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I have an existing 24VAC power supply that supplies 650mA. I see that the one sold on the site is 500mA. Any issues with higher amperage?
Higher amperage is fine. As long as the output voltage is rated 24VAC, the amperage just means the maximum current it’s capable at outputting (and does not mean it will always ‘pump’ that much current into the device).
I was wondering how a 500mA power supply is capable to power up to 48 stations plus the electronic. Considering that each valve need 100-200 mA
Ok, that makes sense. But suppose someone try to turn on 15 valves at the same time with a power supply of only 500ma. In that case something could get broken or the valves just wont work?
Because the power supply cannot sustain that much current, if you try to open 15 valves at the same time it will cause the voltage on the power supply to drop instantly, and that will trigger a reset of the controller thus releasing all valves.
I have a similar question as the original post. Would it be possible to run a 24vac 2A pump threw the OpenSprinkler if a 3A 24vac transformer is used? Or is a pump start relay needed?
Thanks
Ryan@Ryan: you will need a relay — 2A is beyond the capability of one channel (800mA max).
If I use a higher current 24 VAC transformer to support multiple zones on at the same time and a pump relay, what is the maximum current limitation of the opensprinkler hardware?
I.E., the traces on the pcb that carry the sum of the current for all open valves. What continuous current are those traces sized for?
Or, what copper thickness is the pcb? I can calculate from that and trace widths.
Thanks,
The trace width of each channel is 0.81mm (32mil) minimum so should withstand 1amp. The sum of current sources from the external COM wire, and returns to circuit ground with a minimum trace width of 1.12mm (44mil). The copper thickness is 1oz/sq^2.
Ray, was this reply for OpenSprinkler Pi or OpenSprinkler hardware?
I’m looking at the OSPi board layout and it looks like 16 mil traces for the channels. And the triacs ground connections appear to be series connected through a trace that’s also only 16 mils in several spots.
Should I worry about reliability if I have more than one sprinkler valve on at a time?
Why I’m asking–I’m not really going to have lots of irrigation zones running at the same time….
One of my OpenSprinkler Pi’s is located in the same area as my pool equipment. I’ll have four irrigation zones there, at most two zones on at a time (but probably just one, depending on the flow I can get at 50 psi at that location).
I’d also like to control the pool lights from the pi. They’re low wattage, LED lights, 5W max, 12VAC. The lights themselves (under water in the pool) are more than just LEDs–their color can be controlled by manually doing an on/off sequence to get the color you want. So, I’d be worried about trying to use DC instead of AC.
I was thinking I would use three channels of the OpenSprinkler board for powering (and color controlling) the three LED lights. I’d have to hack the board to power those channels from 12VAC instead of 24VAC needed for the irrigation valves.. Since I’d be hacking the pcb anyway, I could add wires not only for the 12VAC, but also the gnd connections for the pool light triacs.
I’d need a 24VAC to 12VAC transformer (haven’t found one yet, any suggestions would be welcome!).
The lights are 5W (max) each. At 12 volts, that’s 417 ma (each). So well within the maximum OpenSprinkler spec of 800 ma per channel. But, I think the sum is too much for the 16 mil triac gnd trace on the OpenSprinkler pcb.
Alternately, I could put 2:1 transformers on the OpenSprinkler channel outputs. That way I wouldn’t have to hack the OpenSprinkler pcb. Current would be 200 ma for the 5 watts at 24 volts, but sum still of the current looks too big for what looks like a 16 mil trace on the OpenSprinkler pcb.
I could also just add jumper wires for the triacs on the pcb and the “downstream” transformers. But, while that approach wouldn’t require me to cut traces on the pcb, I’d still have to do an “add wire” hack AND use multiple transformers.
So, I’d to hear that I’m missing something and the OpenSprinkler pcb can actually handle more total channel current than what a 16 mil trace would limit. But, I can certainly make it work, if I can find the transformers. Worst case, I guess I could wind my own.
@davethomaspilot: the trace width is just a basic guideline and in practice it also has to do with the length of the trace. For example, a short trace with narrow width is not as bad as a long trace with narrow width. In the end it’s the resistance on the trace that matters. Obviously the longer the trace, the wider you want it to be to reduce the total resistance on the trace.
Before I proceed to answer your second post above, let me make sure if your LED runs on 12V AC voltage instead of DC — most LED lights I’ve seen run on 12V DC voltage, so you probably want to check to make sure of that. The reason I am asking is that OSPi cannot switch DC power — due to the way triacs work, it can only turn on DC current but will not be able to turn it off. Actually you can run LEDs on AC power anyways, but you may notice considerably flickering compared to running it on DC.
Anyways, back to your questions: although the ground trace is not wide, there is a whole ground plane, which means each ground trace will only run a short distance before it goes into part of the ground plane. So the ground can actually run a fairly large amount of current.
Another option, if you don’t want to modify the OSPi circuit, is to use relays to switch your LED lights. Specifically, you can connect a 24VAC relay to a station, and that way turning on/off the station actually turns on/off the relay, and you can use the relay to switch whatever device you need. We have published a blog post that describes several 24VAC relay options:
https://opensprinkler.com/using-24v-ac-relays-with-opensprinkler/What guideline do you think I should use for the sum of all currents in an OSPi? What trace temperature rise will result?
The LED lights run on 12VAC, not DC. They have some sort of controller built in, so I worry that even trying 12VDC might damage them.
On using 24VAC relays to switch the 12VAC…
I don’t have any 24VAC nearby. So, I’d have to add an outdoor, 120VAC to 24VAC transformer then route both 24VAC and 12VAC to the OSPi enclosure, or route 120VAC and use a local transformer inside the OSPI weatherproof enclosure to get the 24VAC needed for the sprinkler valves.
It seemed better to use a transformer to double the 12VAC that’s already there to run the sprinkler valves. This would only require the small “12 0 12” transformer and could easily fit in the same weatherproof enclosure.
But that’s really the question. Should I add the 24VAC relays and a 120VAC to 24VAC transformer so I don’t have to hack the OSPI? Probably, but still thinking about it.
Thanks!
OSPi can be powered by 12VAC supply and that’s not a problem. But 12VAC is probably not sufficient to drive sprinkler solenoids if you plan to use the same controller to drive both solenoids and LED lgihts.
Another option is to use two separate power sources: one 24VAC to drive solenoids, and one 12VAC to drive LED lights. You can have one of them power OSPi too. They need to share a ground pin. Say you use 24VAC to power OSPi. To use 12VAC to drive LED lights, you connect one wire from 12VAC to the top pin of the orange terminal block (that pin is connected to circuit ground). The other wire from 12VAC will be the common wire for LED lights. If you have multiple LED lights, one wire from each of them will come together and go to the common wire of 12VAC. The other wire will go to an individual station port. This way, when a station turns on, the triac completes the circuit from 12VAC to LED light, thus turning on the light.
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