danb35
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- Aug 16, 2011
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Other method with an oscilloscope (or a DMM with fast peak hold): buy a clamp-on current probe like this one for about $50 US. It runs on a 9V battery, clamps over the wire you want to measure current on, and converts the current into a voltage. The model I ordered has two switch-selectable ranges, 1 mV / 10 mA and 1 mV / 100 mA. If you then set your probe multiplier to 10x or 100x respectively, you can directly read the current from the screen.
Advantages: You don't have to build anything, or cut any wires in your drive wiring. If you set up your scope correctly, you can directly read current on your screen. Because it clamps over any single wire, you can easily measure the particular rail you're interested in. It's completely isolated from your server, so no chance of shorting anything out on the scope or the server.
Disadvantages: It's $50--3x the price of @Bidule0hm's solution, and that assumes you've already got a 'scope. And that's a cheap one from China--brand names are hundreds of dollars. It has a bandwidth limit, though this one's stated at 30 KHz, so it shouldn't be a problem here.
I've ordered one, thinking it will be interesting to see how well it works. I'll post a few traces when it comes in.
Advantages: You don't have to build anything, or cut any wires in your drive wiring. If you set up your scope correctly, you can directly read current on your screen. Because it clamps over any single wire, you can easily measure the particular rail you're interested in. It's completely isolated from your server, so no chance of shorting anything out on the scope or the server.
Disadvantages: It's $50--3x the price of @Bidule0hm's solution, and that assumes you've already got a 'scope. And that's a cheap one from China--brand names are hundreds of dollars. It has a bandwidth limit, though this one's stated at 30 KHz, so it shouldn't be a problem here.
I've ordered one, thinking it will be interesting to see how well it works. I'll post a few traces when it comes in.
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