Whats the VA rating of this toroidal transformer ? - Page 1
Forum section: electronics / beginners

author: BravoV
author_rank: Super Contributor
timestamp: September 08, 2015, 08:24:17 am
content: Bought from a brick n mortar shop when I was traveling, as its dirt cheap.As you can see at the label, there is no VA rating.Or from the printed line there -> (RH 125 C2A) , I can only guess that the output maxed at 2 Amps ?Physical size :OD : 4 inch / 9.5 cmID : 1.5 inch /4 cmHeight : 2 inch / 5 cmLooking at the size, whats the reasonable VA rating ?

author: bktemp
author_rank: Super Contributor
timestamp: September 08, 2015, 08:28:07 am
content: Compared the dimensions with other toroidal transformers it looks like 60-80VA.

author: mij59
author_rank: Frequent Contributor
timestamp: September 08, 2015, 08:36:46 am
content: Could be more like 120VAhttps://www.ringkerntrafo.nl/shop/ringkerntrafo-s/120va/172/2x-12v-ringkerntransformator-120va.html

author: Gyro
author_rank: Super Contributor
timestamp: September 08, 2015, 08:39:23 am
content: Based on the ones I have lying around I think it's in the 120 - 160VA range, different manufacturers have slightly different form factors (diameter/height). As bktemp says, try a number of manufacturer sites, eg. Antrim Transformers. NDE seem to have a site too.Edit: It definitely won't be more than 160VA

author: bktemp
author_rank: Super Contributor
timestamp: September 08, 2015, 08:43:31 am
content: Could you try to measure the primary and secondary resistance? This should give a more accurate estimation, because the power rating is only based on the temperature rise. From the dimensions it is possible to estimate the thermal resistance and from the wire resistance the power dissipation.The primary resistance should be no problem, but the secondary resistance is probably in the <1ohm.

author: BravoV
author_rank: Super Contributor
timestamp: September 08, 2015, 10:48:45 am
content: Quote from: bktemp on September 08, 2015, 08:43:31 amUsing 4 wires measurements with LCR meter (DCR) :Primary : 13.8 OhmSecondary : 0.32 Ohm (from end to end 12v to 12v skipping the CT)Since I was using LCR, hence the inductance ...Primary : 6.3 H @100 HzSecondary : 132.4 mH @100 Hz100 Hz test signal is the lowest freq selection available at my LCR meter.Capacitance between primary and secondary : 450 pF

author: BravoV
author_rank: Super Contributor
timestamp: September 08, 2015, 10:52:31 am
content: Quote from: mij59 on September 08, 2015, 08:36:46 amThanks, looks very similar, assuming its 120 VA, so max output will be 5 Amp @ 12V (x2) or 24V ?

author: bktemp
author_rank: Super Contributor
timestamp: September 08, 2015, 10:59:56 am
content: Based on the dimensions and the resistance values my software tells me 95VA -> 2x 12V 4A.

author: BravoV
author_rank: Super Contributor
timestamp: September 09, 2015, 03:21:42 am
content: Quote from: bktemp on September 08, 2015, 10:59:56 amThank you !And I'm content with this impulse purchase as I'm planning to use it for DC PS 24V at 3 Amps, this should be more than enough right ?Btw, it cost me only about $5 as its a surplus and NOS.Curious what software is that ?

author: mij59
author_rank: Frequent Contributor
timestamp: September 09, 2015, 03:43:42 am
content: Quote from: BravoV on September 09, 2015, 03:21:42 amFor 72W output power a 150VA transformer would be better.

author: Shock
author_rank: Super Contributor
timestamp: September 09, 2015, 06:32:39 am
content: I suspect from the model number it's 60VA across the entire secondary, 2A would be the conservative current across the entire secondary as well. Something like the 12V model from the MCTA060 Series shown herehttp://www.farnell.com/datasheets/1829278.pdfIf you can find another datasheet to show a 60VA with same dimensions and close to 0.32 Ohm across both secondaries, you are onto a winner. Either way you still need to load test it.

author: bktemp
author_rank: Super Contributor
timestamp: September 09, 2015, 06:54:54 am
content: The MCTA060 has 0.36 ohm per secondary output but BravoV did measure 0.32 across both secondaries-> 0.16 ohm per secondary.This matches the MCTA100 almost perfectly. Also the mechanical dimension fits much better than the 60VA version.I did calculate 0.6 ohm total resistance when combining primary and secondary resistance. At 4A it dissipates 9.6W and matches the MCTA100 with a specified dissipation of 10.3W perfectly.

author: Smokey
author_rank: Super Contributor
timestamp: September 09, 2015, 07:25:47 am
content: Compare against avel lindberg y23 series. They have all sizes from tiny to 1kva.

author: FreddyVictor
author_rank: Regular Contributor
timestamp: September 09, 2015, 09:02:07 am
content: Quote from: BravoV on September 08, 2015, 08:24:17 amsays: LP-60just a guess, but maybe 60VA ?

author: Circlotron
author_rank: Super Contributor
timestamp: September 09, 2015, 12:54:47 pm
content: Maybe weigh it and compare to known toroids.

author: SeanB
author_rank: Super Contributor
timestamp: September 09, 2015, 08:14:20 pm
content: At that diameter 60VA is about right, I used them for downlighters ( only thing that fitted through the holes in the dropped ceiling) at one per 50W lamp. They were also used in some Titzio desk lamps which used a 55W automotive lamp.

author: BravoV
author_rank: Super Contributor
timestamp: September 10, 2015, 03:17:53 am
content: Thanks for the replies guys.Now, I measured and it's weight= 1.7 Kg (without the mounting plates and the nut & screw), looking at the Multicomp transformer's datasheet pointed by Shock, and pointed out by bktemp, its more like MCTA100 which is a 100 VA unit, that weight about 1.13 Kg.While on Avel Lindberg Y23 series (Datasheet), the closest model by dimensions "and weight" is a 120 VA type.All 60 VA models are about 0.7 Kg, does weight matter ?I'm aware that ideally a load testing should clarify this, its just I don' have high enough dummy load, mine is DIY type which maxed out only at 1.5 Amp.

author: johansen
author_rank: Super Contributor
timestamp: September 13, 2015, 04:53:15 pm
content: 120va will dissipate 3.5 watts in the primary if you indeed have that many ohms.5 amps from the 24v coil will dissipate 8 watts.so with a resistive load 120va will cause 11 watts lost in this transformer.if that results in a rather conservative temperature rise, you could pull 180va from the coil, with 22 watts of lossesyou could probably safely pull 240va from that transformer with forced air cooling provided the secondary can safely dump 32 watts.also due to the great discrepancy between the primary and secondary, you probably did not make an accurate 4 wire measurement....

author: BravoV
author_rank: Super Contributor
timestamp: September 14, 2015, 12:38:36 pm
content: Quote from: johansen on September 13, 2015, 04:53:15 pmWhat great discrepancy ? Mind elaborate further ? I can re-measure it though once I'm at home.

author: technix
author_rank: Super Contributor
timestamp: September 14, 2015, 12:43:50 pm
content: Man I wish I can have a toroid transformer this large - for both my PSU project and an experimental inverter - how much did it cost you?Should this kind of powerful toroid be used in an inverter the switching MOSFETs have to be very, very big...

author: bktemp
author_rank: Super Contributor
timestamp: September 14, 2015, 12:57:35 pm
content: Quote from: BravoV on September 14, 2015, 12:38:36 pmTypically the power dissipation on the primary and secondary side are equal. Otherwise the wire on one side is unnecessarily thick: It needs more space and costs more money but does not help much because most of the power is dissipated on the other winding. Nobody would design such a transformer.Quote from: technix on September 14, 2015, 12:43:50 pm120VA is rather small for a toroidal transformer. You can easily get >1kVA toroidal transformers. They aren't so expensive.

author: Smokey
author_rank: Super Contributor
timestamp: September 14, 2015, 10:21:26 pm
content: check out those Avel Lindberg transformers. They are about $100 USD in 1s.or go tear open a classAB stereo amplifier.