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Continuing with the capacitor/condenser issue

Sarastro

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I have a good replacement capacitor for the unreliable ones that are currently being sold by the usual suspects. I got a few of them from Allied Electronics, https://www.alliedelec.com/. the part is Illinois Capacitor no. 224PPB102K, which has the allied stockno. 613-0592. There are others that should work; this one is overkill, for sure, but still is less than $3. And, it should last forever; no need to replace it periodically.

The first picture below shows them. they are a little large, about 1.25" x 1" x 0.5", and definitely won't fit inside the distributor. Even smaller capacitors, which might be OK, probably won't fit either. I mounted the cap on a piece of printed circuit board (second picture) so it could be mounted right on the coil (third pic.) This is a little clumsy, and not terribly attractive; for many of you that matters, so maybe a little more thinking about this is in order.

The next picture shows the test setup. I mounted a distributor in my little lathe, so I could spin it, and connected it all to a coil and spark plug. I powered it from a little power supply I have ($10 at the local electonics mart). It all worked well; I could see the plug sparking and the points as well. I was surprised at how little sparking there was at the points, but of course there can't be much or they wouldn't last. The main reason for all this was to monitor the waveform at the coil, so I could be sure it was doing the same thing that the standard system does. I had measured the waveform in the car before converting to the electronic ignition, and I was pleased, but not at all surprised, to see that it was virtually identical (last picture).

So, I think that this idea works, and certainly should be lot more reliable than those depressing caps I took apart.

If you want to try this yourself, and can't find the exact capacitor I used, you might look for a capacitor of 0.22 microfarads, at least 600 volts dc breakdown voltage. If you can find a "dv/dt" spec, multiply this (in volts per microsecond) by the capacitance in microfarads, which of course is 0.22. This should be at least 5 or 6. If the catalog doesn't have that spec, which it probably won't, use a fairly large, polypropylene film capacitor (like, 0.5" dia by ~1-1.5:" long). Something like this should be husky enough to handle the current. The PPA series, which Allied also has, should work fine (Allied part 613-0667). Don't use an electrolytic capacitor, or one of these teeny radio capacitors.

I'm still a little troubled by the need to mount this sensibly; I'm not sure what's the best, simplest way to do this. Most important is to strain-relieve the leads. Just soldering wires to the leads, and letting them flop in the breeze, probably will result in them breaking from fatigue before long. That's why I mounted the cap on the piece of board; I could put a dab of epoxy on the wires and they won't flex at the connection.

Remember also, the connections: one lead of the capacitor to the points (can be the points side of the coil, of course), the other to chassis ground. Don't forget to remove the original capacitor!
 

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Pot the hole thing with the leads long enough to the dizzy.
amixture of modeling 15 minute epoxy would do it and would last for ever.
Scope looks pretty flat.
 
Yeah, I was thinking of something like that. I'd want to have some kind of mounting tab, too. That could be the ground connection.

For those who speak "oscilloscope," here's what you're looking at:

The first blast at the left of the screen is the high voltage that fires the plug. This is 10V/cm with a x10 divider probe, on the coil primary, so the peak is about 160V. It's not always clear, because the scope doesn't necessarily trigger on the first positive slope. The slower oscillation starts when the spark dies and the circuit is effectively changed, since there is no load on the coil. Finally, the voltage drops to zero when the points close. You can't see this last transition on the screen, as it happens after the end of the trace.
 
Anybody here remember the Mallory condensors?
Huge things, almost as big as a D cell battery.

I've had those go bad.

With electronics, bigger is not necessarily better.

When I pick up an old vacuum tube radio, and get it to work, generally the filter caps are shot and MAYBE you can hear discrnable signal over the 60-cycle hum.
 
Excellent work Steve.

On a tangent to this, is that the DC motor/controller on your Sherline lathe? How steady is the speed control? The one I have in storage has the old variable speed AC motor. I never liked that drive. I was going to change the motor and drive when I decided instead to buy a 7x14 hobby lathe from Micro-Mark.
 
The sherline uses a 90V DC motor. It's pretty steady, and the control is quite good--not touchy or anything like that. I like the Sherline, but I'm not an experienced machinist so I don't have much to compare it to. I would like something a little larger though, eventually.
 
For a larger lathe you can move up to the 7x10 Seig (Chinese) family of lathes sold by Harbor-Freight (among others). There are MANY vendors of that series of lathes and there is an active Yahoo group for the 7x10 lathes. There are also several vendors of parts and accessories for the Seig lathes.

I have a Unimat-3, the Sherline, and the Seig. I use the Seig for most real machining. I converted the Unimat-3 to a 90V DC drive with speed readout and use that for all my tachometer and speedometer calibration work. I like the Sherline but frankly I don't have the bench space for it at the moment. When I finally put it back into service I'll convert it to the DC motor/drive.

Recently 8x lathes are showing up more and more. On sale they are close to the 8x lathes in price. Most reviews I have read say they are VERY stable due to their added mass. However, the last thing I need is another lathe at this point of my life.
 
Steve,

I need an address for you. I sent you a capacitor for analysis back on August 7th and the package I sent you was returned today.

Thanks, Phil

Please pm the address to me and I'll send it off again.
 
Steve, I saw this topic resurface recently and it occurred to me that I meant to ask you your thoughts on an alternate to the cap you recommended above.

Would you look at this following please?
Cornell Dubilier 940C10P22K-F
available from both Mouser and DigiKey (less expensive at Mouser.com)

https://www.mouser.com/ProductDetail/Cornell-Dubilier/940C10P22K-F/?qs=2QDSxDVy%2b9YL9mneHhAGNA==

At first blush this looks to have similar specs to what you tried.
(Datasheet here: https://www.cde.com/catalogs/940C.pdf )
However, it's an axial cap about 5/8" OD by a little under 1-3/8" long. I would solder leads to this, fold them back against the cap's OD, then cover it all with a piece of heat shrink.

The dv/dt x cap value is way higher than 5 or 6 as you mentioned above so I must be doing something wrong or misunderstanding your intent with the math.
 
That capacitor looks good to me. The main things of importance are (1) right capacitance, (2) high enough breakdown voltage, and (3) the "dV/dt" spec, which indicates the maximum current in an odd way. All these check out.

I used the ones I chose simply because they were admittedly overkill, but better to start high and work down, rather than the other way. I really hate dealing with high-voltage fireworks....
 
Peter Caldwell of World Wide Auto Parts in Madison WI sells an electronic condenser that will fit inside the cap, and will also last {possibly} forever. The condenser even has a small red LED in the end, so that you can set your points opening by the flash of the light. He has run this in his Mini for almost 4 years on one set of points. It keeps everything looking stock, which is of importance to me.
If this is of any interest, you can contact Peter at 800-362-1025.
I don't make anything off this, but Peter is a good guy, and not only offers this interesting "factory looking" upgrade to electronic, but also offers THE ABSOLUTE BEST rebuilt lever shocks on the market.

Brad
 
Brad,

Welcome over to LBC.
 
TequilaBrad said:
Peter Caldwell of World Wide Auto Parts in Madison WI sells an electronic condenser that will fit inside the cap, and will also last {possibly} forever. The condenser even has a small red LED in the end, so that you can set your points opening by the flash of the light. He has run this in his Mini for almost 4 years on one set of points. It keeps everything looking stock, which is of importance to me.
If this is of any interest, you can contact Peter at 800-362-1025.
I don't make anything off this, but Peter is a good guy, and not only offers this interesting "factory looking" upgrade to electronic, but also offers THE ABSOLUTE BEST rebuilt lever shocks on the market.

Brad

I am not sure Peter handles those condenser modules anymore, but I highly recommend him. He is a stand-up guy and definitely takes great care of his customers.
 
He was handling them < 6 months ago. Send him a note. They are made by a buddy of his.
 
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