will this shield be ok for these stepper motors please?

Hi, seeking advice before purchasing parts for a home build cnc router...

Will this shield be ok (not burn out if stepper motor is under maximum torque, during a cnc cut)
Adafruit Synthetos gShield
(grblShield) V5
2.5 Amps per winding

planned stepper motors (3) for X,Y,Z axis so X and Y could be moving at once
Nema 23 stepper motors Rated Current/phase 2.8A

It seems not when simply comparing 2.5A and 2.8A but some are somehow using them and I am keen to have as much torque available with this range of stepper motors.

I could be misreading the specs or not understanding the basics of loads and drawing amps...

All help appreciated !

Thanks of reading this far.
Brian.

You need to post a link to the datasheet for the shield. If it is what I think then it probably uses A4988 or DRV8825 stepper drivers and they are not at all sufficient for a 2.5amp motor.

You should get a stepper driver that can provide about 50% more current than the motor requires. Those drivers will be much too big to plug into a shield but you probably could connect them to the shield using wires.

...R
Stepper Motor Basics
Simple Stepper Code

thanks for the reply.

can't find a data sheet but found this info:
Synthetos gShield (grblShield) V5 (mod edit)
3x Robust TI DRV8818 Stepper Drivers

From a quick read of the datasheet that driver is a bit more powerful than the DRV8825 - it says "Up to 2.5-A Current Per Winding". I have no experience of the device but speaking personally I would want a driver that could provide 3.5amps or more - especially for the 2.8 amp motor. It is not a good idea to operate electronic components at their limit.

...R

Thank you Robin2.

The term 2.5a per winding is a new one for me. (guess I will find out what it means to overall amps drawn when I hold the item, once purchased, and ran under load...)

I get your reasoning about not working at the limit of any equipment.

It throws up another general electrics Q... is there such a device that can trip out the circuit if an amp overload is spotted?

Most drivers have a thermal overload cut out.
However it is still possible to burn them out.

My preference here is the cheaper chinese shields.
Replacement of a driver is exceptionally easy.
The shield will run (here at least) 36 volts with zero issues.
You can change the microstepping with jumpers.
You can set the Amps range to suit motors better.
You can get a larger variety of drivers.

In most cases I would suggest adding heat sinks to the drivers with a small fan running air across for a couple of reasons.
A. It will help the drivers live longer.
B. You can run the amps a little closer to the limit.

Polou has a good breakdown of motor drivers

BrianPollard:
The term 2.5a per winding is a new one for me.

It shouldn't be.

You already mentioned 2.5amps and 2.8amps in your Original Post - they all refer to the same thing.

...R

thanks for the info Bob.

I like this shield because it has grbl and drivers built in and as a beginner it all helps!
I see the drawback to having drivers built in and any damage means replacing all the board...
Guess I will just give it a go...

Here's my CNC router build:

Robin2, - it was the 'per winding...' that confused me.

The thing is that shield does NOT have GRBL built in.
GRBL resides on the UNO that you will be mounting the shield on.

BTW Dremels are ok as a starter spindle but I would not use it for serious work.
Oh and get some spare brushes for it as they chew them up more than a decent spindle.

Good choice going with ballscrews.
Just about to order a new machine (pending wife’s approval LOL) and will be moving to ballscrews.

I would still consider adding heatsinks and a fan to the drivers as a matter of importance especially if it is your first CNC to aid the longevity of the drivers.

The close tolerance of movement with ballscrews comes with a slight (but consistent) increase in resistance for the motors.
Which is one reason why many use NEMA 23’s as a starting point for some of the CNC machines.

BTW sounds like a Yorkshire accent in the video ?

Thanks for the info and help bob!

Will take onboard your advice re: heatsinks etc.

re: accent… My town used to be ‘in’ Yorkshire, before boundary changes so yes, well spotted!

(I mocked up a larger router last night, just to plan for any future needs)

Brian.

2.8A is beyond the scope of single-chip stepper drivers. 1.7A is about the practical limit. Some drivers with massive heatsinks claim upto 3A handling, but they are large and power-hungry. For high current steppers you would normally use industrial units with discrete MOSFET output stages, devices like the Gecko drives are at the cheaper end of the market for such units.

Note that as dissipation in motor drivers rises with current-squared, the difference between 2.8A and 1.7A is much more than you might think - about a factor of 3 in heat dissipation in fact. Single chip drivers are forced to use integrated DMOS output FETs, which are 0.25 ohms or so.

A motor driver using discrete MOSFETs can achieve down 0.002 ohms or even less, vastly increasing the current handling over single-chip drivers.

thank you MarkT, too late tho' as parts ordered...
Guess I will be less hasty in future but for now I will just enjoy the 'testbed for my lack of knowhow'...

When you build your own CNC there are some details in this thread you may also want to take into account.

Neither of us are "exxspurts" but I think we covered a lot of basic groundwork.

Re-Accent ... Now live in BFN Canada for the last 18 yrs, but born and bred in West York's.

cheers Bob!