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Suitable design for a home made Flocking Applicator ...

odintheterrible

Thread Starter

odintheterrible

Joined Jun 16, 2010
6
Greetings one and all ...

I recently decided to refurbish the interior of my '91 Toyota MR2 and decided that I would like to 'flock' the dash, centre console and other bits etc to inprove things. As this is all I have in mind, buying a professional flocking applicator seems a little extreme at around £700 a pop !! So, I started looking round to evaluate the possibility of building a unit myself ... give the limited use it will get.

The problem I've encountered is that most of the stuff out there on the 'Net seems to be quite old and much of the schematics and component used appear to be based upon older, and now unavailable items or steam driven technology. I have tried looking at buying a 'kit' (based upon the Cockroft-Walton Multiplier pricipal) but the supplier can't/won't quote a figure for the output (needs to be in the range of about 35KV + pullin' about 40 micro amps if I use battery power (6 or 9VDC) although mains power (230VAC) would be preferable) and it seems like a bit of a waste of money to have to buy the kit in order to establish the output !?!

Now I must add at this point that my experience of High Voltage applications is ZERO !!!! ... so I'd be most grateful for assistance with the following ....

... I came across an article which appears to describe a circuit which meets my needs almost exactly, trouble is that some of the components appear to be unavailable (due to age of article) and a bit of the circuitry leaves me mystified; so ... and here's the big ask ... would one or other of you kind souls care to step up to the plate and update what I've found so that I can have a fighting chance of building it ??? ... PLEASE :rolleyes:

My main sourcing issues seem to be mainly associated with; C2, L2, T2 and Thy1 (have the pdf spec sheet if required)
------------------------------------------
Thy1 Thyristor S0802MH by Tag Semiconductors Ltd (pdf spec sheet available)
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T2 Transformer 240v : 240v 12vA type DB247
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T1 Motorbike ignition coil from any bike repair shop or scrap yard
------------------------------------------
Here's the circuit diagram I found ...



... and here's the info that went with it ...

For safety, a 240:240 volt mains isolating transformer is used. This could be replaced with a 240:350 volt transformer to increase the output voltage but you would have to make other changes to compensate.
The isolated AC mains voltage is full-wave rectified by diodes 1 - 4 to produce positive going sine waves at 100 Hz. Each one charges up capacitor C1 and , as the voltage reaches its peak, the thyristor switches on to discharge the capacitor through the ignition coil primary. The rapid change in current induces a voltage of around 30kV peak on the coil primary. This voltage pulse is connected via 30 diodes to a metal plate which acts as a capacitor and holds a positive charge with respect to ground. The diodes each have a reverse breakdown voltage of 1000 volts minimum.
Resistor R1 limits the current flowing through the thyristor when it turns on. The resistor chain formed by R2, R3 and R4 sets the point on the sine wave when the thyristor turns on. Ideally this should be close to the peak but some allowance must be made for locations where the mains voltage is less than the nominal 230 volts. The value of R4 can be altered to change the switching point. If a 350 volt transformer is used, the value of R4 can be reduced accordingly, so that the thyristor switches closer to 340 volts than 230.
Please note that resistors R1, 2 and 3 are high voltage resistors rated at 350 volts. You should use the ones specified as ordinary resistors could break down.
C1 is chosen for its ability to withstand the rapid change in voltage (dv/dt). If you use a different type from the one specified, it may not survive.
C2 and L2 are included to minimise the "noise" going back to the electricity supply. Neither these, nor the transformer, T2, are required for correct operation but they are essential to meet the best safety and emission requirements. (Note that they may not be sufficient to meet CE and other legislation so please do your research carefully if you plan to manufacture equipment based on this prototype.
Switch S1 is a press-on release-off type for safety. This ensures that you always have one hand on the switch while the unit is running. The switch has an insulating plastic cover fitted.
Click to expand...
 

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beenthere

beenthere

Joined Apr 20, 2004
15,819
If you only need 30 KV or so to attract the flocking, then that circuit is really crazy. Auto ignition coils produce 30 - 40 KV from a 12 volt input. I would think that driving the primary with 20 times the usual voltage might simply fry the coil.

The circuit at the link should do for the high voltage - http://www.instructables.com/id/High-voltage-ignition-coil-supply/ . You will need to run down some 1N4007's to rectify the output so you place DC on the parts.
 
Last edited:
D

Darren Holdstock

Joined Feb 10, 2009
262
That's a capacitive discharge ignition circuit, the output of which can be lethal. Mind how you go, to say the least.

In its proper state with the secondary terminated by a spark gap, the peak voltage at the secondary will be limited by the width of the spark gap. With no gap to flash over, the secondary voltage can be huge, and all that energy has to go somewhere. Usually it flashes over the insulating resin in the transformer and blows up the primary drive circuit. Indeed, this is what happens to many modern ignition systems if the spark plug is absent - they self destruct.

If you're not familiar with HT circuits, this isn't the one to start with. If the Cockcroft-Walton kit mentioned is sold for flocking application purposes then I'd go with that one, it would be much less likely to kill you. It would still be tricky - all the circuitry at the HT end would require special construction techniques to prevent flashovers, and I couldn't vouch for the effectiveness of the inherent current limiting, but you'd live to have another go if it doesn't quite go right first time.

If you must use the OP circuit, then replace the vehicle ignition coil with the transformer from a gas cooker ignitor. It's the same circuit, except that the output energy is limited by design, and by legal safety standards. Work out how much energy is discharged by the cooker ignitor primary capacitor (0.5XCXV^2), and don't exceed this figure.
 
odintheterrible

Thread Starter

odintheterrible

Joined Jun 16, 2010
6
Darren Holdstock said:
That's a capacitive discharge ignition circuit, the output of which can be lethal. Mind how you go, to say the least.

<snip> ... If the Cockcroft-Walton kit mentioned is sold for flocking application purposes then I'd go with that one, it would be much less likely to kill you. <snip>
Click to expand...
Thanks for the valuable input/info ... the Cockcroft-Walton kit isn't sold specifically for flocking ... I believe it is offered as a negative ion generator ... the suitability for the flocking application was a suggestion from another source ... but it's difficult to judge the fitness for purpose without the output figure which the supplier won't quote.

I was wondering, since posting, if this kit might be more suitable ...

Rich (BB code): 
http://www.brocott.co.uk/electronic-diy-kits/miscellaneous-kits/negative-ion-generator-kit-p-459.html?osCsid=g7a1po7mi3vsqjqgab1h2df1i3


Negative Ion Generator Kit

Input: 9...12VDC, output: 3...7kVs. This ion-generator regenerates negatively loaded air particles (air-ions).

Technical data:

  • Operating voltage: 9...12VDC
  • Current consumption: approx. 80...150mA
  • Output voltage: static, approx. 3.000...7.000V peak value
  • Board dimensions: approx. 54 x 44 mm
Again, thanks for the info and guidance.
 
D

Darren Holdstock

Joined Feb 10, 2009
262
odintheterrible said:
I was wondering, since posting, if this kit might be more suitable ...
Click to expand...
I'm afraid I don't know the requirements of the flocking process, so I couldn't say. I can tell you that this kit will give a very spiky output, if that's OK, and the voltage won't be very well regulated.

Bear in mind ionisers usually have current limiting on the outputs in the form of a long chain of 10 Mohm resistors (or thereabouts), otherwise they tend to give off painful little lightning bolts when touched. Safe, but painful. Be wary of smoothing the output with a high-voltage capacitor though, as this will increase the amount of energy delivered per shock. Even if the HT PSU circuit is current limited to a safe level, the addition of a large enough output cap can make it dangerous again.
 
John P

John P

Joined Oct 14, 2008
2,026
People building model railroads sometimes use these devices to make grass stand up on the scenery (the scenery base is previously coated with glue). Here's a thread about it:

http://www.modelrailroadforums.com/forum/showthread.php?t=8678

The high-voltage components are taken from electric fly swatters or negative ion generators. They say it's safe, as there's very little current available from the high voltage source. I hope that's true.
 
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