MTFCA Forum

How many amps does a coil box draw. It is my understanding that a single coil should be set at 1.5 amps. Is it as simple as 1.5 x 4 = 6 amps?

Modeltmike wrote: ↑

Wed Nov 08, 2023 5:27 am

How many amps does a coil box draw. It is my understanding that a single coil should be set at 1.5 amps. Is it as simple as 1.5 x 4 = 6 amps?

Only one coil is fires at a time, so only 1.5 amps.

1.3 amps per coil if it is adjusted correctly.

Instructions for installing an E-Timer say to add a 4 amp fuse to the coil box. Total run amperage needs to be somewhere below that.

Only one coil at a time is in operation, and for some of the time during engine operation, no coil is operating. Average coil current during coil operation is in the 1.2 to 1.5 amp range. A 4 amp fuse would be correct, if a fuse is present. Coils behave differently when operating on battery current (6 volts DC) as opposed to magneto (Alternating current, about 5 volts AC to about 30 volts AC) Two coils will fire during each revolution of the engine.

To add to the discussion, and of course be criticized, if you observe your ampere meter, set the ignition switch to battery, and turn your motor by hand crank, with the coil buzzing, you should observe that the meter will show a discharge of about 2 amps, or one line to the left (a discharge). Of course if you use a buzz box with a three ampere meter, you will note a current draw of 1.5 to 2 amperes.

The Ford ammeter installed in the dash is far from a precision instrument, and is certainly not accurate enough to set coil current using the buzz box method. It's just a rough guide that everything is working properly.
The 4A fuse specified for the E-Timer is to protect the E-Timer itself, in case a coil is completely short circuited.