Condensor query

[Mickwhitt 5,131]

Hi all.

Been looking at condenser matters for Fred since some of you mentioned a faulty condenser could cause all manner of problems.

I learned how to test a condenser to see if its functioning. But that didn't show me the actual capacitance value for the condenser. 

So I bought a testing machine that can measure the value of a given capacitor. The condenser originally on Fred came in at 0.18 uF

The one I bought from a motor spares shop came in at 0.20 uF

Most websites with information on condensers relate to vintage cars and bikes, they state a value of 0.22uF is best for an ignition system. 

So I bought an electronic components capacitor with that value which I will trial on Fred to see how it runs and if it prevents points burning.

Does anyone have any opinions, comments, suggestions about such a strategy?

One guy even said he hollowed out old condenser cans and inserted a modern capacitor in it to look authentic.

Mick 

[ebinmaine 72,669]

[oilwell1415 563]

Seems like a reasonable test plan.  Just make sure the caps have enough voltage rating.  When the points open and the electrical field collapses the primary voltage can spike to a few hundred volts.  You probably need a cap rated to at least 300 or 450 volts to live.  A higher voltage unit should live longer than a lower voltage unit.  You are basically installing a shock absorber for the ignition system, so the capacitance is specific to the characteristics of the system.  It doesn't have to be exact, but it needs to be pretty close.

[JohnD 145]

Capacitors typically have fairly wide tolerance, +-10% or +-20% are fairly normal; some are even wider, so your 0.18 uF to 0.22 uF are all in the same range. 

Edited December 8, 2020 by JohnD
word fix

[lynnmor 7,815]

If your points transfer material from side to the other the capacitance is not optimal.  Too low or too high will determine which side gains or loses.  If the wear is about the same, don't replace, the new one may be worse.

[JohnD 145]

Knowing how similar circuits work, it seems like the condenser and points would be matched at one engine speed for minimal material transfer, presumably 3600 rpm (or whatever the mfg recommended speed is for a given engine).  Seems like idling for a while could be a bad thing for point life.  Maybe that's why automobiles of old went through points so often due to the varying engine speed?  These ignitions are before my time until I got my WH! 

[Mickwhitt 5,131]

When I bought Fred, he was fitted with a coil and condenser combo. I never started the engine so I can't say if they performed ok.

As I rebuilt the engine I bought a new coil and condenser, the motor spares shop knew bugger all and just sold me what they thought might be ok. This new pairing worked and runs fine but I've not checked the points transfer.

I tried the original condenser just to see what happened, wouldn't start nicely at all, despite the condenser testing ok with my meter. It also showed a value of 0.18 uF.

The newer condenser is 0.20 uF and seems to be ok but as I said not enough running to check points wear.

I will try a brand new 0.22 uF capacitor today to see if that makes a difference. When I ordered them from Ebay I slipped up; I thought they were £1.87 each so bought two. Turns out they were £1.87 for ten, so I have 20 of the little orange buggers sat on my bench lol.

Mick 

[Mickwhitt 5,131]

So.

Today I soldered up a test wire to connect one of the new capacitors into Fred's ignition circuit. 

Effectively im able to swap between the existing condenser and the new capacitor.

Running and warmed up I unplugged the condenser.

Immediately the engine started to die so I plugged in the capacitor and it ran great, no discernable difference.

So the theory works, this new fangled orange drop works just like a car condenser.

Obviously its not very robust and I will make one up in a metal can which will make it tougher and easier to replace. 

At 8 pence each its way cheaper than a new condenser. 

Its rated at 630v so should be up to the job and its a 0.22uF capacitor. 

A nice metal box to house it will be knocked up on the milling machine and I can examine points burning to see if we are in the right value area.

Mick 

[953 nut 59,967]

19 hours ago, Mickwhitt said:

So the theory works, this new fangled orange drop works just like a car condenser.

Obviously its not very robust

  It will be interesting to see how long the smaller capacitor works when attached to a Kohler rather than a printed circuit board.

[Mickwhitt 5,131]

Nut,  yes I'm wondering the same thing. 

Im hoping that with a suitable case it will be protected from the environment. And that I will be able to swap a failed condenser fairly easily.

Im imagining that the electronic component is no different to a condenser but im sure one of our electronic boffins will be able to comment.

 

Mick