Large Capacitor - UK Vintage Radio Repair and Restoration Discussion Forum

spaceelectronic · 19th Aug 2018, 5:06 pm

Hi All
Thought this might be a talking point. Have you every used a capacitor as large as this one before. 4000pF. 15kV?
Dave

19th Aug 2018, 5:33 pm

At Pye we had 25kV 8uF ones, the size of a large suitcase.

broadgage · 19th Aug 2018, 5:50 pm

I have seen larger ones, used for power factor correction on 11Kv circuits.

lesmw0sec · 19th Aug 2018, 5:50 pm

Quote:

Originally Posted by merlinmaxwell

At Pye we had 25kV 8uF ones, the size of a large suitcase.

I had one such device (ex-TV transmitter). I kept it charged from the EHT supply of an old 12V TV. It was used as an electric fence to keep the foxes from my chooks. I used to discharge it in the morning by throwing some wire at it. Occasionally the discharge would set fire to the grass. I should add that this was in the remote Australian bush...

GrimJosef · 19th Aug 2018, 6:11 pm

My second job involved building a bank of 1.35uF 100kV ones. If you were doing it safely then each one was a four-man lift. The bank had 24 of them in.

In the end the size of capacitors tends to reflect the amount of energy you can store in them and the fundamental technology. If I've done the sums right the OP's will store about half a joule. Merlin's will store 2500 joules. My work ones would hold 6750 joules each. They're all film caps of course.

The biggest I've got in the workshop are a few of the tiddlers in the attached pic (75mm diameter, 145mm long). 2200uF at 450V stores 220 joules or so (electrolytics store energy at higher density than film). Discharging that into the air is likely to make people in the same room drop their cuppas.

Cheers

GJ

G6Tanuki · 19th Aug 2018, 6:37 pm

That's nice. In the past some of the HF ATUs I had designed for me involved ceramic/mica "doorknobs" of 300pF 20KV but their main design-issue was being able to handle the crazy circulating currents for a few seconds until the combination of switched and roller-inductors got their act together.

If you're storing it I'd seriously recommend you putting a shorting-link across it, to avoid the issue of it becoming 'hot' again through slow dielectric-recovery of old un-dissipated charge.

Malcolm G6ANZ · 19th Aug 2018, 6:59 pm

When we scrapped a linac I rescued 4 caps rated at 2000pF 20Kv and passed them on to Astral Highway for his experiments.
In the circuit the caps were in series to get the required working voltage.
Malcolm

spaceelectronic · 19th Aug 2018, 8:49 pm

We used these when manufacturing RF/HF Induction generators. I think a company called Unilator used to manufacture them.

19th Aug 2018, 5:06 pm	#1
spaceelectronic Triode Join Date: Aug 2018 Location: Stratford upon Avon, Warwickshire, UK. Posts: 18	Large Capacitor Hi All Thought this might be a talking point. Have you every used a capacitor as large as this one before. 4000pF. 15kV? Dave Attached Thumbnails

19th Aug 2018, 5:33 pm	#2
Guest Guest Posts: n/a	Re: Large Capacitor At Pye we had 25kV 8uF ones, the size of a large suitcase.

19th Aug 2018, 5:50 pm	#3
broadgage Nonode Join Date: Jan 2010 Location: North Somerset, UK. Posts: 2,130	Re: Large Capacitor I have seen larger ones, used for power factor correction on 11Kv circuits.

19th Aug 2018, 6:11 pm	#5
GrimJosef Dekatron Join Date: Sep 2007 Location: Oxfordshire, UK. Posts: 4,311	Re: Large Capacitor My second job involved building a bank of 1.35uF 100kV ones. If you were doing it safely then each one was a four-man lift. The bank had 24 of them in. In the end the size of capacitors tends to reflect the amount of energy you can store in them and the fundamental technology. If I've done the sums right the OP's will store about half a joule. Merlin's will store 2500 joules. My work ones would hold 6750 joules each. They're all film caps of course. The biggest I've got in the workshop are a few of the tiddlers in the attached pic (75mm diameter, 145mm long). 2200uF at 450V stores 220 joules or so (electrolytics store energy at higher density than film). Discharging that into the air is likely to make people in the same room drop their cuppas. Cheers GJ Attached Thumbnails __________________ http://www.ampregen.com

19th Aug 2018, 6:37 pm	#6
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: Large Capacitor That's nice. In the past some of the HF ATUs I had designed for me involved ceramic/mica "doorknobs" of 300pF 20KV but their main design-issue was being able to handle the crazy circulating currents for a few seconds until the combination of switched and roller-inductors got their act together. If you're storing it I'd seriously recommend you putting a shorting-link across it, to avoid the issue of it becoming 'hot' again through slow dielectric-recovery of old un-dissipated charge.

19th Aug 2018, 6:59 pm	#7
Malcolm G6ANZ Octode Join Date: Feb 2006 Location: Bristol, UK. Posts: 1,042	Re: Large Capacitor When we scrapped a linac I rescued 4 caps rated at 2000pF 20Kv and passed them on to Astral Highway for his experiments. In the circuit the caps were in series to get the required working voltage. Malcolm

19th Aug 2018, 8:49 pm	#8
spaceelectronic Triode Join Date: Aug 2018 Location: Stratford upon Avon, Warwickshire, UK. Posts: 18	Re: Large Capacitor We used these when manufacturing RF/HF Induction generators. I think a company called Unilator used to manufacture them.