Fibergeek's VCCS Power Supply Diagrams Posted

[jnbsystems]

Here is a circuit diagram for a VCCS power supply for use with the new LCD Anodizing Kit.

This schematic comes courtesy of Fibergeek, and it is a modified and updated version of the circuit mentioned in the instructions for the LCD kit.
I have posted them on my website so everyone can access them.

I will post a parts list shortly, referencing Digikey.com's part numbers for the parts in the diagram.

The best way to make use of these files is to copy them to your hard drive and open them locally. You will need Adobe Acrobat Reader to open them.

I want to personally thank Fibergeek for making this diagram available to the anodizing community, and for his continuing efforts to help us out on this forum.

http://www.jnbsystems.com/anodize/VCCS1.PDF
http://www.jnbsystems.com/anodize/VCCS_NOTES.PDF

Thanks,

Bruce

[Fibergeek]

I need to provide this addendum to the VCCS construction notes:

Don't overtighten the screws holding the TO-220 package MOSFETs to the heatsink. I just did this on a similar power circuit; and burned out the MOSFETs, and I know better.

The data sheet for the IRFZ48V specifies the mounting screw torque to be 10 ft. lbs. (look it up at www.irf.com). This is the case for all TO-220 packages. If you crank it down hard you will distort the tin plated copper body of the MOSFET and ruin the thermal connection. You don't really need a torque wrench, the screw should be just tight enough to prevent the MOSFET from pivoting on the screw, and no tighter. Thermal compound between the MOSFET and the heatsink is MANDATORY.

[wildman]

Parts List

Bruce,

How is the parts list coming?

I am very interested in building the VCCS portion for a power supply. I have been building CNC power supplies for years but they have always been unregulated.

Dan

[jnbsystems]

HI Wildman,

This has taken a little longer than I expected due to a product that I've been trying to get out (and have had more than a little trouble with . . . )

Here is the link to the list, at least what I have done. Please understand I haven't really checked to make sure it's 100%, but it should be pretty close.

http://www.jnbsystems.com/anodize/VCCS1-PARTS_LIST.PDF

I'll let you know when I have it all 100% (in a few days, I hope )

Bruce

[wildman]

Thanks for the parts list Bruce.

I bought all of the parts for the VCCS circuit from Digikey for about $30.

The schematic shows that input voltage should be between 20-30 volts. I have several supply options with all of the parts that I have in the shop.

Fibergeek......do you know how many amps the VCCS circuit can safely handle?

My options are either using my Mig welder: output is 21-28 volts but amps are unknown, or a regulated power supply that is 13.8volts and 20 amps, or I can build a toroid coil unregulated supply that outputs 28 volts at 10 amps.

Would it matter if the input supply is regulated ot not?

[clab]

Power input

I'm an experienced EE and this looks like a good design to me. If you use a mig welder as a power source, you'll need to add some major capacitors across it to reduce ripple (without them it might be 100%), and check polarity first! Mine can be set up either way, and reverse polarity will fry this circuit instantly. I'd suggest using a fuse of some sort in series with the Mig welder, but after the capacitor connection (so the charging current of the caps doesn't blow the fuse when you turn on the Mig), quick blow. The old rule of thumb is about 1000uF per amp needed, but you can go up from there if you want it really nice. The bigger the difference between input and output voltages, the more heat the fets will have to dissipate for a given current. Use LARGE heatsinks, and keep an eye on the temperature. Here I have a supply about equivalent to a Mig, but on a variac, so I can keep the in out differential voltage close by an occasional manual adjustment.

This design could easily be adapted for lower current used in (non chrome) plating, and ought to work well for that too. For that I would use larger source resistors for the fets and a more dc accuate opamp. It *might* work ok as is if you simply increased the series R from the voltage reference, but that would make it really drift sensitive.

[Fibergeek]

Chrome plating? This thing was originally designed (by me) to provide 6 Amps, it will do 10A without problems. The application was anodizing. If you want more information, look for a thread "VCCS Questions" active in Oct. 2003 in this forum. You'll get the complete picture on ripple reduction capacitance, they were discussing values on the order of 27,000 uF. The heatsinks were on the order of 0.7 deg. C. per Watt. Forced air cooling was also intended.

The limiting component(s) for current regulation and drift are the three paralleled source resistors, they are cheap wire wounds. The opamp, voltage reference, and the ordinary carbon film resistors are negligible here.
As shown this circuit will provide both current regulation and drift to better than +/-1% over a 10 mA to 10A range, and was tested to that. Why would it need to be any better for anodizing or plating?

The limiting components for power dissipation are the three paralleled MOSFETs. Although these MOSFETs are rated for 55A and 115W each, the thermal resistance of the TO-220 MOSFET package to the heatsink lowers this considerably, which is why there are three. Using MOSFETs with TO-247 or TO-3 packages will improve this considerably.

Raising the value of the source resistor(s) will only serve to reduce the voltage compliance, why would you want to do that?

A nicety would be to use the other half of the dual opamp as a gain of +10V/V amplifier for the current monitor, now it will read directly, 1V = 1A. For this, I would use a better opamp; say an LT1013, and 1% metal film resistors in the current monitor amp.

[kickn]

I know I had just posted a question in the same area as this but I thought I would ask here as well. I was thinking of using a welder as a power supply as well. Is the output of the welder DC or AC - and if AC has anyone ever put a bridge rectifier on the end of it?

Also - whats the difference in using an arc vs. mig welder? Is it the AC/DC or is it the separate currant/volt control?

Thanks

[kickn]

I've been doing some searching on ebay for a cheap psu and came accross this - http://cgi.ebay.co.uk/ws/eBayISAPI.d...e=STRK:MEWA:IT

Would it be feasible to put a variant on the VCCS circuit on the front of this?

[kickn]

Sorry for bringing this up again but who realistic is it to make this schematic a 20A or 25A unit?

Also - Was there a schematic posted here Fibregeek about adding a CC controll to an existing PSU? If so I think I've found a 28A that only has VC for a good deal but would need to modify it.

Cheers

[Fibergeek]

Yes it could be modified for 20-25A, dealing with the resulting power dissipation would get to be interesting.

The real question is do you have the skills and test equipment? You will need both.

Modifying an existing unit would actually be harder than designing from scratch. The first thing you would have to do is reverse engineer the existing unit.