Re: super m coil problems

Posted by John T on March 06, 2006 at 04:58:24 from (66.244.90.98):

In Reply to: super m coil problems posted by super_m on March 05, 2006 at 19:21:01:

Super, if you smoked the old Ballast Resistor you may still need a new one regardless what coil you use now. They are usually in the 0.5 to 0.85 ohms range if they are good, theres a chance it may still work if thats what it now reads.

Heres what may have happened: First, some of those co called super or hot or high voltage coils are designed for use with electronic switched ignitions (instead of mechanical points) capable of handling and switching higher coil currents with primary winding resistances lower then conventional coils which are rated for somewhere around 4 amps. THEREFORE such a hot coil may have caused more current flow through the ballast then it was designed to handle which smoked it.

Next, do you actually need a ballst for that MSD coil??? The answer depends: IFFFFFFF the coil is a full 12 volt rated unit, it needs no ballast when used on a 12 volt tractor. HOWEVER if its labeled "12 volts for use with external ballast" or "6 volts" then it indeed requires the series voltage dropping (12 to 6) Ballast Resistor. ANOTHER HOWEVER if the coil is designed specifically for an electronic ignition and has low primary winding resistance,,,,,,,but youre using points instead,,,,,,,THE BALLAST would have to be of different ohms and power rating then the typical ballast and the typical ballast may burn up if the MSD coil is used.

The problem is it sounds like youre mixing and comparing apples to oranges. If you wanna use one of those super coils and be able to take advantage of what it can offer, you really need to convert to an electronic switch. An elec switch coupled up with a high energy coil produces more spark energy then the stock ignition. The use of a high energy coil alone still switched with mechanical points isnt gonna gain you all that much if anything over the stock coil PLUS you may be over currenting the points which burns them up prematurely and smoke a ballast thats designed for only 4 amps or so. Also, the voltage at which the plugs fire is a function of the plug gap distance and the medium (fuel and compression) in which it fires, therefore, given the same conditions, the hot coil is still gonna fire at the same voltage as the stock one.

Its true the high performance coils may be more efficient then a cheaper stock coil which can gain some spark energy, but using a hot coil with points just isnt that great (depending on the coils primary winding resistance and if its designed for an elec switch) as the points can burn up quickly and the firing voltage is the same although some improvement may be there due to more eficiency of coil design.

If you insist on using that coil and its actually a 6 volt coil which requires a ballast (remember if its full 12 volt rated, none is usually required and most those type coils are 12 volts) the ballast ohms should be near the same as the coils primary winding resistance which acts as a 50 50 voltage divider dropping 6 volts across the ballast leaving 6 at the coil. HOWEVER I bet thats a full 12 volt rated coil i.e. no ballast used.

Finally, I would EITHER use a stock coil if youre still using mechanical points,,,,,,,,,,,,or,,,,,,,if you insist on using that coil, use an elec ignition switch OR ELSE at least confirm the coils correct voltage and get a correct sized ballast if one is actually required. Again, its ohms should match the coils ohms plus it has sufficient power rating.

ALSO the coil should be wired to match your polarity!!!!!!!! as that affects its performance plus its heating. You at Pos or Neg ground???

As far as the genny and voltage, I have seen 6 volt gennys charge at 12 volts simply by using a 12 volt Voltage Regulator but thats NOT any ideal situation.

John T, retired electrical engineer in Indiana

Replies:

• Re: super m coil problems ChadS 07:33:17 03/06/06 (2)
  • Re: super m coil problems John T 10:43:03 03/06/06 (1)
    • Re: super m coil problems ChadS 12:54:54 03/06/06 (0)

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