2 thermostats 1 variac 3 options DIY attempt

[gioufis80]

Hello everyone!
I want to build a small automatisation system for my grow room and I need
some help to make sure I don’t do anything stupid! My electronics skills are
not the best (it’s a hobby for me) so please let me know if I thought this right.
What I want to do is to control one exhaust fan with 3 options. These are:

1. When the temperature in the grow room is below 23°C the fan is off.
2. When the temperature in the grow room is above 23°C and below
28°C the fan is working at 60% speed through the Variac.
3. When the temperature in the grow room is above 28°C the fan is
working at 100% speed bypassing the Variac.

The drawing below is how I am thinking of connecting the various components.
Can you please confirm if it is correct or not for my purpose?
Furthermore what should be the characteristics of the relay I am going to buy?
Will this one do? http://www.darlas.gr/comersus/store/comersus_viewItem.asp?idProduct=2225687

My fan is this: http://www.canfan.nl/cfrk160l.html
And the Variac I got is this: http://www.wattbits.com/2f-1.html

 

[Harry Gypsna]

I'm doing something similar with an ATC800 and a 5step transformer speed controller.
The ATC800 is an aquarium temp controller with heating and cooling relays. Set the temp you want and set the amount of swing before it kicks in either relay and you are in business.
I built a controller using these parts before and it worked splendidly until some micro-penis fuckbag stole it. The new one will be slightly different, Ill have low speed, medium speed and full speed all from the same parts, as opposed to just low speed and full speed on the old one.
Can't help you with wiring I'm afraid, I always get someone electrically minded to make a diagram.
Have a look at the ATC800 as you won't need a 2nd stat for what you are planning and it is very affordable on fleabay.

 

[gioufis80]

Harry one of the two Thermostats I got is the SCT-1000 which is the same as ATC800
I believe. Through that I will control an air heater when the temp falls below 20 degrees.
It cannot help me though with the fan speed. Thus the variac in the circuit. I have already
tried some other solutions (triac based mostly) but because the fan is pretty strong it hums
loudly.

 

[Harry Gypsna]

Harry one of the two Thermostats I got is the SCT-1000 which is the same as ATC800
I believe. Through that I will control an air heater when the temp falls below 20 degrees.
It cannot help me though with the fan speed. Thus the variac in the circuit. I have already
tried some other solutions (triac based mostly) but because the fan is pretty strong it hums
loudly.

I've seen those SCT1000, but I prefer the ATC as it is a thinner body, so easier to get an enclosure for.
I am using a 5 step transformer for speed control, generally cheaper than the variac and it comes in a housing of its own. The ATC switches between different settings on the transformer, If temp is within range it is medium speed, if it gets cold the speed drops and a heater comes on, and if it gets too hot it goes to full pelt.
Happy building mate

 

[gioufis80]

Bump! No electrician here?? I d love some reassurance folks! I would hate
having to find out if I dind't think something correctrly through an explosion!

 

[Harry Gypsna]

People are less than eager about giving electrical advice beyond "Get an electrician" as nobody wants to feel responsible if you go wrong and kill yourself/burn your pad down.
There are websites around who you can pay to make you a diagram.
I'll try to dig out my diagram for the old controller I made and see how it corresponds to yours. It may take me a while to find it though as it is in one of many boxes of tat and it's not where I am right now.

 

[rives]

First the caveat - reducing the voltage to a motor is never a good idea because the current will inevitably rise as a result. In the case of a fan motor, this is compounded by the fan running slower and having less than designed-level cooling. That said, some fans just really don't work well with triac-based controllers.

If I am understanding what you want to do correctly, you have the NO/NC contacts on the relay reversed. As it is shown, the relay in it's unpowered state will drive the fan at full voltage through the NC contacts. After t'stat #2 closes, the relay turns on and the variac starts powering the fan. So, between 23 & 28 degrees the fan will go full speed, and then slow down after you hit 28 degrees.

I'm not familiar with the t'stats that you are using, but most electronics have a "settling time" after powering up. You would probably be better off having the power applied to t'stat #2 all of the time (parallel it with #1), and leave the contacts fed as they are. This accomplishes what you want to do, and keeps from turning the t'stat on & off. Also, the fan is going to be directly powered off of the t'stat #1 contacts, and without knowing what they are rated for, I would be very cautious. Motor loads, even small ones, are a difficult load for small contacts to handle.

The relay looks like it is too small to me for the reasons detailed above, and has a 24vac coil that you are feeding with 220vac. Find one that has a motor, hp, or inductive load rating that is bigger than your fan size, and has the correct coil voltage.

 

[gioufis80]

Dear Harry thanks for all the efford!

Rives your post has been enlightening! Indeed you are correct about the thermostat
beeing on continiously so I modified the drawing. I also changed the NO NC contacts
(silly of me!) and added a switch and fuses too. I am doing some final touches for
an on off indicator light and maybe an analog voltmeter too...

I have high hopes! hehe

 

[gioufis80]

So this below is the modified drawing for the system I want
to build. The 1st switch turns on and off everything.
The second one is for a selection between auto mode - where the
fan is beeing controller from the thermostats, off - where the fan
doesn't work but the thermostats do and finally another 3rd option
to be able to work the fan at 100% nomatter what the thermostats
temperature is.

Rives , you think this looks ok? Tommorow I plan to go and buy the
components. The fuse for the fan is 0.6A because the fan is rated
to operate at 0.5A max (100W-220V). To protect the variac I used
3A because the variac is rated for 2A. For the whole system I used
a 10A fuse because I plan to connect to it a 2000W air heater.

 

[rives]

That looks better, but have you checked into the contact ratings on the T'stat or found a more appropriate relay?

Another concern (for me, anyhow ) would be the way that you have the Variac output and the full voltage bypass tied common at the switch. You will be back-feeding the Variac on that line when the fan is running at full speed, and the [+] side of the Variac is going to be driven at the inverse ratio of it's setting. In other words, if you have the Variac set for 1/2 voltage, the Variac it going to work to double the voltage on that terminal. This means that at the half-voltage setting, you will have 330v (and potentially far more) on the fuse and the relay contact that feeds the Variac. There are discrete steps in the rated insulation levels for electrical components, usually 300v & 600v, and you could easily exceed the lower level. A DPDT relay in place of your SPDT would allow you to isolate the Variac completely.

Regarding the fan fuse - it might be too light. Motors can easily draw up to 300% on startup, and depending on the speed of the fuse, it might blow when everything is actually fine.

 

[gioufis80]

Rives thanks a lot mate! You are expanding my knowledges on the field
quite a bit with your sayings!

I replaced the drawing on the 1st post with the updated version after
your comments. I believe this is what you meant and indeed it is much
better like that. Do you agree with this final drawing?

My thermostat's relays are 10A and 12A so they should be able to provide enough
power even if the fan draws more than 10 times its normal current.

For the relay I found this one:

http://venieris.com/ΗΛΕΚΤΡΟΝΙΚΑΗΛΕΚ...1/List/0/Level/a/productid/33982/Default.aspx

It is rated for up to 10A 240VAC so I guess it ll do fine

 

[rives]

That will work, but is not quite what I had in mind. If you want to turn off the Variac like you had in your earlier version, with the additional contact on a DPDT relay you could feed your toggle switch with the common, the NO contact with the Variac output, and the NC with the 220vac from the T'stat #1>T'stat #2 line that is feeding the common contact on the SPDT relay. This gives you a NO contact on each side of the Variac and a NC contact fed with 220v for the high speed bypass. If this doesn't make sense, let me know and I can draw it up for you.

I can't read whatever language the relay information is in, but you need to find a relay (and check the t'stat spec's) that has ratings for an inductive (motor) load. All amperage is not created equal, and most specifications are written for "resistive" loads, which are by far the easiest load for the contacts. It is not uncommon to see contacts that are rated for 1800w (15a) resistive load, but are only capable of switching a 1/4hp motor (185 watts).

 

[Agaricus]

The fuse should come before the switch, so the switch is protected too.

 

[rives]

The fuse should come before the switch, so the switch is protected too.

Good point. I confess that I hadn't gotten to that portion of the circuit yet!

 

[gioufis80]

That will work, but is not quite what I had in mind. If you want to turn off the Variac like you had in your earlier version, with the additional contact on a DPDT relay you could feed your toggle switch with the common, the NO contact with the Variac output, and the NC with the 220vac from the T'stat #1>T'stat #2 line that is feeding the common contact on the SPDT relay. This gives you a NO contact on each side of the Variac and a NC contact fed with 220v for the high speed bypass. If this doesn't make sense, let me know and I can draw it up for you.

Mate please try to do that! I tried to reconnect according to your
comment but I lost it somewhere... And white widow is not helping
at the moment...

I attach a clear of connections scheme for you to do your lines in.

I have moved the fuse of the fan at that one.

Furthermore at the store I will make sure for what the relay switch
is intended for so as not to take one with a smaller than needed amperage.

 

[rives]

I apparently got lost in the versions and in the mental conversion from a wiring diagram to a schematic. This is what I had in mind, if not what I said!

R1 is the relay, R1A is one set of contacts, R1B is the other.

*edit* - I just reviewed your intent for the switch doing speed control/off/on, so I changed the point where the bypass side of the switch is fed from.

 

[gioufis80]

Damn I am trying for an hour now to understand the drawing
you made Rives... I admin I cannot read electrical drawings
(my hobby knowledge ain't that advanced).

It looks so explaining but when I try to visualize it into cables
and component connections I black out!

Would there be any chance that you could "translate" it into my
blank drawing??? Pretty pretty please with sugar on the top!!!

 

[rives]

Sweet Jesus! Paint Shop is not my forte'.

Anyhow, however clumsily, I think this is it. The fuse between the relay and the on-off-on toggle should be moved to the leg feeding the fan so that it is protected regardless of which power source is selected, but I got frustrated with PS by that time.

If you train yourself to think in terms of a schematic, rather than a wiring diagram, you will be much further ahead. It is sometimes difficult to figure out how to wire something when you are staring at the devices, but if you reduce it to simple contacts it gets much simpler. It is also transferable across any type of device, programmable controller, etc.

The resolution is low enough that I was having difficulty reading the contact descriptions. From the number of characters I believe that, from top to bottom, they are NO, C, NC.

 

[gioufis80]

rives mate I can't thank you enough for your patience and helpfulness with me!

Tomorrow I am going out to buy the connections stuff. I ll start working on the box and connections
as I wait for the Variac to arrive here. I ll post some pics for anyone interested in doing
something simular.

I am even thinking on expanding the box further by adding an analog voltmeter and ampmeter
to the sides of the box. Parallel connection for the voltmeter and in series for the ampmeter
just before the fan right?

 

[rives]

I'm glad to be of help.

That is correct for a volt meter and for a direct-reading ammeter. If you get an ammeter that takes a current transformer, the CT just slips over one of the motor leads and the leads hook to the ammeter.

Try going back and forth between the wiring diagram and the schematic so that you can visualize the logic that is driving the circuit. It is a little different way of thinking about it, but very effective.