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Author Topic: Simple electronics question  (Read 338 times)

Offline nate80

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Simple electronics question
« on: February 13, 2018, 17:25:14 »
I think it's simple anyhoo!   :laugh:  And it's kinda off topic but electrics are electrics, so here goes.

To set the scene: I'm building a 2 tiered enclosure for a couple of 3D Printers.  Each of the 2 tiers has a fan and some LED strip lighting.  Before I buy a transformer I just want to be sure I'm buying the right one (or 2, if that's the more sensible approach).

The fans are 12V and 0.16A max (1.92W) each, and there's 2 of them (which will both run at the same time), so that's 12V 0.32A (3.84W).  Math's extraordinaire, me!   ;)

The white LED strips are 12V 5050's with 60 LED's per meter.  Each SMD is rated at a MAX 0.24W, so that's 14.4W per meter.  I'm using 2 meters (one meter per enclosure) = 28.8W (2.4A) and will want to wire them up so the lighting for each enclosure can be switched on and off independently.

So my main question is, is there any reason I can't wire the 2 fans and the LED strip lights into one 240V AC to 12V DC transformer? As far as I can tell a 12V 36W LED driver would happily power the lot.

Otherwise (and it may be more sensible incase the one transformer dies for any reason) I reckon I could power the 2 x fans off of a 12V 5W transformer and the LED's off of a 12V 30W transformer.

What's the thoughts?  One transformer or two?

Cheers.  ::)

Offline ched999uk

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Re: Simple electronics question
« Reply #1 on: February 13, 2018, 18:04:44 »
As long as the wattage is bigger than max load plus a bit more (some things take a surge when starting up) you will be fine. When you say 'transformer' I assume you mean a power brick adapter running from mains voltage to 12v dc? Only reason I ask is that a transformer is normally an AC to AV voltage converter and LEDs and most little fans run on DC!
Have you not got an old power brick kicking about? Think old set top box, router etc type power brick they are normally marked with their output voltage and power.

Offline nate80

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Re: Simple electronics question
« Reply #2 on: February 13, 2018, 23:31:31 »
Cheers mate.  I've spent the evening re-stoking the fires of my mind when it comes to electronics.  I've got plenty years experience, but I tend to forget specifics until I remind myself of the 'rules' again.   :rolleyes:

By transformer I mean a 240 AC to 12V DC power converter offering suitable power output.  So technically a driver I guess.

I was thinking it's maybe a better bet to run the LED's and fans off of separate drivers.  From my experience LED driver's fail fairly regularly (tend to overheat and go pop) and I don't want the fans to stop spinning.  Maybe that's just me being paranoid.

I may have a power brick in the old cables box in the loft.  It's proper freezing tonight so I'll go check it out tomorrow - when it'll probably be just as cold!  :laugh:

Offline mo_miah

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Re: Simple electronics question
« Reply #3 on: February 14, 2018, 09:15:56 »
I'd stick to a single 12v power supply, and as said above get one with the rated load you need and add a bit more, power supplies will have an efficiency rating which will need to be taken into account, i think the average is about 85%

Offline nate80

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Re: Simple electronics question
« Reply #4 on: February 14, 2018, 10:30:51 »
Sounds about right.  From my experience its always best to go a minimum of +10% on the load.  In this instance the LED strips, rated at 60W per 5 meters, are reported as only actually using half that at 12V so, as I'm only using 2m length plus 4 more watts (fans), I'm certain a 36W driver will be more than enough.

I was more concerned about current pulsing or fluctuations caused by the fans that could lead to LED flicker etc.  Not the best example, but when installing 3 x LED spots in the ceiling of a bathroom, for example, you'd never use a single transformer to power the lights and a wall fan (it's not even legal afaik).  A poor quality fan can lead to the lights flickering, which will wear the driver out faster.  Plus, it's inconvenient as if the single driver blows you loose all the lights and the extraction.  Same principle here, I was thinking.  But because the load of the parts I'm installing is so small maybe it's not so important.
« Last Edit: February 14, 2018, 10:40:28 by nate80 »

Offline mo_miah

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Re: Simple electronics question
« Reply #5 on: February 14, 2018, 11:29:37 »
all the components are in parallel so if one fails the others will work, if the lights turn off no big deal, but extraction is important
a single power supply will be ok, just get something decent quality and not a cheap ebay job

Offline ched999uk

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Re: Simple electronics question
« Reply #6 on: February 14, 2018, 11:44:42 »

I was more concerned about current pulsing or fluctuations caused by the fans that could lead to LED flicker etc.  Not the best example, but when installing 3 x LED spots in the ceiling of a bathroom, for example, you'd never use a single transformer to power the lights and a wall fan (it's not even legal afaik).  A poor quality fan can lead to the lights flickering, which will wear the driver out faster.
As far as I am aware the single transformer (I think AC to AC) per downlighter is for 2 reasons. 1 they are small enough to fit through the downlighter hole, so when they fail its easy to dake downlighter out and pull transformer out to replace. The second is that downlighters used to be upto 60 watts and the transformers get hot, so having smaller single units there is not a concentrated source of heat. Remember that there might be insulation around downlighters and transformers etc.

Anyway your LEDs and fans will be fine on a single adapter. If you are concerned about the LEDs taking out the fans maybe fuse them appropriately i.e. in the 12v supply to the LEDs, you can just use car type blade fuses. That way just the LED fuse blows and the fans on their own fuse continue to run.

Have fun and stay safe.

Offline nate80

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Re: Simple electronics question
« Reply #7 on: February 14, 2018, 15:45:32 »
As far as I am aware the single transformer (I think AC to AC) per downlighter is for 2 reasons. 1 they are small enough to fit through the downlighter hole, so when they fail its easy to dake downlighter out and pull transformer out to replace. The second is that downlighters used to be upto 60 watts and the transformers get hot, so having smaller single units there is not a concentrated source of heat. Remember that there might be insulation around downlighters and transformers etc.

Anyway your LEDs and fans will be fine on a single adapter. If you are concerned about the LEDs taking out the fans maybe fuse them appropriately i.e. in the 12v supply to the LEDs, you can just use car type blade fuses. That way just the LED fuse blows and the fans on their own fuse continue to run.

Have fun and stay safe.

Thanks, that's great. I'm sure you're right and I've bought an appropriate 40W driver that will power everything happily - including 2 digital thermometers I've added into the mix. Fuses - of course. Should've thought of that. :rolleyes:

Now just got the wait for the slow boat from China.  :waiting:

Cheers

Nate