Who has a PM-932V? Couple questions

[Ischgl99]

Another option that could work is to mount a small junction box at the machine that just has wiring terminal blocks for all the machine controls and then run a cable to the larger panel with the VFD that you mount in a convenient place further away. The motor wires would be run in a flexible conduit from your VFD panel directly to the motor. I have my lathe set up that way, I removed the panel on the back of the lathe since it was placed up against a wall and mounted a small junction box on the side of the stand for all the controls that then is wired into my VFD panel that is mounted about 6 feet away from the machine.

The VFD cabinet needs to be a minimum size for cooling air flow of the VFD. If you look in VFD manuals, they give minimum distances away from the walls in all directions. Machine tools are used intermittently, so unless you live in a hot area, you shouldn't need a cooling fan in the enclosure for one small VFD. I have a metal 24x24 enclosure with my mill and lathe VFDs as well as a 24v power supply and have never had a heating issue, but my shop is in the basement and never gets above 70F.

 

[arty1]

15" wide, 21.5" tall and 8.5" deep with the handle adding 1.5" for total depth/clearance of 10". Please remember mine is a PM940V wich over all is a bigger machine; but, I cannot see the box varying to much.

Thanks for taking those dimensions. Yeah, comparing photos from PM website it appears the two boxes are very similar, if not identical.

 

[arty1]

Another option that could work is to mount a small junction box at the machine that just has wiring terminal blocks for all the machine controls and then run a cable to the larger panel with the VFD that you mount in a convenient place further away. The motor wires would be run in a flexible conduit from your VFD panel directly to the motor. I have my lathe set up that way, I removed the panel on the back of the lathe since it was placed up against a wall and mounted a small junction box on the side of the stand for all the controls that then is wired into my VFD panel that is mounted about 6 feet away from the machine.

The VFD cabinet needs to be a minimum size for cooling air flow of the VFD. If you look in VFD manuals, they give minimum distances away from the walls in all directions. Machine tools are used intermittently, so unless you live in a hot area, you shouldn't need a cooling fan in the enclosure for one small VFD. I have a metal 24x24 enclosure with my mill and lathe VFDs as well as a 24v power supply and have never had a heating issue, but my shop is in the basement and never gets above 70F.

Yet another great option. I do have some unused wall space near the machine where the box could go. For some reason I was stuck on trying to keep the box attached to the machine.

I think I'm gonna go forward the purchase, including the cast stand, and if I can't fit the enclosure next to the stand I can always mount it on the wall somewhere or even on the side of the column.

 

[Ischgl99]

Yet another great option. I do have some unused wall space near the machine where the box could go. For some reason I was stuck on trying to keep the box attached to the machine.

I think I'm gonna go forward the purchase, including the cast stand, and if I can't fit the enclosure next to the stand I can always mount it on the wall somewhere or even on the side of the column.

A lot of the cabinets get installed on the machine so that it is easy for the factory to wire and ship, but are rarely in a good position in actual use. I don’t need to get into my control panel often, but when I do, I’m glad it’s in an easy to access spot.

Another benefit of a panel separate from your machine is you can power all your machines through one panel and share some components. The downside is if you sell it, then you need to separate the panel. I have the VFDs for my mill and lathe in the same panel, so only need one power source, and things like a 24v power supply can be shared between both machines. I only run one machine at a time, so this setup is easy to do. If you had a CNC running and a manual machine you might use while it is running its program, it would be a bit more complicated since you would need to take into account the total power usage, but it can be a nice space saving move.

 

[graham-xrf]

URL to Photo of my machine below. Box mounted on the side and the stand is on casters. However, after I get it where I want it I block it off the casters for stability. I can put in on the casters and wheel it out for working on the back if need be. I also put down thin bath shower rubber under it to keep the oil off the concrete.

https://www.hobby-machinist.com/attachments/pm940m-cnc-front-i520-jpg.274812/


I should have put stand offs between the box and the column so that the doors cleared better. After I did mine I suggested this to @ptrotter and he did so. He did his own CNC conversion and so his box was smaller than mine from the factory.

The cables on many of the machines come in a plastic flex type cable wrap and this is what I am talking about. Mine are metric. I swapped some of my cables around and made them work out, but the one that goes to the stepper motor at the end of the x-axis is a stretch. I also had to drill some holes in the top and bottom of the box for the cable exits to be closer to their final destination. The cable wrap stops at the box surface strain relief so you can have plenty of individual wire length inside the box.

Most VFDs have heat sinks built on the back of them and these bolt to the box. In my pm940M case there was a large heavy steel plate which all components were mounted to. So the heat sink was attached to it and this would spread the heat out over large distances quickly.

Dave L.

Now that I see the picture of electronics cabinet, I have to say that, regardless of even the most conservative multi-nod to "thermal management", that one is truly OTT ! The steel backplate inside is surely capable of huge dissipation..
.. but caution..
If all it has is stagnant air in there getting ever hotter, the heatsinks will be well above that (remembering the constant °C/Watt). The junction temperature of the semiconductors is more above that yet. Some simple grille and vent holes, bottom and top, lets it all work.

 

[verbotenwhisky]

Now that I see the picture of electronics cabinet, I have to say that, regardless of even the most conservative multi-nod to "thermal management", that one is truly OTT ! The steel backplate inside is surely capable of huge dissipation..
.. but caution..
If all it has is stagnant air in there getting ever hotter, the heatsinks will be well above that (remembering the constant °C/Watt). The junction temperature of the semiconductors is more above that yet. Some simple grille and vent holes, bottom and top, lets it all work.

I noted that my VFD has a small fan in it to blow across the heat sink, I think there is likely enough air in the box for it to be okay; but now that you mentioned it I will, out of curiosity put a thermometer in it....

 

[arty1]

I went ahead and placed an order for the PM-932V...latest delivery estimate is in April, and that's just an estimate. If I'm still waiting by then I can get my deposit back. Doesn't really matter since I don't know what other new machine I'd order, unless they had another similar sized model in stock. China is going through another big COVID outbreak...hopefully the town in China where the factory is located isn't affected too much.

 

[B2]

@arty1

I'm about to place an order for a PM-932V.

Sorry I am a bit late with this response. I typed it up and then forgot to sent it. Anyway, for what it is worth...

I meant to mention that my PM940M CNC is not a great machine. I did not know enough about these machines when I started out. I have been working on mine, .... trying to understand and correct its limitations, ever since I got it. It is a manufacturing quality issue. It appears that some 940 machines maybe made better than others (mine) ..... So.... If you can afford it I would pick one out that is made in Taiwan rather than China... even if it is a smaller machine. From all that I read it seems that, in general, the Taiwan machines are much better made. Even PM acknowledges this by always mentioning that a machine is made in Taiwan. For example, look at the write up on the PM 833 or the PM728.

Dave L.

 

[B2]

I think the 2HP Delta VFD that came in my mill has a fan that blows across the heat sink. I put an Hitachi 3HP VFD in my PM1440GT lathe when making the VFD conversion... and I know it has a fan mounted to the heat sink.... in fact it is physically reversible as I took mine off and turned it over so that it was blowing rather than sucking the air through the heat sink. This way the air also blows across my home made braking resistors. As far as heating up is concerned, I have found in my lathe conversion that the electronics enclosure (cavity in the back of the lathe stand) does not get very warm as long as there is an air convection path, nevertheless I went ahead and mounted a fan to the plexiglass to ventilate the cavity. From what I have read about VFDs their life time is commonly limited by the life of the high voltage capacitors and these will last longer if they are kept cool. So why not blow a little air around the VFD? You can see a photo of the VFD in the back of the stand on my PM1440GT. I replaced the steel cover with a 1/4" plexiglass cover so that I could see in without unscrewing the cover plate. I also offset (black frame) the plexiglass cover a bit ~1" and left an opening at the bottom to let air in and then added the surface mount fan on the plexiglass to pull air out of the cavity. You can see pictures at the following posting.

VFD conversion using solid state electronic components.

Dave L.

 

[arty1]

Hi Dave, sorry to hear you're having issues with your 940M CNC. Yeah I'm fully aware of the Taiwan vs China quality differences. For what I'm doing and have planned a good Chinese machine should fit my needs...knock on wood.