If I cannot get a triphase engineconnection, then

Precious Plastic Machine Development
#1

Hello Guys,

here in Cambodia it seems difficult/expensive to get a triphase connection, at least in the area where we intend to run the shredder.

I have an IT background and no experience with engines. From what I learned so far a triphase engine is just stronger than a monophase engine with the same dimensions. So if I want to get the same output, I need a bigger monophase engine, right?

Why does the guide say we cannot/should not use monophase at all? Just because the framework is not designed for a bigger engine or what is the problem?
The output can be the same if I take a monophase engine with bigger dimensions, no?

Any advice is really appreciated.
Thanks a lot in advance.

#2

@denyo1986 then get a VFD which has monophase input and triphasic output. So you don’t need triphasic electrical connection but you’ll be able to connect triphasic motor to it. But those are expensive. It won’t make much difference if you buy a monophasic motor though. just get motor around 2HP and you’ll be fine

#3

@denyo1986 were you able to test your motor? did it perform well?

#4

I was just thinking it might be possible to use a gas powered post hole auger. They have 50cc-200cc engines and have a gearbox that reduces the rpms to about 250rpm. They cost between $150-$400 new based on engine size. They are very simple. Just an engine right on a gearbox with a output shaft.

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#5

Have you considered a small gasoline engine? That is what I plan on using here in the Philippines. It is about 120USD vs 1000usd for a Sumitomo 3hp AC motor and gearbox.

I have had good success running a large air compressor converted from electric to gasoline. The trick is to get a larger HP than you need but run it at a high idle, or the sound and vibration gets too much.

#6

@denyo1986 so if Steinmetz circuit work perfectly ?

#7

@tinch:

Yes I tried it and it did work. However, I was only able to run the motor without any load due to early stage of the project. I dont know how much torque the motor has with one phase and whether it’s enough to shred but to me it seemed quite strong. I was not able to stop or slow the motor down by hand.

I only had to buy a capacitor with 150mF (since I have a 2KW motor and you need about 70mF per KW) and wire it up, that’s it.

I will attach a photo….

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#8

@denyo1986
hi daniel! i had no idea about this ‘steinmetz circuit’, so thanks for that. i’ve been googling a bit about it but in meantime i’d like to answer: have you tried it out yet?did it resulted good? tell us a bit about that!

#9

Hey Guys,

sorry for my late reply. I thought I had replied already to this thread, but apparently not.
Thanks so much to @flo-2 for your extensive explanations that actually helped me a lot to understand the whole thing.

I went for a 2HP three phase motor now and we yet have to see its performance.
One interesting point that I wanted to share is that in order to test the motor (while not having three phase power available), I tried something out that is called the “Steinmetz circuit”. It is a very smart way to run three phase engines on single phase power. You only need a right-sized capacitor and the wire the engine in the right way, and off you go. Again, we dont have the shredder fully assembled yet so I cannot report about the load it can handle but we got it running and the engine seemed to be strong (was not able to stop or slow it down by pressing a piece of wood against the pulley with force).
If someone needs more information or help setting this up, get in touch with me.

#10

A 3 HP single phase motor will perform the same as a 3 HP three phase motor. The three phase motor will be more efficient and cost less.

I am using a 3 phase motor + VFD with a single phase connection input. Basically you give it single phase input, and it spits out the 3 phase the motor wants. The VFD doesn’t need to special, you just need to oversize it (because there are losses in the VFD when going from single phase to three phase).

I’m in a similar situation that I’m definitely not going to have 3 phase power installed.

For me, getting a VFD with a 3 phase motor was about the same price as getting a single phase with no VFD. Not to mention, without a VFD you’d likely want to get a reversing contactor to switch direction, or worst case get a single contactor to start the motor, so you’ll have additional cost there. Nice thing with the VFD you can easily increase speed, automatically program it to reverse direction if it overloads.

#11

@denyo1986

The 3HP or 2,2kW is the power, the motor is built to withstain. A motor generally consumes the power it needs, so for example a 2,2kW Motor won’t take 2,2kW of electricity when not shredding. However when a 2,2kW Motor needs 4kW because plastic got stuck etc., it will also consume 4kW, damaging itself.

1HP =~ 0,736 kW = 736 Watts. Since Watt = Voltage x Ampere, the HP/kW number on your motor is the energy consumption rather than the power it delivers. Hovewer there is also a number on the typesheet of the motor indicating its efficiency (output power over inputpower) with a letter looking like an “n” with one end of it longer down than the other (picture) mine is 76% or 0,76. However when looking at the power of a shredder motor what’s more interesting than the HP/kW is the torque measured in Nm. Nm = F x r. My motor delivers ~280Nm of torque, so we can do a little mathematics here: 280Nm = F x 0,1m (distance from middle of shredder axe to tooth of blade) if we divide by 0,1m , we get: F= 2800N (the force with which the tooth press at the plastics), again divided by 9,81 m/s^2 (about 10 😀 ) gives us ~280 kg. So it feels like the shredder blade is laying on top of the plastic with 280kg pressing onto it. That should be good enough to shred also thicker parts 🙂

Back to the topic, a singlephase motor IS in fact less efficient than a triphase motor. And here is why: a monophase motor is in fact a normal triphase motor, connected to monophase AC. However this way only every third electromagnet of the motor is powered which results in a position, from where it could not start (if you want to, I can explain this more detailed too 😉 ) That is where the capacitor comes to work. While the first magnet is powered, the capacitor gets charged. It releases that charge after a few ms, immitating a second phase. Some motors (mine for example) have a second capacitor to immitate the third phase. This way the motor can start spinning no matter at which angle its axis is. The fact, that two of the three phases are just immitated, reduces the power output, that way monophase motors have only about 80% of the power of triphase motors.
I hope this is useful,
Greetings Flo

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#12

Hi again and have a great week,

the problem is dual and we are also learning by doing.
The single phase motor (like any motor u may choose) might come to the issue that some plastic gets stuck hence you will need to reverse the motor. This cannot be done manually since a motor connected to a reducer (to go below 70RPM) then to an axle blocks any movement towards the other direction.
Additionally, yes the 3phase delivers more torque even at the same HP.

You have then the following options.

– Single phase – get the largest you can find just make sure that you can also then attach the basic electronics to reverse when it gets stuck. (i got some schematics but depends if your motor has 1 or 2 capacitors). Make sure you have access to the connector box of the motor.
– 3 phase – You can either make a 3phase motor to single phase – which is a bit pain in the ass and preferably done by an electrician or you get a VFD over ebay which get single phase input and then gives 3phase to the motor.

The pdf i attach is a basic circuit for controlling the rotation of a single phase motor…just to give u a heads up

Hope we were helpful.

Best,
ALex

#13

@seyn-sustainableenergyyouthnetwork:

thanks a lot for your help, advice and for taking the time to go into detail.
For us the biggest problem is to find a location to run the shredder that has a triphase electrical connection. Getting a new property connected with triphase costs about $2000 or something and is therefore completely out of question.

If I have to go for a monophase engine, can I not just take one that is big/strong enough?

I am sorry but I am not an Engineer, just a logically thinking IT-guy. 3 horsepowers should be 3 horsepowers….no? It is a measure of how strong the engine is, not how efficient it is.

So why does a 3hp triphase motor work well and a 3hp monophase motor does not? Does the monophase not have enough torque? If so, can I not just take a bigger monophase motor to get the torque that I need?

Sorry to bother you with this so much but once I get my head around this it will be much more easy to find suitable solutions.

Thank you.

#14

Hi,

just to give you a small hands on xperience. We are building PP machines in Greece right not and for the shredder we used a 3HP single phase motor (also thinking like you for using single phase input), with a reducer 50:1, thinking we could be fine since the machine would be used in an educational program.

It was jamming quite often and then is impossible to rotate it back by hand since the axle is connected to the reducer and then motor, so we had to make a small system to reverse the rotation.
End up that it was not possible with this motor, since the cables were buried inside the winding.

Now we are going for a second hand 3phase motor with the reducer included, where you end up with 2 options.
Option 1: VFD with all the programming you can imagine, rotation, speed etc and gets single phase input and 3phase output as mentioned.
Option 2: Find a cool electrician (or you) to make the 3phase motor to a single phase one (you will lose some of the power but still)

Small advise, for the shredder dont go for used single phase motor. The used 3phase ones usually have longer lifetime and you can find them all over the place…

Do some research on motors so you can recognise what you are looking for when going around…

Best,
ALex from PreciousPlasticGreece 🙂

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#15

Thanks for your advice.

Why does the engine guide state in red letters that we should not use monophase?
I dont get it…

Does it only mean that my engine will be bigger to get the same output or are there any other reasons why to not use monophasic?

It seems rather pricey and tricky here in Cambodia to find triphasic engines and power supply….
I would be very happy to go for monophasic but am a bit worried by this advice in the guide doc since we need to have a well-functioning shredder that can run without interruptions.

@davehakkens : what is your view on that?

#16

I agree with sharma-sigar. A rotary or static phase converter would be your best option. If you source it from Ebay or Amazon you should be able to drive down the price a fair bit and then you can use single phase connection to get 3 phase power. check the link below for a rough idea of what you should be looking for.

http://www.ebay.ca/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR12.TRC2.A0.H0.Xphase+converter.TRS0&_nkw=phase+converter&_sacat=0