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| "Dallas" <Cybnorm@spam_me_not.Hotmail.Com>: May 04 03:03PM Hi guys, the motor run capacitor for my rolling shutters tubular motor died. The cap case size is 35mm x 78mm and this is critical because it must fit inside the motor enclosure. I've looked at hundreds of 20 µF capacitors and they all were at least 40mm diameter (too wide). Then I found a capacitor that is 25mm x 56.5mm. This is tiny and I'm thinking it must be too good to be true. Can you help me decide if this capacitor will run this motor? The printing on the original capacitor is: Arcotronic – (purchased by KEMET) Part Number C.87.7ZF2 MKP 20 µF +/-5% b 320 V~ HPF N 560-8/A1 (In the USA voltage is 120 volts) (out of production for years, none available) And the data sheet for the prospective new little one: https://www.farnell.com/datasheets/2755239.pdf -- Dallas |
| Chris Jones <lugnut808@spam.yahoo.com>: May 05 12:29AM +1000 On 27/04/2019 11:59, Trevor Wilson wrote: > **I've had the odd X-ray and, being an inquisitive chap, I usually > examine the equipment as best as I am able. I've never found an X-ray > machine that operates below 75kV. The lower keV x-rays are not useful for diagnostic purposes, because for example, 10keV photons would be totally absorbed in your body, (still very probably damaging your DNA), and basically none of it would make it through to the cassette with the intensifying screen (fluorescent stuff) and film, so it does not help with making an image of your innards. So, to maximise the benefit and minimise the harm, medical x-ray machines use relatively high voltages and are also required to include a filter equivalent to a certain thickness of aluminium in the beam path between the tube and the patient. This filter removes the lowest energy photons (that are useless and harmful because they would be totally absorbed in your body) without causing too much loss of the higher energy photons that are still harmful but are also potentially useful because they have some chance of passing through you and making an image. All vacuum tubes will generate photons internally with some energy. Any photons shorter in wavelength than roughly 300nm can damage your DNA, and that corresponds to only a few volts on the anode. Whether the vacuum tube will emit hazardous photons externally depends on whether the photons can pass through the vacuum envelope of the tube. I would be quite careful at 5kV or even below 5kV, if there is absolutely no shielding other than a thin glass envelope. Whilst the tube envelope may attenuate the x-rays by a large factor, on the other hand the anode current, tube-to-human distance and exposure time with e.g. a RF amplifier being serviced, might be much less favourable than in the case of a medical x-ray. Medical x-rays usually use a few milliamps for a second or less. Big amplifiers may run several hundreds of milliamperes for hours. The other thing to be aware of is that many Geiger counters are very (or totally) insensitive to 5keV photons. Whilst the Geiger counter may tick furiously with the accelerating voltage set at 40kV, and fall completely silent as the voltage is turned down to 5kV, that does not necessarily mean that the x-rays have stopped, it might just mean that they are now at a wavelength that the counter cannot detect. |
| Fox's Mercantile <jdangus@att.net>: May 04 10:00AM -0500 On 5/4/19 9:29 AM, Chris Jones wrote: > machines use relatively high voltages and are also required to include a > filter equivalent to a certain thickness of aluminium in the beam path > between the tube and the patient. While working at ScanRay (airport baggage equipment) it was a "you learn something new, everyday" when I learned they used aluminum for lenses. Unless you work with this stuff, it just doesn't occur to you. -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com |
| Don Kuenz <g@crcomp.net>: May 04 01:42AM > Also there are some people starting to make chips at home these days: > http://sam.zeloof.xyz/first-ic/ > Maybe he will even fabricate your design! Good information. It looks perfect for DIY. Thank you, 73, -- Don Kuenz KB7RPU There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night. |
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