Irrigation controller queries

13 years ago

Hi folks.

Our old Oasis Dundee 6-9 station controller is acting strangely - only the 'Program' buttons are touch-responsive. It's not possible to set the time, station watering times etc, or to operate the stations manually. Everything was fine last time I used the controller (autumn), but evidently something has gone haywire over the winter.

So, I suppose I need to buy a new controller. I'm looking at Total Eden's own brand, Rainmaster, Toro (the cheapest outside 6-station controller I can find), Rainbird or Holmans. They all seem pretty similar. Only need a basic model to replace the Dundee. ie: 6 stations, 2 programs+, to be fixed to wall outside.

There's the background. My questions are as follows (enumerated for the sake of clarity and ease of response):

1. Today's controllers come with transformer inbuilt, whereas the Dundee transformer is external. I assume it's somewhere in the roof cavity - don't like going up there. It's certainly not inside the house. So, if I attach a new controller to the existing wiring, I'd be using the Dundee transformer - correct?

2. Is it possible to bypass the Dundee transformer and use the inbuilt one on the new controller? I'm guessing not, since the Dundee transformer is probably plugged into the power outlet somewhere in the roof cavity.

3. I believe it is possible to use the Dundee transformer with a new controller just by using the existing wiring, effectively bypassing the new controller's inbuilt transformer. If this works, fine, but if the Dundee transformer is faulty and is the reason the Dundee controller no longer works properly, it will likely mess with the electronics of a new controller also - correct?

If the old transformer is faulty, could it destroy the electronics of the new controller as soon as it is wired up and turned on?

4. Is there a way of testing whether the old transformer is faulty without getting up into the roof and unplugging it? I have no idea where it is up there. Would it be plugged into an electric power socket, or were these old controllers hardwired into the power in some way?

Would appreciate some advice on 1-4 above from folk who know more about this stuff than I, which means just about anyone!

Cheers!

Ross

Featured Answer

southpark

9 years ago

last modified: 9 years ago

Most welcome tropicbreezent. You could be right about the proportionality issue. Our best bet might be to just go for a series resistor and inductor model, where increased lengths of the cable (wire) leads to proportionally linear reduction in the voltage at the output side of the cable. All the best in your setup! Should be ok.

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Comments (9)

Mark_K70
13 years ago
Hi Ross,
I'm no sparky so I can't comment on the testing of the transformer. By I've used and installed the Toro Greenkeeper several times over the years. It seems like its been superseded by the Toro DDC. According to online manuals, both have external transformers. So I can't see why you couldn't just use you existing 24 volt wiring.
They are a simple unit to program and 2 station expansion units are available. Hope this is helpful.
Regards
Mark
PRO
Hydrawise
11 years ago
Check out the Hydrawise, it is EPA WaterSense approved, so customers in the US may get a rebate. It is a full smart controller, with predict weather. You do not need a subscription plan to use the system and get all the features that the others offer. There is a subscription plan as well that offers features above what others offer, such as flow and electrical sensing alerts sent to your phone or email and up to 5 weather stations.
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southpark
9 years ago
last modified: 9 years ago
Five years too late. But....... the first thing I would do is to replace the two electrolytic capacitors (a 100 microFarad, 35 Volt, and a 470 microFarad 63 Volt). The dundee oasis irrigation controller is built rugged, and excellently. Hats off to the person or team that designed and built this system. They obviously knew what they were doing.

Recently, I found that my 9 Station dundee oasis developed a clock issue, time was running too fast. It turned out that the 470 microFarad capacitor had degraded, and I measured it to be 380 microFarad (due to aging/degradation). The result was probably noise affecting the system. After replacement of the 470 microFarad capacitor, the system is now as good as new again.

It is just sad to see fantastically built systems to be thrown out when simply replacing the only two electrolytic capacitors on the circuit board can make the system last another 20 years. Although, it's pretty bad how our technology has still a way to go (in 2017) before they can make electrolytic capacitors that don't degrade. Electrolytic capacitor degradation is probably the main cause of issues in most electronic devices... tv's, radio's, everything.Regards, Kenny.
tropicbreezent
9 years ago
To not waste a resurrected thread on irrigation I've a question you might be able to answer. I have an Irritrol Rain Dial 12 station controller and I'd like to know what the maximum length of the cable from the controller to the solenoid can be and still operate effectively. I've asked around a lot and no one seems to have any idea.

Logically, there would have to be a limit to the distance the electric output from a controller could go and still do the job. The only figure I have on voltage is from the American manual and don't know whether that still holds for here. They say maximum output per station is 24V AC, 0.5 Amps.

If you have any idea I'd really appreciate it, thanks.
southpark
9 years ago
last modified: 9 years ago
I believe that those irrigation companies estimate the maximum wire length between station and solenoid according to estimated resistance of the wire, and the estimated inductance of the wire. These will depend on the particular sort of wire/cable being used. One way to possibly figure out a maximum length is to take whatever system you have at the moment, and use an AC voltage measuring device (eg, multimeter) to measure the voltage at the solenoid when the controller is supplying AC voltage to it. The controller output will be about 24 V AC (RMS). But the voltage across the solenoid is expected to be smaller, due to resistance and reactance of the long cable. If you know roughly the length of the existing cable, then you can take the difference (call it "DIFF") between 24Volt AC (RMS) and the measured RMS voltage across the solenoid. This will be the estimated voltage drop for that length of cable you currently have.

Then, the voltage drop per unit length will be equal to DIFF/existing_cable_length, ie. DIFF divided by existing cable length. Call the result of this something like dpu (drop per unit length).

So, this should let you calculate (estimate) the voltage drop for a particular length wire/cable. As long as the drop is not more than say '4 Volt', then it should be ok. This means, the AC RMS voltage across the solenoid terminals themselves, should be at least 20V AC.

The voltage drop calculation will be dpu times length_of_new_cable.
tropicbreezent
9 years ago
Thanks for that Kenny, I never really though about doing it that way. I suspected that it might not be directly proportional over the full length. I have a number of solenoids but the wiring for one (around 8 metres) is easy to measure, and another at about 20 metres also easy to measure. That should give a reasonable indication. Thanks again.
alexis_bookman
9 years ago
Please view
the chart below for our recommendation for maximum one-way
distance between the controller and the solenoid.
tropicbreezent
9 years ago
Thanks for that table Alexis, it's very helpful. If Dr Google is right then double 18 gauge wire (1.02mm) will be effective up to 310 metres. That should cover the distance I need easily.

Irrigation controller queries

southpark

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Mark_K70

Hydrawise

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