condensers

zefarelly · 22 Jul 2004, 09:59 (Ref:1042973)

how do they work ? how can you test one, and why did mine clap out on the start line on Sunday?

I'm trying to think of a reason why it just died, no warning and no apparent reason . . . .the car was perfect up to that point . . .could it have been damaged by the scrutes making me hit over 3k revs then yanking the cut out switch ? a dodgy rev counter ? or just my bad luck at Brands ?

StephenRae · 22 Jul 2004, 13:29 (Ref:1043397)

I don't know how they work, but you can pick one up from the workshop floor and it will work for years or be let down by a new one! I think they are sensitive to voltage.. if the wrong coil is used they don't last.
Don't your regs allow electronic ignition?

TPB · 22 Jul 2004, 19:54 (Ref:1043807)

A capacitor, or condenser as it used to be called,is a device for storing electricity for a limited time.
On your engine it is used for spark quenching,i.e to prevent arcing at the points.
In a points operated ignition system, self-induction causes a high voltage sufficient to produce a spark across the points at the instant they open. Fitting a capacitor in parallel with the points allows the energy to be momentarily absorbed. When the capacitor discharges, the gap at the points is too large for arcing to occur.
If the capacitor fails in most case's the primary voltage travels straight to earth,no spark and quite often as in your case no warning.
As Steve recomends check your regs and if its allowed fit an after-market electronic system. This will get rid of the capacitor and in most cases give you a variable dwell angle, two big advantages.

hth

zefarelly · 23 Jul 2004, 08:29 (Ref:1044264)

thanks chaps, I'm not sure we're allowed electronic ignition (for FiA regs) . . . .I have it waiting in the wings though!

as you say . . .a 2nd hand one out of an old box of bits is fitted and the car sprang to life . . . .unfortunately I couldnt do it on the grid !

zefarelly · 26 Jul 2004, 09:32 (Ref:1047478)

someone suggested using a lower voltage coil and a ballast resistor . . .apparently it'll prolong condenser life, can anyone verify that ?

electrical stuff does my head in !

Dave Brand · 26 Jul 2004, 09:52 (Ref:1047492)

Quote:

Originally posted by zefarelly
someone suggested using a lower voltage coil and a ballast resistor

That was done to improve starting. A six volt coil was used on twelve volt systems, with the full twelve volts supplied to the coil while the starter motor was operating; when the starter switch was released the ballast resistor was switched into the circuit to drop coil voltage back to six.

Quote:

. . .apparently it'll prolong condenser life, can anyone verify that ?

I can't see any reason why it should.

zefarelly · 26 Jul 2004, 14:42 (Ref:1047821)

Quote:

Originally posted by Dave Brand
I can't see any reason why it should.

neither can I, I'll put it down to pub talk, thanks for the reply

I might just stick a spare in the glove box just in case !

thebear · 26 Jul 2004, 23:33 (Ref:1048329)

Quote:

Originally posted by zefarelly
neither can I, I'll put it down to pub talk, thanks for the reply I might just stick a spare in the glove box just in case !

Throughout the history of electrical devices, the lowly capacitor has had the highest failure rate of any device in mass production.

Early TV sets were more failure prone from capacitors than they were from vacuum tubes (including the picture tube).

During the 2nd WW studies were made and manufacturing processes refined to alleviate most of the problems in radios of the day.

Paper capacitors (the ones that look like flattened peas) were the most reliable. Electrolytic ones (automotive ignition systems/some radios/TVs) the least.

I can recall repairing radios and TVs that had `leaking' capacitors.

They were simple to diagnose as one merely looked at the underside of the chasis for the `goop' dribbling out.

**dtype38** · 27 Jul 2004, 17:00 (Ref:1048975)

Quote:

Originally posted by zefarelly
. . .could it have been damaged by the scrutes making me hit over 3k revs then yanking the cut out switch ?

I'm not an electrical expert, but I believe that if you have a simple "disconnect" cutout switch in the battery line, then yes, switching it off at 3k revs can cause damage. At the instant the battery is disconnected, the alternator is still supplying current to the electical system. If this is above the total load, then it has nowhere to go and may cause over-voltage and other strange effects. This is avoided by using one of the "FIA" cutout switches which has additional contacts to cut the supply to the ignition coil directly, and to ground out the electrical system through a ballast resistor to avoid any damage when the switch is used.

R59 · 27 Jul 2004, 19:15 (Ref:1049105)

The trick is to connect the alternator to the battery, and then the alternator always has a load on it. The simple cut-out still works in the normal way. Shall I draw a picture? It's far easier that those unreliable FIA switches (which have cost me lots of points in the past!), and fully effective.

Condensers, capacitors, easily tested. Just buy a multi-meter with a capacitor test facility. Most condensers have their capacitive values on them. They should be within 10% I would expect.

It's sometimes quicker to change it for a new one than take it off and test it, and let's face it, they are not exactly expensive.

Rob.

Rob

**dtype38** · 28 Jul 2004, 07:50 (Ref:1049522)

Quote:

Originally posted by racing59
The trick is to connect the alternator to the battery, and then the alternator always has a load on it. The simple cut-out still works in the normal way. Shall I draw a picture? It's far easier that those unreliable FIA switches (which have cost me lots of points in the past!), and fully effective.

Wouldn't say the simple ones are any more reliable. I used to have one on my current car and had to send it back for randomly shutting down my electrics during a race weekend

zefarelly · 28 Jul 2004, 11:39 (Ref:1049731)

I have an Fia switch but dont trust it ! the alternator feeds the solenoid direct, I guess I could send it straight to the battery then its always got something to charge, good thinking. the FiA switch cuts the coil quick enough though.

BrettFrancis · 4 Aug 2004, 10:21 (Ref:1055961)

I should probably start a new topic for this, but this one seems well developed...

Just fitted an AIM data logger into a FF1600 and everything is dandy, until you look at the RPM while the engine is running. It jumps all over the place. I now know that AIM make an "RPM-ECU Interface Module", however, that will not help me tomorrow.

I'm lead to believe that a capacitor will help smooth things out, and so I tried sticking an old condensor into the wire between the Coil -ve and the Logger. Blow me down if it didn't work...

... until the revs got up around 4000 or above. Then it starts jumping around again.

So my question is- is this because the condensor/capacitor I chose wasn't up to the task, and if so, what sort of capacitor should I be looking to stick into the system (running standard FF points, not these flash electronic units that we aren't allowed)?

And if the condensor should have done the job, what else might I be able to do?

275 GTB-4 · 4 Aug 2004, 11:28 (Ref:1056031)

Quote:

Originally posted by BrettFrancis
I should probably start a new topic for this, but this one seems well developed...

Just fitted an AIM data logger into a FF1600 and everything is dandy, until you look at the RPM while the engine is running. It jumps all over the place. I now know that AIM make an "RPM-ECU Interface Module", however, that will not help me tomorrow.

I'm lead to believe that a capacitor will help smooth things out, and so I tried sticking an old condensor into the wire between the Coil -ve and the Logger. Blow me down if it didn't work...

... until the revs got up around 4000 or above. Then it starts jumping around again.

So my question is- is this because the condensor/capacitor I chose wasn't up to the task, and if so, what sort of capacitor should I be looking to stick into the system (running standard FF points, not these flash electronic units that we aren't allowed)?

And if the condensor should have done the job, what else might I be able to do?

Hmmmmmmmmmmmm, well if you have another of those pesky little condensers lying around you might try putting it in parallel with its mate thereby doubling the capacitance....it may just work at the higher revs...caveat emptor

BrettFrancis · 4 Aug 2004, 12:19 (Ref:1056075)

It's gotta be worth a go. If one is good, two must be better.

Should I be chucking any sort of resistor in there just for good measure? (Don't ask me why, I don't know, but I feel it would make the whole thing look more impressive, and that's what really counts...)

zefarelly · 4 Aug 2004, 12:30 (Ref:1056092)

if you run 2 condensers won't you be sapping power from the spark plugs ??? ( I don't know either!)

the revs jumping around is almost definitely points bouncin . . .mine does the same on the rolling road with a digital strobe gun on it, possibly why I had so much trouble with rev counters !

BrettFrancis · 4 Aug 2004, 12:49 (Ref:1056104)

Will look into the points, zefarelly. There'll be no bouncin on MY shift.

Have just read more words of wisdom, and there is some talk that place a 10k ohm 1/2 watt resistor between coil and tacho pickup wire could solve the problem.

The plot thickens.....

275 GTB-4 · 4 Aug 2004, 13:27 (Ref:1056145)

Quote:

Originally posted by BrettFrancis
Will look into the points, zefarelly. There'll be no bouncin on MY shift.

Have just read more words of wisdom, and there is some talk that place a 10k ohm 1/2 watt resistor between coil and tacho pickup wire could solve the problem.

The plot thickens.....

That would lower the voltage at tuther end....could also fix your problem.....now remember only one thing at a time!!! (and no a resistor in series with your two capacitors will only serve to drop the voltage when you are not sure it is voltage related).

Condensers do not pass DC current, therefore they will pass pulses but serve to clip them in their prime!! Its the pulses either finding a path into the wrong part of your black box or the points are a bouncin....let us know!!

**dtype38** · 4 Aug 2004, 17:14 (Ref:1056327)

Got rid of all those sort of probelems by fitting Luminition optical points and electronic amplifier. This mod usually complies with "non-managed spark" rules as it can't be programmed or adjusted other than in the usual way for dizzy timing. Needs fully suppressed ht leads though. :-)

zefarelly · 5 Aug 2004, 07:37 (Ref:1056747)

Dtype38 . . .do you think thats acceptable for FiA historics ? It doesnt say you specifically can't use points although I was under the impression you had to stick with the original . . . .

what would the resistor in line with the tacho do ?

**dtype38** · 6 Aug 2004, 14:45 (Ref:1058330)

I would only be guessing about the FiA Historic Rules, but its acceptable as original equipment for 1950s-on Jaguar Sports car and Saloon racing with the JEC because the spark is still generated by "distributor points" and cannot be mapped or adjusted. May help to know that the technical name for the Luminition System is "Optical Points" so it still counts as having "Points" but you'll need to check with specific rules if they have to be "Contact Breaker" type (traditional).

As for a resistor in line with the tacho, I run an electronic tacho in line with the supply to the coil. It works by sensing the tiny voltage blips as the coil fires and needs all the signal it can get. A resistor in series would reduce the coil voltage and damp the signal so would definitely be a no-no for my car. Trouble Unfortunately there are probably lots of variations on tacho and coil wiring and I'm not an expert.

**Tim Falce** · 6 Aug 2004, 14:50 (Ref:1058338)

Quote:

Originally posted by zefarelly
Dtype38 . . .do you think thats acceptable for FiA historics ? It doesnt say you specifically can't use points although I was under the impression you had to stick with the original . . . .

Whether you need points or not would depend on the regs for your own particular series, have you checked and what series are you in?