failing low-voltage dimmer

[jbishop]

hi all,
i have some 600VA low-voltage dimmers being used with a 120VAC/24VAC magnetic transformer. this transformer is rated for 450 Watts. the loads are 24V cove lights which have drawn as much as 350 Watts from the transformer.

back on the primary side, it is the dimmers that have been failing. the measured amps from the dimmers is only around 3 Watts.

1) could the 350 Watts on the secondary side of the transformer equate into more than 600VA for the dimmer on the primary?

2) could in-rush current be a problem with a setup like this?

thanks for any help you can provide!

brother jb

 

[itsmoked]

Transformers present an inductive load to dimmers. They are often not designed to deal with the current offset this causes. The result is blown dimmers.

Dimmers made for motors face the same problem.

Have you tried a "Motor Rated" dimmer in your setup yet?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jbishop]

I haven't tried a motor-rated dimmer. the 600VA low-voltage dimmers are designed for magnetic, so i had hoped it would work.

can in-rush current be a problem with magnetic transformers?

brother jb

 

[ScottyUK]

What do you mean by 'low voltage' dimmers? What is the rated voltage of the dimmer? I assume 120V AC but best to check. Otherwise Keith is on the right lines: cheap dimmers tend to use a single trigger pulse to fire the triac or thyristors and with an inductive load the timing of the gate firing pulse can be such that the triac / thyristor does not latch on. Look for a burst-fired or hard fired type which either applies a series of firing pulses or a continuous gate current. Dimmers suitable for inductive duty usually advertise the fact somewhere because it is unusual and therefore a selling point.



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