If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Experimentonomen wrote ...
And that specs are almost always highly overrated. Can sometimes be overspecced as much as twice actual power
Well, how do you know? The insulation materials commonly available today can withstand temperatures up to 220 °C, so the actual temperature of the transformer surface can exceed 100 °C by far without any side effects.
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Thanks for all of the advice given here! I hadn't noticed before but the photo makes it look smaller than it actually is.
Dr. Dark Current wrote ...
For 230 V mains the power is around 1200/R_pri (for small transformers - tens of VA, the constant is larger - around 2000, for very big transformer in the kVA range, it is smaller, like 1000.)
Using this method I get about 28VA since 2000/70.2=28.490. But since other people have commented that it looks more towards the 20VA mark, and my own findings regarding temperature rise I don't think I will let more than 24VA pass through it if I am using it for a project where it will be inside of an enclosure.
Shrad wrote ...
1527 could be a charted code meaning something like 15VAC 27VA, and keep in mind those transformers are usually a couple volts higher than specs
Hmm I hadn't noticed that, after I searched the web for the part number and found nothing I just assumed it was some internal part number. Perhaps that is its power rating, I will carry out another test with a 1.8amp load and see if the secondary voltage does indeed drop to 15vac (whilst keeping a close eye on the temperature of-course).
klugesmith wrote ...
Please share any experimental data you get, e.g. temperature rise vs. load.
Some things I have learned along the way:
1. Transformer temperature rise and VA rating depend on the RMS current. That can be significantly higher in circuits with a rectifier, filter, and DC load, compared to an AC resistive load with the same load current. It's because of the crest factor in current waveform that periodically boosts the capacitor voltage. The VA debating factor depends on the type of rectifier and filter. Some transformers come with a rectifier rating (not to be confused with rectifier transformers). Here's a reference to start with:
2. For a given transformer weight, VA ratings will of course depend on acceptable temperature rise and operating duty cycle. Yours looks like it's from a consumer electronics or appliance product, so it's probably intended to be energized continuously, and should never get hot enough to feel or smell like it's about to start a fire.
3. Some transformer applications (e.g. MOT's, certain UPS units) spend most of their "on" time at loads near maximum. They can get more VA per pound by using thicker wire and fewer turns, to reduce copper loss at the expense of higher core loss (which is practically independent of load current). I guess they could be distinguished by having lower primary winding resistance than other transformers of the same size and voltage.
It wasn't too hot to touch, but it was getting pretty warm considering it was set up outside in the garage. Just from feeling it I would say it was probably around the 45c mark, but I need to run a proper test when I manage to find my thermometer (I have a bad feeling it got thrown out ).
Sulaiman wrote ...
The 'rule of thumb' that I use for continuous current rating is, Idc = 0.62 x Iac.
e.g. 18Vac 18 VA transformer is rated for 1 A rms, with a bridge rectifier and capacitor, Idc = 620 mA.
For 4HV use you can run the transformer hotter !
I didn't know this until now, I think you might have just prevented a fire lol. Makes sense now thought when you consider what the mains waveform looks like.
teravolt wrote ...
it looks to me like about 10w
Really? I'm not trying to sound arrogant but I am sure it can handle a bit more than that (during testing it did).
On a related note I have found a much bigger transformer that has 42v and 6.3v windings wound with some 22-24SWG wire, a 30v 30SWG winding and a "hidden" 17v winding
Its about 40 years old and has wax paper insulation.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
Unknown transformer VA ratings
).