 Trying to read SMPS current
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IamSmooth
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Sun Jan 09 2011, 03:27AM
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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
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I have a buck converter. I have a voltmeter across the output and a DC analog current meter in series with one of the output leads. The output of the converter goes through a 750uf capacitor in parallel with a 1.5EMI film capacitor and common mode choke.
I read the AC current (current1) coming out of my wall socket using a current clamp meter. The mains voltage goes through a voltage doubler giving a DC output 2*1.4*Vac. I read the DC current coming out of the smps (current2)using an analog current meter. I read the AC current going to my induction heater coupling transformer using a current sense transformer (current3).
Current1 and current3 are almost identical. Current2 is barely 10A when I am reading close to 40A on current1 and current2. Is it that there is DC and AC current that I am missing? Is there a good way to read the current coming out of the smps? The volt meter reads correctly.
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Sulaiman
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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
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Moving coil (d'Arsonval) meters respond to AVERAGE current,
- the clamp meter has it's scale adjusted to read rms current
- ONLY if the waveform is a sinewave.
If there's a voltage multiplier the current will be in pulses so dc average and rms will be very different
- the analog current meter measures the AVERAGE current from the doubler.
- the current transformer may have a few weaknesses;
- you are trying to measure a unidirectional pulsing current using a transformer !
A meter that doesn't use a transformer is required here.
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Arcstarter
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Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
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Sulaiman wrote ...
- you are trying to measure a unidirectional pulsing current using a transformer !
A meter that doesn't use a transformer is required here.
Current transducer comes to mind.
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