what causes hum in HMI magnetic ballasts

Patryk_Rebisz

Patryk_Rebisz

Veteran
I recently got 1.2 LTM HMI for close to nothing but the ballast causes hum/noise. My step father is an electrician so he might point out the issue but he's on vacation so in mean time i'm trying to do some research. Anyone can enlighten me? How easy is the fix?
 
Its just resonances setup in the windings of the transformer. Resonating at the line voltage frequency (60hz for USA) and that is in audible range unfortunately. Not much can be done about it. The hum tends to get louder as they age as well.
 
Patryk_Rebisz said:
So would changing the coils help?
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Put it outside the room would help. Do you have double head cables?

If it is an electric ballast turn off FF and it might reduce the noise. You only need FF when shooting off speed.

Careful you don't wrap that thing in ferni pads, it will get real hot.
 
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You can tame those things by potting the transformer in resin but it has to be done by a good tech that knows their stuff. My HMI guy is Gilbert at Galaxy Lighting 661-946-3373. He did one for me and it took care of the problem. He's near L.A. but call him he might know of someone in your area. Those old LTMs are workhorses, you're lucky to find that one. Is it a PAR or fresnel head? If it's a PAR you go to Kennedy-Webster near Chicago for new globes.
 
Changing the transformer to a newer one, particularly if its a good quality one could help. The resin idea isn't bad either.
 
Yeah i'll talk to Gilbers just wanted to hear some advice here firs. Yes this is SE PAR. Head and headers in great shape but the ballast in good visual shape but loud.
 
So i looked further into this issue and it looks like sometimes the capacitors that don't hold the current well enough anymore are the reason for the hum. Sometime this week i'll test it out with tools and let you know more.
 
Farnell/element14 or RS Components sell some high quality capacitors. Look for Nichicon, Rubycon, Sanyo (OS-CON) or Panasonic capacitors.

I use Rubycon ZL, ZLG YXH series or Nichicon HE series or Panasonic FC series mainly.
 
Patryk_Rebisz said:
So i looked further into this issue and it looks like sometimes the capacitors that don't hold the current well enough anymore are the reason for the hum. Sometime this week i'll test it out with tools and let you know more.
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There are many sources of 'hum' in circuits. In the case of transformers, for older 'iron', or alloy metals, the fact that a magnetic flux is involved, changes the physical dimensions of the material, inducing pressure on air... aka sound... this is similar in nature to the piezoelectric effect in crystals.

Even with no transformers in sight, 'audio' frequency electronic signals can produce human sensible audio, or even very high frequency signals, if modulated with a 'audio frequency' pulse train. (for example the GSM chirpping of cell phones...). The age of the components can figure into the mix as well.
 
Patryk_Rebisz said:
So i looked further into this issue and it looks like sometimes the capacitors that don't hold the current well enough anymore are the reason for the hum. Sometime this week i'll test it out with tools and let you know more.
Click to expand...
Capacitors causing hum. That's a new one on me. Did the guy explain the mechanism?
 
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