Completely random question

[Tim Watts]

Are 12V SELV lighting toroidal transformers DC (ie do they incorporate a bridge rectifier)?

Just wondered (for miles in the future) if they would be suitable for a 12V pond pump in principal.

[The Natural Philosopher]

Not the ones I have, no. Is SELV a brand?

easy enough to stick a bridge rect on em. But toroids are getting hard to find. Easier to use an old PC power supply.

[Tim Watts]

On Thursday 25 July 2013 19:14 The Natural Philosopher wrote in uk.d-i-y:

Separated Extra Low Voltage

It would be easy enough to stick a real toriodal into a box - but a type tested SELV PSU has the advantage of being "safe" vis-a-vis mains isolation.

I'd rather not - th esimplicity and isolation reliability of a simple trasnformer appeal (and it is driving an inductiver load[1]) - TLC have plenty of toroidals - though I don;t approve personally of the mains and SELV wires being in immediate vicinity of each other with no barrier - porr design fo rthe sake of a strip of plastic.

[1] Though 12V pond pumps of any flow rate are likely to be AC moters with DC driver circuits built in so no idea what that looks like as a load.

Perhaps it would be easier to make a custom unit...

[Bob Minchin]

Beware most lighting transformers are now switch mode power supplies and will not switch on until they see a significant resitive load. The waveform is none too clean and they might misbehave if rectified. A brushed or brushless motor may well not work due to the pulses of current they draw.

[The Natural Philosopher]

I would say not.

Cost for a simple brushed motor about $1.20. Minimum cost for a brushless unit and controller at least $8.

a 60 mm can motor is ubiquitous beast and they are spat out in million quantities by e.g. Mabuchi.

You will find them in most cordless tools.

able to kick out a couple of hundred watts maybe. Less if reliability and efficiency is desirable.

Its its a simple on/off scenario its the best way to do.

[Tim Watts]

On Thursday 25 July 2013 20:15 Bob Minchin wrote in uk.d-i-y:

Yes - I was looking at real toroidals:

[Tim Watts]

On Thursday 25 July 2013 20:18 The Natural Philosopher wrote in uk.d-i-y:

I'm look at bigger units than than - around 150l/min, 100W range. Those tend to have wet rotors like a CH pump and therefore are inherently AC.

[Brian Gaff]

And in any case putting a bridge on one of those will probably result in about 20 v DC in any case depending on load and the regulation of the transformer. Brian

[John Rumm]

Not usually...

even the SMPS ones are AC (at 10's of kHz)

[dennis]

No rectifier in the ones for lighting circuits AFAIK, there wouldn't be any need to.

AC motor, just needs a matching transformer unless it has speed control somewhere in which case you need to read the label to see what it needs.

[Tim Watts]

On Thursday 25 July 2013 22:04 John Rumm wrote in uk.d-i-y:

Thanks John.

[Alan Braggins]

'IEC defines a SELV system as "an electrical system in which the voltage cannot exceed ELV under normal conditions, and under single-fault conditions, including earth faults in other circuits".' (Where ELV is extra low voltage.)

[Dave Plowman (News)]

Where did you get that idea?

[Dave Plowman (News)]

No. Just a plain transformer.

When such things are made in vast quantities, it's usually cheaper to simply buy one than mess about making one. Unless you have a good reason to do so.

[Bob Minchin]

Those are electronic not toroids.

Bob

[The Natural Philosopher]

I used newey and eyre and they essentially dropped them. Good to see TLC still carry them.

[The Natural Philosopher]

go further down the page.

[Bob Minchin]

You mean I have to look further than the end of my nose? lol

Oops!

[Dave Plowman (News)]

Scroll down the page...

[Dave Plowman (News)]

I like TLC because they generally keep in stock everything in their cat they say is stock. But get things in for the next day otherwise. And have a decent car park. ;-) Only problem is getting stuck behind someone who doesn't really know what he needs or wants to buy and doesn't speak good English. The counter staff have the patience of Job. Most of the time.