Electronics > Beginners
Where to find 230V - 24V transformer
Cliff Matthews:
If OP can find a couple of MOT's, knock out secondary and series-wire primaries for a little extra PSU grunt (cool running too). Just grab some wire and wind-in whatever secondary you need.. :-+
soldar:
--- Quote from: Zero999 on March 26, 2019, 10:00:49 am --- Be careful, some are electronic halogen lamp transformers, work at a much higher frequency, than the mains. They consist of a Royer oscillator driving a small ferrite core transformer and are completely unsuitable for most electronic projects.
--- End quote ---
Be careful? Who? Because I assume someone who is looking for a mains transformer knows what a mains transformer looks like and can tell the difference between a mains transformer and, say, a can of tuna.
But, OK, I will add a disclaimer to my previous post: Do not go looking for mains transformers if you cannot tell the difference between a mains transformer and a can of tuna. ;)
Zero999:
--- Quote from: soldar on March 26, 2019, 11:39:46 am ---
--- Quote from: Zero999 on March 26, 2019, 10:00:49 am --- Be careful, some are electronic halogen lamp transformers, work at a much higher frequency, than the mains. They consist of a Royer oscillator driving a small ferrite core transformer and are completely unsuitable for most electronic projects.
--- End quote ---
Be careful? Who? Because I assume someone who is looking for a mains transformer knows what a mains transformer looks like and can tell the difference between a mains transformer and, say, a can of tuna.
But, OK, I will add a disclaimer to my previous post: Do not go looking for mains transformers if you cannot tell the difference between a mains transformer and a can of tuna. ;)
--- End quote ---
Not you of course, but the original poster. Someone who can't find a 24V transformer, might not know what one looks like. Don't forget this is the beginners section!
mariush:
There's
Farnell : https://uk.farnell.com/c/transformers - filter further by Isolation Transformers and Toroidal Power Transformers
Note that there's an "official distributor" for Croatia : Altpro D.O.O - see https://export.farnell.com/export-portal or just try https://export.farnell.com/
RS Components - they have a Croatia sub-site: https://hr.rsdelivers.com/
See https://uk.rs-online.com/web/c/power-supplies-transformers/transformers/ - filter further by PCB transformers , chassis, toroidal ...
TME.eu - good Polish company, should ship to Croatia : https://www.tme.eu/en/katalog/transformers-and-ferrite-cores_100440/
Also, should be more clear about exactly what you need.
Do you need 24v AC or 24v DC (after rectification using a bridge rectifier, linear regulator etc) ?
Transformers have a VA rating ...
IF you need 24v AC , like for example to light a 75w incandescent lightbulb, then you could go for a 75VA transformer.
if you want to convert output to DC by using a bridge rectifier, then you can approximate the DC voltage and DC current with the formulas:
Vdc peak = sqrt(2) x Vac - 2 x Vdiode = ~ 1.414 x Vac - 1.5v
Current DC = ~ 0.62 x Current AC
Capacitance required = Current / 2 x AC frequency x [V dc peak - Vdc min]
So for example, if you have a 24v AC transformer with a 100VA rating ( 100VA / 24v = 4.16A) then you'll get a DC voltage with a peak close to 1.414 x 24 - 1.5 = 32v peak and current would be ~ 0.62x4.16 = ~ 2.6A
You'd need C = 2.6 / 2 x 60Hz x (32v - 24v) = 2.6/960 = 0.002708 Farads or ~ 2700uF 50v minimum to keep the DC voltage above 24v at all times.
So if you want a voltage up to 32V DC (depending on how big your smoothing capacitor would be) and up to 3A, you'll need more than 100VA...
exe:
If you go with a transformer, be sure to de-rate it properly (for capacitive load it's about 50% derating is comonly accepted), and take into account mains voltage variation.
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