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Inrush and DC limiting
Inrush and DC limiting
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Old 14th August 2019, 07:18 AM   #11
Mrcloc is offline Mrcloc  South Africa
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Ok, let me fix this one up a bit better. Back EMF will be properly sorted here now.
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Old 14th August 2019, 01:38 PM   #12
Mark Tillotson is offline Mark Tillotson
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Originally Posted by Mrcloc View Post
Thanks, I will do if I still have the buzz after the DC blocker. The transformer is high quality, and has acted the same since the first turn-on. It's 625 VA, and the buzz does go away when the mains cleans up (geyser, fridge, etc. all turned off).

Just to say check that the transformer primary has the right rated slow-blow fuse to protect it - saturating a transformer due to DC offset can lead to large currents flowing, and if these get too great the thing may cook or even catch fire.
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Old 14th August 2019, 01:52 PM   #13
Mrcloc is offline Mrcloc  South Africa
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Originally Posted by Mark Tillotson View Post
Just to say check that the transformer primary has the right rated slow-blow fuse to protect it - saturating a transformer due to DC offset can lead to large currents flowing, and if these get too great the thing may cook or even catch fire.
Yes! Definitely one of my reasons I want to install the DC blocker. Thankfully it doesn't get too hot at all, but sometimes the thing will suddenly buzz very loudly, and I must say, I do stress a lot when that happens. I can't remember the fuse, but it wasn't ridiculous - something like 6 or 8 A.


ETA: Yes - I just checked, it's an 8 A ceramic slow blow.

Last edited by Mrcloc; 14th August 2019 at 01:55 PM.
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Old 14th August 2019, 02:13 PM   #14
avtech23 is online now avtech23  Australia
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Inrush and DC limiting
What is the purpose of the bridge rectifier and 4700uF caps?
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Old 14th August 2019, 02:53 PM   #15
Mrcloc is offline Mrcloc  South Africa
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Originally Posted by avtech23 View Post
What is the purpose of the bridge rectifier and 4700uF caps?

To block DC.
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