Just purchased a 16 zone Rachio III
This is for a new install.
Spent the time running 1" pipe assuming this controller could operate more than 1 zone at a time.
Can the software / app be upgraded to allow the controller to run more than one zone at a time?
Is the Rachio III hardware capable of this?
Would be nice to be able to run 5 zones at a time for example.
You can always wire multiple valves to 1 zone. Iām running 2 zones this way and its working fine for me.
May I ask what kind of schedule you are planning on using?
For best results I always recommend flex-daily and costuming it to emulate other schedule types, if needed. With flex-daily, your zones will quickly go out of sync, because they are watered on as-needed basis. With all 16 zones used, you will probably see less than 4 zones watering at any given day, all in all this will take less than 1 hour.
To answer your question, I do not know of any way to force Rachio to run more than one zone at a time. Power supply provided with your purchase, can usually support up to 3 zones which accounts for a master valve (1st), a zone actively running (2nd) and hardwired zone expansion (like @wafflesngravy has).
How many selonoids can you run off one zone safely? More accurately, What is the maximum safe current draw of a single zone?
If I rewire a few sprinklers to one zone, I would need to re-wire them back anually for a staged compressed air purge just prior to winter.
Iām not sure yet on the schedule. Iām open to suggestions. Iām just wrapping up the installation of the first 8 zones for the front yard. As I was doing the quick run tests to aim everything, I was hoping to fine tune the āthrowā by increasing the number of active zones only to realize I could only accomolish one at a time.
I wanted to start a topic on that too but was lucky to find this thread just before asking the same question.
Sure you can wire multiple valves to the same zone in the Rachio 3 controller but this definitely lacks the comfortable option to select single zones for child entertainment on warm summer days. 
This would really be a nice option to have concurrent zones setup.
If you donāt have a master valve or pump in the system, you can have up to 3 solenoids wired up to 1 zone. I have done this in two areas of my yard where old spray nozzles were replaced with Hunter MP Rotators, and I can easily hold pressure with 3 zones running. But, all these zones will run at the same time, and schedule, so they will need to have the same watering needs. If you are starting from scratch and you have a couple zones that you could combine, it would be best to pipe them this way.
Support suggested up to 4 zones to a single output.
This was suggested based on my measured 100mA draw. (I did not measure inrush current -yet and the draw was measured dry. I will re-test. [1" Rainbird])
They say the unit can supply up to 1.2A but to avoid loading it that far.
I was just really hoping I would have been able to tell the system what each zone flowed (e.g. 7 zones, 3.0gpm each) then define a maximum allowed flow-rate where a setting of 3-5gpm would limit system to 1 zone. 6-8 would limit it to two zones, etcā¦
This way I could define say 20gpm as the cap and Rachio would resultingly calculate that it could run any 6 (of the 3gpm) zones at once.
Wiring two sprinklers to one zone reduces system control, and as you mention the zones need to have the same watering needs.
Since I bought a 16 zone unit, but Iām currently only using 8 zones. I think I am going to put some isolation diodes on a breadoard, then run zone 9 to it to trigger 3 other zone at the same time, while still allowing me to run them independantly.
Not sure how it will affect schedules, etc, but Iām sure it will work out.
From a hardware perspective, will it ever be possible for the Rachio 3 to run more than 1 zone at a time, or is that basically something that will never happen?
Thanks.
Actually, right after I wrote that, I realized these are AC, not DC, so that wonāt work 
You curently need a 24VAC NO DPST relay as the Rachio 3 does sadly not support concurrent zones, see: Run Multiple Zones At Once
Hope to get support for native concurrent zones setup in near future but yet support didnāt give a statement on the suggestion.
Here is my take on concurrent zones, specifically utilizing Flex Dailyā¦if anyone cares.
Flex is an awesome, dynamic, always changing schedule, and if Rachio allowed multiple zones to run (thru programing), some days you might have 1 zone run, another day 2 zones, and another day 3 zones depending on how the fluid schedule ran that day. Issue I see is, when I combined 3 of my grass zones (thru wiring), I had to adjust the spray patterns of the nozzles to account for the change in pressure thru the system. Combining the zones actually brought my zone pressure into the sweet spot for my particular nozzles, so it worked out well for me. But, if you are dialed in with 1 zone running, and Rachio decided to run 2 or 3 at the same time, you can have a drastic drop in pressure and volume, thus reducing the PR of your sprinklers and making the Rachio algorithms inaccurate. I know it sounds miniscule, but depending on the GPM of a zone, it could make a significant difference in how the zone performs.
Just my $.02.
Exactly: Thats why I feel a simple āsystem gpm limitā would allow users who experience pressure drop, to define a limit to avoid this, while other users who do not experience a drop can set a higher bar.
If you had one or two heads that this was a problem, and others that did not - you could exclude the zone from concurrent operation in theory with a check box.
I ran 1" pipe, and found that even running 3 heads at a time, there was no change in how far each head would throw water.
Iām currently only using 3.0gpm heads, but plan to try swapping out a few nozels to 8.0gpm, then re-test.
Personally, I think that is asking a lot of a system. Not saying Rachio canāt get there in the future, but now you are talking about adding the need for flow/pressure sensors to monitor the system as it is running in real time. Hey, Iām on board if it ever comes, but people complain about the complexity of the system as it isā¦
You are still on the design/instal phase of your system, right? If you are building a system that can run 10 rotors at a time, why not just pipe it that way from the start?
To add my 2cents, Rachio flow meter is rated up to 25 GPM, about 8 of the 3GPM heads, or only 3 of the 8GPM type.
Besides that, running multiple zones at the same time would hinder Rachioās ability to quickly identify zone issues, especially near the max limit of the meter.
What I am saying is that it is not as easy to just turn on the ability to run multiple zones, designers have to accommodate extreme cases.
Well, it certainly depends on how many nozzles per zone you have. In my case it is a maximum of 2 nozzles. 
I set up 10 zones on 180sqm yard and wanted to take control of single nozzles for child entertainment on hot summer days. 
The problem now is that a single schedule lasts for about 14 hoursā¦ 
I think I have to go with this solution to combine at least 4 nozzles per zone:
Can your piping support more than two? I have 2 āzonesā that I have wired 3 solenoids to each terminal. I was lazy and didnāt want to dig up and re-pipe just yet, so this was a quick fix. I went from 18 zones to 12. My main motivation was the same as yours. I have Hunter MP-Rotator nozzles, and each zone would run for over an hour, leaving little time for anything else to run in a day.
Yes of course! I use 1" piping. I have anough pressure and water throughput for at least 5 nozzles per solenoid.
As far as I know, the Rachio support stated that 4 solenoid per terminal will work.
If concurrent zone setup will not become available in the near future, I will follow the suggestion of DLane using 3 relays to drive all my 10 solenoids.
Relay 1 on terminal 11: 4 solenoids
Relay 2 on terminal 12: 3 solenoids
Relay 3 on terminal 13: 3 solenoids
This leaves me the freedom to still control all my 10 zones independently, as I said for child entertainment or whatever. 
I donāt want to loose this freedom of control by repiping the 10 zones to just 3.
lolā¦ so true! Thatās why I hope to see concurrent zones setup in near future. 
I disagree, its not that complicated, nor are any extra sensors needed.
You simply enter a (gpm) number you feel is the max, and the system automatically limits itself to only run as many units as it can below that number.
Hard Pairing the heads limits your options.
Just curious, why are you trying to run more than one zone at a time? Most residential systems are generally 15gpm or less per zone (or at once, maybe even less if going uphill). If you tell me your meter size and wayer pressure Iāll give you the recommened gpm (the five gallon bucket is not accurate). Your nozzles may ālookā like theyāre running properly, but they are probably wasting water and money if the system is overloaded. It can be difficult to tell visually. 1" pipe may not be large enough if youāre trying to run 25 or 30gpm nozzles.
Gpm refers flow (volume) if you want to put more water down itās best to look at the precipitation rate (inches) in the manual for the nozzle.
Gpm = dollars
Precipitation rate = time needed for watering