multiple pH meters, solenoids, PLC and IOs

[dave w]

Roberto, when I double check the amp draw on the solenoids lets hope that it's less than 400 mA. Perhaps 400 mA was on the 24vAC valves which I bought first and the DC amp draw may be less. And putting jumpers is something so easy even I could do it. I will look up the valves and get right back to you.

[dave w]

OK Roberto, I double checked the amp draw on the 24v DC solenoids and it is indeed 400 mA. So instead of putting 100 relays on the board, would it be better to do 60 relays for the first go-round and save the next 60 for the next upgrade? I can probably get by with just 60 solenoids to start.

[tkeracer619]

Awesome!

Dave have they shipped the solenoids? You might want them to hang tight for a bit. If Roberto is going to custom make you a relay board it might be easier to run AC...

Roberto what do you think is the easiest route to take?

[dave w]

tkeracer619, I've already asked the valve company to change the order once, I can ask them to change a second time if I need to. Three times would be embarassing. Just let me know if the valves should be AC or DC and I'll email them asap on the final determination.

And Roberto, I understand that 128 solenoids at 400 mA is a total of 50 amp draw if they are all running at the same time, but in all liklihood not 5 or 10 would ever start at the same time so 5 amps may be the most that will get pulled. Actually if I start including pumps and lights I'd be completely wrong on that point, wouldn't I? But purely for solenoids, 400 mA is probably the starting amperage required to open or close the valve, the running amperage may be half of that.

It's a little like a house with 200 amp service, if you added up all the circuits in the house you would have 500 amps. I also assume (hope) that there'd be some type of automotive 10 or 20 amp fuses for circuit protection?

[rimai]

There is also no difference in which coil you will use as far as the relay board is concerned, because you will be using a jumper wire anyway. We can't run this through PCB trace. It's too much.
So, the higher the voltage, the less the amperage and less gauge wire you will need to use.
If you go with DC coil, you will need a big power supply that can deal with the coils draw and also the little inrush they will produce. You could make several parallel circuits too, which would give you less amperage in each circuit and use a smaller DC fuse for each one.
If you go AC mains voltage, you can dedicate a breaker or two in your power distribution box for the coils and not have to worry about anything.
So, I think AC 110V coil will get you less equipment to worry about for failure, that's it. I don't think there is any major difference.
DC coils are easier to maintain in the future, because you will not need to shut the power to replace them.
It's all about balancing the pro's and con's and picking which one works best for you. Not always what is best for others is best for you.
Also, there is no benefit on splitting 60-60 relays. In fact, it is actually better to place them all into a single one.
One thing I'd like to point out too is that since the relays will be jumpered, it is very easy to have a block of DC and a block of AC coils. You can even split a few relays for AC sockets to control heaters or lights, a few relays to control AC solenoids, a few to control DC solenoids and a few to control exhaust fans to keep humidity at certain level. Yes, we can monitor humidity too
We could even get one of those light sensors that output levels of Red, Green and Blue spectrum and adjust LEDs to give you optimum spectrum for each of your cultures
That would be neat, huh?

[dave w]

I got hold of the solenoid company just in time. They inform me that they only have the valves in 12vDC and 120vAC. Let me know which you prefer and I'll change the order. For safety purposes I prefer the lower voltage valves around water, although 18 and 20 gauge wires can't carry much amperage either way. Let's go with 110vAC main voltage because it's in a dry room near my current house panel.

Let's put all the relays on one board as you suggest. I agree that putting a block of DC and a block of AC is a good idea.

The only way I know to lower winter humidity in a greenhouse is when it's raining indoors on me. So any humidity control will make the room easier to work in. It would be very neat to be able to mix frequencies on algae lighting, but probably it is overkill. I think total lumens is more important than spectrum with them.

[rimai]

Cool. The coil voltage is your choice because the relays can handle either one.

[dave w]

then let's go with 12v DC.

[rimai]

I'll PM you with the price details.

[dave w]

Roberto, we are in no hurry on this, the details can wait a few days. Enjoy.

[dave w]

Roberto, I may end up using a number of float valves and probably should set up some water leak sensors. What type and how many I/O devices should we look at? And I told the solenoid valve company to send the first 30 solenoids as 12VDC.

[rimai]

We can have several inputs for your floats and water leak detectors.
How about 16? Will that be enough?
They would be digital input at TTL level only. Usually they are used only to detect switch closures, like reed switches, float switches or relay switches. Would this be sufficient for your needs?

[dave w]

Roberto, if another 16 inputs for floats can easily be upgraded in the future, then 16 is enough for now. Please let me know the price difference and I may go with 32 rather than 16. Thanks.

[rimai]

We can make 32... no problem.

[rimai]

Do you think you would need these inputs to be optically isolated?
Optical Isolation would create an isolation barrier which prevents the inputs to be burned up should you have any electrical discharge of any sort and also help with noise immunity a lot, especially when you are talking about so many inputs.

[dave w]

Roberto, how do we take care of the GFI requirements for these relays? I would assume that I will just wire up a bunch of GFCI outlets into large gangs for protection. Alternatively, I can plug a power strip of a dozen outlets into a GFCI outlet to save a little money. Please let me know if there is protection built into your board like reset buttons or fuses.

[rimai]

Like we've talked before, the relays are not going to be powered relays.
So there is not going to be any protection on the board.
You will use jumper wires on the headers, so you can come up with your own power board with breakers/gfci for each block of relays.
Check the attached picture.
It will be a relay with the contacts brought to the header.
So each pair in the header will be use on the hot phase of the AC coil.
All neutral phases will have to be jumpered out together by you either in a ground terminal block or with twist-on nuts. Whichever way you prefer. That's going to be your side of the project. Then, if you want to place gfci on the AC circuit, it is also up to you.
I hope it's a little more clear to you.

[dave w]

Thanks, now it is much more clear. I will take care of pulling power to the device and protecting the circuits.