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Author Topic: Copper tape  (Read 621 times)

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Offline MalcolmAL

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Copper tape
« on: September 27, 2017, 11:17:45 am »
Sticky backed copper tape is used widely in the crafts / hobbies to carry simple electronics project wiring  but I wonder what is its current carrying capacity,, good enough for us?
Anyone done any 'test to destruction'?
 Would depend upon its width of course, and if it comes in various thicknesses ?

Today arrived in the post 30m of 5mm tape ! so in the spirit of enquiry I suppose I could :) , forgotten what it was described as, most seem to be 40-ish micron, oh or was that mil

Edit over a cup of coffee  == no problem for flickering bonfires or arc welders, ok for led lighting for buildings, but would it carry the pulse of a CDU point switch. Current draw of locos is modest these days, so should carry that ok ??
« Last Edit: September 27, 2017, 11:31:37 am by MalcolmAL »

Offline ntpntpntp

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Re: Copper tape
« Reply #1 on: September 27, 2017, 11:35:31 am »
I should think it's perfectly capable of carrying the sort of currents we use.  Think about how thin the cross section is of fine wire?

Google comes up with some interesting stuff. There was a discussion on rmweb which suggests looking a DCCSupplies  items, which gives some detail.  Looks like it should take 5 amps with no problem.

Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline MalcolmAL

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Re: Copper tape
« Reply #2 on: September 27, 2017, 11:45:29 am »
thanks, @ntpntpntp  good ref, yep 5amp more than enough !!
Mine ( via ebay) was not spec. for conductivity of the sticky but various 'tube vids suggests that it is easily soldered to bridge to the edges of a second layer.

Offline Lazy-Ferret

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Re: Copper tape
« Reply #3 on: September 27, 2017, 12:29:17 pm »
From doing a quick look up, the general thickness seems to be around 0.035mm, so a 5mm wide strip would have a cross section area of 0.175mm2

There are many factors that affect the Ampacity of a wire, like how hot the area it runs through, and how quick it can dissipate heat, but since this is for a model railway, we can expect reasonable ambient temperatures, and as this tape has such a large surface area, heat dissipation should be fine, provided you do not bury it under a tonne of plaster!

Since copper tape is going to be very similar to a circuit board, I put these figures into a printed wiring board track width calculator tool, and making a few assumptions, a 1 meter length of 5mm x 0.035mm open side track can carry 7.68 amp.

Try this web page for other sizes.

I do not know what sort of current the points motors draw, but as it is only for a very short duration, effectively meaning the wire would have a low duty cycle where it was off for long periods giving it plenty of time to cool down, and only on for a very short burst, I would have thought you could get away with doubling the current.
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Online The Q

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Re: Copper tape
« Reply #4 on: September 27, 2017, 12:56:31 pm »

Since copper tape is going to be very similar to a circuit board, I put these figures into a printed wiring board track width calculator tool, and making a few assumptions, a 1 meter length of 5mm x 0.035mm open side track can carry 7.68 amp.


[/quote]

At 12V ?

Offline MalcolmAL

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Re: Copper tape
« Reply #5 on: September 27, 2017, 01:12:07 pm »
provided you do not bury it under a tonne of plaster!

 the wire would have a low duty cycle where it was off for long periods giving it plenty of time to cool down,
nor a mountain of polystyrene !

Thanks, I like your analysis re pcb.  also it is going to be well supported, not under tension like a 'quick-blo'.

Quote
by Q > At 12V ?
Independent of voltage, the heating of a wire is defined by its unit resistance and current flowing. (and by its ability to dissipate that heat)

Online The Q

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Re: Copper tape
« Reply #6 on: September 27, 2017, 01:36:01 pm »
So What is resistance per metre length?, so that I can work out the maximum Voltage I can use, before melting the copper or the nail being used as a fuse in the controller :D

Offline MalcolmAL

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Re: Copper tape
« Reply #7 on: September 27, 2017, 01:50:10 pm »
Ah, there is another interesting thing, the length does not matter either, surprising I know, but think back to the era of the 6"nail when fuses were proper fusible real bits of wire sold wrapped round a bit of cardboard ! it was 5A or 15A regardless without telling you how much to use, likewise the nail didnt actually have to be 6 inches long, just very fat  :)

If it is the product of 12v x 7a = 84w and your thinking that is an awful lot of watts that is worrying , nope the 12v is not across that length of tape, most is across the device attached to its end. For 12v to be across the tape it would need to be miles long ( well I exaggerate a bit perhaps :) ) and then there is plenty surface area to dissipate those watts.
 

Online The Q

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Re: Copper tape
« Reply #8 on: September 27, 2017, 02:00:31 pm »
That's why I said a short on the end of the tapes :D .

I sit here generating 100A across 8milliOhms quite regularly and some of those that come into the lab are frightened by that, but that's only at 0.8V.

Currently I'm putting 1000V into a bridge network and measuring that against another 1000V -ish
« Last Edit: September 27, 2017, 02:02:22 pm by The Q »

Offline MalcolmAL

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Re: Copper tape
« Reply #9 on: September 27, 2017, 02:01:17 pm »
So, thanks guys, looking good for all sorts of usage.

I bought 30m not cos I wanted so much ( only a few inched for my re-railer and possibly (rountuit) a few m for use inside cassettes)  but because it was so cheap that it was not worth the bother to source something shorter (postage costs accounting for a big % regardless )

Maybe even for a coffee table layout  :bounce:

Offline MalcolmAL

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Re: Copper tape
« Reply #10 on: September 27, 2017, 02:09:48 pm »
That's why I said a short on the end of the tapes :D .

I sit here generating 100A across 8milliOhms quite regularly and some of those that come into the lab are frightened by that, but that's only at 0.8V.
:laughabovepost:
Shall I tell you about how we were given two large AC machines to parallel using cables as fat as two thumbs  ?  Test for being in-phase was to put a bulb between ,,, light = out of phase dont do it,,, no light means no volts thus in phase so OK - - -   NO ! bang, balls of molten copper all over the lab floor and "Sir" cracked up clutching his sides across the other side.
"Next time, "  he says "you will remember to test your bulb aka your test equipment" , , , yep lesson learned.

Online The Q

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Re: Copper tape
« Reply #11 on: September 27, 2017, 02:41:31 pm »
Pull up a sand bag and I'll tell you a story..  :D

The favourite just after training was to ask the newly trained radar technician to test the "No break Trigger system" the manual (air publication)said to turn off one side and make sure it changed over....
then it told you to turn off the other side and see if it switches back..

Notice the bit missing?


Luckily I did, but there plenty who didn't and tripped the Radars..

There was the guy learning on the next rack to me during training, who decided to test the Current using an AVO 8, by putting the prongs across the input supply. Big blue flash and the lab power tripped, he had to hacksaw the remains of the prongs off the back of the socket...


But anyway I'm using slightly more scientific processes today or tomorrow.

Tomorrow I'm testing a test station for up to 100A which I'll be measuring phase error in Milli degrees.

It's safer than the days when I had to change 3 phase 400V 120A contactors with the input live!!!

Offline MalcolmAL

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Re: Copper tape
« Reply #12 on: September 27, 2017, 03:27:01 pm »
[ Ah the tales I could tell about molten copper turning me away from heavy electrical (dangerous)  to light electrical  aka electronics , much safer I thought till I found myself high up hanging off the battlements of Edinburgh Castle, setting up a microwave link :( perhaps we should qsy the General area ? ! to chat  ]

Back to Topic, y'all be pleased to know that my wee Jinty does not draw sufficient current to fuse an inch of copper tape ! It is thicker than I expected too, not fragile.

Hint : ordinary sticky tape stuck on the sides of the thin roll stop it unwinding in a demented fashion !

News : the sticky is not conductive, no worries, but a closer look on ebay just now and I could have got conductive adhesive for even less  - and > the really really  bad news is that I would have saved a good 25% on the cost =  all of £1 !

Now where is that 12v car battery and a 6" nail > > >  :)

Offline sprogman

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Re: Copper tape
« Reply #13 on: September 28, 2017, 03:08:52 pm »
If it is the product of 12v x 7a = 84w and your thinking that is an awful lot of watts that is worrying , nope
That's exactly how one large, well known DCC supplier used to rate their cable :)

Saying it can carry X Amps is totally meaningless unless you also know the resulting voltage drop.

Andrew

Offline MalcolmAL

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Re: Copper tape
« Reply #14 on: September 29, 2017, 01:07:42 pm »
If it is the product of 12v x 7a = 84w and your thinking that is an awful lot of watts that is worrying , nope
That's exactly how one large, well known DCC supplier used to rate their cable :)

Saying it can carry X Amps is totally meaningless unless you also know the resulting voltage drop.

Andrew
That is true but playing devil's advocate for the DCC suplier for a mo. (just for fun ?!)  they perhaps assume that the  resistance of the tape will be small compared to that of the load and that therefore the current flowing will be determined to a large degree by the load impedance. Perhaps assuming that most folk may be more familiar with load wattage rather than amperage, they chose to express it in that fashion.
On the other hand , , , the failure mode (if any) is going to be as a fusible link ?  :)

The news is that I cannot find my spare car headlight bulbs to do a test to destruction at 12v, and cars dont come with ammeters anymore :( so that'll have to wait awhile. Totally irrelevant now as we have established that it is more than adequate for my DC, (not sure what amperage the DCC boys will need,,, pass. !)

What shall we do now, I need a coffee :)


 

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