Powder Coating System MK-II Progress

I have had a few questions and requests for additional documentation regarding my next powder coating machine build.

I have drawn up some proper schematics of the powder coating controller including the subsections for variable HV supply.

The full controller schematic is here:

You'll notice I just specified 28VDC input; its really up to you how to obtain this; you can get cheap switching modules off ebay; laptop power supplies, or you can build your own power supply with a transformer and rectifier (My preference as its most robust option).  I didn't go into it here as its pretty standard stuff

I have also done a schematic and board for just the HV supply; again its just a simple switching power supply which drives the flyback transformer.  There are other popular flyback drivers which use the resonance of the flyback itself to set the frequency, but I have found the timer based designs easiest to build and having the easiest to obtain parts.

Here is the schematic:

And the board layout:

I'm going to have boards made for this driver; If you're interested I'll be selling them for $10 each + $2 shipping (I will just send them as "letter mail").  Let me know via e-mail or comments if you're interested as that will get me motivated to put them up on the store http://www.thegreatgeekery.com/store/

I'm also playing with the idea of moving the flyback (and a HV cascade) onto the gun,  I havn't made too much progress in this area, just a box of parts really...

Powder Coating Build Follow Up

Update: Build Progress of the next version here; including schematics and board layouts
http://thegreatgeekery.blogspot.com/2011/10/powder-coating-system-mk-ii-progress.html

In case you came in from somewhereelse; Check out the mainpage of the blog: http://thegreatgeekery.blogspot.com/

I havn't done much modifications to my powder coating machine in a while since its been working pretty well.
See the original post here: http://thegreatgeekery.blogspot.com/2010/07/powder-coating.html

I have had a lot of request for schematics and more plans;  I'll use this post to try to get some of the details together.  Nothing too revolutionary about it;

Overall Topology:
The design is a fairly simple topology;  It consists of several voltage rails which come together to generate between 10-25KV.

Air and voltage is controlled via a trigger on the gun.

If there is interest I can have some boards made for the adjustable HV supply.  I have been thinking about making up PCBs for the main part of the supply; including everything after the step down transformer.  Let me know if you're interested and I'll do up a board; or maybe some kits.

Output: 32VDC
Current: 5A
Source: 120VAC
Notes:
Build around a 24V toroid transformer I had kicking around.  Stepped down to ~32VDC using a pair of bridge rectiviers and some filter caps.  Filter Caps are ~1000uF 60V if I remember right. I added a bleeder resistor to discharge the caps when powered off.

Pretty much this circuit; with a indicator lamp and bleeder resistor; 24V transformer instead of 12
http://ecelab.com/circuit-power-supply1.htm

Output: 12-30VDC

Current: 4A

Source: 32VDC

Notes:

This is the main supply used for driving the the flyback transformer; its based around an array of LM317 adjustable voltage regulators in parallel.  The output is controlled via a relay driven by the trigger on the gun.  The relay also drives the air supply solenoid.

This circuit (and much of the rest of the power supply are similar in concept to this design http://www.pocketmagic.net/?p=1162)

Note that I used only one 2N3055 transistors since I don't need nearly as much current.  

Output: 12VDC

Current: 1A

Source: 32VDC

Notes:

Standard 12V supply based around a LM7812 linear regulator; nothing too exciting.  Its used for the 555 pwm generator used for the HV supply as well as for the coils of the relays and solenoids.

Output: 10-25KVDC

Current: ~0

Source 12-30VDC

Notes:

I used a standard flyback driver architecture as seen in the circuit below.  I used a larger driver mosfet and added a diode across the flyback primary and a zener to protect the gate of the drive mosfet.  Used the same totem mosfet driver topology.  The potentiometer off the 555 was adjusted until I smelled ozone and heard the air ionizing around the HV output of the transformer.

I used the 12V supply referenced above instead of using another regulator as in the diagram.

Powder Coating

Update2: Description, Schematics and boards
http://thegreatgeekery.blogspot.com/2011/10/powder-coating-system-mk-ii-progress.html


Update: added some more details
http://thegreatgeekery.blogspot.com/2010/12/powder-coating-build-follow-up.html

So over the last few months I have built a number of powder coating guns as well as a powder coating oven. I'm trying to make something better than the $60 harbor freight gun, from what I have read the HF gun tends to not give consistent powder output and struggle with multi coat.


Mark I:
This gun was inspired by this design http://hackaday.com/2006/07/05/diy-powder-coating-gun/
The overall design was pretty much the same; I used an old toaster oven to bake it. It worked ok, but the voltage was too low to get good powder adhesion on additional coats, and it was hard to clean and didn't put out a consistent powder flow.

Mark-I ghetto gun

BMW E36 caliper support brackets (before and after)

Mark II:
The second prototype moves the high voltage electronics into a separate unit; I also added previsions for a variable voltage supply, solenoid controlled air supply, and a separate powder chamber. Results were pretty good.  Its still very much a prototype, for the next revision I'm moving things around and sending PCBs to be made.

Main Power Supply and Control system

The system as I use it; lots of hours on it now.

Here is a picture of the power supply; There are three stages; a generic 110VAC to 36VDC 3A power supply; Provisions for an adjustable stage (36V to 10-32VDC 3A); High voltage step-up stage (10-32VDC to ~25KV done in the switching power supply section)

The AC-DC input stage is built around a standard toroid step down transformer; full bridge rectification and capacitor bank. The supply is controlled by a switch on the front.

The adjustable stage is currently not implemented; instead I have simply added a 12VDC regulator used for supply of the switching section of the HV supply and for the actuator control. In the next revision I will be adding the variable voltage control using a standard adjustable regulator (LM317) with pass transistors to provide additional current. This stage is controlled via a relay which is controlled by a switch on the gun.

The high voltage step up stage is basically a switching power supply driving a flyback transformer out of a CRT computer monitor. The frequency and pulse-width of the drive circuitry is tuned to match the transformer. I set the duty cycle to 20% and adjusted the frequency until maximum output was observed (by measuring arc length). A 555 timer was used for pulse generation; it feeds a IRF240 power mosfet which drives the primary winding of the transformer. The primary winding was made by wrapping 8 turns of 14 gauge transformer wire around the ferrite core of the transformer.

The flyback transformer is directly connected to the tip on the gun via 50KV high voltage wire bought off ebay.

The air supply is set via an adjustable regulator on the front of the chassis; after the regulator the air is connected to a solenoid which is activated by a switch on the gun.

Flyback and air control

The regulator air supply is fed to a powder container; it feeds at the bottom of the container in order to fluidize the powder; the powder then travels to the gun.

Third itteration of the powder pot; this one is quite solid and works very well

The gun its self is very simple it is simply PVC fittings which allow for attachment of various nozzles. The nozzles were purchased from powder by the pound (they're cheap ~$12 so It was easier to buy rather than build).  I've added a switch to the gun (not pictured) which switches on the HV and air.

When it all comes together I have had some pretty good results; powder attraction is much better than with the Mark-I gun and powder flow is more consistent. Multiple layers work well (tested up to three layers so far).

Oven:
  Powder coatingis great; but the hard part is getting a big enough oven to cook the parts in. I ended up building my own oven from sheet metal and steel studs. Since I wanted to keep costs low I used left over bits from various projects and friends and family. It turned out pretty good; it doesn't look like much but it heats up quickly and holds its heat well.

Oven; inside dimensions 2' x 3' x 4'

240V 30A

30A contactor for controlling the elements

Auto Tuning PID temperature controller for driving the contactor

Some formerly brass trim from my fireplace (ready to be cooked)

For temperature control; the elements are fed by 240V at 30A; they are connected via a electrical contactor which is controlled by a auto-tuning PID temperature controller.

 

Powder Coating System Mark-III:

I've started building the MK-III version of my powder coating system. Here is the plan.

Features
- Move to larger 19" rack mount chassis
- Provisions in chassis for second regulator and PSI gauge for future addition of powder pump.
- Adjustable low voltage DC supply in chassis, all HV moved to gun
- Switching supply and AC fly back mounted on gun
- 5x Voltage multiplier on gun to bring output voltage up to 100KV for large number of coats
- Use custom PCB for switching supply;
- New Gun cabling using circular connectors
-