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lv lights dimming #206120
05/27/12 08:01 AM
05/27/12 08:01 AM
Alan Belson  Offline OP
Member
Joined: Mar 2005
Posts: 1,803
Mayenne N. France
I have some GU5.3 12v dichroic halogen luminaires [5 x 20W in a string suspended on a pair of catenary cables]. These are fitted in a utility room. I avoided low energy bulbs because of the lights being switched on and off regularly as we pop in to tend the machines. Yesterday I hung a row of wall cabinets, and spent a couple of hours in there fitting them and hanging the doors. The bulbs noticeably dimmed during this time. The 230v-12v transformer is a big wirewound unit, not electronic, and it got quite hot. Once it cooled off, normal output resumed. Anyone else noticed this problem?


Wood work but can't!
Work Gear for Electricians and the Trades
Re: lv lights dimming [Re: Alan Belson] #206124
05/27/12 01:26 PM
05/27/12 01:26 PM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,298
Estero,Fl,usa
What is the rating of the transformer?


Greg Fretwell
Re: lv lights dimming [Re: Alan Belson] #206125
05/27/12 03:12 PM
05/27/12 03:12 PM
L
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
Hang a voltmeter off of the transformer output terminals to see if the output voltage sags as the transformer heats up. If it does, check the input voltage to determine if it is sagging too.

The heat could be from overloading the transformer or a high resistance connection(s).

New thought: Is the transformer a 60 Hz transformer? Running a 60 Hz transformer on 50 Hz will cause it to over heat due to less inductive reactance. It is the same reason 60 Hz motors operated on 50 Hz run much hotter.

Re: lv lights dimming [Re: Alan Belson] #206126
05/27/12 05:54 PM
05/27/12 05:54 PM
G
geoff in UK  Offline
Member
Joined: Dec 2002
Posts: 193
UK
I would suspect that your transformer is marginally rated for the load you have on it. Think temerature coefficients.
As the transformer temperature rises so does the winding resistance, hence reducing the output voltage.
As the lamps consequently dim and the filaments cool their resistance will reduce, so increasing load. I think I can visualise a potential runaway effect here which could kill the transformer.

Re: lv lights dimming [Re: Alan Belson] #206130
05/27/12 07:44 PM
05/27/12 07:44 PM
Alan Belson  Offline OP
Member
Joined: Mar 2005
Posts: 1,803
Mayenne N. France
It's rated 105VA, 12V output, 230v 50hz, with 5 x 20W bulbs. Made in France, BTW. I have 3 of these units in various locations. No probs with the other two, tested today. I'll check out the wiring tomorrow.


Wood work but can't!
Re: lv lights dimming [Re: Alan Belson] #206136
05/27/12 11:29 PM
05/27/12 11:29 PM
T
twh  Offline
Member
Joined: Mar 2004
Posts: 947
Regina, Sask.
100 watts at 12 volts is 8 amps. If a connection was even half an ohm, it would drop a couple volts.


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