Diesel Engine Starter

you mean that the external magnetic switch is just to save copper using smaller x.sectional cables.but i think that cost of magnetic switch is much greater than the cables. may be i am wrong.tanx

The solenoid on the starter. The armature of it throws a lever that pushes gears on the starter motor to engage on the flywheel. When the solenoid is all the way forward and the the gears engage contacts in the starter solenoid make turning the motor. Since the engagement of the gears slow the make speed. These contacts arc and can weld. Not an every day occurrence but can happen. Then you would have then running motor turning the starter at speed it's not designed for. Wearing quickly the fly wheel gear and the starter motor gear. The other solenoid cuts power. If the starter solenoid contacts did weld with no power hold forces on the starter gear it will disengage. This usually will cause the welded contacts to break.

Sorry ,i did not get your point That well,can u explain a little simply.

A little simply is for you to google motor starters to get an idea first on how they function. Then ask your questions.

It's so the heavy battery cables are only short runs,the "magnetic switch" is a starter solenoid which in turn opperates the solinoid that engages the dog that turns the ring gear on the flywheel,Now why it's like that is the question,my guess is that it's a security device to stop anyone starting it with a screwdriver, Is this a piece of equipment or a stationary engine?

Bazzer

The amperage required to operate the starter's solenoid is too high for the small contacts of a key and/or push button starter switch. The magnetic switch, on the other hand, can be activated with low current and then it can handle the switching of the current necessary to activate the starter's solenoid which is designed to then switch even higher levels of current necessary to spin the engine for starting. As was said, it is also a safety facility if the starter unit should ever become stuck in the engaged position.

That's all. The current to operate the solenoid is too great for the keyswitch so it's done in two stages.

I'm not up on these things, but might it be a series-parallel switch? My son has one on a 1962 Autocar, but I don't know if they use them on modern trucks.

Perhaps a visit to delcoremy.com and looking up instruction sheet 10511650 will probably answer all the questions. In fact, it does answer all the questions. Instructions, diagrams...everything including magnetic switches.

Isn't Google great? I got there by looking up 42MT Delco starter.