Electrical help required for 12v lighting

[bonzodog]

I have acquired 2 x 12v LED work lamps which are very bright and as they are also quite small they are perfect to put one on top of each PA speaker to light us up. I've attached some coloured gels to the front of them and although they don't flash I've basically got enough light to illuminate a decent sized pub stage for nothing.

However I'm a bit confused with watts and amps so want to ensure I'm doing it safely.
The lights are 15w each (5 x 3W leds) and have a positive and negative wire coming out. I have connected each of
them to a 12v power supply from maplin which is rated at 1.5amp load but I am unsure if this light is too powerful for the power supply.
Ideally I want to connect both lights to the same power supply and thus only have one plug.

I was always under the impression you divided watts by volts to get the amps which means a 15w light at 12v is 1.25 amps but am confused whether this makes a difference now it's connected to a 240v mains plug.

Maplin do power supplys with much higher amp ratings but they start getting expensive.

Any electrical help would be appreciated.

[Dad3353]

[quote name='bonzodog' timestamp='1467122863' post='3081319']...which means a 15w light at 12v is 1.25 amps...
[/quote]

Your maths is right; each lamp will draw 1.25 A, so you'll be needing either an 1.5 A psu for each lamp, or a single psu able to support a minimum of 2.5 A. Running both from the 1.5 psu will overload it, and could cause trouble. It would be normal to have a little bit of margin, so I'd say a 3A psu would be better if you're running both from the same one. On the other hand, separate psu's would be more 'fail-safe', and could make for better cable runs.

Edited June 28, 2016 by Dad3353

[bonzodog]

[quote name='Dad3353' timestamp='1467123773' post='3081325']


Your maths is right; each lamp will draw 1.25 A, so you'll be needing either an 1.5 A psu for each lamp, or a single psu able to support a minimum of 2.5 A. Running both from the 1.5 psu will overload it, and could cause trouble. It would be normal to have a little bit of margin, so I'd say a 3A psu would be better if you're running both from the same one. On the other hand, separate psu's would be more 'fail-safe', and could make for better cable runs.
[/quote]

Great. Thanks Dad for the reassurance. Yes separate runs would be better anyway.

Although they don't flash it's a nice compact system. Just need to decide what colour gels to use as I have a selection to try.

[Dad3353]

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[4stringslow]

Just to add a minor point, most small psus these days are 'switch mode' devices and decent ones will be short-circuit and overload proof. So, if you did overload them they will simply limit their output to protect themselves from failure. As Dad rightly pointed out, this might 'cause problems' insofar as the lamps would not work, but it's unlikely to actually damage anything.

I agree with Dad's suggestion of running each lamp from a separate PSU.

[rmorris]

[quote name='Dad3353' timestamp='1467123773' post='3081325']
Your maths is right; each lamp will draw 1.25 A, so you'll be needing either an 1.5 A psu for each lamp, or a single psu able to support a minimum of 2.5 A. Running both from the 1.5 psu will overload it, and could cause trouble. It would be normal to have a little bit of margin, so I'd say a 3A psu would be better if you're running both from the same one. On the other hand, separate psu's would be more 'fail-safe', and could make for better cable runs.
[/quote]

Yes - definitely adviseable to have some headroom on the psu spec.

[Norris]

Why not use a proper "LED driver" - less than a tenner each on Amazon? They are transformers specially designed for the job