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

Hello All, I'm back again and still haven't finished my machine! Anyway, I'm just looking to purchase the steppers and came across these:-

https://www.ebay.co.uk/itm/Dual-Shaf...QAAOSwHu5b5ADz

They look almost identical spec to the 3.1Nm ones currently on CNC4You that I saw recommended elsewhere, well all apart from the Voltage?
https://www.cnc4you.co.uk/Stepper-Mo...YGH301B-Nema23

It says voltage of 24-48 volts in the spec but my Toroidal power supply should be around 70v when I actually assemble it. Are they a different motor and therefore not suitable?

Cheers,

Charlie

Going by the key spec (current and inductance), they are pretty much identical motors.
However I'd say 70V is too high. The recommended max voltage is 32 * SQRT(L) (L is inductance), which puts the recommended max voltage around 57VDC when running with parallel/unipolar wiring.

A higher voltage won't have much effect at lower speeds, however if you're running at higher speeds, overheating is likely to become an issue if running at the rated current.

Thanks for the reply, I probably should of said I plan on connecting them in series so the max voltage works out at 114v given the above formula unless there is a reason not to connect in series🤔

Cheers

Charlie

You'll get better performance for any given voltage using parallel.

Inductance is the killer of performance, which is why you normally want steppers with as low an inductance as possible.

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?

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Originally Posted by 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?

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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

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.

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Originally Posted by Clive S

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

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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.

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

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?? Attachment 25523

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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.

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

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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.

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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.

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Originally Posted by 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?? Attachment 25523

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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.

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Originally Posted by Voicecoil

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.

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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.

Thanks for explanation :) it seems I have 3 options then...

1. Risk the 3.1Nm (57v) steppers with the 70v PSU
2. make a lower voltage supply for the 3.1Nm steppers
3. choose the less powerful 1.89Nm stepper which is 81v?

Option 3 seems like a step back to me though so I may try and build the supply and see what voltage I get and decide whether to change out the Toroidal transformer.

Cheers Guys

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Originally Posted by CharlieRam

Thanks for explanation :) it seems I have 3 options then...

1. Risk the 3.1Nm (57v) steppers with the 70v PSU
2. make a lower voltage supply for the 3.1Nm steppers
3. choose the less powerful 1.89Nm stepper which is 81v?

Option 3 seems like a step back to me though so I may try and build the supply and see what voltage I get and decide whether to change out the Toroidal transformer.

Cheers Guys

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Hi charlieRam.

I think what everybody is saying: there is no real risk.
Else they would say:
Dont do it, it is going to fail.
People here will tell you if your going in the wrong direction.

What i am reading between the lines is :

- They key factor is limitting the max current in the stepper driver settings.
- Higher voltage is an advantage to go fast.
- To high voltage can become a problem. -
- You need to check while running at max performance (rpm) for long periods.

I guess you will not be running at max rpm all the time.

Steppers are easily monitored by checking the temperature of the steppers.

Do this while commisioning the setup and learn to know your machine.

For me, motor calcs advised 57 volts. I run 4nm nema23 steppers, i have unregulated 72volts psu.
Until now i run 15% under max current.

I have to check software driver setup to set my drivers at the exact max.


My steppers never get above 40 deg.
My drivers reduce to 50% current at hold conditions

I have no performance issues.

I calculated for 2m/min cutting speed @50N cutting forces.

I have been cutting mdf @ 3m/min.

I am very happy with the guidance i got from here.

Grtz Bert.



Verstuurd vanaf mijn SM-A320FL met Tapatalk

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I think what everybody is saying: there is no real risk.
Else they would say:
Dont do it, it is going to fail.
People here will tell you if your going in the wrong direction.

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Exactly All the machines I have done the motors have never gone above 40C. There is a big difference between theory and practice, too many variables.

Very seldom will the motors draw full current.

Cheers guys 😁

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Originally Posted by Clive S

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

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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

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Originally Posted by CharlieRam

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

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

What's the likelihood I'll get stung on import duties? What kind of cost should I expect to have to pay if I do get stung? ��

It all seems to depend on what shipping method is used. Typically for stuff coming by the big carriers (Fedex, DHL, UPS etc.) it'll be 4 to 5% duty, a handling fee of between £10 and £15 and then 20% VAT on the whole lot.

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Originally Posted by CharlieRam

What's the likelihood I'll get stung on import duties? What kind of cost should I expect to have to pay if I do get stung? ��

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When I have ordered stuff like this in one's or two's very seldom I have paid anything if done with China Post.

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Originally Posted by Clive S

When I have ordered stuff like this in one's or two's very seldom I have paid anything if done with China Post.

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That's my experience too on small orders.

Another warning though for larger orders or when sent via courier: ALWAYS make sure that the vendor includes the shipping cost on the commercial invoice. The nice XinLichuan stepper people forgot to do this on the order I've just recieved, and HMRC took it upon themselves to estimate the freight cost.... at 3x what I'd actually paid = an extra £46 duty & VAT. Thankfully I can claim most of it back on the business, but a private individual would either have to battle it out with HMRC or accept the loss :disturbed: