Load sensing switch for saw and vacuum

[Phil_S]

What do you guys think about this? http://www.ibuildit.ca/other%20projects ... tch-1.html Skip all the written BS, the schematic is about 25% of the way down the page.

I don't think I can sanction a build with pigtail cords in a plastic pipe when putting this in a proper ABS or metal box with a couple of outlets is simple enough.

As you can see the, idea is to use the saw switch to also turn on the vacuum. I've seen more complicated, where a delay is employed to turn off the vac after powering off the saw, but I don't care about that. I can just run the saw for an extra couple of seconds. Is it possible to simplify this even more?

I forgot to mention, the 6V:120V is simply a 6V transformer wired backwards. However, it it sees 120V on the 6V side (intended secondary but used as primary), I think that means it sees 2400V on the secondary. Something must be wrong with this picture.

[Phil_S]

Hmmm...no bite yet.

I know just how dumb this next comment sounds. I can do the math. If the saw is 15A and the vac is 6A, then the 20A circuit I'm using is likely to blow, particularly if I switch both on at the same time. I don't have a household circuit available with more current.

I'm thinking I need to abandon this idea/project because I need to plug the vac into the 15A circuit, which is the other house circuit that's nearby.

Or, does each machine actually pull as much current as the product plate says it does? You see where I'm going? Not such a good place, huh?

[vibratoking]

I see where you are going. IMO, there is margin in the labeling of the devices and in the house wiring. I bet you don't blow a fuse. If you do, then you can implement a workaround. That's how I roll.

[sluckey]

Scott Phillips of American Woodshop is using a remote control for his vac system. I like this idea.

[JazzGuitarGimp]

Notice how the bridge rectifier is used in this circuit: The + and - outputs are tied together, and the AC inputs are wired in series with the load (saw output). This will cause a small AC voltage (two diode drops) to develop across the AC terminals of the bridge when the saw is running. That small AC voltage then powers the seemingly backwards-wired transformer, which provides enough AC voltage (then rectified and filtered) to turn the 12V relay on.

[Phil_S]

Thanks to all for chiming in on this.

VK: Yes. worth trying. I sometimes run the saw on a 15A feed because I'm too lazy to run the extension cord back to my kitchen where I have 20A. That 15A branch is on an actual fuse not a breaker. (Weird, there is a 2-fuse sub-box.) I'm convinced it never asks for 15A. I'd have to leave it running for an extended period of time, I think. The 20A circuit ought to withstand getting slammed momentarily when I turn it all on.

Lou: So, to be sure I understand a little better, that circuit that has the relay functioning as the switch on the hot side of the slaved outlet? This means the Vac will power up when the switch on the relay closes, just an itty-bit (technical jargon) of time after the saw? That's good, I guess, because it spaces out the surge at power on. Maybe the 20A breaker really will hold.

I've seen plans for something more sophisticated, including a gizmo for delayed on and delayed off for the vac, but that seems unnecessary. The saw can stay on for 5 more seconds to clean up the dust and if there's a need to pound the off switch in a hurry, I'm not going to be thinking about dust.

BTW, I built a nice cyclone dust extractor from a 5 gallon paint bucket, some old 1/4" plywood, a few pieces of PVC pipe and then I had to buy a proper vacuum hose at the home despot. I think I must have $22 in it and $20 was the hose. It works. This thing keeps the filter on the shop vac from getting clogged. In fact, almost nothing goes into the vac tank. I haven't been able to try it on the saw, but I have don't some cleanup around some other sawdust producing work and it seems to have plenty of oomph (sorry, more technical jargon.)

[JazzGuitarGimp]

Hi Phil, I would agree to an "itty bit" of a delay - it won't be more than a tiny fraction of a second. But the good news is, I do believe both the saw and the vacuum will pull maximum current for a very brief period just as they are starting up. Once they are running, the current draw will be less than the startup current (as long as you don't bog the saw down by feeding material into it too quickly). Circuit breakers, like fuses, open because of excess heat. If you pull 25A from a 20A breaker for a quarter of a second, that likely won't result in enough heat to trip it.

The diagram at the right side of the schematic: the circle K and the capacitor looking thing right next to it, represent the relay. The circle K being the relay coil, and the capacitor symbol is the relay contact. I only point this out because this is rather unusual symbology for a relay.

Cheers,
Lou

BTW, I have a zero clearance insert coming for my ancient table saw - should be here Monday. It's amazing all the things you can learn about by watching youtube how-to videos. I never knew there was such a thing as a zero clearance insert.....

[JazzGuitarGimp]

By the way, Phil, if you have never seen this, you need to drop everything you're for a minute, nineteen seconds and watch this video. When the blade hits the hot dog, your jaw will drop to the floor!

https://m.youtube.com/watch?v=T3IGPCkirdU

[Phil_S]

Lou: The guy whose post on the load sensing switch is really a woodworker. He has an interesting youtube channel that I watch sometime. Personally, I think he does some interesting things, but I also think he should take more care around the table saw. I can understand his dislike of a blade guard, but I can't fathom his rejection of the riving knife or splitter. I think he is a bit too cavalier. Anyway, I think this explains his unconventional combination of symbols for the relay. He identifies K1 as the relay.

I've known about the SawStop for quite some time. I'd get one if I could justify the cost and had space for it. If you don't already know, when you trip the brake, you have to buy a new one and they aren't cheap. Still, a bargain compared to a new finger. It's a very nice product. It's enough to make all the other saws illegal.

On the zero clearance insert, in my limited experience these are a must for serious cross cutting, but you don't need one if you use a sled. The slot in the sled is zero clearance. For ripping, tear out isn't much of an issue. I have back burner plans for making a ZCI for myself. It is a matter of rough cutting the shape and then finishing it off with a flush cutting router bit that rides the OEM metal plate as the template. The rest, cutting the slot, fitting a few leveling screws and other odd 'n' ends look pretty straight forward to me. If I ever do it, I'll be sure the let you know. That said, they sell nice ones guaranteed to fit your saw for reasonable prices.

I confess to holding back on the two schematics I'm now posting. These came from an EE forum where I feel rather intimidated. (I had to register to get these. Can't see what's so special that they need to protect them.) These look more complicated and I'm not sure there is much added benefit on the master-slave board. BTW, on that particular board, I keep looking for where to plug in two things (saw=master, vac=slave) and I"m not finding it. What is that about? And then there's a floating switch at the top of the drawing that connects how? Anyway, I diverge. The better piece of work, IMHO, is the delay module. It seems this is worth building (delay on, delay off), but I can't help but wonder if it could be simplified, and then there's the question I can't figure, which is where do I connect AC1 and AC2 to the other circuit.

[JazzGuitarGimp]

The nice thing about the slave / master design only becomes apparent when the vacuum is a good distance from the saw. The high current of the saw is contained at the saw, which is where the CURRENT SENSE portion of the circuit resides (the master part of the circuit). I know your vac only draws 5A, but let's say it draws 12A for a minute. Locating the SHOP VAC DELAY portion of the circuit (the slave part of the circuit) at the shop vac keeps that 12A current contained at the vac. The two-conductor cable (I am going to call this the Control Cable) that is required to connect the master to the slave is low voltage and low current - a twisted pair of 24awg wire will do nicely here. So, no need to run a cable that can carry 15A all the way to the vacuum. This is good if your saw is at one end of a 50' shop and the vac is at the other end, which wouldn't be unusual in an industrial wood shop.

In connecting the two halves of the circuit together, in the SHOPVAC DELAY page, delete the Remote Start Stop switch (SW1), and replace it with one end of your twisted pair Control Cable, then wire the other end of the Control Cable to the COM and NO contacts of the relay in the CURRENT SENSE SWITCH (Master) portion of the circuit.

Incoming AC, Saw, and VAC connect as follows:

- Incoming AC for the saw and Master portion of the circuit is applied at P1 in the Master schematic.
- Saw is plugged into J1 in the Master schematic.
- Vac. To connect the vacuum, the two AC pins of the solid state relay (SSR on the SHOPVAC DELAY page) are seen as a switch contact, so you would wire this as you would any other mechanical switch, between the incoming 120VAC and the vacuum.

Also note that a 12VDC power supply will be needed for the SHOPVAC DELAY circuit, if you separate the two halves of the circuit.

There is one thing that doesn't make sense to me: I don't understand why the mechanical relay (K1 in the Slave schematic) is used. That relay could be deleted with the following modifications:
- Disconnect the left end of R5, and instead, connect it to the emitter of Q3
- Connect pin 4 of the SSR to COM (which is the net where the bottom of the RLY1's coil was connected.

Also note T2 in the Master schematic. You need to remove the secondary winding, and replace it with three turns of #12 stranded wire.

Another cool thing about this design: If you employ it in a shop with multiple tools, a Master section can be created for each tool you want to command the vacuum, and the twisted pair control cables can all be connected in parallel at the Slave end.

[Phil_S]

Thanks for taking the time, Lou.

Cool, yes. Too complicated for my non-EE mind. I am unable to sort this out. Also, I was really turned off by the note to unwind the secondary and replace it with 3T 12AWG. I've fiddled with windings before and it seems like too much effort. I thought maybe I could build it in a single box as the vac and the saw will always be near each other, but I'm no longer sure I can do it well and on the cheap.

It's too bad, Sears used to sell a master-slave thing for $20. It appears it is no longer available. There is a similar one on the market. It sell for about $35 up to about 2x that if you don't know where to buy it. This thing: http://www.rockler.com/i-socket-110m-to ... uum-switch I might just treat myself.