Bridge rectifier diode order.

Thread Starter

Bod

Joined Sep 18, 2016
311
I've created a small full-wave bridge rectifier for 12VAC. Even open circuit, when it's powered it gets quite hot quite quickly. I'm sure it's a case of not having the diodes correctly connected, but I can't seem to spot it no matter how much I compare it to other circuits, and I need a second pair of eyes to point out what I'm missing.
I've linked the schematic below. The rectifier is used to power a relay coil. The relay is an ORWH-SH-112D1F. The coil's only 360mW, equating to about 0.03A (at 12V). I don't think this should be enough current draw to cause the rectifier to get that hot. The diodes I chose are 1N4001. Potentially could have done with 1N4007 instead, but I didn't even measure a noticeable difference in voltage drop across the two different diodes (the voltage drop being about 0.5V), and the 4001 are still rated abover 12V. The cap is 25V, 1000uF.

1656857603187.png

I've gotta be missing something obvious, but I just can't see it. Any ideas?
 

Capernicus

Joined Jun 24, 2022
87
Those diodes are correct as far as I can see, I can see the type of rectifier it is, makes sense.

Whats the cap and the other diode for? (the other symbol with a block and diagonal line through it is the solenoid coil right?)(
 

Capernicus

Joined Jun 24, 2022
87
Those diodes are correct as far as I can see, I can see the type of rectifier it is, makes sense.

Whats the cap and the other diode for? (the other symbol with a block and diagonal line through it is the solenoid coil right?)(
looks like the other diode is the wrong way around and the cap... MHR is right.
 

Thread Starter

Bod

Joined Sep 18, 2016
311
For starters you have the Electrolytic cap around the wrong way, also D5.
IOW the bridge is outputting the wrong/reverse polarity.
Yes, the diode polarities are reversed.
Does that mean all dioes need to be flipped?

Whats the cap and the other diode for? (the other symbol with a block and diagonal line through it is the solenoid coil right?)(
Cap is there for smoothing, the other diode is a flyback diode. Probably not necessary in that scenario as theres no sensitive control circuitry (and in fact I hadn't even added it before testing the circuit). The block with the line throught it is the coil yes - a relay t comes as two parts in EAGLE.
 

Thread Starter

Bod

Joined Sep 18, 2016
311
Bridge rectifier diodes D1-D4 need reversing.
Cheers I'll give that a shot.

I've always found bridge rectifiers the hardest circuits to recreate even though they're so simple. Squishing the diodes from a square (like in rectifier schematics) to a stack of dioes like above, I just find really hard to match the connections up.
 

Tonyr1084

Joined Sep 24, 2015
6,896
Aside from the argument about polarity - this is what I'm keying in on:
Even open circuit, when it's powered it gets quite hot quite quickly.
Just a guess here but either something is wired wrong in the real world (not the schematic) or one of the diodes is shorted.

You also said:
I've created a small full-wave bridge rectifier for 12VAC.
This isn't one of those square box BR's that have four terminals, two marked for AC and one for + and one for -. I remain concerned that something in the actual circuit is wired wrong - or one or more diodes are shorted.

You said it gets hot with an open circuit. How much is open? Just the diode output on its own? Or with the cap? Or with cap and relay? It COULD be a bad cap if that's in your "Open" circuit. You've reverse polarized your cap and that could be causing issues.
 

Capernicus

Joined Jun 24, 2022
87
Bridge rectifier diodes D1-D4 need reversing.
Need to see all different topologies of rectifiers, all of them are hand/eye traceable, then move onto voltage doublers, then your amps, latches. How long have you been doing electronics for- I bet not that long, youll definitely get better with xp. But this rectifier I hadent seen it before this either, but I pretty much could read it pretty easy.

Good goin'
 

Irving

Joined Jan 30, 2016
2,797
The GND is the return path from OUT - you need two connections to make a circuit!

And yes, the bridge diodes are reversed so D5 is shorting them out so they all get hot! They should be like this:
1656861124069.png
 
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