Transformer hookup for mini lighting

V8C · Aug 20, 2008

Hi,

I'm looking for some advice if possible regarding a project that I'm trying to complete. I have some mini lighting (single LED) that at the moment runs from 3xAAA batteries (4.5v). I've done some testing with the batteries in and I'm getting a supplied power of 4.66v @ 122mah from the batteries into each unit. I want to change from batteries to mains supplied power via a 4.5v transformer. Firstly, is this possible to do and secondly, what sort of transformer can I use? Secondly, I want to string a load of of these lights together to all run from the same switch - should these be in series or parallel? I have spotted a 4.5v, 600ma transformer (DAGNALL ELECTRONICS | D3613 | Transformers & Accessories | Electrical & Circuit Protection | Farnell UK). Is this suitable? How many lights would I be able to use from this unit?

All advice very greatly appreciated.

Ben

wayne · Aug 20, 2008

you seem to know your numbers so can work out how many .parallel circuit,
what do you need to do toget mains voltage to the tx

Mike P · Aug 20, 2008

Hi V8C.

LED lights require a constant current supply (a bit of a speciaised kit) so I don't think the just the transformer you are sugesting will do the job. you are using a DC supply (batts) at the moment so it probably needs to be a DC regulated power supply.

wattsup · Aug 20, 2008

You could wire in series, say from a 50v transformer, but you are limited to 11 led's, no more can be added, and none can be taken away, if one fails they all fail.

So you really need to wire in parallel, from a 4.5 transformer. You will need to check wattage on each lamp and total up. If possible the switch should control the transformer feed and not the output lighting feed, otherwise you may get vd probs -

not sure, but led's should work on ac or dc, all my led's run on 230v ac, yours run on dc...fluros should not be ran on dc, even though they will work, for a while!

V8C · Aug 20, 2008

Okay, so lets see. Assuming I got a 230v ac input, 4.5v dc output transformer - putting the switch inline from the mains source to the transformer, then this should work right?
You guys seem to be saying that leds will work with ac as well? In which case then this appears to make the choice of transformer a bit easier.

FYI, background info - I'm a bit of a bodger, in that I'm buggered if I'll pay £40 - £50 for something I can probably make myself for a tenner. So in this case, rather than buying a light kit with mini led lights and a transformer that plugs into the wall socket I'm making my own with a set of mini led's that are currently batt operated and a seperately sourced transformer unit wired into a suitable mains power supply to simulate the battery input.

----------------------------------------------

Me again....

Actually I'm finding issues getting a transformer that only posts 4.5v out... most seem to be 6v+. Now if I hook 6v up to these LED's I'm going to burn them out very quickly right (or blow them immediately)???

tony.towa · Aug 20, 2008

I must admit I was under the impression that LEDs work on either a DC voltage or pulsed DC as they have an anode and cathode. That being the case a rectified and smoothed DC produced from a 4.5 volt transformer would be approximately 7 volts.

V8C · Aug 20, 2008

Fixed Voltage Regulated Mains Adaptors > Maplin

MG77J ??

Will rigging the lights in parallel not drop the impedance / bugger the supply?

wattsup · Aug 21, 2008

I though all diodes would work either way, ac or dc?
Mine seem to be doing ok after 6-months, none blown (unless they have some secret inbuilt device in the lamp)

greekislandlover · Aug 21, 2008

A diode can be used as a rectifier, and if you put ac through it, it will light on one half of the cycle, and not on the other. If you could see this in slow motion, it would be flashing at 50hz rather than the constant light of a dc supply. So you can put AC through it, but not the most efficient way of driving an LED methinks. The diode won't blow unless the reverse bias is higher than it's rated at.