ZombieSS's power stage for Lebowski's controller video pg17

[zombiess]

ZombieSS,

Post some measurements and desired enclosure details. There might be a way to use available boxes, perhaps joining several to get what you need without a custom machine shop solution or at least reduce the machine shop hours.

I already have the mechanical side figured out and the pieces to assemble it. Its big but this is my first revision. Next one will be MUCH smaller.

I have 6x6x0.125" alum square tube 12" long for the enclosure. Heat sinks are three 1.5"x0.125 U channel 6" long. I have spacers to join all the boards together into a solid unit that can withstand vibration. What I need now is 24 holes, 8 on each one side of the U channel to mount the FETs and then mounting holes on the opposite side in a pattern to match up with holes in the square tubing.

Anyone who works with metal would laugh at the simplicity of this. I estimate it would take a pro about 30mins start to finish because I could do it in about an hour if I had my mini mill working...it's still sitting in the crate it was delivered in 6 months ago all sticky with cosmoline.

 

[dbaker]

Sears has a 10 inch drill press with laser locator:

http://www.sears.com/craftsman-10inch-bench-drill-press-with-laser/p-00934983000P?sid=IDx01192011x000001&kpid=00934983000&kispla=00934983000P

You can clamp a fence to the table and slide your extrusion from hole to hole to get the fet holes aligned. A drill press is an asset to any shop. I have no personal experience with the press above. Just that most of us have a Sears nearby. Other option is Harbor Freight but their stuff often needs calibration and setup.

 

[Lebowski]

Wasnt there this web-based service where you could download a CAD program, draw your design and get an immediate quote ? Also for one offs ?

www.emachineshop.com

 

[zombiess]

I think you guys missed the last part where I said I have a mill. Its just not setup. I purchased it instead of a drill press. I guess setting it up will be this weeks project.

 

[nieles]

i found a driver chip very similar to what you are using but with build in opto-couplers

could be interesting, to eliminate some parts from the driver stage.

http://www.fairchildsemi.com/ds/FO/FOD8318.pdf

or without the led driver build in:

http://www.fairchildsemi.com/ds/FO/FOD8332.pdf

 

[zombiess]

i found a driver chip very similar to what you are using but with build in opto-couplers

could be interesting, to eliminate some parts from the driver stage.

http://www.fairchildsemi.com/ds/FO/FOD8318.pdf

or without the led driver build in:

http://www.fairchildsemi.com/ds/FO/FOD8332.pdf

Nice find Neiles. I have not seen that one before. It's almost the same cost as the TD350E + two 6N137 optos and uses less board space. I only glanced at the data sheet, but it looks to have all the same features. The propagation time is about the same as well. I've been working on an SMD design to get my board space down and finally have a good layout that is small, 1.2"W x 1.6"L without boost stage, with the new chip I could probably shrink that down to 1.0" x 1.2" and eliminate several components. I'm still using human sized hand solderable components, smallest is 0805.

 

[Lebowski]

yep, very nice find Niels !

 

[Njay]

I have this one in my mouser basket for some time now to try:
http://pt.mouser.com/Search/ProductDetail.aspx?qs=PDcOBBvbsyjGuefSy9KqmA%3d%3d
It's a very basic driver, but the 60ns max propagation delay...

 

[nieles]

I'm still using human sized hand solderable components, smallest is 0805.

i am doing the same.. everything i design now is all smd.. (no more pcb drilling after etching a board )

wish i would have more spare time.. so i could work some more on my own design..
i enjoy reading about all the controller projects on the forum though (and the technical debate of course)

 

[zombiess]

I have this one in my mouser basket for some time now to try:
http://pt.mouser.com/Search/ProductDetail.aspx?qs=PDcOBBvbsyjGuefSy9KqmA%3d%3d
It's a very basic driver, but the 60ns max propagation delay...

That driver lacks all the cool features, not even a miller clamp which I know consider a must have feature. I'm even thinking desat detection is needed for anything I do because I am designing for reliability as well as function. This new layout I am working on has 0 electrolytic caps in the gate driver and power stage. Polypropylene or ceramic only.

I was going to try this design with a avego hclp series driver that had a miller clamp and was driven by an integrated opto, but after crunching the numbers with assuming I could go to small scale production in the future it just wasn't worth the price difference of about $20 for a complete 3 phase bridge. That $20 includes the extra board space into it as well. For the extra $20 of parts and board space I gain desat protection, 2 level off. Based on how many people post about blowing up MOSFETs on this site, myself included due to those damn eb324 controllers, the $20 is absolutely with it.

BTW, the new power stage is either 12 or 18 to-247 devices depending on if I can keep the length under 8". The poly DC link caps are not exactly small, but are cheaper and smaller than electrolytics since I only need 2 vs 8 to handle the RMS amps. $13 total!

Setting up my mill this weekend to finally get my heat sinks done.

 

[Njay]

Yes you're absolutely right, as I said it is a very basic driver. But I'm still willing to give it a try.

How much total power input capacitance will you have on your next prototype?

 

[zombiess]

Yes you're absolutely right, as I said it is a very basic driver. But I'm still willing to give it a try.

How much total power input capacitance will you have on your next prototype?

I need to recalculate for 18 FETs, but 12 FETs was 20uF min and I planned on using 2 20uF caps. I will probably need to go to 2 30uf DC link caps for 18fets. I already have the perfect enclosures for my design.

 

[Njay]

We'll have to ask HighHopes about the caps resonating with battery wiring. I'm still studying the subject, but if I had to go with my eyes closed, I wouldn't put less than 1000uF. My conclusion so far is that the resonant frequency of the cap with the wiring must be way less (I'm thinking one order of magnitude) than your PWM frequency.

 

[zombiess]

I'm now stuck because I need metal work done.

I can do electronics but frock this metal working stuff. I can't find anyone local who will help me out with making heat sinks and getting them into the case. No machine shop I called will work with me because I don't have a $10,000 job for them. The online places want way too much money to drill and tap holes in some aluminum unless I'm doing something crazy like 50 pieces.

I have zero interest in setting up this "mill" that I purchased and will be selling it. The more I read about what it takes to make it work, the less I want to unpack it.

 

[Futterama]

I have a minimill myself and I love it. I would be happy to help you but shipping just 5kg to Canada costs 103 CAD.

 

[speedmd]

I'm now stuck because I need metal work done.

I can do electronics but frock this metal working stuff. I can't find anyone local who will help me out with making heat sinks and getting them into the case. No machine shop I called will work with me because I don't have a $10,000 job for them. The online places want way too much money to drill and tap holes in some aluminum unless I'm doing something crazy like 50 pieces.

I have zero interest in setting up this "mill" that I purchased and will be selling it. The more I read about what it takes to make it work, the less I want to unpack it.

Hi Zombiess

Try your local (vocational high) trade school. They are always looking for this type of real world stuff to help keep the kids focused. You could possibly get the auto mechanics dept (they need to be learning all they can on all the hybrid and plug ins coming into the market/ teacher included), the machine shop, and the electrical side if you showed them one of your builds and had a few teachers that were savvy enough to see the big picture. Most times it takes buying the materials and a thank you via some pizzas and soft drinks. Good place to find apprentices also if things take off.

If none are near by, I always resort to laying stuff out with a scribe and center punching hole locations before drilling. You end up with a much better job on tiny holes. Best luck with it.

 

[zombiess]

I reluctantly gave in and uncrated the mini mill, spent about 1.5 hours removing as much cosmoline as possible while simultaneously coating the entire machine in oil (PB Blaster, WD-40 is for rednecks, I have a more refined pallet). Went to the local Harbor Freight looking for a vise and a clamping blocking kit. Found a small cheap vise for $17, but they did not have the blocking and clamping kit in stock of course. Got home, realized the redneck method I had planned to mount the vise to the mill table wasn't going to work. Hmmm, time to enjuneer a temporary solution... double sided tape... Tadaaaa! Stuck my aluminum channel to the mill so dang well I could lift the front end of it off the stand (it's not bolted down to the table yet, just bolted to the shipping crate bottom... more awesome enjuneering).

Mounting solution found, look at dials, realize they only go to 62.5 which means 1 turn = .0625 math. Spend next hour trying to figure out the correct way to do 62.5 modulus math, then finally calculate # of turns on a spread sheet and then the thousandths past the turn to get my exact measurement.

I now have 3 heat spreader bars made from aluminum U channel that is 0.125" thick, each with 8 pefectly spaced holes waiting for the 3mm tap to be run through. Tomorrow I'll figure out the other side and the 6" square tube "enclosure". This thing isn't going to be small or pretty, but at least it will be in an enclosure and mostly protected.

Now the bad news. Somehow during the cleaning of the machine I hurt my back. Feels like the left Rhomboid area and it really hurts Not even sure what I did. I had help lifting the heavy little mill. As long as it doesn't get worse, I should be able to complete the enclosure tomorrow and get this project back on track.

Off to look for a digital read out for the mill, a real vise and a blocking/clamping kit. At the least I'll get a new dial or screw, holy crap 62.5 sucks. I understand that 4 turns = 0.250" and 16 turns = 1.000" but dang it's almost impossible for me to do it in my head and I'm pretty good with the numbers thingy. Now that I finally have this setup I can see myself doing more with it, mainly heat sinks and enclosures for prototype electronics work.

 

[Futterama]

Pictures of the mill and the stuff you made with it, would be nice

 

[zombiess]

Finally got all the holes drilled and now I can't seem to tap them. Tried 3mm 0.5 and it just mangles the aluminum, went bigger and tried 6-32, same story. I've tapped aluminum several times before and never had this kind of issue so it's probably the taps are shitty. Now I have to put this on hold until I can order some real taps. I've thoroughly frocked up every hole in one heat sink, but I can sorta get 6-32 hardware in so I should be able to mount the FETs with the Nylon 6-32 hardware I have on it. Problems like this are exactly why I prefer to pay someone else to do this kind of work.

 

[Njay]

I'm not experienced with it (actually I think I made maybe 3 taps in my life), but I use 3 "depths" of "taping screw", so that it goes smoothly a little piece at a time. Work slowly, avoid going back more than a few degrees (better to not go back at all I think), use oil.

 

[Lebowski]

I'm not experienced with it (actually I think I made maybe 3 taps in my life), but I use 3 "depths" of "taping screw", so that it goes smoothly a little piece at a time. Work slowly, avoid going back more than a few degrees (better to not go back at all I think), use oil.

Same here, I always use 3 taps increasing the threads as you go. With aluminium, use alcohol for lubrication.

 

[Futterama]

I have a plenty of experience with tapping in aluminium. You need coolant/lubrication, and the best for aluminium in denatured alcohol/denatured ethanol. Aluminium will also pack the chips around the tap, so you need to make sure the chips are cleared. A good way to do this to tap 1 turn, then turn the tap half a revolution back, tap another turn, half turn back and so on. This breaks the chips into smaller chips and if you use plenty of coolant (denatured ethanol), the coolant will flush the chips out. If you tap a bottom hole (one that is only open where the bolt goes in) you cannot flush the chips out while tapping and you need to turn back and remove the tap for every 2-3 tap revolutions you make, and clear out the chips. Compressed air through a hollow needle going to the bottom of the hole, will do a good job here.

So, are you tapping a hole that goes all the way through the "plate" or do you tap a bottom hole?
Do you turn the tap by hand or with the mill?

The pictures I asked for will help us, help you. Post some pictures and I could perhaps post a video of how I tap holes in aluminium successfully.

By the way, I have some special taps for aluminium where every second thread is missing to make more room for the chips to avoid packing. Those are highly recommended. They seem to be called "interrupted thread" taps.

Edit: I use only 1 tap for a hole. I think mine are what would be called spiral point, interrupted thread, machine taps.

 

[Arlo1]

Zombies everyone forgot the most important step. Get it started then go about 1/2 turn in and back it out about 1/4 turn this will brake off the shavings and stop the tap from plugging up with aluminum. Also you will want to take it out a few times and clean the shavings out of the hole. If its hard to start it strait then I use a drill press by hand (not powered) but it holds the bit square while you turn it and lightly pull down on the handle.

 

[Lebowski]

have you thought about nuts ?

 

[zombiess]

I'm 99% sure it's my shitty tap set. China junk. The larger taps work fine and I have used them in the past on steel, but the small ones are worse than crap, make out of CCS, Chineese Cheese Steel. Unbelievably the threads have been mushed by ALUMINUM and they have never been used before! I use to have some good high quality 6-32 and M3 taps but I can't find them now and I really like them because they had a long centering point with a taper to get a great easy start I just ordered some 2 6-32 and 2 3x1.5mm new ones form McMaster Carr. Not cheap, but ruining my freshly made stuff is worse.

I'm going to go 6-32 for the TO-220 FETs and use Nylon screws. I've done this before and it's worked great. All you nay sayers on this can hold your trap This has been battle proven for me on 2 controllers, one seeing FET case temps of 100C at times and they never had an issue in the years I ran that controller. My other alternative is longer M3 screws with nuts on the end. I think I have enough left overs to build this. I'll make the decision after I can get some clean threads. Ordered some hardware as well. I was trying to go M3 since I have lots of left over M3 from the garbage Xie Chang EB324 controllers which will never be sold.

I also just ordered a proper vise and blocking/clamping kit so I can hold my work to the table properly. I'm mainly prototyping aluminum heat sinks for testing so my work is pretty easy, drill hole in bar, tap, install.

All the taps I have are plug type so they are for through hole. One of the heat sink bars I will be making soon will have 1 through hole and then threaded from both ends for the screws. BTW, I was using oil to lubricate the tap, something similar to WD-40 I have used in the past that has worked very well and given me very clean threads... with a good tap. I already know the method of going 1/2 turn, backing up 1/4 turn, been doing that in the past with taps that actually cut vs wipe threads.

I hate working with metal, but I'm not totally dumb (I have Google and one friend who has done quite a bit of machining at home) when it comes to it, I just really dislike it since I'm not very good at it and it's time consuming.