Showing posts with label but. Show all posts
Showing posts with label but. Show all posts
Saturday, January 14, 2017
Carbon a Nonmetal ! But why it is used in Dc motor brushes
Carbon a Nonmetal ! But why it is used in Dc motor brushes
One reason is the high melting temperature of carbon.
The inductances of the energized windings, and the mechanics of a brush type motor or generator make arcing and sparking an unavoidable characteristic of the machine at the brush interface. Electrical arcs produce very high temperatures. High enough to melt metals.
Carbon has a very high melting point (~3500degC) compared with other conductors. Brushes made with copper or steel would wear out faster because of factors including:
1) The melted metal will break away from, or even be vaporized, leaving the brush with less material to do its job.
2) If the melted material doesnt vaporize or otherwise move away from the interface, it creates a mess for the brush. It can weld together bristles of the brush. It can build up material that interferes with the motion of the rotor.
3) As the metal melts in the presence of an arc, conductive material can be liberated, therby prolonging the arc, exasperating the wearing action.
Carbon is less prone to those high temperature effects and associated impacts to the generator operation.
Source : Dan Church
Available link for download
Sunday, October 2, 2016
Make Your PC Shut Down at Night But Only When You’re Not Using It
Make Your PC Shut Down at Night But Only When You’re Not Using It
If you normally like to power off your PC when you’re not using it, do you ever forget and leave it on? Here’s how to configure Windows to automatically power down at night, but only if you’re not using the PC at the time.
To accomplish this, we’ll setup a Task Scheduler job that tells the computer to shut down, and make sure to configure the rules so that it doesn’t kick in if you are up late using the PC.
Create a Task Scheduler Job to Shut Down the PC
You’ll need to open up Task Scheduler to create the new job, so open it up and click the Create Task link on the right-hand side.
Now you’ll want to give the task a name, and make sure to check the box for “Run with highest privileges”, since the shutdown utility requires admin access.
Now switch to the Triggers tab, click New, and then setup a schedule that makes sense for you, like every night at midnight.
Now flip over to the Actions tab, click New, and then enter shutdown into the Program box, and /S into the parameters box. If you want to force a shutdown and kill every app, you can use /S /F to force it to happen right away.
Next head to the Conditions tab, and make sure to check the box to only start the task if the computer is idle for more than x minutes. You can also choose to stop the task if the PC isn’t idle to help make sure it doesn’t kick in if you are on the PC.
Lastly, head to the Settings tab, and you can choose to restart the task every 30 minutes if the task fails—that way, if you are on the PC for a while past the normal time, the job will start up later on and shut down the PC.
Once you’re done, your PC will shut down automatically. Enjoy!
Available link for download
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