adjusting output voltage

[kellogs]

Hello,

The OS I have is a DIY kit purchased last year – I have yet to install an irrigation system, doing it now. Because of the electrovalves being placed at a distance from the controller and because I would like to use UTP cat 5e cable (which I have plenty of) I would also want the output voltage adjusted to something higher than 24 VAC – I shall be getting > 2VAC losses on the thin 26 AWG (0.4 mm) wires the UTP cable has. From what I gather, electrovalves wont jumpstart with anything less than 22 VAC, so, is it possible to recompile the firmware after tweaking it for a bit more output Volts ?

 

Thanks

[Ray]

It’s very likely that the valves will start just fine with less than 22VAC. As I explained in this blog post:
http://rayshobby.net/understanding-24vac-sprinkler-valves/
the solenoid valves typically require a high impulse voltage to get energized. Once energized, the voltage can go much lower and that’s enough to keep it energized.

The firmware will not be able to adjust the output voltage — this completely depends on the output voltage from your transformer, and the firmware has no control over it.

[Augustin]

I just finished my installation using 0.5mm wires (not sure AWG ratings), they are sold as alarm system wires, indeed the maximum distance between controller and the farthest valve in my case is only 15m (under 50 feet) and the valves are RainBird DV series 24VAC.

Everything worked perfectly during the test phase, I will start a full irrigation program in a couple of weeks if you need more feedback.

 

[catalin]

Thanks Augustin, but I am quite sure you won’t run into any problems with that distance and AWG 🙂

As for my case – I must correct myself – on the cable box there is a 0.4 mm print. It does not say what does that 0.4 mm represent. However on the cable sheath “24 AWG” is printed, meaning a conductor diameter of 0.5 mm, not 0.4 mm. So I have used these two calculators and they both came up with similar voltage drop:

http://www.powerstream.com/Wire_Size.htm

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=84.22&voltage=24&phase=ac&noofconductor=1&distance=52&distanceunit=meters&amperes=.3&x=42&y=11

 

of around 2.65 V – for

distance = 52 m

current intensity = 0.29 A

diameter = 24 AWG

material = copper (CAT 5e UTP cable)

 

More than that, I did a dry run on a 52 meters cable (tested with actual hardware, but electrovalve was not installed at location yet). The solenoid actuated in this test, and I did the readings:

25.9 VAC at source outlet

22.2 VAC at solenoid inlet

So, uhm.. I am confused about this. The calculated 2.65  VAC and the measured 3.7 VAC are pretty far away from each other. Although 22.2 ought to be enough for the solenoid to operate even a pressurized valve, I am still confused about this discrepancy. Where did I go wrong ?

 

Thanks again!

 

[Ray]

You may want to directly measure the resistance of your 52 meter cable. In theory (according to data sheet) it may be x ohm, but in practice it may be y ohm. Also, remember the current runs round-trip, so you will be calculating the voltage drop on a 104 meter long cable.

[catalin]

Hmm, wait a minute, cable was not laid out straight on the ground but was a bit coiled… and we are dealing with AC.  I’ll measure its resistance.

 

LE: measured – came out at about 0.42 ohm / meter. Confused again. Should have been 0.084 ohm / meter according to http://www.powerstream.com/Wire_Size.htm 😐

[Ray]

If the cable is very coiled, it will have non-zero inductance, and hence its resistance to AC will be higher (causing high voltage drops).

0.42 ohm / meter does sound quite high. According to this, even without considering inductance, it will be dropping 0.42 * 52 * 0.29 = 6.33V, which is quite a bit higher than your measured voltage drop.

[catalin]

Hmm, this is not OS related any longer, so thanks for replying Ray, I shall live in confusion, f*** it 😀

[dun4cheap]

I have been diving in to POE for a few months now and I have learned quite a bit. You may want to visit http://find-a-poe.com/ , which is texas wifi company. Their website has some good info what you are trying to do. I am now using the information I have learned here to inject 12v, 24v and 48v over cat 5e. I am using using the Opensprinkler micro controllers along with ubbiquity radios and hikvision cameras, all being powered with poe. Anyhow good luck, and maybe this will help you out.

 

[catalin]

thanks for sharing, dun4cheap, might be useful in the future 🙂

[catalin]

Hello again,

laid out the cable to valves box – about 40m distance, managed to shorten it. Using 3 x HV100 valves and 1 x DV100. They all work without any water pressure, but they all also buzz like they are going to blow up. Some tremble too while active and buzzing, others just buzz. I think OS even turns them off at times and will not run them for a full minute as I request. Pulled the meter and read 21.6 VAC :-0 – on HVs. DV came out at 20.8 VAC.
Next I have connected two wires together for one valve in order to halve the impedance (one-way, the return wire was not doubled) and read 22.3 VAC- but still the buzz was there. Took out that solenoid and tested it straight at OS outlets. These HV100 valves seem to be a little noisier than humming, but still, I managed to get rid of its buzzing by firmly pressing its wires against OS outlet screws (not so firm /wonky contact resulted in same buzz). There also is another valve box closer to the OS outlets and those valves inside hum, not buzz. I am thinking about attempting with a 30 VAC transformer. Other ideas ?

Thank you!

[catalin]

This is over my head… today 3 out of those 4 valves stopped buzzing. Without me doing anything other than turning the mainline valve thus allowing water to the valves. I have just swapped the remaining buzzing solenoid with another one from another zone – a zone which will seldom get activated.

Regards

[Augustin]

Lack of water in the pipes could increase the noise of the valves? Acting like a flute effect?
Pipes being under water pressure now could become a lot more sturdy and reduce the vibration?

[Author]

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