Ignition condenser

[Pomorza]

Hello all

This past weekend I was changing out the coil in the Z with a stock unit; the blaster II coil is great (MSD) but sadly I'm tired of going through rotors every few months. Well in the process I unplugged the condenser that sits atop the coil mount. The wire that connects it to the coil broke off from old age. I spent the large part of this week searching endlessly for a new one. Sadly the only condensers I could find only had one wire and not the two that the one in my Z has. I ended up going to the local wreching yard and pulling a rather nice looking condenser out of a late 70's maxima (I want to say it was 79). It looks exactly like the one I have in the Z and has the same values.

So I have a few questsion for you all. First off, is there a reason that it is grounded? I ask as the condenser, accordoing to THIS is connected to the positive side of the coil. I was alway lead to believe that the negative side is the ground on things. Secondly does anyone have any idea where one could get a new one of these? Thirdly, since I have a "new" one that I pulled out of that maxima (810) does it matter which way it goes? Its not labeled + or - anywhere that I can see.

Thanks for all your help guys,

Jan

[240260280z]

Condensers are capacitors.

In the automobile's ignition circuit, they are used to "pass" high frequency AC spurious noise transients (generated from the coil) to ground without affecting the DC voltage. This prevents cars from being radio stations broadcasting the hard rock sound of a band called COIL. (ie you would hear your coil on your radio and so would blasting equipment at construction sites

The spurious noise can be drained to ground through the coil at the +pos side or the -neg side of the coil.

Most capacitors are polarized and have a + and - side.

[Pomorza]

Condensers are capacitors.

In the automobile's ignition circuit, they are used to "pass" high frequency AC spurious noise transients (generated from the coil) to ground without affecting the DC voltage. This prevents cars from being radio stations broadcasting the hard rock sound of a band called COIL. (ie you would hear your coil on your radio and so would blasting equipment at construction sites

The spurious noise can be drained to ground through the coil at the +pos side or the -neg side of the coil.

Most capacitors are polarized and have a + and - side.

Thanks Blue. I use it for a slightly different reason but basically I need to get rid of the electrical noise in the circuit. I can't really tell you which side of the condenser is postive and which side is negative. I wired it the same way mine was wired. I haven't run the car yet as I would like to make sure I did it right. What could go wrong if I have it wired backwards?

Thanks again

Jan

[240260280z]

Some caps just fail open or closed when installed backwards. Some explode.

If the cap is not marked (text or bands) and there are no different coloured wires coming from it then it is 99% likely to be a non-polarized cap and can be mounted either way.

[Pomorza]

Some caps just fail open or closed when installed backwards. Some explode.

If the cap is not marked (text or bands) and there are no different coloured wires coming from it then it is 99% likely to be a non-polarized cap and can be mounted either way.

Thanks blue. The capacitor had two black wires coming out of each end. There's nothing on the case color wise and the only writing it has is "c-122 250-0.47 Sy" if that tell you anything. I'll have the fire extingisher ready just in case the thing explodes.

Thanks

Jan

[Wade Nelson]

Condensers are capacitors.

In the automobile's ignition circuit, they are used to "pass" high frequency AC spurious noise transients (generated from the coil) to ground without affecting the DC voltage. This prevents cars from being radio stations broadcasting the hard rock sound of a band called COIL.

Keeping the ignition circuit from broadcasting is only one function of a condensor in an ignition circuit. The other is making the points last longer. A LOT longer.

Without a condensor, metal will migrate from one point to the other until they're unusable. With a condensor exactly matched to the size of the coil (capacitance = inductance) there will be no metal transfer. Too much capacitance and the metal will move the other way.

You can never exactly balance the two, so all you're really doing is GREATLY slowing down the transfer. When the points open, current stops flowing. Well current doesn't LIKE to stop flowing, so, without a condensor it will make a nice big arc --- which carries the metal from one point to the other. With a condensor, that "arc" essentially gets shorted out. It gives it a place to go.

W-ARC, btw, is the station COIL plays on, and you can hear it ANYWHERE on the dial.

Typically an ignition condensor has one wire and the case is grounded. With a meter you could figure out if a 2-wire condensor is actually two capacitors in a single case, (like for a dual-point ignition) or if they simply ran a second lead rather than using the case for ground.

[Wade Nelson]

If you're "going through rotors" every few months, you probably have your aftermarket coil wired wrong.

A coil should ONLY full receive B+ (battery positive voltage) when cranking. Typically you run the 12V from the starter solenoid right up to the coil + terminal.

Once the engine is running a so-called "ballast" resistor is used to drop the voltage delivered to the coil down to 8V or so.

You can buy a ballast resistor at NAPA, or go steal one off an old FORD at the junkyard. Its a big, heavy wattage, typically ceramic resistor often mounted on the firewall.

I ran a Subaru with some OMG big aftermarket coil wired directly to B+ for awhile. After less than 3000 miles I pulled the plugs. I couldn't figure out where my spark plug electrodes went to. It was simply vaporizing them. A GM HEI ignition "only" puts out 40,000 volts. One of those MSD coils hooked directly to B+ may put out 200-300,000 volts. Upside: You'll never foul a plug. Downside: You may wonder where your plug electrodes, points, ... went to.

And THAT is what is most likely eating your rotors.

[Pomorza]

Guys,

So here's a question. Going of what Wade said in the post above, I could use a standard one wire capacitor instead of the one that Datsun used correct? I ask as at the moment my car is not getting spark period, none, nada. Its not helping my injection system either (aftermarket) as its not getting a tach signal from the coil. I don't think the actual condenser has anything to do with it but I don't like using 30+ year old condensers with brand new coils and dizzies. I was looking at just getting this one from autozone earlier in the weekbut chose to use the one I had found at the junkyard.

That being said I chose to use the stock coil to see if the ignition problem I was having was coil based or something different. Sadly it was the "something different" case, now I just need to figure out what.

Thanks for all your help guys

Jan