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 Post subject: Instructables Circuits Projects- Antique Radio B-Battery P.S
PostPosted: Sep Fri 27, 2019 4:28 pm 
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Joined: Jan Mon 17, 2011 2:10 am
Posts: 223
Location: Revere,Massachusetts U.S.A.
Hi Forum, I built this project and have a few questions regarding the filter capacitors, the schematic calls for 4 "330uf @ 250volt caps. The physical size difference between 33uf and 330uf is a great deal, I built the power supply using 33uf caps. I also built the nixie power supply that goes with the filter cap / Zener board, I use a wall wart to power the nixie supply.

I measured the current draw from the wall wart to the nixie board and it's over 200ma? The output voltages are close and the supply is clean as for ripple, did I make a mistake in using the smaller caps? I wanted to add the scans of the nixie supply & filter / Zener board but the file size is too large?
Any help would be appreciated.
Tony

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 Post subject: Re: Instructables Circuits Projects- Antique Radio B-Battery
PostPosted: Sep Fri 27, 2019 11:40 pm 
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Joined: May Tue 30, 2006 4:46 pm
Posts: 9957
Location: Santa Rosa, CA
330 uF seems like overkill.

I disagree with the comment on the web page that the caps eliminate Zener noise. An electrolytic cap is not very effective in eliminating high frequency noise.

The current draw from the wallwart has to be enough to supply the output power and inefficiencies. If you want 90 volts output and the wallwart is supplying 9 volts, then the wallwart current has to be at least 10 times the output current. Power out < power in.

Rich


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 Post subject: Re: Instructables Circuits Projects- Antique Radio B-Battery
PostPosted: Sep Fri 27, 2019 11:53 pm 
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Joined: Jan Mon 17, 2011 2:10 am
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Location: Revere,Massachusetts U.S.A.
Thank You

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 Post subject: Re: Instructables Circuits Projects- Antique Radio B-Battery
PostPosted: Sep Sat 28, 2019 2:06 am 
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Joined: Nov Mon 06, 2017 2:35 pm
Posts: 120
Location: Texas, U.S.A.
Tony,
The output voltage given for the Lumos dc to dc switching converter referred to in the instructables Antique Radio B-Battery Power Supply article is 120 V, and the rated power output without additional heat sinking is 5 watts. 5 W / 120 V = 41 mA. This means 41 mA can be drawn from the converter. (it should be provided with free airflow).

The 1N4748A zener is rated 22 V typical at 1 W at 50 C, 3/8" lead length.
1 W / 22 V = 45 mA
So the full 41 mA from the converter can be run through the zener string (good idea to provide 3/4 inch lead length and free air flow for the zeners, this includes ample ventilation of any enclosure).
120 V - 88 V = 32 V.
32 V / 41 mA = 780 ohms for the dropping resistor. 820 ohms is a standard value and close enough (this is the resistor given as 3.3 k in the project web site. 3.3 k is too high).
32 V / 820 ohms = 39 mA zener current.
39 mA x 32 V = 1.25 watts for the resistor. I'd use at least a 3 watt with lead length as given for the zeners and free air flow.
I'd choose the minimum zener current to be 11 mA, to keep the zener impedance down.
39 - 11 = 28 mA
So up to 28 mA total can be drawn from the zener string taps, unless I've made a blunder of some sort.
For example, 10 mA from the 90 V tap, 5 mA from the 67 V tap and 7 mA from the 22 V tap = 22 mA. Which is less than the full 28 mA capability.

A 1N4749A could be used for the 2nd diode in the string to give nominally 22 - 46 - 68 - 90 volts output.

If the Lumos thing is about 80% efficient and using 10 V dc input, the input current would be around 585 mA at 39 mA output current.

RF filtering and shielding may need to be added to that dc - dc converter (chokes on wire leads from PCB, possibly toroidal or shielded inductor for Lmain).

----------------
Eric LaGess
WB5HDF


Last edited by infzqi on Oct Tue 01, 2019 2:38 am, edited 5 times in total.

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 Post subject: Re: Instructables Circuits Projects- Antique Radio B-Battery
PostPosted: Sep Sat 28, 2019 4:19 am 
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Joined: Dec Sat 24, 2011 9:17 pm
Posts: 6226
Location: Vancouver Island, Canada
Here's the link to that project, I think:

https://www.instructables.com/id/Antiqu ... er-Supply/

I predict it will gobble 9 volt batteries for breakfast. You could wire a few in parallel.

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 Post subject: Re: Instructables Circuits Projects- Antique Radio B-Battery
PostPosted: Sep Sat 28, 2019 8:04 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2307
Location: Saskatoon
westcoastjohn wrote:
I predict it will gobble 9 volt batteries for breakfast.


Yeah. I built something similar a couple of years ago, but I used a 6V lantern battery to supply the boost converter.

As others mentioned, the 330uF caps are ridiculously large. No doubt there were noise issues, but they would have been unrelated to the zeners. It would have been the switching noise from the boost converter, and it would likely be very bad. On my unit, I installed the entire unit (battery and all) inside a shielded enclosure and built a multipole low pass filter to get rid of the converter noise. It worked pretty well, but the noise was not completely inaudible on weak DX stations, so I will likely add an additional stage of noise filtering in order to get it a bit better.


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 Post subject: Re: Instructables Circuits Projects- Antique Radio B-Battery
PostPosted: Sep Mon 30, 2019 4:46 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 3714
Location: Lexington, KY USA
I agree that the smaller capacitors are probably the least of your worries.

The switch-mode boost converter will be a powerful generator of wideband noise. No problem for your Nixie tubes, but not so good for a radio.

The shunt regulation (zeners) used on the output means that the unit will draw maximum power at all times. Not what you want for battery powered operation. A wall-wart may handle this power consumption OK, but then the DC input will also require careful filtering to keep the noise inside.

The current drain at 9V will be wildly in excess of what a regular transistor radio battery will provide for any length of time. A series string of D cells, or a 12V lantern battery would be barely big enough for actual listening use.

The boost converter is here:
https://www.lumos.sk/high-voltage-power-supply-kit/

This is a simplified schematic of the converter:

Image

Note that the converter is rated for a minimum of 10VDC input, so 9V may not be quite enough.

Image

Ted


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 Post subject: Re: Instructables Circuits Projects- Antique Radio B-Battery
PostPosted: Oct Tue 01, 2019 7:23 am 
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Joined: Jan Mon 17, 2011 2:10 am
Posts: 223
Location: Revere,Massachusetts U.S.A.
Thank You to all for the efforts & information, yes there's know doubt that this supply maybe more trouble than useful. Live & Learn
Tony

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 Post subject: Re: Instructables Circuits Projects- Antique Radio B-Battery
PostPosted: Oct Tue 01, 2019 2:18 pm 
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Joined: Oct Thu 04, 2018 2:11 pm
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Location: Suburban Chicago
It was surprisingly hard to find noise plots of Zener diodes. Some of the ones I found contradict the measurements found in the link below but they were aimed at building RF noise sources and so they probably used coupling caps too small for audio noise. The avalanche noise in a Zener diode is supposed to have a 1/f^2 characteristic. At RF frequencies the avalanche noise is probably buried under other noise sources that have a flatter noise spectrum, But, if you are building a power supply for an audio amplifier with little to no power supply noise rejection the noise of a Zener diode could be an issue. That is probably why such large capacitors are used in this design.

http://www.ciphersbyritter.com/NOISE/NOISRC.HTM


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 Post subject: Re: Instructables Circuits Projects- Antique Radio B-Battery
PostPosted: Oct Tue 01, 2019 10:00 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 3714
Location: Lexington, KY USA
Zener noise is a red herring in the context of this power supply. You will never hear any zener noise from this power supply in an old radio, even if you substitute very small filter capacitors.

330uF is far larger than needed, but usually not harmful. The large value will make the sparks bigger when your screwdriver slips. 33uF caps should work fine.

It might be beneficial to bypass each voltage output actually being used to ground with a 0.01uF to 0.47uf capacitor. These small capacitors will better bypass RF. They actually work best installed in the radio.

I would never suggest building one of these power supplies for powering a radio. However if you have already got one built and working, it would be interesting to see just how bad the noise really is. We would be interested in hearing about what you discover.

Ted


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