Author Topic: Generator Controller - High Current Indicated, with No Load.  (Read 1056 times)

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Offline kolbep

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Generator Controller - High Current Indicated, with No Load.
« on: January 20, 2017, 07:37:12 pm »
Hi All,
Here is my next little repair project (or if it is not a fairly easy fix, it will just be replaced, it is for a customer, so I do not have unlimited time).





It is a Generator Controller for a 3 Phase Generator.
The generator would shut down after about 30 Seconds of running. I eventually managed to navigate the Chinese menu, to set it to English,
and then I could see the problem. It was shutting down due to Overcurrent. Controller reporting over 1100A per Phase! almost Identical current reading for each phase. And that was with No Load, and with the output breaker switched off.

The Generator has 3 CT's (1 per phase) connected to the controller. I disconnected the CT's from the Controller, and bridged out the CT Inputs on the controller, and was still geting over 1100A per Phase. Which means that the CT's are fine. I also tested, I have no leakage from the Phases to the CT's.

So I know the problem is definately in the Controller. Here are pics of the Main Input PCB


and a close up of the CT Input Section.


The CT Inputs to the controller are rated at the usual 5A.
If I look at the Board, I see that the Inputs go through the Black CT's that are on the board. The Black CT's connect to a Transistor (for some reason), and then to a TL0841 JFET OPAMP (U17). From the Opamp, they then go through a HEF4051B Mux/Demux (U19), and then goes to the headers to the microcontroller/display board.

There are also Voltage inputs (and these seem to be reading fine).

Now, If all 3 Channels are reporting the same (or similar) current, which is Very High, with the inputs shorted out, do you think that the Opamp or the Mux/Demux might be faulty. I just want a general idea of where to look. The Board does not have any signs of overheated or burned or damaged components, so I am flying blind until I get it on the bench tomorrow.

And I Love the Series of SMD Resistors on the Voltage inputs, the long rows of them (for the resistors voltage limits) look very sexy.

Thanks
P

« Last Edit: January 20, 2017, 07:39:42 pm by kolbep »
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Offline SeanB

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Re: Generator Controller - High Current Indicated, with No Load.
« Reply #1 on: January 21, 2017, 08:24:26 pm »
The transistor is there as a voltage clamp for spikes, and I would bet the opamp is dead from voltage spikes. Easy to check, give it a 5v supply in the appropriate pins and check the outputs are still around half rail.
 


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