Bosch miter saw.. 3 wires to motor, 2 hot, and a neutral???

[woodchucker]

I don't understand the wiring here. I am adding a shadow line for the blade... because I can (not because I need it), it seems more effective than a laser.

Anyway here's what's going on.
Cord has black and white.
Black goes to switch which gangs yellow which goes back to the motor (not switched)
Red is switched from the black power lead and goes back to the motor.
White is crimped from power cord and goes directly to the motor.
So there are 3 wires going to the motor, and one of them (yellow) is HOT.
What is this doing? This is a universal motor. The miter saw is a CM10GD.
There's no problem here, I just don't understand why there is an unswitched hot going directly to the motor.

 

[strantor]

Brake maybe

 

[woodchucker]

good point, so that's why it would be hot all the time, it's only active after the trigger is released.
I didn't think about the brake.

 

[rwm]

Is it hot all the time, or hot when the trigger is released?

 

[woodchucker]

Is it hot all the time, or hot when the trigger is released?

so it turns out it is not ganged. I ran the multimeter on it while it was wired. After trying to run attached to the yellow, I found out it only activates when the saw is on...
So I moved to the black power lead.
So it appears the yellow is powered when the saw is on... It may be powered for a few seconds after the trigger is released, I didn't bother to check.
So not sure how the brake works.

 

[rabler]

so it turns out it is not ganged. I ran the multimeter on it while it was wired. After trying to run attached to the yellow, I found out it only activates when the saw is on...
So I moved to the black power lead.
So it appears the yellow is powered when the saw is on... It may be powered for a few seconds after the trigger is released, I didn't bother to check.
So not sure how the brake works.

I *would think* (verses know) that these brakes are spring activated, with a solenoid to pull the brake off at the same time the motor is started. That way power loss, or any other oddity on the electrical side and the brake will activate via the spring.

 

[strantor]

I *would think* (verses know) that these brakes are spring activated, with a solenoid to pull the brake off at the same time the motor is started. That way power loss, or any other oddity on the electrical side and the brake will activate via the spring.

According to the Bosch manual it will spin longer if power is lost.

 

[rabler]

According to the Bosch manual it will spin longer if power is lost.

Hmm. Yeah, until the trigger is released. So probably using back EMF or eddy currents internally rather than a true mechanical brake(?)

 

[rwm]

The brakes on the battery tools work by shorting the motor leads. The brakes on the AC universal motors supposedly work by putting them in reverse. That explanation is incomplete. There must be more to this. I don't think many tools use a mechanical motor brake.

 

[strantor]

In theory you should be able to get some braking action by shorting the terminals of a universal motor as residual magnetism will be generating current, but I've never tried it and don't know how effective it is. The wording of the manual (shown in post #2) seems to indicate a mechanical brake the way I read it.