Help replacing the power cord on an old clock.

[Spork Schivago]

Hi,

I have an old clock, Cosmo Time, Model: E529B. My mother loves it and she's having trouble adjusting to different alarm clocks. The power cord broke. It broke real close to the transformer. I'd like to unsolder the wire from the transformer and replace the whole thing.

I've taken the transformer casing apart and gotten to what I would call the actual transformer. Here's my question. There's yellow tape around it. I've cut it open to get to the wires I need to unsolder but I'm curious as to what the purpose of this tape actually is. I've seen it on many transformers. Is it just to act as an insulator? Can I just use normal masking tape to tape this yellow tape back together, where I cut it? It was very brittle and I just used a pair of tweezers to gently pry up to take a peak underneath and it just tore.

Thanks!

[lookimback]

Re: Help replacing the power cord on an old clock.

I'd prefer something like Kapton, because it's heat resistant and I have it already. But I think masking tape would be fine over the original tape. I don't know what the actual tape is. It's purpose is probably just insulation. Maybe to protect the windings?

[mariushm]

Re: Help replacing the power cord on an old clock.

To protect the end user, a transformer has to be made in such a way as to follow several safety standards, one of them requiring a certain insulation between layers of windings on the primary coil. For example, in case the transformer gets too hot and the normal wire insulation (enamel) burns out or it's scratched or damaged in some way the layers of extra insulation help prevent arc-ing between layers of windings or in general help with protection of the primary winding.
The material used has to reach some minimal technical parameters like not absorbing humidity from air (as regular paper would slowly do), be insulator enough to resist let's say 2500v between layers of primary windings etc etc

The tape over the transformer (on top of everything) is most likely for protection.. like don't let user accidentally scratch the primary windings with a screwdriver, add insulation just in case a designer routes some small signal wires near the transformer.

Plastic is very cheap and easy to use when the transformer is made, kapton is much better (more heat resistant, better insulation, basically better overall) but it's more expensive, masking tape is not great (if it's sticky masking tape the sticky stuff may not be a good insulator, it absorbs humidity from air etc) but it would be good enough to use over the windings.

I'd rather you use proper electrician tape instead of masking tape.

[Spork Schivago]

Re: Help replacing the power cord on an old clock.

Okay, I got it all back together and she works like a charm! Thanks for the help! I used a combo of electrical tape (the black stuff) and masking tape (the whitish coloured stuff) to make sure the black stuff held onto the yellow stuff!

[Spork Schivago]

Re: Help replacing the power cord on an old clock.

To protect the end user, a transformer has to be made in such a way as to follow several safety standards, one of them requiring a certain insulation between layers of windings on the primary coil. For example, in case the transformer gets too hot and the normal wire insulation (enamel) burns out or it's scratched or damaged in some way the layers of extra insulation help prevent arc-ing between layers of windings or in general help with protection of the primary winding.
The material used has to reach some minimal technical parameters like not absorbing humidity from air (as regular paper would slowly do), be insulator enough to resist let's say 2500v between layers of primary windings etc etc

The tape over the transformer (on top of everything) is most likely for protection.. like don't let user accidentally scratch the primary windings with a screwdriver, add insulation just in case a designer routes some small signal wires near the transformer.

Plastic is very cheap and easy to use when the transformer is made, kapton is much better (more heat resistant, better insulation, basically better overall) but it's more expensive, masking tape is not great (if it's sticky masking tape the sticky stuff may not be a good insulator, it absorbs humidity from air etc) but it would be good enough to use over the windings.

I'd rather you use proper electrician tape instead of masking tape.

I didn't get your post until I had finished mine. I used the black tape. We call it electrical tape. I believe that's the stuff you're talking about. I used that to hold the yellow tape together where I cut it. But because I couldn't wrap it around like they originally did (there was some square bracket heat-sink type looking thing in the middle going around the whole thing that I couldn't remove, I just used the electrical tape to go as far down as I could without touching the heat sink. Then I went the other way around with masking tape, just to make sure the electrical tape would hold. I then put the covers back on (which should theoretically hold the tape in place anyway.) These covers have some sort of insulation on them as well. There seems to be a lot of redundancy. Maybe back then, houses weren't as safe and if an electrical device failed, it could easily start a fire or something? I dunno. But she's back together and seems to be working just fine.

Keep in mind, all the tape I added was just to secure the yellow tape back into place. The yellow tape is still there, it's just been cut. We folded it back into place and then tried taping that together.

[budm]

Re: Help replacing the power cord on an old clock.

http://www.alibaba.com/product-detai...57.35.1.z3NSJZ

MYLAR TAPE

[keeney123]

Re: Help replacing the power cord on an old clock.

It should be alright depend on how hot the transformer gets. The black tape is vinyl tape. Has a tendency to dry out with heat making it brittle. Because it is on the outside of the yellow tape it should be fine. Rubber tape holds up better with temperature. When I was an electricians assistant at 18 years old we used rubber tape on lug connection for 660 volts AC. Then after wrapping then many times with rubber the vinyl tape was used.

[stj]

Re: Help replacing the power cord on an old clock.

i would have painted it with epoxy.

[Spork Schivago]

Re: Help replacing the power cord on an old clock.

http://www.alibaba.com/product-detai...57.35.1.z3NSJZ

MYLAR TAPE

Thanks for the info. I've read the PDF from Digikey, very informative. I've also researched these bobbin wound transformers after reading it.

That link to Alibaba.com, I can't order nothing from them. I've tried before. I mean that link says I need to order a minimum of 30 but even if I tried, I can never actually order it. It sends me to some site where I have to write a message to the company selling it and ask them to sell me stuff and they never get back to me.

Was that link just so I'd know what to get? Or was I supposed to actually order from them?

Thanks.

[budm]

Re: Help replacing the power cord on an old clock.

Just to show what the MYLAR tapes look like.

[Spork Schivago]

Re: Help replacing the power cord on an old clock.

Thanks Budm. I have some questions that I came up with after reading that PDF. I didn't understand all of it. I feel kinda stupid for asking them because they don't really have much to do with the transformers. However, I feel I need to know the answers to truly understand this.

So, does anyone know what a kVA? I've read it's just 1,000 Volt Amps (which is just 1,000 volts * amps?). Isn't volts * amps = watts? Doesn't the magic circle show us V * I = P, where V is volts, I is current, measured in amps and P is power, measured in watts? If so, I'm good there, but I get lost with the differences between real power, apparent power, complex power and absolute power.

http://www.coresite.com/resources/faq-what-is-kva

That website says "A term called apparent power (the absolute value of complex power, S) is equal to the product of the volts and amps." So apparent power and watts are the same thing? Apparently not. The site says a watt is the measurement of real power. It also says apparent power and real power are equal only when voltage and current of a circuit coincide. Whatever that means. "However, as waves of current and voltage coincide less, less real power is transferred, even though the circuit is still carrying current."

Those last two parts are where I'm getting confused I guess. The whole part about when the voltage and current coincide and when they coincide less...what the heck are they talking about?

[budm]

Re: Help replacing the power cord on an old clock.

VA rating is not the same as Watts. For the example, you have reactive load and the PF factor is only 0.5 so if the device real power for works is 500 WATTS, the electric company will have to produce 1000VA of power. Volt x Amp is fine when you deal with resistive load, PF is 1.

http://www.power-solutions.com/watts-va
https://powerquality.eaton.com/thoug...=&cx=3&x=9&y=9

http://www.powervar.com/education_details.php?id=11

[keeney123]

Re: Help replacing the power cord on an old clock.

Volt * amps does equal watts. 1000 watts can be got at many different ways by varying Volts and Amps. Real power is the actual resistive power that is used. There is resistance that a coil display other than real resistance, it is called XL which is inductive resistance. Xc is opposite of inductive resistance in the same circuit, series circuit or parallel circuit. How I learned this is by a saying ELI the ICE man. So in the ELI in and inductor L one has voltage E Leading the Current I by 90 degrees, where the voltage is in-phase with the source voltage. In ICE we have C a capacitor with current I leading the Voltage E by 90 degrees, where current is in phase with the source current. So the current lags by 90 degrees in and inductor and the voltage lags the current by 90 degrees in and capacitor. These degrees are on a full circle graph. Here is where one has to study polar rectangular conversion and right angle trigonometry. Then one will get into the various quadrants and imaginary numbers and how they behave. Apparent power is a combination of resistive, XL= inductive resistance and Xc= capacitive resistance figure into the power equation.Then one also has inductive power a combination of voltage and current in and inductor plus there is capacitance power also a combination of voltage and current in a capacitor and lastly true resistive power figured by OHMs Law.