I have this transformer which is 240VAC to 11.4VAC. But when I hook up my multimeter I am only reading about 1.2V. I have my multimeter configured to read AC and the scale is also correct. However my multimeter isn't true RMS. Could this be causing a problem? If not what else could be the problem?
Electronic – Transformer Output Problem
mainstransformer
Related Solutions
I've never had much luck in using isolation transformers to clean up power. I've always had to use an isolation transformer plus something else (filter network, ground breaker, etc.).
If you're looking for overkill, how about hooking up a power conditioner? There are cheap power conditioners that are a waste of money. But if you spend a decent amount on a good name brand, it should provide all the isolation you need from any of the nasty stuff going on elsewhere. If you've got the money, I defiantly suggest using a power conditioner on critical sound applications.
To take it one step further, I find that opening up the speakers and placing ferrites around the speaker wires that actually go to the voice coil helps reduce the noise induced by GSM cell phones. So that might be worth exploring as well. And it's a whole hell of a lot cheaper.
That is not a schematic.
Yes, you can use it, with a full-wave bridge rectifier. Instead of grounding the (nonexistent) center tap of the transformer you ground the minus side of the bridge rectifier.
Similarly one side of the filament should be grounded rather than the (nonexistent) filament winding centre tap.
simulate this circuit – Schematic created using CircuitLab
Be extremely careful and don't electrocute yourself.
Best Answer
Your link points to the description of a device marketed as a "transformer", but obviously containing much more. It seems like this device is designed specifically for the use with 12 V halogen lamps.
If it was a true transformer (and nothing more), it would work at mains frequency (50 or 60 Hz), and you would have this frequency at the input (primary) and at the output (secondary). In this case, a cheapo multimeter would likely give you an acceptable reading when you were measuring the output voltage.
Your "transformer" seems to be a switching device. I assume it works like this: The AC input voltage is rectified to DC and fed to an internal electronic switch (likely MOSFET). This electronic switch chops the input current to an AC current with a frequency of 40 kHz (cf. your link, see output frequency specification!). This AC current at 40 kHz is fed into a transformer, and the secondary side of this transformer seems to directly accessible at the output wires.
I assume your multimeter uses a low-pass filter when it measures AC voltages, and this filter blocks most of the voltage at 40 kHz, giving you a reading of only 1.2 V when you should actually see > 11 V.
To be really sure, you could measure the output voltage with an oscilloscope. I am fairly sure you would see a somewhat rectangular waveform at 40 kHz = 40000 Hz, and not a somewhat sinusoidal waveform at 50 or 60 Hz like you would with an ordinary transformer.
For a voltage with a frequency and waveform like this, I would even carefully check the manual of a good RMS multimeter because even one of those might have a low pass filter around 1 kHz.