Need power relay


I'm in need of an, um, extension cord that, when power is requested by the attached device, an additional outlet on the box goes live.
The purpose of this plan is to provide power to an auxiliary exhaust fan when the fume-generating equipment is switched on.
The scheme seems infinitely simpler than hooking up wiring to the primary device.
Any suggestions would be welcome.
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HeyBub wrote:

How many Amps does each device draw?
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Most woodworking shops have stuff like this, for exactly that purpose: turning on a dust collector when you power up your table saw. Check out places like Lee Valley (http://www.leevalley.com) and other woodworking outlets.

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HeyBub writes:

Make your own using a 20 amp definite-purpose contactor with 120 VAC coil:
http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?ItemId11778537
This will be cheaper and more rugged than the usual woodworking gadget.
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Richard J Kinch wrote:

Richard, how would he use a VOLTAGE operated relay to do what he wants to do?
He needs a CURRENT sensing relay, doesn't he?
Here's a "fancy one" which looks like it'd have enough range and capacity to sense the first unit's current draw and power up the second unit:
http://www.crmagnetics.com/newprod/ProductView.asp?ProdName=CR4395
But it does seem to me that this $20 device from Sears will give eggsackly what he wants:
http://tinyurl.com/2x65u5
Jeff
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Jeffry Wisnia
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On Thu, 25 Jan 2007 13:26:00 -0500, Jeff Wisnia

Looks to me like that's just a power-strip witha strange configuration.. IOW, if it's on power is available to all three devices, and if it's off, there's no power.
I thought OP was looking for something that would supply power to the other devices only when the primary was actually DRAWING power.
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Goedjn wrote:

I'd be willing to bet you $50 to the 501C charitiy of the winner's choice that your "Looks to me" is dead wrong, Goedjn.
The link I posted may not work, but going to www.sears.com and searching for 00924031000 will bring it up.
If you zoom in on the photo you'll see the top outlet is labeled "power tool" and the bottom two are labled "accessory - accessory".
Plus if you click on and read the "Reviews" you'll see users describing doing what the OP wants to do. The only limitation might be its 15 amp capacity.
Wanna place your bet? <G>
Jeff
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Jeff Wisnia writes:

Mount contactor inside and outlet box outside of tool cabinet/base. Splice contactor coil in parallel with the tool's switched power. Splice tool's incoming cord power into one side of contactor poles, outlet to the other side. Or, use separate AC circuit for contactor supply if you do not want to load the tool's cord. Now the outlet powers on/off with the tool on/off, but the outlet does not load the tool's switch.
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Richard J Kinch wrote:

But Richard, that's not what the OP said he wanted. To wit:
"I'm in need of an, um, extension cord that, when power is requested by the attached device, an additional outlet on the box goes live."
Note that it reads "requested by", not "when someone flips the power swith on the tool."
And the OP continues, "The scheme seems infinitely simpler than hooking up wiring to the primary device."
Your suggestion that "hooking up wiring" stuff, right?
Hair splitting an RCH I freely admit, but that's what engineers do for fun, isn't it? <G>
Peace,
Jeff
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Jeff Wisnia writes:

Right. I told him what he needed, not what he wanted. What engineers do for fun.
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wrote:

Is the device at the far end automatic, or is this "requests power" event manually induced? THe usual technique is to replace the switch for the equipment with a DPST switch. (or just put the power supply through another DPST switch, in which case the fan would run anytime the power is available, reguardless of whether it's being used.
Depending on what the "fume generating equipment" is, you probably can't just find a fan of the same current-draw, and put them in series. So the last choice is to use a current-sensing relay like this one:
http://www.crmagnetics.com/newprod/ProductView.asp?ProdName=CR4395
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HeyBub wrote:

I second the wood working shop dust collector switch.
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Joseph Meehan

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Joseph Meehan wrote:

Thanks. I finally found one. It seems as if you flip the switch on the switch and power is delivered to the outlets on the box, one of which can be the dust collector.
I want something such that when I turn on device #1, device #2 gets supplied power. I don't want to make an electrical connection directly to device #1.
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I saw one done in a serious fashion, for a different but similar application. The person used an old air conditioner contactor, and when he powered up, a transformer got power too, kicked on the contactor.

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