Safer Coil Power Supply

3 08 2012


All Photos (1/2)
All Photos (2/2)

The capacitor bank which powers the coils is very lethal; when fully charged, it dumps more than a megawatt into the coils. Needless to say, If I were to accidentally complete the circuit through my body, it would rearrrange my insides. To decrease the likelihood of such an occorence, I’ve done my best to idiot-proof it. Here’s how it looked before:

Pretty easy to thoughtlessly reach in and touch the dangerous parts.

So first, I took a broken shipping pallet that someone across the street was throwing away, and made a box out of it

The box fits nicely on the crate that we’ve been using as a controls stand


I also left the front partially open so they we could get at the controls

With this setup, the only thing you can touch is wood, plastic controls, and the grounded metal face of the box, so it would be pretty hard to blow your hand off.

The next step was making the HVDC out wires safer. (the fat green and yellow ones in the first pic) The way we had it, the only way to dissconnect them was to reach into the supply and unscrew the ring terminlas to which they were connected. Not great. To fix this, I installed a high current outlet onto the back of the box and connected some shorter wires.

The other hole is where the cord which plugs into the wall goes

Took the wires we had and connected them to a matching high current plug

Assembled (and labeled):


So now it’s pretty safe. In fact, it’s so safe that getting into the power supply at all istoo much of a pain. We don’t want to have to move this box every time we need to reset the breaker. To make access easier, I put hinges on the bottom of it (see above), and chains on the side, so it opens like a tool box.

MakerBot mailed me an iron-on patch with some supplies I ordered, so I taped it on for good luck. (top right)

Look’s pretty badass, kinda like a ten-cylinder car engine.



Here’s one more safety feature I added:

If you open the “hood”, the power cord is automatically pulled out. This way, it’s impossible to open the power supply while it’s plugged in.

The coil supply is idiot-proof, but isn’t so locked down that minor repairs and upgrades are too much of a hassle. This is one more step towards a streamlined, repeatable, experiment procedure.

Domenick Bauer


Safety Upgrade

20 02 2011

As readers have pointed out, it’s time to put a lid on the power supply. Took care of that today:

I also added a fuse for the AC side:

Added a chassis ground for all surfaces:

Insulated this diode which could have shorted the bus bars:

Added a permanent voltage meter (steampunk):

Permanently attached bleed resistors to slowly drain the capacitor bank by default.

Radiation Survey & Pump Prep

3 01 2011

All photos.

I’m preparing to send the broken pumping station back to Pfeiffer Vacuum. Did you know “pfeiffer” is German for “piper; player of the bagpipes”!

Pfeiffer requires a radiation survey of the pump. In our case we are looking for radiation from neutron activation.

I used the sparkfun USB geiger counter for this survey:

I started with a 10 minute background reading 9.7 Meters from the pump.  91 clicks or 0.1516 clicks per second:

The UBS geiger counter produces a digit for each click. You can actually hear the geiger counter make a sizzling sound with each click… it’s wild.

Next I did a reading at the exterior of the pump. 88 clicks in 10 minutes. 0.146 clicks per second.

Again with the geiger counter inside the pump. 83 clicks in 10 minutes. 0.138 clicks per second.

I’d say the pumping station is clean.

I put the pumping station back in its crate:

As a side note, this USB geiger counter produces high quality random numbers:


I asked P. Andrew Karam, Ph.D (radiological specialist) to comment on my survey approach. He says:

Looks good, Mark – the biggest thing you are looking for is a significant number of counts above background.  You really don’t need to convert everything to CPS – the big thing is to make sure that the readings are all made using the same instrument and for the same amount of time.
In counting statistics we normally use a few concepts – LLD (lower level of detection) and Lc (Decision level).  These are the levels at which we feel we can definitively say that there is contamination (or activation) present.  The LLD is usually about 2 standard deviations higher than the average count rate – using Poisson statistics, one standard deviation is approximately equal to the square root of the total number of counts. So with a background count of 91 in 10 minutes one standard deviation is about 9.5 total counts.  That means that anything less than about 19 counts above background (so less than about 110 counts total) is within the expected statistical variability of your instrument.  The Lc is a somewhat more difficult calculation in that it depends on your survey speed as well as the size of the probe, counting time, and background counts.  Having said all that, the fact that your highest reading was background and everything was within 1 standard deviation of background tells us that you don’t have any neutron activation that is detectable with a GM.
One question – 90 counts in 10 minutes is not very much for a GM – I am used to seeing about 50 cpm (or almost 1 cps) from my GM.  I suspect that the reason for the low count rate is the relatively small size of the GM tube itself – the counts you get are a function of the cross-sectional area of the tube.  Not disqualifying – just a comment!
The only other question that might come up is whether or not your GM is calibrated – if Pfeiffer were to find elevated rad levels (which I doubt they will find, by the way) they might ask for calibration documents on your meter.

Fast Neutron Counter

28 10 2010

Dear community,

Please help me evaluate this fast neutron counter:

Is this appropriate for measuring fast neutrons from deuterium-deuterium fusion?

Accurate neutron counts are crucial for both the research and safety.

This meter comes calibrated and is in my budget (barely).

Dept of Health

23 07 2010

All photos.

Got a visit from the New York City Department of Health. They had several super hi-tech radiation meters. Dr. Karam on the left.

Neutron detector:

Taking readings while the fusor is running:

Generally they found that it’s producing a small amount of x-ray and neutron flux, but both were below harmful levels even at close range. Full report pending. Dr. Karam wants to do a longer test so the fusor can reach full neutron flux after bakeout.

ALSO: Just received this huge capacitor bank from ebay. I have to admit, this was an inpulse purchase!

48 X (1800 uF, 450V) capacitor bank. BAD ASS.

Fire Brigade

1 07 2010

All photos.

So the local fire house read about the project in the news and figured they would pay me a visit!

The guy on the left has a geiger counter in his hand! Awesome.

These guys pretty much made my day.

Emergency Stop

14 02 2010

I put together an emergency stop button for the reactor:

This will be positioned a safe distance from the reactor, so you can kill the high voltage from a distance. I’ll wire it up and test it today.

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