Relay basics

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BillB
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Relay basics

Post by BillB »

I looked threw the Acorn install manual and all Acorn docs webpage looking for info on how to wire and the basics of relays. Were would I find that? I did see the relay data sheet but it’s Greek to me.

Couple questions
If the relays can input 28VDC does that mean it can only do 28Volts or can it do anything 28 and lower?
Are the wiring options for them either normally open or normally closed based on what leads you use?
Can you pretty much control any type of device using the relays? For example Could I wire up a small airbrush type compressor? It’s 110V not sure what the amps are need to look.

My plans are to add Acorn/programmed air and a drip line type lubricant/coolant, not flood but a low volume drip system.

Would these solenoid valves be good options with Acorn? Not sure what coolant I will be using but I would like to use a non oil based. I was thinking a Koolmist type synthetic might work, even though it’s made to use as a mist I don’t see any reason it would not work as a drip coolant. Cutting stainless and aluminum.

The round valve has VITON seals so it's probably good with coolants I would think. Was thinking the cheaper one to be used for the air.



tblough
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Re: Relay basics

Post by tblough »

Operating a valve at lower than the specified voltage will cause increased current draw and may not reliably open/close. Best to use coils at the rated voltage. Relays can use any voltage up to the ratings. Relay amperage is rated for resistive loads. Inductive loads like solenoid coils and motors can have much higher in-rush currents than their rated running amperage so be careful with these. Inductive loads also need a snubber across the coil or you will destroy the relay controlling them.

3-way and 5-way valves can be normally open or normally closed depending on how you plumb them. 2-way valves are normally closed until energized.

IMHO, chip removal is much more important than cooling while cutting. I'd look at something like Fog-buster or Kool-mist instead of just dripping coolant on the work.
Cheers,

Tom
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Re: Relay basics

Post by Muzzer »

tblough wrote: Fri Sep 24, 2021 8:18 am Inductive loads also need a snubber across the coil or you will destroy the relay controlling them.
I think you meant to say the snubber should be fitted across the contacts. The coils themselves are inductive, so should have a snubber or flywheel diode across them anyway, if none is provided in the driver circuit.

Totally agree clearing chips is more important than lubricating the cutter. Most of my cutter breakages have been due to recutting chips, caused by failure to evacuate them from the work zone. Even a dry air blast would be more effective than a slow dribble of oil.
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Re: Relay basics

Post by tblough »

Coil is at one end, contacts at the other. It's best to place the snubber at the source of the voltage spike.

Edit: A coil of wire is an inductor. If the coil is in a contactor, fan, motor, transformer it will generate a back EMF when shut off. A snubber prevents this and should be placed as close to the source as possible - the coil of the fan, motor, solenoid, transformer, etc the relay is driving.
Last edited by tblough on Fri Sep 24, 2021 1:07 pm, edited 1 time in total.
Cheers,

Tom
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I have CDO. It's like OCD, but the letters are where they should be.
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Re: Relay basics

Post by Richards »

A relay consists of two parts, the coil and the contacts.

The relay board supplied with the Acorn has 5VDC coils, which are totally controlled by the Acorn if the relay board is connected with the flat cable supplied by Centroid.

The contacts are rated up to 28VDC or up to 240VAC.

Because the individual relays are soldered to the board, they are not easily replaced; however, the entire relay board is inexpensive and is easy to replace.

I use the relay board to drive 24VDC indicator LEDs and to active 24VDC coils on higher powered relays and contactors. I always install a 1N4004 diode as a snubber across the COIL of the 24VDC higher powered relay and contactors. The diode suppresses the huge voltage spike that occurs when current to the coil is shut off.

Each relay on the Acorn relay board has three connections, COMMON, N/C (Normally Closed), and N/O (Normally Open). IN one application, I wire the COMMON of relay #1 to DC GROUND. I wire one side of a contactor's coil to +24VDC and the other side of the contactor's coil to relay #1's N/O contact. Relay #1 is configured as NoFaultOut. When the Acorn asserts NoFaultOut, the contactor turns ON. When the contactor turns ON, the contactor's contacts turn on a Teknic IPC5 power supply that supply power to three ClearPath servo motors. I use the separate contactor with the IPC5 power supply so that I do not overload the contacts on the Acorn relay board. The contactor has three sets of contacts. The IPC5 power supply is single-phase, so it only needs one set of contacts to turn it On or Off. I run 24VDC through another set of contacts to turn on an LED indicator lamp so that I can easily tell if the 75VDC power supply is on.

The relay board supplied with the Acorn is fairly robust, but, over time, relay contacts tend to pit because of the minor arcing that is part of the contacts opening under load. A heavier duty relay or a contactor from AutomationDirect costs about $15. To me, that is well worth the additional cost.
-Mike Richards
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Re: Relay basics

Post by BillB »

Good education guys thank you.

Makes sense to go the route of adding external relays. Do you guys think it’s worth it if the use of these machines may only be low use machines or do you think it would not matter, just go for the most robust build from the get go? Realistically what is the service life of the Acorn relay board relays? Would I really burn it out?

Would anyone like to provide a good option for external relay and the the snubber for me? Or give me a sense of what I should be looking for? I looked on Automation directs Website and not sure what to be looking for other than I know I would like to stick with 24v.

Could someone provide some images of how these are wired up? is it 2 wires +&- ? Or is it just wiring into the relay on one wire to break the circuit? Can someone lay it out in laymen terms?

As per my question regarding those solenoid valves no one commented on that, would they be a good option?

Also the question about the small compressor, was thinking of using it for chip removal? I’m kind of liking the idea of adding it as well as air from my 60 gal but sometimes running the machine a few mins may not warrant fillling my 60 gal so I like the idea of having the option.

I knew the flood vs drip vs mist would come up. I don’t have an enclosure, I don’t want be breathing the mist. If I build an enclosure I may add mist but for now needs to be low volume drip for lubricant. And yes chip clearing is the most important thing that’s why I’m installing both into the build. Keep in mind guys these are small Sherline machines. Most people just use brush and oil applied by hand I’m trying to add a bit more functionality than that.
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Re: Relay basics

Post by BillB »

Is there a How to wire relays for Acorn video, I looked but not finding one?
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Re: Relay basics

Post by Richards »

Here's a simple circuit that shows how an Acorn relay can control an external relay or contactor. It shows that the external relay or contactor is controlling the coil on another device (solenoid, relay, contactor, etc.).
.
Acorn_to_relay.png
Acorn_to_relay.png (10.93 KiB) Viewed 2389 times
.
When the Acorn relay is turned ON, it lets current flow through the coil on the external relay or contactor. When the Acorn relay is turned OFF, the Diode diverts the voltage spike that is caused by the coil back to +24V. That limits the amplitude of the spike to +24.7VDC (instead of 50 to 100 VDC).

When the coil of the external relay or contactor is turned ON, it controls current flow through the other coil (solenoid, relay, contactor, etc.). That coil also has a snubber diode to control the voltage spike when that coil is turned OFF.

Note that I'm using 24VDC devices. There are two reasons for using 24VDC devices. (1) They allow the use of the Acorn's 24VDC power supply. (2) Because they are DC devices, a diode can be used as a snubber. If they were AC devices, then a resistor/capacitor snubber would need to be used. I like to keep things simple.

Using this type of circuit, the load on the Acorn is small. It only has to control enough current to turn on an external coil. The external relay or contactor can handle much larger loads, or even a third coil, like the schematic shows.

If the Acorn controlled a contactor, then the second device would normally show three SPST circuits. A SPST (Single Pole, Single Throw) circuit consists of the common (pin 2 in my schematic) and a N/O contact (Pin 3 in my schematic). In that case, Pin 2 might be connected to AC Line and Pins 2 and 3 would act as an electronic switch to turn AC power On/Off to a 1-phase motor or other device.

The top photo of the solenoids in the first post in this thread showed a 12VDC device that can take a full second to turn on. It also has a limited ON time duty cycle. I would try to find a 24VDC device that turns on in 50msecs or less. I would also look for something that can remain ON indefinitely.
-Mike Richards
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Re: Relay basics

Post by martyscncgarage »

BillB wrote: Fri Sep 24, 2021 5:46 am I looked threw the Acorn install manual and all Acorn docs webpage looking for info on how to wire and the basics of relays. Were would I find that? I did see the relay data sheet but it’s Greek to me.

Couple questions
If the relays can input 28VDC does that mean it can only do 28Volts or can it do anything 28 and lower?
Are the wiring options for them either normally open or normally closed based on what leads you use?
Can you pretty much control any type of device using the relays? For example Could I wire up a small airbrush type compressor? It’s 110V not sure what the amps are need to look.

My plans are to add Acorn/programmed air and a drip line type lubricant/coolant, not flood but a low volume drip system.

Would these solenoid valves be good options with Acorn? Not sure what coolant I will be using but I would like to use a non oil based. I was thinking a Koolmist type synthetic might work, even though it’s made to use as a mist I don’t see any reason it would not work as a drip coolant. Cutting stainless and aluminum.

The round valve has VITON seals so it's probably good with coolants I would think. Was thinking the cheaper one to be used for the air.




Normally, you don't flow coolant through the valve. Just air.
You will want a mist system of some type. MQL (Minimum quantity lubricant) there are many plans on the web, there are many options for nozzles.
Look up the Noga Mini Cool

Both those valves need a 12VDC power supply to actuate them. Not super convenient unless you buy a 12VDC power supply.
I would prefer 24VDC coils. But they will work as long as you buy a 12VDC power supply to actuate the coils.
Marty
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BillB
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Re: Relay basics

Post by BillB »

I made a mistake choosing those 12 Volt valves they are available in 24VDC as well. These will work without power supply correct?

As for the mist system, I don’t have an enclosure and I don’t want to breath the fumes. I may build one but that is to be decided based on how much chip and fluid this little mill and lathe are going to throw around. I had a mist system on my Roland mill years ago and never used it because the mist in the air was terrible. I will looking more into this but will ask as well, is there a way to choke down the mist with a different nozzle do it’s a low volume drip feed?

If not I will just set up a pump for the drip system.




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