Ac Power forValve

I need to control about 10 on/off valve for fan coil units. The valve uses 24 VAC as power.

For the power:
What it the size of Transformer needed for the power?
Can i use just one transformer to supply to all the valves ?
How to calculate the trsnsformer rating?

You might try finding the current used in one coil and multiply that be ten...
That is of course if all coils are similar.
If that fails ask your teacher for help with basic electrical theory 101

DFN http://www.plctalk.net/qanda/images/icons/icon7.gif
Smile

And, what size is the current of the valve?

Heng Swee, at the risk of being rude I feel compelled to point out that this is not the place to learn fundamental electrical engineering. In a couple of posts you have given the impression that you haven't got a firm grip on fundamental practices. If this is a translation or language problem, I apologize. If you are a student, say so. If not, I strongly advise you to get some assistance locally from a professional.

First of all, you can't expect good answers to poorly phrased questions that do not include necessary information. Second, some of these questions indicate a lack of formal training. And finally, how do you know you are not being given an incorrect answer, maliciously or inadvertantly, if you don't have the background to evaluate the answers? If I told you you needed ten 1.0 kVA transformers, sized using the formula kVA = I x V x 0.00173 would you know that I was wrong?

This stuff can kill!

The guys on this forum can answer a great many questions, but they can't assume your professional responsibilities or judge your ability to utilize the answers given. If you are not in a position to properly evaluate the information, obtain assistance.

Well said Tom.

Gentleman, i apologise for the lack of information and professionisam in the earlier posting.

I am not experience in this line of work. I will try to provide as much information as possible before posting.

Thanks for your advise.

Why can't you guys just help the person ?
Why isnt this the place to learn ?

Maybe he is just learning and cant afford schooling or books.
I know i have learned alot via the internet becouse i dont
have the funds to persue other means of learning.
Also have poped many circuit breakers and im still here.
I started playing with Electric when i was in the 7th grade
of high school, Learned everything from books and trial and error.
Im very close to 40 now. Still have all my toes and fingers.

sure Electricity can kill, so can your car ...
if your not sure double check and triple check your stuff
before fliping that switch. and keep one of hands in your pocket.


Basic Electricity, E over I times R (E/I*R)
got any of the 2 and u can get the other

for your valves if there is no information on them besides
the voltage measure the resistance of the coil with a ohm meter

24 volts / coil resistance = I (current)

I * number of valves = total current

yes you can use one xformer to run all the valves.

VbSparky said:

for your valves if there is no information on them besides
the voltage measure the resistance of the coil with a ohm meter

Click to expand...

DON'T DO THAT!

This is AC circuit, not DC. If there is no information on the coil itself, try to get it from the valve manufacturer.

Measuring the resistance with an ohmmeter will give you just that - the resistance. However, in AC circuit, the current will be determined by the coil impedance as well - and to a greater degree.

Sure, nobody will get killed if you do it this way. But the transformer will be much bigger and way more expensive than necessary.

If you know the coil's current, multiply it by the number of the coils and then by the voltage (24 Volt in your case). This will give you the total power consumption in Watts. If the coils are rated in Watts - just multiply that value by the number of the coils.

Add at least 20% safety overhead. The transformers are usually made in standard power ratings, pick the nearest one from a catalog that exceeds your result.

Edit: to be precise, your total power will be measured in VA (Volt - Amps), rather than Watts. The transformers are usually rated in Volt-Amps as well (or in kVA, which is 1000 VA). For the purpose of this exersise, the difference between Watts and Volt-Amps does not matter. Consider them two names for the same thing.

LadderLogic, very true, I was just giving some basic and quick
info how to come up with the total current his valves would need.

Not knowing how big these valves are i dont think the the xformer
would be that much bigger and I know i always end up hooking up
other stuff later on that i didnt plan for.

dang some indicator lights would be nice ...


Just waiting for the valve specs to show up ...

Well, Spraky, I wuz tryin' t' help the feller. I coudn't give him the answer he wanted, cuz they wuz info missin' in his question. But I truly felt thet he wuz in a little over hiz hed. Ladder gived him the kerrect answer, but if'n he ain't got the background t' use it he iz gonna have all kinds of trubles.

My point wuz thet ya has to know the basics. Ya kin git thet from books, or from more knowledgeable fellers, but it ain't within the scope of this hyar Q & A forum to teach Circuits 101.

You may want to look at http://www.patchn.com

Measuring the resistance with an ohmmeter will give you just that - the resistance. However, in AC circuit, the current will be determined by the coil impedance as well - and to a greater degree.

Click to expand...

Probably a miss quote, but its not resistance and impedance. Impedance is the total opposition to the flow of electrons in an AC inductive circuit. Impedance is the square root of the resistance squared + the inductive reactance - the inductive capacitance squared. Inductance is a "built in value" of an inductive load measured in henrys. Inductive reactance is how that inductance effects the electrical cicuit. The above formula is for series circuit.

Point being he's right. Resistance in this circuit is only small part of load calc.

here's a thought ...

heng_swee,

why don't you just give us the brand name and the model numbers of your valves? ... chances are that we can find the current draw information on the manufacturer's website ... if so, then anyone who is qualified and is willing to help can do the calculations for you ...

as always, specific information gets much better results ...

if all else fails and it proves impossible to research the current draw, then try putting an ammeter in the circuit with one of your valves and just MEASURE the amount of current required ... you'll have to factor in a healthy safety margin to handle the initial "pull in" current, but at least you won't be making wild guesses as to what capability you'll need ...

PS edit ... I just noticed that this "just measure the current" approach was originally suggested by "Guest DFN" at the very top of this thread ... what ever happened to that simple idea? ...

Chances are very good that the current rating is marked on the valve coil. If not energize the coil and measure the current. When you do this be sure the coil is in place on the solenoid.

Tom, your response was very eloquent. I dont think you were rude at all.

g.robert said:

Probably a miss quote, but its not resistance and impedance.

Click to expand...

Thank you, g.robert. Of course it is inductive reactance I meant.

My bad, although I have an excuse...