Automatically powering 220V dust vac when 220V saw starts

--There's a widget for sale at Woodcraft stores (and other places) that gives you wireless control of your vacuum system. It's only $30 or so; howzabout keeping it simple? Oh, and for needless complexity check out my system:

Thanks for the reply. I'll look over your site, thanks!

All the auto-switches of this type I have seen for sale so far, like this at Woodcraft are for 120 volts:

Sears used to sell one also, again, 120 volts.

There's also this remote control, $70 for the 220 version

I could easily rig up one of these from 2 All Electronics bits, total cost about $30, but I know from experience if it doesn't turn on by itself, half the time I'll forget until after making a cut!

Dan

If you don't want to modify the saw's wiring, install a homemade extension cord with a junction box and receptacle at the saw end. Wire a transformer in parallel with the receptacle, and a switch in series between the power cord and the receptacle. Leave the saw switch on, and control power to the receptacle and transformer with the added switch. The transformer can power whatever circuit you use to control the vac.

Switch || ----- Mains =========|Recpt|===SawCord ----- || Xformer

For the delay, and the circuit to trigger the RF keychain transmitter, you could use CAT# RLY-89 with a 3300 uF

------- D1 |Xformer|CT---[330R]--->|---+---------+ | | | | ---o To RF | | [3300uF] [RLY-89] ^--o Xmitter | | | | | |-------------------+---------+ -------

The 330 ohm resistor limits the surge current through the cap when the switch is turned on, and lowers the peak voltage so that cap gets charged to about 24 volts. (Peak would otherwise be ~28 volts). When the switch is turned off, the cap holds the relay energized while it discharges for about 10 seconds. The relay contacts operate the RF transmitter.

Ed

Thanks for the reply, great ideas. I'd probably forgo the cord/receptacle & just tap into the saw's wiring.

Makes sense.

You kind of lost me on the last part, but I think basically, the 2 xformer arrangement is simply a 24vdc half wave rectified power supply (using a single diode), right?

There is one confusing issue with the RF remote. The control appears to work with 2 momentary contact buttons, push & release one to turn on, push & release the other to turn off. So simply have a relay with closed contacts during the entire "on" phase may not work to keep the unit on, and simply opening that connection will not shut the unit off, nor would a SPDT arrangement which kept one set of contacts closed when the relay is energized, another closed when it's not. What I'd need is something to briefly close one set of contacts when the saw powers up, then briefly close another set after a delay when the saw is powered off.

Dan

Right. Since you have 240 vac input, the recommendation was for 2 cheap 120 vac input xformers in parallel on the primary side. On the secondary side, with the secondaries wired in parallel (and in phase), the voltage from the center tap to either end is 20 volts with the part specified. With the components specified, the circuit produces about 24 volts across the cap.

Ok. For push and release for on, and push and release for off, you need additional circuitry. Since you seem comfortable using relays, we'll stick with them. Use the circuit above, but change RLY-89 to RLY-481. You may want to add a 1000 or 2200 uF cap in parallel with the 3300 uF cap, because RLY-481 will drop sooner than RLY-89. The change to RLY-481 is needed to provide SPDT contacts, because RLY-89 is SPST. (Allelectronics part #s)

With the new relay, add two more relays and two caps, a diode and resistor, like this:

D2 +24 ---+--->|---+----------+ | | | [RLY-481] [C2] |> |

one

this

You can get power boards that have switched outlets that only turn on when the device plugged into the main outlet switches on. They are designed for home theatre systems and computer systems etc.

Dave.

Thanks for the reply. I see what you mean, using RC circuits to time the relays. I'm not averse to a solid state solitution, if it would be more straight forward. I actually studied all this 20-odd years, and I've built a ton of stuff, etching circuit boards, etc., just don't remember any of it, unfortunately...

Dan

Not in 220, though.

Thanks for the reply.

Dan

^^^^^^^^ series

Ok. You can hack a 120V GFCI and trigger it with the

Or you can use a CT (current transformer) feeding a resistor, rectifier and filter cap to make a DC voltage that is fed to an opto-coupler. The output side of the coupler can operate a relay (with cap in parallel for your turn-off delay) that operates the vac - again, no need for the R/C stuff.

So - do you have a neutral? If so I can post the schematic for the GFCI modification.

Ed kludge.

Ed-Yes, the outlet does have a neutral. Thanks for your continued input on this!

Dan

Dan,

I can e-mail the full schematic to you, or post it on ABSE, your choice. I'll describe the GFCI modification here. It applies to a receptacle type GFCI using the LM1851 chip.

AC Hot --------XXX--------------------+---+---+ | | | --->|----+ | | | \\ | [180R] | | G [1K] | | | | MOC3031 | | [.01uF] | ------ | | | +--[3.3K]--[LED]---|1 6|--+ | [100R] |+ | | | | [4.7uF] | | [TRIAC] | | | | / | | +------------------|2 4|--+ +---+ | ------ | Gnd [Relay] | AC Neutral-----YYY------------------------+

Not shown is the wiring from the gate (G in the diagram) of the SCR to the LM1851 chip in the GFCI, the wiring to the anode of the SCR, or the remainder of the GFCI circuitry.

The lines marked XXX and YYY are connected to the LINE hot and neutral of the GFCI. The hot LOAD side of the GFCI is connected to your saw. The neutral LOAD side is not used.

Wire the relay contacts to control your vac. Wire the saw to the AC hot in the above diagram and the other AC hot lead.

As shown, there is no delay on dropout. To get that, wire a transformer in place of the relay, use the secondary to feed a DC supply, and use the relay and parallel cap mentioned in the earlier post.

With the above wiring, when the saw is turned on, there is an imbalance in the AC Hot and neutral currents. The GFCI senses that, and turns the SCR on. (It turns off every time the AC crosses zero, but is turned back on again by the GFCI chip) Pulsating DC appears at the cathode, and is smoothed by the 4.7 uF cap. That turns on the MOC3031 opto coupler, which turns on the triac and powers the relay or transformer. When the saw is off, there is no imbalance, so the GFCI does not turn the SCR on.

Ed

Ed-Posting it on ABSE would be great. Could you include the one for the multi-relay circuit as well? Having a hard time making sense of the ASCII schematics!

Thanks again Ed!

Set your newsreader (or Outlook Express, if that's all you have) to use a monospaced font:

or Cut & paste into a monospaced text editor like Notepad.

or Use Google's archive:

I just posted the modified GFCI schematic on ABSE. I don't have the multiple relay schematic as a jpg.

Ed

Thanks Jeff, a major improvement!

Dan

Got the schematic, thanks Ed!

Dan