Cheap Current Meter

[Kiwi_Roy]

If you have a cheap multimeter without a current scale it doesn't mean you can't measure current in the Amps range,
All you need to have is a Millivolt range and you can make a shunt that will convert Amps to milivolts.
It turns out that 28 inches of No 16 wire will drop 10 millivolts for every Amp you put through it
By the same token 2.8 inches of No 16 will drop 1 Millivolt per Amp.
For No 14 the space between the meter taps is 4.5 inches for 1 Millivolt per Amp

I wanted to measure the current through the main fuse of my V7iii so I made a shunt that I could plug in the fuse holder
Note: my expensive Fluke meter can measure up to 10 Amps directly through the leads but I wanted to pass on how to do it with a $5 meter



Hows it made?
Take about 6" of No 16AWG, bare 2 points 2.8 inches apart, terminate the ends of the wire however you want to, I just used a couple of pieces of brass strip to poke in the fuse holder, if I had found a blown fuse I might have used that
The main thing is your length wire must be in one continuous length and your meter cannot terminate at the main current connection points.
I could have just touched the meter leads to the bare points or poked them between the wire strands but I wanted to have meter sockets, It turns out that the blue butt splices are just about the right size to accept meter probes, I just had to run a small drill in to open them out a tad I did this while I had the connector still in the crimper so the drill couldn't grab and wrap the wires up. With 20/20 hindsight I should have made a probe holder of the same brass shim and soldered those to the shunt with heat shrink to protect the bare metal.
I then soldered these short leads to the main wire at 2.8 Inches apart.
I checked the shunt on my bench power supply at 3 Amps.the Fluke read 3.00 so I was happy
Note the meter tails can be any size or length as the current there is almost zero.

Heres a picture of reading the main 30 Amp fuse current. Notice I'm on the millivolt range with 5 Amps going to the battery (it was a almost drained)


If anyone out there doesn't have access to No 16 AWG send me a PM and I will tel you how to figure it out with the wire you do have.
I could easily read 50 Amps with this shunt for a short time, I have one made from wire a couple of sizes larger that will handle the main starter current up to 170 Amps.
A cheap meter might not read mllivolts to 1 decimal pace, in this case use 30" of wire tapped at 28 inches and mentally add the decimal place

Cheers
Roy

[Zoom Zoom]

Just a question of clarity for anybody reading this. Does the type of wire matter? Is a solid wire going to yield a different reading than stranded?

Thanks,
John Henry

[lucky phil]

If you have a cheap multimeter without a current scale it doesn't mean you can't measure current in the Amps range,
All you need to have is a Millivolt range and you can make a shunt that will convert Amps to milivolts.
It turns out that 28 inches of No 16 wire will drop 10 millivolts for every Amp you put through it
By the same token 2.8 inches of No 16 will drop 1 Millivolt per Amp.

I wanted to measure the current through the main fuse of my V7iii so I made a shunt that I could plug in the fuse holder
Note: my expensive Fluke meter can measure up to 10 Amps directly through the leads but I wanted to pass on how to do it with a $5 meter



Hows it made?
Take about 6" of No 16AWG, bare 2 points 2.8 inches apart, terminate the ends of the wire however you want to, I just used a couple of pieces of brass strip to poke in the fuse holder, if I had found a blown fuse I might have used that
The main thing is your length of wire must be in one continuous length and your meter cannot terminate at the main current connection points.
I could have just touched the meter leads to the bare points or poked them between the wire strands but I wanted to have meter sockets, It turns out that the blue butt splices are just about the right size to accept meter probes, I just had to run a small drill in to open them out a tad I did this while I had the connector still in the crimper so the drill couldn't grab and wrap the wires up. With 20/20 hindsight I should have made a probe holder of the same brass shim and soldered those to the shunt with heat shrink to protect the bare metal.
I then soldered these short leads to the main wire at 2.8 Inches apart.
I checked the shunt on my bench power supply at 3 Amps.the Fluke read 3.00 so I was happy
Note the meter tails can be any size or length as the current there is almost zero.

Heres a picture of reading the main 30 Amp fuse current. Notice I'm on the millivolt range with 5 Amps going to the battery (it was a almost drained)


If anyone out there doesn't have access to No 16 AWG send me a PM and I will tel you how to figure it out with the wire you do have.
I could easily read 50 Amps with this shunt for a short time, I have one made from wire a couple of sizes larger that will handle the main starter current up to 170 Amps.
A cheap meter might not read mllivolts to 1 decimal pace, in this case use 30" of wire tapped at 28 inches and mentally add the decimal place

Cheers
Roy

I just bought a clamp style ammeter Roy for $75. Measures a/c and dc volts. Brilliant and no connections to make just slip it over the cable and close the clamp. helped me troubleshoot a suspected battery drain issue on my wifes car.

Ciao

[Kiwi_Roy]

Just a question of clarity for anybody reading this. Does the type of wire matter? Is a solid wire going to yield a different reading than stranded?

Thanks,
John Henry

I don't believe so No16 Copper is No16 Copper but I will double check I have a roll left over from a reno.

Update, no difference as Wayne says
I didn't have 16 gauge solid but 14 gauge is the same as 14 gauge stranded, 4-1/2 inches between the meter taps

[Wayne Orwig]

Just a question of clarity for anybody reading this. Does the type of wire matter? Is a solid wire going to yield a different reading than stranded?

As long as it is copper. Solid or stranded is the same for DC. High frequency AC , it does matter, but we will not notice.

I've had one of these on my workbench for eons. Has alligator clips on the ends. I like the spade lugs to replace the fuse idea. 
And hang a tag on it to remind you in two years what it is. 

[Kiwi_Roy]

I just bought a clamp style ammeter Roy for $75. Measures a/c and dc volts. Brilliant and no connections to make just slip it over the cable and close the clamp. helped me troubleshoot a suspected battery drain issue on my wifes car.

Ciao

That type of DC Ammeter (Hall Effect probably) used to be hundreds of dollars, there is another type (Moving Iron) from 60 years ago, they were also very expensive.
It would be interesting to make a shunt and compare the two.

[Kiwi_Roy]

As long as it is copper. Solid or stranded is the same for DC. High frequency AC , it does matter, but we will not notice.

I've had one of these on my workbench for eons. Has alligator clips on the ends. I like the spade lugs to replace the fuse idea. 
And hang a tag on it to remind you in two years what it is. 

I was just thinking there might be a difference depending on the copper purity, I worked in a mine in Papua New Guinea where they recovered copper by flotation and smelting as opposed to the one in Chille where it was by electrowining.
A good point on the labeling, i've chopped up a few.

[moto]

I would worry about the possibility of additional conductivity in the completely tinned, very fine-stranded wire I've recently started to prefer. 16 AWG is defined by the total cross-sectional area of the conductors making up the wire.* The tin coating on each strand would not be accounted for.

I have a nice, cheap Sperry meter, the ADM-18A, that directly measures up to 10 amps. It has been discontinued in the US, but seems to be for sale in El Salvador and Cambodia. Dale Electric Supply in the US has six of them now at $29.95:



https://www.dale-electric.com/products/browse/manufacturer/A_W_SPERRY/00193/sort:itemnumber

Moto

*[EDIT] My 16AWG wire has 252 strands, each 0.08mm in diameter, for a combined cross-sectional area of 1.27 square mm, versus the 1.31 sq mm standard found in gauge tables. I have to admit that, for all I know, the tin could make up the difference.

[EDIT #2]: There is a separate standard for tinned, multi-strand wires, but at $60 it's beyond the reach of this Guzzista.

[Kiwi_Roy]

Moto, its very easy to check, take a length of your preferred wire for example 35 inches, bare a section near each end and then pass a known current through it.
Measure the millivolts between the two bare points then back calculate the distance between the meter points you need for 1 mV per Amp.
Just be aware if you use your meter to check the Amps then use it to check the Millivolts drop you may get an error because the current went up when you removed the Ammeter
Again I stress the meter leads need to be inside the current connection as the joint drops a lot more than the wire.

Nice soft wire, too good for a simple shunt, Nice meter

[berniebee]

I like this - appeals to my sense of thrift. Having said that there are two caveats to be observed. First, there are limits to how much you can measure with any given gauge of wire. Too much currrent through the wire and the wire will heat. It's resistance will increase. The temperature coefficient for copper is about 0.4 percent / Degree C, so a 10 degree of temperature rise while measuring is not significant for motorbike measurements. But if you are measuring high currents with a gauge of wire that heats up by 30 or 40 C, your meter reading is going to be significantly too high.

The other thing is that if you are fooling with anything wired to a vehicle battery, make sure all soldered connections are covered by shrink tubing, lest you short that wire to the frame. Even a 16 gauge wire can make a nice fat spark, and melt the insulation within a harness, forcing you to completely cut open the main harness, rewire a substantial part of the bike and therefore miss a week long bike trip to Florida . Uh, not that this has ever happened to me.

[Chuck in Indiana]

And hang a tag on it to remind you in two years what it is. 

Man, that's no sh!t.. 
I was helping a guy assemble a homebuilt airplane one time. He was holding a complicated weldment, and said.."You know, Chuck.. I made this. I have no freakin idea what it is.."    And.. we were a lot younger then. <shrug>

[lucky phil]

That type of DC Ammeter (Hall Effect probably) used to be hundreds of dollars, there is another type (Moving Iron) from 60 years ago, they were also very expensive.
It would be interesting to make a shunt and compare the two.

Yes Roy, exactly what my friend said. Ones that also did DC were expensive. Not anymore and massively convenient. Sounds like a something you'd be interested in Roy,an accuracy comparison.

Ciao   

[Kiwi_Roy]

-----------
The other thing is that if you are fooling with anything wired to a vehicle battery, make sure all soldered connections are covered by shrink tubing, lest you short that wire to the frame. Even a 16 gauge wire can make a nice fat spark, and melt the insulation within a harness, forcing you to completely cut open the main harness, rewire a substantial part of the bike and therefore miss a week long bike trip to Florida . Uh, not that this has ever happened to me.

This is a very good point especially if you are using it in an unfused location like I happen to be, I left the joints exposed so you could see how it was made
If you are going to use the shunt in place of a fuse it really should incorporate a fuse
 

Yes Roy, exactly what my friend said. Ones that also did DC were expensive. Not anymore and massively convenient. Sounds like a something you'd be interested in Roy,an accuracy comparison.

Ciao

When measuring small currents with the AC type we would often wrap several turns through the jaws to increase the resolution, I imagine this also works for DC type
Knowing how easy it is to make a shunt perhaps you could incorporate one into the wiring for example the main wire feeding a fusebox could have a couple of meter jacks spaced apart to give 1 mV/A

[Tom]

I like the old analog meters.....that's so I can guess and really screw things up.   

[Kiwi_Roy]

Analog meters still have their place, sometimes a digital is too slow.

[ozarquebus]

What kind of accuracy you are after will determine the method.

For troubleshooting a bike, not much accuracy is usually needed. If you are trying to figure out exactly how much current something is taking, you would probably want to insert a longer piece (ie:2.5 ft of 16 awg?) of wire that you have calibrated to be 10 milliohm to read an accurate 1 mv per amp. in series in the circuit.

Here is one of many wire resistance charts from across the net.





or get  a real shunt like this, but that would violate spirit of the original post of using a cheap voltmeter without buying anything new.





Like this guy:

https://www.youtube.com/watch?v=j4u8fl31sgQ

[Kiwi_Roy]

Ha, you can use the table and calculate it if you want but using my method you don't get a headache.
Pass a known current through several feet of your unknown wire
Measure the millivolts at two points a known distance apart, this tells you how many millivolts per amp you produce.
Then just back calculate the distance between two points will produce 1 mV per Amp.
I like the video, the guy is entertaining and knows his stuff.

[Kiwi_Roy]

What kind of accuracy you are after will determine the method.

For troubleshooting a bike, not much accuracy is usually needed. If you are trying to figure out exactly how much current something is taking, you would probably want to insert a longer piece (ie:2.5 ft of 16 awg?) of wire that you have calibrated to be 10 milliohm to read an accurate 1 mv per amp. in series in the circuit.

Here is one of many wire resistance charts from across the net.





or get  a real shunt like this, but that would violate spirit of the original post of using a cheap voltmeter without buying anything new.





Like this guy:

https://www.youtube.com/watch?v=j4u8fl31sgQ

That guy is an idiot either that or he knows what he's doing but trying to be funny burning his fingers and overloading his equipment.
it is entertaining, ill give him that.

[slowmover]

Will this work?

[Kiwi_Roy]

Will this work?

No, that belongs in a museum
I don't think it has an Amps range