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Author Topic: M3 M4 switching  (Read 4758 times)

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Offline rcaffin

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Re: M3 M4 switching
« Reply #20 on: March 12, 2016, 03:42:39 PM »
I use a bunch of JQX-13F relays myself, on my 180 VDC spindle motors. They seem very reliable. I use 24 VDC coils, but that only is because I have a fair amount of 24V power available. I also use the sockets sold with the relays. Mine came from eBay, 22newcentury.

Cheers
Roger

Re: M3 M4 switching
« Reply #21 on: March 13, 2016, 08:57:52 AM »
Those relays are only rated for 28 vdc.  I read a thread on another forum (HSM) that warned about the difference in arcing of the contacts between switching DC vs. AC and the consequent shorter lifespan when using under-rated switches & relays.  I think it may be wise to chose relays that are rated correctly for the job?  I'm sure those will work fine now but if they see heavy usage, may cause a problem down the road & the contacts stick closed at the worst possible time.  Just a thought.

You guys with more electrical smarts & experience can tell me to shut up & go back to my hole if need be.:)
Milton from Tennessee ya'll.

Offline rcaffin

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Re: M3 M4 switching
« Reply #22 on: March 13, 2016, 05:44:08 PM »
No, that's not quite correct. They mfr give specs for 240 VAC and 28VDC because they are two common voltages, but the relay can be happily used for a wide range of voltages, AC and DC. (28 VDC: over-voltage on 2 x 12V batteries.)

Yes, there is a difference in how contacts work. These are silver oxide / cadmium oxide, and they are designed for heavy currents. There is ALWAYS arcing when contacts are opened, and that's why the contacts use those materials. It's a bit hard to 'burn' an oxide surface, after all. Other switches and relays use gold-plated sufaces instead: gold is good for LOW-level SIGNALS, but not for power applications.

One of the advantages of using plug-in relays (ones using a socket) is that if there is ever a problem, you can pull out the doubtful relay and replace it with a new one. That is a lot smarter than soldering onto the terminals of the relay.

'Shorter lifespan' - debatable. If the relay is rated at 28 VDC & 10 A, but you use it at 48 VDC and 1 A, will it have a longer or shorter life? If you have the spindle motor howling away at full load and you open the relay, there will be some arcing - although the relay is designed to handle that. On the other hand, if you kill the supply down to 2 VDC & 0.5 A before turning the motor off, how much arcing?

In this day and age of modern semiconductors, it turns out that power relay technology is pretty good. Even a wall switch works pretty well.

Cheers
Roger
Re: M3 M4 switching
« Reply #23 on: March 13, 2016, 08:30:53 PM »
Okay, back to the original subject  ;)
Sorry RT, you're absolutely right!  When you get your relay setup working, please post up a diagram.  I'd like to have it around for possible future use.:)
Milton from Tennessee ya'll.

Offline rcaffin

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Re: M3 M4 switching
« Reply #24 on: March 13, 2016, 11:14:40 PM »
Hi DB

There's one circuit diagram at the bottom of the first page. It works very well for me.

Cheers
Roger