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Registered Member #3904
Joined: Sat May 21 2011, 10:32AM
Location:
Posts: 28
Józef C wrote ...
There are lot of HV probes on eBay pretty cheap, or you can construct your own.
Is it generally safe to use multimeter probes with a scope (using a banana to BNC adaptor)? There are quite a few low cost HV multimeter probes around, but I haven't seem many HV scope probes. I wonder if the difference is just in the frequency response of if there's something fore fundamental.
After reading through this post I realised that I was not grounding the low terminal of the HV secondary. However, when this terminal is grounded, the frequency seems to decrease a lot. I don not own a scope, but the change is obvious by the pitch of the sound. Is this normal, and if so, why? I am using a 555 driver with IRFP450 mosfet.
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
kimbomba wrote ...
After reading through this post I realised that I was not grounding the low terminal of the HV secondary. However, when this terminal is grounded, the frequency seems to decrease a lot. I don not own a scope, but the change is obvious by the pitch of the sound. Is this normal, and if so, why? I am using a 555 driver with IRFP450 mosfet.
By grounding that pin which was previously ungrounded, you altered the circuit. By doing so, either the tuning or the loading on the flyback (or both) has changed, which is causing the change in pitch of the sound. With the low end of the secondary grounded, you may now experience higher high voltage on the output (or possibly lower, if the change greatly affected the tuning and/or the loading).
Registered Member #3904
Joined: Sat May 21 2011, 10:32AM
Location:
Posts: 28
Xray wrote ...
With the low end of the secondary grounded, you may now experience higher high voltage on the output (or possibly lower, if the change greatly affected the tuning and/or the loading).
I've noticed the higher voltage when secondary grounded before, but I don't have a good understanding of why this happens. What losses would grounding the secondary be reducing?
Registered Member #4107
Joined: Sun Sept 25 2011, 07:30PM
Location: London
Posts: 53
Another thought, OP. A lot of equipment is manufactured with a ground that is not at earth potential. You have a possible solution - stick the whole thing in some bitumen and let it go hard. There'll be no corona losses and you'll be protected from electric shock. You can buy bitumen in tins for sealing roofs, gutters, that kind of thing. It starts as a liquid but exposed to air, forms a thicker and thicker skin and eventually goes solid. It's exactly what they used to do with flyback transformers in TVs. What do you think?
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Dangerous ZVS Driver 'floating' at 30kV+ ungrounded - Safety advice please!
