Transformerless power supply

Is it reasonable/possible to build an 8 amp 20 V transformerless power supply from a 120Vac line. I calculate about 180uf plus or minus depending on other components. Maybe 9- 20uf caps in parallel? I'd like to build it into a leaf blower. All plastic, absolutely no metal exposed.

I think I've answered my question, I have 12, X rated caps in my junk box, but they are only 1uf. The cheapest 20uf I can find is $3, so $27 for 9 caps. Not reasonable.

Just had another thought, I could mount a power supply with transformer on the wall and have a cord go to the leaf blower. Just trying to build a light weight Leaf Blower for the wife to clean the garage once a week. Daughter gave me the leaf blower after the battery charger gave up.

Input encouraged. Mikek

Fix or replace the charger ??

No, I looked at the charger, could not get a schematic and is was full of surface mount ICs and parts, not a simple charger, plus the batteries are no good. I already have leaf blower, it is larger, this would be nice just for the garage.

Mikek

I frequently see some large AC rated caps in the surplus catalogs so I think I'd hunt for some better prices. The newer film caps... I wouldn't use an AC motor starting electrolytic, and would have some safety devices built too.

regarding a low voltage supply to the blower... You may not be happy with the voltage drop...

Google for "line voltage drop calculator" plug in wire size, distance, current, then see how much you will lose between a source and the leaf blower.

DC motors pull more than their working current when starting up. (that may just be an annoyance with a long line - waiting for the blower to spin-up to speed)

There are all kinds of relatively inexpensive DC supplies on Ebay and surplus electronics outlets, you may find a charger on line too.

Lithium batteries and sealed batteries can be dangerous if they aren't charged properly. So don't just connect a DC supply to a battery, call it a charger, and expect things to work or be safe.

If it were me, I'd try to fix or replace the charger as Plan "A"

PS Check the price of a replacement from the manufacturer. I was getting all set to rebuild the power supply on my wife's big fancy sub-woofer computer speakers and for the hell of it called Altec Lansing only to find the whole sub-woofer box with amp and supply was only $20 as a new OEM replacement.

You could buy some DC supply... meanwell? Or get a 30V 10 A bench supply? About ~$150 here.

George H.

That is the way it is for many items. You can buy a new one for just the parts to repair something. I seldom even think of repairing many low dollar items just because the parts are worth more than a new one.

Ya, just not interested, It would just be a lightweight blower to set at one end of the garage and easily blow out the garage. I threw out the Original charger and batteries and the weed whip that used the same batteries, I think it even had a hedge trimmer.

I bought a $450 Bose Subwoofer speaker system at a yard sale for $5, they wanted $10, but when I ask if it worked the said no. So, I offered $5. I took it home, and contacted Bose, the said the problem may be this cable and sent one. It wasn't the cable. So they said They would fix it at no charge, But I had to pay the shipping there. They paid it back. It did cost almost $40 to ship, but a nice system for $45!

Mikek

My wife picked up a low set exercise bike, the electronics were built into a plastic ass'y that many would use as a handle. It was broke, along with the PCB, Having fixed many, many cracked PCBs. My wife thought I could fix it. Nope, too many pieces. I checked on line and found it was only $26 for the whole assy. That was such a deal. And I don't use it as a handle. Mikek

I'm still thinking about simple Transformerless supplies for 20V 8 amps from 120vac. I recalled this Third harmonic generator, it's design is for very low power, but can it be increased? The design is for 10MHz to 30MHz, going from 60hz to 180hz makes the inductors huge, but... any thoughts.

Here's the two diode version.

Lots of reactive power, which means I'm not creating lots of heat. But can it be made to work.

Mikek

Reactive power works at 60 HZ as well as 10 MHZ the parts just get too cumbersome and expensive. The math work very well; the practicality doesn't work at all.

And you aren't dealing with a fixed load. Start-up current may be many times the run current with something like a motor. You'd probably end up needing some form of active voltage regulation to make it work.

If you're talking about inductors you might find selling the copper windings and iron cores as scrap metal will more than pay for a replacement power supply.

It (capacitive reactance) is very handy when you just need a few milliamps to light a LED or power a small circuit like the timer on an automatic coffee maker directly from mains voltage, but isn't often used for amps of current because there's better ways to do it.

depends what you mean "transformerless"

You are nuts! using a capacitive dropper to make 8A is crazy. what is your plan for reinforcing the insulation on the leaf blower? Is this a plot to kill your wife?

That seems half safe so far.

That seems more reasonable, regular iron transformers with large rectifiers work well for powering DC motor loads. switching supplies can work too, but they usually need a current limit so that they can survive a stall, it may be possible to attach a switching supoply directly to the blower.

I guessing you don't have an air compressor (the type used for air tools, not a mere tyre pumper) in your garage.

--
  Jasen.

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** With a low resistance load, the inrush surge from a 180uF cap would trip the breaker.

SMPS have resistors or NTC thermistors in series with the AC supply stop this.

..... Phil

On 8/10/2018 1:24 PM, amdx wrote: ...

Fix, build, or buy a battery charger.