Merc 170 Coil voltage

[dpatzari]

All

Does anyone know what the coil voltage should read when the key is turned on (not running) I am getting 11.91v to ground on the + side. Is there a difference between start coil voltage vs run coil primary voltage ?
The purple wire which is supposed to be the resistance looks fine. Is there a spec. on the resistance value of the wire? I am about to codemn the coil and i want to make sure. It "ohms out on the primary side, but not on the secondary.. If i trick the points, i can get a little spark , but it is weak. Any help would be appreciated


Thanks
David

 

[Lyle29464]

Re: Merc 170 Coil voltage

Need a bit more info. What motor etc. Sounds like a point type setup. Normal voltage with the Key on and the engine not running and the points open is the battery voltage. 12V or close. You sound ok there.
In the start position you still get the same reading less what the starter draws . When the engine is starting the voltage on the resistor wire is by-passed and you get the battery reading 12V or so. When it starts the out put of the alternator 14+ volts goes through the resistor wire and is dropped down below 12 volts. ( That voltage is changing because of the points grounding it and then opening.) Your meter most likely reads the average. Weak spark could be the coil. bad points ( most likely) shorted tack.

 

[stonyloam]

Re: Merc 170 Coil voltage

170 4cyl. 470 engine? Resistance wire should be 1.8 to 2 ohms. Coil primary 1.5 ohms, 1.1 minimum. So it should read something less than battery voltage. Start voltage is battery voltage, run voltage is reduced by the resistance wire. You get your start voltage from the slave solenoid on a 470 type engine, from the starter solenoid on others. Hope that helps.