I keep frying bridge rectifier on power supply

[js412000]

I am bench testing my servo system and put together a dc power supply for it.

When I apply power, the transformer hums and the rectifier pops shortly thereafter.

I have not hooked up the servo drive or motor yet.

The transformer is hooked up to output 60 volts. The rectifier is rated 1000v 50a. I put a 200 ohm resistor in the transformer output for testing purposes .

It works ok with just the smallest capacitor ,100v dc 1000mfd. When I hook up any of the others, 200vdc 1000 mfd and the big one 450 vdc 1500 mfd, the resistor gets very hot even with no load on the power supply. (The fuse is removed)

Electronics is not my area of expertize, so I have been working slowly and carefully to avoid damaging anything expensive.

All the grounds are connected to the bar on the left side including the dc negative wire. The ground bar is connected to the ground wire outside the service panel in my basement.

I have four more rectifiers coming by mail order from Hong Kong plus I picked up a couple of eight amp units at Radio Shack to use until I find out what I am doing wrong!

[Al_The_Man]

If you have the AC grounded as well as the DC common, you have a short circuit through the rectifiers, I would say it is either that or you have the bridge connected wrong.
You will get the transformer over load and rectifier pop if it is as I first mentioned.
What is the resistor for in series with the transformer secondary lead?
Al.

[js412000]

The first pop was because I had the bridge hooked up wrong.
The second and third "pops" I am not sure about.

The ac coming out of the transformer goes straight to the rectifier and is not grounded . The frame of the transformer is grounded. The heat sink for the rectifier is grounded. The green wire coming out of the disconnect on the wall is connected to the ground bar. I have 245 volts (both live wires) going into the transformer .

I put the resistor in the transformer output to prevent the bridge from popping instantly while I am checking things out.

I read in Jacob Tal's book something about hooking up ground wires ,at first, with a 10k ohm resistor and then measuring the voltage across it to avoid unpleasant surprises.


I think the problem may have something to do with the medium size capacitors. (200 vdc 1000 mfd)

I bought all the capacitors on ebay and they appear to be new. When I test the big and small ones with an ohm meter, The needle jumps momentarily to zero,then settles back to the maximum resistance position.

The medium size capacitors test ok at the 10x position on my ohm meter, but at 100x and 1kx the needle stays at 0 resistance for about 6 seconds then lingers at the half way point on the scale for a minute or more then slowly drops but never goes back to the maximum resistance position.

I am not sure what that means.

[Al_The_Man]

Hook things up one at a time, leave the caps disconnected and just connect the transformer and the bridge, when checking caps with an ohm meter, you are essentially charging them with the voltage from the meter, so you should see a gradual climb, on reversing the meter, you will see a high reading which slowly tapers off as it charges up the opposite direction.
Al.

[js412000]

Thanks Al,

It seems to be working, now, with only the big and small caps hooked up.

I will leave the medium caps disconnected,for now.
Maybe they are leaking, or something.
I probably don't need that many any how.