Could someone please explain to me the purpose of a magnetic starter on an air compressor. I may be a little thick, but I can't see what possible advantage there is. Seems to me that all you are doing is putting a relay between the pressure switch relay and the motor. The motor vendors seem to push those, but they are making profit, so I don't trust them entirely.
It gives you a great deal more control over the motor. The magnetic coils will disconnect the circuit when power is removed. Power might need to be removed because of overload or any other number of safety devices. Nothing complicated about the benefit of magnetic starters.
My compressor needs something to remove the load while the motor starts. Back pressure.
Magnetic starters exist so that if the power goes off for whatever reason, the on switch has to be manually reengaged before the machine turns on again. Imagine a situation where you have a leak, the power goes off and doesn't come back on. It's the last day before your vacation. Do you want to sit there waiting for the power to come back on? Will you remember to turn off the switch? Or will you leave for three weeks in the Bahamas only to come back to a machine that's overheated or run itself out of oil?
I know it's a stretch but it's to keep the machine from just coming on after the power had failed. Maybe you might be working on the compressor after it pops off trying to get it going again and get your hand caught in the belt when it suddenly energizes again?
Anyway, you get the idea. I'd like to have a magnetic starter on all my tools but have to admit the need on the compressor seems to be less than a tablesaw.
The most common reason that a motor starter is used is because the motor control sensors, in this case, the pressure switch, cannot handle the motor current. In most cases it's actually cheaper to use motor starters than it is to provide sensors that can handle the motor current. As stated by others, there is a safety factor also.
Ok, that makes sense.
I'd like one on my computer. The power goes out and I come back to find the computer has just the windows desktop, and nothing I had on the screen. The only way I know the power went out is to look at my digital clock to see it flashing 12:00. If that clock had a battery (like it should), I would not know what happened and blame my computer.
Both my computers will stay off if power goes out. It avoids power surges that way too.
That's usually an option in the BIOS settings.
Decent UPS units have a software program that shuts your computer down after a period without power. I have an energizer that I bought for $80 that works very well, so well you are tempted to work during outages, but it beeps until you shut down, or if you aren't available it shuts it down for you.
I've got a 12 volt car battery connected to mine and my wifes ups. We just keep on computing when the power goes off.
I have a UPS on my computer. If the power goes off for more than 5 minutes, the associated software shuts the computer down for me. If the power outage is less than 5 minutes, I just keep on computing as if nothing happened. The vast majority of power outages are momentary so the real effect is that I have a very smooth power supply without surges. The UPS provides the computer with power at all times so there's no switchover blip. The wall provides the UPS with power to replace what goes into the computer. If the supply out of the wall fails, the UPS just keeps on trucking off its battery until the timing software activates.
I actually have small UPS's around the house. I've got one on my telephone answering machine. I've got another that feeds my TIVO and a digital clock in my living room. It doesn't feed the TV. I've found if the power cuts off, it takes a while to reboot the TIVO (it was the same with the satellite receiver I had before)... a PITA to be avoided.
I bought the biggest UPS I could afford for the computer. I bought the smallest I could find for the other stuff.
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