Power factor correction circuits

[gearheaddruid]

I have recently started work on PFC for several projects. The main one being a large Tesla coil. PFC involves a special type of boost SMPS to appear to the incoming power as a purely resistive load. It draws current throughout the sine wave not just at the peaks.
I have one circuit handling 4kw constant with a 400 volt output. This will then become the input to a large full bridge inverter. Most modern "universal input" power supplies use this topology. If people are interested, I have a large supply of 1kw power supplies from the telecom world that are all in good working order just missing the heatsinks. This board is a wealth of parts for people experimenting with smps. It has three different control chips and a bunch of gate drive and current sensing transformers on it. There are also five IRFP460 mosfets and numerous high speed diodes.

The main transformer is an EC70 3c85 material.

I cut the pfc section off of one and with some slight mods, it was putting out 1550 watts with a 120 volt input.

If interested, I will sell them for $10 US each. Buyer to pay the shipping. A group buy for overseas would be great, I will work with you on getting them shipped. I currently have thirty of these in stock. I have a ton more of other supplies with similar parts on them I am going to be selling.

I will be posting my progress on the pfc development and schematics as I get a chance to draw them up.

[gearheaddruid]

A bit of load testing on the large pfc. Stovetop elements are cheap and reliable for this kind of work. Just be careful of the fire thing. (No, not the voice of experience)

[luka]

damn, this is a big unit, since I have 1kw+ unit, and its about 1/5 or smaller... and I don't wan't to compare it to yours... I guess this is 120/230v or is it true "universal input"?
Your design right?

[star882]

PFC is often a waste of money for US residential users since US residential users are usually not billed by power factor. That means you'll be adding more cost and complexity while (usually) reducing efficiency for no gain. (It does, however, make sense for commercial and industrial users.)

[gearheaddruid]

Luka, the pictures are of a board with pfc and three outputs. I am selling them for parts. I rescued them from a recycler, managed to talk them into just unbolting the heatsinks rather than hammering them off. The pfc I have built is 3 by 4 by 2 1/2 inches. I will get a picture up shortly.

Star, the point is to be able to draw more power from an outlet without tripping breakers by averaging out the current draw. For Tesla coils, this is very important. For bench power supplies it helps also if you have limited power available.

[Iain McNeill]

Originally Posted by star882

PFC is often a waste of money for US residential users since US residential users are usually not billed by power factor. That means you'll be adding more cost and complexity while (usually) reducing efficiency for no gain. (It does, however, make sense for commercial and industrial users.)

True, it does reduce efficiency. But it's the right thing to do. Having seen the harmonic trash that comes out of the wall, I have to say that the poor PF of the many household devices we all have (fluorescent lights are particularly bad) is ultimately degrading our audio experience due to interference and intermodulation.

[zigzagflux]

I'm with you, Ian. The issue for residential users is not one of power factor correction, but the lower harmonic content we demand from the already taxed supply voltage. Those PFC circuits just drive the switching frequency up, though, so we may still have to contend with noise whilst we fix our harmonic footprint.

My local utility is running ragged trying to get my voltage distortion below 5%, which is required by IEEE and PSC. Every little bit helps, and PFC supplies are nearly sinusoidal.

Personally, I avoid flourescents like the plague. Ugly light and nasty on the power grid. I'll take my power hungry incandescents, thank you very much.

[Eva]

In applications not requiring tight regulation of output voltage, such as audio amplifiers, PFC provides constant output voltage (with some ripple) regardless of input voltage, avoiding a further regulation stage and voltage selection for worldwide operation.

[gearheaddruid]

Most modern pfc circuits approach 95% efficiency so they are not too bad energy wise. Two problems with them is they are not isolated from the mains and when there is an over current, the supply will shut down but the catch diode still passes current from the incoming power. If you have a failure post pfc, it will continue to feed current until a fuse (or something else) blows.
I was thinking about winding a transformer on one of the cores and see if I can still get the same throughput with isolation. Any ideas on this Eva?

[Sch3mat1c]

PFC SEPIC? S'pose it's possible, doesn't seem worthwhile though. When your average forward converter fails, it will end up blowing the fuse anyway, it's just going through an extra choke and diode this time. Potentially more to replace, but all the more reason to not make something prone to explosion in the first place.

Tim