D/C Current Sensor Turn off Delay - How to?

[Daryl Upole]

I've read a lot of the posts on parts of this question. I am using a Grainger current sensor to a relay to turn on my D/C system when I turn on my machine power on that circuit. It has worked great for a few years now. As I read these forums, I'd like it to stay on for a little while when the power to the machine goes off. Can someone fill in the blanks on how I could do this? I've read some of you have done this - but could not quite tell how. I know a fair amount about electrical wiring - but not on how to accomplish this delay. The sensor has a delay feature to delay the turn on - but that's not what I want. My D/C is on a 220volt 20 amp circuit that the relay controls. I also have a manual override switch to power the relay.

[Tom Veatch]

I installed one of these (http://www.alliedelec.com/Search/ProductDetail.asp?SKU=519-5185&SEARCH=&MPN=4710A%2D8%2DB%2D3&DESC=4710A%2D8%2DB%2D3&R=519%2D5185&sid=477048004DBEE17F) in the circuit that powers the relay coil. There are many similar products that could be used.

In a nutshell, this device is inserted into the circuit between the switch and the relay coil. A variable resistor is used to set the time delay - from 2 sec to 1000 sec in this particular case. When the switch is turned on, power is fed to the load - the relay coil in this case. When the switch is turned off, the device maintains output power to the load until the delay time expires.

Here (http://www.artisancontrols.com/pdf/4710.pdf)is the spec sheet for the device. It shows how this specific device is wired into the circuit. Other devices might be different.

[Tom Veatch]

Here's the wiring diagram for the installation in my system. The control system for my DC has two modes, Manual and Automatic. With the main switch on, setting the mode switch (DPDT center off) to "Manual" turns on the DC. Setting it to "Auto" puts the timer and tool sensor switch in the circuit such that when a tool is turned on, the "tool sensor" switch closes and turns on the DC. When the tool is turned off, the "tool sensor" switch opens and the delay time interval begins. The DC is turned off at the end of the delay interval.

The delay interval is controlled by the 5meg potentiometer and the 5Meg resistor in parallel with the SPST High/Low range switch. With the range switch closed, the 0-5meg potentiometer selects a delay interval of 2sec to 500sec. With the range switch open, the total resistance in the delay circuit is 5meg to 10meg and the delay interval is 500sec to 1000sec.

Hope this helps.

[Daryl Upole]

Thanks, Tom. That is exactly what I was looking for. Do I just put a resistor of different values to get the time I want between the two terminals? Are they just the cheap low-watt resistors you get in a bundle at Radio Shack?

Thanks again for the schematic.

[Tom Veatch]

Thanks, Tom. That is exactly what I was looking for. Do I just put a resistor of different values to get the time I want between the two terminals? Are they just the cheap low-watt resistors you get in a bundle at Radio Shack?

Thanks again for the schematic.

It will vary depending on the specific timer you use. Some have the variable resistor (trimmer pot.?) built into the device. This particular one uses an external resistor (each additional Meg is another 100 seconds of delay up to 10Meg/1000sec). The spec sheet in the link in the previous post shows the Seconds/Ohms relationship. According to the specs for this device, the worst case for the timing delay power dissipation is 3 milliwats, so a cheap 1/4 watt resistor is more than adequate.

Note, this is specific to this particular timing module. For other modules, the specs may be quite different.

[Matt Meiser]

Tom, that's great! For a while I was using a surplus PLC as the heart of my DC and heating/cooling control, but the comm module went bad and I didn't want to spend the $$$ to buy a new one so I ripped it out. Back to regular control for the heating/cooling and just blast gates for the DC. But having microswitches on the blast gates really lends itself to an off delay to give you time to move from one tool to the other without cycling the blower. I had mine on about a 15s delay before which worked great for me.

[Daryl Upole]

Thanks for the info. I have a package of these from when I did not want to pay to have a new resistor key for my Caddy (the old one started to work kind of funky in the ignition switch) - so I just wired them right into the theft control feature to bypass that and had regular keys cut.

[Tom Veatch]

Thanks for the info. ...


You're more than welcome.

My current shop upgrade project is to automate the blast gates so they actuate with the tool - like the Grizzly/Ecogate gates. But, the commercial 6" gates are outside my financial window. Right now, damper type gates with push-pull solenoid actuation is the front runner being considered.

[Bruce Wrenn]

For my DC system, I use the SSAC current sensor that was used in article in FWW, Aug 2000. I added a delay on off timer, from Grainger, to it. DC runs about ten seconds after machine shut down. All parts, including the relay are mounted in bottom of the power panel. One leg of each 240 circuit, except welder and air comp. pass through sensor. I use multiwire branch circuit wiring, so half of my 110 outlets also control DC. At each location, I have two 110 duplex recpt. and a 220 recpt. The duplex on the left controls DC.

[Doug Hobkirk]

...the more I write in this post, the less I realize I know...

Daryl, Tom, Matt -

First, you guys open my eyes and make me start to think... I had planned on using a $20 Sears current sensor in-line plug but I do not know if it can handle triggering a 240V device. Now I am considering other issues.

Turn-on DC Sensor
Could the Sears sensor rated at 15A control my DC by controlling just one leg of the 240 circuit? (The induction motor on my 2HP Grizzly DC lists it as 12A at 220V)
This current sensor relay (Grainger item 4GY65 (http://www.grainger.com/Grainger/items/4GY65)) cost $60 has a 12 amp "resistive" amp rating ("inductive" rating would be about half that?) - is this sufficient?
Does an adjustable trigger (e.g., 2A to 20A) mean if I set it at 2A anything over 2A will trigger the relay? (My tools that I would like to trigger the DC range from 15A down)
Does the "maximum inrush current" (when listed) apply to the triggered tool, acting like a time-delay fuse to accommodate the motor "over-drawing" on startup?Delayed DC Shutoff

I thought that delayed DC shutoff couldn't really be done unless it was built in, but now I wonder if something like
this (http://www.grainger.com/Grainger/items/4EB23) for $60 would be sufficient? (Sorry Tom, but I just don't know enough to fully understand your schematic.)

Bruce -

Then, I read "...I use the SSAC current sensor... I added a delay on off timer... DC runs about ten seconds after machine shut down... One leg of each 240 circuit, except welder and air comp. pass through sensor. I use multiwire branch circuit wiring, so half of my 110 outlets also control DC. At each location, I have two 110 duplex recpt. and a 220 recpt. The duplex on the left controls DC."

You made my knees buckle! And you make me rethink my soon-to-be-started garage sub-panel wiring job.
Does "multiwire branch circuit wiring" mean you have two 120V outlets, each to one 120V circuit breaker, and a 3rd 240V outlet?
Are all of your left outlets (your tool outlets) (excluding welder and compressor) on one circuit?
Would draw on a 240V outlet also trigger the DC?
Continuing my point 1 above, how much does a current sensing relay that can handle a home shop cost? (My only 240V tools is my DC, although I had planned on having at least two extra 240V outlets)
Do you have a diagram?Thank you all for your stimulating discussion!

[Matt Meiser]

Delayed DC Shutoff

I thought that delayed DC shutoff couldn't really be done unless it was built in, but now I wonder if something like
this (http://www.grainger.com/Grainger/items/4EB23) for $60 would be sufficient? (Sorry Tom, but I just don't know enough to fully understand your schematic.)



Here's (http://www.factorymation.com/s.nl/it.A/id.763/.f?category=100) a similar but much less expensive 120v off delay relay.

Something like this (http://www.grainger.com/Grainger/items/6C055) can be used to detect current flow, but if it was me, I'd use it to control a contactor that actually switched the motor.

[Ken Garlock]

Hi Gents.

I also did a semi-automatic dust collector system. I had bought some 50 Amp/250V solid-state relays several years ago to use as the motor relay on the cyclone. To drive those two relays(one on each 240v hot line) I built a small 12V DC supply to provide the needed switching voltage for the relays. At five of my stationary tools, I placed a solid-state current switch (http://www.crmagnetics.com/newprod/ProductView.asp?ProdName=CR9321), and then ran thermostat wire back to the relay panel from each switch. When the tool is turned on, the current switch activates a NPN transistor internally, that in turn completes the 12V circuit that closes the big solid state relays and starts the motor. I placed about a 12,000 MFD capacitor with current limiting resistor across the switched side of the 12V line that discharges slowly after the tool is turned off, and keeps the cyclone running for an additional 10 seconds.

I too would like to build an automatic blast gate, but that is down the list of things to do.:o

[Matt Meiser]

Tom, have you thought about using pneumatic cylinders for automation? Seems like they would be relatively simple to deal with and surplus ones aren't too expensive.

[Tom Veatch]

Could the Sears sensor rated at 15A control my DC by controlling just one leg of the 240 circuit? (The induction motor on my 2HP Grizzly DC lists it as 12A at 220V)

I'm going to decline comment on the specific devices since I'm not familar with them. However, controling the motor by switching only one leg of the circuit will work. In reality, that's what you do when you switch only the "hot" wire in a 120v circuit. Someone please correct me if I'm wrong, but I believe switching only one leg of a single phase circuit is acceptable to code as long as the voltage is less than 400 volts.

I built my current sensors from the plans in "Automated Dust Collector", Woodwork Magazine, Issue 91, Feb '05 (http://www.woodwork-mag.com/back_issues.html).


I thought that delayed DC shutoff couldn't really be done unless it was built in, but now I wonder if something like
this (http://www.grainger.com/Grainger/items/4EB23) for $60 would be sufficient? (Sorry Tom, but I just don't know enough to fully understand your schematic.)


Something like that could work. That particular one couldn't be used to directly control the DC motor because of the low HP rating of the relay. It could be used to control the motor contactor coil, but you'd need a 24v power supply. I think you'd be better off with something like the solid state timer I linked in a prior post. That particular one was about half the cost of the Grainger link and can be used with 120v power. There are a lot of other brands/models (http://www.google.com/products?q=solid+state+timer&oe=UTF-8&scoring=p)of solid state timers available.

Most of the complexity of that schematic is due to the frills - dual mode and variable timing. I've simplied the schematic for a fixed time automated system without the frills. See the attached image below. That schematic is pin-specific to the one that I used and might not be pin-compatible with a different brand/model.

[Tom Veatch]

Tom, have you thought about using pneumatic cylinders for automation? Seems like they would be relatively simple to deal with and surplus ones aren't too expensive.

Yes, indeed, I have. In fact, post #5 in this thread (http://www.sawmillcreek.org/showthread.php?t=71943)shows a pneumaticly operated gate built by Todd Crow that I'm very interested in. I haven't looked into surplus cylinder prices, but Grainger prices for all the components would run about $100/gate. Much better than the Grizzly/Ecogate 6" gate prices, but I'm thinking I can get there for somewhere in the $30 - $50 range using the design of Post #9 (Jeffrey Makiel) in that same thread. I'll almost certainly build a prototype based on the Makiel gate for testing and design verification.

[Bruce Wrenn]

...the more I write in this post, the less I realize I know..
Bruce -

Then, I read "...I use the SSAC current sensor... I added a delay on off timer... DC runs about ten seconds after machine shut down... One leg of each 240 circuit, except welder and air comp. pass through sensor. I use multiwire branch circuit wiring, so half of my 110 outlets also control DC. At each location, I have two 110 duplex recpt. and a 220 recpt. The duplex on the left controls DC."

You made my knees buckle! And you make me rethink my soon-to-be-started garage sub-panel wiring job.
Does "multiwire branch circuit wiring" mean you have two 120V outlets, each to one 120V circuit breaker, and a 3rd 240V outlet?
Are all of your left outlets (your tool outlets) (excluding welder and compressor) on one circuit?
Would draw on a 240V outlet also trigger the DC?
Continuing my point 1 above, how much does a current sensing relay that can handle a home shop cost? (My only 240V tools is my DC, although I had planned on having at least two extra 240V outlets)
Do you have a diagram?Thank you all for your stimulating discussion!
Multiwire branch circuits use a double pole breaker. Each hot leg is connected to a recpt. along with a neutral. This gives you two 120 circuits. Then I feed through the recpts. into another box with a 240V, 20 amp socket Only one of the hots passes through sensor. Either the 240, or the 120 leg that passes through sensor will operate DC. I have a total of six machine circuits (220) in my shop. On each set of circuits, I have multiple recpt. sets. I chose to make the left recpt.at each location the one that controls DC for 120 machines. No specific reason, just did. When I bought sensors back in 2000, they were about $40 and delay timer was about $20. They relay I used has a 120V coil, so no extra transformer is needed. It was a stock Grainger item. You only need to break one leg of the 240 to DC. By using 3/4 EMT., I didn't have to pull a ground wire. With the price of #12 copper THHN being what it is, that is both a savings in time and money. You still have to bond recpts. to the metal boxes though. PM me an address and I will do you a diagram, along with specific parts #'s

[Rob Will]

I think this discussion is leaning toward the complicated side.:o

All you need is a magnetic starter on the DC equipped with a time delay auxillary contact (off the shelf stuff at the local electric motor shop).

How you handle the control is up to you. With most current sensing relays, remote control switches and push-buttons, you will simply be "switching" the coil voltage to the much heavier magnetic starter.

If you can't source a magnetic starter with built-in delay off, I would get a time delay relay (and the cooresponding mounting socket) from a local electronics shop or Grainger.

Rob

[Daryl Upole]

Hi Doug & All;

Doug, I purchased my SSAC sensor from Grainger a few years ago. But I could not find the instruction sheet recently so I Googled to find it; which I did. In the process, I did see it somewhere for under $50. So, you might want to Google the exact part number and you may find better pricing.

I went with Tom's suggestion & ordered the delay relay from the link he provided. ( they may even have the SSAC) It will go between the sensor and the 220Volt relay to the D/C. I should have it in a few days.

TOM - on that - I think I've got the resistor stuff figured out. I'm barely knowledgeable in this area. I found the package of 1/4 watt Radio Shack resistors I had. With the scale on 2000k - I get the reading of approx 1,500. And, the color banding looks like 1 and 5 @ 100k multiple. So, this would be the 1.5MEG? Which is 1,500,000 ohms? From the charts, that should give me a little over two minutes.

I ended up taking an old breaker panel and setting up all the relays, etc. in there just underneath the power panel. That gave me a lot of room to work.

On the split circuits - in my shop I use GFCI for all 110 circuits. Without special receptacles, breakers, etc. you need a single circuit to work properly - I won't work right on a split circuit. I have alot of respect for electricity and with my concrete floor and the possibility of using tools outside the shop, I feel better doing so. I'm pretty sure local code would require that for me as well. Also, outlets need to be 24" off the floor - I think that has to do with minimizing problems from vapors settling near the floor. I've never had a problem with false tripping of the GFCI.

I'm glad to know that one leg of the 220 runs through the sensor - that's the way I've got it set up awaiting the rest of the parts and my new saw.

Doug - yes, you can adjust it from 2 amps up. From the spec sheet, I think you can wrap the wire around the sensor if you need it to be a lower start up. For example, I leave mine at the minimum. A 100 watt bulb (less than 1 amp) will not trigger it - but just my 3/8" electric drill will. There is also a delay on setting you can use.

[Larry James]

... In reality, that's what you do when you switch only the "hot" wire in a 120v circuit. Someone please correct me if I'm wrong, but I believe switching only one leg of a single phase circuit is acceptable to code as long as the voltage is less than 400 volts.

Tom, I think you are correct about switching only one wire being acceptable. The double pole/single throw disconnect, as shown in your drawing, is required. Nice control circuit Tom.

In a 120 volt circuit the neutral (usually color coded white) is the "grounded conductor" and connected to ground at the service entrance. Therefore, the neutral is not "hot" with respect to ground at the equipment. However in a 220 volt circuit you may control the load by switching only one leg (wire), but unlike the 120 volt circuit, the second un-switched wire remains "hot" at the equipment.

Safety: it is very important to understand that if only one wire is switched in a 220 circuit, you must unplug, or turn the circuit breaker off to remove voltage to the equipment before working on the equipment.

Larry

[Matt Meiser]

Safety: it is very important to understand that if only one wire is switched in a 220 circuit, you must unplug, or turn the circuit breaker off to remove voltage to the equipment before working on the equipment.

That's safe working practice regardless. There was a recent thread on magnetic switches that started on their own after a physical shock. A disconnect switch by your DC might even be a good idea.

[Tom Veatch]

...I think I've got the resistor stuff figured out. I'm barely knowledgeable in this area. I found the package of 1/4 watt Radio Shack resistors I had. With the scale on 2000k - I get the reading of approx 1,500. And, the color banding looks like 1 and 5 @ 100k multiple. So, this would be the 1.5MEG? Which is 1,500,000 ohms? From the charts, that should give me a little over two minutes. ...


It's been a long time since I tried to read resistor color codes, but if I remember the "Bad Boys Ravish..." mnemonic correctly, a 1.5Meg resistor would be Brown, Green, Green and yield about 150 seconds or 2 1/2 minute delay. Two resistors in series would double that to 3Meg and 5 min delay, etc.

[Daryl Upole]

Hi Tom,

I got the delay unit in and installed today. Works great. I put in 470k ohm resistor and that gives me about 70 seconds which seems about right.

What would I use if I wanted this to be variable? Can you point me to the right part?

Daryl

[Bruce Wrenn]

Daryl, did you think about the fact that you have to have GFCI on the 110's, but not the 220's. Here , we only have to have GFCI on outlets closest to the door. You can do the "multiwire branch circuits with GFCI recpt. on the 110 legs. You will have to feed a couple of hots for the 220.

[Tom Veatch]

Hi Tom,

I got the delay unit in and installed today. Works great. I put in 470k ohm resistor and that gives me about 70 seconds which seems about right.

What would I use if I wanted this to be variable? Can you point me to the right part?

Daryl

Assuming that you got the same module I did, the adjustment range runs from 2 sec @ 0 ohms to 1000 sec at 10Meg ohms. You can use a potentiometer in place of the fixed resistor and dial in whatever resistance/delay time you want. A 0-10meg pot will give you the full adjustment range.

I just went by a local "mom and pop" electronics store and picked up a single-turn linear pot similar to this (http://www.radioshack.com/product/index.jsp?productId=2062297&cp=&sr=1&origkw=potentiometer&kw=potentiometer&parentPage=search). They didn't have a 0-10Meg in stock so I got a 0-5Meg plus a 5Meg carbon resistor and a small SPST switch. I got a little fancy with it (for no good reason other than just playing around) and wired them such that the switch and resistor are in parallel and that combination is in series with the pot. I believe the first schematic I posted shows that arrangement. Doing it that way gives me a High (500-1000sec) and Low (2-500sec) range on the potentiometer/delay setting. With the switch closed, the resistor is shorted out and the total resistance in the timing circuit is the potentiometer's 0-5meg (2 to 500 sec). With the switch open, the 5meg resistor is in the circuit and the total resistance is 5-10meg (500 to 1000 sec). All times and values are approximate.

What parts? If you are pretty sure about what maximum delay you want, just get a potentiometer with a maximum resistance at or above that required for your maximum delay time. You should be able to find one at any local electronics shop for a couple of bucks. You don't need a "precision", "high wattage", "low-noise", "audio", etc. type. Cheap is good. I would say Radio Shack except the stores around here seem to have become cell phone stores and are very short stocked on any electronics components.