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Best Tools to measure current draw from Devices?

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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I've been on the hunt for a device that can test Current Draw from devices, Mainly amps so I can choose the appropriate fuse and in current rush fusing for my PDM.

What can I use for this? I've seen a few cheaper tools on Amazon for around £10 that are used to measure Solar Panel output but there must e a more specific/professional tool for this?

The closest tool I have at the moment is a Fluke 115 but that is only good up to 10Amps. Here is something I've found but again I'm looking some something more suited to the job :) - https://www.amazon.co.uk/Precision-Analyzer-Consumption-Performance-Backlight/dp/B07M5XD4G9/ref=asc_df_B07M5XD4G9/?tag=googshopuk-21&linkCode=df0&hvadid=309857966843&hvpos=&hvnetw=g&hvrand=6747717506861722272&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9046513&hvtargid=pla-633698426290&psc=1

Would an Oscilloscope be for this? Or would there be another tool more suited towards it?

You want a current loop. You can get a current loop probe for use with on osciloscope, such as these from Pico:

https://www.picotech.com/accessories/current-probes?gclid=CjwKCAjw77WVBhBuEiwAJ-YoJJ68Gr_owPhdR6fdbgKOBOLkhUhMGexaSANb866WC2ACARaSRD8gPBoCX3cQAvD_BwE

Here are some current clamp meters on Amazon:

https://www.amazon.co.uk/current-meter/s?k=current+meter

I've heard current clamps are widely inaccurate? No?

Hey Reece,

Some PDM can show you the current of each output. Have you check if yours have this feature? Then you could decide to limit that current from this value.

Yes my PDM does have this feature but this is to test the Amp draw before I select the wiring gauge size for some Daytime running lights... I've already wired them in but not sure hoe many amps they are going to pull as I've used a thinner guage wire than I normally would.

To use the PDM just wire up one output, connect the lights and measure the current? There may be some inaccurate current clamps, but my experience has been very good using the ones shown in the Pico-scope pages. In the Picoscope software you can zero them to account for the magnetic field environment they are installed in.

I've not got it at the moment, I've got everything wired in but I just want to double check. I was looking at the fluke clamp meters because I'm running other fluke products. I guess I'll just invest in one then? I can't really find Any other tools suited to measuring amps.

The Clip on standalone type current clamps can be inaccurate if not used correctly, but the ones that I have used have all tended to be accurate and precise when used correctly (i.e. having the cable in the correct location for the clamp to read the current, not using a clamp designed for use on 400A systems to read 4A). A current clamp designed for use with a scope should be highly accurate and repeatable in its measurement. The clamps that are used with the scopes will also have a much higher refresh rate than the standalones, most of the standalone units that I have looked at have sampling rates of 1Hz or longer.

Are there watt ratings on the devices that you are using? Does the manufacturer specify a recommended fuse for them?

No unfortunately not, some products are from aftermarket sellers and some of them are foreign and don't really understand when I'm asking for steady state and in rush currents.

What device would you recommend then? A clamp with a amp rating designed around 40/50A for example and possibly plug into a scope?

I'm pretty certain about the majority of my devices but the odd ones I can not find any info on what so ever.

bump

I was looking at the Picoscope 2204A in combination with some current clamp or possible a handheld fluke 325 Current Clamp. Which one of these would be more suited to the job?

Or should I opt for a Handheld Oscilloscope as my PDM and ECU have in board ones? This is merely to test some current pulls from devices I'm still determining wire and fuse sizes for.

Hi Reece,

I and the team that I work have all bought Picoscope 2204's for work reasons, they are a well featured USB scope that is relatively cheap. For the current clamp I have a Hantek CC-65 that I bought off of eBay. Some of the others use a TecPel CA-60. We have tested these clamps against each other using a calibrated current supply and they have been accurate and repeatable in their measurements.

All of the handheld scopes that I have looked at have been disappointing in their features and operating methods compared to the cost of them, unless you spend multiples more than the cost of the Picoscope, you are engine up with a device that has lower specifications and a higher price than the Picoscope.

1. Can oscilloscopes replace other useful tools? Or possibly make my life easier wiring in any way? 😁

2. Whats the advantage of using a full standalone oscilloscope over a driven one like the picoscope 2000 series? Is it mainly just the screen and controls or would I benefit in other areas?

3. Would you recommend just getting a amp meter or going for a oscilloscope as I'm probbaly looking for half a amp accuracy just to get wiring gauge and fuse sizes.

Hi Reece,

1 Complement, not replace. They will assist, especially in reverse engineering a loom or engine.

2, The standalone units will typically have higher specifications, but in the automotive world these are not needed. Our desktop units have almost totally been replaced by the PicoScopes. There are a number of advantages with the PicoScopes over a standalone, convenience, portability and ruggedness, are some, not needing a mains power supply to operate them makes it easier to use them in a vehicle that is moving.

3, Amp meters typically have a 1hz or slower update rate, and will not capture the inrush current spike, the current clamp on a scope will do this. I carry one of these in my wiring tool chest, and I have a second one that is kept in my briefcase. I'm aware of their limitations but for a quick test unit they are very handy. If I want to get more detail, then the pico comes out.

1. Exactly what i need it for really which is good to know.

2. Sounds good to me, I'll never need the best of the best as this is more of a hobby build but i am planning on switching to making a mil-spc harness for my k-swap.

3. I did see that the fluke 325 has a decent frequency range but I'm assuming I'll get more use out of the Picoscope combo as they are both similarly priced.

1. Exactly what i need it for really which is good to know.

2. Sounds good to me, I'll never need the best of the best as this is more of a hobby build but i am planning on switching to making a mil-spc harness for my k-swap.

3. I did see that the fluke 325 has a decent frequency range but I'm assuming I'll get more use out of the Picoscope combo as they are both similarly priced.

I use a 10a bench top DC power supply. Was a gift but I think they are like $100 on amazon or Alibaba. The 10 amps part is limiting but it allows me to get a sense of power draw and scale up from there. I just set up some test leads in plug in whatever I'm testing.

Alternatively I have a bench test for PMU-16's that I can test larger draws from and get inrush and such.

+1 having an O scope around, there really isn't a replacement for that tool when you need one