Charger squeals like a pig (not the fan)

[mrelwood]

I bought a 5A 84V charger. Didn’t go for the big bucks, so I got a bit of a bad one. The voltage and current seem steady monitored with the Charge Doctor V2, so I see potential!

I removed the fan, no change. Charger connected just to the mains gives no noise, it’s only when I connect it to the wheel as well. The noise is like a pig’s squeal combined with an old analog modem, and it’s louder than a busted fan could ever be.

I’m baffled. The only thing I can think of is the transformer coils, but this loud?!

[dmethvin]

Seems like it has to be the transformer then. You could try putting some coil dope on the windings to stop the vibration. Sometimes just pressing on the windings changes their position enough to prevent the vibration. When we used CRTs and they started to squeal the typical solution was to whack it, and that usually shut them up. 

[Witos]

Noise from a transformer sometimes means that the laminations  have come unglued and are vibrating against one to another. This happens sometimes and it is not a problem 

[mrelwood]

I’m surprised to hear that a sound so horrible might be that harmless. I wish I had a way to engage the charging mode without connecting the charger to a $2000 wheel...

When working with guitar effect pedals I found out that an oscillating opamp was able to emit an audible noise. That is one source of my fears here, that a part of the charger circuit is oscillating way above it’s designed parameters.

[mrelwood]

How about that! Pressing down on one corner of the tranny completely removed the noise! I unplugged everything and removed a bit of the tape, but the laminations are not visible. I gently moved and pressed on a few windings near that corner, and simple as that the noise is now completely gone!

15 hours just became a mere 5 hours!

I will still watch the Charge Doctor amps like a hawk and listen like a dog for a few charge cycles, yee am still of little wary in faith on this cheapo...