UK Stationary Engine Forum

Go Back   UK Stationary Engine Forum > Main Engine Section > Engine-Only Stuff > Ignition Systems

Thread Tools Display Modes
Old 31-10-11, 06:43 PM   #31
Forum Supporter 2011
Join Date: Aug 2009
Location: Adstock, Buckingham
Posts: 831

Originally Posted by piston-broke View Post
hi i have found this info whilst looking for a replacement condensor for myself. the rs part numbers are ok but you need to have an acount to order anything from them or go to one of their trade centre

Guidelines for replacement capacitors / condensors

0.22 microfarad

AC Voltage rating: 400V continuous
Operating temperature: 80 degrees C.
Dv/dt: 1000 or higher
Dissipation factor: 0.05% or less.

Preferably teflon/foil cap

or polypropylene/foil.

try to avoid metalized polypropylene

Sources for capacitors/condensers

RS: 190-8400
917,5x18mm RM=15mm

RS: 334-934
712,5x18mm RM=15mm

RS: 210-522
11,316,5x24mm RM=20,3mm

farnell: 9717358, RS: 206-7746
12x22x27mm RM=22,5mm
To set up "an account" with RS online only requires a simple registration.

I believe from information which I have seen relative to magnetos used on model T Fords, etc, that the dv/dt characteristics of a magneto system are greater than those on an automotive points and coil ignition system. My experience of the latter suggests that a figure in excess of 800v/uS is common, thus I would not suggest using a capacitor rated less than 1000 v/uS on a mag. system. Also beware AC voltage ratings, these are usually for fully symetrical sine waves, you need a capacitor rated for at least 600v dc (transient spike characteristic). The latter was the reason that a lot of the early automotive "electronic ignition units" failed, as they used a thyristor rated around 600 volts or less to switch the primary voltage to the coil.
Douglas VS25; Douglas SV (both under restoration)
oldchadders is offline   Reply With Quote
Old 03-01-14, 05:06 PM   #32
Forum Supporter 2011
smenkhare's Avatar
Join Date: Sep 2010
Location: luxembourg
Posts: 561

Originally Posted by oldchadders View Post
The sole purpose of the condenser is to decouple the points to supress arcing across them due to the back emf generated by the coil. It's value relates to the inductance of the coil and thus is critical when replacing. I used to be the senior electronics engineer for Buckingham Electronic Engineering Co.(then part of the Wipac group), designing gas ignition systems which involved considerable consultation with the automotive ignition guys in Wipac.
The so-called "decoupling effect" of the capacitor is a relatively unimportant function. It does increase the life of the points, that is true but the capacitor (I am of the old school, I prefer "condenser") is there to provide a rapid path to ground for the induced EMF in the primary, giving a rapid change of current and inducing a high voltage in the secondary. Without the condenser, you will get no or very little spark. This is not a technical explanation, which would involve theory which most Engine people have not learned. Forgive me for that!

1957 Lister D, 1951 Stuart Turner R3C with S-T water pump, 1951 Villiers Mk 10 with Alcon pump, Alco Featherweight. 1920(?) Stuart W2. ca.1936 Amanco WC Chore Boy, Sachs KM37 Wankel engine(1972?), Bernard W0, 1938/39, Bernard W2, 1932. Bernard D1
smenkhare is offline   Reply With Quote
Old 19-09-15, 09:29 AM   #33
keith rees
Forum Light User
Join Date: Sep 2015
Location: shrewsbury
Posts: 17
Default Wico Type A magneto

I am still struggling with the impulse concept.
I'm led to believe that it's function is to increase the spark output and retard the ignition at startup?
I have a Wico A mag with impulse fitted to a Wisconsin AHH.
Lets assume that the plug should fire at 20 degrees before TDC under normal conditions.
If the lag angle of the impulse mechanism is also 20 degrees then the initial setting of the mag is for the mechanism to 'click' at TDC?
Once running at normal speed the mag should revert (advance) to 20 degrees before TDC.
Does this make sense to everyone?
keith rees is offline   Reply With Quote
Old 19-09-15, 10:33 AM   #34
Admin Team
Forum Supporter
martinpaff's Avatar
Join Date: Mar 2007
Location: Lincoln, UK
Posts: 11,693

Yup! You have it in a nutshell Keith.

martinpaff is offline   Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT +1. The time now is 05:13 PM.

Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.