Spike Mar 26 at 16:44
  • \$\begingroup\$ I thought that too but I only found questions about the strips drawing less power than expected. Nothing about safety or fire hazards. If you find a similar question I would be very interested! \$\endgroup\$ – Mr.Yellow Mar 26 at 16:50
  • \$\begingroup\$ Are you asking about using high current capacity power supplies with 5V strips, or are you asking about daisy-chaining a number of strips, where strip C gets its power from the far end of strip B which gets its power from the far end of strip A which is plugged into a power supply? \$\endgroup\$ – TimWescott Mar 26 at 17:58
  • \$\begingroup\$ for larger setups, you want to deliver power to more than just one end of the strip; at least both ends, sometimes in the middle as well if needed. I don't like to go more than 100 LEDs w/o another rail, except 144/m, where you can go one meter safely since it's of short length... \$\endgroup\$ – dandavis Mar 26 at 20:34
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How many Amps are safe when powering LED Strips?

The number of Amps supplied by a power supply is essentially irrelevant when compared to the Amps flowing within an LED strip. In terms of safety, the only issues is that of current flow is enough to cause a significant overtemperature in the connections/wires that could cause a fire.

How many Amps per strip?

I see some crap predictions of how many Amps are required per strip, but the manufacturers of the LED strips do provide guidance as shown here.

The note here provides ample guidance: "Do not exceed 2 meters in a single circuit. Longer runs should be powered from both ends to reduce voltage drop."

While the WS2182B LED chip will work with an applied voltage from 3.7-5.3V the current drawn from the supply will vary since an internal step up DC-DC converter provides the voltage for the constant current driver. The latest WS2182B datasheet shows that the CC drive per LED is 12mA, and this will be reflected as a current from about 27mA @5.3V (per LED) through to almost 40mA *3.7V (per diode).

This means that for your example of 180 LEDs @5.3V you might expect:
0.027 * 3 * 150 = 12A.
If your power supply was dropped to 3.7V (or there was voltage drop in your supply lines) then the current would increase to about:
0.04 * 3 * 150 = 18A.
So as the voltage drops the current required increases and the I^2R losses in your wiring increase.

Along with this current you can now see that the manufacturers recommendation for no more than 2m of LED strip (and powered from both ends) comes into play.
Your application could consist of two 2m strips and a 1m strip. The current for the 2m strip would be:
0.027 * 3 * 60 = 4.86A
...and for the 1m strip about 2.5A
If you power the 2m strips from BOTH ends, then the current per end is about 2.5A

The 2m strips would be powered from both ends, the 1m strip from one end. With these current densities the strip copper conductors should adequately handle the load.
It's up to you to ensure your external wiring can handle this load, but since the maximum load current is 2.5A then you only need a 20-22AWG wire.
It's also worth noting that most of the LED strips come with JST connectors on one end and flying leads for the supply on both ends. the JST plugs/sockets are only rated to 3A and so should not be used to power long strips.

Would moving to a 12V based WS2811 help?

It depends, the WS2811 driver chip does not have the DC-DC converter but when used at 5V offers no real advantage. However when used at 12V you can drive 3 * LED pixels with one driver and get at least a 50% drop in current. The downside is that you address three pixels with one driver. This works out fine if you want general lighting, but is not suitable if you want control of every pixel LED in the strip.

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This chip uses only 3.5V minimum so that the voltage drop at max current is less than 1.5V and temp rise ought to be acceptable for the conductors of 5m at 9A < 1.35W. You should expect that it is safe.

Some SMPS floating supplies may introduce EMI on data by Common mode noise if excessive , which may requires attention to supply noise specs and possibly better suppression with better 1nF CM filter choke + caps to earth gnd.

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  • \$\begingroup\$ Thank you for your comment on interference, I will look into it! \$\endgroup\$ – Mr.Yellow Mar 27 at 7:19
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I found a Video showing possible outcomes of such a situation. A fuse is highly recommended. Translation of Title: Flexstrip without fuse can cause fires. A thermocam makes it visible...

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