Schematic for dimming a 50W transformer

[jap]

dimming a transformer

I would like to find schematics for dimming on the primary winding of an 50W transformer. It seems that halogen dimmer schematics would be suitable, but did not find any :-(

The transformer secondary is 1.5-3VAC, so it is hard to effectively dim on this side.

 

[batdin]

Re: dimming a transformer

Do you think that a normal bulb dimmer will not work for this purpose?
In the worst case an additional snubber will be needed.

 

[jap]

Re: dimming a transformer

Do you think that a normal bulb dimmer will not work for this purpose?
In the worst case an additional snubber will be needed.

It is not a good idea because of the varying inductive load. It can produce a DC component on the transformer and it can catch a fire.

Yet I have no idea how inductive the transformer is when it is loaded. But when empty, it is surely inductive.

 

[flatulent]

Re: dimming a transformer

One trick is to use a transformer with several voltage taps on the primary and switch between them. This will not produce a continuous range, but might have enough steps for your use.

If you cannot find one with the 3 V output you need, you can put a 1:1 transformer with primary and secondary taps in tandem on the primary side.

You can also use a "Variac" type autotransformer which has a continuous range. https://variac.com/staco_Variable_Transformer_Map.htm

 

[FANT]

Re: dimming a transformer

Already tryed with a dimmer and a transformer:
bad results, the regulation is not linear and is going at steps instead than be smooth.
Some impruvements obtained applying in parallel the transformer a lamp or a resistor with the same power of the transformer.
A snubber ( at least in my case ) didn't help.

Mandi

 

[echo47]

dimming a transformer

Yes, a variac is an excellent solution if your application can accommodate the size and weight. Feed the variac output into your step-down transformer. Nice clean waveform, unlike a triac lamp dimmer.

 

[jap]

Re: dimming a transformer

One trick is to use a transformer with several voltage
taps on the primary and switch between them. This will not produce a
continuous range, but might have enough steps for your use.

I thought of a sliding tap, but I'd like to use the existing transformer and
housing, only add a potmeter and a triac-based controller.

I could even program a microcontroller for this task if I'd know how to
control the triac.

 

[batdin]

Re: dimming a transformer

Now this is funny.I have seen a dimmer connected on the primary side of the transformer of an unregulated DC power supply so that the output voltage can be adjusted.It worked fine even with such a strange load.Suppose you didn't try the right circuit.

 

[bomba]

Re: dimming a transformer

I was doing a motor control speed last week and I found interesting info in to Applications Note, some of them are:
**broken link removed** in this one there are a ckts for solving your problem, I didn’t test it.
**broken link removed** in this one, you have a good theory and applications about triacs. I found it very useful.

Best regards

 

[Borber]

Re: dimming a transformer

What do you think about circuits like this? They were taken from an Italian page.

 

[SAR]

dimming a transformer

Go here:

**broken link removed**

**broken link removed**

 

[yeechyan]

dimming a transformer

You can try using an autotransformer.

 

[jap]

Re: dimming a transformer

I was doing a motor control speed last week and I found interesting info in to Applications Note, some of them are

Thanks for the useful info! I used the triggering method described in ST AN308, but as I found no schematic, I built my own controller.

It operates between 0-180 phase angles, and unlike a standard dimmer, sends a series of pulses after the set angle. The pulses are 100 usec long with a delay of 500 usec between them.