Moderator edit: added quote tags

-- Thanks for fixing quotation layout, moderator. I am not familiar enough with the forum site (or any forum site) to do this yet but will seek out smarts on this

 

The load determines the size and structure of the relay contacts.
The relay contacts determine the size and structure of the relay coil.
The relay coil determines the size and structure of the coil driver component.

ak

 

The load determines the size and structure of the relay contacts.
The relay contacts determine the size and structure of the relay coil.
The relay coil determines the size and structure of the coil driver component.

ak

See? He's starting with the output and using that information to design what drives it.

 

-- Thanks for fixing quotation layout, moderator. I am not familiar enough with the forum site (or any forum site) to do this yet but will seek out smarts on this

Don't type into the middle of the reply without using quote tags.

Quote tags are inserted as a pair of [QUOTE] with the original quote here [/QUOTE] .

In other words, your reply is entered like this:

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If you are replying at the bottom of the quote after the final [/QUOTE] , you don't need quote tags.

 

The amount of power being switched by the relay contacts directly affects the amount of power the relay coil needs to operate.

-- key point I had not realised. Thankyou for pointing that out. I hadn't read anything like that till now.

Switching 12 V at 1000 A vs 12 V at 1 A require two very different relays.

-- yes

So, what is the load the relays are driving? You've said it is 12 Vac? Current?

-- oops I did say 12v AC but I just looked at the specs sheet- see attached - and it's 18v AC ("minimum"). sorry

-- The current drawn by the selenoid valve is less than half an amp. Attached spec says 0.48A

Since this is not in an office environment, do the relays need to be sealed or at least enclosed, or can they be open frame?

-- no there's no need for them to be sealed. they will be safely tucked away with the other components in an all weather enclosure. I envisaged components will just sit in an open frame inside the enclosure

If the current required by the solenoid valves is low enough, a PhotoMOS device might handle it. Depending on who you ask, this is either a high power opto coupler or a low power solid state relay.

-- Are these SS options still ok for the load?

How many of these circuits will you need to build?

-- only the one. it can stay breadboaded

Many thanks for your perseverance
ak

 

Hi #12, Hi AnalogKid,
Just letting you know I'm still keen on this project. I am using yr advice above and working on specifying the output requirements of the system. I want to do this first before I ask you for anymore help and I apologise for not paying enough attention to this.

I am starting with the selenoid specs and then I will know the specs of the relays. Once I settle on which precise selenoid valves and relays I need to buy (including the part numbers) I will provide a pdf on both products. I'm hoping you'll then be able to firm up yr thoughts on the best design of the circuit to match the output requirements.

Sound OK?

Thanks again for helping me.

 

Sounds good to me.

ak

 

I have reworked the specs, as foreshadowed:

Solenoid valves: The solenoids are the switching load for the relays. The PDF attached entitled Solenoid.pdf shows the solenoid specs. I bought one and tested it with my newly purchased multi meter. It draws 140mA at 24v AC. I could hear it’s mechanism click when energised and when I connected it to the water supply it turned the flow of water on by opening the normally closed valve.

Relays: The PDF attached entitled Relay.pdf shows the specs. I bought one and did some measurements and testing:
Firstly the relay coil: The coil is rated at 5v DC. I couldn’t find the current rating in the specs. I tested it and it draws 83mA at 5v (holding). Just for practice, I used ohms law to see if I could predict its current. (This was my first foray into ohms law.) The coil resistance measured 57 ohms. Substituting these two variables into the RHS of the equation, I = V/R, yielded a quotient value for the current of 88 mA. Seems legit.

Secondly the relay contact switch: the contact switch is rated at 5A at 250v AC, which is within the requirements of the switching load (see above). It is NO and when I applied the power to the coil I could hear the armature click closed, reducing the measured resistance to zero ohms.

Upon hooking up the relay and solenoid, the relay switched the solenoid valve open when the coil was energised. Nothing overheated, smoked or made strange noises so I am definitely on to something!

Could u please continue helping me with the design of the circuit taking into account these final relay specs?

 

Relays: The PDF attached entitled Relay.pdf shows the specs. I bought one and did some measurements and testing:
Firstly the relay coil: The coil is rated at 5v DC. I couldn’t find the current rating in the specs. I tested it and it draws 83mA at 5v (holding). Just for practice, I used ohms law to see if I could predict its current. (This was my first foray into ohms law.) The coil resistance measured 57 ohms. Substituting these two variables into the RHS of the equation, I = V/R, yielded a quotient value for the current of 88 mA. Seems legit.

Secondly the relay contact switch: the contact switch is rated at 5A at 250v AC, which is within the requirements of the switching load (see above). It is NO and when I applied the power to the coil I could hear the armature click closed, reducing the measured resistance to zero ohms.

Using the resistance method for DC solenoids is valid, but of no use for AC type as the current is limited by the Inductive Reluctance.
Max.

 

It sounds like you're doing very well on your own. This weekend is a bit busy, but I'll get back into this thread by Monday. Where are you located?

ak

 

Relay: 12VDC, 320 ohms, 37.5 ma
Contacts: 5 A
Min load = 10 ma.

Firstly the relay coil: The coil is rated at 5v DC.

Something is very wrong about the voltage specifications.

Post #12 says 230 volt mains and 12 VAC to be provided.
This suggests that Melissa is in England with 50 Hz power.

The valves want 24 VAC 50 Hz. 444 ma start surge, 250 ma run.

The solenoids... I bought one and tested it with my newly purchased multi meter. It draws 140mA at 24v AC.

There is something very wrong about this measurement.

@Mellisa_K
The valves want 24 VAC. Your idea for a 12 volt transformer will not work.
You seem confused about a 5 volt relay coil while posting the specs for a 12 Volt (DC) relay.
Your measurements seem wrong for the solenoid current.

Time to back up and sort things out.
The logic section is easily adapted to whatever voltage and current the solenoids need. The relays can be replaced by triacs if the solenoids want AC, or transistors if they want DC. Right now, we need to nail down the specifications. As much as you have tried, you don't have solid answers yet.

 

Have you considered an Arduino?

For a person who is having difficulty with the difference between a 5V relay and a 12V relay?
And you want her to learn a programming language?
I don't think so.

 

Hi again.
This was accidentally deleted so here we are again

Have you considered an Arduino?
The Arduino series was developed to teach programming and are quite useful.
Google askmanualrev5.pdf for a very good intro book that I believe has been released for free download now.
With an Adruino the circuit operation can be very easily modified to suit, and extra features added as required, like temperature/humidity sensing, light, air pressure... And a Liquid Crystal Display is always useful.
I have been in electronics for 50 years (a bit scary that) and made quite a few dedicated hardware controllers but now would not go that way as there are a great many programmable controllers like the Arduino available that make it a lot easier, particularly to add features or change the operation, so I'd not really even consider a dedicated hardware design.
Have a look at the downloaded book. This is a good beginning. I use it in a class I'm running to introduce people to electronics and programming. One of the students is building a fish farm/ hydroponics system and wants to learn how to make all the controller himself. That is a great project!
So is yours. Having a project in mind is a very good way to start as it gives you something to aim for.

And #12, it has been my experience that people do not need to really understand the difference between 5V and 12V to learn to program.

The first post asked for help to develop an easily expanded and adjustable system and an Arduino would suit that very well, and a logic based one would not.
It does seen many people on this forum are quite against Arduinos and that is a shame. They are a great teaching tool!
My background is in industrial control and I have designed many PCBs that are Microchip PIC base. Also a number of 6502 core micro controllers and a vision system based on the RTX2000 Forth engine.
I am not trying to hijack this forum in any way but truly feel the Arduino is the best solution to this project. There are other platforms that can be used but the Arduino "ecosystem" makes it an obvious choice.
If need be I could put up some circuits to help.

 

And #12, it has been my experience that people do not need to really understand the difference between 5V and 12V to learn to program.

I am not trying to hijack this forum in any way but truly feel the Arduino is the best solution to this project.

OK. Present your circuit, your code, and your Bill of Materials, just to give the Thread Starter what we were going to do in 2 chips and a few triacs. Be sure your Arduino can operate on 5 volts or 12 volts to demonstrate that one need not know the difference.

 

It does seen many people on this forum are quite against Arduinos and that is a shame.

Did you see these that the TS said in the first post:
I want to learn about electronics from this and future projects. So I would favour a transparent design that allows me to "look into" the circuit and understand how it works over a possibly more opaque "black box" approach.

If you using a Arduino then how can she learn the basic circuit, in her mind using the virtual circuit?

The helpers just provided the properly ideas to suit what the TS needed, learning Arduino is in the other level, if the TS like to use it then the helpers will support her to complete her project, you can also help her.

A real EE player maybe don't like to using Arduino, or depends on the cases, and they will using the same chips with C in C compiler environment but not in Arduino, the original design of Arduino was for non-EE players have a shortcut to get into the uC controller world, Arduino is good, but does not everything should be using Arduino, it should be depending on what the TS needs, the suitable way is the best way.

 

I'm sorry if you are all offended by my posting. It was not my intention to be a spammer but was TRULY trying to help.
I'll leave it alone now.

 

I'm sorry if you are all offended by my posting. It was not my intention to be a spammer but was TRULY trying to help.
I'll leave it alone now.

Please don't feel sad, when you join the forum more and more and the links related with the topic then the links will be stand.

Every forums has its own rules and limitation, we all have to follow the rules, I think you just concentrate how to help our members to solve their problems, if you could using your good experience provide the suitable and correct solution for the members then you can be a great helper as other older helper members, good luck.

 

Relay: 12VDC, 320 ohms, 37.5 ma
Contacts: 5 A
Min load = 10 ma.

Something is very wrong about the voltage specifications.

Post #12 says 230 volt mains and 12 VAC to be provided.
This suggests that Melissa is in England with 50 Hz power.

The valves want 24 VAC 50 Hz. 444 ma start surge, 250 ma run.
There is something very wrong about this measurement.

@Mellisa_K
The valves want 24 VAC. Your idea for a 12 volt transformer will not work.
You seem confused about a 5 volt relay coil while posting the specs for a 12 Volt (DC) relay.
Your measurements seem wrong for the solenoid current.

Time to back up and sort things out.
The logic section is easily adapted to whatever voltage and current the solenoids need. The relays can be replaced by triacs if the solenoids want AC, or transistors if they want DC. Right now, we need to nail down the specifications. As much as you have tried, you don't have solid answers yet.

hi #12 thanks for your reply.

youre right i do need to once again backup and get it right for you and the others kind enough to read and consider my posts seeking help.

before i start though please be aware that in my post number 26 i foreshadowed re-specifying the output stage of this project with the words:

"I am starting with the solenoid specs and then I will know the specs of the relays. Once I settle on which precise selenoid valves and relays I need to buy (including the part numbers) I will provide a pdf on both products. I'm hoping you'll then be able to firm up yr thoughts on the best design of the circuit to match the output requirements."​

So my last post #28 was saying 'ive taken your advice and all bets are off and so looked harder at the specs and i have come up with different ones'. i should have then said: "so pls ignore any earlier posts talking about the relay specs because here are the new ones...".

First some background about me.

I am in austraila which uses 240v ac.

i have some experience with electric circuits using soldering and tinkering on a family farm in my youth. i know nothing about electronics and i want to learn. I have earmarked this goal as my big passion for 2017.

Just to clarify regarding your comment in #32. I have actually had alot of experience coding with VBA (excel), SPSS and SAS. I think i could pick up whatever arduino uses pretty easily. as i will explain below the mix up with the 12v and 5v relay although regrettable was inadvertant. But i can assure you i can both code and tell the diference between 5 and 12v. my professional background is statistics and i can do maths also. so these are the skills youre dealing with.

I dont want to learn arduino right now if i can avoid it because i want to understand how more basic individual electronic components work based on transistors. i might make 2018 my arduino year! first things first.

I am impressed with this site and have chosen it to learn about electronics. i have a vegie patch which currently has three sprininkler stations ie three pipes feeding 4 sprinklers each. i want to automate these irrigation stations and then maybe move on to expanding it to a bigger vegie patch. this project is my way into learning about electronics. ive chosen this project because its immediate and practical. i am ready to invest NOW in having a dialogue with the AAC forums experts to learn about solid state electronic circuitry by building this one off application. i wont take you and your colleagues for granted and i will always be respectful and grateful. i will apply your advice within a day or two and i will update you quickly with feedback and progress. staying current like this should help you because you dont have to hold outdated information in your head.

that said, lets start with the 5v vis a vis the 12v relay:
my relay that i have here says 5v dc and it operates on 5v dc. attached is a jpg of the relay, the transformer driving the solenoid valve and the solenoid valve (and breadboard). also attached are 2 screen shots of this relay on its retailers website. One shows a close up of the relay and the other shows a brief description of the relay. the web address is https://www.sparkfun.com/products/100 . THis page offers a detailed datasheet to download. if you click on this you get the pdf i attached to my last post. unbenown to me its a datasheet for a 12v version of the same relay. so i apologise for giving you the wrong datasheet. i should have checked it. i have just gone back to this site and i cannot find the datasheet matching the adverstised relay. i googled it and looked elsewhere but i cannot find the datasheet I need. But i can assure you i bought the 5v version and its brief product describption in the third screen shot attached here is all the specs i can find. I hope this makes sense to you now.

I think i measured the current and the resistance of the relay coil correctly. I can assure you i used a 5v DC source to energise this relay. (I used a USB cable with its cat2 end cut off. pls see pic called "5v dc usb power source.png").

Now for the relay swithing contacts.
i apologise for saying it was 30v DC. It actually is but i gave you a bum steer because the relevant feature here is the AC rating not the DC rating which is 250v AC up to 5A. this is what i should have said. its relevant because my solenoid is rated at 24v AC (pls see the pdf in my last post). i have mislead you on this for which i apologise.

Regarding the current draw of the solendoid valve, the last image entitled "current of solenoid" shows the reading on my multi meter. I have never used a digital multi meter until now. i only bought it the day before yesterday and this like everything here for me is new. the one i last used was analogue when i was a kid and i didnt own it. Anyway you can see that my DMM reads 0.15A. (I just measured this and its 0.01 up on the reading yesterday of 0.14 - i dont know why). I multiplied this by 1000 to get the milliamps of 150mA. I dont know what i am doing wrong here. I cant verify it by ohms law like i did with the relay coil because of the huge no. of secondary windings of the transformer?

I hope this clarifies it all for you

thanks for your help #12

regards

mellisa

 

I'm sorry if you are all offended by my posting. It was not my intention to be a spammer but was TRULY trying to help.
I'll leave it alone now.

hello dendad,
i really appreciate your interest in my post and especially the fact you went to the trouble to write such a detailed and helpful reply.

you copped a bit of flak for mentioning arduino in this forum. dont worry about the purists! hehe.

i would like to learn arduino but i want to do the hard yards learning about solid state electronics first by using transistors and resistors and diodes and capacitors. previous responders to my posts have indicated i can achieve what i currently want to do with this component based circuitry. if not i will be on your doorstep.

i have been thinking about some other uses for arduino or something similar that has a whole computer in it. this includes some home automation and some web based remote control applications but they are only a dream at the moment. i need to crawl before i can run and i am likely to get much more satisfaction from working with an embedded computer like arduino if i have some electronics knowledge to beging with.

thanks again and best wishes

mellisa king

 

It sounds like you're doing very well on your own. This weekend is a bit busy, but I'll get back into this thread by Monday. Where are you located?

ak

Thankyou analogue kid

I appreciate your ongoing interest and encourage ment.

Regards

Mel king