View Full Version : PRTAlpha Control Box Heat

01-11-2005, 08:47 PM
Very excited and happy with my Alpha upgrade. Just got it up and running today and am very pleased...
But when I shut it down I noticed the control box was warm. I realize the box itself is used as a heat sink, but I didn't expect to feel the heat, it's in the low 50'sF in my shop these days so maybe that's why I noticed the warmth. Has anyone else noticed the new control box being warm? Am I worring for not?

01-11-2005, 09:00 PM
Mine too... I assume it's normal.

01-11-2005, 09:07 PM
Warm is totaly normal.In fact some may consider it hot.

01-12-2005, 02:19 PM
Thanks guys, I feel better. I've got enough to worry about and now there's one less!

01-13-2005, 01:07 PM
Why do they not come stoakc with a fan? Would it be better with one?

01-13-2005, 01:07 PM

01-13-2005, 02:15 PM


01-13-2005, 02:15 PM
Paco just gave the short answer.

Here is the long.

In some electrical apllications heat can be dissapated simply with a heat sink. This is the case with the Shopbot control box.The large metel box is the heat sink. They choose this method because they wanted to keep out the dust. A fan would'nt last a year with all the dust it would recieve in this application.

01-13-2005, 02:20 PM
... neither keyboards!!

01-13-2005, 03:21 PM
I don't know the Alpha at all, but have been involved with cooling "airtight" boxes. Often there is a fan inside the box to get the heat away from hot spots and move it to the outer skin surface area. The (turbulent) movement of air inside the the box is much better than static air.

Anyway, the judgement of "hot" is too subjective - use a domestic min/max hold thermometer and measure the temps to see if they exceed the limits given by the electronics suppliers.

The box must also be kept clean of sawdust and clutter which acts as a blanket and keeps it warm.

01-13-2005, 03:47 PM
That makes sense. What about creating air flow over the exterior of the box as well or instead?

01-13-2005, 04:38 PM
As Gerold says, hot is much too subjective. Quality electronics will perform to specifications so long as operating temperatures are within the specified maximum and minimum.

However operating at any elevated temperature will degrade life expectancy. Typiclly a 10 degree C temperature rise will reduce life by 50 percent. We test electronics at 80C for months to see if a design is likely to survive several years in the field.

Mix humidity or (worse yet) condensed moisture with dust from a more acidic wood. Add a voltage difference and you have a condition that can destroy a circuit board in a few days. Shopbot has both heat and dust to contend with, and has probably designed a good compromise. If operating in a hot environment, airflow directed on the box could be worthwhile. My box is elevated on two lengths of 2x4 (what's the metric equivalent?) to allow natural airflow to the bottom surface.

01-14-2005, 03:46 AM
I have 25 years experience with industrial electronics. The control box is well within normal operating temps. If you are still worried, go to a local electronics shop and buy a large heat sink, install it on the back of the box with a good heat conducting compound and call it good.

01-14-2005, 12:38 PM
I would think though that maybe a 2 fan configuration, one behind the other with maybe a reed system. That way nothing can come in and everything would only blow out, and maybe even blowing down

07-28-2005, 04:38 AM
I have an Alpha with two Z's, a spindle and drill head.

Have had the occasional connection problems and a couple of erratic z moves....all of which I intend to chase down using advice from the forum.

Yesterday I ran the rosette 3d file from project wizard, and it was the longest running file to date, at around 3hrs.(nice result).

After the first hour the control box tripped out (driver fault location) and resetting the box and using resume continued the cut, progressivly more frequent trips led to the reset not working untill waiting around a minute, and after hearing a small click from the box, I could reset and resume.
During this phase I turned off dust collection, grounded bits of the system, moved cables...all the usual interference tricks....no change. After the second hour realised that the control box was too hot to touch with the palm of hand for more than a couple of seconds.

Put a free standing fan pointed at the back of the control box (which is bolted to the end of the table and has free flow of air around). From here on the rest of the cut, another hour, went without fault. My workshop airtemp then was 28C.

Seems fairly clear that with an extra Z driver and highish ambient temps the control box needs extra cooling....

Be interesting to see if other control box issues would resolve with a cooler running box...


07-28-2005, 10:42 AM
Hummm... sound interesting...

ron brown
07-28-2005, 10:46 AM
Lowering the control box temperatures couldn't hurt. Eelctronics and heat are not normally friends.


07-28-2005, 12:07 PM
Kiawa Has the best idea if you think you need extra cooling. None invasive and if you like use a fan to move some extra air over the heat sink. Large heat sinks are not that hard to find in my backyard. Warm / Hot is a relative thing too warm for you is not always too warm for what you have your hand on.

07-28-2005, 12:34 PM
Well now this conversation has me thinking. I will be going down to Durham next week for training and to pick up my new Alpha. This is something I am going to look into. I have 40 years of working with electronics in the industrial and RF communications field and having never had the chance to look inside of a Alpha control box I am sure I will.

07-28-2005, 01:26 PM
Gerald's idea about having a small fan INSIDE the box to keep the air moving inside the 'air tight' case seems to be a good idea. When I installed my spindle earier this month, the shop temperature was 104-106 F. (I don't use the customary desert 'swamp' cooler around wood.) Even with two large fans blowing on the box from the outside, having a fan circulating the air on the inside of the box would probably keep the components at a more uniform temperature.

07-28-2005, 01:29 PM
Welcome Gus,

It looks like we are of the same vintage, and have similar experience. I'm now in the Southern Minnesota area, and have worked in RF communications since 1962. Hope to meet you when we get a nearby camp.

What are you planning for your Alpha?


07-28-2005, 03:28 PM
Anything for a buck.

You have mail.

07-28-2005, 05:29 PM
On the subject of heat.

I have grounded everything I could find Including the usb cable and Run wires thru the dust extractor and re-grounded the spindle etc.. and still I get the limit switch indicator activating.

I get the fault when I am cutting or using the probe and not using the dust extractor, vacuum hold down and have no power to the vfd.

When the fault starts after about 3 hours of constant use it occurs every minute or so and gradually increases so that the fault occurs every 2 seconds.

As soon as the above happens I open the control box door which is very hot and run the machine with the control box door open and the limit switch fault stops immediately and does not repeat.

I still love the machine.

Comments appreciated.

07-28-2005, 05:39 PM
Sounds like the same problem..heat.

I have also mailed shopbot with the problem, maybe you should do the same so they can build a file on heat problems and modify new boxes suitably...saving owners wasted time and effort.

I still love my machine too!


08-13-2005, 11:29 AM
Just to close the loop....had a mail from Gordon at shopbot who said that after much heat testing they had modified the control box to include a heat sink, which they offer as a retrofit to any earlier boxes sold without it.

Looking forward to getting and fitting mine, as the noise of my cooling fan annoys me (and costs money).

Any Alpha owners without heat sinks on the outside of the box should chase shopbot for the kit.


Aaron Shaad (Unregistered Guest)
08-23-2005, 10:35 AM
We run the PRTAlpha to cut aluminun, .063 &.100, and the control box frequently gets too hot to touch. I am here in Kansas and the humidity is high here in the shop around midafternoon. My solution was to open up the control box and let a fan blow on it for only a minute or two and we are back up and running. A fan blowing on the outside of the box keeps it cool enoughto work for most of the day except on hot hot hot days. I am going to install a small fan inside the box and drill small holes in the the skin to draw air thru and out with the fan. We don't have the big dust problem because we only cut aluminum. I will let everyone know how this works.

Brady Watson
08-23-2005, 04:33 PM
Earlier Shopbots had flow-thru cooling, but this ended with the Alpha series. The box can get pretty hot, but it is designed for this and the very expensive stepper drivers (price them out lately?) NEED to be shielded from ANY dust, including AL.

The proper way to add additional cooling to the Alpha control box is to add a heatsink, if not already equipped. If you still think things are too hot, then add the cooling fan OUTSIDE the box so that it blows on the heatsink.


08-23-2005, 08:20 PM
I agree with Brady that there should be no 'flow through' air flow; however, as Gerald D pointed out, having a fan inside the box to circulate the air (with no vent to the outside) will reduce hot spots inside the control box.

08-23-2005, 11:26 PM

Have you installed the heat sink kit yet? If possible, please post a picture.

08-24-2005, 10:35 AM
I have done little box cooling, but have a lot of experience cooling RF power transistors.
If the heat concentration is local to a specific area inside the box, stirring the internal air with unvented fan, as Gerald suggested, can help considerably. SB probably has thermal compound under the hottest parts, which will help if properly applied in a very thin coat to increase surface area contact. Thick applications make heating worse, by increasing thermal resistance. In my industry we often have difficulty training assemblers to apply thermal compound correctly.
Internal hot spots can also be reduced by mounting heat generating assemblies on a heat spreader plate of lower thermal resistance in intimate contact with the aluminum box. Brass or copper work well. (Probably not something an owner should try)
A light sanding of the control box outside can drop temperature a few degrees by slightly increasing surface area.
And some of you might try convincing the boss that cool air inside the building will reduce maintenance cost. Un-manned cellular equipment is cooled for a reason.

08-24-2005, 07:45 PM
If you have one of the earlier versions of the Alpha Shopbot the box will not have additional heat sinking on the outside. The heatsinks that now appear on the control boxes serve two purposes, increase surface area and provide a rigid flat surface for the drivers to mount to on the inside.

I believe (for the early boxes at least) that the swaging of the bolts for mounting the drivers and the bending of the aluminium to create the box itself, has the effect of rippling the aluminium surface the drivers currently mount to. The result is that in some cases the driver only makes contact to the panel at the two mounting studs.

As Jim pointed out, a thick coat of thermal compound to fill the gap does more harm than good.

08-25-2005, 04:54 AM

Kit not arrived yet...will post again when I have it.


08-26-2005, 01:17 AM
Just curious, as I tried fixing mine with a pair of large extruded heat sinks. More for flattening the mounting surface rather than dissipating the heat. The drivers make better surface contact now but I am starting to wonder if I did enough.

09-02-2005, 11:21 AM
If you have compressed air avilable look into exair cabinet coolers. Our cabinet runs at 65 f

09-02-2005, 07:54 PM
Last summer we cooked a contactor due to excessive heat in the control box. The box would get so hot it was impossible to touch the box witout suffering burns.

Shopbot sent us some heat fins to install which we subsequently did however the box was still hot. We also had innumerable driver errors particuarly late in the day when everything was extremely hot.

Last week we modified the heat sinks on the back of the box replacing the shopbot fins with three large aluminium extrusions each about 80mm square we mounted a fan on each end of the extrusion and wired them in two banks. The top fans switch on when the shopbot is turned on and the second bank is operated by a thermal switch. We are still tweaking the temperature at which to turn them on.

We also mounted a 20mm thick aluminiium plate inside the back of the control box and mounted the drivers and the contactors directly to this plate. This provided excellent surface contact to dissapte the heat through the heatsinks more efficiently.

So far the box runs at around 30C even under heavy usage however the real test will come this summer.


09-08-2005, 05:00 PM
I think my control box might have a heat problem. Machining is interupted at increasingly frequent intervals after an hour or so's cutting.

Has anybody tried fitting an internal fan as suggested by Gerald? I thought I might try fitting a computer fan inside the box. I believe these are 12v, does anybody know if there is there a suitable supply available in the box?


09-26-2005, 06:44 PM

Our box also gets very hot and it was interupting the machining as it would stop and have to be reset. What we did was have a fan blow at the front of the box and since have had not the machine stop its been about 3 weeks.

Hope this helps


09-27-2005, 05:12 AM

thanks. It certainly looks like heat is a problem. I've moved my box away from the under table storage rack I'd made, and this seems to have helped so far. I wasn't keen to have a fan blowing outside the box as I imagined it would make the workshop air very dusty.

I would use a fan as you suggest if necessary, but I think my next step will be to fit inside the box a couple of 12v computer fans wired in series, connected to the 24v supply inside the box.


10-09-2005, 06:18 AM
Hi all,

Weve just solved our heat problem by installing 2 computer fans. One drawing air into the box thru a filter and one expelling it from the box.

The limit switch error stopped and also interesting enough the lost port connection problem seems to have been cured at the same time.

It's been a pleasure running the machine without having to stop and open the control box door to let it cool down.

John... I've also purchased and installed the Axminster 6000 (I still haven't had much chance to play with the vcarve wizard yet).

10-09-2005, 04:00 PM
Robert, I hope you've got a good fine filter on that air intake, the control box is sealed for a reason. Otherwise can you duct it from outside?

That's a decent sized extractor you've got, it must suck up everything. I've not had much chance of playing with Vcarve Wizard either, but whereas I can always open dxf file I havn't been able to open eps files at all. Also I've found that RhinoCam does some of the stuff, so might not be purchasing VcW.

10-09-2005, 04:33 PM
Hi John,

We've got a very fine filter.... I made sure of that.... You can feel the cold air going in and very warm air coming out. The control box is alot cooler to touch.

The dust extractor is a great improvement but it is fighting the Vacuum bed which is seriously strong even thru the 6mm mdf. We still follow the cut line around with a shopvac.

I managed to cut yesterday afternoon 25 8x4 6mm ply sheets in just under 2 hours into berlingo van kits as shown on our website. I used to have to pay 8 each for these to be done by our wood supplier.... I Couldn't be happier!!!

ron brown
10-10-2005, 11:32 AM
An automotive intake air-filter makes a good computer or control box intake filter. A "prefilter" will keep the primary filter in near like new condition.