Saturday, March 14, 2020

HP/Agilent 6621A removing fan noise.

This "mod" not only takes all the fan noise from the Agilent/HP 6621A as it goes a step forward, disables it completely...

I got this power supply to equip the lab with something professional grade, it is in fact a really nice power supply with lots of features but has a fan that no one can stand being near by. Imagine a vacuum cleaner to have an idea.

In the past I did a box to bring the two output from the back to the front along with a voltage meter (converted one of 250v to 25) for visual reference of the output, it's easy than looking at the LCD, below indicating 5V on output 2:

Back to the fan noise, initially was thinking in making a thermostat control to actuate only when needed but I'm not going to use the equipment that often so just disconnected the fan, now I can only hear the hum from the massive transformer, that is still noticeable and something I didn't eared/noticed before. To have an idea the power supply weights around 17Kg

The supply has an internal thermal shutdown circuit so hopefully that will be enough for day to day and low current supply. There is also a small gap on the back panel that latter on I can put a switch to enable the fan without the need to open it.

Here's the fan connection:

and without the plug... end of the fan noise:

Interesting enough the fan is a 115V version, here's the diagram:

as you can see the fan will connect to mains transformer terminals 4 and 5 (120V), clever design.

The massive transformer inside:

and one of the two power modules, amazing engineering:

I might revisit this in the future if I decide on thermostat control.

Have a great day!

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