Upgrade for Powder Coating Guns (Electrostatic Magic and any similar version)

[gtudoran]

Hey guys. I would like to start this topic with a big thank you for Ice-9 (a really nice guy). So the story is this:

After a long time in which i was struggling with paint cans and paint sprays and liquid paint guns i've decided that is nothing better then powder coating, so i've managed to buy one from my country.  A little bit overpriced but, let's say that if i was to buy it form US the shipping + the system price would be in the same range with the price that i've paid here.
So... all good and dandy (i was excited as a child in the Christmas Eve) the gun arrived and the first thing that i checked was the HV and this is where i've begun to have some doubts, the spark was tiny (the spark between the gun tip and the ground connection) 1-2mm max.
All in all i've managed to find that "grosso moddo" you have 1mm spark per KV soooo... that would be aprox. 2-2.5KV which as far as i've read is a little bit too low, i was expecting at least 6 to 10KV

And ... i've done some research and i've came up with a plan: modify the $#@$#@ PSU to get some more juice.

First, what i do know about my PSU:

- it uses mains AC voltage (220V to generate HV)
- the HV supply is cast in resin
- i'm 100% sure that the HV supply is made with Diodes+Cap (voltage multiplier)
- the wire that is used for HV is 50KV rated (that is excellent as i'm not forced to change it)

What i had to order:
- a toroidal transformer with a primary for 230V and 2 secondary winding: 1st 600V @ 1mA / 2nd  300v @ 2mA (i will explain later why i've used 2 voltages) - ohhh and use the lowest current available you will not need it and it would be much safer.

So, the schematic that i've used is this:



Caps needs to be ceramic with at least 2 x voltage rating (i've used 2KV ceramic caps) / diodes needs also to be rated for the voltage (UF4007 / 1N4007 will be just ok). The resistors that i've used are 10Mohm - use the highest power that you have available (mine were 3W) 3x10Mohm in series should be very safe (again you don't need any current but you will need a good ionization of the air)

Now regarding the dual voltage:
- for big flat surfaces is better to have a higher voltage, as the powder will have a better attraction (and you can paint bigger surfaces)
- for a surface in which you have holes or big recessed areas having a very high voltage will not help you because of the "Halo Effect" for the holes and "Faraday Cage" for the recessed points/surfaces - so a lower voltage is proffered as the field will not be so strong.

The first tests were with excellent result and far more better then the original. I will have to cast the HV in some resin also (i like to be safe) but right now is under test so ...

Ohhh yes, and i will post some pictures with the modification when everything will be ready.

Best regards,
Gabriel    

[gtudoran]

Today was the repair day...i had to stick my hands into the powder-coating system and i've made some picture along the repairing process.
First, i've made some modifications: handle of the gun was put to ground, the whole system is using 5V DC supply (i'm getting aprox. 12KV at the output of the gun).
Some conclusions were made:
- much better adhesion of the powder
- i do think there is a connection between the powder type (epoxy, polyurethane etc.) and the voltage that should be used(i will have to make some more tests and confirm this, but for example it's way easier to apply candy-apple red then semi-transparent yellow, or any yellow color for that matter)
- with the new HV PSU the lost powder was considerably less then with the original PSU.
And now the pictures. If you have any questions please do not hesitate to ask.

[Ice-9]

Hello Dexter,
Great improvement to the powder coating psu, I would like to mod mine to the higher kV output. Have you any more info on the psu mods, is it a different type of mod now than the %^&*croft-Walton type  multiplier ladder ?

[gtudoran]

Hello Ice-9,

The PSU that i'm using can output from 12KV to 30KV for an input between 5v and 12v. I was a little bit too lazy to build a variable output supply (5v to 12v) so i'm using 5v input right now (all the voltages are DC).

This model of PSU was bought from here: http://www.ebay.com/itm/30kV-HV-Generator-Modul-12VDC-30-000VDC-Negative-Ion-Generator-High-Voltage-/271393108102?pt=LH_DefaultDomain_77&hash=item3f304a3086

And yes you will need negative voltage to the tip of the gun. The rest is just wiring and ... adding some options. Also i've found a great improvement using a grounding rod - a copper pipe stick in the ground and that is the grounding for my painting rack (you will see a huge difference between using the ground of the gun and the one from the grounding rod).

If you have more questions please do not hesitate to ask and i will gladly answer.

Regards,
Gabriel