I have a quick question about switching a transformer. Cabinet lights that I want switched powered from a 12V transformer. Is it better to switch prior to the transormer or after the transformer or does it matter. I guess the question is whether having the transformer energized all the time (switch after) or turning the transformer on and off (switch before) will affect the longevity/performance of the transformer. As always thanks for your help.
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Source control, ventilation, and filtration are the keys to healthy indoor air quality. Dehumidification is important too.
Featured Video
SawStop's Portable Tablesaw is Bigger and Better Than BeforeHighlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
Switch before.
I usually throw away the factory transformer, and use one with more capacity, or wait until it burns out (about 24 months) and then switch it out.
I install them in remote locations, basement, attic, closets, etc, and run a 120v switched line to a duplex outlet to which the transformer is plugged in.
Regards,
Scooter
"I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
So if I understand you are turning the transformer on and off. I have a nice system from eterna lighting with separate transformer etc. I'll be placing the transformer in a basement joist bay, running 12/2 to that and then on to the built in cabinet lights in a dining room which will have a wall switch for control. I guess I'm thinking of flourescents where I've been told leaving them on is actually better than turning them on and off. I don't know if that is true or not and whether thats an issue for ballast life or what. I wondered if the same may apply to a transformer in terms of switching on and off or having constantly energized with the switch downstream form the transformer. Thanks for your help.
sorry, I just noticed the first line of your post. Switch before. Thanks
I always switch before. Put fuse(s) or mini-breaker(s) in the low voltage circuit to protect the wire and the transformer.
There are no electrons! It is all made up. Don't believe it.
Electricity is made by GREENIES.
The transformer will, in most cases, last at least a little longer if you switch it on and off. Also, having the switch ahead makes it possible (if a little unsafe) to change out the xformer without having to choose between killing the circuit and doing the switchout "hot".
Note that if you switch the secondary, the switch must be rated for the current, which will generally be about 10x the primary current. Finally, some switches do not work well at low voltages, since they tend to have significant contact resistance that they rely on the high voltage to "burn away".
No electrons were harmed in the making of this post.
Of course, you should never put a transformer on a dimmer unless both units are rated for that duty.
--------------
No electrons were harmed in the making of this post.
DanH et al,
Thanks for the responses. The consensus is obviously to switch before the transformer which is what I'll do. One more question. What is a mini breaker that was mentioned, something that goes in line in the circuit itself? Thanks
Not entirely sure what was meant, but it's a good idea to install some sort of overload protection in the secondary circuit. This can be a fuse or some sort of breaker. I don't know where you'd get them, but I've seen breakers installed in equipment that were intended to stand alone (not in a breaker panel) and which had a "push to reset" button.
--------------
No electrons were harmed in the making of this post.
I wonder if there are transformers that have their own internal overload protection i.e. reset button.
Most have some sort of built-in overload protection, usually an auto-resetting thermal switch. (In fact, I'm pretty sure it's a UL requirement for lighting transformers.) But these tend to be unreliable and have a pretty limited cycle life.
--------------
No electrons were harmed in the making of this post.
I went to the web site of the company that has this lighting system and they actually offer two transformer types, electronic and magnetic. They both seem to have some sort of overload/short circuit protection built in. Is one type preferable to the other?
the advantage of electronic trans. is their smaller size, the disadvantage is their need to be close to the fixture(s) they are supplying. voltage drop is more noticeable with elec. ttrans than with magnetic, so they have to be in close proximity.. almost next to the fixtures...also, if you choose electronic transformers and you use decide to dim them, you will need an electronic dimmer as wella magnetic dimmer on those trans. will cause noticeable flickering of the lamps"
Most real electrical transformers will have a reset button on the unit.If you want to place an inline 12v fuse, similar to an automotive type fuse, that certainly wouldn't hurt. Me, I rely upon the reset button on the actual transformer.Regards, Scooter"I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
Well, my plan calls for the transformer to be in the basement and then have a run of about 25' to each of two corner cabinets that I'll be lighting. One thing this system uses is 10/2 cable for the low voltage side of things. Does that help to mitigate the voltage drop or would a magnetic transformer be a better choice? I don't plan on dimming so that is not an issue. The magnetic trans. are siginificantly more expensive and according to the website you need one that is rated such that the wattage you use is about 50% of the transformers stated range. So much for my simple question which started this thread ;).
its been my experience with the lighting that the small electronic trans. are almost in the fixture if not in a j-box next to them...as per some designer , architect, or the lighting guy...sometimes the location is in the job specsso yes, you will have better performance with the old magnetic type..event hough 25' is not that long for 10/2"
The electronic unit will generally be quieter, and should run slightly cooler. Will generally have more reliable/durable overcurrent/short protection than a magnetic unit. A minus is that it may produce some electrical noise that could be picked up by nearby TVs, etc.(Note liberal use of "generally/should/may" -- units can vary a lot from mfg to mfg.)
--------------
No electrons were harmed in the making of this post.
Very slight preference for before: There are tiny losses in the xformer that cost power and eventually a few pennies. Very remote chance of an internal insulation failure causing a fire, having it switched would make it more likely that you'd be there and awake.
That being said, doorbell and HVAC control xformers have been run 24/7 for nearly a century. I just took one out that was in continuous operation since 1926. For electrocution, the floating low voltage from the secondary may be a little safer.
-- J.S.