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25μF capacitor—Coil On Plug ingnition

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Morris

Morris

Yoda
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Almost done with my COP setup for me megasquirted 1500. The wiring diagram I am working with calls for a 25μF capacitor between the coil(+) and ground. So I am wondering... what is the typical range for your work-a-day off the shelf condenser? Or... where would one find a capacitor suitable for this application. (I am thinking the junk yard, but I would feel a lot better about buying new).
 
That splash of gobbeldygook is supposed to be "25 micro farads." The "micro" character did not render correctly. Also, apparently I can't spell ignition.
 
How does one test for farads?

On the Megasquirt forums, guys are saying that close is good enough for this application.
 
If you have a digital meter with farad measuring capability then it's simple. Most don't have this, the Fluke 113 does.

To simply see if your condenser has capacitance with a digital multimeter this always worked for me:
Set the meter to ohms, if it has multiple settings then something around 1000 or 2000 ohms or lower would probably work.
YMMV

Meter across the two wires of a capacitor or the wire and the body of the condenser.

Watch the display, it should go from zero up the scale gradually then back down. This is an interaction with the circuitry in the meter and means nothing more than that the meter is sensing capacitance.

Again - YMMV - all meters are different, I personally use a Fluke 77 for anything important and a cheapo chinese DMM that has tach and dwell settings for other stuff.
 
Capacitors come in standard values; 0.25 is not one of them. 0.22 microfarads is closest, which should be close enough.

Any electronics place will have capacitors, but for your application you will need a fairly high breakdown voltage; I'd say at least 1000 volts. Higher is OK.

The capacitor also must handle a fair amount of current, any most ordinary capacitors for electronic applications won't do that. You need a "dv/dt" rating of about 100 volts per microsecond or more. Unfortunately, this spec may not always be available. If it isn't, the capacitor probably isn't what you want, anyway.

Try https://www.alliedelec.com/search/productdetail.aspx?SKU=6130669
or https://www.alliedelec.com/search/productdetail.aspx?SKU=6130592

These are much better quality than the junk sold for automobiles, and you'll never have to replace them.

Also, take a look at Digi-Key https://www.digikey.com/

or Mouser: https://www.mouser.com/
 
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