Power Supply Blows

[ilango1]

Recently I have mounted a pump control panel consist of relays, stepdown transformer and dc power supply. This panel mounted at lightening risk area (inside an isolated cabin in middle of a field). The problem is the DC power supply blows at first or second time I switch it on. Its a single phase system. Can anyone suggest what could bre the reason?

 

[melone]

What analysis have you performed, i.e. voltage / current readings, load analysis, fuse sizing, etc.?

 

[peebee]

My first guess is that it's overloaded. My second guess is that it's bad and should be replaced.

You'll need to provide more information if you want better answers than that.

 

[CarlPugh]

Everyone is guessing so I will too. The power supply doesn't fail when you turn it on. It fails when you turn it off. You only become aware it has failed when you turn it on.
A common failure mode is that when the power supply is turned off, there is a high di/dt causing a high voltage on the transformer. This high voltage causes the rectifier diodes to fail. When power is next applied, the failed diode/diodes cause a short circuit causing fire and smoke or whatever. This problem is worse when the power supply is unloaded. The cure is to place an AC capacitor across one of the transformer windings, or add DC filter capacitor.
The other common failure mode is that there is a large capacitive load and the rectifier diodes are overstressed on turn on. The cure for this problem is to use higher short circuit current rated diodes.
Good Luck
Carl Pugh

 

[peebee]

To paraprase my last post, maybe the problem is exactly the same as the title of this thread: Power Supply Blows.

 

[etarhan]

Zillions of possible causes can be the reason, but I would prefer to start with the simplest.
The simplest is this: It is not very clear from your message (pardon my lack of understanding) whether you have replaced the power supply and it happened again, or this is the first and only time it has happened.
If this is a once-in-a-row happening, you have no chance but try again.
Are you sure that you have wired it correctly?
Was it checked before installing in the field (did it work at least once)?
Which part(s) were blown (might give a clue)?
etc., etc.

good luck

 

[dydt]

hi...

its a brand new power supply?

anyway, try a bench test first and if it works you know
that the problem is on the field....

dydt

 

[ilango1]

hi all,

Thanks for taking the time to read and generate feedbacks
to my problem. Actually the 24V DC power supply is a brand new switching power supply. I have already tested the power supply in my office with some load and its fine. The problem only happens at the field. Let me elaborate how the field looks like, its an open area, the cabin is some kind of a control room, we use the computer to switch on and off
the water pumps and log some soil moisture data. The DC power supply is used to power up the Digital Output modules,
relays, and some sensors. The incoming single phase Ac power was tapped from the main three phase electrical pole, straight to a fuse and into the ELCB and MCB and then to a AVR before plugging it into the computer and the control panel. "But the Computer's power seem to be ok"

I have already replaced 3 DC power supply. And I think it not going to be cost effective if I keep replacing them
without finding the problem. The power mosfet and some resistors and fuse is the commom parts blown.

 

[busbar]

ilango1, more information is needed. The only thing to do is pick the hardware and the problem apart piece by piece.

What is the voltage rating of the source [the site electrical service entrance]?

Is the utility’s 3ø transformer-bank secondary solidly grounded?

What are the voltage and voltampere ratings of the stepdown transformer?

What is the input voltage rating of the DC-out power supply?

Is the stepdown transformer a listed machine-tool control power transformer, a constant-voltage/ferroresonant type or something else?

Describe exactly how the stepdown-transformer primary is connected.

Describe exactly how the stepdown-transformer secondary is grounded.

What overcurrent devices are connected between the stepdown-transformer secondary and the DC power-supply input terminals?

Describe exactly other loads connected to the stepdown-transformer secondary.

Aside from overcurrent devices, is the DC power-supply input connected in any way besides to the two-wire secondary of the stepdown transformer?

Have you personally made field measurements to confirm that the various nameplate electrical ratings match the electrical characteristics on both sides of the stepdown transformer?

 

[peebee]

Here's one more to add to busbar's list: you mention that "This panel mounted at lightening risk area". Are your failures occuring during electrical storms?

 

[dydt]

hi...

try to power it up without the load...output module, relays, sensors, etc....then if the power supply still okay then step by step connect the load .. and if something blew then you know that the last component you connected is the one giving you trouble...

good luck..
dydt