How to test an alternator the right way!

I will show you how to test an alternator the right way for voltage and amperage without using expensive amp meters. We will make a homeade shunt (amp clamp) to measure the alternator amperage output for under $5.

If this channel has ever been useful to you please use the above link when you shop amazon. A small portion of all your normal purchases will go to help keep this channel running smoothly.
Thank you you are much appreciated.

If you enjoy these quick informative Jeep Videos and would like to be a part off this Fast growing Channel. Please visit

[malcookie]

I thought this was going to be another useless alternator voltage video, but turned out to be one of the most amazing videos I’ve seen! Never knew this could be done.

[rpyczfv]

I am going to follow your steps and make a living out of it as i cant afford a clamp meter for my shop. I will appriciate you and pray for you every time i get benefit from this setup

[nikat]

I'm an Electrical Engineer and I approve of this video. Amazing DIY tool!!

[RHAD-syoi]

The "Shunt" here, I think, is actually a voltage divider.

First, about meters. Internal to the meter, between the "AMP" and "COM" connectections, is a shunt made from a calibrated size of copper. Although copper is considered a "conductor" there is still a resistance to copper that can be measured - although it will be in the milliohm or micro-ohm range (.001 to ohms). Suppose the internal shunt inside the meter for the amps function has a resistance of 1 milliohm. And now you hook the meter up to the battery while it is drawing 10 amps. Using Ohm's Law were E=IxR. That is, voltage = current x resistance. So, 10 amps x 0.001 ohms = 0.010 volts, or 10 millivolts. The meter is actually internally measuring 10 millivolts across the internal copper shunt (which is actually a precision 1 milliohm resistor) and the meter is actually displaying 10 millivolts... but since the human operator has selected the AMP function, the display scale is re-calibrated to be shown as amps so that the human operator does not have to keep using Ohm's Law to convert the meter reading.

The meter's internal shunt has a limit of safely handling 10 amps without damaging the very sensitive voltage measuring circuits. To measure current greater than 10 amps requires the use of an external shunt.

Think of his black wire, which has an overall resistance of about .002 milliohms (or 2, 000 mico-ohms), as a long string of 2, 000 one micro-ohm resisters connected end to end. At the end connected to the battery (at the first of our imaginary resistors) there is no voltage drop. At the 2, 000th resistor at the other end there is about an 8 millivolt drop. So, along the length of the shunt, there is a gradient of voltage from 0 to 8 millivolts. By using the pin to probe through the insulation, he is finding the exact spot where the voltage drop is exactly 4.3 millivolts. He picked the spot where number of millivolts would equal the number of amps. He could have picked anywhere - but there would have been more math involved to convert the ratios. This way, we can just read the millivolts reading on the meter and know that it has a one-to-one ratio correspondence to the number of amps.

The theory for his shunt / voltage divider is actually covered in the first few days of DC Series Circuits. But, what Carolina Custom has done to turn a chunk of wire into a semi-calibrated meter multiplier is brilliantly clever!!

[waltp]

I have an amp clamp. It's nice because you don't need to disconnect anything but your shunt is a clever way to measure high amps. Good video.

[CXensation]

Very good video for the home mechanic.
Explaining and showing how to fabricate a highly usable measurement tool with simple means.
Even how to calibrate it - and that is pretty important - because you want to be sure that you have 1amp, when you are actually reading 1amp on the meter.
Great 💚

[thomasjefferson]

I learned something tonight. I worked as an electrician for years and did not know this, I always had a clamp meter at work but don't have one now that I'm retired. Very clever and now I'm going to make one so I can use it at home. Thank you for making this video :)

[goobermintheretik]

Just plain and simply AWESOME! Recently purchased high amp alternator. Also DC amp meter. Meter isnt showing anything to speak of. Ive got to insure the price of both articles was worth it. This homeboy shunt will do it. Thanks many times.

[stevecano]

Wow, I have never seen something so ingenious!

[hopskustomaudio]

You are awesome! I knew there was a way to do this I just couldn't figure it out myself. Thanks man

[peterclancy]

Going to make one right now. Pricing amp clamps yesterday for a single use. Brilliant!

[Derwin]

Yeah, I'm a 12V shop owner and I too like this video...well presented, sir.

[mikeymikemichaelfiofoftp]

You have opened up a lot of room with this video again thank you

[paulhelmuth]

Awesome Video! Thanks for the education. So cool to see this alternative method/how to measure amps indirectly

[scottneels]

Hey thanks for this. I really appreciate you taking the time to share this.

[st.charlesstreet]

One of the most helpful car electrical tips I have ever seen. Thank You for the amazing post!

[ashwinprakas]

Thanks for the video, I'm from a place where its not that easy to source a decent amp clamp (though Multimeters are easily available) and your video has really helped me and several others stuck in a similar situation.
Cheers,
A.P.

[stuckinmygarage]

That was fun! I'd probably be more neurotic about insulating those clamps, myself, but, your point was clearly made ( no pun intended) THANK you ☺

[mikealejo]

Nice. I can now test the actual charging current of our service vehicle to determine if my alternator is still working, without buying that expensive amp clamp. Thank you.

[josephobrien]

Wow, i know a enough to get me by but this is new knowledge to me. Being an entry level tech with limited funds, this seems like a really good technique to get a quick reading on a budget. thanks for the upload!