Advice on these steppers -Nema 24 Stepper Motor 24HS34-3008D

[CharlieRam]

Am I looking at this all wrong? I'm thinking of getting the EM806 or AM882 80v drivers, I have a 2 x 25v toroidal transformer and 4700mf 100v caps and rectifier to build the PSU which should deliver 68v, I am scratching my head at what stepper motors I should get to match the Power supply....if those 3.1Nm steppers only require 57v would I be better to go for 50v drivers and a smaller PSU?

[Clive S]

Am I looking at this all wrong? I'm thinking of getting the EM806 or AM882 80v drivers, I have a 2 x 25v toroidal transformer and 4700mf 100v caps and rectifier to build the PSU which should deliver 68v, I am scratching my head at what stepper motors I should get to match the Power supply....if those 3.1Nm steppers only require 57v would I be better to go for 50v drivers and a smaller PSU?

Personally I would go with the 68V p/s with the drives above or https://www.ebay.co.uk/itm/2DM860H-2...frcectupt=true

There are plenty of people using this setup without problems

[CharlieRam]

Clive, Are you saying the 57v rated Steppers will be fine with the 68V PSU and either of those drivers? I am sure this is what people have used in the past but m_c says the voltage is too high! I'm a little confused now.

Personally I would go with the 68V p/s with the drives above or https://www.ebay.co.uk/itm/2DM860H-2...frcectupt=true

There are plenty of people using this setup without problems

I saw those drives but was a little unsure....have many people used them? It doesn't look like it has stall detection although I do understand that if the motor has stalled the job will be wrong even with stall detect.

[Voicecoil]

It's worth doing the sums and working out exactly what voltage you need - for some motors 50V would be fine, for others a big hindrance. Thankfully, @Irving2008 has put it all into a handy-dandy spreadsheet which ties together all the variables (apart from using pulleys/gears with a non 1:1 ratio) for which he deserves a beer - go looky here:

http://www.mycncuk.com/threads/1524-...tor+calculator

[CharlieRam]

This is part of my problem...the spreadsheet says the motor has a good margin but will it be ok on a 70v power supply??

[Voicecoil]

This is part of my problem...the spreadsheet says the motor has a good margin but will it be ok on a 70v power supply??

As long as you set the current limit on the drivers correctly, it didn't ought to be a problem. OK the current will rise quicker, but the peak current should be the same as it would be with a lower voltage, it'll just happen quicker.

[m_c]

As long as you set the current limit on the drivers correctly, it didn't ought to be a problem. OK the current will rise quicker, but the peak current should be the same as it would be with a lower voltage, it'll just happen quicker.

The big issue is as the motor spins faster, the back emf increases (emf = Electromotive Force, essentially voltage). Back emf is why you need a higher voltage supply, as in order to over come the emf and 'force' enough current through the windings, you need a higher voltage.
A modern drive only controls current which in turn limits voltage. The voltage over a motor coil, is related to the back emf being produced (higher inductance = higher back emf), with the highest voltage being the maximum supply voltage. As back emf reaches the point at which the supply voltage is unable to fully overcome the back emf, the coil current starts to decrease (and torque, as motor torque is proportional to current)

Now the problem comes when you have too much speed, and too much voltage.
Take the motors in question, with their recommended 57V, and 4.2A current. At a high enough speed to use the full 57V, the motor is using around 240W. Bump that to 70V, and power jumps to 294W, about a 20% jump.
Now can the motor dissipate that much heat?
(not all that power ends up as heat, but steppers are not that efficient)

It's where you've got to judge where you want to compromise.
If you never run the motors that fast, a higher voltage supply is not likely to be an issue.
You could reduce motor heating by reducing the current, but then you loose torque.

Ultimately, the best measure is how quickly the motors heat up in use.
If they get too hot to touch within a couple minutes of running, you've probably already cooked and demagnetised the rotor, and now have a poorly performing paperweight. Rotor overheating is what will kill a stepper motor, and as it's got no direct cooling, you're relying on heat transfer to the motor body to cool it, and that heat transfer is pretty poor.
If however after an hours running, they reach and plateau around 60-80deg C, you've probably got them on their ideal limit.

[Clive S]

Clive, Are you saying the 57v rated Steppers will be fine with the 68V PSU and either of those drivers? I am sure this is what people have used in the past but m_c says the voltage is too high! I'm a little confused now.

I have always used 68 V with no troubles, everybody has their own opinion so you have to make your own mind up.

I saw those drives but was a little unsure....have many people used them? It doesn't look like it has stall detection although I do understand that if the motor has stalled the job will be wrong even with stall detect.

I found them about 2 years ago and have used about 8 of them Dean (Jazzcnc) I think has used more than 12. re the stall detect you are correct they don't have it. But the AM882 and EM806 does have it but if I remember correctly it only kicks in at about 300 rpm.


As m_c has stated go with a parallel setup.

[CharlieRam]

Personally I would go with the 68V p/s with the drives above or https://www.ebay.co.uk/itm/2DM860H-2...frcectupt=true

There are plenty of people using this setup without problems

I was just looking at those drives and tried to search for ones in the european union to avoid any duty but are these fake? it says the max voltage on the drive is only 70v DC!
https://www.ebay.co.uk/itm/Stepper-M...EAAOSwyHxcfEjv

[Clive S]

I was just looking at those drives and tried to search for ones in the european union to avoid any duty but are these fake? it says the max voltage on the drive is only 70v DC!
https://www.ebay.co.uk/itm/Stepper-M...EAAOSwyHxcfEjv

Try this one. https://www.ebay.co.uk/itm/NEW-CNC-2...EAAOSwikJb7QmM