pulsed DC and transformers

Keep the DC out of the transformer, especially a torroid as they have little tolerance for DC offset. Transformers or inductors that tolerate DC offsets have air gaps or the equivalent to limit saturation.

The simple way is to drive the transformer through a capacitor, thus blocking all DC into it's primary. The secondary will convey the pulse, but the zero volt position will be somewhere in the middle of the pulse so that the area above zero equals the area below zero. DC can be restored with appropriate diodes.

For example say the original pulse train was positive going 4 Volts for 1 msec. then zero volts for 3 msec.

If the transformer ratio is 1 : 1, then the secondary would show 3 Volts positive for 1 msec and 1 Volt negative for 3 msec. The positive area equals the negative area. Of course, if the pulse width changes, the zero line would shift to equalize areas. Faraday's law.

Yes, I'll second that. Else the time from core saturation to plume of smoke can be just microseconds. Last time I did that (experimental PWM stalled while I was doing other work in the office) it took two days to get the stench out of the area.

Gee, power electronics seems like so much fun. Maybe I chose the wrong major at the university... ;-)

Thanks,

Michael

Chemistry can be fun, too. One of my friends ended in the hospital. "My lab is now one hellacious black hole and the door is gone as well."

little

What did he try to do... make nitrogen tri-iodide or something silly like that?

Yep, chemistry can be fun. So far I made 40 cc's of ethanol from the kids' leftover food scraps. Just have to scale it up by a factor of

Michael

little

I don't remember. But it made the news.

There was an ad for an ethanol machine that can make 30gal/week or so at home. In the fine print: You had to pour in lots of leftover booze. Yeah, right. Who'd have gallons of "leftover" Whiskey for that?

little

offsets

Haha.

A co-worker told me he was going to buy this:

Only $6,988 after tax credits.

"To operate simply load EFuel100 feedstock (table sugar with ethanol yeast mix) into the fermentation tank and select the fermentation option on the control panel to begin the process. It will take between

He asked me for my comments on the process flow diagram. I gave him about 5 areas where I would do it differently... plus I told him, with sugar about $2.50 for 5 lbs at Wal-Mart, it didn't seem economical. But he's already sent in the down payment... we'll see how it goes...

Michael

little

offsets

It's disturbing. I see many well-educated people fall prey to hype technologies. Predominantly the overly eco- bio- whatever leaning folks. The millisecond they get criticized they often react with "Ah, baloney" but without being able to furnish any data to support their own theory. Kind of like warmingists ...

~snip~

Yes, truly.

The site I posted above used to mention some sort of tax-free, cheap inedible sugar from Mexico. I tried seeking more info via the web, but no luck. (What kind of sucrose is inedible ??? And why?) The website's FAQ has since removed the reference to the cheap Mexican sugar.

One of the ways I would have done it differently, by the way, would have involved just going to restaurants and collecting starchy food scraps (rice, bread, potatoes)... toss in a little bit of alpha- amylase enzyme (0.1% by mass) to convert starch to glucose, that the yeast can eat.

Global warming... well, if it's true, I can start a coconut farm in Alaska...

Michael

Very shortly thereafter you'll read in the papers that some crooks lifted a vat of starchy food scraps from the so-and-so diner. There ain't enough of that stuff. Look at the theft cases of "discarded" french fries oil. Some people are becoming desperate.

A while ago I was passed by a Mercedes 300 TurboDiesel in the Bay Area. He pulled into the right lane in front of me but I had to back off. This car let off such a strong burger shop smell that my mouth began to water.

Not likely. We used to be able to grow citrus around here. No more, that stuff dies in freezes every winter.

Ok, thanks.

If I'm reading this right, I want RC to be

More like 22uF. Calculate it so it's less than 1/10th of the transformed load impedance, depending on your needs.

Theoretically yes. But be careful, electrolytics can only take a certain amount of ripple. Found that out the hard way as a kid. Of course I had to build the biggest honking amp a 230V/16A circuit could stomach. A

IOW ceramic would be better.

~zap~

Ah, thanks! A good thing I asked the experts. "But be careful, electrolytics can only take a certain amount of ripple." didn't appear in MY circuits book.

Just in time for Fourth-of-July fireworks...

(I'd better test my circuits with small loads first.)

Michael

Small loads, see if anything gets hot.

BTW the carpet turned out to be a pain. Needless to say my parents were not enthused and I vowed to fix that. Found a carpet remnant on sale at a store 5 miles away, 15ft by 7ft, barely large enough. Paid, rolled it up, strapped it to the frame of my bicycle and pedaled home. Got a cramp from that unhealthy position and had to push it the last 4.9 miles. Stopped at the library, picked up a book about floor covering techniques. At least I learned how to lay carpet and how to replace broken spokes on bicycle wheels. All because that one dreaded capacitor couldn't hang on.

...

And the ceiling?

That was just a little crater, some of the plaster and concrete had fallen out. Pa gave me a gypsum bag, I mixed some up, went on a ladder and spackled it. Of course, then I had to re-paint the whole ceiling and that is not one of my favorite tasks.