Harbor Freight Router Speed Control Mod

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About: Engineer/Scientist Interests include: * Physics based toys and demonstrations * Things that spin, like Levitron, Fidget Spinners, Origami spinners * Electronics * Cooking authentic ethnic food * Magne...

Intro


The Harbor Freight Router Speed Control is a bargain-priced (on sale for $19.99, with a 20% OFF coupon, just $17.40 with the tax) general purpose electrical controller, despite its very limited name. It is widely used for controlling heating elements, motors (be careful here, it only works with certain types of motor), and high-power stage lighting, just to name a few uses. I bought one to control a popcorn popper to roast coffee. The popper was getting too hot so I needed to be able to control its temperature and had read about using this device for the purpose. You just plug in the power cord and you can use the 3-way switch for Var(iable), Off, and Full. It is spec'ed to be able to handle 15 amps (1500W).

The need to mod…

After using it several times, I decided that the chip, which is a BTA26-600B A320 Triac, was getting too hot. Touching the backplate, with the unit not even on full power, I could only stand the heat for about 2-3 seconds. This was designed to provide intermittent power to a router, not continuous power to a heating element. Even though I can replace this chip for around $2 on eBay, you never want to overdrive a component like that, so I decided to add a heatsink, like the guys who use this unit for controlling heating elements for beer brewing and controlling industrial lighting. The heatsink cost me more than a replacement chip and some time and labor but I like to 'do it right the first time' (old IBM slogan), or in this case, the second or third time ;), whenever I have the luxury to do so.

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Step 1: The Mod

The heatsink


So I ordered this nice 60x150x25mm High Quality Aluminum Heat Sink for LED and Power IC Transistor H148 from eBay seller goldpart.

It took weeks to get here from China but it is a quality product and only cost me $4.49 shipped. The backplate on the controller, which serves as a poor heatsink, measures 110mm x 54mm. You can get a heatsink on eBay that closely fits those dimensions but, for a dollar more, I opted to get this oversized one.

Detach components from the backplate

I decided that the easiest way to do this was to simply detach the components from the backplate and mount them directly to the heatsink.

Upon removing the backplate's 4 screws, the first thing to do is to detach the mounted components from the backplate.

Drill out ground wire rivet

Drill out the rivet holding the 2 green ground wires. I used an electric hand drill with a 1/4" bit.

Go slowly to the point where the flange of the rivet just releases.

There was a steel or aluminum ball inside that I poked out with an awl.

Not done yet. The inside of the rivet still has the crimped sleeve attached to it. I carefully drilled that out with a drill bit that was small enough to avoid damaging the rings of the terminals on the ground wires. Probably around 1/8" but YMMV.

One terminal freed but the other one is still attached.

Easy does it.

Freed.

Unmount the triac

Remove the screw attaching the triac, with a screwdriver.

Drill out the rivets of the hanging clip

I also removed the hanging clip from the backplate so I could use the plate as a template for drilling the holes in the heatsink.

Terrible heatsink…

I was horrified to see what the manufacturer thought was a heatsink. A pebble-grained rectangle of 1/8" aluminum and NO heatsink compound! There are so many things wrong with that. First of all, a heatsink has, you know…, fins, to dissipate the heat quickly, not act as a thermal mass, building up heat to the point where it burns your fingers. Second, a heatsink is nice and smooth on the side where you mount your heat-generating component. I've even seen where over-clocking fanatics will actually lap their heat sinks with a progression of grits up to 6,000 to get mirror-finish smoothness. Over-clocking overkill to be sure but it does make the point about the requirement for smoothness. Reserve pebble-grain for leather hand bags or something else… Third, heatsink compound is absolutely mandatory to insure intimate contact between both surfaces, to promote maximum heat conduction. It fills in any micro-gaps, that surely exist on both mating surfaces, with a heat-conductive paste.

Lousy soldering job…

I was also horrified by the lousy soldering job I saw on the neutral wire direct from the wall socket.

Had to re-solder…

So the first thing I did was to re-solder it.

Not perhaps an expert job, but a lot better than it was.

Prepare the heatsink

Lay out the drill hole template

Lay out the positions of the drill holes for the mount holes and the components on the back of the heatsink. Note that the side of the backplate that was OUTSIDE the box is placed against the back of the heatsink to assure the greatest accuracy.

I first drew lengthwise guidelines by measuring the widths of the backplate and the heatsink, subtracting them and halving the remainder, and then using that value for the offset from the side edges of the heatsink. I then carefully positioned the backplate, aligning its sides with the guidelines, so that the inner edges of the mount holes just snugged up against the edge of a fin opposite them, tracing each hole with a fine permanent marker. Note that the holes for the 'bottom' (component side) are opposite the left side of the 6th fin from the left, and the holes for the 'top' side are opposite the right side of the 7th fin from the right. This was the best I could do to avoid drilling into those thick extrusions next to the fins. I drew lines under the 'inner' edges of the 5th and 6th fins and measured and marked the 'horizontal' and 'vertical' center between them for the drill hole for the 2 ground wires. I somehow messed up when drilling, and the hole ended up against the 6th fin. No biggie since I was able to get a rivet through it anyway. The hole for the triac just happened to line up with the left side of the 8th fin when the mount holes were lined up. I carefully selected a drill bit that was small enough to allow me to tap the hole for the screw.

Drill the holes

I clamped the backplate to the heatsink, being careful to line up the mount holes with the traces on the heatsink. I placed a strip of wood under the fins to avoid damaging them and rested the whole thing on 2 pieces of wood. I then drilled the 4 mount holes and the triac mount hole, using the backplate as a guide. Choose a drill bit that fits the mount holes of the backplate. Then choose a smaller bit to drill the triac hole--one that is small enough to allow tapped threads. Be sure to tap the triac hole with an appropriate size and pitch tap. You'll have to determine this on your own. I drilled the 1/8" rivet hole for the ground wires by center-punching the cross-hairs and then drilling, but my bit slipped a little as mentioned before. I couldn't use the backplate as a template because the hole would've gone right through the 6th fin.

Smooth all rough edges

Sand the cut sides and file the edges of the heatsink

I didn't take any photos of this tedious step. I first sanded the 2 saw-cut sides of the heatsink with 400 grit wet-or-dry to remove any rough spots. I removed any rough edges from the holes I drilled, both on the bottom and between the fins, with a small fine needle file. I then filed every rough edge of every fin with a small fine flat file. The tops are smooth already so didn't require filing. I beveled the sharp-pointed corners at the tips. I beveled the 4 bottom edges and the 4 corners. I went over it several times until I was satisfied it was smooth with no sharp edges or corners anywhere. Then it was ready to mount the components to.

Mount the components

Ground wires

Place a 1/8" pop rivet through the 2 ground wire terminals and into the 1/8" hole on the left. Arrange the wires so they are both down far enough to allow plenty of room for the triac.

This was the original placement:

Pop the rivet, and the wires should be firmly in place with no movement.

You could tap the hole and use a machine screw instead, if you don't have a pop rivet tool, but the Harbor Freight Hand Riveter Set is cheap ($4.99 sale price) and is a great addition to your tool collection.

Triac

Apply a generous quantity of heatsink compound to the back of the triac package.

Carefully position the triac so the holes line up.

Push down on it to start spreading the paste, and then tighten the screw firmly, but not too tight, or you could crack the plastic triac case. The paste will spread out very thinly, which is what you want--just enough to fill any gaps while maintaining as thin a layer as possible. I tapped the hole with the closest tap I had. It was off by about 1 TPI but I was able to get a good firm connection. You will have to determine the best tap to use from what you have on hand.

Put it all together

Finally, screw the heatsink in place and you are done. I had to replace the original sheet metal screws with ones that had smaller heads because the original heads were too large to fit between the fins.

Finished at last…

Here is the modified controller with the popcorn popper coffee roaster plugged in and ready to go. Even with the pot set at full power (1250W), the heatsink gets barely warm. Now I have much better control over the profile of the roast.

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    43 Discussions

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    Foxtrot70

    4 years ago on Introduction

    Excellent Instructable. After reading some of the comments, some folks want higher current capacities. I am reminded of my first electronics design classes where the instructor impressed upon my class the need to design in a 100% safety factor. Too often manufacturers design a circuit with components that just meet the circuit need and nothing more just to save a penny or two granted a good quality product does not generate repeat purchases due to product failure. When that is done you have a design that will last. I like the over sized heat sink. Since this circuit is fused at 15A my personal preference is to parallel two of the BTA26's giving greater total current capacity of 50A thus reducing the strain on an individual triac. I like the fact you re-soldered the wiring in the unit. One thing I like to do is use silver bearing solder to give better electrical conductivity also a little higher melting temp to counter the heat of the current draw of the 15A. Keep up the good work. ;)

    3 replies
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    LaralFoxtrot70

    Reply 4 years ago on Introduction

    Thanks for your comments. I agree about 'just meeting' the design requirements, or in this case, falling short I suspect. That's a good idea, paralleling 2 triacs but still keeping within the 15A requirement. I hope others will read this. For my requirements this would be overkill though.

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    Foxtrot70Laral

    Reply 4 years ago on Introduction

    You are correct it is definitely overkill in the end however your equipment is more reliable. The only other consideration is the price of the triac for the most part not a real budget breaker. The other is construction technique which is as important as the components used. Amazing that it takes no more time to be neat and accurate than it does to be sloppy and inaccurate.

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    LaralFoxtrot70

    Reply 4 years ago on Introduction

    I don't know about your second point. It took me the better part of a day to do this mod right. Careful measurement, careful drilling and alignment, lots of filing, getting everything to fit back in tight quarters, all ads up to a lot of time.

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    Ghostrider513

    3 months ago

    This is great and FYI, when using my CNC machine, it is on for a long time and would get hot too. That being said, can you create an addition to this mod? Make it show what RPM is running when connected to a router. Thanks

    1 reply
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    FerretPDGhostrider513

    Reply 2 months ago

    Sadly...to do it right; that would take a much more complex PWM Control that will compensate for load...something like this: http://www.kbelectronics.com/data_sheets/kbcc.pdf
    The best you could do is use Laser Printer, and a weatherproof adhesive Label (like an Avery 94215) to make a cover Label. (Use a piece of paper for your test measurements.)
    Get a rotary Tach; and mark the spots for different speeds by measurement (I have heard a lot of scuttlebutt that these cheapo controls are *not* linear in their output... so measure carefully.)
    Hope this helps!

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    LowMemory

    8 months ago

    Wow! What a great idea! I have two if these things sitting in my workshop and a box full of randomly size heat sinks. I’m going to go nuts now and see what kind of crazy contraption i can come up with next! Thank you!!

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    PaulJ14

    4 years ago on Introduction

    Very informative instructable; thanks for posting.

    Due to carelessness, I've created a problem for myself. While drilling the back plate, I accidentally broke two of the tabs on the BTA26-660B. Now I need to find a replacement (or buy a new unit from Harbor Freight). When I search BTA26-600B on the internet, a bunch of stuff comes up. But what's the A320? Do I have to find a part that also has the A320?

    12 replies
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    LaralPaulJ14

    Reply 4 years ago on Introduction

    The 320A is a mystery. I could not find it anywhere either. The spec sheet I posted does not show that suffix so I would assume it is irrelevant. I just bought a backup chip on eBay for $2.82:

    http://www.ebay.com/itm/1-PCS-BTA26-600-BTA26-600BRG-BTA26-600B-Triac-600V-25A-New-ST-/251064161926?pt=LH_DefaultDomain_0&hash=item3a74971686

    eBay search:

    http://www.ebay.com/sch/i.html?_odkw=BTA26-600B+A320&_sop=15&_from=R40|R40&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.XBTA26-600B+&_nkw=BTA26-600B+&_sacat=0

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    wptskiLaral

    Reply 4 years ago

    Followed your link and the Triac is $1.79 as of today! Glanced at my back plate and the Triac is riveted in not screwed. Ordered a heat sink.

    Nice mod for me as I plan on using the unit to control the speed on a HVLP turbine compressor where duty cycles "might" be longer.

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    Laralwptski

    Reply 4 years ago

    That's a great price. Curious that the triac is riveted. That is usually discouraged in the data sheet because it can break the case due to uncontrolled pressure.

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    wptskiLaral

    Reply 4 years ago

    I did order one just in case. I should open it up to see how it looks on the inside.

    How did you know how/if the four screws for the back plate would land between the fins on the heat sink? If I don't get lucky on the one I ordered, I'm able to machine it to whatever is needed. Aluminum is easy to machine.

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    Laralwptski

    Reply 4 years ago

    Read how I did it. I just barely got it right.

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    wptskiLaral

    Reply 4 years ago

    Ah, I see now as I didn't read all the details closely. I notice now that I made a mistake on my heat sink as fins are going the wrong way so machining will be required for sure. I may cut it to fit the back plate pocket exactly now.

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    Laralwptski

    Reply 4 years ago

    Wrong way?! Which way? Down or vertically? LOL!

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    wptskiLaral

    Reply 4 years ago

    Fins run parallel to the long side of the box! I was paying too much attention to the overall size and missed that. Oh well........

    The pic is a bit overexposed but the bad soldering point isn't that bad but look at the fuse, a sure current reducer there. I'll have to loosen the nut to check the other side.

    VarSPMC_1.JPG
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    Laralwptski

    Reply 4 years ago

    That definitely needs a touch-up.

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    wptskiLaral

    Reply 4 years ago

    Ya think? The other side looks okay. The fuse holder is marked as 10A and the fuse is bit hard to read but looks like a 20A. One metal cap moves too, a real cheapo!

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    Laralwptski

    Reply 4 years ago

    Think of it more as a Speed Controller KIT. 'Some assembly required'. ;-) Still, for the money, it is quite a useful little unit.

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    wptskiLaral

    Reply 3 years ago

    I got this heat sink from Amazon but didn't know that they had Amazon stores from China; http://www.amazon.com/gp/product/B00BGAO2W0?psc=1&... so it took 17 days to get here but now showing it "to be" sold by Amazon when in stock.

    Like I mentioned I forgot about the direction of the fins so I had to machine slots, not too bad with a stout drill press and the proper end mills. I taped a 8-32 hole for the ground wires and had to use a smaller 6-32 for the smaller mounting hole on the triac. I also machined the pocket that the old cover sat in which proved to be a PITA since the plastic was rubbery and harder to cut without a wreck.

    I packed the case with paper towels to keep the chips out. At one point the end mill grabbed the paper towels which caught the dangling wires. Luckily I stopped the drill press quickly with no damage and removed what paper toweling that was still left.

    I ran my HVLP turbine which draws 13A at just over the low/medium mark for five minutes and it barely got warm.

    Thanks Laral for idea! :-) Fuji Spray Systems now has a 5-stage turbine with a variable speed control but I wonder how they dissipate the heat as these turbines already generate lots of heat. I've burned my knuckles removing the hose at the unit right after using it!!

    Heat Sink_1.jpg