A 110:220 volt transformer for precipitator PS

[Rich Feldman]

To join the ranks of "Chinese precipitator PS users", following Finn Hammer and many others, I ordered a "300W" specimen (about $45) and also a nominal 110:220V 500-watt transformer ($30) via ebay. Seen here at Grainger website: https://www.grainger.com/product/DAYTON ... age-16V986 Don't want to be tied down to 240V outlets here in USA, or use extension cords from circuits on opposite sides of the panel (as demonstrated by JB).

Transformer arrived first, and I started putting it through its paces.
Would not be surprised if its power is over-rated. How hot will it get with actual input current and power factor of the "300W" power supply at full blast?

The shipping package includes molded Styrofoam blocks. I bet it would withstand a normal and fair cushioning test: hold box at arms length and drop onto pavement. (Will the same be true for the precipitator PS package?)
In my only instrument measurement so far, metal-cased transformer weighed 2.2 kg (4.8 lbs). Good clue about real kVA capacity.
Front panel has 220V and 110V receptacles and a lighted power switch.
Back panel has a 15A fuse and a slide switch for input-110 or input-220.
Cooling slots offer a view of toroidal transformer windings.
One of the cover-attachment screws is only partly driven, at an oblique angle.

First round power testing, with temperature rise judged by hand:
1. No load, half voltage (plugged into 120V with input switch at 220V): no perceptible warming after 1 hour.
2. No load, full voltage (plugged into 120V, input switch at 110V): maybe a few degrees of warming after an hour. So core loss is negligible. It will be same or slightly smaller when transformer is put under load. I have not measured the primary current.

Part 2, done without any electrical instrument or 220-240 volt test load:

With input switch at 220V and transformer plugged into 120V, front panel had full voltage (120) at the "220V" receptacle, and half voltage at the "110V" receptacle, as estimated from the speed of an electric hair clipper.

A 120V, 600W / 900W / 1500W room heater was plugged into the 110V receptacle.
We expect that at half voltage, it will operate at 1/4 power, assuming its resistance wire's temperature coefficient is small.

There was not enough voltage to illuminate the neon indicator lamps in heater control switches.
Heater and transformer got progressively warmer at 600W and 900W settings.
At 1500W setting (estimated to be 375 real watts, with corresponding currents in the transformer windings),
after an hour, the room smelled of hot electronics. Base plate of transformer case, to which the transformer is bolted, was just about too hot to touch.
In my judgement, the transformer could work continuously under those conditions. It would be much happier with some forced airflow from a fan, internal or external. Have I missed a significant factor, in guessing that the high and low winding currents are about the same as normal operation with 375-W 240-V load?
For next session: Operate in normal mode, with input switch at 110, and with 240 volt loads on 220V receptacle. Properly measure voltages and currents, and take a stab at measuring temperature of transformer.

[Rich Feldman]

Whoops, I fooled myself about equivalent currents,
and was much too hard on the poor transformer this morning in half-voltage tests !
Should have at least done some figuring on the back of an envelope. Don't think I did any permanent damage.

The transformer nameplate rating is 500 W: 110 V x 4.55 A on low tap, 220 V x 2.27 A on high tap.

My heater rating at full power is 1500 W: 120 V x 12.5 A .
In the half voltage experiment, it would be 375 W: 60 V x 6.25 A on low v. tap, 120 V x 3.13 A on high v. tap.
So I exceeded the rated currents by 37%. Copper loss power would be 89% above rating.

It was fair to test with heater switch at 900 W, ideally 120 V x 7.5 A.
Half voltage power would be 225 W with 3.75 A.
That would be 83% of rated current in the transformer windings.
IMUO (in my unreviewed opinion).

For noobs: my initial mistake was thinking of power equivalence, which isn't meaningful. Serious transformers are rated in volt-amps. Voltage limit comes from frequency and Bmax and core loss. Current limit comes from i2r loss in windings. It's handy to report the product, especially since it's constant in a product series with different V,I options sharing bobbin and core size. But as I was reminded today, running at reduced voltage does not affect the max current allowed.

[Rich Feldman]

A proper full-load test indicated that my $30 transformer is suitable for energizing the precipitator PS. Needs a safety note and a reliability note.
Its cost-reduced construction is so shoddy, I wonder if this is a counterfeit product. Anybody here got a functionally similar product from Best Buy, or Grainger, or flea market, for comparison?

My test load was 120V incandescent lamps: four 100's and two 60's, with two matched triplets in series. Measured current was 2.05 A with transformer output 220V under load (451 W), compared to 246V immediately after load was removed! More about that later.

After an hour of power, with transformer case open, the toroid hold-down washer was marginally too hot to touch, and there was a trace of new hot electronics smell. That's within normal design range for most magnet-wire-wound parts. Would be hotter with slotted cover installed; we can get more scientific later.

[Rich Feldman]

Safety note:
The unit has hardwired power cord with NEMA 5-15P connector, and a matching 5-15R receptacle labeled "110V". The "220V" universal receptacle can accept the same kind of plug, or its polarized 2-blade sibling, but the Neutral and Line connections would be swapped! Who is familiar with the Neutral side convention of 220V plugs for which this is intended?

Incidentally: in past 10 years or so, those American plugs are often identified as Type B and Type A. I guess the international letter codes were recently invented and popularized by some travel agents' organization. It was about time! But I've been unable to find any real standard, or claim of control. Hints welcome!

Safety and reliability note:
When tilting the transformer all the way left or right, a clunk was heard and felt. With lid off, it's apparent that toroid can slip sideways about 1/4" (or easily be twisted) because its attachment bolt is loose. I could even turn the nut by hand! This should be tightened to prevent fatigue of the casually routed winding terminations... see below.

Reverse Engineering:
There were no surprises in wiring topology, except for reversed colors in the power cord. Xeroxed (?), stapled manual says fuse should be 5 A, but what's there sure looks like a 15 A.

Quality:
Here's where I seriously think this might be a counterfeit product. Aside from cord wire colors and fuse and loose bolt, we have receptacles secured with glue. The toroid winding start, center tap, and end connections have no mechanical support before short pigtailed wires are soldered to receptacle terminals.

The magnet wire is on the thin side, I think, for this rating. Total winding resistance was about 7.6 ohms at room temperature, and over 10 ohms at the end of a load test this morning, with the sheet metal cover back on. With 125V in, output was 225V loaded and 252V unloaded. (R can be measured across 220V receptacle with power off, or across the power input plug with slide switch at 220.) It was hard to carry the transformer with bare hands touching bottom plate 'cause it was so hot. Thermocouple measurements might come next week, at work.

[Rich Gorski]

Rich,

Interesting work exploring the step up transformer. I was also thinking of purchasing one of those precipitator supplies. Not that I really need it but it would be fun to understand their capabilities better.

Have you thought about connecting the precipitator supply directly to 220VAC (no transformer)? From what I can gather from the supply videos online it appears there are two connectors for the 220VAC and no neutral connection. I assume one could connect one hot line from each phase of the 220VAC
to the input and connect one side of the secondary to the neutral/ground and the supply should be happy. Any thoughts?

Rich G.

[Rich Feldman]

Thanks, Rich.

I bet you're right, the PPS would be fine with its AC input connected to a North American 240 volt circuit. Isn't center-grounded 240V the way most fusor.net users over here have done it? Both sides half-hot with respect to the Grounded Conductor (official electrical code term for Neutral). Fusor chamber's tied to Grounding Conductor for safety, and (per code) puts no current in that wire unless there's a fault.

There are many reports to find and study. PPS AC Input circuit is symmetric (except the right side goes to a fuse, and left side has a couple of axial-leaded components going to stuff other than the bridge rectifier). HV output coils are completely isolated from everything else in PPS.

My interest in transformer was just for flexibility in finding outlets. (It also provides a handy lighted on/off switch.) We don't have the luxury of 220V everywhere you might want to plug in a blender or clock radio or desk lamp.

This evening I exercised the titular transformer in step down mode, just for completeness. Expected and got similar losses at similar power level.
Started with center-grounded 240V from the 0-to-290V Variac in 2018 thread "277V Power at Home". viewtopic.php?p=80140#p80140
Unloaded voltages were 240.4 in, 120.3 out. Loaded with all six lamps in parallel: 238.5 in, 110.4 out.

[lanewaddell]

I actually just bout the "LiteFuze" 1KW steup up for my 600W/60kv transformer. I'll let you know how it works out. Right now I'm trying to figure out how to best insulate the HV leads coming off this thing. The insulation is very very little and not great quality so it will need something added to prevent arcing.

[Rex Allers]

A bit different approach...
Here's some thoughts on converting these HV Precip supplies, designed for 220VAC input, to possibly operate, with mods, on 120VAC.

Intro:
Back in around 2019 I got two of these Precip supplies, one 30kV version and one 60kV.
I hacked the circuits of these and worked out all connections. That was not converted to full schematics but diagramed how the parts interconnect on the board traces.

This was presented in this thread:
viewtopic.php?t=12919

If you wish to have these details, I linked them as 4 zip files near the top of that thread. Please download and view the circuit images.

It is now several years later. These same general types of supplies are still available. I suspect the basic designs and principles are probably the same or similar but maybe not the same as what I hacked in 2019.

If, following this presentation anyone has precip supply details or thoughts, please share.

== The Idea of 120 V ===================
So I thought of a way to maybe convert these common precipitator HV supplies to run from 120 VAC input.

Their circuit has an input from 220 V that goes through a diode bridge device and then filtered by a largish electrolytic capacitor. This makes a DC supply of about (220 x 1.414) 310 VDC which is what gets switched into the transformers to make the HV output.

So looking at the circuits, there is a commonly used way to make the same (about) 310 VDC from 120 VAC input.

This circuit is a stripped down version that I got from the book
"Switching Power Supply Design, Pressman 1998, chapter 3)
I removed the circuits for typical switching supply that followed.
Here only the DC bus from 120 or 220.

So with S1 open the circuit is the same as the precip supplies except that the single filter capacitor is replaced with two in series (C1, C2). If that change is made (two caps in series vs original one) and a jumper is added from the junction of the two new capacitors to one of the AC inputs, the circuit is identical and becomes a doubler from the 120 V input. This makes the same ~310 VDC into the rest of the precip supply.

Ok, that simple mod of replacing one capacitor with two in series and adding a jumper is a pretty easy conversion. Unfortunatly there is another issue. The semiconductor chips that do the supply's control functions need a low voltage supply to run. This seems to be +12 above common circuit ground.

From my hacking of the 30 kV supply this comes from a large (270k) resistor off of one AC input, that drives a zener at 12 V, to, with a filter cap, make the low voltage supply.
For 120 input I think this might work with only adding an equivalent (or close) 270k resistor in parallel to the existing dropping resistor.

I haven't tried it but seems like these two mods should work for the 30 kV version.

====================

On the 60 kV version that I looked at, the same doubler mod for 310 VDC should work but the low voltage (12V) is very different.

On the 60 kV supply that I hacked the circuits for, the low voltage comes from a small transformer that is then rectified and regulated by a 7812.

I can't see any way to have the input at 120 VAC drive the primary of the small transformer and have the output enough to regulate at 12 V.

If one wanted to try the doubler on the input to ~310 V, the low voltage (12 VDC) must also be addressed.

The easiest might be to create a small external 120ac to 12vdc supply; cut source traces on the precip supply board, then add jumpers from the new 12v external supply.

A lot of work and circuit details hacking.

------
Those are my thoughts on modifying these precip supplies to work from 120V.
Please share any details that might add to these supply details or other thoughts.