This is a common augment, that the NTC does not have time to cool in 15 seconds. But I also ask if the filter caps have time to discharge through the bleeder resisters in 15 seconds?
If designed correctly the two time constants would be about the same. Maybe about 120 or 180 seconds for both. Also, you can design a linear supply with a CRC filter where the "R" limits inrush, It is not impossible you just have to work it out. In the old days when they only had vacuum tube rectifier there was no option, they had to use CRC filters with the first C limited to about 50 uF so as to protect the tube from inrush. This approach still works On Thu, Jul 29, 2021 at 1:35 PM John Dammeyer <[email protected]> wrote: > I looked at using the NTC resistors to limit inrush. I have some but > never used them for this. The issue is simple as they are meant for > systems that have high inrush and are then powered continuously for a long > period of time. (Like an old style Tube based TV or Radio). > > That may also well be true of CNC systems too but all too often I've also > had to switch off the power and switch it on again. For example, does the > ESTOP remove the AC input to the high voltage supply or remove the DC. I > think the regulations say the AC side. > > Anyway, if the NTC resistor doesn't have a chance to cool before you > switch power on again (and they do get very hot) then the next power cycle, > which may only be 15 seconds after power off, now presents full current > into the system as if the inrush limiter wasn't there. Assuming the input > filters on the DC side have completely discharged. And then pop goes the > fuse or circuit breaker. > > That's why I used the relay to bypass a series resistor. > > John > > > > > > -----Original Message----- > > From: andy pugh [mailto:[email protected]] > > Sent: July-29-21 11:02 AM > > To: Enhanced Machine Controller (EMC) > > Subject: Re: [Emc-users] Lathe Spindle Drive Questions > > > > On Thu, 29 Jul 2021 at 17:58, Chris Albertson <[email protected]> > wrote: > > > > > The way to deal with inrush today is to use a thermistor on the > > > high-current side of the transformer. > > > > They start to become hard to spec when you are working with > > steady-state power input of a few kW, though. > > > > I tried to use one for my servo power supply, and decided that I > > couldn't find one that was up to the job.. > > > > -- > > atp > > "A motorcycle is a bicycle with a pandemonium attachment and is > > designed for the especial use of mechanical geniuses, daredevils and > > lunatics." > > � George Fitch, Atlanta Constitution Newspaper, 1912 > > > > > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
