Thread: Capacitor info required, any help would be appreciated.

Hi Crocy

one of my favourite old books is "Electrical Engineers Reference Book" by MG Say.
Very useful.
I keep a hardback copy in old fashioned paper form, whereas I have given away a lot of my old collection.

If you need an interim repair, try three Jarcar RS5380 0.01MFD 3KV ceramic caps in series, and jury rig it with BPs and cable ties etc.

cheerio, mike

Originally Posted by mike48

Hi Crocy

one of my favourite old books is "Electrical Engineers Reference Book" by MG Say.
Very useful.
I keep a hardback copy in old fashioned paper form, whereas I have given away a lot of my old collection.

If you need an interim repair, try three Jarcar RS5380 0.01MFD 3KV ceramic caps in series, and jury rig it with BPs and cable ties etc.

cheerio, mike

Well Mike, the Ebay capacitor finally turned up, but was stuffed, so $20 wasted, but worth a shot. I cannot find the capacitors you listed, are they from Jaycar or the RS catalogue? Will the caps you mentioned take the high current this set up needs?
In the meantime, I have found a guy in the US that has a lot of tesla gear online, and he has given me some options to pursue. I also spoke to Steven?, I think, at Token Tools and he was also very helpful, would probably buy one of his welders, but the waranty could be a problem from way up here, but not insurmountable. He also may have an option of supplying a retrofit HF from one of his machines, and if I can convince SHMBO to make a quick run to Sydney in June, I will drop in to his factory and have a look at it.
Thanks and regards,
Crocy.

That is because there is a small error in the part number. Try this instead Part number RC5380

Originally Posted by mike48

one of my favourite old books is "Electrical Engineers Reference Book" by MG Say.
Very useful.
I keep a hardback copy in old fashioned paper form, whereas I have given away a lot of my old collection.

I'm with you on this one Mike... My two favorite books are "Principles and practice of electrical engineering" by Alexander Gray (published 1917) and a later one "Electrical engineer reference book" which may be the one you refer to, by Molloy, Say & Walker from 1948.
Some of the best information, and all still relevent, out of those two books.

Mike and Bob, thanks again for your input, but those little caps will not take the amount of current that moves in the HF circuit, hence why the correct one costs $500+, Just waiting for the guy in the US to answer some of my questions and if his alternate doorknob? ones will do the job, I will try his way first,
regards,
Crocy

Hi Crocy

oh dear - two errors in one line; must have been a bad day for me.
Apologies.

My suggestion should have read (as Bob correctly indicated) -
"try three Jaycar RC5380 0.01MFD 3KV ceramic caps in series".

I would have thought that it would work, as the caps are "low K type ceramic", and capable of some RF current.
What happened?
Did it work at all?

Anyway, I went through my junk box, and the only thing I could find is a French Steafix brand (good quality) 0.0026 MFD, 12 KV block cap with 8mm ISO coarse threaded lug connectors.
It is round, 60mm dia and 90mm long, and weighs 600grm.
I think it is mica, but there is a small chance it may be polyester.
I have tested it for capacitance, and for leakage and DC breakdown at 750V DC.
All OK.

You are welcome to this, at no charge.
Send me a PM for address or phone number etc.

Don't do anything drastic like buying a new welder yet.
I will also ask some of my mates for a block mica cap for you, similar to the original.

This particular capacitor came out of the transmitter section of a French manufactured Air Traffic Control type ground surveillance pulse radar, rated at 2 MW power at L band. That's not milliwatts, but megawatts.
I used to work on these very radars, and then taught pulse radar systems.

cheerio, mike

Thanks Mike, PM sent,
rgds,
Crocy.

Hi Crocy

PM reply sent with address.

The .0026 Steafix (type 433) cap holds it charge OK and a leakage test at 750 V DC has less than 0.1 microamp leakage, which should be OK. (It used to have a normal working voltage of 11 KV DC pulsed at 1kHz).
I have not got anything which tests at a higher voltage unfortunately.

However, as it possibly is mylar or polyester, it also may just not like continuous high RF current. No matter, worth a try.

I cannot find an old Steafix catalog to see what this exact type of capacitor is made from.

So, I will still attempt to see if my friends have a block mica, which normally have a rating stamped on them for RF current.

It is normally just a matter of temperature rise due to internal RF resistance, which is hard to see let alone measure at HF.
Mica is very good in this regard, and can handle RF well.
However "low K" ceramic types are OK also, and I was a bit surprised that your trial of the three ceramic caps "popped" off.
I can only assume from that failure that the Jaycar caps were "high K" (an RF parameter of the ceramic dielectric) types, which are lossy at RF.
So called ceramic "doorknob" types are normally good for HF RF but the only ones that I have in my junk box are 470pfd, or .00047mfd, and you would need four in parallel.

Anyway, try out the Steafix .0026 mfd, and see how it goes, while I search.

You know, years ago, we used to dump wheelbarrows of old HV mica capacitors like you need. There just wasn't any more need for them as transmitters changed from valves with high voltage, to transistors with lower voltage and ferrite transformer coupling.
I used to have some really large ones in my office as curiosities to impress visitors.
They were 400 mm high, with cylindrical white ceramic bodies and large metal end caps, and came out of 5kW MF/HF transmitters and antenna couplers.

cheerio, mike

Hi Crocy

as per PM, one 0.0026 mfd 12 kV capacitor posted off Friday.

Let us all know if it works please.

It is still worth looking for a known mica unit, with an actual RF rated current, but at a reasonable price, ie less than $20 plus post.

Good luck!!

cheerio, mike

Originally Posted by mike48

Hi Crocy

as per PM, one 0.0026 mfd 12 kV capacitor posted off Friday.

Let us all know if it works please.

cheerio, mike

Just to let you all know, Mike kindly gave me a capacitor, and I hotwired it into the machine as a trial, and hey presto we have a pilot arc again. Because it is larger and the two on their way from the US are huge, I will have to get some copper cored spark plug wire from the local drag racing supplier and make up a remote mount above the metal box that it was all in, as a permanent fix.
But again, thanks to Mike for his generosity, allowing me to get back to welding Ally,
rgds,
Crocy.

Hi Crocy,

Glad to hear the good news.
Can you let me know the physical dimensions of the old capacitor, and its markings please.

And ... greetings from Abu Dhabi in the UAE, where I am visiting and staying with family, and where they do not have a Bunnings nor Jaycar.

cheerio, mike