Power supplies - black magikk

[Mrs Pingu]

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

[Kim]

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.

[Pickled Onion]

Wouldn't a set of rechargeable batteries be cheaper and more convenient?

[Kim]

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...

[Mrs Pingu]

Plus the cupboard where the scales live is at the north east corner of our flat, therefore cold, and winter is coming.

[wajcgac]

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

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

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

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.

[Kim]

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.

[PaulF]

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.

[MattH]

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" 

[grams]

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.

[Kim]

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.

[PaulF]

Thanks, I think I understand that

[quixoticgeek]

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

Where can we get these stickers?!?

J

[Kim]

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

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?}

[Mrs Pingu]

I've found a guide that will help you

AC adaptor selection guide

Thank you

[Kim]

That's quite a good article, I've bookmarked it for later.

[Mrs Pingu]

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).

[Cudzoziemiec]

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. 

[Kim]

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.

[Pickled Onion]

Votes for Kim to write the next 'O' Level Physics text book.

[ian]

What are beavers then?

[Kim]

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.}

[wajcgac]

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

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)

[ian]

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.

[yoav]

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.