On 01/06/2016 01:54 PM, Gene Heskett wrote: >> When you turn off the machine and the SSR starts to bleed, and then >> turn on the machine before the caps are completely empty, then you >> will have the bleeder load on there permanently. > > Exactly the reason for the forced time delay in the turn on as I > described. That, and the low voltage AC in series with the load > resistors to encourage its turn off when the DC volts gets down to the > 6 volt range if it does not recover from lack of sufficient holding > current, but that may be several T=RC's depending on the minimum holding > current of the individual device. This applies to the spindle psu only, > and other initializations of the machine, like homing & touch offs, can > continue while this is taking place.
I'd do it differently and use an active bleeder setup. See atached diagram and simulation result. The setup uses the voltage from the cap an energy source for bleeding the cap. The bleeder kicks in at about 40ms after the power is turned off and is disabled instantly when the AC source is enables. The cap is discharged using a constant current bleeder. This reduces the need to have a high-power resistor in the circuit. Most of the power is dissipated in the mosfet, which should be mounted on some cooling fin to dissipate the instantaneous heat (but it is not too bad or much). This setup is probably also cheaper than using SSRs. -- Greetings Bertho (disclaimers are disclaimed)
bleeder_1.pdf
Description: Adobe PDF document
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