What voltage at points? GT250A

[daxman]

HI All

I'm seeing about 10.8 volts from a battery that reads 12.4. Would that be about right. I guess it drops some across the coil primary - yes?

Cheers

[jabcb]

No.

Presumably you are measuring the 10.8V at the open points.
But if the 12.4V at the battery is with no load (key off), then part of the voltage drop from 12.4V to 10.8V will be the difference between no-load & load battery voltage.

Consider the ignition as 3 sections: (1) wiring from battery + to coil +, (2) coil primary, (3) coil - to points.
The voltage drop in the wiring is a function of the current. The coil resistance is ~ 4 ohm. All 3 sections have voltage drops.

For the closed points, most of the voltage drop is across (section 2) the coil primary.
Its fairly common to have a 1V or so drop (for section 1) from the battery + to coil +. That can be improved by cleaning the switches & electrical connectors.
The voltage drop (for section 3) from the coil - to points should be pretty small because its a short run of wire, but the connectors can also be a problem there.
Suzuki used a fairly small gauge wire, so you will have section 1 & 3 voltage drops even with perfect connectors & switches.

The two coils see pretty much the same voltage because most of the wire from the battery + to the coil + is common. (The wire splits into two wires near the coil.)
For the open points, the current in (section 2) the coil primary, and (in section 3) from the coil - to open points will be tiny — it’s only what your multimeter needs to measure resistance. So those voltage drops will be close to zero.
So the 10.8V you measured at the open points is pretty much the voltage at the coil + for both coils.


Sorry the the complex explanation. A diagram would make this much easier to explain.

[daxman]

Thanks. Perfect answer. Once I wedged both set of points open (so no load from coil to earth connection) The voltage reading went back up.