AC test transformer

A short on a doorbell transformer is not likely to blow a fuse, They are typically designed to be energy limiting.

The transformer design won't help if the primary short to the case somewhere between 0 and 120V. In an audio amp I was servicing, that precisely happened. No fuse blew because it used a 2 prong cord. So, the metal chassis/knobs were say at 60VAC.

There is reasons, at times, to fuse both.

Fuses primarily protect the wiring.
 

Thread Starter

timbaker0365

Joined Aug 11, 2020
32
Without looking at it I'm pretty sure the 8V tap which I'll be using is rated @ 10VA, so it appears 1.25A is max on that. So if I put a 1A fuse on the secondary I should be good, correct? And what I meant earlier about not fusing both pri and sec is, if the sec is drawing say 1.25 amps max, or 1A with my fuse, and it blows that should protect the primary since it won't "conduct" current if the secondary isn't drawing any... correct? Thanks again.
 

Thread Starter

timbaker0365

Joined Aug 11, 2020
32
There is reasons, at times, to fuse both.

Fuses primarily protect the wiring.
Thanks KISS.
Well, I have set of duplex outlets in a box on its own circuit with a 15A breaker and good ground where I plan to plug in the transformer, and I intend to ground the box/transformer housing as well, so if something shorts on the primary side I think I'll be covered so I'm not planning on splicing in a fuse there at this time. I will put one on the secondary side though, as was planned. At this time I only have 1A fuses though, I have to get some more smaller ones though as most of my devices I'm working with aren't rated for high wattage I don't think. It seems in the back of my mind that the resistors I have are 1/4 watt - does that sound right? And if so if I only have protection @ 1A, that could lead up to 8 watts with the 8V supply... I don't plan on any circuits anywhere near one amp right now but just to be safe(r). Thanks.
 
This is a gizmo you would like to "play with"? So, I would put a panel mount fuseholder on the secondary so you can vhange the size of the fuse as necessary for your "current project" and I would put a LED lamp on the secondary after the fuse. Power in to the fuseholder goes to the back of the fuseholder to make it "shock safe". I'll bet your box is too small?

I'd use binding posts as well.

There is all sorts of LED stuff you can get. You can even get a switch that would have a 24 VAC LED lamp in it. Push button, light comes on.

These A6 https://www.idec.com/language/english/catalog/Switches/A6Series.pdf series are not cheap and may not even have the right ratings, but you can label the buttons using either transparency film or black on clear and the info is protected.
You can use it for the lamp, if nothing else and label it say 16 VAC 1A or whatever.

You can install using crimp terminals.

They don't seem to have any 24 VAC ratings, but who cares, you can switch the primary of the transformer. The LED color needs to match the Lens color.

The A6 style, you can tell the position of the switch without power. The 22mm style has all sorts of contact blocks.

The 22mm versions might be even better.

I've used a few hundred of these for projects at work.

I used another companies style (ALCO) which I liked because the switches clipped in and the base disconnected from the switch, but unfortunately they redid the design and created much worse reliability than what they had. As they died, they got replaced by Idec. They were incandescent lamps.

The heat and UV light would degrade the nylon lens clips and they would just break. Then what did they do? They put an o-ring seal around the lamp and plastic and they died faster.

If you want a reliable product, you have to pay attention to the ratings. There are AC ratings, DC ratings, switching current, carry current, inductive ratings, minimum current ratings,

You don't use a 20A contactor to switch a few mA, There is a wetting current typically needed to "clean" the contacts or contacts need special plating. How they activate is another problem.

Case in point. A ceiling fan slide switch that reverses the fan direction. Always switch the direction when the fan is off. The fan can last for decades if you do that.

If you want to use a standard LED, you need to use a diode to get DC because the reverse voltage max is about 7 Volts. You also need a current limiting resistor and you can include the LED voltage drop which is dependent on the color of the LED which is about 2.1V. A diode drop is about 0.6V.

These are just ideas.
 
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