# MachTach Build



## Blackjackjacques (Feb 3, 2018)

Ok - got some free time and wanted to at least commence tackling set up of my RF45, which includes DRO install, tramming, and building of the MachTach tachometer product.   It has been sitting in its half-opened yellow envelope for a few months now, so now it is at least assembled and soldered together and has passed the preliminary vendor tests.  It went together pretty easy, however, it is smaller than I prefer.   I was pretty impressed with the supplied plastic case that was constructed on a 3D printer.  This is my first application where I had a chance to fondle a 3D printer product, and it much beefier and dimensioned than I expected.  My next step will, of course, be to attach to the machine, but I think I will so that simultaneously with the DRO install.  Has anyone built and/or used this MachTach product?


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## LEEQ (Feb 3, 2018)

I built one in a serpac enclosure. It worked fine when I test drove it on a desk fan. Looks good and took a minimal of tools. For me it was also a good excuse to fleabay an awesome WD1 weller soldering station,the one nice tool I used.


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## Cadillac STS (Feb 3, 2018)

I built two, one a few years back for my lathe and one recently for my mill with the 3D printed case.  I was impressed with the case as well.  I used the magnetic induction sensor and with that there is a small 3D printed case, that is interesting with the internal passage printed perfectly for what it needs to do.

It is a high quality kit.  I get what you mean with it sitting in an envelope until I got around to soldering it all together..

You can buy a cheap tachometer but not with the SFM function.  Push the button, dial your diameter, lathe stock or end mill and get surface speed.

The place that sells them is very accommodating. The instructions let you know how to wire one unit up to two machines if you have two machines close to each other.  Can order with whatever sensor you want.

Can mount it inside the case of your tool if there is room.

The little plastic colored window needs to be trimmed down to fit the cut out in the 3D printed case.  I did that easily by clamping the red plastic in a vise and carefully filing the edge down to size.  Thought about cutting it on my mill but I worried about cracking it.


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## mksj (Feb 3, 2018)

Built a few of the MachTachs, although I prefer to mount them in Hammond diecast enclosures. Not as easy to do vs. the 3D case. I use the SFM on larger diameter work on my lathe, helpful to tell you if you are ball park SFM. Most recent version does metric.  More recently I have also been adding a precision 3 turn speed pot in my tach enclosures. Much better quality pot and I do not need to take up a larger 22mm hole. One minor issue I have had with the MachTachs is they require a 9V power source, typically most low voltage control systems are 12 or 24VDC. Some systems I needed yet another step down converter or add a heat sink to the regulator if there is room (you can see below that the heat sink needed to be modified to fit the case). I also used a more standard round threaded hall sensor on lathes if you have the room. In one case the tach was  sensitive to VFD electrical noise, but I managed to work that one out. The documentation in the manual is very clear, also availability of different sensors makes this tach a bit more adaptable.  Had a recent discussion with the builder and some suggestions, nice person and listens to comments.


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## Firestopper (Feb 3, 2018)

Thant's a sweet setup Mark


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## Blackjackjacques (Feb 3, 2018)

LEEQ said:


> I built one in a serpac enclosure. It worked fine when I test drove it on a desk fan. Looks good and took a minimal of tools. For me it was also a good excuse to fleabay an awesome WD1 weller soldering station,the one nice tool I used.



Aye - the Weller WD1 is a slick tool.  I started with an old Weller TC 201 and then slid over to my Hakko FX 888 and batted cleanup with my Hakko FR 810B hot air unit.  My eyes are not what they used to be and last night I needed the microscope more than usual.  But it cleaned up nicely and worked the first time powered up.


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## Blackjackjacques (Feb 3, 2018)

Cadillac STS said:


> I built two, one a few years back for my lathe and one recently for my mill with the 3D printed case.  I was impressed with the case as well.  I used the magnetic induction sensor and with that there is a small 3D printed case, that is interesting with the internal passage printed perfectly for what it needs to do.
> 
> It is a high quality kit.  I get what you mean with it sitting in an envelope until I got around to soldering it all together..
> 
> ...



I'm glad to hear there are others out there who relate to half-opened envelope projects.   I have a few more envelopes yet. I have the standard optical sensor shipped with the unit, but I purchased the hall effect sensor along with this killer neodymium magnets, but I'm wondering if I should instead go with the variable reluctance sensor instead to detect gear teeth.  My preliminary plan is to access the geared drive behind the front access plate. From that point, I can go either with the hall effect unit or the var reluctance, but I debating with myself if it is easier to just use the var rel since I do not need to space and install magnets, etc.    The display unit itself will be installed external to the machine but flush mounted to the front plate (I think)


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## Blackjackjacques (Feb 3, 2018)

mksj said:


> Built a few of the MachTachs, although I prefer to mount them in Hammond diecast enclosures. Not as easy to do vs. the 3D case. I use the SFM on larger diameter work on my lathe, helpful to tell you if you are ball park SFM. Most recent version does metric.  More recently I have also been adding a precision 3 turn speed pot in my tach enclosures. Much better quality pot and I do not need to take up a larger 22mm hole. One minor issue I have had with the MachTachs is they require a 9V power source, typically most low voltage control systems are 12 or 24VDC. Some systems I needed yet another step down converter or add a heat sink to the regulator if there is room (you can see below that the heat sink needed to be modified to fit the case). I also used a more standard round threaded hall sensor on lathes if you have the room. In one case the tach was  sensitive to VFD electrical noise, but I managed to work that one out. The documentation in the manual is very clear, also availability of different sensors makes this tach a bit more adaptable.  Had a recent discussion with the builder and some suggestions, nice person and listens to comments.
> 
> View attachment 256638
> 
> ...




Nice slick black. I was considering using a Bud Cu-124 case similar to your Hammond, but the Serpac plastic 3D printer case was so nice, I put the Bud box back into inventory.  But if I experience a noise interference issue as you described in your case, I may have to go the metal enclosure route -- we'll see.  I see the speed pot you added to your unit - what does it do?  I have not mounted a heat sink to the 3-terminal regulator yet. I have low profile TO-220 heat sinks that go taller rather than wider, and need to figure out which one to include.  A note on regulators: on Ebay, there are a ton of China smt buck boost regulator packages that essentially go from any voltage to any voltage, for about 80 cents apiece. You can easily interface a 9V to 12V, 18V, 24V, or even 5 and 3.3 V with a device about the footprint of a postage stamp.


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## mksj (Feb 3, 2018)

The electrical noise issue was not the enclosure, but the shielded cable between the hall sensor and the MachTach. Convention would be to ground the shield at the source (not both ends), but any grounding of the shield (either end or at both ends) made the MachTach go wild. So if you use shielded cable, my recommendation is float it on both ends. Grounding is always one of those funny things, doesn't always work the way it is suppose to.

I would go with the hall sensor, you also only need a single magnetic to KISS. The IC hall sensor provided with the kit is a bit fragile, I used it on my lathe but wouldn't want to use it again if possible. You can get the cylindrical  threaded type, NPN in 8 or 12 mm diameters. You connect the hall sensor brown power to wire to +IR, the blue negative to -RCV, and the black switched sensor line to +RCV. Works very nicely and no need for a pull down resistor.
Examples of sensors:
NJK-5001C
LJ12A3-4-Z/BX

Gear tooth sensor can be a bit more temperamental, you need the assembly he provides with the two capacitors in order for it to work correctly. At least he has it as an option. One problem on mills with a back gear, is you cannot take the tach off of the drive head, you need to pull the tack signal off of the spindle so need a very compact pickup assembly.  One place where the small hall sensor is more desirable. On my mill which came with a factory tach, it uses an output from the VFD for speed and they also have a back gear sensor which rescales the tach range when in back gear. I recently build two integrated Halo Light and tach sensor for some PM 949 mills that where 1/4 thick and slid up on the mill ram. They required a very small hall sensor, it was very temperamental to magnetic flux.


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## Cadillac STS (Feb 3, 2018)

Would there be any problem if I were to glue a strong magnet on the back of the 3D printed half size case?  If I could do that there is a place to stick it up but also be able to move it easily.  

Would a strong magnet bother the electronics?


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## royesses (Feb 3, 2018)

I built 2 of them and have a third for backup. Very well engineered kit and a really great guy who designed and sells them. I used a magnetic pickup with six magnets on the mini mill and a gear tooth pickup on the mini lathe. They work great.

Roy


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## mksj (Feb 4, 2018)

Cadillac STS said:


> Would a strong magnet bother the electronics?


No, it would not have an effect on the electronics.


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## Alan H. (Feb 4, 2018)

mksj said:


> Built a few of the MachTachs, although I prefer to mount them in Hammond diecast enclosures. Not as easy to do vs. the 3D case. I use the SFM on larger diameter work on my lathe, helpful to tell you if you are ball park SFM. Most recent version does metric.  *More recently I have also been adding a precision 3 turn speed pot in my tach enclosures. *Much better quality pot and I do not need to take up a larger 22mm hole. One minor issue I have had with the MachTachs is they *require a 9V power source*, typically most low voltage control systems are 12 or 24VDC. Some systems I needed yet another step down converter or add a heat sink to the regulator if there is room (you can see below that the heat sink needed to be modified to fit the case). I also used a more standard round threaded hall sensor on lathes if you have the room. In one case the tach was  sensitive to VFD electrical noise, but I managed to work that one out. The documentation in the manual is very clear, also availability of different sensors makes this tach a bit more adaptable.  Had a recent discussion with the builder and some suggestions, nice person and listens to comments.
> 
> View attachment 256638
> 
> ...



Mark, 
What does the additional 3 turn precision POT you add do?  

How are you typically providing 9V for power?   Do you think the gent who sells the package would consider an option for 12VDC power?


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## Blackjackjacques (Feb 4, 2018)

Alan H said:


> Mark,
> What does the additional 3 turn precision POT you add do?
> 
> How are you typically providing 9V for power?   Do you think the gent who sells the package would consider an option for 12VDC power?



I simply get the 9V DC from a standard spare wall wart transformer.  However, if you want to derive 9VDC from a 12 VDC supply you can use a device such as linked here : https://www.ebay.com/itm/DC-DC-Buck...874540?hash=item36216ab22c:g:Tf4AAOSwK31Zujhc


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## Alan H. (Feb 4, 2018)

Blackjack thanks. 

A little more context to my question - I am fortunate to have a custom Mark Jacobs (mksj) Control System on my PM1340GT lathe and it provides 12VDC for Tachs and accessories.  I was wondering if Mark does something with his control system or uses something external like a wall transformer.


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## mksj (Feb 4, 2018)

When I build control systems, I real do not want others having to deal with wall warts and the confusion of multiple voltages and additional wiring. I standardize all my systems with a 24VDC power supply and a 12VDC step down regulator. This can be used for the relays, lights, tachs, etc. having to add yet another step down converter for the MachTach is a real pain, and requires extra wiring/cost for the 9V power. I try to keep my Tach enclosures to a minimum size, so heat generation/heat sink is also a problem. On the MachTachs I either add a heat sink, or I add another step down converter. I try to minimize wires and cables, so when it works out I will integrate each subsystem connections into a single cable. I have one 240VAC power cable to the machine which then provides power 240, 120, 24, 12V etc. to all the subsystems.

The MachTach uses an older style linear voltage regulator which dissipates excess voltage by generating heat. So anything above 9V and the regulator will not last w/o a heat sink (and even with that it generates a lot of heat). Nowadays with IC switching regulators with high efficiencies, one can input a wide range of voltages w/o the heat issues. I had some emails with the builder and indicated a drop in fixed 5V switching regulator as an alternative to the linear voltage regulator, the switching regulator has an input voltage range of 7-28VDC and is around 2.60 each.  He will look into it, it certainly would make the kit easier to install in most VFD systems that use 12 or 24VDC power supplies. Since his design dates back for many years, inexpensive drop in switching regulators were probably not available back then. It is also the economics of the total parts costs.

When I get a request for an integrated tach build using my control systems, I have been putting the speed pot in the Tach housing which either mounts under the DRO or on the mill head. This puts the display/speed pot in a convenient location and you adjust the speed while looking at the tach. I have been using a compact military grade 3 turn Spectral potentiometer, which gives very nice speed control and fits well in the enclosure. I program the VFD for a lower and upper speed limit, so you get a very nice adjustable range. The Automation Direct 22mm speed pots are ok, but the speed pot used is not what I would consider a high quality unit. Long term, I have had failure of factory speed pots in some of the factory installed VFD machines, so I am always balancing the quality-cost equation.


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## Blackjackjacques (Feb 4, 2018)

mksj said:


> When I build control systems, I real do not want others having to deal with wall warts and the confusion of multiple voltages and additional wiring. I standardize all my systems with a 24VDC power supply and a 12VDC step down regulator. This can be used for the relays, lights, tachs, etc. having to add yet another step down converter for the MachTach is a real pain, and requires extra wiring/cost for the 9V power. I try to keep my Tach enclosures to a minimum size, so heat generation/heat sink is also a problem. On the MachTachs I either add a heat sink, or I add another step down converter. I try to minimize wires and cables, so when it works out I will integrate each subsystem connections into a single cable. I have one 240VAC power cable to the machine which then provides power 240, 120, 24, 12V etc. to all the subsystems.
> 
> The MachTach uses an older style linear voltage regulator which dissipates excess voltage by generating heat. So anything above 9V and the regulator will not last w/o a heat sink (and even with that it generates a lot of heat). Nowadays with IC switching regulators with high efficiencies, one can input a wide range of voltages w/o the heat issues. I had some emails with the builder and indicated a drop in fixed 5V switching regulator as an alternative to the linear voltage regulator, the switching regulator has an input voltage range of 7-28VDC and is around 2.60 each.  He will look into it, it certainly would make the kit easier to install in most VFD systems that use 12 or 24VDC power supplies. Since his design dates back for many years, inexpensive drop in switching regulators were probably not available back then. It is also the economics of the total parts costs.
> 
> When I get a request for an integrated tach build using my control systems, I have been putting the speed pot in the Tach housing which either mounts under the DRO or on the mill head. This puts the display/speed pot in a convenient location and you adjust the speed while looking at the tach. I have been using a compact military grade 3 turn Spectral potentiometer, which gives very nice speed control and fits well in the enclosure. I program the VFD for a lower and upper speed limit, so you get a very nice adjustable range. The Automation Direct 22mm speed pots are ok, but the speed pot used is not what I would consider a high quality unit. Long term, I have had failure of factory speed pots in some of the factory installed VFD machines, so I am always balancing the quality-cost equation.



The output voltage of the LM 340 3-terminal regulator on the MachTach board is 5 volts.  Max input voltage for the LM340 is 35 Volts.  I just checked on my unit with the 9V @ 300 mA wall wart.  Apparently, the no-load voltage of the wall wart happens to be 12.1 Volts, and when energizing the MachTach, the voltage still reads 12.1 V at 140 mA.   The current demand at 9V using an external power supply still reads 140 mA.  I have not yet installed a heatsink for the regulator, however, the stabilized tab temperature at both voltages is about 135 degrees F.   Therefore, you should be able to run the MachTach at either 9 or 12 volts.   I love those old 3-term regulators because they can take a beating and bounce back owed to internal therm cutout, they are easy to use, cheap, forgiving, and readily available.


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## Blackjackjacques (Feb 4, 2018)

Alan H said:


> Blackjack thanks.
> 
> A little more context to my question - I am fortunate to have a custom Mark Jacobs (mksj) Control System on my PM1340GT lathe and it provides 12VDC for Tachs and accessories.  I was wondering if Mark does something with his control system or uses something external like a wall transformer.



Gotcha.  I ran up some quick tests on my unit and it appears you can run your 9V MachTach at 12V without a problem. See my response to Mark.


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## Blackjackjacques (Feb 4, 2018)

mksj said:


> The electrical noise issue was not the enclosure, but the shielded cable between the hall sensor and the MachTach. Convention would be to ground the shield at the source (not both ends), but any grounding of the shield (either end or at both ends) made the MachTach go wild. So if you use shielded cable, my recommendation is float it on both ends. Grounding is always one of those funny things, doesn't always work the way it is suppose to.
> 
> I would go with the hall sensor, you also only need a single magnetic to KISS. The IC hall sensor provided with the kit is a bit fragile, I used it on my lathe but wouldn't want to use it again if possible. You can get the cylindrical  threaded type, NPN in 8 or 12 mm diameters. You connect the hall sensor brown power to wire to +IR, the blue negative to -RCV, and the black switched sensor line to +RCV. Works very nicely and no need for a pull down resistor.
> Examples of sensors:
> ...


Yeah -- I think I will go with the Hall-effect sensor.  After all, I already have it on hand. Thanks


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## Alan H. (Feb 4, 2018)

Thanks Blackjack.  

Here's a snippet from Mark's detailed response - _ "The MachTach uses an older style linear voltage regulator which dissipates excess voltage by generating heat. So anything above 9V and the regulator will not last w/o a heat sink (and even with that it generates a lot of heat). "   _

So my takeaway is that it appears best to feed the device what it wants without sending excess voltage up in heat.


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## Blackjackjacques (Feb 4, 2018)

I don't see a conflict with what Mark has to say.  The LM 340 generates heat requiring dissipation via a heat sink anyway -- at 9V, at 12 V, at 18V. Even the newer switch mode power supplies generate waste heat requiring dissipation via some means. However, the newer regulators are more efficient and therefore generate less waste per watt than the older linear regulators.  But the main thing to take away is that, based on my tests and the product data sheet, that the quiescent current demand, as well as the regulator's temperature, is the same whether it is energized by 9V or 12V.  In other words, 12V does not place any additional stresses on the regulator, or such stresses are well within the product's design as detailed in the product data sheet (attached for your ref).  Therefore if you have a 12V dc supply on hand, you can connect it to the MachTach without need to reduce the voltage.


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## Cadillac STS (Feb 4, 2018)

Blackjackjacques said:


> Yeah -- I think I will go with the Hall-effect sensor.  After all, I already have it on hand. Thanks



When I put the Hall effect sensor together I did it just like the pictures in the instructions. Cut the leads to quarter inch and solder the three wires. With the solder and the wires there was little room between the leads.  And then you are supposed to push it up into the channel of the 3D printed housing. I was concerned about the wires shorting out when it was pushed into the channel. What I found helpful was to take the heat shrink tubing that comes with the kit, cut 1/4 inch of it, slit the tubing then work that around the middle lead. Don’t heat shrink it. That way if the leads do shift right away or later in use you have some insulation to prevent failure.


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## mksj (Feb 4, 2018)

My experience with linear regulators and the one in the MachTach differs from your findings. MachTach also supplies a heat sink for individuals wanting to run their tach at 12V.  It may be that your wall wart voltage sag or limited current makes it appear to be different than if you use a larger power supply. When I power my MachTach at 9V using my BK regulated power supply, the regulator gets warm to the touch. When I power it at 12V I can barely touch the heat sink, I do not have a thermal gun. Since the regulator draws the same current (106-109 mA) at 9 and 12V, the power difference is given up as heat.  Without a heat sink the regulator has very limited thermal dissipation abilities. Switching regulators are more efficient thus run cooler and do not require a heat sink. They can generate more electrical noise which can be an issue for some circuits. I guess I do not have a fondness for linear regulators,  they made nice room heaters in the winter time, and then there is my tube amplifiers.


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## Blackjackjacques (Feb 4, 2018)

mksj said:


> My experience with linear regulators and the one in the MachTach differs from your findings. MachTach also supplies a heat sink for individuals wanting to run their tach at 12V.  It may be that your wall wart voltage sag or limited current makes it appear to be different than if you use a larger power supply. When I power my MachTach at 9V using my BK regulated power supply, the regulator gets warm to the touch. When I power it at 12V I can barely touch the heat sink, I do not have a thermal gun. Since the regulator draws the same current (106-109 mA) at 9 and 12V, the power difference is given up as heat.  Without a heat sink the regulator has very limited thermal dissipation abilities. Switching regulators are more efficient thus run cooler and do not require a heat sink. They can generate more electrical noise which can be an issue for some circuits. I guess I do not have a fondness for linear regulators,  they made nice room heaters in the winter time, and then there is my tube amplifiers.



That is what they used to say about tube equipment only--how it heats the room. Now linear regulators are lumped in with tubes. I'll take the simplicity and low parts count of a three term regulator any day. While I use switching regulators here and there, I'll look for a passive solution first, heat and all.


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## Blackjackjacques (Feb 5, 2018)

mksj said:


> My experience with linear regulators and the one in the MachTach differs from your findings. MachTach also supplies a heat sink for individuals wanting to run their tach at 12V.  It may be that your wall wart voltage sag or limited current makes it appear to be different than if you use a larger power supply. When I power my MachTach at 9V using my BK regulated power supply, the regulator gets warm to the touch. When I power it at 12V I can barely touch the heat sink, I do not have a thermal gun. Since the regulator draws the same current (106-109 mA) at 9 and 12V, the power difference is given up as heat.  Without a heat sink the regulator has very limited thermal dissipation abilities. Switching regulators are more efficient thus run cooler and do not require a heat sink. They can generate more electrical noise which can be an issue for some circuits. I guess I do not have a fondness for linear regulators,  they made nice room heaters in the winter time, and then there is my tube amplifiers.



No voltage drop with my wall wart and no current limit issues.  The voltage under no load is 12.1 V and at 140 mA, what the MachTach pulls, it is still 12.1 V.  The wall wart is rated for 300 mA, so given the actual test results, the wall wart is performing as specified.  Additionally, I am getting the same heat dissipation from the heat sink at either 9V or 12V -- as described in the LM340 spec sheet, and as verified with my Fluke thermal device.  Therefore, no surprises on my end and everything appears to be in concert with the LM340 manufacturer.   However, if you are burning your fingers as 12V and not at 9V, your heat sink may not be properly coupled to the device.  You can fix that by using heat sink compound between the device and the heat sink, or perhaps some other problem.  Switching regulators have their place, but such technology would be incredible overkill in this particular application -- in fact, given the low current demand of the MachTach, a simple Zener diode arrangement would have sufficed.


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## Blackjackjacques (Feb 5, 2018)

Cadillac STS said:


> When I put the Hall effect sensor together I did it just like the pictures in the instructions. Cut the leads to quarter inch and solder the three wires. With the solder and the wires there was little room between the leads.  And then you are supposed to push it up into the channel of the 3D printed housing. I was concerned about the wires shorting out when it was pushed into the channel. What I found helpful was to take the heat shrink tubing that comes with the kit, cut 1/4 inch of it, slit the tubing then work that around the middle lead. Don’t heat shrink it. That way if the leads do shift right away or later in use you have some insulation to prevent failure.



Thanks - sounds simple enough - will do.  Looks like the trick now is how I am going to penetrate the gearbox, but I see several options that I just need to comb out.


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## Alan H. (Feb 6, 2018)

Blackjackjacques said:


> No voltage drop with my wall wart and no current limit issues.  The voltage under no load is 12.1 V and at 140 mA, what the MachTach pulls, it is still 12.1 V.  The wall wart is rated for 300 mA, so given the actual test results, the wall wart is performing as specified.  Additionally, I am getting the same heat dissipation from the heat sink at either 9V or 12V -- as described in the LM340 spec sheet, and as verified with my Fluke thermal device.  Therefore, no surprises on my end and everything appears to be in concert with the LM340 manufacturer.   However, if you are burning your fingers as 12V and not at 9V, your heat sink may not be properly coupled to the device.  You can fix that by using heat sink compound between the device and the heat sink, or perhaps some other problem.  Switching regulators have their place, but such technology would be incredible overkill in this particular application -- in fact, given the low current demand of the MachTach, a simple Zener diode arrangement would have sufficed.



Can you share the specific LM340 spec sheet you are looking at?   How are you confirming the same heat dissipation?   

BTW, I am sure anyone who's read this far into this thread knows about heat sink compound.


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## Blackjackjacques (Feb 6, 2018)

Alan H said:


> Can you share the specific LM340 spec sheet you are looking at?   How are you confirming the same heat dissipation?
> 
> BTW, I am sure anyone who's read this far into this thread knows about heat sink compound.




I have already attached it earlier to this tread, but will do so again here as DS00781.pdf.  I'm sure you will understand it.  Given the broadband expertise amongst members and similar applications in most other arenas, I don't believe I was being presumptuous in my identifying heat sink compound.  For those not familiar, heat sink compound is a special grease-like material used between the semiconductor and the heat sink.  It beds the semiconductor device to the heatsink and ensures maximum thermal coupling.  I identified earlier how I was making thermal measurements: I am using a Fluke 62 mini IR thermometer.


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## Eddyde (Feb 6, 2018)

mksj said:


> The electrical noise issue was not the enclosure, but the shielded cable between the hall sensor and the MachTach. Convention would be to ground the shield at the source (not both ends), but any grounding of the shield (either end or at both ends) made the MachTach go wild. So if you use shielded cable, my recommendation is float it on both ends. Grounding is always one of those funny things, doesn't always work the way it is suppose to.



BINGO! I had the exact same problem but with the optical sensor (I felt magnets and steel dust might be an issue). When I rough installed the MachTach on my Bandsaw project I used a scrap of unshielded Cat5, it worked perfectly. Then, when I wired it for keeps, I used shielded cable grounding it only at the MT end, the readings were wildly erratic. Snipped the ground and it was fine. 

I also went the three turn potentiometer route, better resolution that way.


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## Blackjackjacques (Feb 6, 2018)

Blackjackjacques said:


> I have already attached it earlier to this tread, but will do so again here as DS00781.pdf.  I'm sure you will understand it.  Given the broadband expertise amongst members and similar applications in most other arenas, I don't believe I was being presumptuous in my identifying heat sink compound.  For those not familiar, heat sink compound is a special grease-like material used between the semiconductor and the heat sink.  It beds the semiconductor device to the heatsink and ensures maximum thermal coupling.  I identified earlier how I was making thermal measurements: I am using a Fluke 62 mini IR thermometer.




You know..if for whatever reason you do not like connecting your MachTach to a 12 V supply and really want to energize it from a 9V source,  there are a whole bunch of other traditional methods of reducing voltage - including a resistor divider or even multiple series rectifiers and take advantage of the inherent voltage drop across silicone diodes.  At 140 mA load, if you connect a 65 ohm resistor to the 12V supply = 9V.   The resistor should be 2 watt and the load demand placed upon the 12V supply is an additional 185 mA.  voltage dividers have been around ever since the creation of electronics and is the most used method of creating a voltage gradient in circuits.  If your 12V supply can handle the extra 185 mA demand, and it most likely can, it provides you another option - probably the simplest/cheapest.  Yes, the resistor will dissipate heat - but that is what they do.


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## Blackjackjacques (Feb 6, 2018)

Alan H said:


> Can you share the specific LM340 spec sheet you are looking at?   How are you confirming the same heat dissipation?
> 
> BTW, I am sure anyone who's read this far into this thread knows about heat sink compound.




Since I have the document open in front of me, and what may help you interpret the doc, if you look on the second  page for LM140A/340A, not at the top for input voltage where they show the performance based on three input voltages: 10, 19, and 23.  .  The table shows you the expected performance for the three evaluated voltages (10, 19, and 23) but the device can assume any voltage between that range (inclusive) but can be driven all the way up to 35 V.  So 12V is clearly an OK input voltage.


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## davidpbest (Feb 7, 2018)

Alan H said:


> Thanks Blackjack.
> 
> Here's a snippet from Mark's detailed response - _ "The MachTach uses an older style linear voltage regulator which dissipates excess voltage by generating heat. So anything above 9V and the regulator will not last w/o a heat sink (and even with that it generates a lot of heat). "   _
> 
> So my takeaway is that it appears best to feed the device what it wants without sending excess voltage up in heat.




Alan, I asked Henry for a heat sink when I ordered the MachTach kit and he obliged.   I power my MachTach with 12V and it has worked just fine off that source using the heat sink.


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## Blackjackjacques (Feb 7, 2018)

Had the chance to run up the MachTach attached to more precise equipment as shown.   The voltages and results are as follows:

Volts     Current (mA)    Temp (degrees F)
7.2          138.3               123.5
9             138.3               125
12           138.3               130.5
15           138.1               142.5
18           137.8               164.5
24           135.6               184.5

I could have taken this all the way up to 35V, but I did not have a heatsink on the device. The temperature was measured using a Fluke IR gun on the regulator tab itself.  The tests shown concur with the manufacturer's cut sheet and demonstrates that one could energize the MachTach board using the LM 340 regulator as low as 7.2 V, to at least 24 V, and as high as 35V.  As a matter of good practice, I would use the matching heatsink even at the low voltages.


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