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lockyg
22-01-2016, 05:40 PM
Hi all,

I have a manufacturer built 8*4 plasma table. It recently blew a stepper driver, so I took the lid off the control box to get details and source a replacement.

Both the motors and the drivers have the table manufacturer`s label on them so it is difficult to see exactly what make they are, however details from them are as follows:

Motors: 4* Nema 23, 80mm long, 4.2A, 4 wire
Drivers: 4* 1.5A which look very similar to 2M415s
PSU: 24V, 6.7A

I have replaced the dead drive with a Leadshine DM422C (set at 1.6A) and all is well again. In fact the motor is now silent, instead of the whine it used to make.

The question is, are these original drivers a bit underpowerd for the motors and the table size (The gantry is aluminium, so low mass), or am I missing something? - I have experienced missed steps from time to time. Should I be looking at swapping them out for M542s and a new 24v PSU around the 16A mark?

The table is designed to be interchangeable to a router, but I cant help but think it would just miss steps with the additional load.

Thanks in advance for your help

Clive S
22-01-2016, 07:54 PM
Some pictures of the setup would help. 24V seems very low for nema 23 motors I see that the DCM422 is only rated to 36V. AM882 I think would a better bet and run them at about 68V but I am sure JAZCNC will chime in with some sense.

Missing steps will probably be caused by the low supply.

dodgygeeza
22-01-2016, 08:50 PM
The drivers are not ideal for the motors, and using a driver with higher current and voltage range will be an improvement, but also change the power supply for a higher voltage.
The EM806 is a good choice, with a 60-70V DC power supply.

JAZZCNC
23-01-2016, 04:56 PM
I am sure JAZCNC will chime in with some sense.

You'll not get much sense out of me. . . . But I'll chime in all the same.!!

Like been said and you probably know your setup is all wrong. Now without knowing the rest of the machine setup, ie: Gantry size Mass, linear motion setup etc then it's difficult to be exact on what to recommend but a good all round setup for Medium Mass machines is this below.

EM806 or AM882 Drives with 60-70Vdc Like Dodgygeeza suggests are great. Now with your motors being 4 wire then I suspect they will be high inductance and probably series Wound. This will restrict the Torque and speed you'll get at higher feeds. It's also be why you are getting stalling motors with only 24Vdc.
Series wound motors provide more torque at low speeds but quickly run out as the speed rises so require very high voltage to get any usable speed from them.
For this reason on machines like Plasma or routers where often cutting or traveling at higher feeds you'll want motors wired parallel which gives more torque higher up the speed curve.
So I suggest you change the Motors has well for Low inductance 8 wire motors that can be wired in parallel.

EM/AM drives with 65-70Vdc with 4Nm Nema 23 parallel wound motors give a good setup for meduim sized machine. Again this does however need to balanced against the Linear motoion set up and Mass etc which will need to be considered before deciding on exactly what is best.

One thing is clear thou what you have now isn't very good.!

lockyg
01-02-2016, 02:29 PM
Thanks all for your above replies, particularly JAZCNC - I love the last line, covers it all in a nutshell!

For now, I have just reduced the rapid speed between cuts, but I intend to retrofit the ctl box when I get a chance. Bearing in mind new PSU, and drivers, I may as well get a new breakout board too and simply build an entire new ctl box which I can swap in when ready. That then gives me a spare (old one) to swap in in emergency.

I will consider the new motors, but will that not involve rewiring the whole machine for the 8 wire setup? (not a big problem, but more downtime and then reduced compatibility with the old "spare" ctl box).

General linear motion setup on X and Y axis is a stationary length of (approx 10mm) timing belt down the axis with a pair of idler pullys around the motor to give the drive gear a good wrap around (180 degrees). Drive gear is approx 30mm diameter - I dont have the tooth counts to hand at the moment. Z axis is simply a leadscrew - again dont have the pitch to hand at the moment.

Its a shame the manufacturer has underspeced the ctl box, cos the actual table is built like the proverbial brick outhouse......

JAZZCNC
01-02-2016, 02:46 PM
I will consider the new motors, but will that not involve rewiring the whole machine for the 8 wire setup? (not a big problem, but more downtime and then reduced compatibility with the old "spare" ctl box).

No still only needs 4 wires. Motors are 8 wires but phases are wired so only use 4 wires.

Clive S
01-02-2016, 02:46 PM
I will consider the new motors, but will that not involve rewiring the whole machine for the 8 wire setup? (not a big problem, but more downtime and then reduced compatibility with the old "spare" ctl box). The eight wire motors will be joined up making 4 wires at the motor so no prob with the wiring being changed.

edit Dean as usual beat me to it:onthego:

lockyg
01-02-2016, 03:25 PM
Ok, thanks - makes sense. Come to think of it, I have a pair of these 8 wire motors in the cupboard from way back when I was intending on building my own machine, before I bought what I currently have. Just need two more on the shopping list!

lockyg
10-02-2016, 12:25 AM
Any suggestions for a decent off the shelf 60 or 70vdc supply?

Clive S
10-02-2016, 08:30 AM
Any suggestions for a decent off the shelf 60 or 70vdc supply?

If you don't want to build one yourself then you won't go far wrong with this. http://zappautomation.clickforward.com/electrical-products/power-supplies-43/ps806-12-linear-power-supply.html