My Turbo and Homemade Driver

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.
Niels Geerits
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My Turbo and Homemade Driver

Post by Niels Geerits » Sun Sep 24, 2017 6:47 pm

I would like to share my turbo and the driver I made for it. The pump is a used Pfeiffer TMH064 from Bulgaria that I found on ebay. The pump has a centertapped motor so the driver was pretty easy. I found that someone on this forum built a driver for a similar pump, so I built forth on that (original thread viewtopic.php?f=10&t=4036). I used an LM358P to amplify the 400mV coming out of the Hall sensor to 3.5V. This output is sent to a digital pin of an arduino. Two other digital pins are used to control the gates of two N FETs. Other than that my driver is the same as Alexi's. I tested the pump at low frequency in air (before I do anything in vacuum I want to make sure that my TC reading is correct). I know you are not supposed to, but I had to test it and figured if I did a slow test I would not damage anything. Here is a video of the pump starting up (I filmed it for the sound):

https://www.youtube.com/watch?v=rNelG-ngSPw

And here a rough drawing of my circuit:
turbocircuit.jpg
The frequency was below 100Hz. To me it sounds like two things might be grinding together as the blades spin, however I have heard this in other turbo pump videos. Something I haven't heard yet is the low hum mine makes.

I was wondering if someone with more experience with turbos could tell me if it sounds normal and if not what the most probable cause is (oil bearing etc.)?

Jerry Biehler
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Re: My Turbo and Homemade Driver

Post by Jerry Biehler » Sun Sep 24, 2017 11:42 pm

Bearings are shot.

Niels Geerits
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Re: My Turbo and Homemade Driver

Post by Niels Geerits » Mon Sep 25, 2017 11:43 am

Sounds like I have another project on my hands then. The pump has an oil lubricated bearing and a magnetic bearing. My guess is this magnetic one is fine (don't see how it could wear. correct me if I am wrong) and only the oil lubricated one needs to be replaced Do you know if any specialized tools are required to take apart the pump to replace the bearings?

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Dennis P Brown
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Re: My Turbo and Homemade Driver

Post by Dennis P Brown » Tue Sep 26, 2017 11:57 am

I have (successfully) taken apart turbo's and removing a bearing is not easy. Be very careful not to bend or break the blades - they are very brittle. Also, blades often are not interchangeable and sometimes (mine for instance) not only is the order critical but mine used two different sets of insert blades! So keeping track of how they went in (order), what the blades look like is important; and do draw/note the correct order for the re-assembly.

Most general tools will break a pump down (allen and screw drivers) but pulling a bearing is not easy nor simple in all cases (might need a bearing puller to get it off the shaft - especially if it has over heated.)

The oil for a turbo bearing is very expensive and you might have to have that with a new bearing (keep that in mind.) Cleaning afterward may be necessary - read up on how that is done for your pump (mine allows immersion but the bearing then has to be re-oiled ... .)

That all said, have you tried the pump pulling vacuum against a high vac gauge? It might work well. Also, maybe just re-oil the bearing? Finally, never again run your turbo in air - that is a really great way to bend the blades! Even slight bending can damage those pumps (yes, some can tolerate some air but unless you know for certain, just don't do it.) So, always run it with power only under vacuum.

Jerry Biehler
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Re: My Turbo and Homemade Driver

Post by Jerry Biehler » Tue Sep 26, 2017 11:48 pm

If this is like my other pfeiffers it is pretty easy. You pull out the oil cart from the bottom, there is a cone shaped nut with an hex hole for an allen wrench. you need to hold the rotor still to unscrew it. There should be something else retaining the outer race. The bearing should pop out from there. There is no need to take the whole pump apart.

Now you need to get a bearing. The one out of my big pfeiffer (1000l/s) was a standard size with a special ball retainer. I ordered another ABEC 7 ball bearing from a supplier in Cali and swapped retainers.

The smaller one I have (500l/s) is a different story, it is a custom bearing so I am going have to get creative with that one. It basically has one side of the race integrated into a 1mm thick shield, all one piece. So I am going to have to get a stock bearing and add what will basically be a precision washer to one end to space it out.

I dont know what the situation with the little bearing in the pump you have will be. You can get a off the shelf replacement from Alpine Bearing. Probably going to run $1-200. Then you will need a new oil cartridge which is about $75.

ian_krase
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Re: My Turbo and Homemade Driver

Post by ian_krase » Wed Sep 27, 2017 3:50 am

Does Alpine Bearing have it?

John Futter
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Re: My Turbo and Homemade Driver

Post by John Futter » Wed Sep 27, 2017 8:17 am

As far as I know
most turbo makers use custom bearings and if you learn a bit about bearings they are right on the edge of what a bearing can do vs speed.
Leybold seem to use Bardin bearings from the UK and I have tried to buy
but they wil not sell and divert you to leybold
Boca bearings have some bearings close in dimensions but not the same
might be worth a punt

Jerry Biehler
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Re: My Turbo and Homemade Driver

Post by Jerry Biehler » Wed Sep 27, 2017 8:59 am

Looking at the cross sections for the tmu071 and the 065 I am pretty sure they use the same bearing. here is the bearing for the tmu071p. It has one of those integral shields like the other bearing I have to replace has. https://alpinebearing.com/ball-bearings/yc1340tphw6/

Give them a call, they were helpful the last time I called, I never got any response from their online form. They should be able to tell you if that is the right bearing. Alpine bearing is who supplies bearings for the rebuild kits for places like PCH Chemlabs. Their search engine for the website sucks.

Niels Geerits
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Re: My Turbo and Homemade Driver

Post by Niels Geerits » Wed Sep 27, 2017 9:46 am

That was helpful. I did not recognize that the conical thing had any grooves for an allen wrench last night, but you are right. I found that by removing the four screws that connect the bottom part of the pump to the central part something pops loose and you can no longer turn the blades by hand, however it appears that if I turn that conical nut hard enough the rotor will still turn. So I will have to come up with something else to keep it still.

I have had contact with both Pfeiffer and Alpine Bearings and got quotes from both for replacements. It is likely that I will only have to replace the lower bearing. Once I remove the old one I will order a replacement.

Jerry Biehler
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Re: My Turbo and Homemade Driver

Post by Jerry Biehler » Wed Sep 27, 2017 5:17 pm

Yeah, the top bearing is magnetic so there is no contact and nothing to wear. When you release the bottom beating the rotor will be pulled up by the magnets.

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