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Breakdown between solder tags?
Breakdown between solder tags?
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Old 10th February 2004, 02:12 PM   #1
eeka chu is offline eeka chu  United Kingdom
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Default Breakdown between solder tags?

I've been laying out a board using standard turrets, not insulated stand offs.

In the plate supply, I decided to use some hyperfast diodes. The legs of these have a 4 - 5mm spacing. I realise I can bend them out, but it looks much neater and saves time if I leave them straight.

Around the base of the turrets is a ledge that is used for the insertion tool to rest on.

Click the image to open in full size.

I can drill the 5mm holes and the diodes will be an excellent fit, but between the two pins, the ledges leave a gap of something around 1mm.

I will be using three hyperfast diodes per side of the transformer, in series, to rectify a few hundred volts. There will be a 1M ohm balancing resistor and 10n cap across each.

I read that air breaks down at around 3 million volts per metre. I make this 3000v per mm. I realise the break down voltage goes thru Paschen's Curve.

Am I going to be okay with this? If the prediction is for 2000 - 3000 volts, 400v shouldn't be anywhere near enough right?

I'll get a friend to drill the holes on a desktop CNC machine so I don't have to worrying about accuracy.
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Old 10th February 2004, 04:16 PM   #2
dhaen is offline dhaen  Europe
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You will need greater distances than any calculation suggests.
The main reason is convection. The air carries dust particles, and they adhere to everything, but especially to high voltage points. This will either narrow the gap, and/or cause a partially conductive layer to form.
In a clever design it may be possible to minimise the convection past these points.

As a rule of thumb, I'd leave 5-8mm between 2 points with 400v between them that are mounted on a flat surface.

Clean the equipment every few years.
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Old 10th February 2004, 09:14 PM   #3
eeka chu is offline eeka chu  United Kingdom
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Join Date: Nov 2003
Location: England
Are there any funky pin bender tools available that might make bending them a bit neater?

I've seen a tool from Hoffman Amps for bending the leads of axial components, and Hakko sell something similar for cutting the leads and forming them. But I've not seen one for radial leads yet.

I may have to bend quite a number of these pins, so some that would do it neatly, and quickly, would be good if such a thing is out the.

I just thought that, since this probably happens often, someone might have come up with an idea to make it tidier.
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