TMH-260 Turbo

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.
Al Nejati
Posts: 12
Joined: Fri May 07, 2021 11:28 pm
Real name: Al Nejati

Re: TMH-260 Turbo

Post by Al Nejati »

Just an update on how I'm currently going. I've got the first version of the driver sent off for pcb fab. The circuit has current sense (with low-pass filter), constant-current hall drive, and (optional) common-mode bypass for potential noise on the hall sense circuit. Time to see how it works in practice. Schematic attached.
Attachments
Screenshot from 2021-07-25 11-53-52.png
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: TMH-260 Turbo

Post by Richard Hull »

Hitting the issue the hard way. Good luck with you efforts to spin up your turbo using a self-designed turbo controller. Keep us in the loop on how it turns out, once assembled.

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
Al Nejati
Posts: 12
Joined: Fri May 07, 2021 11:28 pm
Real name: Al Nejati

Re: TMH-260 Turbo

Post by Al Nejati »

Thanks Richard.

Some more design notes, in case it's helpful to anyone.

The mosfets are driven through a pair of drivers, each driver controlling the two windings of the same phase. So A and C are controlled by one driver, and B and D are controlled by the other driver. The benefit of doing this vs putting A and B on the same driver is that you get hardware shoot-through prevention and dead time, which is important for soft switching (more on this below).

Ideally, you don't want the mosfet for each phase to be fully on during the whole part of the cycle; instead you want to have PWM control. This enables a more controlled ramp-up of the motor with minimal torque ripple, which helps extend bearing life, and eliminates the need for multiple power supplies for the motor. Because PWM involves switching at relatively high frequencies, it is best to avoid hard switching of the mosfets to reduce switching losses. This turns out to be straightforward to do. Whenever a winding of a phase turns off, the induced back EMF 'swings' the other winding down towards zero. So, for example, when winding A is on, C is at 2xV_supply. When winding A turns off, it swings up towards 2xV_supply, and thus C swings down to near 0. The dead-time allows the other mosfet to swing back to 0V as it turns on, reducing turn-on losses. Turn-off losses for A can be reduced by switching it off as quickly as possible and having some capacitance (in this case, a few hundred pF) between A and ground. The mosfet's own C_ds is sufficient for this here.
Al Nejati
Posts: 12
Joined: Fri May 07, 2021 11:28 pm
Real name: Al Nejati

Re: TMH-260 Turbo

Post by Al Nejati »

Got pcb back and wired everything up, and it works. The pcb has an inexpensive STM32F103 board stuck on top to control everything. Done a few basic tests spinning up to very low speed (~6000 rpm) just to make sure current draw, voltage, etc. are within expected bounds. Will spin up to higher rpms when I put my actual vacuum chamber together, and I add the hardware watchdog. The hardware watchdog is important when using a microcontroller to generate the drive frequency. Picture and short video attached (sorry for poor quality). The rundown time (unpowered) from 6000 rpm to 0 rpm is about a minute or so.

Some notes: There's more electrical noise from the motor drive on the hall sensor lines than I expected. There's likely some kind of coupling inside the motor. This causes a problem because the hall sensor voltage output is trapezoidal and goes near zero for a good period of time during each cycle before polarity reversal. This can cause spurious output from the comparators. I've added some debouncing in software, but this is less than ideal. I'll look at more hardware noise filtering in the next prototype.

Current draw at 6000 rpm is about 0.7 A @ 20 V. The mosfets are cold to the touch. I noticed some noise from the turbo around 4800 rpm, I wonder if this is just a resonance and not to worry about, or if there's a problem with my pump. Is your pump similar, Gustavo?
Attachments
IMG_20210822_114946.jpg
VID_20210822_114957.mp4
(2.63 MiB) Downloaded 264 times
IMG_20210822_115409.jpg
Denis Tikhonov
Posts: 3
Joined: Mon Oct 23, 2023 2:32 am
Real name: Denis Tikhonov
Location: Yerevan

Re: TMH-260 Turbo

Post by Denis Tikhonov »

Hi Gustavo and Al, I'm impressed with your result, could you kindly re-upload the schematics since they all don't seem to open?

I have a Pfeiffer TPH180 with no controller, and the motor coils and hall sensors in it have the same arrangement as in the 260 you have spun up. They also seem to share the same TCP380 controller.

You would help a lot to avoid the extra pain of figuring out the signal and phase sequence.

Many thanks in advance.
Post Reply

Return to “Vacuum Technology (& FAQs)”