Home Built CNC

[Jala2]

HI, I have a home built CNC based quite loosely on the Black toe design.

Been using it successfully for a couple of years but recently after upgrading the motors from NEMA 17 to NEMA 23 i have started to have issues.

I would like to team up with someone who may be able to offer help to get me back on track

[JAZZCNC]

What would you like to know.? what are your issues.?

[Jala2]

Hi Jazz,
Since the upgrade to the NEMA 23 motors, I have started to get one of my Axis dropping steps, I think I have traced the problem to lack of power from my Power supply.
When I made the change I did not change the settings on the Drivers, the old NEMA17 motors where 2.5 Amp and the new ones were 2.8Amp so rather than messing with the drivers I left them at 2.5 Amp. I then started to do stuff on the CNC and noticed that the X Axis which is slaved to A was dropping steps. Checked the Tightness of couplings etc. but could not find a fault. Decided, as I had the machine apart, to change Drivers to 2.8Amp. This has now resulted in X & Y Axis dropping steps. Aha I thought not enough power, I only had a 10Amp power supply. I have bought a new 25Amp Power supply and I am now waiting for its delivery tomorrow. Hopefully this ill have resolved this issue. But really, the thing is I'm retired and building this on my own without a contact to bounce problems off and was looking for such a person, someone who would not mind giving some advise when required.

[JAZZCNC]

Ok well, the difference in amps wouldn't really cause any issues and to be honest the increase wouldn't probably either with a 10amp supply. So I've got a few more questions.

What type of PSU were you using and what voltage.? ie: Toridal or linear PSU, regulated or unregulated, and how many motors pulling from them 3 or 4.

How are the motors wired, parallel, or series and what Drives are you using.? If you have the motor datasheet post it.

What Control software and did you re-tune for the new motors.?

One of the main problems could be the motor spec, if it's a cheaper motor then the inductance will most likely be very high meaning you'll require a much higher voltage to get the same speed as the much smaller and lower inductance Nema 17.
If this is the case then I suspect your problem is more lack of volts than Amps and your speed/torque curve is much lower. This is the problem with upgrading, if the system isn't balanced then you can actually make the machine worse, not better.

I'm happy to help and give advice on the forum, or if you prefer I'm also happy to speak on the phone, it's often much easier and quicker to help fix problems so just drop me a PM and I'll send you my numbers.

[Jala2]

Thanks for your reply, I'm new to this Forum business, what's a PM?
The PSU is one bought from Amazon "https://www.amazon.co.uk/gp/product/B01DDX7J68/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1" I have 4 motors X Axis has a slave to A. The motors are wired directly to each TB6600 driver. The Motors are JK57HS56-2804-0, can't see how to paste in data sheet.
I'm using Mach3 and I did not change anything in Motor tuning for the new motors.



I went into advanced and found the add attachment clip

[JAZZCNC]

Ok first of all edit that last post and remove your number before you start getting strange phone calls from Hot breathers in middle of the night...Lol

PM stands for private message. If you click on my name near the union Jack you'll see a pop down box with send Private message option.

Looking at the Motor spec the inductance is low enough at 2.5Mh however I'm 99% sure your problem is the voltage. The larger motors require more volts to get the same speed as the smaller motors and you only have 24Vdc which isn't really enough for Nema 23 motors.
This means because you didn't change the motor tuning in Mach3 you are trying to get the same velocity as the old motors and the new motors can't acheive that speed so they are stalling.
If you lower the velocity in Mach motor tuning your stalling will stop.

However the correct solution is more Volts, Now however your drives become the bottle neck.? The TB6600 have a max voltage rating of 42Vdc but these drives are very flaky so you don't want to be running the voltage any where near this as they could blow up. I wouldn't be running these drives above 36Vdc.

So if you want to keep these drives then I'd up the voltage to 36Vdc. It will give you the speed back and should stop the stalling.

However if you want the best out of the motors then I'd replace the TB based drives with digital drives with minimum of 50Vdc running motors with 42-44Vdc. This will transform the machine. You'll get higher feed rates and much smoother motion.

Now regards the PSU then these are Regulated switch mode supplys and not really advisable for CNC use because of how the motors can send voltage/current back to drives/PSU when de-accelrating. They basiclly become dynamos and instead of using electricty they start creating it. These regulated supplys have built in safety circuits designed to stop this, so when they see it happen they shut down. For CNC you want unregulated PSU.

It will work, but if it starts chutting down for no reason this is why.