hello,

I constructed the following power supply to drive a dc motor

this one worked well , then I needed to supply two motors so I constructed the following circuit

one of the bridges blew up , is there something wrong i'm doing , what can I do to make it work

 

Are you connecting any outputs from the two bridges together?

 

I found out that one of the caps was connected with the wrong polarity , it must have been the reason why the bridges blew up.

I will get a new bridge and try again , do you think that there is nothing wrong with this connection ?

 

Why not just use a three phase rectifier? That way you are using a balanced load on the transformer. A three phase rectifier uses six diodes instead of four like a single phase rectifier. Like shown in the attached image.

 

Your loads are un-balanced across the transformer secondary. Wrong capacitor polarity is probably what caused its destruction. Using all three phases will result in much less AC ripple < 5% on the bridge rectifier output and you can do away with the capacitors.

Cheers, DPW [Everything has limitations...and I hate limitations.]

 

If you need a common ground for the motors, then you have to connected as the circuit from shortbus provided.

In any conditions that you can't connected the output together from two motors as your second circuit.

Why your rectifier blew up, i think that is like this:
Because the capacitor connected the wrong polarity, so it blew up first and it became shorted, when it shorted then the output of rectifier will overload, so it blew up too.

You can check the capacitor.

 

so , with the second connection I mentioned , it is not possible to combine the grounds of the output from the rectifier ? because I have to combine the outputs .

 

so , with the second connection I mentioned , it is not possible to combine the grounds of the output from the rectifier ? because I have to combine the outputs .

How can you just connected the output together and let the ground alone, if you doing so, then the current of circuit will loss the loop condition, it just go out but didn't come back, and you can't get the power from the circuit.

The current flow from :
city power → transformer → rectifier → capacitor → (+)Motor
city power ← transformer ← rectifier ← capacitor ← (+)Motor

So if you want to using the second circuit then you can't just connected two output of voltage or two ground together, it doesn't mean anything, this circuit should be used in two motors alone.

If you want that two motors has common ground, then you can using the circuit from shortbus.

 

this is the complete schematic , is this connection possible or not ?

thanks

 

the controller is what cobines the grounds of the rectifier outputs

when I tried this coneection , the controller burned , and the igbt gate drivers in one of the two channels burned , what can I do to make it work ?

 

I'm not sure the current is enough no not, but you can try the half rectifier, and it will has a common ground.

O1 → diode → capacitor → to motor 1 power
O2 → diode → capacitor → to motor 2 power
The ground is common terminal for transformer and motors and controller

Or the ground in series a diode common
Transformer N ← (-)Diode(+) ← the common ground of motors and controller .

 

what if I separate the grounds of the controller for the two pwm signals like this

http://forum.allaboutcircuits.com/cache.php?url=http://s24.postimg.org/64xj0wgqt/untitled_page_1.jpg

would that work ?

 

If you look at your drawing and draw the four diodes out for the bridges, I think you will see that the lower left diode will have ground tied to both ends. Does that make any sense at all? A bridge rectifier depends upon either an input supply isolated from ground or an output isolated from ground.