Homemade shunt for amp meter

[shovel52]

Here is a simple shunt for a digital multimeter. It is only 1 inch of # 10 copper wire and allows you to use a cheap digital meter to measure high current. Harbor freight has meters for $3.

http://i40.photobucket.com/albums/e243/shovel52/Picturemeter.jpg

[BoyntonStu]

12" not 1 " unless you would rather measure microvolts vs Milli-Volts.

#10 AWG wire is 0.99 ohms per 1,000 ft.

using 1 ft you measure amps directly in Milli-Volts.

BoyntonStu

[Q-Hack!]

12" not 1 " unless you would rather measure microvolts vs Milli-Volts.

#10 AWG wire is 0.99 ohms per 1,000 ft.

using 1 ft you measure amps directly in Milli-Volts.

BoyntonStu

While I agree that it would take 12" of #10 AWG for this to work... It is only good for up to about 15 Amps. After that, you start to get real hot with that shunt.

[Omega]

Zero Fossil Fuel uses what appears to be AWG #12, single conductor, for a shunt in this video:
http://www.youtube.com/watch?v=65EiiE4NoDI

[BoyntonStu]

While I agree that it would take 12" of #10 AWG for this to work... It is only good for up to about 15 Amps. After that, you start to get real hot with that shunt.


Well let's see:


P=I^2 R

.001 ohm x 50 amp x 50 amp = 2.5 Watts


2.5 Watts isn't much power to dissipate in a foot of #10 solid copper wire.

AAMOF I always use a foot and I have measured currents up to 60 Amps.

Your 15 Amp limit is unreasonably too low.

Also, it is much more accurate to measure a foot and make contacts that to do the same with only an inch.

BoyntonStu

[dennis13030]

...15 Amp limit is unreasonably too low...

I agree with BoyntonStu. The 15 Amp limit is low.

Here are some important tips for doing this.
1. Ensure that high current carrying wire is rated to handle your amp needs. AWG#10 copper wire can easily handle up to 30 Amps.
2. Make certain that you know what the resistance is. This is the resistance of the high current carrying wire that is between the volt meter leads. Use as much accuracy as possible for this resistance value.
3. To determine the current,
a. measure and note the voltage across the piece of high current wire.
b. divide the voltage from step 3a above by the resistance in step 2.
c. the result is the current

[shovel52]

Mr. boynstu Again you are calculating yourself to death, Why push a bunch of numbers into your calculator, when you have a meter measuring micro amps for you .The math is already done, and more practically. Simply follow instructions and then place your amp meter in the circuit to calibrate it if it's not exactly on the money. You will see that I am accurate to 1 amp or so. You are simply measuring the magnetic flux from the wire on the micro amp scale. it will only safely measure up to the wire size #10 which is 30 amps. simple.

[dennis13030]

One common problem with using a wire as a "current sense resistor" is the temperature effects on it. Yes, a AWG #10 copper wire can safely handle 30 Amps, but at 30 Amps it will get hot.

As with all standard conductors, as they get hot their resistance increases. The means that when the temperature rises on the shunt(AWG #10 copper wire) your current measurements will have more error.

To overcome this inaccuracy problem you can do;

1. Use a real "current sense resistor". It is a very low resistance resistor designed specifically for this purpose. Smaller resistance is better like a 0.001 Ohm. Just watch out for Power rating, price and package style.

2. Use an over-rated shunt like one of these http://www.emproshunts.com/webstore/item.aspx?sku=HA-50-50
The over-rating(based on max current) will allow accurate measurements because it will not get as hot.

[Q-Hack!]

Well let's see:


P=I^2 R

.001 ohm x 50 amp x 50 amp = 2.5 Watts


2.5 Watts isn't much power to dissipate in a foot of #10 solid copper wire.

AAMOF I always use a foot and I have measured currents up to 60 Amps.

Your 15 Amp limit is unreasonably too low.

Also, it is much more accurate to measure a foot and make contacts that to do the same with only an inch.

BoyntonStu

Isn't the shunt in series with the HHO cell? Doesn't that mean that it is required to handle the same amps as the cell (amps in a series circuit are the same).


One common problem with using a wire as a "current sense resistor" is the temperature effects on it. Yes, a AWG #10 copper wire can safely handle 30 Amps, but at 30 Amps it will get hot.

As with all standard conductors, as they get hot their resistance increases. The means that when the temperature rises on the shunt(AWG #10 copper wire) your current measurements will have more error.

To overcome this inaccuracy problem you can do;

1. Use a real "current sense resistor". It is a very low resistance resistor designed specifically for this purpose. Smaller resistance is better like a 0.001 Ohm. Just watch out for Power rating, price and package style.

2. Use an over-rated shunt like one of these http://www.emproshunts.com/webstore/item.aspx?sku=HA-50-50
The over-rating(based on max current) will allow accurate measurements because it will not get as hot.


I agree, looks like our thought process was in the same direction. You just explained it better.

Going by the chart here:
http://www.interfacebus.com/Copper_Wire_AWG_SIze.html

You can see that the current rating is about 14-15 amps after that it starts to heat up. So while a #10 AWG copper wire will handle the current it starts to heat up after 15 amps and thus becomes inaccurate for use as a shunt.

[shovel52]

Yes I agree . You can simply recalibrate using larger wire if your planning on running higher amps than 30, but if you are planning on staying below this current level like every one is, this wire does not heat enough to throw off your readings. This is the same principle that is in your cheap meter to begin with except that they only rate to 10 amps. I would not use an expensive meter "20 amp" for fear of frying it. I have this setup on my system now and drove around with another meter in series to calibrate it. it is accurate and cheap and is ideal for simplicity like most people in this forum are looking for. When most people see math and other complications they overlook the simplicity and run.These are the people that have all the ideas. People are talking about running out and buying expensive measuring devices to experiment with, this is for them. thanks for your help, you are correct in your assessment, lets try to keep things simple for folks.

[BoyntonStu]

Isn't the shunt in series with the HHO cell? Doesn't that mean that it is required to handle the same amps as the cell (amps in a series circuit are the same).




I agree, looks like our thought process was in the same direction. You just explained it better.

Going by the chart here:
http://www.interfacebus.com/Copper_Wire_AWG_SIze.html

You can see that the current rating is about 14-15 amps after that it starts to heat up. So while a #10 AWG copper wire will handle the current it starts to heat up after 15 amps and thus becomes inaccurate for use as a shunt.


Not true.

Those charts are for house wiring for L O N G spans of wire.

A most conservative rating for the electric industry.


Starts to heat up? Like about 1* F or 150*F?

I use 1 ft to measure 60 Amps.

Try it and you will see.

Or visit: http://reuk.co.uk/Make-a-Shunt-Resistor.htm


BoyntonStu

[BoyntonStu]

Mr. boynstu Again you are calculating yourself to death, Why push a bunch of numbers into your calculator, when you have a meter measuring micro amps for you .The math is already done, and more practically. Simply follow instructions and then place your amp meter in the circuit to calibrate it if it's not exactly on the money. You will see that I am accurate to 1 amp or so. You are simply measuring the magnetic flux from the wire on the micro amp scale. it will only safely measure up to the wire size #10 which is 30 amps. simple.

>"You are simply measuring the magnetic flux from the wire on the micro amp scale. <"

Untrue.

You are not measuring "magnetic flux" with a dc micrometer.

You are measuring the potential difference between point A and point B.

The only magnetism involved in within the non-digital meter which pushes the pointer.

BoyntonStu

[Q-Hack!]

Not true.
Those charts are for house wiring for L O N G spans of wire.
A most conservative rating for the electric industry.

Starts to heat up? Like about 1* F or 150*F?
I use 1 ft to measure 60 Amps.
Try it and you will see.
Or visit: http://reuk.co.uk/Make-a-Shunt-Resistor.htm

BoyntonStu

That is a real good site... I like how they calibrate the shunt.

I don't think I ever said it wouldn't work, I was just referring to the fact that as amperage increases so does temperature which in turn uncalibrates the shunt. If, however, you calibrate your shunt for your operating current, then you will be accurate at that point and anything off of that would indicate a problem with the system. Its cheap... I like it.

[shovel52]

Mr. B, you dont supply enough information. What do you mean micrometer?? A micro meter has numerous functions. You are confusing everybody.
To measure a potential of difference you have to use the voltage setting.
If you will look at my diagram I am using the amperage setting, there is a difference. Measuring amperage through the wire is done on the micro amps scale. current, not voltage. the meter is set for micro amps and is measuring the current flux "you need to read" through the wire, not the voltage. Again you are attempting to use math to troubleshoot which again shows you have no hands on.

[BoyntonStu]

Mr. B, you dont supply enough information. What do you mean micrometer??
To measure a potential of difference you have to use a voltage meter.
If you will look at my diagram I am using an amperage meter, there is a difference. Measuring amperage through the wire is done on the micro amps scale. current, not voltage. the meter is set for micro amps and is measuring the current flux "you need to read" through the wire, not the voltage. Again you are attempting to use math to troubleshoot which again shows you have no hands on.

Keep on shoveling, you are making the hole bigger for yourself.

I was measuring Amps before you were born.

Amateur radio operator since 1955.

I have more electronic experience in my pinkie that you do in your entire body.

BoyntonStu

[shovel52]

You might be right, however some of the information you provide us with shows that you dont read the information before you answer the question and others you are answering simply for the sake of arguement which confuses and "isses people off. That is why people here have voted to ignore you! and other forums have voted to ban you. Please answer only questions that you have knowledge of, or that you have read first. Thanks!

[goatherder]

All right - you want ignorance? Here's a little for ya.

Why can't you employ one of those round ampere guages from the auto parts store like you would hook up in your old buick to measure alternator output?

They are under 20 bucks, look alot better than the cheap shit from Harbor Freight, come with mounting hardware and instructions, and they...uh...measure amps?

Would this work? And if not why not?

Am I missing something here?

[shovel52]

Sure, to each his own, Like you said, it cost $20 instead of $3. and a multimeter can be used for any kind of electrical problem, and if your project didn't work out you would have a nice mantle piece.
Just kidding around with you here. Yes that would work great!