Ok, hi kids! Welcome back to hannah’s bug! to remove the paint and rust from my bug, i’m going to use a lot of sandblasting. now, sand blasting requires a lot of air volume, not so much air pressure.
Air pressure is measured in psi while air volume is measured in scfm, or sustained cubic feet per minute. you might think that I can buy, just, an air compressor with a really large tank, however, that will not work because the air tank will only supply me enough air for about 25 to 30 seconds of sandblasting and then the air compressor will need to refill the air and it’ll never be able to catch up.
For me to feel confident that i’m getting enough compressed air, I need to have 25 scfm at 80 psi. There aren’t many air compressors on the market today that can give me that on standard household 240 voltage.
There are many on the market that can give me that on three phase power, however, on the street that I live on here in teddyland, I can’t get three phase power off the poles. one affordable solution would be to rent a diesel screw-type compressor.
Those would really only cost my producer and camera-dog under 200 dollars a week. However, I don’t want to do all my sandblasting in one week, and to rent this over the entire course of the project would become extremely expensive, and I do not want to do that.
So let me ask you a question. What would chris hemsworth do? chris hemsworth would use multiple inexpensive compressors in parallel. Bernoulli got me these four compressors at about $140.00 each.
Good boy bernoulli! to run them in parallel, the air connection is actually very simple. You can see how i did them here, with more tube than 25 me’s. Yup, more.
The final one. And now for the real problem: the electricity! First, obviously, you need to make it so that each compressor is on an individual circuit because each household circuit only supplies 15 amps, while each compressor takes around nine.
In simpler words, no 2 compressors in socket or else house go boom-boom! So you’ll need to run a lot of extension cords.
You need to plan this beforehand that way you get as short a run of extension cord as possible, because each foot of extension cord adds resistance to the circuit. there are many problems to face ahead.
The first problem is that reciprocating compressors have what’s called a duty cycle, which means that they’ll turn on so that they can fill their tank then take a break until it’s time to fill their tank again.
Since these individual compressors are not in coordination, one of them may decide to be the hero and stay on all the time so that it burns itself out. so I have to figure out a way to turn them all on in unison, but that will create another problem.
It will create a power sag, which means there won’t even be enough current to turn them on, and they would all stall. Each compressor has a pneumatic switch, which means the compressor will turn on when the tank is low, then turn off when the tank is full.
You might just think that I can adjust these points so that the compressors are in coordination, but this won’t work, because the on and off points will change depending on the load.
So i’m going to need to use electrical relays. if these are my compressors, this will be my control, and these four will be my slaves. what would happen is, I would turn this one on, then there would be a 2 second delay before this one turns on, then another 2 seconds before this one, then another 2 seconds before this one, then another 2 seconds before the fourth slave.
If I could see into the future, i would say I don’t really need a fourth slave, but since I can’t see into the future, i’m going to set up my distribution box so that I can set one up in case needed. because each compressor has its own pneumatic switch, I need to make it so that my slaves are always on.
The way to do that is to make the cutoff pressure for my control compressor lower than the others. According to the chart on the back of this cap, the way to do that is to turn this screw counterclockwise.
Before I get started electrically, there’s a few things I need to take care of pneumatically. The first is obviously, open this output regulator to be wide open. The second, the pneumatic switch, when it turns off, releases the pressure in the cylinder head.
But, for the slaves, since I need the pneumatic switch to stay on all the time, I need to find a way to relieve that pressure manually. The way to do that is simply loosen this valve so that I have a slight leak, and that way, once it turns off, all the pressure will be gone within just a few seconds. the only change you need to make electrically to your compressors is to your control compressor. these two connections are the power connections to the motor.
I need to get a signal from these, that way I know when to turn on my other compressors. So what you’re gonna do is drill a hole in your cap, and then attach two wires to these connections, then run the wire to your distribution box.
For your distribution box, you’re going to need a micro-controller. I suggest using an arduino, which you can get for $20.00 at multiple online sources. You’re also going to need a 12 volt wall wart, which you can find basically anywhere for $8.00 if you don’t already have on around your house.
You’re also going to need prototyping board, which you can find for a few dollars at normal electrical stores. For each slave compressor, you’re going to need a 3 prong male outlet – er – plug, your standard house outlet, an outlet box, for each slave compressor, you’re also going to have 3 step-up relays.
Your first relay is an npn transistor which you’re going to run to saturation. I’m using a tip 120 from digikey. Com that I got for about 60 cents each.
Your second relay is a 120 volt spdt relay. I’m using the sanyou sru-s112l that I got from mpja. Com for 99 cents each. Your next relay is going to be an hvac fan relay.
Mine is a supco 90382 that I got from amazon. Com for 13 dollars and 46 cents each. you’re also going to need a 1 k ohm resistor each and a one hundred k ohm resistor each. these I got for about 10 cents each.
This here are the 2 pins from the control compressor. When you turn on the compressor, the wall wart will turn on, which will then in turn, turn on the arduino.
For each slave compressor, you’ll have an output pin which runs through a 1 k ohm resistor which then turns on the first relay, the tip 120 with a bridging 100 k ohm resistor. The tip 120 will turn on the next relay, the sanyou, which will then turn on the supco, then allowing it to flip a switch to the individual household circuit to power the outlet which will then turn on the slave compressor. here’s the code that you’re gonna need to program your arduino.
This here is my initialization where I show my arduino which pins i’m going to be using for output. This here is my delay. if you’ll notice, my first delay is shorter than my other delays because one and a half seconds is roughly the amount of time it takes for my arduino to actually turn on. before you actually hook everything up, I suggest testing out your circuit on a breadboard, which you can get for about 10 dollars at normal electronic supply stores because burning down your house is a terrible way to die! I’m going to do a sample circuit on my breadboard, and in place of my fan relay and 120 volt circuit, i’m going to use and led. this arduino has been programmed to turn on and off instead of doing a simple delay.
That way I can tell whether or not it’s working. Girl power! here is my finished distribution box. These male plugs will connect to individual circuits through extension cords.
This is my tip 120, my first relay, and my second relay, my sanyous. here’s my arduino. Here’s my wall wart, then on the other side are my final relays, the supcos, which will attach to my wall sockets.
Here is the control wire, which will end up powering the wall wart from my control compressor. And now with the cover on, we’re ready to go. As you can see, I have everything hooked up now, and after, of course, putting in my hearing protection, i’m going to turn on the control. and after 2 seconds for each one, the first one is gonna start, then the second one, then the third.
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