60-70v unregulated power supply recommendations

[Clive S]

That sounds like you're talking about the AC PSU input fuse. You definitely don't want any diodes in that position!

Have you read the post? The diode is to go across the DC fuse output of the power supply to the drivers to give a circuit for the bemf to be able to be dumped into the caps. in case the fuse blows

[Agathon]

Have you read the post? The diode is to go across the DC fuse output of the power supply to the drivers to give a circuit for the bemf to be able to be dumped into the caps. in case the fuse blows

I have been following carefully. Joe mentioned a single "flip down type" fuse holder which I interpreted as possibly being an MCB - his video shows one on the 240vac side. Just wanted to make sure he wasn't confusing the two lots of fuses with disastrous consequences!

[Clive S]

I have been following carefully. Joe mentioned a single "flip down type" fuse holder which I interpreted as possibly being an MCB - his video shows one on the 240vac side. Just wanted to make sure he wasn't confusing the two lots of fuses with disastrous consequences!

No Prob. But in #39 John show a diagram showing the fuse holder clearly showing the fuse connected to the drive +ve

[john swift]

Hi Agathon

the circuit from post 34


when every thing is working
the fuse short circuits the diode its connected to
so the power supplies DC output is connected to the driver

when a fuse fails power from the DC power supply is blocked
and now the diode provides a path any for excessive voltage
generated by the motor to be returned to the power supplies reservoir capacitor(s) and used by any other axis driver

if the FET's have become short circuit then a large fault current will blow the drivers supply fuse and the motor will be short circuited so no generated current can be returned via the diode


inside a stepper driver the FET's that form the H bridges
have built in diodes connected across the drain & source terminals

the diodes form a bridge rectifier that converts the AC voltage generated in a mechanicaly driven motor into DC that adds to the external DC supply that powers the stepper driver



John

PS
as an aside
one of many DIY hand cranked torches using a stepper motor as a generator

https://www.eeweb.com/blog/extreme_c...otor-generator

[Agathon]

No Prob. But in #39 John show a diagram showing the fuse holder clearly showing the fuse connected to the drive +ve

Yes, I saw that.

Hi Agathon

the circuit from post 34


when every thing is working
the fuse short circuits the diode its connected to
so the power supplies DC output is connected to the driver

when a fuse fails power from the DC power supply is blocked
and now the diode provides a path any for excessive voltage
generated by the motor to be returned to the power supplies reservoir capacitor(s) and used by any other axis driver

if the FET's have become short circuit then a large fault current will blow the drivers supply fuse and the motor will be short circuited so no generated current can be returned via the diode


inside a stepper driver the FET's that form the H bridges
have built in diodes connected across the drain & source terminals

the diodes form a bridge rectifier that converts the AC voltage generated in a mechanicaly driven motor into DC that adds to the external DC supply that powers the stepper driver



John

PS
as an aside
one of many DIY hand cranked torches using a stepper motor as a generator

https://www.eeweb.com/blog/extreme_c...otor-generator

Sorry about this, I seem to have sowed some confusion about my own clarity. My A-level physics knowledge is a bit rusty but I understand the back emf issue and the role and function of the diodes - excellent and clear explanation though.