HVAC: Potential Relay Explained (Potential Relay Wiring Diagram) 521 Relay Sequence Of Operation
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- čas přidán 19. 06. 2024
- HVACR (Heating, Ventilation, Air Conditioning / Refrigeration) Potential Relay Explained (Potential Relay Wiring Diagram) 521 Relay Sequence Of Operation / Potential Relay Wiring / Potential Relay VS Current Relay / Potential Relay Troubleshooting / Potential Relay Refrigeration / Potential Relay Connection / Potential Relay Start Capacitor Wiring Diagram
HVACR POTENTIAL RELAY:
Potential or “voltage” relays are used with single-phase capacitor-start/capacitor-run motors, which need relatively high starting torque. Their main function is to assist in starting the motor.
Knowing the sequence of operation for this type of starting relay can help you diagnose, confirm, or rule out certain service problems.
Potential starting relays consist of a high resistance coil and a set of normally closed contacts. The coil is wired between terminals 2 and 5, with the contacts between terminals 1 and 2.
Terminals 4 and 6 are used for capacitors and/or condenser fan connections and have no electrical significance to the starting relay itself, as shown in Figure 1. In fact, terminals 4 and 6 are sometimes referred to as “dummy” terminals and are simply used for wire connections.
OPERATION:
When power is applied through the cycling control, both the run and start windings are energized. The run and start capacitors provide the phase shift for starting torque because their capacitances add up when wired in parallel. In fact, both capacitors are wired in series with the start winding and in parallel with the run winding.
The run capacitor limits the current that will pass through the start winding when the motor is running, because they are wired in series. The run capacitor also provides running torque when the motor is up and running.
The operation of the potential relay is based on the increase in back-electro-motive force (back-EMF) or a bucking voltage that is generated across the start winding as the motor increases in speed. The large metal mass of the motor’s rotor turning at high speeds with motor windings in close proximity has a voltage-generating effect.
The generated back-EMF opposes line voltage and can be measured across the start winding or across the coil of the potential relay at terminals 2 and 5. The back-EMF is usually a higher voltage than the line voltage and can be in the 400-V area.
All motors have different magnitudes of back-EMF, thus requiring different potential relay designs.
The back-EMF voltage generated across the start winding causes a small current to flow in the start winding and potential relay coil, because they are in the same circuit. When the back-EMF has built up to a high enough value (referred to as pick-up voltage), the contacts between terminals 1 and 2 will be picked up (“opened”). This will take the start capacitor out of the circuit.
Pick-up voltage usually occurs when the motor has reached about three-fourths of its speed. The start winding is still in the back-EMF circuit, keeping the relay’s coil energized while the motor is running at full speed.
The contacts open because of the electromagnetic force (magnetism) generated in an iron core around which the relay’s coil is wrapped.
When the cycling control opens, line voltage is taken away from the motor. The motor’s rotor decreases in speed. Thus, the back-EMF generated across the start winding decreases in magnitude. The relay’s coil now sees a lower back-EMF and no longer can generate enough magnetism in its iron core to keep contacts 1 and 2 open.
The contacts therefore return to their normally closed position by spring power as the motor coasts to a stop.
With the start capacitor out of the circuit, the motor becomes a permanent split capacitance (PSC) motor in the running mode only. - Věda a technologie
1,2,5 relays are one of the most overlooked parts in diagnosing a so called bad compressor. Many unseasoned Techs don’t understand them, they are very simple but extremely critical. You explained them perfectly, I hope less experienced techs will take a little time to watch this video.
Best explanation of what that device does. I couldn’t figure out why it can only be oriented one way. Now I know! Keep up the great videos!
Great video, thanks for putting this together. I'm familiar with these in well pump controllers, where they serve the exact same purpose -- put the start cap in the circuit to get the pump motor running, and then remove the start cap from the circuit. Although, I never knew exactly how they worked -- and now I do!. You have to love the simplicity! Thanks again.
This is a phenomenal explanation.
Thanks mate for heads up, this video actually help wired one myself. Jumper man tech still the best.
Sir, you are one of the best HVAC teachers on the Internet. I tip my hat to you. God has truly blessed you with the ability to communicate complex ideas in a simple way. We cannot thank you enough for all you have done for us.
Vrey very good potshionall rel emf sfety ac. Systomm no .521 power give l1 l1 enrzing coil
Thank you from a pipe fitter apprentice. Making it seem easy!
Tyvm! Very succinct. I will forward this to our Service Department Technicians.
Interesting and helpful video. Great job JMT as always.
great video JMT. very helpful info!!
Pretty cool, thank you
Thank you for sharing this valuable information
Nice work here. I followed the explanation and it work for me. I have release the report of this video on my profile
Great explanation thanks
Nice video! Thank You.
Helpful video, thank you Sir for sharing this video
Great video once again. Excellent explanation as well keep up the great work
Thank you once again for the easy to follow explanation on a rather confusing piece of item the potential relay. I know understand it better. Thanks to you and your depth knowledge of this field.
I wonder if you can help me and others like me with the pictorial sketch and explanation of the wiring on freezer box with the power connection, dual pressure switch, thermostat, solenoid valve, defrost timer and heater connection starting from the very same box with normally house the potential relay, start and run capacitor.
Great video as usual 👌
Just subscribed. Thanks for the information. Great video.
Great explanation as always! Could you possibly make a video of wiring a potential relay, start cap, run cap and the compressor coming from the contactor? Thanks and great job as always JMT!
Top Draw 💯💯💯👍👍👍
👍💪❄🙏🇺🇸 another great presentation. There's always voltage at 5 n 2 n then when call for cooling it goes up n opens contacts.
Wonderful....... Very helpful video for me🙏 🇮🇳🙏💐☺🕉🙏
Thanks for the precise explanation. I will like to know if both potential relay and the current relay can be used together on a compressor.
Great vid….. question, will a bad potential relay cause my compressor to cut on and off 10 seconds?
Great explanation, how can I know if this relay is not working properly or damaged
Could you do a similar video as this one but show with arrows the flow of electricity through the system? How the compressor and fan start and how the electricity flows through the capacitor and through the 521 relay. Thanks
Another banging vid. Troubleshooting tips and tricks?
Very informative video. I do have one question though. On the side of the potential relay there are numbers and letters. Do they mean anything and if so how do we read them? For example on the relay you demonstrated RVA3AG6D 917 U433 the three sequences of numbers and letters do they represent the specs and model number if not what do they mean? Thanks in advance.
,hello sir,, very nice explanation..may i ask a question what f the close contact of potential relay will not open?
I've always shrugged when thinking about how back EMF can increase voltage across a motor to well above the incoming voltage from the source. After all, if voltage across the windings is 470V, and if incoming voltage is 240V, why doesn't current go backwards up the line? What drives current to continue flowing antegrade to a higher potential leading into the motor? The only thing that comes to mind is the phase shift that you see in a normal RLC circuit, which happens even in a simple inductor without back EMF.
Back EMF is generated in the motor itself. Pick-up voltage, generally speaking, 0.75 percent of total back emf of motor start winding at operational speed. Relay only sensing back emf of start winding.
Glad someone pointed this out. Its the back-EMF from the start winding that causes the relay to open !
How would you test this component on a system? What symptoms would indicate a bad relay?
I ask because I found one of these with the points welded closed and wouldn’t open. The compressor started for a second and then would shut off so I guessed this was the faulty component and it worked for me, but I’d like to test it next time
What about if don’t have a potential relay, or start cap. Are there any alternatives in a pinch
Great video.....I guess here in the UK your L2 is our Neutral....right? 🙂
Never understood nor took the time to see how those worked. Thanks for the excellent explanation and keep these types of videos coming. BTW… You sound a lot like my cousins from Long Island, lol.
Do Universal Pontential Relays work good? Even If all their specs match?
The 4 or 6 termanal Could be used as a neutral right?
Hello, I have one of these 521 in a 240v 3 phase converter (Cedarberg 75A), i have doubt if it is good or not, as this converter does not have/use run capacitor. Can this be possible in you experience ? Actually is a 240v motor converter, but the capacitor says 120V
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👍👍👍🙏🔧⚡️🤙
interesting, but I miss one thing : what happens to 2 after starting up? what's the electric potential at 2?
Can u ues this realy just for start capacitor?
What's that music at the end?
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Trying to understand how the system works with a contractor and no potential relay. The unit I'm looking at has a contactor and no potential relay. The start capacitor was replaced and blew up in 30 seconds so I thought stuck potential relay but all I see is a contactor.
I think the terminal of relay 1&2 had interchange please check
The it was explained to me was that the compressor when running creates its own voltage like how electricity is created at a hydro electric plant. After all it is just a rotor and stator.
Bonjour, la valeur du condensateur est de 88 microfarad 250v. Peut-on remplacer un condensateur de même valeur 330v? Sans le compresseur danfost ne subisse aucun dommage ? Aidez-moi svp
very nice I'm a plumber. do they go bad offen I like knowledge
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I need to record this diagram in my brain
5 -2-1 Common - Start - Run 👍
Probably should explain that the coils becomes an electromagnet and that is what caused the contacts apart and opens the circuit
Agree, it would add a bit more clarity.
Why is it important to orient the relay vertically? Thankyou
Gravity...
Because the coil has to pull the pole up which opens the contacts and taking the start winding out of the circuit. If you mount the relay upside down the Normally closed contacts will be open thus not putting the capacitor in the circuit and the pole couldn't pull up because it would already be up. The pole moves freely in your hand when you flip it over. If you put a ohmeter on contacts 1 and 2 it will show continuity and when you turn it over the contacts will OPEN. Test one and you will see!!
As a 5 yr old.... I now understand this perfectly. Our brains are configured to think coil voltage will close/make the circuit (N.O.).... this concept (N.C.) is opposite and I believe the reason for difficulty understanding. Thanks and following.
5 21 reay potacte realy enizing hot potact capcater us img ac systom ..
in uk we dont use the line 2 that is very confusing, we say neutral or N, line 2 is associated with 3 phase poer supply only. please use the neutral word instead if demonstrated your idea, dangerous