Must-haves for EASY DIY controller?

[BryanS]

I'd like to hear more....I will follow this thread.

 

[terahz]

BTW I was under the impression you are designing the arduino itself as well, not a shield for available arduinos... that will bring the price of the unit down quite a bit. I guess either will work but if you are doing a PCB might as well keep it all together (including the arduino part).

 

[der_wille_zur_macht]

terahz, I'm open to suggestions. My thought for going the shield route was that it allows compatibility with other shields, plus it strikes me as more "beginner friendly."

Though, you're right, designing on a single PCB would be cheaper ($8 more in parts for a bootloaded ATMega, crystal, etc instead of $30 for a Duemilanove). And it seems more fitting to design a "permanent" project that way, instead of the shield approach, which seems more suited to rapid prototyping.

I suppose one approach would be to design a custom PCB including the processor, then put headers on it in the standard Arduino locations, which would let people stack shields on if they desire.

At any rate, I'd assume we want the relay board separate (so it could be placed remotely from the "head unit").

 

[williah]

I'm on board! I just start teaching myself basic electronics for this very purpose. Can't wait to see how it goes

 

[terahz]

I suppose one approach would be to design a custom PCB including the processor, then put headers on it in the standard Arduino locations, which would let people stack shields on if they desire.

Yep, that's really what I was thinking would happen, but either way should be good. I guess it is better for people with arduino already, but if someone just wants a controller an all in one base unit is better (and cheaper )

At any rate, I'd assume we want the relay board separate (so it could be placed remotely from the "head unit").

Yes, the relay board should be separate, I agree. Ideally in the outlet box I'd say. On the same note I just got my relays today and I'll be playing with that on the weekend and next week so should make some progress on it. I opted for SSRs because my magnetic relay in the ATO is already failing and is only 2-3 months old.

 

[terahz]

The concept was that it operates over 1-wire ( Dallas Semi) communication to the Dual Switch device (DS2413).

That's a nice IC, but not really in scope for this project because it is only available as SMD.

The entire 1-wire idea is great but unfortunately Maxim makes most of their ICs SMD only .

Anyways, I think I'll go with plain I2C for the relay box and just use a simple port expander to control a bunch of SSR. 2 analog pins for 8 relays should be good. The generic OAC5 relays can be found at 9-10 bucks from mouser/digkey or for 3-4 on ebay and most are rated at 3A so in theory they should be able to handle a 250W MH lamp.

How many outlets are we aiming at? I guess 8 is the minimum and I was thinking of using plain power entry modules so these can be wired in pairs to give 16 outlets that are controlled in pairs.

 

[SpacedCowboy]

That's a nice IC, but not really in scope for this project because it is only available as SMD.

The entire 1-wire idea is great but unfortunately Maxim makes most of their ICs SMD only .

Anyways, I think I'll go with plain I2C for the relay box and just use a simple port expander to control a bunch of SSR. 2 analog pins for 8 relays should be good. The generic OAC5 relays can be found at 9-10 bucks from mouser/digkey or for 3-4 on ebay and most are rated at 3A so in theory they should be able to handle a 250W MH lamp.

How many outlets are we aiming at? I guess 8 is the minimum and I was thinking of using plain power entry modules so these can be wired in pairs to give 16 outlets that are controlled in pairs.

That 3A relay isn't going to work well, at least IMHO. I took a quick look at the datasheet for the first couple I saw on digikey (GH7022-ND & GH7018-ND). These match your $9-10 price point, and have a 3A rating at 25 degrees C.

Unless you're planning to use active cooling, or happen to have an existing "well ventilated environment", I think you need more headroom than you're talking about using. Don't forget that your ballast won't be 100% efficient - let's assume you have an electronic ballast (not magnetic), and it's still running at 90% efficiency - that's going to require 250/0.9 = ~277W or ~2.5A nominal, even under optimal conditions. If the temperature rises just 15 degrees (ie: to roughly skin temperature), you're at the absolute maximum that the device can sustain.

I don't know about you, but I'm not comfortable trusting my line-level power circuits with such small tolerances. If you have slightly too small an enclosure, or the device is slightly less capable than specced, or ... well, it could be a very expensive saving... If you "double up" the sockets, you just make it worse, of course. Be very careful not to plug two lights into a doubled-up socket pair...

If you absolutely must use SSR's, the cheapest I have found that would be likely to let me sleep at night are at futurlec.com (10A, $9.90 each). You'll probably want the heatsinks as well; that puts the price up to $16.80, but you probably could then "double up" the sockets - you'd have ample headroom.

Just my 2p-worth

Simon

 

[BeanAnimal]

Also note that motors do not start well at zero cross... for motor loads, random turn on is usually a better choice. For that matter, random turn-on is preferred for inductive loads of any type (motors, transformers, ballasts, etc). If it were me... I would be looking for random turn-on INSTEAD of ZC for all of the outputs. We typically only use ZC devices for resistive loads

 

[der_wille_zur_macht]

We're getting ahead of ourselves! :lol: Here I was hoping it would take a week or two to get a really solid list of requirements, but we're deep in the design details on day three.

I'll let you guys discuss power handling because, as I said before, it's not my area of expertise. My plan for my own controller was to snag the "biggest" relays I could afford on eBay. Seems like 10A - 20A relays come up for $6 - $8 each from time to time. But if we're trying to make this repeatable by a large audience, it might make sense to go with something available at a conventional supplier.

Last night, for the shield portion, I put terahz's pH circuit on a shield with an RTC and a port expander for driving an LCD, plus headers (outside the typical shield outline, so they'll be available when stacked up) for I2C, one wire, and the PWM pins. Lots of tweaking to do but that should cover all the "core" functionality we've discussed so far. If people have any other wishes, now's the time to speak up.

 

[BeanAnimal]

eBay is a good place to get SSRs. The CRYDOM brand is reliabe and well documented. The only issue with snagging the "biggest" SSRs you can find is not knowing the leakage current. That is, an SSR never really "turns-off" the outputs, there is always some leakage current that gets through. This is not an issue for most equipment, but some equipment will see the tiny current and never fully shutdown.

You can ALWAYS use regular old mechanical relays for the large loads (lights, return pumps, heaters).

 

[terahz]

That 3A relay isn't going to work well, at least IMHO. I took a quick look at the datasheet for the first couple I saw on digikey (GH7022-ND & GH7018-ND). These match your $9-10 price point, and have a 3A rating at 25 degrees C.

I'm all with you on this one, I did check that the relay starts dropping current rating after 25C-30C and I have two things in mind:
1 - The only thing that requires a big relay are the MH lights. Maybe if someone has a 300W heater, but that's about it. I don't see why we need to spend the money on 10A relays to switch powerheads and pumps. We certainly can, but I just think it is a waste of money. Not to mention more powerful relays will make the case much larger.
2 - because of the 1 what do you think we just add 1 or 2 high rated relays and assign them to the lights?

Just my 2p-worth
Simon

Thanks a lot for the input. That's the way to end up with a good project.

 

[terahz]

BTW something like this is a drop in replacement for the relays I was referring to initially and will handle the load of a big heater and/or a MH light.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CC1549-ND

 

[der_wille_zur_macht]

. Maybe if someone has a 300W heater.

Well, I'm going to need 500 - 600w of heater on my tank, so at least *I* will be using a larger relay for that circuit. :lol:

I never realized relays were so specific - zero crossing, random start, different load requirements, leakage current, etc. Will it be possible to pick relays that will work for everyone? Sounds like "NO." Then, what route do we take? Design a board that has some relays of each type, or design a board that can accept a wide range of relays and let the user choose?

 

[BeanAnimal]

BTW something like this is a drop in replacement for the relays I was referring to initially and will handle the load of a big heater and/or a MH light.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CC1549-ND

Again, note that ZERO CROSSING turn-on is NOT desirable for most of the loads we are running, and instead a RANDOM turn-on is. The part listed above is ZC. The proper RANDOM part is http://search.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keywords=CC1550-ND

Note that for HEATERS the Zero Crossing part is prefered.

 

[BeanAnimal]

Well, I'm going to need 500 - 600w of heater on my tank, so at least *I* will be using a larger relay for that circuit. :lol:

I never realized relays were so specific - zero crossing, random start, different load requirements, leakage current, etc. Will it be possible to pick relays that will work for everyone? Sounds like "NO." Then, what route do we take? Design a board that has some relays of each type, or design a board that can accept a wide range of relays and let the user choose?

Sure... mechanical relays can be chosen to be universal

You can also pick a FAMILY of SSRs and design for them. Both the ZC and RANDOM variants of the crydom LS family are listed above and have the same footprint

But the better answer is to provide suitable relay drivers in your project and let the end user choose the relays, be they machanical or SSR.

 

[terahz]

Well, I'm going to need 500 - 600w of heater on my tank, so at least *I* will be using a larger relay for that circuit. :lol:

Well that's fine, the question is, thought, will that be a single unit or several 200W units?

I never realized relays were so specific - zero crossing, random start, different load requirements, leakage current, etc. Will it be possible to pick relays that will work for everyone? Sounds like "NO." Then, what route do we take? Design a board that has some relays of each type, or design a board that can accept a wide range of relays and let the user choose?

I really don't want to go the mechanical relay route, but maybe that will be the way to go...

Again, note that ZERO CROSSING turn-on is NOT desirable for most of the loads we are running, and instead a RANDOM turn-on is. The part listed above is ZC. The proper RANDOM part is http://search.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keywords=CC1550-ND

Note that for HEATERS the Zero Crossing part is prefered.

Thanks BeanAnimal, too late in the morning to be paying attention to details on digikey.com

That being said If we want to do this right I guess we'll have to have types of outlets for different devices.

Sure... mechanical relays can be chosen to be universal

You can also pick a FAMILY of SSRs and design for them. Both the ZC and RANDOM variants of the crydom LS family are listed above and have the same footprint

But the better answer is to provide suitable relay drivers in your project and let the end user choose the relays, be they machanical or SSR.

It is not as easy to have a universal board for both mechanical and SSR and the goal here is to keep it simple enough so that people can do it themselves. I guess if we're going to spend 20 bucks for a SSR we might as well get a bunch of mechanical relays in the end. I was aiming at the SSRs more because of cost than anything else, but if we must have 10A per relay that changes things a bit.

I guess I have to do my research properly first.

Thanks for the input everyone.

 

[stugray]

For AC power control it would be best to use COTs ( commercial off the shelf ) to eliminate any liability issues.

One of these is what I have:

You just screw in up to eight Grayhill SSRs.

It is part # GH3032-ND at digikey and I purchased the GH3039-ND modules:

By going this route they are UL listed so you take no responsibility for malfunction.

Just run a ribbon cable from your I/O board to this.



Bean, could you explain why we would NOT want a zero-crossing SSR?
I dont see why it would matter.

Stu

 

[BeanAnimal]

Or... design the project to be DIN rail mounted. Choose a suitable case and then people can mix and match what they need for outputs, circuit breakers, fuses... etc.

 

[stugray]

"Or... design the project to be DIN rail mounted."

I was originally going to use this, but it was a few months from being released when I bought the Grayhill stuff:

Electronic terminal block with miniature switching relay

http://www.wago.com/wagoweb/documentation/857/eng_dat/du30300e.pdf

Fits on a DIN rail, has LED indicator, Max cont. current = 6A, only pulls 17mA ( low enough to drive with the Dual Switch device - DS2413), less than 1/4 inch wide and only ~$16 each.

Stu

 

[SpacedCowboy]

Sure... mechanical relays can be chosen to be universal

You can also pick a FAMILY of SSRs and design for them. Both the ZC and RANDOM variants of the crydom LS family are listed above and have the same footprint

But the better answer is to provide suitable relay drivers in your project and let the end user choose the relays, be they machanical or SSR.

[grin] Or you can use the circuit I posted earlier, and choose when to turn on the device. The ZC event is an input to the AVR, and some simple timer code can be used to determine when to turn the device on. The user just says "input #7 is a motor", for example

Simon