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Bassman
09-28-2007, 03:40 PM
Does the transformer on a low voltage lighting system, such as a monorail, put out AC or DC. Inquiring minds want to know. Thanks.

jwelectric
09-28-2007, 05:49 PM
The transformer will state the voltage, wattage and hertz

Speedy Petey
09-28-2007, 05:53 PM
Usually AC, but what Mike (jw) said is better.

BrianJohn
09-28-2007, 07:20 PM
A Standard transformer coil to coil (primary to secondary) no rectifier will only transformer AC voltage. With the addition of a rectifier it can produce DC.

Bassman
09-29-2007, 11:22 AM
Thanks, I have a reasonable understanding of what transformers do, but I wanted to know whether to buy a DC or AC for the monorail light system. I'm purchasing online and the sites carry both. I'll be using two pin xenon lamps in the fixtures.

jwelectric
09-29-2007, 11:40 AM
They should be able to advise you on which one you need when you make your order.

jimbo
09-29-2007, 08:07 PM
A transformer can only take and AC input, and output an AC voltage. A power supply, which would include a transformer and some type of rectifier ( half wave, full wave, bridge) and would output DC votage.

Most light bulbs are rated for AC or DC, but not both, although with the proper circuit, you could possible use one either way. Basically, you should find out the voltage , number of volts, and AC or DC, for the bulbs you will use, then get the appropriate power.

hj
09-30-2007, 07:21 AM
Basically, for the same load DC requires larger wiring, (which is just one of the reasons the country does not run on DC), although for small loads the difference may be acedemic.

Furd
09-30-2007, 10:32 AM
Do you have a source for that, HJ? I've actually studied this a bit and while I can not find any specific source for D.C. ampacities it might be just the opposite of what you state because A.C. has a tendency to travel on the surface of the conductor. This is known as the "skin effect" and is why increasing the size of a conductor does not necessarily give a proportional increase in the ampacity.

Bob NH
09-30-2007, 10:45 AM
The skin effect is negligible at 60 Hz. The resistance is substantially the same for AC and DC.

One disadvantage of DC is that it is harder to extinguish the arc in switches because the voltage and current don't transition through zero. Therefore, most switching devices have lower ratings for DC than for AC.

Also, many (most) dimmers will not work with DC.

geniescience
09-30-2007, 11:03 AM
... I wanted to know whether to buy a DC or AC for the monorail light syste....availability of the bulbs,
cost of the bulbs, and
lifespan of the bulbs. - Some DC voltage systems are known to blow their bulbs a lot.

Those are three factors that would make me order one system over another.

Also, if I wanted to mix it with another type of bulb, I would have to stick with 110 V AC bulbs. No choice.


The manufacturer will say what the output of their transformer is. It keeps AC input as AC, and DC input as DC.

Another word for rectifier is inverter. A transformer combined with one of these is now a more complex device. Can be called a power supply. Cannot be called a transformer because it alters the type of output waveform, from AC to DC. or from DC to AC.


David

Bob NH
09-30-2007, 03:19 PM
A DC to DC device is a converter; not a transformer.

A transformer connected to AC is a short circuit, or very nearly so.

A transformer requires the inductance together with the alternating nature of the current to provide enough impedance to prevent the circuit from darwing too much current.

jwelectric
09-30-2007, 03:34 PM
A transformer connected to AC is a short circuit, or very nearly so.

Didn't you mean to say DC instead of AC in the statement above?

geniescience
09-30-2007, 05:40 PM
DC bulbs' lifespan may be shortened by the DC power source ("supply") even though the bulbs themselves may have an official lifespan in the thousands of hours. I have heard of that happening.

Someone else signed in here may know more and tell you more; I'd like to know too.

Bassman, this is to stay on topic and tell you things that relate to your question.

As for the guys wh want to discuss short circuits, impedance, inductance, converters and all that, I think I'll wait a bit and let Electrical Engineers add definitions and a little bit of direction. I am sure someone knows how to explain it all in a few words.

Besides, Bassman, you deserve an answer to your first question. After that, if people want to keep on discussing other things closely related to your question, I won't speak up to disagree.


David

Bob NH
09-30-2007, 07:59 PM
Didn't you mean to say DC instead of AC in the statement above?

Yes, DC will make it approach a short circuit; not AC.

Bassman
09-30-2007, 08:38 PM
Besides, Bassman, you deserve an answer to your first question. After that, if people want to keep on discussing other things closely related to your question, I won't speak up to disagree.

David

I figure I'll get an answer to my question eventually. :) In the meantime I'm learning some things! I think that for the layman end user the stores call all the above "transformers" even though technically some may be converters, etc. I'm sure when I place an order they'll be happy to sell me the correct thing.

jwelectric
10-01-2007, 06:11 AM
I'm sure when I place an order they'll be happy to sell me the correct thing. And here-in lies your answer as was given to you here (http://www.terrylove.com/forums/showpost.php?p=100828&postcount=6)

jimbo
10-01-2007, 06:34 AM
And herein lies the reason for his confusion, and he still doesn't have an answer, but maybe has been given enough information to figure out what he needs:

[quote=Bassman] I'm purchasing online and the sites carry bothquote]

Bassman
10-01-2007, 08:43 AM
And here-in lies your answer as was given to you here (http://www.terrylove.com/forums/showpost.php?p=100828&postcount=6)

Correct you are. I got an email from the vendor who states that their DC "transformers" are only used, and not often, in very long runs where voltage drop is a real problem. 99.999999999% of the time, AC is called for. That was the answer I was looking for.

tjbaudio
10-01-2007, 09:59 AM
It (A transformer) keeps AC input as AC, and DC input as DC.

Another word for rectifier is inverter. A transformer combined with one of these is now a more complex device. Can be called a power supply. Cannot be called a transformer because it alters the type of output waveform, from AC to DC. or from DC to AC.


David
Wrong! A transformer will convert Voltage and impedance for AC. If you feed a transformer DC it will block it. Depending on the transformer, circut voltage and power capasity some thing may get damaged. In other cases this blocking propterty is used to advantage.

An inverter does the oposit of a rectier. A rectifire takes AC and converts it to DC with ripple, filters in a power supply reduce this ripple to sute the application. An inverter takes DC and converts it to AC. This is a complex process.

A power supply in this case is a unit that takes the main house current and converts it to soem usable form for the system. It will contain a transformer. If it outputs AC that may be it. If it outputs DC there will be a rectifier also. None of this talks about a switch mode supply which is a compleatly different animal and beyond the scope of this conversation other than it can also supply DC current for your system. Recently the cost of complexity of a switch mode unit is offset by the cost of raw materials for a transformer.

BrianJohn
10-01-2007, 10:03 AM
Maybe he does not understand BUT THE answer was given more than once and VERY CLEARLY.