Linistepper cooling issues (james, roman, anyone?)

[posix]

Ok guys, I've run linisteppers at 12v all this time and I have never run them for more than, say 30 minutes or thereabouts.

Now I'm trying to run them at 24v and this is getting silly. Both in grin factor and frustration at the same time. Read on to find out why and how.

I have attached a long piece of aluminium L profile (that's otherwise almost too cold to touch) connecting all transistors and this thing is hot to the touch within 10 seconds of power-up. After about 1 or 2 minutes drivers get a cramp and don't respond anymore. Then I have to disconnect everyhing, let it cool off for about 15 minutes or so and then try again, it works but again, only a couple of minutes.

Now, the way this is going I figure I will need a heatsink so big that it would be more expensive than the linisteppers themselves. I'm thinking a few kilos of aluminium would be able to cover it. Don't forget I'm running a 12v fan blowing across all transistors at the same time and it's STILL hot to the touch. The aluminium profile that is, the transistors are hot when I put my finger an inch away from them so I can only imagine the temperatures on these babies.

So, this leads me to my question: is all this heat due to low rating of the TIP122 (BD901 in my case) or something else? Can the TIP122 be swapped out for something else a little less hot? Something beefier? How about a straight-swap for a MOSFET?

I have a set of choppers on my desk and it would be easy for me to just throw linisteppers away and install the choppers but I don't want to even try them untill I've exhausted all avenues with linisteppers. Untill now there was allways a solution so I bet there is one now, too!



BTW to all those newbies out there Linisteppers impressed me as a newbie but then they were starting to show their weakness - they were sloooow. At least I thought it's due to linisteppers. Well, I can report that with 24v and laserjet steppers these things are SCREAMING!!! I'm running them nicely at 20revs/sec (albeit 1 minute at a time, untill I've sorted out my cooling problems) with my very rough machine that hasn't been executed too precisely or adjusted properly. Before at 12v the motors would stall at the slightest misalignment and 6revs/sec was all I could get out of them reliably. Once all that is ironed-out I'm thinking 30revs/sec (1.75mm lead) would be attainable. I haven't cut anything yet but I have a good feeling it'll be able to cope with MDF and hopefull aluminium too!

[High Seas]

Aren't the Linisteppers rated for 1.5 amps per phase? What are the lasers steppers? 1.4 amps per phase?
Maybe just a tad too close for the design? I'm currious too as this looks like a good low cost approach to a mini-cnc; laser steppers + PC powersupplies + Linisteppers.

Let's hope James/ Roman have some insights for us!
Jim

[Fifty_ohm]

The "L" profile you mention is there to allow an easier way to mount the whole thing to a bigger heatsink. It wasn't meant to be the only heatsink as there isn't enough surface area to dissapate it (especially at the higher voltages). If you have any old pentium II/III heatsinks they work pretty well, with forced air across them. You'd be amazed at how much surface area there is with all those fins. I mounted mine on an old power amp heatsink that has 1.5" fins spaced every 1/4" with an overall dimension of 9"x4" (I mounted 3 linisteppers to it). There is a fan blowing across it which just happened to be already in the case I used for this so I went ahead and placed the heatsink in the direct path of the air.

If you read the linistepper building page it says the following on the second line:

* HEATSINK! Cut and drill the alloy heatsink bracket
Please note that this is the heatsink bracket and is not a heatsink itself. A (much) larger heatsink should be clamped to the bracket.

Since this design is not a chopper it dissipates A LOT of heat. Works great though and I'm really happy with mine.

[pminmo]

You have found the weakness of the linistepper. The transistors bear the brundt of power dissipation. If your rated coil voltage is 4V at 1.4A for example and the motor supply is 24V, the transistors (minus sense resistor voltage) will dissipate 20V * 1.4A or 28 Watts per coil. Mucho hot. My suggestion is to get a piece of aluminum the size of a AMD athlon heatsink 3/16" think or so and use it in conjunction with a cheap heatsink like http://www.newegg.com/Product/ShowIm...k%20-%20Retail

Phil

[H500]

The bottom line is that the efficiency cannot be increased by using better components. The only solution is to use a bigger heatsink, a fan, or use chopper drives. A chopper would allow you to use an even higher voltage for better performance.

[Fodder1]

Hi All,

I am currently going down the track that High Seas suggested to get my Jgro off the grond.

I'm currious too as this looks like a good low cost approach to a mini-cnc; laser steppers + PC powersupplies + Linisteppers.

I have not got the Posix Verison of the Linisteppers going yet. There seems to be a problem with the code I have for the PIC chips.(they are a newer version, soi am told) I am posting in another part of the forum to see if i can get some updated code for the chips.

But as High seas said this seemed to be great low cost option for people like me that are on low budget. As i work in the IT industry PC heat sinks are a everywhere.
To get this straight, mount the PC processor Heatsink to the alluminum flat someplace near the transistors using heatpast. Say 1 per transistor, Space allowing. Ok sounds to easy.

I would guess that it would dissapate a lot of heat that way, as some of the Intel Processors get pritty hot for there size. And if you leave the fan on the top, positon the heatsinks so the suck fresh air the cooling would be pritty good.

Not sure about the noise. May be a modified PC fanbus and some of the temp sensors would be good.

CH

[abasir]

For reference sake from Wikipedia
The Mobile P4 still used 70 W of power, which let it bridge the gap between the full Pentium 4 (using about 82 W), and the Mobile Pentium 4 M (using about 35 W).

[posix]

hmm, so no way around this? I remember people asking why I was using tip122 and not mosfets. I thought it had something to do with efficiency (and my mind read that as less heat) rather than anything else. but I guess I was wrong. oh well.

so caveat emptor would be - if you have loads of old scrap computers lying around build linisteppers as you'll need all those peltiers (and maybe even vapochill) later on. otherwise stick to choppers?

[James Marshall]

Hello!! I know that I am new to this hobby, but have been looking into different drives for my cnc when I get around to building it. A couple of things come to mind. James site states that you should only use 3 or 4 volts over your rated motor voltage, and to only use more voltage if you absolutly need speed. In doing so you need large heatsinks in addition to the bracket of aluminum that is bolted to the transistors. Also he states that the transistors are used to dissipate extra heat that will not in turn heat up your motors and burn them up. You mentioned "stall at the slightest missalignment". Are your motors big enough? Do you have excessive play or runout? What rate are you trying to run at? Dont get me wrong, I am just throwing these things out in order to understand because I am interseted in these drives and want to know their deficencies.

[posix]

Their only deficiency it seems is the transisrot heat. I have a chopper here and a linistepper and they both run at 24v. Linistepper "sounds" sweeter and it seems it runs faster as well before stalling. This is strange as I always thought a chopper would go faster and stall higher up in the rev range. Anyone care to correct me in my assumptions?

[James Marshall]

When useing the chopper do your motors produce alot of heat. Saw the other post, you are using the 100 oz laser motors right. What brand chopper drive?

[posix]

I don't know what I like better, burning my finger on the driver board or burning my finger on the motor. Which do you prefer?

P.S. it seems that once I switched to a chopper driver all that heat that used to be on linisteppers just transferred to motors themselves!