Converting 480 volt 3 phase air compressor to 230 volt single phase with a VFD - 2 of 2
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- Опубликовано: 7 фев 2025
- In this second video I cover the actual wiring changes, insertion of new contactors, connection of the air compressor control system and VFD, how the VFDs are activated via the controller and a host of other goodies!
I hope it helps someone considering doing the same!
While most of our needs will vary, here are the parts I used.
www.amazon.com...
www.amazon.com...
Great info here, learned quite a bit and will refer back in the future. Subscribed, thanks!
Thanks for the sub! Im glad you found it useful! I try to track all comments, so if you have questions, or even a video request, drop a comment and ill do the best to fulfill!
Thank you for sharing this. We are installing a screen printer and we need a 10HP with CFM of at least 33 / rotary screw with a dryer and our shop is running single phase. It's a challenge to find one that is a 10HP in a single phase. I talked to a sales rep who sells different brands, and he stated that we should not convert a 3-phase air compressor to a single phase as it will shorten the lifespan of the compressor. However, I am seeing folks converting compressors over and I don't see anything neg on doing it. My question though is, you've laid out a very detailed plan of doing it but if we are just going to be needing to convert and run 1 air compressor, is there easier way you would recommend, you mentioned something about a rotary converter. The compressor will be almost running all day at 33 CFM and I want to we do this without having issues, so if need to spend a little more to get something that will hold up to the daily use. What would you recommend? Thank you so much.
The sales representative you spoke with does not sound like they are educated on the methods of adapting three phase equipment to a single phase supply. It is correct that a static phase converter (phase shifter) is bad for any three phase motor (reasons below), but there are additional options which are specifically designed for this purpose and used in, literally, millions of use cases identical to yours.
While converting 3-phase equipment to single-phase power might seem appealing, there are important considerations and limitations to be aware of, especially when dealing with continuous use applications like your air compressor. Here's a breakdown of the options, highlighting potential issues and safer alternatives:
Static Phase Converters (Phase Shifters):
Problems:
Imbalanced Power: They create an unbalanced electrical load on the single-phase supply, stressing the wiring and potentially causing overheating or equipment malfunctions.
Increased Current Draw: This method increases current draw on the single phase supplying all three phases, exceeding the capacity of your existing wiring and potentially tripping breakers.
Reduced Motor Efficiency and Lifespan: Running a 3-phase motor on unbalanced power leads to decreased efficiency and increased heat generation, shortening the motor's lifespan.
Safer Alternatives:
Variable Frequency Drive (VFD):
Benefits:
Safe and Efficient: VFDs convert single-phase power to variable frequency three-phase power, seamlessly powering your 3-phase equipment without overloading your single-phase supply.
Soft Start: Gentle start-up reduces stress on the motor and extends its lifespan.
Speed Control: VFDs provide adjustable speed control, allowing you to optimize compressor performance based on needs.
Rotary Phase Converter (RPC):
Benefits:
Efficient Power Conversion: RPCs use a dedicated motor and capacitor bank to create a balanced three-phase output from single-phase input.
Suitable for Continuous Use: They are better suited for continuous duty applications compared to static phase converters.
Cost-Effective for Larger Motors: As the current draw of the 3-phase equipment increases, the price of a VFD can become significantly higher than an RPC. However, RPCs require additional components and installation compared to VFDs.
Additional Considerations for RPCs:
Complexity: Setting up an RPC involves additional components like a breaker box, control panel, and potentially larger gauge wiring compared to a VFD installation. Consulting with a qualified electrician is crucial for safe and proper installation.
Maintenance: While generally robust, RPCs have an idler motor that requires periodic maintenance, such as checking belt tension and replacing worn bearings.
Recommendation for Your Air Compressor:
Given your requirement for a 10HP air compressor with continuous operation needs (33 CFM), a Variable Frequency Drive (VFD) remains a strong recommendation due to its overall ease of use, efficiency, and built-in functionalities like soft start and speed control. However, if budget is a significant concern and you are comfortable with the additional setup and maintenance involved, an RPC can be a viable alternative, especially for larger motors where VFD costs become very high.
@@MountainLaurelMetalworks , thank you so much for your valuable input and advice. I'll review this information in detail
Do you have part #'s for the contactors, bar and connectors?Facebook? Or a way to contact you besides facebook?
Here are the amazon links I used. But be aware, there are MANY options available and what works for my requirements may not fulfill yours.
www.amazon.com/gp/product/B07GXM2Q3S/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
www.amazon.com/gp/product/B07NVVP9X7/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
How much of a difference would it have cost to replace the three phase compressor motor with a single phase motor compared with that converter panel. I have an old three phase five hp compressor that I use to have in my shop years ago but don't have three phase power at my house that would like to hook up my old compressor again.
That is an option and many people do exactly that. For most home air compressors 5hp is sufficient and finding a replacement motor at 5hp and 240v single phase is cheap and easy. For larger equipment (motors over 5hp) a single phase motor can be hard to find greater than 5hp at 240v single phase. Also, they are usually more expensive than these cheap VFDs.
Another plus of keeping the 3ph motor is that the VFD will allow you to adjust the speed and direction of the motor (you can't change rotation direction of a single phase motor). For example, my old compressor setup was a 240v single phase that I converted **TO** a 3ph motor and VFD combo. This would allow me to run the compressor at a much slower speed when full air volume wasn't needed. This dramatically reduced the noise in my shop as that compressor was EXTREMELY LOUD!
@@MountainLaurelMetalworks thanks for the info maybe one day if I decide to run a VFD I could contact you to walk me thru that setup. Thanks , your compressor is very quiet.
Let me know any time I can help!
Do you know why the schematic had you loop the 3rd leg around to the bottom of the relay?
I meant contractor
If you are talking about the segment around the 10:00 mark, with the lead going to the black and blue devices, those are current overload protectors (thermal breakers if you will). The load passes through those on it's way to the rest of the circuit. These are sized for the load they will drive. If the motor starts drawing excessive current for some reason (a bad bearing, seized motor, etc.) the current draw will increase and these will trip, opening the circuit and cutting off power to the motor.
In many 2ph -> 3ph conversions these are omitted as many, if not all, VFDs have circuitry and programming to perform this function. This is one reason it is so critical to enter the motor information into the VFD when configuring the VFD.
In this particular example, I retained them to actually simplify things. Since this compressor is computer controlled, and I wanted to retain that control, It was easier to leave them in the circuit.
I hope that helps.
@@MountainLaurelMetalworks sounds good, I was actually wondering about the wire that is pulled to the bottom of the contactor at 4:30.
Ok, got it. So, that's a little hard to explain. The compressor was available in 3 phase and single phase models, so they include wiring for each. Basically I am running all the electronics in the compressor in 240v single phase. This re-routing is to get power to the internal transformer which then powers the internal computer control of the compressor. That power had been supplied by the 3ph leg that is no longer present, that is why it needed to be moved.
If I were changing the motors to single phase motors (and as such not using a VFD), all I would have needed to do was re-wire the inside per the single phase instructions. However, since I am keeping the 3ph motors, I needed the VFDs to power the motors. You should never place a mechanical switch on the outputs of a VFD, it can damage them. If mechanical contacts, such as the contactors inside the control box, would not damage a VFD all I would have needed was 1 VFD, large enough to run both motors, and connect it to the input terminals all all would have been done in 15 minutes. However, this would mean the internal contactors were on the output side of the VFD and may damage it.
To prevent this, I wired the internals to my standard 240v single phase power, per the diagram. However, I did not run power through the contactors, as would normally be the case. I simply connected the contactor terminals to the dry contact input for each VFD. Basically using them as an 'on/off' switch telling the VFD to send power to the motor directly. In this way, I kept all internal controls and prevented placing a mechanical switch on the output side of the VFD.
I hope that helps. It's a bit hard to convey without going through the entire procedure since it was all related.
@@MountainLaurelMetalworks I totally get it, I'm doing almost the same exact thing with my compressor, but the transformer that feeds my 115v controls uses legs 1 and 2 of the original 3 phase to power it, so my 3rd position on my large contractor is empty. My plan is to wire the switch that tells the VFD to send power to the motor directly to that empty 3rd spot on the main contractor.
Nice!
Thanks!
So i have an 80 gal vertical air compressor that is 220 volts 3ph. Motor is 7.5 hp and unit will do 25cfm max output. I do not need 25 cfm 90% of the time so i like the option of a VFD to be able to reduce speed and noise level . unit has a pressure switch and a starter no control board. from my understanding i would need a 15 hp VFD ? And would i still need the starter if i went with a vfd on a ramp up delay? Sorry for the questions i have been around VFD a little but never wired one.. this compressor was surplus and was free.
Thanks for commenting. Generally when sizing a VFD, you want to go about 25-30% larger than the motor rating, so for a 7.5hp device, you would need a 10hp VFD. Larger is find, but smaller would put too much stress on the VFD and limit your motor output.
When connecting a VFD to a motor, interruption of any kind should be between the VFD output and the load (the motor) should never be used. The reasons are long and well documented on the internet, but in short, it can cause a massive surge back to the VFD and damaging it.
Basically, any signaling on the compressor (pressure switch in this case), which had controlled power to the motor, should be converted to dry contacts and then connected to the input terminal strip of the VFD telling the VFD to output voltage (documented in the VFD manual, specifics vary by VFD manufacturer).
No motor starter should be needed, the motor would be wired directly to the VFD output. On, off, and motor speed would all be controlled via the VFD (either front panel or terminal strip, some VFDs permit both to be used simultaneously). A ramp up / ramp down is good under all circumstances as it is easier on the motor and VFD, simply 1-2 seconds dramatically reduces the overall impact.
For anyone else reading, the comment about sound is important to consider when using a compressor. While a single phase compressor cannot have it's speed adjusted, a three phase can. This means that if you do not need the full CFM (you will still get the same pressure) you can run the three phase motor at a lower speed by adjusting the output frequency of the VFD. In the US, all power is at 60Hz (single and multi-phase). If you set the VFD to output 30Hz, the motor will run at half speed and run significantly quieter.
Here's one a lot of people don't think about, but you can also run the motor at a higher frequency to speed it up. In the case of a compressor, running it at 70Hz, would increase the CFM of the compressor. While this slight increase will not hurt the motor, one must consider the impact of the remainder of the system (compressor pump). There may be too much heat generated, inadequate lubrication, etc. But it is a method of getting a higher CFM from a compressor.
How can i run 2 air compressor with one VFD ???
At one time only one compressor runs..
The trick here is you can't (shouldn't) put a physical switch between the VFD 3 phase output and the motor, as this can instantly damage the VFD when the switch is thrown. There should be no physical interruption between the VFD and the driven load (the motor of the compressor). If you wanted 1 VFD to power 2 compressors, I can't see a way to do it without a switch between the output and the load. If you were to shut everything down, switch the load, then start everything back up you could avoid the danger to the VFD, but you would also need to switch the pressure switch trigger as well. With the complexity and additional equipment necessary your cost wouldn't be much more to buy a second VFD. Also, a second VFD would prevent the risk of switched outputs destroying your VFD.
I actually have the reverse on a compressor here. My compressor has 2 heads, thus 2 motors. I have 2 VFDs on that unit so each compressor can run as dictated by the ECU in the control box.