Using Ultrafast Rectifier in place of 60Hz Bridge

That is fed with a 52V CT Transformer also &#; into two 6A diodes and while a small amount of current is bled off (and filtered) to run the timing electronics, the unfiltered output from the diodes is switched by some normal T03 transistors to pulse some 24v solenoids on and off.

So &#; the 50hz unfiltered supply is switched at around 1Hz and 50% duty cycle.

These things run maybe up to 20 hrs a day for 20 years plus &#; so despite the lack of sophistication, they run ok.

The first one I ever saw had shorted diodes, and as I didn&#;t have any suitable ones in stock and the customer was in a desperate hurry &#; I mounted a 35A 600V bridge rectifier on the side plate and used only half of it.

As I started to see more of them, I just did the same thing and never really thought anything of it. Have fixed maybe 100.

Fast forward 4 or 5 years and I got a couple back in with the bridge diodes shorted !!!

Again, I didn&#;t really think too much and bolted in a 50A 600V bridge.

Blow me down if 12 months later, a couple of them came back in with shorted bridges again.

At that point I stopped and thought about the issue.

How come the majority of them could run 20 years with absolutely no problem &#; with 6A diodes in them &#; and these few were blowing up 50A diodes.

I figured it had to be voltage spikes of some kind getting in the system. Other, electrically noisy equipment or poorly located wiring perhaps.

Now, these original units have been superseded by some later ones, which despite being micro controlled, adjustable via a comms line etc &#; still use the same system of feeding through raw unfiltered dc to drive the solenoids.

What is different though, is that they use some TO220 DL, 20A 800V diodes in the same location as the original type unit with 6A diodes. And &#; they have a couple of varistors across the input supply to (I assume) take care of any noise coming in.

Having seen all that, I figured I&#;d do the same thing and promptly started fitting the DL diodes to the old units, along with a couple of the same varistors.

I have had virtually none come back in ever since &#; so I love those diodes and varistors.

It&#;s also why I wanted to find better diodes to replace the bridges in these latest modules I started this thread about &#; as well as fit a pair of varistors across the supply input.

If I stuff up, it has the potential to mess up my relationship with my o/seas customer, and I'd prefer not to do that.

Anyway, I finished them off this afternoon and need to pack them all and send them back ... so time will tell.

Thanks everyone for your input, you are a wealth of knowledge.

The same company that made the above mentioned modules, also makes a device that I have been fixing for years.That is fed with a 52V CT Transformer also &#; into two 6A diodes and while a small amount of current is bled off (and filtered) to run the timing electronics, the unfiltered output from the diodes is switched by some normal T03 transistors to pulse some 24v solenoids on and off.So &#; the 50hz unfiltered supply is switched at around 1Hz and 50% duty cycle.These things run maybe up to 20 hrs a day for 20 years plus &#; so despite the lack of sophistication, they run ok.The first one I ever saw had shorted diodes, and as I didn&#;t have any suitable ones in stock and the customer was in a desperate hurry &#; I mounted a 35A 600V bridge rectifier on the side plate and used only half of it.As I started to see more of them, I just did the same thing and never really thought anything of it. Have fixed maybe 100.Fast forward 4 or 5 years and I got a couple back in with the bridge diodes shorted !!!Again, I didn&#;t really think too much and bolted in a600V bridge.Blow me down if 12 months later, a couple ofcame back in with shorted bridges again.At that point I stopped and thought about the issue.How come the majority of them could run 20 years with absolutely no problem &#; with 6A diodes in them &#; and these few were blowing updiodes.I figured it had to be voltage spikes of some kind getting in the system. Other, electrically noisy equipment or poorly located wiring perhaps.Now, these original units have been superseded by some later ones, which despite being micro controlled, adjustable via a comms line etc &#; still use the same system of feeding through raw unfiltered dc to drive the solenoids.What is different though, is that they use some TO220 DL, 20A 800V diodes in the same location as the original type unit with 6A diodes. And &#; they have a couple of varistors across the input supply to (I assume) take care of any noise coming in.Having seen all that, I figured I&#;d do the same thing and promptly started fitting the DL diodes to the old units, along with a couple of the same varistors.I have had virtually none come back in ever since &#; so I love those diodes and varistors.It&#;s also why I wanted to find better diodes to replace the bridges in these latest modules I started this thread about &#;fit a pair of varistors across the supply input.If I stuff up, it has the potential to mess up my relationship with my o/seas customer, and I'd prefer not to do that.Anyway, I finished them off this afternoon and need to pack them all and send them back ... so time will tell.Thanks everyone for your input, you are a wealth of knowledge.

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