In a week before our "Autostrada 2013" festival (see video http://vimeo.com/68535631, my T started to run on 3 cylinders. I asked friends to bring me new spark plugs from Moscow (they had) - but plugs replacement was unsuccessful. So, after testing of wires, we found that 2nd coil doesn't work: it has sparking on it's top, but no spark on a plug contact.
Of course, I started a procedure of buying new coil from US. But you might heard that Russian Post setting records one by one - three days ago my girlfriend got shoes she bought in US on March 12th...
So we decided to try to fix a coil. I found a video from coildoctor.com and Ron Patterson's thread about capacitors http://www.modelt.org/discus/messages/2/33940.html?1326134722
We demounted coil box (to clean contacts and look how it is.
Next - tar removing with a heater.
Old capacitor (i think this coil was rebuilt in 1960s) was 1 microfarad and WV 200V.
So we decided to install 2 capacitors .47mf the only tyme I found - WV 630V (as on Ron's picture) - to double dV/dT rating.
Now it works - and today we'll fill it with a tar.
Really, I understand that it is not professional rebuilding - we have no special testing equipment. But now I have real result to continue using T while waiting for parts from USA
I think that it is first coli rebuilt in Russia )))))
Hope this post will be useful for somebody)
Sorry for mistake - "So we decided to install 2 capacitors .47mf the only THAT I found - WV 630V (as on Ron's picture) - to double dV/dT rating."
You have doubled the capacity only but you have not doubled the dV/dT rating and if you have not yet repotted the coil then STOP!!! The new capacitors you are using are only going to last for a few minutes and all of your work will be for nothing. Assuming you are going to redo all 4 capacitors then the ideal value for the capacitor is .47uF and not the 1uF that was in there. The bigger problem however is that you must not use a part that is "metalized" since its dV/dT rating will be less than 1/10 of what you must have to make the capacitor last. The dV/dT rating has NOTHING WHATEVER to do with the working voltage that is usually marked on the outside of the part. Raising the working voltage from 200 Volts on the original capacitor to 630 as on our replacement part has nothing whatever to do with getting the needed dV/dT rating up to what you need. Send me a PM directly and I can give you some guidelines as to what you need to find.
John, that is the only capacitors I found here. What can I do - it is to cut one of them. Should I?
This coil worked at last 10 years with that 1uF capacitor. And, as I remember, if I use 2 capacitors, I double capacity as well as reliability
and we used 400V, not 630)
Would a conventional distributor ignition condenser work in a T coil? Seems like I read someplace that they have been used and should be easy to find in Russia. I don't know, just a thought.
I'll see what capacity it has)
Please listen to John. All your work will be for nothing. Proper capacitors are important. I understand the unavailability of parts can be frustrating but do use some search engine to find the correct part. Dislike doing things over again, just a waste of time & effort.
Anyway, if I haven't proper one now, it's easy to replace if it will fail to work. I'll try to find correct capacitor
A friend of mine has use a regular auto condenser mounted to the top of his coil for many years. Mount the base to one side and the lead to the other. I don't think 6 or 12 volt condenser matters. Can't put the lid on the coil box but should work till you get the proper one.
I've encountered enough failed 'modern' capacitors to know that John Regan is correct.
Why not carry on, but don't pot it and don't nail the side, but carry a few more of the capacitors which are available, and a soldering iron?
They might last an hour.......but they might last a year!
If it fails on the road, connect a new one on top under the contact nuts and, if necessary, cut the failed capacitor's wires.
It would also be good to get at least one spare coil.
Chris - that's my logic: while searching correct condenser (and waiting new coil from US), use the car with our result
Many years ago, I used some wrong capacitors. Some were wired inside, some were mounted outside. Some worked for a good while, some failed quickly. But I got some mileage out of those Ts I had back then.
John Regan was just a young fellow back then (so was I). He knows this stuff. Listen to him. He and Ron Patterson together know more about model T coils and electrics than any four other people.
My suggestion. For now, try what you can get. Carry spares and hope. If that isn't enough, drive slowly and limp. Order the right things for the long term fix. If at all reasonably possible, get the final adjustment done on a proper test tool (like a Hand Crank Coil Tester. I have no experience with the modern electronic one and don't recall what it is called, but I think you could buy one of them and ship it to Russia for a reasonable cost). Then your T should run better and be much more reliable.
Thank you Michael G, for posting as you did. Many of us do like to hear how you are doing. Good luck, and do keep us informed with updates.
Drive carefully, and enjoy, W2
There was a guy in the club here who used to use distributor condensers in his T coils. He had to keep a soldering iron and spare condensers under the seat due to constant failures.
Once I rebuilt his coils with high dv/dt types, that was the end of that problem.
A Model T coil does not work under the same conditions as a distributor coil.
Ordinary modern polyester capacitors like those shown above just aren't suited to high current pulse circuits. Old paper capacitors are, but they eventually leak.
The high dv/dt types from Fun Projects are so inexpensive and easy to order, that there's no need to use anything else. Never had one fail for the 10yrs I've been putting them in Ford coils.
Michael say's he has to use what he's got and give it a whirl and if it fails, he will repair it. It's easy in this land of plenty to tell folks in other parts of the world how they should get the proper parts and fix things. It's not very easy for folks in other places to do so. I didn't see any offers from to Fed Ex him the correct capacitors.
Ted - you're right: the problem is delivery. I can buy coil from ebay, capacitors from any american shop - but I'll get it after 2 months...
So I will continue searching correct condenser in Russia, and will use our construction - and will tell You all about results.
And what can You say about that high pulse capacitors? (they are present in Moscow shops):
EPCOS B32653 0.47uF, 630VDC, dV/dT 300V/usec
2. WIMA MKP 10 0.47µF / 1000 VDC, PCM 27.5 mm which offers a dV/dT of 900V/usec.
Which is better? I have some doubts about 1000VDC
Maybe an expert can give their opinion but just based on the what has worked as outlined in the previous thread you linked, I would choose #2
Both are Film Capacitors
Both are .47µF
Both have a working voltage of 400 VDC or more. Based on my reading of the requirements, a higher working voltage will not hurt.
However, #1 has a dV/dT less then the previously recommended 700V/usec and #2 has a dV/dT between 700 and 1700 V/usec that have been show to work well.
Just my opinion.
I have used ordinary car condensers for at least 20 years with no problems
Use the 900V/uS type. The Wima MKP types are ideal for this application. I've used them in all sorts of high power high frequency pulse applications.
Thanks to all I ordered both types. I'll start from testing EPCOS (they said me that it is equal to WIMA 630 and it's real dV/dT close to 600V/usec - but it is 4 times cheaper than WIMA 1000).
So - I'll write about results.
Well Michael, How has it worked out? I hope you are not still waiting on the post office. Tell us of your coil adventures. What has worked, not worked, and the "current" situation.
Michael ; Is it an option that I send you some Capacitors . I have some here .I like to send some if that helps .
As you live close to us I will help you with my HCCT .!!!!
greetings from Holland
Coming from an extensive electronics background, I second the Wima MKP types. One of the things I do is rebuild magnetos for cars, motorcycles, and airplanes, and they are my condenser of choice. They are a bit bigger and bulkier than other types, but their specs are top-notch and they are extremely well-built. I have yet to see one fail on me for any reason.
It looks like your coil box is a good original. Have you ever had to do any work the box itself?
If it still works OK that's fine and "if it ain't broke don't fix it."
I only know I decided to finally rebuild mine in my 1919 Runabout. Completely went through it with new bolts, and etc. My car ran pretty good but I decided to do it anyway because it was an old original.
It did make a very noticeable difference.
No more occasional misses, and quicker starts.
Maybe the wiring and contact surfaces on the old contact screws weren't making a really good contact.
Not sure as everything looked pretty good I thought.
Its better now!
Any updates on this project?
I do like the idea of using the heat gun to melt out the tar. Gonna try that soon.