mach3 wont reset keeps saying external emg stop requested

[Clive S]

Just a note that automotive relay coils generally take a lot of current compared with GP electronics ones. I haven't looked at your wiring, but I wouldn't use oneanywhere but on a vehicle.

Plus one

[Doddy]

Trying not to stray too far off topic, and knowing we have SMPSU engineers in here who could wipe the floor with me. Whilst Kitwn is almost completely correct in what he's saying I'd also throw in that voltage regulation can be compromised, particularly with poor design (for that read "cheap") if the presented load is completely inappropriate for the PSU rating.

The conversation about efficiency - the SMPSU efficiency would be measured at a given load - maybe 100%, maybe 80%. The efficiency at low % loads will be horrendous (consider that off load the efficiency tends towards 0). It'd be worth considering the efficiency under load and rule-of-thumb and assume that this is the worst-case thermal load and budget for that in your design.

All I'd say is that AS WELL as cost and size, I'd consider whether a PSU rating is appropriate using a wet fingered order-of-magnitude approximation - I would avoid a 1kW design for a 1W load. I'd be happy to use 1kW for something that could be expected to draw a couple of hundred watts. Common sense applies.

[Kitwn]

Doddy,
Agree with everything you've said. Though common sense isn't as common as we'd like it to be!

I was concerned that some readers trying to grapple with this stuff for the first time could get the impression that a 75W supply will waste a s**tload more power than a 40W one in the same real-world application. This just isn't the case.

[cropwell]

I would presume that an SMPS when off load only draws enough input power to keep the output stage at voltage. Off load the efficiency will therefore be 0. The current drawn from the mains will be enough to compensate for leakage in the output capacitor(s) and this will depend on the design of the unit and the quality of the output stage electrolytics (in the main).

Similarly in a transformer based supply, in an off load situation the self inductance of the primary will limit the input current, but not as much as an SMPS in the same state. Again the idle current will be dependant on the transformer design.

Are these valid assumptions?

Rob.

[Doddy]

Gods I'm bored being home-bound. Bored enough to look on Farnell and RS at both power relays and automotive - to be honest there's not an awful lot in it - which looks to be more around the switching capacity (not really surprising) and what you could imagine the associated switch gear and return springs, and with most of the 50A relays around the 90R coil resistance (around 130mA). Automotive are likely more suited to the environment (high vibration, humidity and corrosion resistance) as well as providing economic switching of the high capacity PSUs we all tend to have knocking about.

[Geoff57]

afternoon all hope you are all keeping well
psu arrived lunchtime all wired up machine working as it should
many many thanks to jazzcnc and Clive your persistance with me has now got my machine up and running sorry i was a pain but with your help and knowledge we got there when all this lockdown is over if you are down my way Barton on sea give me a shout i owe you guys a beer or two
Great Forum
thanks Geoff

[JAZZCNC]

Your Welcome Geoff pleased your making chips again. Take care and stay safe.

[Geoff57]

thanks jazz