Wiring a Transformer for a Lab Assignment

[eev_carl]

Hi,

I'm taking a remote course and providing my own lab equipment.  This question is about the lab setup and not the course contents that I'll be graded on. 

I have to build the following circuit which involves a transformer.  A F-44X is suggested.  When I look up the product on Mouser, it shows 3 leads on one side and two leads on the other.

https://www.mouser.com/ProductDetail/Triad-Magnetics/F-44X?qs=b1anAsPanWwbs2JWOI%252BOnw%3D%3D

How would I go about working with this (including the fuse)?  I usually use my power supply or batteries for my circuits.  Are 1/2 W resistors the 1/16A fuse and hookup cable adequate for the circuit on the secondary coil side?

If you know of any commercial training materials that package a similar transformer as a fused cable ready-made for an outlet, please post.

Thanks,
Carl

[ledtester]

Let me take a crack at this...

The 553-F44X is a 115V to 12.6 Vct (2 A) transformer.

For a 12.6 VAC RMS voltage source the peak voltage will be 12.6*1.414 = about 18V.

The 1n4007 will drop maybe 0.5V, so the peak will be say 17.5V.

Power (P) = V*I = V^2/R so now you can compute the (max) power dissipated through the resistor at any point in time.

(In this particular circuit it could be argued that you could get by with a much lower power rating because of the half-wave rectification performed by the diode and considering the average power dissipated by the resistor, but it is always safer to perform this calculation based on the extreme conditions.)

For the fuse...

Let's say the secondary side draws about 20 mA (peak). The transformer has about a 10-to-1 turns ratio, so that means 2 mA on the primary side, so it would appear that 1/16 A (about 62mA) would be plenty.

The problem is that you also have to account for inrush current when power is initially turned on. Probably a 1/16A fuse will suffice. And it will depend on whether you use a fast-acting or slo-blow fuse. You might just have to try it and see if you start blowing fuses.

Btw - if you are going to play around with bare transformers and mains voltages I would invest in a "Quicktest" connector:

https://www.cliffuk.co.uk/products/tools/quicktest.htm
https://youtu.be/_DTmL73th7Y

It is a much safer way to connect mains power to your circuits.

[eev_carl]

Thanks.  Would a product like this work for my lab and be similar in safety to the Quicktest?

https://www.amazon.com/Jameco-Reliapro-MGT2450P-Transformer-Terminal/dp/B01N3ALUBS/ref=sr_1_1?dchild=1&keywords=jameco+ac+transformer&qid=1599100226&sr=8-1

[ledtester]

If you know of any commercial training materials that package a similar transformer as a fused cable ready-made for an outlet, please post.

Back in the last century a lot of devices ran on low-voltage AC power and so AC-AC adapters (even center-tapped ones) were widely available. For instance, a lot of 1990s modems and other consumer telecom equipment ran on low-voltage AC power. You might be able to find something suitable at a local surplus store or thrift store.

Getting exactly 12.6 VAC CT might be difficult, but you could, for instance, combine two 9VAC adapters to create a 18 VAC center-tapped one -- i.e . with two of these:

https://www.amazon.com/AC-AC-ADAPTER-9VOLTS-1000mA-2-1mm/dp/B00ATECBMM

You'll have to get the phase correct, but if you don't get it right you just reverse it. This article talks about transformers in series and phase:

http://engineering.electrical-equipment.org/forum/general-discussion/difference-between-series-parallel-transformer

Combining two AC-AC adapters like this won't get you something that is fused although they will be in a safe enclosure and the mains wiring will be robust and there also might be (non-replaceable) thermal fuses embedded within the transformers.

[ledtester]

Thanks.  Would a product like this work for my lab and be similar in safety to the Quicktest?

https://www.amazon.com/Jameco-Reliapro-MGT2450P-Transformer-Terminal/dp/B01N3ALUBS/ref=sr_1_1?dchild=1&keywords=jameco+ac+transformer&qid=1599100226&sr=8-1

Yes that would be a good and safe option.

[WattsThat]

If the secondary voltage isn’t an absolute requirement of 12.6 volts and 12 is sufficient, there is this style of plug in:

https://www.mouser.com/ProductDetail/Hammond-Manufacturing/BPD2E?qs=jcD%2FCkGBYeMCHHP9rapZhA%3D%3D

[WattsThat]

Upon more thought, you may need the recommended center-tapped transformer style for later labs and the plug in styles are not center tapped.

An option is an inline fuse holder with leads and just wire nut everything together (twist on connectors). For short term bench top testing, it’s okay. Just pull test all connections before powering. This unit is pricy, not necessary just a reference to the style.

https://www.mouser.com/ProductDetail/Littelfuse/01500603Z?qs=5aG0NVq1C4yGYRoxCosmNA%3D%3D

[eev_carl]

Thanks for everyone's help.  I'm going to use one provided by the school since I can't get one here quick enough.  The school's transformer is outfitted with a plug. 

The Quicktest recommendation seems perfect for what I was going to do.

On to rectifier circuits...