# Which power supply do i need?

#### Lampy

##### New elf
Hi, i am making 8 led light tubes. they consist of two led strips in each. Each strip has 80 leds which are 0.3w each.
The strips take 5v. My question is what are the specs needed from a psu to power all of the strips (16) with them running at full load? I want the full brightness possible.
I have a psu from a computer which says it has 12amps DC output on the 5v line. Would this be a seperate 12amps down each of the red 5v wires or spread across all of them? Thanks

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#### fasteddy

##### I have C.L.A.P
Global moderator
From this thread we can get the current of the 64 LED/metre strip (and other strip) which is calculated to be 3.06 amps per metre.

Now all you have to do is add up all the current of all your strip which is 16 x 1.5 metres = 24 metres

So 24 metres x 3.06 amps = 73.44 amps total. So you may be best dividing the load between 2 x 5vdc 350 watt power supplies as the computer power supplies will not produce enough current to sufficiently drive these

#### Lampy

##### New elf
Thanks very much for the reply. Would you say it's ok to use the 5v part of a atx psu or would it generally not give enough amps/watts? Cheers

#### fasteddy

##### I have C.L.A.P
Global moderator
Lampy said:
Thanks very much for the reply. Would you say it's ok to use the 5v part of a atx psu or would it generally not give enough amps/watts? Cheers
Considering you need 73 amps to drive it all then you will need a few ATX power supplies and depending on the age and type then these may not work with using the 5vdc side as they are designed to use the 12v rail as well. If you had a few of these lying around that could drive this all then i would just test and see how it goes, but yoyu will definetly need a few of these to make up 73 amps.

As far as what the output rating is of the ATX power supply is hard to say without looking at the rating plate on the power supply because some will just give the total current of the rail and others use seperate rails and rate the individual rails. In the end the best solution is to use 2 x 350 watt power supplies that i mentioned earlier

#### Lampy

##### New elf
Yeah, that all makes sense. Was trying to keep costs down by using items i could get easily.
Seeing as i need 76.8 amps, i think i will split it into a psu for each side (4lights) 38.4 amps each.
Seems like the only source for high amp 5v psu's is from china.
This will be a bit costly due to import tax but may be [SIZE=small]the best option.[/SIZE]

#### ecbailey

##### Full time elf
It is definitely sensible to use normal transformer or switch mode power supplies instead of computer PSUs (power supply units).

Remember that you need over 70 amps at 5 volts. This PSU, from a well regarded name brand, is capable of 550w total output, however for 5 volts, is capable of only 18 amps. Therefore, you would need 4 of them. Whilst this would probably save some \$\$, it would be more time consuming then using a normal power supply.

Also, the PSU also needs to be started (I think) (I can't remember how to do this sans computer). A normal power supply, as you probably know, is turn on at the wall and away it goes.

However, if you needed a mixture of 12 and 5 volt power, then the computer PSU would likely be a more sensible option.

#### fasteddy

##### I have C.L.A.P
Global moderator
The calculated load is 76.8 amps but with most power supplies you need to have a 80% to 85% rule which means that the total load applied to a power supply should only be 80% to 85% of the rating of the power supply, this is to take into account the inneficiencies of the average power supply. So the total rating you should be looking at very least is 88.32 amps or approx 441.6 watts of power.