As Tom has repeated, it's always really great, and leads to the quickest and most accurate response from various people who nearly "live and breathe" this kind of stuff. It seems, as you suggest, that you need an SSR or Mosfet to be able to switch the load quickly, which your Nano can't because of it's limited load capacity. With that being said, I also wonder if you may have, due to the amount of content now here, overlooked some of that which may be the most pertinent. For example, it seems to me that Hexen is extremely knowledgeable about Mosfets, and most importantly exactly how to drive them in a way most suitable for your application, and even provided a link to his store, and seems very willing to explain to you anything and everything in detail as to how to apply them to suit your needs. I'm pretty sure that the arduino combined with the Mosfets:
I mentioned a module, though be it quite expensive, and then someone else mentioned some as well. All of which could easily handle the load and be controlled by the Nano. I think if you read back through some of what's here you'll be able to bring together exactly the resources to get done what you need to get done.
Just some of my thoughts, and wishing you well in finally coming up with something that works for you. My experience is mostly that of a programmer, 20+ years with some involving a lot of "tinkering" with hardware along the way, so I'm not the "best" to advise on this. But this place is full of people that are.
Since I, the OP, am Hexen, I think you may have gotten that just a little wrong. No biggie.
Either a Mosfet or a type of SSR that can switch DC loads is fine. I just need a specific example. I've been sent a LOT of links to pages displaying hundreds of different types of SSRs or MOSFETs which does me no help because I don't know which to pick from the very long list of options.
The valves I have were originally designed for a CO2 cooling system. The controller is a specialized unit to control a reactor. I will not be touching the controller or using it in any way. It needs a VAST amount of inputs before it will control the valves. I'm using the valves in a slightly different application, misting water on a much smaller reactor that must be kept within a very small temperature window.
I had it working FINE with an arduino nano, but the mechanical relay would stick as the pulse width would shrink when I finally got within the temperature range. I'm using a PID on my Nano and the software side is perfect.
Since someone seems to be heading down the path of asking me what color sprinkles I want and what flavor ice cream I enjoy when asking about SSRs, I'll save myself the trouble of posting here and just buy the mentioned FL3100/IRF3708 combo that was already linked here.
Hexen:
Since I, the OP, am Hexen, I think you may have gotten that just a little wrong. No biggie.
Ha, ha. So maybe I was seeing into the future when "you'll" be the one extremely knowledgeable about these things - got a chuckle out of that.
So anyhow, everyone else is talking Mosfet, which as I said about me not being as good with hardware as them, so don't take my choice of hardware too seriously, but if you were to throw away the controller, and just connect this to one of the output pins of your Nano, connecting the "+" to an output pin and set it high whenever you want it to turn on, the "-" to your Nano ground, and however many loads as sum up to the total 25amp load capability, you'd be set. BUT, keep in mind there may be other variables to take into consideration, which may be part of the reason Tom has been so persistent about more information on the hardware, such as things like inductance, and how much actually current that SSR would see when whatever it switches on and off since it could be much different than switching a resistive load for example. It my be able to handle only 1/2 that actual "constant flow" load. And perhaps just a few additional components such as caps or whatever, may make it all work fine. The output pin from the Nano may also need a pull-down resistor to make sure the SSR is actually turned off completely when not on. Just things like that. Now, hopefully the others jump in with better and more detailed information.
If you wonder how to use the "load" side of that particular SSR, just connect positive lead from your main power source to the "+", and one or more of "whatever your loads are" to wherever you would have originally connected that positive lead to, and connect the grounds together from the power source and the loads.
And "if" you're going to try that one, and pushing it to the max, don't forget to get that heat sink that's shown there along with it.
Grumpy_Mike:
Just what was wrong with the DC SSRs I posted a link to?
I too suggested that. In fact the link I provided just a little ways up was one of those ones you posted a link to. Not sure if I chose the best one, but figured it would suffice.
edit: oops - noticed based on Hexen's post after this one, that the one I chose for him was actually from the ones that outsider posted a link to. But Crydom is a well known brand of SSR, and I think Digikey beats Mouser for pricing both for those SSRs, and of course shipping.
Grumpy_Mike:
Just what was wrong with the DC SSRs I posted a link to?
I went through the list, but I'm not sure how well thats going to work.
Out of the 45 on that page, there are only 9 that handled DC output, 3 of those worked on a 5v arduino input. Of those 3, only 2 of them could handle up to 10A output. Both of those are rather pricey and I'm worried the output might spike to 15-20A. Better safe than sorry.
justjohn, the last link you posted to the DC SSR on Amazon just might be the one I'm looking for. Will handle 5v control and 12V output just fine, up to 25A. I don't see any reason it won't work. It looks like it may be a low-trigger relay which is a shame, but I have an easy workaround for that.
My ONLY complaint about a DC SSR is their size. A small MOSFET breakout is going to be much smaller and easier to mount in a case. I'll likely purchase one of each and try them both.
Something to consider when considering a Mosfet, is that they aren't "exactly" as cute and innocent as they look - in other words don't be fooled by "small package" huge load. For example the one here shows that without a heat sink, at 25C, it can handle 87 watts before it starts heating up, which is only about 7.25 amps . . . before you need to consider a heat sink. Since the current handling capabilities is affected by package heat, as it heats up it's current handling capability begins to diminish until the combination of the two leads to, as someone else mentions with each post - the thing that actually makes it work - the smoke inside - comes out, and there's no way to get that smoke back inside to make it work again.
Add a large enough heat sink and the 7.25 amps starts to climb up to the rated 52 amps. Just something to think about if you haven't already.
Out of the 45 on that page, there are only 9 that handled DC output, 3 of those worked on a 5v arduino input. Of those 3, only 2 of them could handle up to 10A output. Both of those are rather pricey and I'm worried the output might spike to 15-20A. Better safe than sorry.
First their are other pages you know.
You don’t need to restrict yourself to 5V input, using a transistor or two the Arduino’s output can simply be boosted. All these SSR’s are is just a FET in a package with heat sink built in. If you are confident that you can do the engineering with a separate FET then fine do it, but I suspect from your questions you can’t.
As to price then yes you have to pay for someone else to have done the engineering for you, anyway once you have the part number you want you can search for the best price on it.
Grumpy_Mike:
All these SSR’s are is just a FET in a package with heat sink built in.
something I doubt most people realize. So looking at a "huge" high-current-capable SSR and tiny little FET, opt for the latter. But then once put into use, actually discovery that the SSR may have been a better choice. However if all this done in the winter, may be delighted to discover that the FET by itself without any heat sinking could serve as a pretty nice compact heater for their home, and perhaps even the entire neighborhood . . . at least for a few seconds or so. :o
Giving this a little more thought, I was thinking it may be a really good idea for the OP to actually get a MOSFET like the one I mentioned and play around with it. Connecting a 1ohm resistor (capable of handling the power) and an ammeter inline with the drain, while just touching the MOSFET with finger to feel for heat, and watching for diminishing current with ammeter, may help with the learning. My guess is that the MOSFET I mentioned may actually be able to handle at least 12 volt, 12 amps (excluding surge current), even without a heat sink, since the specs of all these devices seem to play it "super safe." But the cost of the MOSFET and driver for a single load at 12 amps, may still come in at around the same price as the single SSR driving 2 loads - the OP having mentioned wanting to drive more than one load at a time being the original quest for this whole discussion.
But then there is always the "nitrogen cooling" 50+ amps from a 25 amp MOSFET option (a little "cryo technology") - what's liquid nitrogen going for these days?
. . . ha, ha.
It is simple to calculate the maximum power by assuming an infinite heat sink. Those exotic techniques only get you incrementally closer to that infinite. http://www.thebox.myzen.co.uk/Tutorial/Power.html
Grumpy_Mike:
It is simple to calculate the maximum power by assuming an infinite heat sink. Those exotic techniques only get you incrementally closer to that infinite. http://www.thebox.myzen.co.uk/Tutorial/Power.html
Something else I'll mention to the OP here, is that if you do "play around" with a MOSFET in the way I mentioned, and things seem to get a little weird as in the thing conducting while the gate is pulled low, note that the gate diode "can" be accidentally blown while "experimenting." To determine if it has been, simply connect the "diode check" function of your multi-meter between the gate and drain and if it's open then it's blown.
