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arun1979
Level 1
Level 1
10 replies posted 10 sign-ins 5 replies posted

I have designed a PFC circuit using ICE2PCS02GXUMA1 to provide about 1000W of output power from the AC source. The circuit is designed to provide 375V output to drive inductive load.

Whenever this board is plugged into GFCI socket on the wall, we are tripping the GFCI outlet whenever the motor is turned on. The board and the motor works fine on a non-GFCI socket.

On the circuit, I have 120V going though bridge rectifier and then using the PFC boost circuit to generate 375V DC to operate the motor. At the output of 375V, I have two large 850uF (450V) electrolytic capacitors.

My initial though is that whenever I turn on the motor, we are draining and charging these two large capacitors and that could be causing the current different between the two input lines from the wall.

I am new to high power stuff and never dealt with GFCI issues before. Would love to get your comments on this and how these issues are resolved on this type of circuit. Attaching a snapshot of the circuit for this.

 

arun1979_0-1687379936600.png

 

arun1979_1-1687379948864.png

 

Thank you,

Arun

 

 

 

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1 Solution
cynic_bandera
Employee
Employee
5 questions asked First question asked 100 sign-ins

You have a huge peak current during electrolytic capacitor charge and motor start-up. Your C78 and R121 are designed not correctly. Normally is used only R121 without a capacitor of about 10-30 Ohm, which limits the charge current. After charging the capacitor through R121, your relay triggers. Your motor ideally should start after the full capacitor charge.

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17 Replies
harshagovind
Moderator
Moderator
Moderator
100 sign-ins 5 solutions authored 10 likes given

Hi  Arun,

Kindy check leakage current flowing into ground and GFCI trip current threshold .  2.2nf Y caps to GND can contribute to leakage current .

Best regards,

Harsha

 

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Hi Harsha,

I actually don't have the Earth ground connected. I see the same results if the earth gnd is connected or disconnected. Both cases GFCI is tripping. GFCI threshold is 3mA - 5mA.

Arun

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cynic_bandera
Employee
Employee
5 questions asked First question asked 100 sign-ins

You have a huge peak current during electrolytic capacitor charge and motor start-up. Your C78 and R121 are designed not correctly. Normally is used only R121 without a capacitor of about 10-30 Ohm, which limits the charge current. After charging the capacitor through R121, your relay triggers. Your motor ideally should start after the full capacitor charge.

Hello,

C78 and R121 are there only to suppress any voltage spike and surge current through the relay contact. This is a safety relay and the circuit only comes on when the relay contacts are closed. When the relay is opened, there is no charging to the capacitors as there is no voltage at the bridge rectifier. Motor is only started after some time after the power on so they are fully charged.

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ah.. I see NTC 10 Ohm at the input which is responsible for the E-cap charging. Do you see this effect at the first connection or after that?  Initially, the NTC is cold and has 10 Ohm at the first line connection. After a minute of operation, it´s hot with almost 0 ohm resistance. It will not work if you connect it a second time, it must cold down.

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Hello, the problem only shows up (GFCI trip) when the load is turned on which is a motor connected to the HVDC. The boards powers up with no issues when power (AC) is plugged in. The motor is turned on after few mins of power on and as soon as the motor turns on the GFCI trip. [No issues with non-GFCI outlet]. I can get full power out of this circuit on non-GFCI outlet.

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Is the MOTOR case grounded? Leakage?

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hello, the motor case wasn't grounded (chassis gnd) previously. I connected the motor case to chassis gnd but still same issue (tripping GFCI outlet).

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Is EGND connected somewhere else? 

Can you manipulate Y caps (change capacitance up and down, disconnect it)? I would check the current through the caps.

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EGND is tied to the motor body. I have tried both with EGND connected and disconnected. Same issue exist with both cased.

Today I removed the Y caps and tested again, however GFCI is still tripping. I am looking into some equipment to measure the input/output current to see how much we are loosing.

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harshagovind
Moderator
Moderator
Moderator
100 sign-ins 5 solutions authored 10 likes given

Hi ,

Any progress with testing? Have you been able to check leakage current and manipulate with Y-Cap ( 1nF can be tried ) .  What make of NTC is being used ( preferred to use 25mm size )?

 

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Hi Harsha, the test without the Y cap did NOT resolve the issue.

NTC being used is SL32 10015-B. This is a 31mm size.

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inrush current, measure it in start-up

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Hello,

I'm now able to measure the leakage current on the EARTH gnd wire between the board and the wall outlet. I am seeing about 5-15mA current depending on how hard the motor is turning. I'm still not able to determine where it is leaking from?

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Do you have any other parts connected to GND apart from Y cap? Is the leakage with Y caps or not?

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Did some additional bench testing with everything removed from the board except the motor and below are the results:

Create setup on bench with HVCB + Function generator and retest first to make sure leakage current still exists.

Setup is now available with new HVCB board and leakage current is 8.4mA when motor is turned ON.

In standby condition when motor is off, leakage current is about 0.22mA.

Remove RV1 and remeasure: 8.3mA leakage current when motor is tuned on.

Remove RV1 + C2: 8.2mA leakage current when motor is tuned on.

Remove RV1 + C2 +C3: 8.02mA leakage current when motor is tuned on.

Remove RV1 + C2 +C3 + Y CAPS (C1 & C4) : 9.35mA leakage current when motor is tuned on.

Remove RV1 + C2 +C3 + Y CAPS (C1 & C4) + L1 : 6.04mA leakage current when motor is tuned on.

Remove RV1 + C2 +C3 + Y CAPS (C1 & C4) + L1 + R2 : 6.03mA leakage current when motor is tuned on.

My next step is to remove the motor load and use resistive load to see if that makes a different to the leakage current.

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harshagovind
Moderator
Moderator
Moderator
100 sign-ins 5 solutions authored 10 likes given

Hope you were able to find the cause of higher leakage in your design . kindly update on your test with other loads . 

Regards,

Harsha

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