5v 2.5 amp adapter (IN 230v ac 0.2 amp max) damaging when connecting to a high power line which is carrying 50 amp current

[Manjunath]

Hi,

I have a product in which 5v 2.5 amp adapter (input 230vac 0.2 amp max) used. The adapter is burning out sometimes usually when I connect it to the one of the phase (in 3 phase line where ac >30 hp motor is connected) carrying upto 50 amp current.

Now my question is why the adapters are burning? As per my knowledge the adapters cannot connect to a phase line which is carrying high current.

But I dont have any option, so planning to connect a high wattage resistor in series between the phase and adapter which will be acting as current limiting resistor. Is this method solve the issue? If this method is correct what resistor value (with wattage) need to be choosed.

Your help will be appreciated.

Thanks
Manjunath

 

[DPG]

Don't just connect a dropper resistor, you are just making the issue.

Can you post a diagram of exactly how you are connecting the adaptor up. Show voltages if possible.

 

[Manjunath]

Thanks for the response. I am not good in circuit design. Please suggest a solution for this
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Thanks for the response. I am not good in circuit design. Please suggest a solution for this. Attached the diageam

 

[DPG]

The current taken by the motor is fairly irrelevant. Can you measure the voltage between the phase connection and the neutral point. Assuming you can do this safely.

What earthing system do you have over there?

 

[Manjunath]

The current taken by the motor is fairly irrelevant. Can you measure the voltage between the phase connection and the neutral point. Assuming you can do this safely.

What earthing system do you have over there?

Yes, the voltage between the phase and neutral is 230v. We are using earthing in some places where neutral is not available. Earthing is perfectly done by using copper plates, salt and charcoal.

 

[DPG]

Yes, the voltage between the phase and neutral is 230v. We are using earthing in some places where neutral is not available. Earthing is perfectly done by using copper plates, salt and charcoal.

I suspect that is the issue. What is your actual measured voltage when measured at various times.

 

[Manjunath]

I suspect that is the issue. What is your actual measured voltage when measured at various times.

I am sure the voltage is 200 to 240v max, only few adapters are damaged.

Not sure, whether damages happening because of phase line carrying 40 amps current. If this doesn't cause any problem to adapter, then the issue is because of over voltage or shorting between two phases. What do you say? Share your opinions
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And I dont think the issue is because of earthing, few adapters damaged when connected to neutral also. As per my observations, the adapters damaged when the power came and the motors started suddenly. So I am suspecting on the current which may go upto 60 amps when the motor gets started.

What happens if I connect a 1.2mega ohm resistor in series with the adapter and phase line.? Any issues with that.? What happens when two phases shorted - increases current or voltage? This limiting resistor doesn't help?

Please suggest

 

[DPG]

Do not just insert random resistors in series with it. You need to measure the actual voltage to the adapter, maybe at different times. Do you have test equipment? I would suggest getting someone experienced to look at this to be honest. It needs more than guesswork.

 

[Manjunath]

Do not just insert random resistors in series with it. You need to measure the actual voltage to the adapter, maybe at different times. Do you have test equipment? I would suggest getting someone experienced to look at this to be honest. It needs more than guesswork.

Thanks for the valuable suggestions DPG.

 

[Manjunath]

I discussed with an expert and he suggested to add a circuit in front of adapter. Please see the diagram attached and share your opinions

 

[DPG]

Has anyone measured the voltage feeding into the adaptor?

 

[Manjunath]

opinions

As we have 3 phase motor connected, the adapter might get damaged because of some noise and electfo magnetic interferences, he said. So suggested to add this circuit
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Has anyone measured the voltage feeding into the adaptor?

I have measured multiple times and the voltage is ~230v always

 

[DPG]

As we have 3 phase motor connected, the adapter might get damaged because of some noise and electfo magnetic interferences, he said. So suggested to add this circuit

It's possible yes. And definitely a better proposition than the series dropper resistor.

 

[Manjunath]

It's possible yes. And definitely a better proposition than the series dropper resistor.

Ok thank you

 

[DPG]

Ok thank you

How is the adaptor physically connected to the supply?

 

[SparkyChick]

If the adapter is connected as shown, and is after a switching element... a contactor for example... is it possible it could be being subjected to huge voltages as the magnetic field collapses in the motor windings?

I've had problems in the past with low voltage relays damaging their switching transistors due to a lack of a back EMF protection diode.

 

[Lucien Nunes]

A resistor in series with the adaptor might not protect it significantly and can cause the adaptor to malfunction, so not recommended. The capacitors in parallel might protect it from voltage transients caused by the switching of the motor. The actual current the motor takes is not specifically relevant, however as it is a large motor, switching transients could deliver enough energy to damage the adaptor.

Possibly a better way to protect against transients is to use a purpose made surge protector based on varistors and this would be my preference. But you need to be sure that it is short, high voltage spikes that are doing the damage and not unexpected longer periods of >250V (your comments on this noted).

Have you looked inside the damaged adaptors to find out which components are failing? That would tell about the nature of the overvoltage.