On 3 May 2016 at 14:31, John Kasunich <jmkasun...@fastmail.fm> wrote: > > Is there any particular reason you are using SSRs instead of > regular contactors? I like contactors because they are rugged > and pretty much immune to overvoltage, dv/dt, and di/dt problems.
Mainly it is a matter of available space (or became such). I found that I didn't have the room in the existing control cabinet in the side of the lathe, and I found another space inside a cover behind the headstock where the feed motor used to live. > > Contactors (or electromechanical relays) also provide an air-gap > between line power and the load, which means I'm comfortable > using them in an e-stop circuit. I do have a proper contactor upstream of the PSU that is controlled by the e-stop circuit. The first SSR is there mainly as part of the power-off discharge arrangement. > Also, is there any particular reason you are running the full load > current through both relays? Yes, the reason is that I didn't think things through properly :-) This PSU is a development of one that I have been using in my milling machine. That one uses a 230V coil relay with a NC contact that connects the discharge resistor when the power to the PSU goes off. On that one there was a second relay controlled by a 555 timer circuit. It was only later that I realised that I could more intelligently control the system via HAL, as the servo drives report bus voltage back to HAL. The specific reason to want to do this is to avoid turning _on_ the PSU while the cap is discharging, as trying to break the discharge (DC) voltage leads to relay failure. So I now have things interlocked so that HAL won't turn on the PSU unless bus voltage is < 2V. Given that I now have intelligent control of the PSU, I can see that your system makes a lot of sense. If there is no reason not to leave the pre-charge relay closed during operation, I could even use the existing mechanical relay that brings in the discharge resistor. Is there a reason to switch-out the precharge relay once the main contactor is closed? I guess the danger is that if the main contactor fails to operate the machine would run through the precharge resistor. Though I imagine that that would cause an easily-detected undervoltage fault in the drives. -- 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, 1916 ------------------------------------------------------------------------------ Find and fix application performance issues faster with Applications Manager Applications Manager provides deep performance insights into multiple tiers of your business applications. It resolves application problems quickly and reduces your MTTR. Get your free trial! https://ad.doubleclick.net/ddm/clk/302982198;130105516;z _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
