Help needed: Laser blower relays

As we touched on before, we won’t be running the power itself for the lasers up to the cutters. Rather, they’ll be relay-controlled.

The lasers already have provisions for this as a 24VDC control line. I think 5V is possible, but not preferable.
The 2 new blowers on hand are 550W 120V =4.6 amps. We’re gonna switch at least one to a 208v 750W soon. The one I looked at just now unfortunately does not have an accessible box to access the hot wire coming off the cord to insert a relay. We don’t want to like butcher the power cord up and electrical tape a relay onto it, although that would technically work and it wouldn’t be the most dicey thing I’ve ever seen.
So, that’s two 24VDC controlled relays switching 4.6A each.
No solid state relays please
No wireless controls please

The relay itself is trivial, it needs an appropriate housing and receptacle and plug. One circuit can handle 2 (potentially 3) blowers, it would be efficient to use one control box, one 120VAC 15A+ power cord, and two blower outlets. A standard electrical utility box- like you normally put the outlets in- could be usable, and has outlets on it. A NEMA enclosure is another option. We could put DIN rail relays on a rail inside a box.

A separate box would be needed for the 208V blower(s).

Someone did mention this:

That looks like a good prebuilt option. But it’s only one relay that switches all the outlets together, so we’d need two. A little pricey for what we need but still ok. Or does someone want to build this simple thing?

This is another slightly-less-prefab option. Same basic idea, but would work for higher voltages.

Are any of the blowers you’re looking at more than 1/2hp?

I’m not sure what that relay mechanism is- some sort of low voltage, and it expects a mechanical contactor to trigger it. Could be AC or DC, not specified.

I don’t see how to use it since it’s not a complete plug-and-receptacle system that covers the high voltage up. It ends in bare wire.

Yes, actually all blowers are over 1/2 hp I’m afraid.

That’s the sort of relay. We just need a housing so we’re not cutting up cords, which would be dicey for safety and a problem if we have to swap out a failed blower.

While it might make a lot of sense to put the relays inside the building’s steel outlet box, tied straight to the MC flex conductors, that makes it part of the building wiring and I don’t think code allows that.

Optoisolation is not strictly necessary, but it does mean we don’t have to rely on a diode at the laser controller to avoid damaging the output with the high voltage spike of depowering an inductive relay coil. But just diode-protecting the output is fine.

Just putting a relay into a junction box isn’t 100% kosher, especially if it’s part of the building wiring. You need separation line-voltage wiring from low-voltage wiring somehow. You could 3D-print or cut some dividers.

The relay I linked was designed to be code-compliant for fixed install – it mounts to a junction box with a locknut so the line voltage stuff is inside the junction box and the low-voltage connections are exposed. You can find the same design on many doorbell transformers.

Too bad its motor rating is so low. I haven’t found a bigger one.

Hmm, actually this enclosed? Says 10A, and the coil will work on 24VDC.

EDIT: maybe not looks like the same sort of switch you had. Same weird “10A resistive, but only 1/3hp (about 2 amps) of a motor”.

I have this not sure if it will work. I’m pretty sure I have at least one more lying around my apartment somewhere.

That is a for a car. I think we need more suited for a shop

This IoT power strip has been used by me to address fire safety concerns with 3D printers doing overnight runs in our woodworking shop. It works great for this purpose and put fire concerns to bed.

I mention this only to endorse the power strip.

I have one of these that Id be willing to donate. Decided that i dont want to mess around with AC at this juncture.

Edit - im referring to the item in Danny’s first post.

Another option found on McMaster: 4PST so could handle all three blowers with single unit: $50.75

We need individual switches, not one that turns them all on at the same time

@lukeyes I think we could really use this, can you bring it up? Does it have the green pluggable part?


We have relays on order.

If I understood @EricP correctly, he ordered two of the “IOT Relay” power strips from Danny’s first post. That’s enough to get us started with laser setups, but we could use one or two more before too much longer. We don’t want to have a bunch of different setups, but if @lukeyes has another of the same we can put it to good use.

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This is the one I have. If y’all currently have enough for what you need Ill hold onto it until another concrete need arises. Dont want it just sitting in storage somewhere to get pitched on the next purge. If you have an immediate use, feel free to hit me up.

This is more for future ideas… If we have an enclosure, we should probably just use standard HVAC contactors. They are rated for the use, and easy to find. $11/each. The only problem is we don’t have an enclosure for them to be in with the blowers we have now. But other then that, it’s ideal for the situation.

The two items @EricP ordered for the lasers is sitting on talking in Amazon bag.