Well, the subject says it all. Let's assume that I have the equipment to measure a 0.1 ohm resistance fairly accurately. I am thinking of maybe rolling it to distribute the heat and the cutting a piece that gives me as close to 0.1 ohm as I can get.
Am I crazy or will this work as good as a wirewound?
Yep, crazy.
Care to add on the "why am I crazy" front? It doesn't seem that unreasonable, except possibly for ppm/C issues, if any.
It does not seem crazy, just not very stable over temp. Is it for DC or are there any high-frequency components? Is for a lab experiment or something more?
For low-cost SMPS design, it is not uncommon to see a wire or a PCB trace used in place of a resistor for current sense. It's a 'close enough' technique. Aluminum will dissipate heat quickly but I have no idea how the resistance will change with temp or if that change will impact your application.
Try it.
It does not seem crazy, just not very stable over temp. Is it for DC or are there any high-frequency components? Is for a lab experiment or something more?
For low-cost SMPS design, it is not uncommon to see a wire or a PCB trace used in place of a resistor for current sense. It's a 'close enough' technique. Aluminum will dissipate heat quickly but I have no idea how the resistance will change with temp or if that change will impact your application.
Try it.
This is strictly for use as a short term DC current shunt. I am going to limit the length of time that current passes through it to five to ten seconds...
Yes, I would agree with the others that your thermal stability will be poor. Also, are you really thinking about dumping 100 amps through this?
OK, I've relegated this into the bad idea pile...
Well, the subject says it all. Let's assume that I have the equipment to measure a 0.1 ohm resistance fairly accurately. I am thinking of maybe rolling it to distribute the heat and the cutting a piece that gives me as close to 0.1 ohm as I can get.
Am I crazy or will this work as good as a wirewound?
And that is related to Test Equipment in what way?
Steel would be better, but stainless even better still (not quite as good as nichrome, but similar). Steel is solderable, aluminum and stainless not so much.
Even assuming a good bond, conductive metals like aluminum and copper make very poor resistors. For most frequencies (over ~kHz, usually), and shapes of conductor, the inductive reactance is several times the resistance. If you're only ever measuring DC, that doesn't matter, but any little transient or ripple will dutifully be transmitted to your sensitive shunt measuring circuit.
Tim
I have successfully used stainless steel for making high current shunts. I sometimes used M4 allthread and adjust the nuts to desired resistance or used 1mm SS plate cut to size for the desired resistance.
There is another problem with using aluminum. Corrosion, anytime You connect aluminum to certain types of metal, you can get a galvanic reaction, which will cause corrosion. Over time this corrosion will increase the resistance, making it unreliable. You can only connect to certain types of stainless steel, and a few other metal, Without having a galvanic reaction. It will be a very expensive experiment. You need to do some research on metal compatibility in electronic circuits.
Well, the subject says it all. Let's assume that I have the equipment to measure a 0.1 ohm resistance fairly accurately. I am thinking of maybe rolling it to distribute the heat and the cutting a piece that gives me as close to 0.1 ohm as I can get.
Am I crazy or will this work as good as a wirewound?
And that is related to Test Equipment in what way?
In the way that I can use the current shunt to calibrate test equipment...
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.
Combined with the fact that the guy's name is "SharpEars" ...
Throwing stones at people that you do not know based on the screen name is not a good way to create a community. Sharp Ears had a curiosity question that anyone on the forum could take a stab at or not. The desire to improvise a DC current shunt has nothing to do with audio specifically so why pull in some silly personal jab?
Participate or not....but personal attacks are weak.
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.
Combined with the fact that the guy's name is "SharpEars" ...
Throwing stones at people that you do not know based on the screen name is not a good way to create a community. Sharp Ears had a curiosity question that anyone on the forum could take a stab at or not. The desire to improvise a DC current shunt has nothing to do with audio specifically so why pull in some silly personal jab?
Participate or not....but personal attacks are weak.
He also made an obvious mistake assuming that any audiophool would use aluminum for anything, when it's all about pure silver, 99.9999999999999999999999% pure copper, silver plated copper, cryogenically frozen versions of all of the above, etc... At no point would any self respecting audiophool use aluminum, the black sheep of the conductive metals family!!
Having said all of that, yes I am a card carrying member of the audiophool club. Fortunately, I know better than to ask questions related to audiophoolery on this forum - an electrical engineering forum.
Specifically, my question was related to creating a current shunt for calibrating the current reading of a power supply. If I told you guys what make and model of power supply, then you would have a genuine reason to laugh at me, so I won't.
Kinda reminds me of this:
http://studiozey.com/invisistor/index.html
...I want off of this planet.
I heard they just found surface water on Mars?
99.9999999999999999999999% pure copper
That 0.0000000000000000000001% wouldn't be oxygen would it? I hope not, no audiophool would dream of anything but OFC.
Throwing stones at people that you do not know based on the screen name is not a good way to create a community. Sharp Ears had a curiosity question that anyone on the forum could take a stab at or not. The desire to improvise a DC current shunt has nothing to do with audio specifically so why pull in some silly personal jab?
Participate or not....but personal attacks are weak.
Cheesus Crust, overreact much? Calm your tits.
Having said all of that, yes I am a card carrying member of the audiophool club. Fortunately, I know better than to ask questions related to audiophoolery on this forum - an electrical engineering forum.
Throwing stones at people that you do not know based on the screen name is not a good way to create a community. Sharp Ears had a curiosity question that anyone on the forum could take a stab at or not. The desire to improvise a DC current shunt has nothing to do with audio specifically so why pull in some silly personal jab?
Participate or not....but personal attacks are weak.
Cheesus Crust, overreact much? Calm your tits.
Having said all of that, yes I am a card carrying member of the audiophool club. Fortunately, I know better than to ask questions related to audiophoolery on this forum - an electrical engineering forum.
Wait, you posted that picture with a response like:
Cheesus Crust, overreact much? Calm your tits.Talk about the pot calling the kettle black! You also quoted me completely out of context, since this thread's question has absolutely nothing to do with audiophoolery as has been already pointed out numerous times...
Improvising a current shunt can be done easily with plain old wire from home depot.
http://www.rcgroups.com/forums/showthread.php?t=393591&page=7I got a nice vishay 20 watt wire wound from mouser.1% .01ohm, for about 5 bucks it think. Im not sure if your looking for improvised or cheap, I understand the need for either, so there are two options
. I got the resistor for a PSU shunt too, its more compact than a wire shunt, and much cheaper than a a bulk metal 4 terminal or a proper high wattage shunt.
Improvising a current shunt can be done easily with plain old wire from home depot.
http://www.rcgroups.com/forums/showthread.php?t=393591&page=7
I got a nice vishay 20 watt wire wound from mouser.1% .01ohm, for about 5 bucks it think. Im not sure if your looking for improvised or cheap, I understand the need for either, so there are two options . I got the resistor for a PSU shunt too, its more compact than a wire shunt, and much cheaper than a a bulk metal 4 terminal or a proper high wattage shunt.
Do you know how much 18 gauge wire you would have to use to create a 0.1 ohm shunt? About 5 meters (16.4 feet). That is a lot of wire...
The point of this exercise was to save ordering time from DigiKey, if it would be something I could do at home in an hour or so...
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.
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.
