Would like help figuring out location of audible noise on a pcb...

[TECH_GEEK10]

I recently bought a electric bike charger on ebay that was for made for charging 48v Lithium packs at ~3A. I however need it to charge my 36v Lithium pack, so I am in the process of altering the various voltage dividers that would essentially lower the voltage to the appropriate levels. So far everything is working fine, I'm getting a stable output voltage and the battery charging controller is doing what it should. The only problem is that it is making an annoying audible whine is made, and has always been there even before I first opened it up. I would like to remove said whine, but it is originating near a part of the circuit with several possible culprits are positioned too close to each other to determine which is making it.

So what I would like help with is this. How would you find which of 4-8 components is making the whine, in about a square inch/25mm area?

[Christopher]

More than likely the coil. If you press on it with your finger (as long as its low volts!) does it alter the tone?

Doubt its the electrolytics but it's a possibility....

[TECH_GEEK10]

Coil is unaltered with finger pressing. It tends to change frequency when the relay's coil is powered up. By the way its present as long as the unit is plugged into the wall will tapper off for a seconed or two when unplugged from the wall.

[TECH_GEEK10]

The center of the picture is my best guess to position of the source.

[TECH_GEEK10]

Sounds like a ~810Hz saw tooth tone.    http://onlinetonegenerator.com/

[G7PSK]

You could try the low tec approach. Get a piece of wooden dowel put one end on each item in turn and the other end in you ear, if you fix a circle of card or thin wood on the end for your ear it helps. Some people use a screw driver but the tip can cause shorts so wood or plastic rod/dowel is best. i find good hard wood dowel conducts sound better than plastic. But my guess is the black plastic square is an inductance and is generating the sound. On second thoughts it's a relay so could be the coil or contacts chattering.

[T3sl4co1l]

Sounds like the compensation is shit.  Trace the circuit and identify the switching controller; get a scope and analyze the control loop performance.

Tim

[German_EE]

My money would be on either the coil or the relay. It's possible that one of the capacitors could be the problem but only if it's dried out and just about to die anyway.

[TECH_GEEK10]

Figured it out. I had it setup to be controlling current for 48v but had it setup for 36v. The tip127 which controls current in pic is switching to fast for what it is designed to do.

[TECH_GEEK10]

Sounds like the compensation is shit.  Trace the circuit and identify the switching controller; get a scope and analyze the control loop performance.

Tim

More like I made it compensate like shit because I am new to electronics and have completely learned everything I know by experimenting! (About 3 months ago I was using relays which activated motors which manually pressed buttons to get my projects to work! I did this for everything because that is all I knew how it worked inside!)