Help - Current For Stepper Motor Driver AM882 - ProTuner

[PaulP]

Good evening all,

I'm using Leadshine's AM882 drivers on 3N.m steppers and am at the point of tuning them all up using Leadshine's ProTuner Software. What I can't understand is the current/phase is stated at 2.1A but can't for the life of me work out if the amp setting in ProTuner is asking me to put in the value per phase or the total value required by both phases combined. I'm running these drivers/steppers at 68v.

I'd be grateful to find out.

This only came to light this evening as it looks like my machine lost some steps somewhere tonight. I've been running the machine without my new dust boot and everything comes out to within 0.05mm but I added my self made dust boot with fairly rigid bristles (rigid compared to a soft paintbrush) to run a program and it definitely caused some loss of position. I suspect the bristles may be causing the issue but at present my drives are set to 2.1A in ProTuner. If it's a lack of amps going to the motors then I can up the amperage but if 2.1A is the correct value to use then I'll have to make a new softer bristle plate for the dust boot. I should mention that I ran the program 4 times, twice with the dust boot on and had geometric errors in the same places then twice without the dust boot both of these were perfect but I was caked in Trespa dust, which I really hate.

Thanks for reading this I really like to know what the score is with this because I can't stand being next to the machine with a hoover hose trying to catch all the dust/chips flying out.


Here's what I mean as an illustration....

[Kitwn]

There has to be something more than just the stiffness of the bristles involved here. Is the frame of the boot catching on something? You'd have noticed that though. Is the boot adding signifficant weight requiring a reduction in acceleration?
I'm fairly confident in saying that currents are always specified per phase where steppers are concerned.

[PaulP]

Cheers for the info Kitwn,

The boot is defo causing the shift, it's repeatedly working fine on this part without it and on other parts without it but with it on it was squashed right down and catching edges, plus if my steppers are 'under amped' by 50% it wouldn't surprise me to fail in the same 2 spots. It'll be easier to re-tune (up the amps) the steppers than it will be to make a new bristle skirt, but only if it's the under-amped issue causing the problem. The boot assembly weighs about 400g so no real weight on the system.

My main concern before looking into the bristle issue is the amps being fed to the steppers. I sense they are too low, it's a dual screw axis on X and a single on the Y both use 5mm pitch screws. Before I changed the "PeakCur(A)" value in ProTuner from 4A to 2A it could do 5mm cuts with a 1/4in 2 fluted cutter, now it struggles and sometimes triggers the stall/estop when doing 3mm passes in Trespa (HPL).

The problem was that the motors were getting almost too hot to touch and I wasn't sure if the PeakCur(A) was too high and would burn the motors out. So I lowered it a while back to 2A but now I noticed some missed steps I'm wondering if it should be set to the 2.1A or the 4.2A.

I get that the currents are always specified per phase on motor specs but what about in ProTuner? Does ProTuner's "PeakCur(A)" refer to the current for each phase or to an individual phase?

Currently I'm set on 2A but am wondering if I should really have set the value in ProTuner to 4.2A, or at least to somewhere closer to 4.2A like 3.8A.

Just for the record I'm running all stepper in series configurations, ie 4 wires.

I'll include some pics of the fusion 360 model for sizing and scale but it's a small 2 part dust boot with about a 4-5mm thick layer of bristles glued into a channel on the underside. The drawings won't show the bristles in situ but it's too cold and late for me to go in and take a pic of the actual dust boot at the minute.

[Neale]

"Almost too hot to touch" is about right for steppers! Particularly if you also use the "half current when stationary" setting, I wouldn't worry too much.

Current sounds low - I think I run my 3Nm steppers at about 3.something amps on the "crank it up until you can't rest your hand on them then wind it back a bit" basis.

Bit worried that you say you are using a series configuration. For best torque, parallel wiring is advised. As long as your PSU can take it (can supply enough current) parallel beats series hands down.

And if you are generating that much drag with the dust shoe, you need to do something about it! I've made mine adjustable by using a series of 1/2" or so plywood plates with small magnets glued in so I can easily adjust height to suit cutter length, etc. I managed to rip the bristle strip off mine recently due to a little accident and as a quick fix staple-gunned overlapping strips of plastic from an old milk bottle round the edge. Crude but effective! Strips are probably around 1.5" long to give flexibility when going over edges of work and so on.

[Clive S]

I'm using Leadshine's AM882 drivers on 3N.m steppers and am at the point of tuning them all up using Leadshine's ProTuner Software. What I can't understand is the current/phase is stated at 2.1A but can't for the life of me work out if the amp setting in ProTuner is asking me to put in the value per phase or the total value required by both phases combined. I'm running these drivers/steppers at 68v.

Like Neal has said if they are 8 wire steppers then I would use them in a parallel configuration as you will get more torque.
I run AM882 drive on my router at 3. something A with twin screws and 68V PS. Steppers are happy at 60'C and above.

[JAZZCNC]

Just for the record I'm running all stepper in series configurations, ie 4 wires.

Ok, this bit is a little confusing.? Are you saying the motors only have 4 wires or it's got 8 wires and your only using 4 of them.?

If it's an 8 wire motor then you have it wired wrong which would explain all your problems, in fact, if I'm correct then I'm surprised it even works.

For series or parallel, you still use all 8 wires but connected in a different order. If it's a 4 wire motor then you don't have the option to wire parallel or series because that is already determined by the factory.
Often 4 wire motors are series-wound but you can get them parallel wound but would need to ask the manufacturer to know for sure.

The problem with Series wound motors is that you need twice the amount of volts to get the same speed/torque as a parallel wound motor. For a Mill, series-wound is a good choice because higher torque is produced at lower RPM but it quickly drops away as the RPM rise which isn't good for a router. So if you do have series-wound motors then it's highly likely you don't have enough volts which is why torque is dropping away as the RPM's rise and your getting missed steps

Like Neale says the best way to wire the coils for a router is in parallel. then you would set the current to 4.2a in protune. When setting current always use the peak value.

Whta voltage are you running and what velocity and Acc do you have them tuned at.?

[PaulP]

OK lots of food for thought given here, thanks in advance for this help...

"Almost too hot to touch" is about right for steppers! Particularly if you also use the "half current when stationary" setting, I wouldn't worry too much.
Current sounds low - I think I run my 3Nm steppers at about 3.something amps on the "crank it up until you can't rest your hand on them then wind it back a bit" basis.

Originally they were set to 4A in ProTuner but I could have fried eggs on them as they were almost too hot to touch. I started to worry a bit which is why I reduced the PeakCur to 2A. At 2A they don't get hot which I thought was better but I now think that might be wrong.

Bit worried that you say you are using a series configuration. For best torque, parallel wiring is advised. As long as your PSU can take it (can supply enough current) parallel beats series hands down.

I've been debating whether or not to switch to parallel as it seems to be what everyone is doing with their routers. I got lazy doing the electronics as I started to get fed up so ended up setting each motor in series. I was mistaken at the time because for some reason I imagined all 8 wires on the motor had to go all the way back to the driver, ie using an 8 core 1.5mm2 cy cable. Each of my motors has a plug with 4 connections going to their respective A+A-/B+B- socket coming from the driver. To go parallel I assume I solder the respective 'spare' wires together on the motor plug. Is that correct?

As for the PSU it's a Leadshine 68v 500W linear PSU from Zapp. Since my machine has 4 motors in total if I changed the wiring to parallel would I need another PSU as I thought 500w/68v = 7.35A and if 2 motors in parallel are set to 3.5A each then my single PSU stated above would only be supplying enough for 2 motors. I'll get another 68v 500w PSU if needs be but wanted to check before shelling out again.

And if you are generating that much drag with the dust shoe, you need to do something about it! I've made mine adjustable by using a series of 1/2" or so plywood plates with small magnets glued in so I can easily adjust height to suit cutter length, etc. I managed to rip the bristle strip off mine recently due to a little accident and as a quick fix staple-gunned overlapping strips of plastic from an old milk bottle round the edge. Crude but effective! Strips are probably around 1.5" long to give flexibility when going over edges of work and so on.

I like that milk bottle idea for skirting it defo beats the tedium of gluing bristles into a channel. I did see that video on youtube of some german chap making one but he used a small metal tube squashed at one end to help with the fiddlyness of the bristles. Similarly to the milk bottle idea I was thinking of drawing up and printing some strips on the 3d printer. Maybe 2 layers of 0.2mm with a rim with holes for securing it.

Like Neal has said if they are 8 wire steppers then I would use them in a parallel configuration as you will get more torque.
I run AM882 drive on my router at 3. something A with twin screws and 68V PS. Steppers are happy at 60'C and above.

Would you recommend another 68v 500w supply for this setup?

Ok, this bit is a little confusing.? Are you saying the motors only have 4 wires or it's got 8 wires and your only using 4 of them.?

The motors have 8 wires but only 4 are in use, the other wires are soldered together in their respective pairs. I'll include a sketch but i think the A+A-/B+B- polarities in the sketch might be different as I can't see the motors at the minute.

If it's an 8 wire motor then you have it wired wrong which would explain all your problems, in fact, if I'm correct then I'm surprised it even works.

They do work but when I fire up their linear power supply you can hear a very slight whistling sound, it's high pitch and really annoying to be honest, when they drivers get the ENA high signal they switch off and go quiet. These motors were bought from zapp some years ago but I can't find them on zapp now so am unable to confirm the drawing is defo for this motor. The motors are labelled as SYS80STH86 - 3008BF. Do you hear any sounds from your AM882 powered motors when they are idle?

Here's the motor pic and what I think is the closest match to the spec sheet for them, the colours are in Hungarian but i translated them manually and they were the same colours. You can see in the pic that the white/coloured wires are paired together to get what you see in the sketch of the wiring.

Like Neale says the best way to wire the coils for a router is in parallel. then you would set the current to 4.2a in protune. When setting current always use the peak value.

So does the PeakCur box in ProTuner refer to the total amperage the driver supplies to each coil or to the motor? If a spec sheet says 2.5A or 4.0A per phase do I double that figure in ProTuner's PeakCur box? This is what I find hard to understand, If Leadshine stated that the figure was for each phase or if it was for each motor in total it would make it much less confusing.

What voltage are you running and what velocity and Acc do you have them tuned at.?

I'm running 4x AM882 drivers with a 68v/500W PSU (Leadshine) to 4x SYS80STH86 - 3008BF currently wired in series. As for vel/acc I'm running OK at 6000mm/min with 1200mm/s2 without stalling.


Thanks again chaps, I can see my soldering station coming out again soon but before I do that will I need another 68v linear power supply to deal with the extra amps required for parallel? I read many posts from those that went from series to parallel and have had better results but it was either laziness or amperage concerns that pointed me to wire them in series.

[Clive S]

Quote Originally Posted by Clive S View Post
Like Neal has said if they are 8 wire steppers then I would use them in a parallel configuration as you will get more torque.
I run AM882 drive on my router at 3. something A with twin screws and 68V PS. Steppers are happy at 60'C and above.

Would you recommend another 68v 500w supply for this setup?

I only have a 500Va toroidal running 68v DC with no problems

[PaulP]

I only have a 500Va toroidal running 68v DC with no problems

Is that PSU of yours running 4 off 3nm stepper motors from that or 3.

Just to confirm when I read 500VA does that mean theoretically it's capable of delivering 500v at 1A and conversely 1V with 500A? So if a 500va psu is set to output 68v then it can deliver (500/68) 7.35A? I know it's quite a generic question but it half confused me back in the days of education.

[Neale]

I only have a 500Va toroidal running 68v DC with no problems

Ditto - although the transformer did go pop one day! But that seems to have been some random internal short as before that time it never even got warm. Those current figures are, to be honest, a bit vague. They don't really correspond with anything very much and in practice the load the drivers and motors put on the power supply is much less than your sums suggest. Hence my comments about motor temperature - for most practical purposes it's as good a guide as any! If you can hold the motor in your hand without it being too hot, then it's no more than 60C and that's fine for a stepper. It's what they do!

Your current/voltage sums are correct - power = volts x amps - but in this case, because the loads are pulses, of varying levels, and don't happen at the same time on all motors, then the average is lower than the sums suggest. In addition, using a linear PSU is a great idea as it is able to cope with short duration peak pulse overloads with ease, as long as the average load stays within spec. Translation - you can safely get away with it! Switch-mode supplies are cheaper, smaller, and lighter but do not like even very short duration overloads and go rapidly into sulk mode.

In your wiring diagram, connect A to C, -A to -C (can't replicate the exact terms in your diagram but I'm sure you can see what I mean), and then A/C to A+ on the driver, -A/-C to A- on the driver. Ditto for B&D. I think you know that you only then need four wires back to the driver.

I did have a strip of draught excluder brush with long bristles for my dust shoe but it was a pain to make - getting the groove right was tricky with the balance between too tight/too loose and bending the strip to fit was just a bit fiddly. My cheap and cheerful solution works at least as well and costs nowt into the bargain! That's an engineering solution...