Transformer Facts
ฝัง
- เผยแพร่เมื่อ 11 ก.ค. 2024
- In this video, Bryan goes over some transformer facts. He also talks about how transformers are rated, how to wire a multi-tap transformer, and what to watch out for when working with transformers.
You will often find 40VA transformers in residential HVAC equipment; multi-tap primary transformers are common, and they allow you to connect the primary to several different voltages via pins or wires of varying colors. The label on the transformer will give you the volt-amp rating (VA), cycles per second (hertz/Hz), and primary and secondary voltage(s).
In the case of the multi-tap primary transformer in this video, you can only use white and one other color (we can't jumper the other two together, either). The unused wires need to be cut or capped off under SEPARATE wire nuts. Connecting the other colors together will cause you to shunt the primary.
A transformer can step voltage up or down from the primary to the secondary; a step-up transformer boosts the voltage from the lower primary to the higher secondary, and a step-down transformer takes higher voltage from the primary and reduces it to a lower voltage on the secondary. The transformer in this video is a step-down transformer. A typical gas furnace generally requires a step-down transformer that takes 120v and reduces it to 24v. On the other hand, a residential air handler would often use a 240v step-down transformer that reduces the voltage to 24v.
Each transformer has two sets of windings (the primary and the secondary). The number of wraps of wire on each winding dictates the amount of voltage that the transformer steps up or down.
Volt-amps can let us know how many amps the secondary of the transformer can handle given the VA and the voltage. (For example, 40 VA / 24v = 1.66 amps.) There may or may not be enough amperage to power zoning panels, IAQ accessories, etc., so there may be cases where we have to upsize the transformer or get another transformer.
Adding a transformer also adds more of a load to the power coming in, so the transformer(s) may have an effect on wire sizing. It's worth noting that VA and wattage are only the same if there is a power factor of 1 (unity). However, when the power factor is NOT 1, the VA will be higher than the wattage. To account for volts x amps and make sure it doesn't exceed the rated VA, you will need to measure voltage with a voltmeter and amperage with an amp clamp; multiply the two and compare it to the VA rating.
You might want to try using your amp clamp on the primary and the secondary to see the difference. If we were to do that to the transformer in the video and read 1 amp on the secondary (24v), we would read 0.1 amps on the primary (240v) due to the difference between the number of wraps.
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/
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I totally understand everything you said,but could never explain it as fast as u did ,u r a boss teacher
Didn't think or know about the wattage part. Thank you. Wattage seems like something techs could stand to think about more often.
Thank you for this and thank you for all you do for us techs especially us newer techs.
Thank yoy Bryan. Very nicely and logically explained. You are a good man!
Thanks for the video, it is very informative and simply explained
Thanks for the knowledge Bryan!
Thanks Brian. I've always generalized by thinking of VA and wattage as synonymous without considering any inductive load. For MY applications, that's never been a problem. However, it's something else to consider.
I've certainly used the VA rating when choosing to add a fuse to the circuit. I hate letting the smoke out of a perfectly good transformer when some hidden short in a control board blows it.
That doesn't happen often, but it has.
Great explanation of a transformer
Awesome job
Please keep the videos coming...i don't mind looking at a blank screen and listening.
Well done sir. I know a lot of techs will add a 3 amp fuse in-line of the red 24 volt side of a 40va transformer to protect it from a t-stat wire short coming back and smoking the transformer. Of course if you have a built in fuse for your transformer you don’t have to do this lol
@hvac school. Thankyou for all the great information
Great content
Awesome
You are a master in HVAC
Would you recommend adding a stand alone transformer for a basic 24 volt coil UV light and for a bipolar 2400, your response would be greatly appreciated.
Thanks Brian. great video.Hvac transformer. can i replace a 25v 40va for a old 25v 18va.
On a 120v furnace do you wire the white com from the transformer to the white or black line voltage from the electrical panel?
75% of my service calls are never set to proper primary tap on commercial rtus..most equipment is tapped at 240volts and installed in a 208volt situation..which drops the secondary accordingly. I would get contactor chatter, or damper actuators failing to complete their travel, or even duct smoke detectors tripping..that is a pain due to some locations of installation.
Thanks but for ones that dont know what wire on secondary side is Hot & what wire common ? ..Red green would assume Red Hot Green common ? but some are blue yellow or yellow blue but does it really make an difference + - side LV ? Thanks
Ty
I have a 240VAC transformer that powers 2 UV tubes at 400VAC. This summer It got 120+F inside the tough shed for the pond equipment, The Transformer was blistering HOT. I know heat can melt or burn xformer copper wire insulation at abt 350F but Im not sure of that figure. I have 12VDC computer fans for cooling I can turn the UV system off if in over temp condition, but what would you recommend as a safe over temp threshold? 275F?
How would you hook up 240? There is no primary/common its 2 hot 120s and a ground?
What about Hz do this matter. My transformer replacement everything matches minus the HZ my old one say 60hz and the one they sent says 50hz
Sometimes I see the green on secondary bonded to the chassis. Is it by the way the voltage is induced or could either leg on the secondary be bonded?
The secondary doesn't care which leg is grounded.
2:45 I can't wrap my mind around the concept. Played it over and over and I hear the words but nothing sticks
Thanks for the videos.
What do you mean?? The wraps??
@@JohnnyJr396 yes exactly....the thought of more length of wire wrapped around itself results in a different voltage.
Have a super and Happy New Year
@@Dancing_Alone_wRentals Happy New Year to you and yours. Check out The Engineering mind set channel. He has one on transformers that should give you what you’re looking for.
@@JohnnyJr396 tHanks. That is a great tip...I appreciate it. I think electricity is very interesting....but I spend my days in carpentry where life is good.
Instead of wraps he should say windings. The ratio of windings on a 120v primary to a 24v secondary is 5-1.
Is there any way I can buy your videos or put them on DVDs I work in a prison and can’t bring in a phone and can’t go to youtube on a government computer
Optimus prime is that you?
Major transformer!!!
Hi, I have a question for a power subwoofer. My fuse kept burning out no matter what fuse sizes I replace it with. The sub indicate to use 1.5 amp only but it kept burning so I moved it up to 3amp and it still burn. I was told it’s probably the transformer. So I opened the sub up and found the transformer to be 70V at 60hz. The model number is atc frost FT2845 which I can’t not find anywhere online. How do I know what transformer I can use to replace it and if you know, would you reference a link to it?
I believe the wattage it’s suppose to get is 210 watts. Thanks in advance.
👍👍
If the transformer is wired incorrectly for 120 V on the primary lines when it should be 240 V, what would happen to the transformer? What would happen to the zone controller connected to the secondary wires? What would happen to the thermostat connected to the zone controller? Thanks.
If you wire it for 240V, and connect 120V to it, the Secondary Voltage would be 12V instead of 24V.
If you wire it for 120V, and connect 240V to it, the Secondary Voltage would be 48V instead of 24V.
The transformer would probably still be ok if the secondary voltage were 48V. The contactor coils would get very hot, and any electronic circuit boards would probably be damaged.
So my HVAC is a heat pump and everything is running but not putting out cool air. My vapor copper line has a frost on it. Opened the blower unit and the transformer was humming and very hot. Found out the evaporator has frozen. So, is this transformer need to be replaced?? Anybody can answer this question, I would really appreciate it.
If I were to accidentally short both the secondary wires together, would that burn out the transformer?
yes
I was working on 230VAC to 24VAC transformer.
The voltage between 24VAC terminal and 0V terminal at secondary side is fine.
But the voltage between 24vac terminal and any other external ground is around 240 volt.
Why is it so? Do I need to earth the secondary side of transformer?
It sounds as if the Primary is shorted to the Secondary internal to the transformer. There should be no electrical connection between the two windings unless you have an Autotransformer (very unlikely).
If the windings are actually shorted internally, by grounding the secondary, you would trip the 240V circuit breaker that feeds the unit. The transformer would probably let out some smoke.
Is it possible to buy a transformer that will step down from 120 volts to 75 volts? I am refurbishing an old wall phone with a hand crank. The magneto produces about 70 to 80 volts to operate the solenoid to make the bells ring. I want to wire it up to my doorbell but the current doorbell transformer only produces about 24 volts. Not enough juice to ring the bells. Any help and advice would be so greatly appreciated. 🍻
You might be able to find one. But you can buy a variably transformer, affectionately known as a Variac. You connect 120V to the outer terminals. You can get anywhere from 120V to 0 by turning the knob. They come in a range of sizes. Sounds as if you need a very small one.
What about phasing two or more transformers.
V x A = Apparent Power - Total Power
Watts = True Power
V x A = Reactive Power which creates angle between apparent power and true power = power factor.
I thought white is common like ground, so for 240 you use black and orange ?
No. Still would be white and orange. The white wire is just a common point on the transformer. The white wire could either go to a grounded point (120v system) or an un-grounded point (208/240v system).As he explained in the video, the primary side (and secondary as well) has turns of wire. The combo of white/black has 5 turns. The combo of white/orange would have 10 turns. If you put 240v on only 5 turns of wire(black/orange combo) you would have 48v on the secondary side of transformer. Does that all make sense?
it's weird for me cuz I'm from switzerland here is black GND
Boss
And don't hook it up backwards. Yep, did that. Hands working faster than Brain....... Scrap
They come from Cybertron
They should change the name to a producer or something. A transformer does not actually transform voltage.
Inducer coil
What ohms and Voltage reading on the 24V side would indicate a bad transformer?
Hi John, I would think a bad xformer will either show no voltage reading on the 2ndy. In a rare case if there IS some voltage (most likely less than the rated 24v/ac) then it could be some turns/windings of the 2ndry jumped over thereby reducing the net number of 2ndry turns - though there are very rare chances of this happening. This from my limited knowledge, though I am sure there are more qualified folks to comment on this. And if this is a center tapped the 2ndry might show just 12 vac between the center tap and one of the output wire which means one half of the 2ndry is open.
Also on the Ohms reading in a bad transformer the ohms reading will either be Open (also no 2ndry voltage reading) or 0 ohms meaning completely shorted or in rare cases as above, might show some ohms (less than the rated reading). You will have to make sure to read the Ohms by disconnecting the 2ndry turns from the circuit/load side, because otherwise it might give false reading due to other components.
Hi
I am seeing a sharp increase in failed transformers in devices in my wide area.
What causes the transformers to fail, without blowing the main device fuse?
My multimeter reads a varying voltage from 111 to 118 volts from mains.
Is our power company in southeast Ontario Canada not providing reliable enough power?
If they fluctuate Hz too much, would that cause this?
My multimeter doesn't measure frequency.
The Power Companies control the frequency extremely tightly - well within 1 Hz. Even so, most transformers are rated to work on 50-60 Hz.
Voltages ranging from 111V to 118V are not a problem either. We expect the voltage to be around 120V + or - 10%.
Low voltage, like 111V would even be a little easier on the transformer than higher-than-normal voltages.
Probably just cheap or undersized transformers, pushed to the limits of their ratings.
Little 40VA transformers can come in a wide range of quality.
Transformers are often upsized enough to leave a comfortable margin between their rated capacity and the expected load.
I have been using industrial control transformers in electrical control panels for decades. I don't think that I have ever seen one of them fail. (Typically 1000 VA)
Your 2 fast
Good info, but to fast in showing illustration. Need to slow down when explaining the concept.
Noted
You spoke to fast ,no pause I didn't get it 🤣🤣🤣👎
I'm sorry,...I will speak slower and more simply for you.
Y speak so fast mate that’s not right way to explain the physics 😊