KAM Powerbar Schematic

[alistermorton]

Could the noise be magnetostriction from the transformer winding? I had a similar noise from a unit I built many years ago, where the coils had been hand wound and weren't perhaps as well made as they could have been.

[Mike Bullock]

7 hours ago, alistermorton said:

Do you think that silver label is also giving a second output rating - below 28V 3.5A there is a partial rating - V 0.5A

There looks to be a second pair of output wires just to the left of the ribbed heatsink, above the main terminal block.

Thanks all!

Yes that IS a second output pair - I think that powers the led light units...? while the main output pair powers the control circuitry (I'm no expert but I connected a simple 12v DC power supply to these and the lights came on statically) - see more detailed pic of these outputs below.

ALSO, the high pitched squealing appears to be coming from the transformer (?) in the centre of the first pic (the one with the translucent yellow tape on it). I put a decibel meter across the supply and it was by far the loudest part of the board..... 

 

[Mike Bullock]

4 hours ago, alistermorton said:

Could the noise be magnetostriction from the transformer winding? I had a similar noise from a unit I built many years ago, where the coils had been hand wound and weren't perhaps as well made as they could have been.

That makes sense - I gently pushed a piece of wood onto this transformer and the squealing changed pitch and volume..... maybe I should look to change this?

[alistermorton]

Probably the two large screw connectors are the actual supply to the LEDs and thinner push on connector is the supply to the control circuitry. Can you get a photo of the silver label unobscured by the mains input?

[indyld]

If the noise is the transformer (in a design that usually works fine), one might surmise that there is some issue with resonant frequencies that is out of kilter with the original design. This could be either on the input or the output side, either a choppy high voltage side after the rectifier/bulk cap or maybe an issue with the PWM controller, feedback, or smoothing on the low voltage side.

Edit: Meant to say, if the noise is high frequency that would point to the secondary side (or at least, the bit of the design that is doing high frequency PWM, rather than mains frequency choppiness).

The @full condition increasing the fault is of interest.

I'd guess that the block wood experiment is rather like holding down a rattling teacup on a moving train.

Edited January 12, 2023 by indyld

[Mike Bullock]

5 minutes ago, indyld said:

If the noise is the transformer (in a design that usually works fine), one might surmise that there is some issue with resonant frequencies that is out of kilter with the original design. This could be either on the input or the output side, either an choppy high voltage side after the rectifier/bulk cap or maybe an issue with the PWM controller, feedback, or smoothing on the low voltage side.

I'd guess that the block wood experiment is rather like holding down a rattling teacup on a moving train.

** laughs out loud **, yes - but I only did that to confirm my suspicion as to where the noise was coming from..... 😂

[Mike Bullock]

20 minutes ago, alistermorton said:

Probably the two large screw connectors are the actual supply to the LEDs and thinner push on connector is the supply to the control circuitry. Can you get a photo of the silver label unobscured by the mains input?

See below pic...

 

[KevinE]

from memory, these Kam bars do whistle loudly when all the lamps are faded up to max. If you do a chase, the power supply sounds a bit musical. Unless you think it's excessive, and the 28V stays fairly steady throughout, I'd say it was ok. 

If you'd rather change the board I'm sure a 24V psu with adjustable output would go up to nearly 28V as they are sometimes used to trickle charge lead-acid batteries at 27.6V. You could piggy back a 1A 3-leg switching regulator off the main output for the 12V if they share a common 0V.

 

 

 

[Mike Bullock]

1 minute ago, KevinE said:

from memory, these Kam bars do whistle loudly when all the lamps are faded up to max. If you do a chase, the power supply sounds a bit musical. Unless you think it's excessive, and the 28V stays fairly steady throughout, I'd say it was ok. 

If you'd rather change the board I'm sure a 24V psu with adjustable output would go up to nearly 28V as they are sometimes used to trickle charge lead-acid batteries at 27.6V. You could piggy back a 1A 3-leg switching regulator off the main output for the 12V if they share a common 0V.

 

 

 

It's REALLY loud - i.e. I just about get away with using it in my rock band, but wouldn't even try to use it with my acoustic setup.....

[KevinE]

Crikey, does sound loud. 

Have a look at this one, see if it will go in. It is nominally 27V and will crank up past 28V on the main output. It also has a 12V 0.5A 'fan supply'. 

rs meanwell smpsu

[KevinE]

2 minutes ago, KevinE said:

Crikey, does sound loud. 

Have a look at this one, see if it will go in. It is nominally 27V and will crank up past 28V on the main output. It also has a 12V 0.5A 'fan supply'. 

rs meanwell smpsu

PS..take the RS specs with a pinch of salt - they're up to standard as usual. The datasheet says it is a 120W version as suggests the part number, and although it is described as having a 'single output' the datasheet also says the 120W version has a supplementary 12V fan supply

[Mike Bullock]

5 minutes ago, KevinE said:

PS..take the RS specs with a pinch of salt - they're up to standard as usual. The datasheet says it is a 120W version as suggests the part number, and although it is described as having a 'single output' the datasheet also says the 120W version has a supplementary 12V fan supply

Thanks for that - I'll take a look 🙂

[DrV]

I've seen (heard) that problem when the Vcc supply cap for the IC was dried out. The sound you hear is not the actual switching frequency but the error amplifier in the chip oscillating as a result of feedback from the Vcc rail. The actual mechanism for producing the sound is magnetostriction but the frequency is well below the switching frequency. I wouldn't normally try to guide someone through surgery on an SMPS on a forum but it looks as though the electrolytic to the left of the little PCB is likely the Vcc cap.

Bear in mind that the main reservoir cap gets charged to nearly 350V and MUST be safely discharged and checked before you go anywhere near the innards.

[indyld]

Regarding the controller IC, this is nearly always a route to a (sort of) schematic for the PSU in that the datasheet likely contains one or more typical application circuits. 

 

[sunray]

What's happened with the DMX connectors?