230V to 12V AC halogen transformer  - Page 1
Forum section: electronics / beginners

author: made2hack
author_rank: Frequent Contributor
timestamp: July 03, 2014, 10:20:39 am
content: Hello,So, I found a 105W 230V to 12V AC transformer used in halogen lighting. The PF is around 0.9 so it's approx. a 94.5 VA unit.My question is:- The manufacturer stated it has a trapezoidal sine wave. Or that's what I understood, I don't know if he meant actual trapezoid, or perhaps triangle sine wave, etc.- Does anyone know if this is the case with AC / AC transformers destined for low voltage halogen lighting? If so, what is the actual sine wave? I don't have an oscilloscope.- How is this different from a regular Sine wave (50 Hz AC) ? Does the frequency change? Or just the peaks? What is my RMS voltage? Does it even apply to this type of wave?- What happens if I use it as opposed to a regular AC / AC transformer? What considerations should be taken?Thanks and apologies if the question is too vague.

author: mij59
author_rank: Frequent Contributor
timestamp: July 03, 2014, 10:57:54 am
content: Hi,This is an electronic halogen transformer, the apparent power of the unit is (105/0.9) VA.It uses a high frequency transformer ( 50 kHz or so ) to generate the 12 Vac output.In the 12 Vac output is the 50 Hz and the 50 KHz signal present , the RMS value is 12V, the waveform doesn't matter.A " conventional transformer" (50 Hz) will be heavier, bigger, and have a lower efficiency.

author: made2hack
author_rank: Frequent Contributor
timestamp: July 03, 2014, 11:19:23 am
content: So can I use 2 of these transformers in series and convert my Hakko fx888d from 110V to 230V?

author: robimarko
author_rank: Regular Contributor
timestamp: July 03, 2014, 11:26:02 am
content: Issue is that FX888D according to Hakko website needs 26VAC on secondary of transformer

author: made2hack
author_rank: Frequent Contributor
timestamp: July 03, 2014, 11:28:29 am
content: Well, from what I've seen people use here, they use 24VAC on secondary, plus the 110V transformer I took out is 23.2V - 24.9V 3.2A.Doesn't AC voltage go as high as 1.4*VRMS? So, 24V is as high as 33.6V?

author: mij59
author_rank: Frequent Contributor
timestamp: July 03, 2014, 11:39:23 am
content: Quote from: trs80 on July 03, 2014, 11:19:23 amHi,I think it is not a good idea, the 50 kHz output frequency of the transformers is not synchronized, and the electronics of the Hakko may not like the 50 KHz signal.Safes way is to use a step down transformer.

author: LukeW
author_rank: Frequent Contributor
timestamp: July 05, 2014, 10:14:19 am
content: You may think that these things can be used as cheap general purpose 12V power supplies for your electronics projects, but no, not really.As shown in the above video, they are basically built to be the most simple, cheap thing that will do the intended function of running an incandescent bulb - the output is poorly regulated messy, noisy AC all over the place without good rectification, filtering or regulation.

author: made2hack
author_rank: Frequent Contributor
timestamp: July 07, 2014, 06:54:07 pm
content: Yeah,I ended up using a normal 24V toroidal transformer for the 230V Hakko conversion. The reason I wanted to use the halogen transformer was due to the fact that it was a short hop to the hardware shop, whereas the toroidal I would have had to order. However, I managed to find one at my local electronics shop that had the VA rating I needed.If anyone is interested, a 24V / 63VA transformer works fine as a Hakko 230V Conversion.Just get a 250V .63A fuse and you are good to go!