View previous topic :: View next topic |
Author |
Message |
bibibo
Joined: 30 Nov 2009 Posts: 168
|
Posted: Fri Aug 23, 2013 11:30 am Post subject: Power supply, triac driver |
|
|
Hello, I develop my irrigation system and i have a problem with fuse on secondary site. There is fuse 500mA. Current consumption is 100mA. After turn on, fuse is burned.
Next question is about driver triac. What du you think ? Is it correct ? |
|
Back to top |
|
|
Paulvk
Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY
|
Posted: Sat Aug 24, 2013 1:40 am Post subject: |
|
|
You need to isolate the triacs from the logic as they produce switching spikes from the back EMF of the solenoid valve (note the 39ohm resistor and 0.01uF capacitor in circuit below) so using an optocoupler like the MOC3081 triac driver for each triac and having a separate supply for your 24v AC is the way to go. Your fuse blowing could be spikes firing all triacs at the same time. It also makes the circuit simple as all you are driving is a LED well within the abilities of an AVR.
Regards Paul
Note This circuit operates at 24v AC with out any problems |
|
Back to top |
|
|
bibibo
Joined: 30 Nov 2009 Posts: 168
|
Posted: Sat Aug 24, 2013 5:48 pm Post subject: |
|
|
Paulvk, thanks a lot. I understand. |
|
Back to top |
|
|
bibibo
Joined: 30 Nov 2009 Posts: 168
|
Posted: Sun Aug 25, 2013 5:09 pm Post subject: |
|
|
I redrawed my circuit. I use the same transformer coil for the logic and valves. I don't know whatever it is well. I cannot supply the logic and valves separate. What do you think about my new circuit ? |
|
Back to top |
|
|
Paulvk
Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY
|
Posted: Mon Aug 26, 2013 12:29 am Post subject: |
|
|
It is much improved though still not good to have logic on the same transformer windings, a transformer with two 12v windings would also help this would lower the voltage to the logic supply making that simpler. Have you already the transformer or can get one with a winding for the logic. It would also be good to fuse the triacs power with a separate fuse and one smaller one on each valve here you could use an in-line holder on each cable this is in case of a short circuit or damage to the cable.
Will update post with more comments later on.
Regards Paul |
|
Back to top |
|
|
bibibo
Joined: 30 Nov 2009 Posts: 168
|
Posted: Mon Aug 26, 2013 8:19 am Post subject: |
|
|
Hello, if i understand well, better is use two 12V windings but still there is common supply for logic and triac. A transformer with two separate windings 24V and 12V it would be better solution but i think it is a custom product. More expensive |
|
Back to top |
|
|
six1
Joined: 27 Feb 2009 Posts: 553
|
Posted: Mon Aug 26, 2013 8:38 am Post subject: |
|
|
Hi,
have a look at Paulvk's image: MOC3021-DIA.GIF
the only things connected to CPU Board are the LED's. All other will be driven by second winding from transformer.
best, michael _________________ For technical reasons, the signature is on the back of this message. |
|
Back to top |
|
|
Paulvk
Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY
|
Posted: Mon Aug 26, 2013 9:50 am Post subject: |
|
|
The transformer with 12v 0v 12v 0v is very common but just as common is this type http://www.jaycar.com.au/productView.asp?ID=MM2008 This one would give a 6 volt winding for the logic the diagram below shows how I would set it up. As the windings come out to a tab in many cases it can be parted at that tab to separate the the 6 volt winding.
With my present watering system I found that the transformers for festive lighting ( most run on 24 volts ) were easy to come by for free or cost little as a set of lights and just plugged into the power outlet with a lead coming out of them that could be connected up to the circuit and again I used 9 volt AC units from wireless home phone units just needed to put a dc connector on the box.
Another thing to note is my valves indicate a 7 watt power consumption so if your unit had all 8 on then you need 48 watts of power to drive them.
Also your LM7805 being fed by a zener is not good you should have a resistor to ground after the zener and very close to the input and output of the LM7805 a 100nF capacitor.
If this is just a one off project for you to use go with two transformers small 9v one for logic and a much larger 24 volt one for the valves this way you can make the control logic and valve driving totally seperate.
Regards Paul |
|
Back to top |
|
|
bibibo
Joined: 30 Nov 2009 Posts: 168
|
|
Back to top |
|
|
Paulvk
Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY
|
Posted: Mon Aug 26, 2013 2:59 pm Post subject: |
|
|
That is a good idea you will keep the two totally separate. A lot of nice cheap stuff at DX , a lot costs less than buying the parts we are lucky here in Australia a lot of it can come via courier in less than a week for a couple of dollars more. You may find this link useful as he has the instructions on building a weather station which you need to know to not over water or maybe more water when its hot and windy.
Regards Paul |
|
Back to top |
|
|
bibibo
Joined: 30 Nov 2009 Posts: 168
|
Posted: Tue Aug 27, 2013 8:42 am Post subject: |
|
|
Hello, One of our local transformer's manufacturer offer me transformer 230/12V 500mA + 24V 1A for 10 EUR. What do you think ? What is it better ? One transformer with two separate winding or transformer valves and switching power supply for logic ? |
|
Back to top |
|
|
Paulvk
Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY
|
Posted: Tue Aug 27, 2013 10:12 am Post subject: |
|
|
For long term reliability the 12v + 24v transformer is the best option switching supplies are efficient but prone to failure I can contest to this with the number that have failed for me even with expensive telecommunications grade units I have used, yet I have transformer linear type units that are more than 30 years old that are still performing as when they were new some have been on 24/7 all that time.
What was needed was to get the 24v and 12v on different windings as spikes induced through the transformer will be even on the other winding and can be filtered out a direct path can not be found through the logic, blocked by transformer and op-coupler. You can place the same resistor and capacitor as on the triac across each of the 12 + 24 volt windings of the transformer now for your +5v supply these are ok I have 4 and are working well http://dx.com/p/dc-3-40v-to-dc-1-5-35v-voltage-step-down-transformer-module-154907 the parts would cost me 4 times as much all you then need is a small bridge rectifier , a 1000uF capacitor and fuse.
Regards Paul |
|
Back to top |
|
|
bibibo
Joined: 30 Nov 2009 Posts: 168
|
Posted: Tue Aug 27, 2013 5:58 pm Post subject: |
|
|
Hello Paulvk, thanks for your reply. I don't know if i understand you well. Please, check my circuit. |
|
Back to top |
|
|
Paulvk
Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY
|
Posted: Tue Aug 27, 2013 11:34 pm Post subject: |
|
|
Yes you understand very well your circuit is good it now should work well with no problems.
Regards Paul |
|
Back to top |
|
|
bibibo
Joined: 30 Nov 2009 Posts: 168
|
Posted: Wed Aug 28, 2013 8:34 am Post subject: |
|
|
Super. Thanks a lot. |
|
Back to top |
|
|
|