What percentage of power supplies have a negative inner?

[Mike Halmarack]

My router power supply died. I got a new one. I also got an adjustable
voltage power supply with 34 interchangeable heads from eBay, to avoid
delivery waiting times in case of future power losses.

Reading up on the subject, I was cautioned to ensure the polarity of a
device's supply, indicating that these tend to vary.
On enquiry to the variable power supply provider I was told that "all
the interchangeable heads are positive" which I don't think is a very
helpful answer.

There appears to be no facility to ensure the polarity of each head
without test equipment. This, nor change the polarity of the heads by
any means.
Is this because a negative inner is too rare to provide for?

[GB]

Post by Mike Halmarack
My router power supply died. I got a new one. I also got an adjustable
voltage power supply with 34 interchangeable heads from eBay, to avoid
delivery waiting times in case of future power losses.
Reading up on the subject, I was cautioned to ensure the polarity of a
device's supply, indicating that these tend to vary.
On enquiry to the variable power supply provider I was told that "all
the interchangeable heads are positive" which I don't think is a very
helpful answer.
There appears to be no facility to ensure the polarity of each head
without test equipment. This, nor change the polarity of the heads by
any means.
Is this because a negative inner is too rare to provide for?

I have one with a switch to change the polarity. I therefore assume that
both polarities are needed.

[Andy Burns]

Post by Mike Halmarack
I was cautioned to ensure the polarity of a
device's supply, indicating that these tend to vary.
On enquiry to the variable power supply provider I was told that "all
the interchangeable heads are positive"

The generic wall-wart I have, is switchable 3/6/9/12v the heads have two
identical pins, so can be reversed for centre -ve or +ve

[Mike Halmarack]

Post by Andy Burns

Post by Mike Halmarack
I was cautioned to ensure the polarity of a
device's supply, indicating that these tend to vary.
On enquiry to the variable power supply provider I was told that "all
the interchangeable heads are positive"

The generic wall-wart I have, is switchable 3/6/9/12v the heads have two
identical pins, so can be reversed for centre -ve or +ve

I wish.

[GB]

Post by Mike Halmarack

Post by Andy Burns

Post by Mike Halmarack
I was cautioned to ensure the polarity of a
device's supply, indicating that these tend to vary.
On enquiry to the variable power supply provider I was told that "all
the interchangeable heads are positive"

The generic wall-wart I have, is switchable 3/6/9/12v the heads have two
identical pins, so can be reversed for centre -ve or +ve

I wish.

Send it back. Buy another.

[Theo]

Post by Mike Halmarack
My router power supply died. I got a new one. I also got an adjustable
voltage power supply with 34 interchangeable heads from eBay, to avoid
delivery waiting times in case of future power losses.
Reading up on the subject, I was cautioned to ensure the polarity of a
device's supply, indicating that these tend to vary.
On enquiry to the variable power supply provider I was told that "all
the interchangeable heads are positive" which I don't think is a very
helpful answer.
There appears to be no facility to ensure the polarity of each head
without test equipment. This, nor change the polarity of the heads by
any means.
Is this because a negative inner is too rare to provide for?

I think centre-positive is most common nowadays. But apparently Sony stuff
(radios etc) all used centre-negative, and I blew something up because I
used a cable lying around that had been wired centre-negative for testing a
Sony thing.

Theo

[fred]

Post by Mike Halmarack
My router power supply died. I got a new one. I also got an adjustable
voltage power supply with 34 interchangeable heads from eBay, to avoid
delivery waiting times in case of future power losses.

I'd expect the polarity to be identified by a symbol such as this beside
the power input.

https://ibb.co/28ZWSF5

[Mike Halmarack]

Post by fred

Post by Mike Halmarack
My router power supply died. I got a new one. I also got an adjustable
voltage power supply with 34 interchangeable heads from eBay, to avoid
delivery waiting times in case of future power losses.

I'd expect the polarity to be identified by a symbol such as this beside
the power input.
https://ibb.co/28ZWSF5

That's the perfect illustration Fred. My confusion is more to do with
the polarity of the output from the "Universal" power supply and the
ability to change this if necessary.

[fred]

Post by Mike Halmarack

Post by fred

Post by Mike Halmarack
My router power supply died. I got a new one. I also got an

adjustable

Post by Mike Halmarack

Post by fred

Post by Mike Halmarack
voltage power supply with 34 interchangeable heads from eBay, to avoid
delivery waiting times in case of future power losses.

I'd expect the polarity to be identified by a symbol such as this beside
the power input.
https://ibb.co/28ZWSF5

That's the perfect illustration Fred. My confusion is more to do with
the polarity of the output from the "Universal" power supply and the
ability to change this if necessary.

I should have added that I have yet to come across a supply of this sort
that does not have centre positive and I would certainly expect a
'universal' replacement to be centre pos if of fixed polarity. As others
have mentioned some do come with a non polarised bi-pin connector so that
the polarity can be reversed if required (and glued in place to avoid
possible future error if easily disconected). Otherwise it will be a 'cut
& shut' operation, neatest when soldered on a staggered cut and insulated
with heatshrink sleeving.

As you're on uk.d-i-y too I expect you will already have a multimeter :-)
, if not you can get a cheapie for about a tenner to check polarities
before risking connection.

[Mike Halmarack]

.

[Mike Halmarack]

.

[Mike Halmarack]

Post by fred
I should have added that I have yet to come across a supply of this sort
that does not have centre positive and I would certainly expect a
'universal' replacement to be centre pos if of fixed polarity. As others
have mentioned some do come with a non polarised bi-pin connector so that
the polarity can be reversed if required (and glued in place to avoid
possible future error if easily disconected). Otherwise it will be a 'cut
& shut' operation, neatest when soldered on a staggered cut and insulated
with heatshrink sleeving.

That seems like an effective approach, though isn't that a permanent
change of polarity? Thanks to your advice Im now looking for a similar
method but one where the wires can be switched back and forth quite
easily, like with a small plug and socket on each wire before it
reaches the connector plug.

Post by fred
As you're on uk.d-i-y too I expect you will already have a multimeter :-)
, if not you can get a cheapie for about a tenner to check polarities
before risking connection.

uk.diy convinced me to get one of these a while ago.

[jkn]

Post by Mike Halmarack

Post by fred

Post by Mike Halmarack
My router power supply died. I got a new one. I also got an adjustable
voltage power supply with 34 interchangeable heads from eBay, to avoid
delivery waiting times in case of future power losses.

I'd expect the polarity to be identified by a symbol such as this beside
the power input.
https://ibb.co/28ZWSF5

That's the perfect illustration Fred. My confusion is more to do with
the polarity of the output from the "Universal" power supply and the
ability to change this if necessary.

most of the (cheap) 'reversible' wall-wart type adapters I have seen,
with some sort of two-pin connector near the interchangeable heads,
have *tiny* '+' and '-' symbols moulded into the heads and the power
lead connector. Once you have spotted this, with a bit of thinking you
can work out which way is which.

I have had to make a couple of centre negative adapters recently. I
don't trust those cheap interchangeable types and so take a
centre-positive one, splice the cable and make it fit for purpose. I
then take care to label it for clarity.

I'd estimate that fewer than 5% are centre negative. I ones I made up
were for audio purposes - a small Roland Guitar amp and a Casio
sequencer. My Brother Label Maker is also centre -ve, "7 volts" IIRC.

J^n

[Mike Halmarack]

Post by jkn
most of the (cheap) 'reversible' wall-wart type adapters I have seen,
with some sort of two-pin connector near the interchangeable heads,
have *tiny* '+' and '-' symbols moulded into the heads and the power
lead connector. Once you have spotted this, with a bit of thinking you
can work out which way is which.

This isn't a feature of the multi- headed power supply I bought from
eBay.

Post by jkn
I have had to make a couple of centre negative adapters recently. I
don't trust those cheap interchangeable types and so take a
centre-positive one, splice the cable and make it fit for purpose. I
then take care to label it for clarity.

I do like the idea of an easily switchable supply, which as it came
with 34 various heads, I expected it to include this option. The
seller has a different definition of "universal" than I expected.

Post by jkn
I'd estimate that fewer than 5% are centre negative. I ones I made up
were for audio purposes - a small Roland Guitar amp and a Casio
sequencer. My Brother Label Maker is also centre -ve, "7 volts" IIRC.
J^n

[Abandoned Trolley]

Post by Mike Halmarack
My router power supply died. I got a new one. I also got an adjustable
voltage power supply with 34 interchangeable heads from eBay, to avoid
delivery waiting times in case of future power losses.
Reading up on the subject, I was cautioned to ensure the polarity of a
device's supply, indicating that these tend to vary.
On enquiry to the variable power supply provider I was told that "all
the interchangeable heads are positive" which I don't think is a very
helpful answer.
There appears to be no facility to ensure the polarity of each head
without test equipment. This, nor change the polarity of the heads by
any means.
Is this because a negative inner is too rare to provide for?

rare, but they do exist.


I have a chunky (1.2 amp) wall wart which came with a DLink router some
time ago - the output is AC only !

Its got a "normal" connector which is alarmingly compatible with the
later DLink models, and about a million other things.

Who needs smoke detectors ?

[Mike Halmarack]

On Wed, 11 Dec 2024 11:05:47 +0000, Abandoned Trolley

Post by Abandoned Trolley

Post by Mike Halmarack
My router power supply died. I got a new one. I also got an adjustable
voltage power supply with 34 interchangeable heads from eBay, to avoid
delivery waiting times in case of future power losses.
Reading up on the subject, I was cautioned to ensure the polarity of a
device's supply, indicating that these tend to vary.
On enquiry to the variable power supply provider I was told that "all
the interchangeable heads are positive" which I don't think is a very
helpful answer.
There appears to be no facility to ensure the polarity of each head
without test equipment. This, nor change the polarity of the heads by
any means.
Is this because a negative inner is too rare to provide for?

rare, but they do exist.
I have a chunky (1.2 amp) wall wart which came with a DLink router some
time ago - the output is AC only !
Its got a "normal" connector which is alarmingly compatible with the
later DLink models, and about a million other things.
Who needs smoke detectors ?

A cautionary tale. Can I insert something switchable or plugable in
the output cable rather than just cutting, reversing and soldering?