neptronix wrote:Thank god for the schematic. The shunt was hiding underneath a giant glob of goo near the output caps. At first glance i thought that i had some bizarre board that had no shunt.
Hi neptronix, I am certainly not God but the idea of reverse engineering the NES schematic was exactly this - to be able to mod it and have an idea what you are doing to the supply, so you can make an assumption of the result...
neptronix wrote:So; I plan on doing the shunt shave method yet again, as i did with my S-350-48.
The way the supply is designed, the small voltage of the Shunt is amplified with an opamp and that feeds into the Voltage feedback of the PWM controller. Even a small ripple or some noise on the current measurement will lead to the PWM controller not gradually throttling back, but to random skipped cycles. You describe a screeching sound and I think that is what might be the effect of noise on the current limit feedback.
I cannot guarantee that modding R134 will have any other effect though. It may be necessary to remove the noise from the current feedback by limiting the bandwidth of the opamp and/or filtering the output. Unfortunately that may lead to instability if done wrong. I do not know what will happen without trying.
Note that the current measurement across the shunt is not supposed to come on normally as that limit is above the max power of the supply, so it may be that MeanWell simply did not pay much attention to the operation in continuous current limit and accepted the screeching when reaching the limit.
neptronix wrote:Now i have a question for you guys:
I do plan on using the constant fan ON modification. However i would like to power a small intake fan up front off the 12v rail. The fan will draw 0.1A. Would this work without any complications?
The 12V is taken off the main transformer with a small winding and passes through a linear regulator. I am not sure how much voltage the regulator drops but the weird situation may arise that adding more load drops the voltage before the regulator enough that the power dissipated in the regulator actually reduces under the higher load. You will know if you measure what happens when doing this.