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I have an approximately 1 meter LED strip in "warm white" running from a 2 amp power supply for some time now with no problems. I want to add another strip, of about 2 meters, to this same power supply. This second strip will have a switch on it, so sometimes the power supply will power 3 m of LEDs, sometimes just 1 m.

Should I up the amperage? Is it better for the amperage to on the high side or on the low side?

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closed as unclear what you're asking by Passerby, Wesley Lee, DoxyLover, pipe, RoyC Nov 4 '18 at 14:55

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    \$\begingroup\$ Possible duplicate of Choosing power supply, how to get the voltage and current ratings? \$\endgroup\$ – Passerby Nov 3 '18 at 20:31
  • \$\begingroup\$ Your power supply's current capacity should exceed your current draw. Often by 10 to 20 percent more. So if you need 4 amps a 5 amp supply us better. For your specific need , you need to know how much current each meter takes. \$\endgroup\$ – Passerby Nov 3 '18 at 20:33
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    \$\begingroup\$ what do you mean by high side and low side ? \$\endgroup\$ – jsotola Nov 3 '18 at 22:09
  • \$\begingroup\$ Sorry #jsotola I meant is it better to have more amps than needed or less? Since posting from other comments and links provided I understand it's more. \$\endgroup\$ – MReinhart Nov 5 '18 at 18:48
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You need to know how much current a 1m LED strip uses. It can work fine with a power supply with a rating of 1000A but yours is 2A and it might be able to power many meters of LED strip.

When you find out the current for 1m then you can calculate how much current 3m uses. Get a power supply that has a maximum output of a little more extra current or a lot more.

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    \$\begingroup\$ Note that LED strip current consumption depends on how the supply wiring is routed to the strip. After a meter or two, the resistance of the strip itself becomes significant and reduces the current draw. So a single 5m length with one supply connection will draw less current than five individual 1m lengths. This is more of an issue with lower voltage strips, but still noticeable at 12V. \$\endgroup\$ – ajb Nov 4 '18 at 6:16
  • \$\begingroup\$ @ajb that's true for 5m, but 3m won't be too noticeable. The typical recommendation is to power both sides or in the middle of a 5m strip for best uniformity, 3m isn't too far from 2.5m \$\endgroup\$ – Passerby Nov 4 '18 at 6:23

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