Adding to Halogen spots

[Gyn_Paul]

I have our temporary kitchen lit by 2 sets of 3 x 20w halogens on a rods-and-catenery-cables system. They are each powered by 60w electronic transformers (convertisseur electronique) I now want to add more lights to the cables (the wires themselves are more than capable of carrying the additional load) but can't find any transformers for 120w.

I plan to gang identical transformers in parallel (obviously paying very special attention to the polarity!)to give me double the current (double the current current, if you see what I mean !). Assuming the internal circuitry is identical in each convertisseur, does this sound like a plan? Given that they devices are kicking out AC, and I don't have access to a scope,, is there any way of checking they are each kicking out 12vac phased the same way? And if they're not what is the likely effect of parallel output connected contra-phase?

paul

[Maricopa]

If they are true transformers, then from the same supply their ouputs would more or less be in sync.  However, fed onto the same lines, I would expect them to double the size of the wave form.  IE produce 24VAC at about 120W not 12VAC at about 120W.  If they were out of sync, then the voltage produced would vary from 120VAC to 0VAC, depending on the phase difference.  However, without a circuit diagram, it would be difficult to ascertain if they are true transformers.  I would carry on looking for one with a 120W output.

[Nick Trollope]

No, it don't, I'm afraid. The chances of 2 "electronic" transformers (basically switch-mode power supplies) being in sync are ... remote... If they ain't you will (could) get lots of current flowing where it shouldn't be...

120 & 150W transformers (and SMPS) are available, from pro suppliers.

[Gyn_Paul]

"....120 & 150W transformers (and SMPS) are available, from pro suppliers."

Yeah, .... at a price which will make my eyes water, no doubt. Not a viable proposition really for a temporary kitchen to be scrapped in a few months time. Nothing for it then but to break up the current cabling into separate circuits of 4 x 3 lamps.

I take it, Nick, that this is because two different units wouldn't necessarilly chop the wave-form in the same place? So a common rail return wouldn't work either, would it ?

Thanks for putting your brains to it, chaps..

paul

[Nick Trollope]

I wouldn't matter if they did, because you can't guarantee the frequency and hence the phase relationship....

Because it is AC, a common rail would give you the same problems....

I can do you a 150W transformer for 33€60 + post + TVA.....

[tracteurtom]

Dont what ever you do connect the o/ps of 2 electronic t/fs together.  Those things are fragile enough (more Chinese rubbish).  The o/p freq is nothing like 50 Hz and probably not sinusoidal, the only thing that would happen is a smell of burning as they go into melt down !

Why not buy another string of lights, full set for a handful of euros ?  Last lot I bought have x5 20 W lamps and a proper transformer, cant remember the price but it wont have been much (I dont like spending !). 

Alternatively,  go LED.  Not checked them out properly yet, but I'm sure you can get LED versions of the 12V/20W halogens.  Check the load and my guess is you could have more lights than Blackpool Illuminations for 60 W worth !