Wednesday, February 11, 2015

Drying transformer oil

I acquired an x-ray head a bit back off of Craigslist:

and was experimenting with some screens:

to produce some images.  The setup is remotely switched and uses a webcam to view the intensifying screens meaning I don't have to be in the room while it runs.  I started to do some "low voltage" tests (maybe 50kV?) but didn't see any images.  I'm not sure what range the screens are sensitive to so I decided to crank up the voltage some.

In the past I had ran my head at 100kV for a number of experiments with no issue.  Unfortunately, as I turned up the voltage this time it generated an internal short a few seconds after turning it on.  Drat!  I had been warned these old GE heads can suck in moisture and its possible that's what happened

Fortunately, I drained the oil and it was still pretty clear indicating *potentially* no major damage.  So I'm taking two paths to get the system back online.

First, some cheap GE x-ray heads showed up on eBay so I picked up a few:

The bottom left unit is my original Craigslist special.  I have need of some high voltage DC supplies so I should be able to make use of  the lot even if they are excess to my x-ray needs.

However, these heads can still develop the same short if the oil has moisture.  I picked up some mineral oil and tried to dry it out under vacuum in a 2L reactor.  Unfortunately, it seemed to steadily bubble for some hours.

I talked to someone and they suggested that the trick is to get a lot of surface area to let the water out quicker.  So I tried to setup something resembling a vacuum distillation rig:

At the bottom is the 2L reactor with 24/40 joints.  The red hose is the vacuum feed.  The bottom hose has a siphon (like you'd find in a vacuum trap) that leads to a peristaltic pump (not shown) and then recirculates to the top.  From there it feeds a Vigreux condenser to give it lots of surface area to outgas.

I knew that the pump wouldn't prime under vacuum but figured it could be primed under atmosphere and then would circulate.  Unfortunately, the oil outgases heavily under vacuum, causing the pump to de-prime.

To solve this, the next step is to try to gravity feed the reactor into the pump.  Thus, even if it outgases, gravity will feed oil into the pump and cause it to prime under vacuum.  I'll likely have to put the reactor partly on its side which means that it could come apart and make a huge mess.  Most of the work will be trying to ensure this doesn't happen.  I have a clamp for the reactor lid and can tape the rest of the ports in.  Under normal circumstances, vacuum should hold everything together but it must be able to prime as well as survive returning to atmospheric pressure.

List of digitized chips

Collected list of chips that I know have had their layout, schematic, etc recovered: