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Siemens micromaster 420
appletree:
Gents (and Ladies)
I have some 1k ohm wire wound pots if I put a couple in series to give 2k and apply 20vac I will have a maximum current of 10ma (disregarding anything in the VFD).
Leave it like that for an hour or 2, ramp up the voltage to 60vac (siemens starting voltage) which will give 30ma, then what?
1 Carry on increasing voltage in 60vac increments with resistance in place?
2 Remove the resistance start at 20vac ramp up to 60vac then follow Siemens recommendations (60v increments)?
3 Do something different?
Regards Phil
John Rudd:
10ma at 20v is one thing in terms of power, (200mW..) but as you wind up the volts, the watts are going to rise too, maybe exceeding the power rating of your pot?
I'd be inclined to follow the ramblings of Mr Siemens......
BTW, have you got an isolation transformer?.....( that would be the way I'd do it....rather than live mains direct from a variac.... :zap: )
appletree:
Hi John
I think I will start as suggested, then option 2 above, still much gentler than Siemens recommendations, most people would not even read the manual, just bang it on line and maybe watch the smoke rings. The pots will be used as a fixed 2k resistance, they are just something of reasonable resistance that can dissipate some power.
Phil
appletree:
A result, I supplied the VFD at 10vac for an hour then ramped up to 60vac over another hour, then followed the manufacturers instructions, basically 2 hours at each of 60,120,180 and 240vac.
The VFD display lit up at around 140v saying low supply voltage, had difficulty programming could JOG and reverse JOG, you could run and the motor “locked” but the frequency would not increase, got there in the end.
The next decision the VFD is capable of 1.5 kw, I want the use it to drive my Raglan 5 inch which is currently fitted with a 1 HP single phase motor.
The motors are both older frame sizes which will fit straight on with the correct shaft size.
1 Unused 550w 2800rpm fully sealed fan cooled
2 little used 750w 1425rpm open frame internal fan
I have a 375w 3 phase 1425 motor fitted to my little John Mk2 which is a bit underpowered (basically the same lathe), I fancy the power of the 750w but the sealed aspect of the 550w motor, additionally there is the RPM issue.
Phil
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