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Trans hum

turbogt16v

Mar 27, 2015
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Hy
I have problem with foam cuter
Its a 220v to 24 2a transformer to led dimmer to nicrom wire setup.
When dimmer is on low knob setting transformer makes hum noise,when on full power it has no hum.
Is that dangeres for transformator
Ty
 

Minder

Apr 24, 2015
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Most foam cutters use a Triac on the primary, this causes hum at low setting due to the short pulse length.
Those I have put together, I have used the triac on the secondary side.
Eliminates the problem!
M.
 

turbogt16v

Mar 27, 2015
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I am low knowledge on eletric.
I yus use laptop trans and chineese led dimmer,its all opened i can wire it differently,i dont know if the trans have triac here is pic
 

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Minder

Apr 24, 2015
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Looks like a wrong mixture, without a diag. it is hard to diagnose, but a triac would not work that well with a SMPS.
(switch mode power supply).
M.
 

turbogt16v

Mar 27, 2015
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Ok,thank you for your time
And just another question
Is it dangerous that trans has that hum or not
 
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Minder

Apr 24, 2015
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Pick up a standard 220v to 24v transformer, that should work better.
M.,
 

kellys_eye

Jun 25, 2010
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Yes - the danger is from destroying the power supply. As mentioned they don't work very well, or for very long, when using a dimmer on the input side. You will stress the circuitry beyond its limits as it constantly tries to compensate for you lowering the input voltage.

By their very design they are always trying to maintain the output at their designed voltage and simply lowering the input voltage only makes them work harder at doing so - eventually causing them to stop working.
 

Alec_t

Jul 7, 2015
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Can you confirm whether the LED dimmer is connected to the power supply input or output ?
 

turbogt16v

Mar 27, 2015
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output

so can i modify existing power supply to be able to work properly with dimmer
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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If the dimmer is connected to the output then it is likely the power supply is making sound at a frequency you can't hear. The dimmer is causing the load to be connected and disconnected many times per second and this modulates the high frequency sound being generated by the power supply. You can hear the effect of the modulation.

It's almost certainly not a problem as long as the maximum current drawn by your foam cutter is comfortably within the specs of the power supply.

If you're using nichrome wire, then the resistance is lower at low temperatures. On a lower setting it will draw more current, so the effect of the modulation is strongest at low settings.
 

Minder

Apr 24, 2015
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output

so can i modify existing power supply to be able to work properly with dimmer
If this is an off the shelf triac style dimmer then they require AC to work, if the ouput of your SMPS is DC then NO.
M.
 

Alec_t

Jul 7, 2015
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Another possible cause of hum is the common-mode choke at the input of the power supply. This gets pulsed at twice the mains frequency. One rated for higher current might reduce the hum, but its larger physical size would prevent it from being fitted in the supply.
 
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