TMP Diagnosis

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
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Richard Hull
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Re: TMP Diagnosis

Post by Richard Hull »

Ion pumps and Ti sub pumps have no place in a fusor vacuum steup.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Johan Reinink
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Re: TMP Diagnosis

Post by Johan Reinink »

Jackson, Getting a working pirani or TC gauge is very useful for vacuumwork, I can definitely recommend it.
Still I don't think a high foreline pressure is the problem. 400 micron is around 0.5mbar which terrible performance for a dual stage rotary vane vacuum pump but it's good enough to test a turbo. A pressure of 10^-2 to 10^-3 is recommended for turbo's without a molecular drag stage but the maximum they can take is a lot higher, usually 10^-1 to 5*10^-1 mbar depending on the pump. With a drag stage they allow up to 10mbar foreline pressure, again lower is recommended. In any case a turbo should rev up to a substantial fraction of it's operating speed if it's working properly.
... it doesn't go. It just sorta stumbles.
That tells me pressure is not the problem, even in air turbo's spin up to several thousand rpm.

How well does the rotor spin? Compare with this:
https://www.youtube.com/watch?v=T8jz1LNJ4L4
Hearing ANY bearing noise when spinning by hand is a very bad sign. Replacing a worn out bearing with a new one is about as costly as a proper functioning second hand turbo.

You're probably going to need electronic knowledge and tools, prepare to invest in things like an oscilloscope. For now a good multimeter would already bring you quite far. In any case this is possibly quite a project, so do it for the fun and learning, not to easily obtain a high vacuum.

Just count the pins of the connector of the turbo. 8 pins? Easy debugging, has 3 for windings and some things like monitoring temperature. Around 15~20 pins? Probably has hall sensors and other fun stuff, a bit more difficult to debug without a manual. A gazillion pins? It's a magnetically levitated pump.
Jackson Oswalt
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Re: TMP Diagnosis

Post by Jackson Oswalt »

The controller side of the cable has 10 pins, but the TMP side has 8 spaces. There are 8 pins on the actual pump.

When I spin the TMP by hand it spins for about 10 seconds, slows down, and comes to a halt. The whole time it makes. 'Whirring" noise. Let me know if I should upload a video.
Youngest person to build a fusor
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Dennis P Brown
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Re: TMP Diagnosis

Post by Dennis P Brown »

Since developing knowledge is a means in of itself, for someone with a good background in electronics, I'd say do all the diagnostics and learn all about the turbo for the fun. That appears not to be either your background nor what you are interested in; as such, there are always deals on diffusion pumps but beware - water cooled ones are cheaper (and often larger) and that means a lot of issues - getting water and drain lines to where you are working; larger flanges/adapters/gate valves which means far more costly unless one (like I) have access to a shop and can do a lot of rather advanced machine work with a lathe. Again, does not look like your preferred path.

All that is just to say, you might want to wait and watch ebay for a small air cooled unit to become available for a reasonable price - not likely but possible. That said, you will still need diffusion pump oil and that could exceed the cost of a diffusion pump.

Since you neither have a good two stage vacuum pump or a proper cheap thermo-couple grade vacuum gauge, these are, in my opinion critical first steps towards creating a useful vacuum system. And you should consider solving these issues first (while a fusor needs many support systems: deuterium gas, power supply, neutron detector system) the vacuum is the most important first support system and one that has the most uses for other projects if one does not do just a fusor. Also, critical for learning the real details (start, at least) of using any system that will support a plasma.

Of course, a pump and TC gauge system are useless unless one can connect the various components together; which means one must buy those connecting components (connecting flanges of some type, hoses of some type) once you have decided on how you want to go (Again, FAQ's under Vacuum.) But I feel KF is the best approach for any newbie with a limited budget and try to use 25 mm size (I use 25 mm all all my support systems except for my turbo inlet which is 15 mm (adapter used, of course).) Lots of both new (and cheap from china) and surplus KF stuff that can create a nice fore pump system for either a turbo or DP is available on ebay. Especially surplus stuff like steel bellow hoses can be a steal if one is careful (always have return option or don't buy - a leaking steel hose is just a boat anchor!)

Always check people here on high end items like DP's, two stage pumps, a specific power supply (but DO read the FAQ's on that critical topic) etc.

A real fusor uses a lot of complex, some very dangerous, and not easy to build support systems unless one can buy working turn key stuff (expensive.)

Good luck
David Kunkle
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Re: TMP Diagnosis

Post by David Kunkle »

I'll second what Dennis said about the 2 stage pump and need for a thermocouple gauge. At least the thermocouple first- that way you'll be able to see where you're at with the 2 stage pump. It is a "must have" if you intend to go any further.

You may as well post a video of spinning the turbine blades- as long as there's sound. ;) "Whirring" could be OK- or not. I've got my system apart lately for changes, and I just spun my turbo this a.m. to check it. Really no sound while it's spinning unless I get my ear less than a foot away- then I hear a little whirring like blades moving thru air/maybe it's bearings turning smoothly. Of course, I know my hearing isn't what it used to be either, so your mileage may vary. Took 12 to 15 secs to come to a stop.
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford
Aaron J Hardin
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Re: TMP Diagnosis

Post by Aaron J Hardin »

Considering that these pumps run between $400-$900 in good condition I would lean towards a faulty pump. The condition described is a shorted winding. Check that the wiring is correct as this will have similar symptoms as will water/condensation on your stator.

A bad hallefect sensor is a possibility, however this would not blow fuses (unless faulty wiring). It would likely overheat or indicate a fault.

The oil is not an issue, it is non conductive and will create minor drag. Once you repair the windings (or evaporate any water) run the pump on low rpm and purge with dry nitrogen. There is a sight glass at the bottom cap of these pumps, the oil should settle at the halfway point.

I know this is an older post but Molecular Turbopumps are vastly superior in many ways and worth the effort to get running correctly. Yes they are overkill for many hobbyists but to name a few benefits:
-They are especially useful in a fusor where the objective is to collide hydrogen^2 (explosive) into helium (also explosive)
-You can control the vacuum speed 100:1 in many applications
-They can operate for extended periods of time uninterrupted
and finally, the cleanliness
John Futter
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Re: TMP Diagnosis

Post by John Futter »

Aaron
what?????
a lot of RAP spelt with a "C"
Helium is one of the noble gasses
Most turbos are on the second hand market because their bearings are past end of life.
In 40 failures in our lab of turbos all except one was bearing failure.
the odd one out was vane failure (read spectacular) a mass of scrap aluminium

Any water vapor would mean that you do not have sufficient vacuum for backing and the pump should not be started.

For fusor work for inexperienced vacuum practitioners I would recommend Diff pumps - less of a mess when making mistakes this applies to the $$$ spent as well

as an aside turbos do not like running at typical fusor vacuums ie on th edge of molecular flow where blade tip damge is foremost
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