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Old Feb 08, 2015, 10:16 PM
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Shunt Resistor Question

So I have been playing around with a INA169 and I have some High power low ohm resistors on their way. In the mean time I got to thinking about Resistance Wire. So my question is, being that you need a tiny resistance to measure High Currents with the INA169 Why not just use a peice of Wire? All wire has a certain amount of resistance.

Some of these low ohm resistors Like this just look like a piece of metal to me. Can anyone educate me on this subject?
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Old Feb 09, 2015, 08:04 AM
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The resistance would be too low in most wire. You might be able to use a piece of stainless steel wire though.
I think the problems would be soldering to it and the length required. You could crimp the connection I suppose, and there's plenty of different formulations of stainless wire.
I guess I would come down to cost. It might be hard to beat a cheap shunt resistor, or it might not be worth dealing with the unknowns of the wire.
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Old Feb 09, 2015, 08:38 AM
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I agree about just using an actual shunt resistor, I was just curious if you could do it, you know in theory. And I know a regular piece of wire couldn't be used but you could use resistance wire where set lengths get you set resistances.
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Old Feb 09, 2015, 09:38 AM
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It can be done with wire, I used some nichrome to build a shunt for measuring high currents, up to 50A.

I calibrated it by putting a known current through it, a big power resistor was the load, measured the current with a meter, and adjusted the length of the wire to give the correct voltage based on 1mv per amp.

Crude maybe, but it worked.
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Old Feb 09, 2015, 12:04 PM
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Originally Posted by srnet View Post
It can be done with wire, I used some nichrome to build a shunt for measuring high currents, up to 50A.

I calibrated it by putting a known current through it, a big power resistor was the load, measured the current with a meter, and adjusted the length of the wire to give the correct voltage based on 1mv per amp.

Crude maybe, but it worked.
That was exactly what I was thinking about doing. Except I was going to use Kanthal wire. Thats really cool though thanks for sharing.
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Old Feb 09, 2015, 01:22 PM
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The biggest problem with using a specific length of wire for a shunt is that it changes quite a bit in resistance with temperature (and most shunts are running a high current so lots of heat). If the fact that accuracy will vary with time of use is not critical, the wire works fine.
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Old Feb 09, 2015, 02:06 PM
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With resistance wire though the fluctuation in resistance is minimal. It is designed to hold its resistance through out a temperature range.
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Old Feb 09, 2015, 04:40 PM
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Copper Wire Shunts?

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Originally Posted by jtroutt19 View Post
So I have been playing around with a INA169 and I have some High power low ohm resistors on their way. In the mean time I got to thinking about Resistance Wire. So my question is, being that you need a tiny resistance to measure High Currents with the INA169 Why not just use a peice of Wire? All wire has a certain amount of resistance.

Some of these low ohm resistors Like this just look like a piece of metal to me. Can anyone educate me on this subject?
Years ago I also used pieces of copper wire as shunts for measuring high DC currents. And, really had problems with temperature caused drift of the meter accuracy.

Here is what I've used for high currents, up to about 60 Amps or so. Some of them have plus/minus 1% accuracy.

http://www.mouser.com/catalog/catalogusd/647/879.pdf

The attached JPG's show my project that showed motor Amps, Ampere Hours for the current flight, Ampere Hours for the flying season, total flight time for the current flight, total flight time for the flying season, and a total flight counter.

Made a bunch of them for my Nicad and Nih powered electric models. Not so useful now days with the LiPo and A123 cell powered models.
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Old Feb 09, 2015, 06:17 PM
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Nice! How did you make your own VIA's. Thats the only thing I have a problem with when etching my boards. Your look really nice!

I ordered These and These and one of these.

I am sure I will use one of them in the final design. I got different kinds because I want to experiment and see what different values get me. You know for educational purposes and all.
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Old Feb 09, 2015, 07:39 PM
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Making Circuit Boards

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Nice! How did you make your own VIA's. Thats the only thing I have a problem with when etching my boards. Your look really nice!

I am sure I will use one of them in the final design. I got different kinds because I want to experiment and see what different values get me. You know for educational purposes and all.
I did a whole lot of etching circuit boards over the past 45 or 50 years, starting off with the old dot and tape methods. In fact, that was my first job in Engineering at work back in the early 1960's. What a pain in the ??? with those dot and tape designed circuit boards.

After using www.expresspcb.com at work for a couple of circuit boards, I never again made any circuit boards at home. Problems with under etching anything less than 30/1000 wide, obtaining and disposing of the used etchant solution, the list goes on.

The expresspcb software is a bit limited, but it is free. They offer a "Miniboard" service which consists of three identical circuit boards 2.5 by 3.8 inches in size for $51.00 plus shipping. The only limitation of the Miniboard is a maximum of around 300 holes for one board. The Miniboard is double sided copper.

The Expresspcb software has a schematic drawing program, which links to the PCB layout software for board design. It is NOT an autorouter, but the board design does highlight all the connections that the schematic shows are interconnected. It works well for fairly simple circuit board layouts.

Take a look at my posting #32 in this thread:
http://www.rcgroups.com/forums/showt...2334181&page=3
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Old Feb 09, 2015, 08:52 PM
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If you haven't checked out etching in awhile, now may be the time.
The new ammonium persulfate method is safe, non-staining, and eco-friendly. A lot of people are also using HCl and peroxide, which is a bit dangerous if not done properly, but really cheap.

Toner transfer is pretty easy to do with glossy paper and a hot laminator.

It is for sure easier and often more cost effective to order your boards. But then you have to wait, and I really hate paying for mistakes when I make them.

P.S. Your homemade boards look pretty great vollrathd!
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Old Feb 09, 2015, 09:21 PM
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Originally Posted by jakestew View Post
If you haven't checked out etching in awhile, now may be the time.
The new ammonium persulfate method is safe, non-staining, and eco-friendly. A lot of people are also using HCl and peroxide, which is a bit dangerous if not done properly, but really cheap.

Toner transfer is pretty easy to do with glossy paper and a hot laminator.

It is for sure easier and often more cost effective to order your boards. But then you have to wait, and I really hate paying for mistakes when I make them.

P.S. Your homemade boards look pretty great vollrathd!
Wish they were home made. None of my home made boards were anywhere near that good.

I did try toner transfer but had lots of pinhole problems. Then there is the issue of drilling a few hundred holes.

Expresspcb will have your boards on your doorstep in two days. Normal miniboard service.
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Old Feb 09, 2015, 09:31 PM
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Harbor freight sells a cheap multi-meter and sometime has it free. This meter has a 10 amp range and the shunt is a length of wire about 2.5 cm long. I have not looked but I would guess all the current ranges use some kind of wire for a shunt.

http://www.harborfreight.com/7-funct...ter-98025.html
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Old Feb 09, 2015, 09:32 PM
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Yeah, it can be tough to get everything right. Once you get it though, you can get really awesome results and crank out prototypes really fast.

I'm lucky in that I have a CNC to drill the holes, but I do drill press them sometimes. SMT is the way to go for so many reasons, a good one is no or few holes to drill.
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Old Feb 09, 2015, 10:30 PM
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I have done several through hole boards. I etch with HCL & H2O2. How is it dangerous if not done properly. It has always worked great for me. Just agitate a bit and the stuffs good. I store it in one of those tupperwares with a locking lid. From this point on I will be doing solely surface mount. There is no reason not to at this point. Via's will be a bit of a challenge and I wish the stuff to electroplate the holes was not on the DEA schedule 1 list cause I would just do it that way. Other than that I am going to start using the dry film solder mask. Comes in sheets and make a really nice finished product. I am going to be building an ESR meter really soon I will post pictures when I am done of what I can do.
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