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another tenuously linked question

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Dave P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 15 Sep 2018 at 12:15
To be honest I don't understand what determines the different value requirements of a condenser. Obviously there are reasons for the varying specifications, I just don't know what they are. Going back to the rusty Honda CG 125,I replaced its' condenser with one from a Triumph T'Bird. It worked fine. Will somebody enlighten me please. Thanks.
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Mike H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2018 at 00:23
Originally posted by jefrs jefrs wrote:

220nf and 1000V would be about right.
Problem is not just soldering wires on but insulation because the operating volts can be around 450V (because of the coil primary). 1kV can jump 1mm in dry air, allow for some oil mist and it is lower, one of the reasons a condenser has a fat can, increased stand-off.

The insulation on normal auto wiring is good enough for 1kV. So is the heatshrink sleeving that you could put on over the solder joints. I have so-called bell-wire for wiring up electronic circuits which looks quite thin but actually is spec'd at 1 kV. I have used it in lots of things including valve amplfiers.


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They're normally an electrolytic type, the polarity has to be the right way round.

No they're not, not at that small value. This is patently obvious by looking at Google pictures. Please do some research before spreading mis-infornation.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpc Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2018 at 06:28
While claiming total ignorance of things electrical, I operate a '71 Fiat 500with a Marelli distributor similar to that on loops, and condenser problems are a regular topic on that other forum.
Posters regularly swear by and recommend this as a much better quality condenser:



Edited by jpc - 16 Sep 2018 at 06:33
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Jerry atric View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerry atric Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2018 at 10:19
Thats interesting. Obviously worth paying a bit more and knowing you wont have a problem. I don't understand why Honda bolted the condenser under a cylinder head nut, one of the hottest places surely? Regarding it not being important which way they are connected, does that mean it doesn't matter which wire goes where? (The Jap condensers mostly have 2 wires, 1 to coil, 1 to points) I really wish I understood wiggly amps but I've been trying for fifty years and nothing is sinking in
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2018 at 10:47
All these "special" or "competition" condensers are merely decent spec condensers which are marketed as "special".

If Maplin was still around you could buy one there for pennies and it would probably last far longer than a special automotve one costng far more.
To start with they fail due to age, and my guess is that most automotive ones are fairly old stock these days, whereas electronic components will be new.

And no, they are not electrolytic.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpc Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2018 at 11:07
Originally posted by Jerry atric Jerry atric wrote:

I really wish I understood wiggly amps but I've been trying for fifty years and nothing is sinking in

Same here, like ballet dancing, if you don't get it by then, I guess you're not meant to Cry

All the condensers I've seen are connected to points, and to earth directly via mounting or a wire.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefrs Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2018 at 12:05
Originally posted by Mike H Mike H wrote:

Originally posted by jefrs jefrs wrote:

220nf and 1000V would be about right.
Problem is not just soldering wires on but insulation because the operating volts can be around 450V (because of the coil primary). 1kV can jump 1mm in dry air, allow for some oil mist and it is lower, one of the reasons a condenser has a fat can, increased stand-off.

The insulation on normal auto wiring is good enough for 1kV. So is the heatshrink sleeving that you could put on over the solder joints. I have so-called bell-wire for wiring up electronic circuits which looks quite thin but actually is spec'd at 1 kV. I have used it in lots of things including valve amplfiers.


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They're normally an electrolytic type, the polarity has to be the right way round.

No they're not, not at that small value. This is patently obvious by looking at Google pictures. Please do some research before spreading mis-infornation.



   

You're quite missing the point here.
The insulation is not the amount of plastic wrapped around it but the distance the high voltage can jump, which is needs a 'stand off'.  If you're building or repairing valve amplifiers as I do with guitar amps, you may well have 450VDC, and the exposed solder contacts have to be separated far enough that the current doesn't jump across. A tiny 1/8 watt resistor cannot take 4kV because the volts will jump and track from one end to the other but a 1/2W resistor is about 13mm long and can.
In an amp we have dry air, in the distributor there is usually an oil mist which can lower the spark gap by a factor of between two and ten fold, depending on how messy the distributor is.
The coil primary can induce a high voltage at the points, we see a good spark there, the condenser is there to quench the spark, to stop the discharge there so the coil secondary imparts full energy to the spark plug.

I've only been messing about with vehicles since the 60s. I've seen and handled hundreds of these things, I so do not need Google. The old school condenser is a small electrolytic, the tin can is a bit of a give away, and the fact that old ones leak the waxy oil out. Back in the day the only type that could take high voltage was an electrolytic, nowadays we have other options, possibly better too.
Negative earth is normal now but on really old vehicles you may well find positive earth, which requires a different polarity condenser. Don't try to re-use their condensers.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2018 at 13:36
I've only been doing this since the 60s too.

Searching around various websites, I have yet to find any reference to an electrolytic being used in this situation, all references being about foil and insulation rolled up.

An explanation found. It also contains a method of checking (roughly) that a capacitor is good, but you do need an analogue multimeter.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 2018 at 16:13
I still have my old analogue meter and that's about the only thing I use it for. I'm never quite convinced by the test however, and usually play safe with substitution (a bit tricky with a magneto!)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 2018 at 21:45
The other thing an analogue meter is very good for is checking the tracking of a TPS. Watch the resistance increase or decrease smoothly. Can't do that with digital.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerry atric Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2018 at 07:25
This has gone WAY beyond my understanding now. I just hope my sparking points were down to the condenser. I'm not even going to Google electroiitic
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefrs Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2018 at 10:13
Originally posted by Brian UK Brian UK wrote:

I've only been doing this since the 60s too.

Searching around various websites, I have yet to find any reference to an electrolytic being used in this situation, all references being about foil and insulation rolled up.

An explanation found. It also contains a method of checking (roughly) that a capacitor is good, but you do need an analogue multimeter.


I have the dubious advantage of being a professional physicist-engineer.  I have even had 11kV high capacitance value capacitors made for me for work, operated at 6kV. I can recognise the capacitor type from the construction.  Somewhere in a drawer I have a capacitor test meter. The difference here is that it not only tests the leakage but also tells us the capacitor value. Such a meter is a bit specialised use and they tend to be expensive.
Surprisingly perhaps, and coming from the physics, the coil itself stores electrical charge, as when the magnetic field collapses that energy is sent down the coil secondary; it's not held in the capacitor.  The capacitor only charges up when the points open and stops the points from arcing too much and draining the energy away to ground. When the current stops flowing in the primary coil, high voltage is developed in the secondary coil, which causes the spark at the spark plug.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote BobV7 Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2018 at 10:37
Another DuracellLOL
V7 Classic Black and gold is the best colour
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2018 at 13:46
I really don't need a lecture on how an ignition coil works, that was more than adequately covered in A level physics..
And by the way, I remember making a capacitance tester when I was a teenager. Remember Heathkit?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony-C Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2018 at 21:04
Remember Heathkit..? I certainly do. . . .It,s me, Ah Cathy, I,ve come ho..ome, I,m so co..o..o..ld. Let me in your window oh.. oh.. oh .." What a great song ..!! Regards, Tony PS, does this qualify as a "tenuous link ..?
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