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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details.

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Old 29th Jun 2019, 10:26 am   #1
lesmw0sec
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Default Early rectifiers.

Recent posts regarding Mercury-arc rectifiers inspired me to included this example, being a mechanical synchronous rectifier. This was installed at the Royal Naval Cordite Factory, Holton Heath and was part of the kit to supply the Cottrell plant for dust extraction from the fume vents. These days, we would probably use a couple of 1N5408's, but at the time of installation, no such convenient device had been invented!

See: http://www.mw0sec.co.uk/hhintro.html

For a bit more information about Holton Heath.

Les.
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Old 29th Jun 2019, 11:19 am   #2
kalee20
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Default Re: Early rectifiers.

Mechanical synchronous rectifiers do have an advantage for low-voltage supplies in that efficiency can be better than almost anything else due to the vanishingly low voltage drop across the contacts.

Mercury arc: 15V wasted.

Selenium/copper oxide: 2V

Silicon: 0.9V or so.

Silicon schottky: 0.5V

Mechanical contacts: 0.05V

So very useful for electro-plating works.

Down side is that they are maintenance-heavy of course, you don't get anything for free!
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Old 29th Jun 2019, 11:23 am   #3
lesmw0sec
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Default Re: Early rectifiers.

Quite - but in the example I quoted, the voltage was around 10 KV!
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Old 29th Jun 2019, 1:41 pm   #4
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Default Re: Early rectifiers.

Hello
I have a early home battery charger with a "Magnetic Rectifier". Some pictures below.
Yours Richard
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Old 29th Jun 2019, 1:47 pm   #5
lesmw0sec
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Default Re: Early rectifiers.

Now that is an interesting bit of kit. Does it work?
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Old 29th Jun 2019, 2:20 pm   #6
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Default Re: Early rectifiers.

And don't forget vibrator power supplies as formerly used to power valve equipment from vehicle batteries or similar.

The simpler vibrator power supplies simply chopped the DC into pseudo AC which was then stepped up in a transformer and the HT rectified as usual.

Some versions were called "self rectifying" these had extra contacts that switched the AC output of the step up transformer and thereby rectified it.
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Old 29th Jun 2019, 3:00 pm   #7
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Default Re: Early rectifiers.

Used to make a hell of a racket in a car radio back in the day. Buzzzzz...

Craig
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Old 29th Jun 2019, 5:00 pm   #8
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Default Re: Early rectifiers.

Richard's magnetic rectifier is a high-current version of the output end of a 'self-rectifying' or 'synchronous' vibrator. I have an example of the Crypto rotary synchronous rectifier for battery charging, and would be interested to hear of anyone else who has, or has used, a unit of this type.
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Old 29th Jun 2019, 6:27 pm   #9
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Default Re: Early rectifiers.

Yes, "synchronous" vibrators were initially popular in car-radio power supplies but they suffered from the inevitable issues of inductivity and hysteresis in the vibrator-transformer which meant that the high-energy peak in the secondary often occurred while the secondary-switching contacts were in transition, so you got spectacularly-high instantaneous secondary-voltages whose energy was not conducted to the output but was left free to tunnel through the secondary-winding insulation....

[synchronous vibrators as an idea seemed to have a short popularity before Raytheon came on the scene with their Argon-filled cold-cathode rectifiers such as the 0Z4. These also had issues - in classic 1930s car-radios running off a 6V generator-charged battery it was not uncommon when driving in stop-start city traffic - where the engine spent lots of time idling so generator-output was minimal] for the battery-voltage to drop to a point where there was insufficient voltage to ionise the rectifier and the radio cut-out. I remember reading a 1930s Chicago Police report on their use of mobile two-way radio where this was a particular complaint!]

If you want 'strange' rectifiers - in the 1970s I played around with 'electrolytic' rectifiers using mixtures of lead, iron, zinc and aluminium plates dipped into jars containing various mixtures of Borax, Lye, Sodiium Sulphate and Potassium Hydroxide.
Though these could definitely rectify, they had at best a forward:reverse resistance ratio of about 5:1 meaning they would get boilingly-hot under extended use - and splashes of the chemicals ruined several pairs of jeans!
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Old 29th Jun 2019, 7:28 pm   #10
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Default Re: Early rectifiers.

A couple of definitive works on the subject and Its history

Metal Rectifier Engineering E A Richards of STC, C 1958

Crystal rectifiers and transistors M G Say Newnes 1954

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Old 29th Jun 2019, 9:39 pm   #11
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Default Re: Early rectifiers.

So many of today's switched-mode power supplies use synchronous rectification with MOSFETs driven by the control chip or, increasingly, software running on a microcontroller. The advantages are the same as those quoted for mechanical synchronous rectification: lower loss especially at low output voltages or high currents.

There's nothing new under the sun!

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Old 30th Jun 2019, 12:44 am   #12
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Default Re: Early rectifiers.

10kV may need a few more than a couple of 1N5408 ;-)
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Old 30th Jun 2019, 11:35 am   #13
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Default Re: Early rectifiers.

On a visit to Appleby Frodingham steel works Scunthorpe many years ago, the guide showed us the mechanical synchronous rectifier which was used to clean the air intake to the huge compressors, by the coking plant. Below the drum was a railway wagon in which the debris fell when the power was switched off and large hammer/gong hit the side of the drum. I think it was operating at 25KV.
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Old 30th Jun 2019, 10:32 pm   #14
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Default Re: Early rectifiers.

Would that have been some sort of electrostatic precipitator?
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Old 30th Jun 2019, 11:07 pm   #15
lesmw0sec
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Default Re: Early rectifiers.

Quote:
Originally Posted by Herald1360 View Post
Would that have been some sort of electrostatic precipitator?
If you refer to my post - yes. The Cottrell type plant was also employed to remove particles from coal-fired power stations. At H. Heath it was employed in the fume outlets of the sulphuric acids factory.
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Old 1st Jul 2019, 6:33 pm   #16
Herald1360
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Default Re: Early rectifiers.

I was referring to the Appleby Frodingham post. The 25kV seemed OTT for any other technique.

Come to think of it- should this be in "Components and Circuits"? Non of the kit described is exactly household equipment!
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