Yet Another Cycling Forum

General Category => The Knowledge => OT Knowledge => Topic started by: Mrs Pingu on 17 October, 2020, 06:47:59 pm

Title: Power supplies - black magikk
Post by: Mrs Pingu on 17 October, 2020, 06:47:59 pm
I have a set of kitchen scales which came with a switching power supply with an EU plug and a UK adapter.
Because of the direction of the plug and cable it's a PITA and I'd like to swap it for a UK power supply.

The scales say 4.6v on them. (It will also run off AAA batteries). The power supply says 6v, 300mA.

A quick snoop on RScomps give me this list
https://uk.rs-online.com/web/c/power-supplies-transformers/power-supplies-psus/ac-dc-adapters/?applied-dimensions=4294405226,4294341987,4293331712,4293332227,4293331713,4294505198&rpp=100

Watts are mentioned just to confuse things  ??? Nothing is coming up with the same number of mA.

What can I get away with? For instance would I be ok with this 5v, 1A job? https://uk.rs-online.com/web/p/ac-dc-adapters/1753307/

TIA :)
Title: Re: Power supplies - black magikk
Post by: Kim on 17 October, 2020, 07:18:05 pm
Officially, 6V and anything equal or greater than 300mA.  The voltage is regulated by the supply, but the current is determined by the load, so the supply's current rating just has to exceed the maximum demand, which we know to be somewhere under 300mA.

5V may or may not work, depending on how the scales regulate internally.  It's unlikely to release any magic smoke to try one.
Title: Re: Power supplies - black magikk
Post by: Pickled Onion on 17 October, 2020, 07:41:56 pm
Wouldn't a set of rechargeable batteries be cheaper and more convenient?
Title: Re: Power supplies - black magikk
Post by: Kim on 17 October, 2020, 08:05:54 pm
Quote from: Pickled Onion on 17 October, 2020, 07:41:56 pm
Wouldn't a set of rechargeable batteries be cheaper and more convenient?

For normal amounts of kitchen scalesing, probably, but I've seen the bread thread... (https://yacf.co.uk/forum/index.php?topic=68753.msg2536331#msg2536331)
Title: Re: Power supplies - black magikk
Post by: Mrs Pingu on 17 October, 2020, 08:28:32 pm
Plus the cupboard where the scales live is at the north east corner of our flat, therefore cold, and winter is coming.
Title: Re: Power supplies - black magikk
Post by: wajcgac on 17 October, 2020, 09:01:59 pm
You'll also need to consider the output plug on your existing power supply - regarding size and polarity of centre pin.

The one you linked to here appears to have a single output connector specified as 2.1 x 5.5 x 12 mm Centre Positive

Power Supply (https://uk.rs-online.com/web/p/ac-dc-adapters/1753307/)

This may or may not be the same as you already have - the centre pin polarity is usually stated on the transformer body . It's not just the size of the connector but some centre pins are negative as well.

I've found a guide that will help you

AC adaptor selection guide (https://blog.banggood.com/how-to-choose-the-right-ac-adapter-for-your-gadget-29870.html#:~:text=If%20you%20are%20measuring%20you,must%20match%20to%20connect%20properly.)

One alternative that would seem a good idea would be to buy a Universal Adaptor - something like this with multiple voltages and connector sizes - usually you can spin an adaptor around as well to swap the centre pin polarity from positive to negative.

Typical Universal AC adaptor (https://www.argos.co.uk/product/9829701?istCompanyId=a74d8886-5df9-4baa-b776-166b3bf9111c&istFeedId=30f62ea9-9626-4cac-97c8-9ff3921f8558&istItemId=ixilqlqxt&istBid=t&&cmpid=GS001&_$ja=tsid:59157%7cacid:534-693-8244%7ccid:9562883196%7cagid:101271439594%7ctid:pla-894275467652%7ccrid:423227398282%7cnw:g%7crnd:16029792943979685342%7cdvc:c%7cadp:%7cmt:%7cloc:9046218&utm_source=Google&utm_medium=cpc&utm_campaign=9562883196&utm_term=9829701&utm_content=shopping&utm_custom1=101271439594&utm_custom2=534-693-8244&gclid=CjwKCAjwrKr8BRB_EiwA7eFapmoLYd9WNWSwZsQ-yfawkh14qBxd5zlBnwDxC00yo9bV9nTXJzZPzxoCB_MQAvD_BwE&gclsrc=aw.ds)

These work well until someone pulls the connector adaptor out who is not electrically aware and then plugs it back in inadvertantly swapping the centre pin polarity and then wonders why whatever it was powering up no longer works.

My advice would be to not use one of these unless absolutely necessary and then make sure everyone else using it is aware of the potential problem.


Title: Re: Power supplies - black magikk
Post by: Kim on 17 October, 2020, 09:08:45 pm
Quote from: wajcgac on 17 October, 2020, 09:01:59 pm
This may or may not be the same as you already have - the centre pin polarity is usually stated on the transformer body . It's not just the size of the connector but some centre pins are negative as well.

Centre Negative is a work of Stan and should come with warning stickers.

(http://www.ductilebiscuit.net/gallery_albums/random/2020_10_17_21_04_21.sized.jpg)
Title: Re: Power supplies - black magikk
Post by: PaulF on 17 October, 2020, 11:05:27 pm
Quote from: Kim on 17 October, 2020, 09:08:45 pm
Quote from: wajcgac on 17 October, 2020, 09:01:59 pm
This may or may not be the same as you already have - the centre pin polarity is usually stated on the transformer body . It's not just the size of the connector but some centre pins are negative as well.

Centre Negative is a work of Stan and should come with warning stickers.


Centre negative keeps the music world going; most guitar effects pedals are centre negative. The reason why is another question entirely.
Title: Re: Power supplies - black magikk
Post by: MattH on 17 October, 2020, 11:20:07 pm
Back in the 80s I had the car charger adapter for a Japanese UHF handheld transceiver. That was centre negative. It helpfully had a warning label on it telling you not to allow the outer of the output plug to touch the car chassis otherwise "serious damage to the fuse will occur"  :)
Title: Re: Power supplies - black magikk
Post by: grams on 17 October, 2020, 11:27:25 pm
Quote from: Mrs Pingu on 17 October, 2020, 06:47:59 pm
The scales say 4.6v on them. (It will also run off AAA batteries). The power supply says 6v, 300mA.

How many AAA batteries?

If this were my house it would have a scrap USB cable soldered to the battery terminals by now.
Title: Re: Power supplies - black magikk
Post by: Kim on 17 October, 2020, 11:42:22 pm
Quote from: PaulF on 17 October, 2020, 11:05:27 pm
Quote from: Kim on 17 October, 2020, 09:08:45 pm
Quote from: wajcgac on 17 October, 2020, 09:01:59 pm
This may or may not be the same as you already have - the centre pin polarity is usually stated on the transformer body . It's not just the size of the connector but some centre pins are negative as well.

Centre Negative is a work of Stan and should come with warning stickers.


Centre negative keeps the music world going; most guitar effects pedals are centre negative. The reason why is another question entirely.

Because with a three-terminal jack socket you can use the presence of a plug to disconnect a battery, and if you want that on the positive side of the circuit, the outer terminal of the jack has to be positive.

Meanwhile, you want the outer terminal of the dangling plug to be at ground potential (if it's not floating) in case it touches something grounded.

Something has to give, and that something was consistency.  But that's fine, because there are already about 83 million size permutations on the bastard things.

Kind of thing that really makes you appreciate USB.

Title: Re: Power supplies - black magikk
Post by: PaulF on 18 October, 2020, 07:06:48 am
Thanks, I think I understand that :)
Title: Re: Power supplies - black magikk
Post by: quixoticgeek on 18 October, 2020, 05:36:51 pm
Quote from: Kim on 17 October, 2020, 09:08:45 pm

Centre Negative is a work of Stan and should come with warning stickers.

(http://www.ductilebiscuit.net/gallery_albums/random/2020_10_17_21_04_21.sized.jpg)

Where can we get these stickers?!?

J
Title: Re: Power supplies - black magikk
Post by: Kim on 18 October, 2020, 05:44:58 pm
Quote from: quixoticgeek on 18 October, 2020, 05:36:51 pm
Quote from: Kim on 17 October, 2020, 09:08:45 pm

Centre Negative is a work of Stan and should come with warning stickers.

(http://www.ductilebiscuit.net/gallery_albums/random/2020_10_17_21_04_21.sized.jpg)

Where can we get these stickers?!?

Your nearest Brother TZe-compatible label printer[1], the BHPC shop and some sort of Mega-Global Fruit Corporation of Cupertino, USAnia fanperson emporium, respectively.  The Toshiba anti-theft one is probably unobtanium, thobut, unless you go back to about 2012 and steal one.


[1] Guess what the power supply is for?
Title: Re: Power supplies - black magikk
Post by: Mrs Pingu on 18 October, 2020, 06:55:43 pm
Quote from: wajcgac on 17 October, 2020, 09:01:59 pm

I've found a guide that will help you

AC adaptor selection guide (https://blog.banggood.com/how-to-choose-the-right-ac-adapter-for-your-gadget-29870.html#:~:text=If%20you%20are%20measuring%20you,must%20match%20to%20connect%20properly.)


Thank you
Title: Re: Power supplies - black magikk
Post by: Kim on 18 October, 2020, 08:42:37 pm
That's quite a good article, I've bookmarked it for later.
Title: Re: Power supplies - black magikk
Post by: Mrs Pingu on 21 October, 2020, 04:41:22 pm
Just had another look at the current adaptor and it's centre negative. Think I might give up for a bit.
Oh and tried batteries and they didn't work so stuff that.( I am not going to wait for freshly charged batteries to dictate when to bake).
Title: Re: Power supplies - black magikk
Post by: Cudzoziemiec on 21 October, 2020, 04:57:31 pm
Quote
Voltage carries the power and the Amps are the measurement of how much power it consumes, think of it like a river, the V is how wide the river is and the A is how fast the water is flowing, so a low volt high amp circuit is a small river flowing fast.
I've always thought of it the other way round; volts as speed, amps as volume of water. I'd say I ought to go back and do Physics O Level again but I'm not sure it did much good the first time round.  :-[
Title: Re: Power supplies - black magikk
Post by: Kim on 21 October, 2020, 06:15:08 pm
If we're doing water analogies, volts is the change in height (so, pressure) and current is the mass of water per second.  Gravitational potential energy/power is therefore a direct analogy for electrical energy/power.  Cross-sectional area of the channel is resistance.  And if you think about it too much beyond that, you end up needing water-wheel-controlled sluice gates and water that flows uphill in special kinds of pipes, and it's probably best to stop plumbing and start thinking in terms of mathematical lego-blocks...

So yeah, you need a wall-wart with the right dam height (too much and the pipes will break, too little and there won't be enough pressure to turn the turbine), and a wide enough intake that the turbine gets its rated flow of water when the inlet valve is wide open.  Note that when everything's working properly it's the inlet valve which determines the flow at a given moment, which is controlled by a guy with a clipboard and hard hat in the turbine control room, not the dam or the upstream water supply.
Title: Re: Power supplies - black magikk
Post by: Pickled Onion on 21 October, 2020, 06:34:02 pm
Votes for Kim to write the next 'O' Level Physics text book.
Title: Re: Power supplies - black magikk
Post by: ian on 21 October, 2020, 06:36:47 pm
What are beavers then?
Title: Re: Power supplies - black magikk
Post by: Kim on 21 October, 2020, 06:51:34 pm
Quote from: ian on 21 October, 2020, 06:36:47 pm
What are beavers then?

A kind of giant Canadian waterproof guinea pig, but that's not important right now.

They're when Davie Dimmers[1] tips sulphuric acid into the moat around the EuroDisney Cinderella's Castle to kill the algae, and they end up with a mysterious ~2V DC bias on all the earth wiring that keeps tripping the circuit breakers.


[1] Super top head theatre techie.
Title: Re: Power supplies - black magikk
Post by: wajcgac on 21 October, 2020, 06:55:49 pm
Quote from: Mrs Pingu on 21 October, 2020, 04:41:22 pm
Just had another look at the current adaptor and it's centre negative. Think I might give up for a bit.
Oh and tried batteries and they didn't work so stuff that.( I am not going to wait for freshly charged batteries to dictate when to bake).

If you do get back to this at a later date this ebay site looks promising.

acadaptersrus (https://www.ebay.co.uk/str/acadaptorsrusltd/AC-Adaptors/_i.html?_storecat=1889116010)

there are literally hundreds to look through so I'd be inclined to email them the following details and let them check their stock for you.

Voltage - 6V DC
Output - 300mA minimum
Centre Pin - Negative.
Connector Gender - Male or Female (you'll need to look at your existing adapter to identify this as per the earlier link)
Output Connector Size - (you'll need to measure this on your existing adapter as per the earlier link again)
Title: Re: Power supplies - black magikk
Post by: ian on 21 October, 2020, 07:03:17 pm
As humans, we're actually electrically powered (true fact, all life on earth is literally electric).

I, alas, have no idea as to the polarity of our centre pins.
Title: Re: Power supplies - black magikk
Post by: yoav on 22 October, 2020, 08:53:24 am
Well .... now that you mention it, electrical activity in the human body depends on the flow of positive ions from outside to inside of electrically active cells, nerves and muscles.
Title: Re: Power supplies - black magikk
Post by: ian on 22 October, 2020, 09:28:18 am
Every cell in your body creates energy by generating a potential difference across a membrane (typically around -100 – -150 mV across mitochondrial membranes. This gradient drives proton flow through membrane complexes that generate ATP, life's primary energy store.
Title: Re: Power supplies - black magikk
Post by: Pingu on 22 October, 2020, 07:19:20 pm
Quote from: ian on 21 October, 2020, 07:03:17 pm
As humans, we're actually electrically powered (true fact, all life on earth is literally electric).

Could you pass that on to Gary Numan?
Title: Re: Power supplies - black magikk
Post by: Sergeant Pluck on 23 October, 2020, 06:53:28 pm
Quote from: Kim on 21 October, 2020, 06:51:34 pm
Quote from: ian on 21 October, 2020, 06:36:47 pm
What are beavers then?

A kind of giant Canadian waterproof guinea pig, but that's not important right now.

 ;D Never again will I be able to see or read about a beaver without thinking “giant Canadian waterproof guinea pig”.
Title: Re: Power supplies - black magikk
Post by: Mr Larrington on 23 October, 2020, 07:01:57 pm
Quote from: Sergeant Pluck on 23 October, 2020, 06:53:28 pm
Quote from: Kim on 21 October, 2020, 06:51:34 pm
Quote from: ian on 21 October, 2020, 06:36:47 pm
What are beavers then?

A kind of giant Canadian waterproof guinea pig, but that's not important right now.

 ;D Never again will I be able to see or read about a beaver without thinking “giant Canadian waterproof guinea pig”.

And Vonnegut's “Breakfast Of Champions” will never be the same again ;D

(click to show/hide)
Title: Re: Power supplies - black magikk
Post by: nicknack on 23 October, 2020, 07:25:06 pm
Quote from: Sergeant Pluck on 23 October, 2020, 06:53:28 pm
Quote from: Kim on 21 October, 2020, 06:51:34 pm
Quote from: ian on 21 October, 2020, 06:36:47 pm
What are beavers then?

A kind of giant Canadian waterproof guinea pig, but that's not important right now.

 ;D Never again will I be able to see or read about a beaver without thinking “giant Canadian waterproof guinea pig”.
My brain always moves straight to Frank Drebin.