Confused on opto relay board for ESS port 3

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djreiswig
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Confused on opto relay board for ESS port 3

Post by djreiswig » Tue Nov 06, 2018 9:18 pm

I'm trying to connect a relay board to some outputs on my ESS smoothstepper port 3.
I have a simple BOB and ribbon cable from CNC4PC. I'm trying to wrap my head around optoisolation. I have found some relay boards online, (I bought the one pictured.) but it doesn't look like they are really isolated. Most appear to have the signal ground and the relay power ground tied together. I believe this conflicts with the optoisolation I want to achieve.
I have gotten some pointers from Andy at Warp9. His suggestion was to use the 5v powering the ESS to run the relays. It seems to me that doing this would totally negate the optos. And I haven't gotten an answer to whether the 5v is capable of running the relays without overloading it.
Am I missing something?
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djreiswig
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Re: Confused on opto relay board for ESS port 3

Post by djreiswig » Tue Nov 06, 2018 9:48 pm

Now I'm hearing that if I use relays I don't need optos.
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Re: Confused on opto relay board for ESS port 3

Post by admin13o5 » Wed Nov 07, 2018 3:54 pm

Relays are about as isolated as you can get! ITs a coil (electromagnet) that pulls a lever and closes the contact . Contact signals never touch the coil side. If you decided to use optos the other side of the optos have to have a separate isolated power source to drive the coils (or there is no isoaltion) . The 5 volts running the ESS card is NOT ( I repeat, NOT) capable of driving multiple relays. 5V bus runs the whole UBOB logic and the ESS logic. That is a BAD idea.

The ESS has output buffer drivers but not enough to drive a relay coil. You need a drive circuit that runs on its own power supply (like a 12V) or the one in the Bladerunner (3A) A relay card taht can take in logic level control signals (3 - 5 V TTL) and uses an aux 12V supply for the 12V coill relays would work. Opto isolators MIGHT work if the realy coils pull less than 25ma when on per relay. Still needs a secondary power source for the relay coils and secondary of the opto. A transistor Opto is simply an LED and a light sensitive transistor in a sealed package and is Open collector (usually NPN) .

If you just wanted to use the opto to drive the coils as a buffer your don't need an isolated power source on the transistor/coil

I always use a small FET (2N7002A) to turn on Relays and but kickback protection on the relay coil. They may have a similar circuit on the relay cards and the optos may not be needed but you won't get much the way of specs or support form China

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Re: Confused on opto relay board for ESS port 3

Post by djreiswig » Wed Nov 07, 2018 7:05 pm

If I can't use the ESS to drive relays directly, then isn't an opto about the only way to do it? How else would I get a 12v supply running the coil to be activated by an output without causing problems?
Good to know that the 5v won't work. I was thinking this was the case.
I found this relay board that uses 2 separate power sources.
https://ebay.us/FFkfQD
I'm not sure if I can use 12v to run the relays and 5v from the BOB to run the optos. I asked, but haven't gotten a response. Do the opto chips specify certain voltages?
Are the 2 relays on the i/o board optoisolated?
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Re: Confused on opto relay board for ESS port 3

Post by admin13o5 » Thu Nov 08, 2018 10:49 am

1. The Opto as I stated is an LED (its a CURRENT device that need 10 - 12ma . Any voltage from 2 to 35 works as long as you size the series resistor to provide the proper current to turn it on. It drives a transistor that can handle about 35 ma or max current and that will operate SOME relays but more likely it just a predriver to trigger a FET like the 2N 7002 that can sink 250 me and is a lot more rugged .
2. The 2 relays on the I/O board are NOT opto isolated (all relays by definition are already electrically isolated) and run off the internal 12V bias and are triggered of the UBOB via the FETS I alluded to. At one time we muxed the outputs in MACH and could driver 8 relays and we had a Quad relay module that ran off the Table I/O (expansion plug) . We sold about 50 units in 3 years. The muxed outputs cause added problems form noise so they were discontinued.

We have engineered the added outputs and inputs into our EBOB products and will introduce a new Quad relay expansion (in addition to the Dual relays on the Table I/O) but I really do not expect to sell very many. The EBOB is a direct Ethernet BoB but it will not run with Windows or MACH.

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Re: Confused on opto relay board for ESS port 3

Post by djreiswig » Thu Nov 08, 2018 11:30 am

So to simplify things, if I get some mosfets and some of the cheap 12v non opto relays with the diodes built in I can hook an ESS output to the mosfet and run the relays off of the 12v from the Bladerunner box? Is that basically what you are saying?
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Re: Confused on opto relay board for ESS port 3

Post by djreiswig » Thu Nov 08, 2018 12:51 pm

Would this board work?
http://www.icstation.com/mobile/channel ... -8899.html
It looks like it needs to be connected to the 5v + & - for the logic to work. The other side can then use 12v to run relays.
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Re: Confused on opto relay board for ESS port 3

Post by djreiswig » Thu Nov 08, 2018 8:38 pm

I think I'm going to try one of these.
https://ebay.us/FFkfQD
Going the mosfet route and sourcing a separate relay board is going to be more complicated and more expensive than this self contained board. Since it uses optos I should be good sending it 5v for logic. I'm not sure if the signal needs to be + or -, but I guess it is switchable in the ESS options. I'll have to trace the circuitry and try to figure out.
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