Author Topic: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?  (Read 9881 times)

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Offline SharpEars

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #25 on: September 30, 2015, 07:18:34 am »
I just purchased a really cheap wirewound 50W 100 ohm wire wound with a slider tap on ebay to use for help in calibrating a cheap PSU. They also do other low ranges like 10 ohm.

But if time is of the essense then strip apart a toaster or hairdryer and use the (nichrome?) instead of bloody aluminium foil. I would use the foil to make capacitors though.

I've gone with a variant on your idea with the toaster and ordered 25 feet of Kanthal A1 16 AWG (1.29 mm - 0.324 Ohms/ft Resistance - Heat Resistant to 1400 C). I can clip a piece of the length I need for the resistance I need and make all the shunts I want, reducing this entire problem to one of measurement only...
« Last Edit: September 30, 2015, 07:20:30 am by SharpEars »
 

Offline SharpEars

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #26 on: September 30, 2015, 07:19:20 am »
Isn't one of the bigger problems consistency? Aluminium foil is a bugger to join to in a reliable manner both electrically and mechanically. You could make it, calibrate it but move /change anything and I would guess it has changed electrically significantly.

Thanks for pointing that out. Even if i would make an accurate piece of geometry, moving it without distorting it would be a pain in the rear.
 

Offline rwgast_lowlevellogicdesin

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #27 on: September 30, 2015, 07:23:23 am »
Yes I forgot to mention kanthal :) can be purchased locally at most vape/smoke shops. I use it to wrap heating coils for my vaporizer, local shop sells 22-30 guage for a buck a yard, and I live in a RURAL area

Offline ez24

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #28 on: September 30, 2015, 07:42:50 am »
Yes I forgot to mention kanthal :) can be purchased locally at most vape/smoke shops. I use it to wrap heating coils for my vaporizer, local shop sells 22-30 guage for a buck a yard, and I live in a RURAL area

FYI on my screen your user name is so long it runs into the title so I cannot read either.  Now I can read the replies.  :)
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Offline Deathwish

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #29 on: September 30, 2015, 07:55:17 am »
Kinda reminds me of this:

http://studiozey.com/invisistor/index.html
...I want off of this planet.  |O I heard they just found surface water on Mars?

Nope it is official.
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Offline nbritton

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #30 on: September 30, 2015, 08:06:37 am »
Specifically, my question was related to creating a current shunt for calibrating the current reading of a power supply.

How on earth are you going to do a precision calibration using a wadded up piece of aluminum foil? If you take all the electric stove heating elements from your stove and wire them in parallel that should give you about 8 ohms. Good for 7,000 Watts, at a fraction of that power it should provide a stable load.
 

Offline Macbeth

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #31 on: September 30, 2015, 08:22:03 am »
He could also use the 10A/20A current shunt on his DMM, it's likely 0.1 ohm. Use the terminals for the 1V load and tap the sense wires inside the meter
 

Offline rwgast_lowlevellogicdesin

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #32 on: September 30, 2015, 10:14:59 am »
Hmmm well I actually typo ed my user name, left the g out! I would like to change it but i wasn't aware it was possible to edit user name?

Offline Wuerstchenhund

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #33 on: September 30, 2015, 03:08:35 pm »
And that is related to Test Equipment in what way?

I use current shunts in my test rigs all the time. Seems rather valid to discuss here.

It isn't. The truth is that this discussion has very little to do with Test Equipment, and for projects like making your own shunts there already is a much more appropriate forum.
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Offline cncjerry

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #34 on: September 30, 2015, 04:00:02 pm »
aluminum foil is cheap, why not just try it?  I think you will give up pretty quickly once you try to solder it...
 
I've tried making precision wire resistors from kanthol without much luck.  If you look inside a decent decade box you will see flat wire wound resistors all over the place so it must be possible unless they are using other types of resistance wire.  Anybody know what they use?  I tried stretching it out and running a meter lead down the length until I hit the right resistance and kanthol, that which I had on hand, had too high an ohms per foot to be accurate.  I tried various gauges.  I guess you can get close then switch to a lesser gauge (thicker wire) for trimming.
 

Offline aargee

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #35 on: September 30, 2015, 05:03:21 pm »
I smell an audiophool.

What? Why?



Kinda reminds me of this:

http://studiozey.com/invisistor/index.html

Combined with the fact that the guy's name is "SharpEars" ...

I love the last line of text under Warranty and Disclaimer...

"Read the Precautions paragraph and above all - use common sense."  ... to which should be added ... "and don't buy the kings clothes."
Not easy, not hard, just need to be incentivised.
 

Offline jwm_

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #36 on: September 30, 2015, 06:35:31 pm »
Aluminum is a darn good conductor. One of the best, a pretty poor resistor material choice. aluminum foil is pretty thick, as thick as a 1/2 oz pcb copper pour. Unless you cut your foil really thin and make it really long, any appreciable resistance will likely be due to your contacts between the foil (which has a tendancy to develop a nice insulating sapphire layer) and whatever you connect to it.

That said, if you have a ohmmeter that can go that low, try it, then try whatever other metals you can find. Steel wire may be good, (pulled from steel wool? inside a twist-tie? section of cheap bike lock cable? you can probably find something around) . When you find something that seems to work, wiggle the contacts and make sure they are not contributing to the resistance, measure it again after it gets warm and see if it changes. ramp up the current slowly and keep an eye on the temperature rise to see if it will stand up to the current.

Offline Performa01

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #37 on: October 01, 2015, 07:20:53 pm »
Apart from all the other problems already mentioned, you also might want to consider the temperature coefficient of metals like aluminum, copper, iron/steel and the like, that is in the range of +4000 ~ +6000 ppm/K. Not exactly a good basis for measurements with reasonable accuracy, let alone calibration.
 

Offline rx8pilot

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #38 on: October 02, 2015, 01:43:23 am »
As a side note....

I was in solder mode on my bench yesterday and thought I would try to solder to a small sheet of aluminum foil. 'Hard' is too small a word. I tried with just the iron and then with a hot air pre-heat on top of a heated steel block. Different fluxes as well. Nothing more than a few balls of solder rolling around.

I did not expect any more, but it did satisfy my curiosity. I learned to TIG weld aluminum years ago and was always surprised how much heat it takes. Anyway it was fun to try. I may put some solder paste on foil and put that in the re-flow oven to see if that works.
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Offline zapta

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #39 on: October 02, 2015, 02:49:24 am »
IIRC there are special alloys to solder aluminum.
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Offline Gyro

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #40 on: October 02, 2015, 03:56:53 am »
Quote
I've tried making precision wire resistors from kanthol without much luck.  If you look inside a decent decade box you will see flat wire wound resistors all over the place so it must be possible unless they are using other types of resistance wire.  Anybody know what they use?

Constantan (55% Copper, 45% Nickel) in the early ones or Manganin (86% Copper 12% Manganese 2% Nickel) in later / better ones - better long term stability and lower (very low) TC.
« Last Edit: October 02, 2015, 04:03:51 am by Gyro »
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Offline -jeffB

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #41 on: October 02, 2015, 09:46:38 am »
Apart from all the other problems already mentioned, you also might want to consider the temperature coefficient of metals like aluminum, copper, iron/steel and the like, that is in the range of +4000 ~ +6000 ppm/K. Not exactly a good basis for measurements with reasonable accuracy, let alone calibration.

So, is it realistic to make a temperature sensor from aluminum foil?  ;)
 

Offline Sbampato12

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #42 on: October 02, 2015, 01:37:44 pm »
As a side note....

I was in solder mode on my bench yesterday and thought I would try to solder to a small sheet of aluminum foil. 'Hard' is too small a word. I tried with just the iron and then with a hot air pre-heat on top of a heated steel block. Different fluxes as well. Nothing more than a few balls of solder rolling around.

I did not expect any more, but it did satisfy my curiosity. I learned to TIG weld aluminum years ago and was always surprised how much heat it takes. Anyway it was fun to try. I may put some solder paste on foil and put that in the re-flow oven to see if that works.

I've seen people using candle wax to allow solder on aluminum. Worked. Good or not, I don't know, but they did.
Also, one time on a company I've worked before, they bought a little bottle of 'aluminum flux' that worked very well... Used once in a decade I think, but when you need...
 

Offline T3sl4co1l

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #43 on: October 02, 2015, 02:52:27 pm »
To 'cheese' it, you rub at the oxide while under a suitable cover (usually mineral oil or wax).  Obviously this does a poor job, and the tin dissolves it (inconvenient for foil), while the lead does not (lead and aluminum are immiscible).

The slightly better way is to use a zinc or zinc-tin alloy that tends to flow along the metal surface, under the oxide layer.  This also needs to be scratched in, but doesn't require a flux for modest results.

Real fluxes include ammonium bifluoride, which is nasty stuff.  But it works on stainless, and I believe titanium as well.

Tim
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Offline hendorog

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #44 on: October 02, 2015, 04:58:57 pm »
To 'cheese' it, you rub at the oxide while under a suitable cover (usually mineral oil or wax). 

Ordinary cooking oil works too.
 

Offline jwm_

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Re: Is it realistic to make a 0.1 ohm 10 W resistor from aluminum foil?
« Reply #45 on: October 02, 2015, 07:13:16 pm »
Apart from all the other problems already mentioned, you also might want to consider the temperature coefficient of metals like aluminum, copper, iron/steel and the like, that is in the range of +4000 ~ +6000 ppm/K. Not exactly a good basis for measurements with reasonable accuracy, let alone calibration.

So, is it realistic to make a temperature sensor from aluminum foil?  ;)

Yes! see this great signal path review of a very fine keithely source meter where he uses liquid nitrogen to show how resistance of materials changes with temperature.


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