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E3634A 4 wire connected to electronic load displays incorrect monitor current

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nctnico:

--- Quote from: Helix70 on November 13, 2024, 04:51:08 am ---Hi all,

I have an Agilent E3634A that I have repaired, but there is one fault that eludes me. Everything works correctly with static loads, and also when the sense terminals are linked at the terminals.

When I run separate sense leads and power leads to an electronic load (Tenma/Korad) set to constant current 4A, and set the E3634A power supply to 2V at 5A limit (CV), the monitor current reads 1.0-2.0A despite the load drawing 4A as expected. Changing the current limit on the 3634A down to 3.9A forces into CC mode and then the monitor reads accurately as expected.

When I probe the sense terminals when I see the fault, there is a 60 kHz ripple of about 0.5V visible, which disappears when CC is forced or the voltage is higher in CV mode.

Anyone else able to replicate? Is it the PS, the load, the idiot operator? Any other ideas?

--- End quote ---
This can happen when the control loops of the PSU and DC load start to interact. Connecting a big capacitor (> 1000uf) across the terminals can help to stabilise the control loop. You have to keep in mind that a DC load in constant current mode has a high impedance (lookup the definition of a current source) for which the PSU isn't designed.

Kean:
And a similar issue was just reported by another user with different equipment.

https://www.eevblog.com/forum/testgear/siglent-sdl1000xsdl1000x-e-electronic-load/msg5718259/#msg5718259

It is a reasonably common occurrence, and I believe often goes unnoticed.

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